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Demersal fish assemblages off the Seine andSedlo seamounts (northeast Atlantic)

Gui M. Menezes �, Alexandra Rosa, Octavio Melo, Mario R. Pinho

Departamento de Oceanografia e Pescas, Universidade dos Ac-ores, Cais de Santa Cruz, PT-9901-862 Horta, Portugal

a r t i c l e i n f o

Article history:

Accepted 13 December 2008Available online 8 January 2009

Keywords:

Demersal fish assemblages

Deep-water

Seamounts

Azores archipelago

Madeira archipelago

a b s t r a c t

Seamounts are thought to support special biological communities, and often maintain high standing

stocks of demersal and benthopelagic fishes. Seamount fish fauna have been described in several studies

but few works have included species taken below 600 m. The demersal fish assemblages of the Seine

and Sedlo seamounts (northeast Atlantic) from the summits to 2000 m depth were investigated based

on longline survey catch data, conducted as part of the OASIS project. A total of 41 fish species from 24

families were caught at Seine near Madeira, and 30 species from 19 families were caught at Sedlo north

of the Azores. Both fish faunas have high affinities with the neighbouring areas of the Azores, Madeira

and with the eastern North Atlantic and the Mediterranean Sea. Overall abundances and mean body

weights were slightly higher at Sedlo seamount, appearing in conformity with the latitudinal effect of

increasing species abundance and productivity from south to north. The differential influence of the

Mediterranean Water at each seamount may contribute to explain (a) the differences found in vertical

distribution of common species, which tend to distribute deeper at Seine, and (b) the observed changes

in the species composition and dominance in deeper waters. Multivariate analysis revealed a vertical

structure that is approximately coincident with the expected zonation of water masses at each

seamount. Physiological tolerance to the prevailing vertical hydrological conditions may explain the

species distribution and the large-scale vertical assemblage structure found. However, further ecological

factors like productivity patterns affecting the amount and quality of the available food appear to shape

the abundance, diversity or dominance patterns of functional groups within those main assemblages. At

Seine, the species Trachurus picturatus dominated the catches, mainly at the shallower edge of the

plateau, appearing consistent with the sound-scattering layer interception hypothesis [Isaacs, J.D.,

Schwartzlose, R.A., 1965. Migrant sound scatterers: interaction with the sea floor. Science 150,

1810–1813]. At both seamounts mesopelagic feeders (e.g., Beryx splendens) dominate the upper-slope

assemblages (o800 m), while the mid-slope assemblages (800–1200/1300 m) and the lower-slope

assemblages (41300 m) were dominated by squaliform species (e.g., Centrophorus squamosus,

Centroscymnus coelolepis, Etmopterus princeps) along with Mora moro or the Antimora rostrata. The

lower abundance of C. squamosus observed at Seine may be a result of the fishing activities in the area,

since the species is an important by-catch of the black-scabbard fish fishery in the Madeira archipelago.

The slightly higher predominance of scavenger species at Seine in deeper assemblages may be the result

of an ecological response favouring this functional group in lower productivity regimes. Especially

relevant was the record of large reproductive aggregations of B. splendens and Epigonus telescopus found

at the edge of the Sedlo plateau.

& 2009 Elsevier Ltd. All rights reserved.

1. Introduction

Seamounts, in general, are thought to support high biodiversityand special biological communities (Rogers, 1994). On a globalscale, the role of seamounts in the biogeography, biodiversity,productivity and evolution of marine organisms has beenhypothesized but is still poorly understood and controversial. It

is estimated that there are potentially up to 100,000 seamountswith summits higher than 1 km above the surrounding seabedand many more of lesser relief. However, few seamounts havebeen studied biologically, only about 350 have been sampled, andless than 100 in any detail (Clark et al., 2004).

Seamounts are highly variable landscapes, acting as a habitatfor numerous benthic organisms and feeding grounds for fishesand other marine fauna (Morato et al., 2008). Seamounts oftenmaintain high standing stocks of demersal and benthopelagicfishes (Boehlert and Genin, 1987; Rogers, 1994) despite theimpoverished nutritional conditions in oceanic regions (e.g., Fock

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Deep-Sea Research II

0967-0645/$ - see front matter & 2009 Elsevier Ltd. All rights reserved.

doi:10.1016/j.dsr2.2008.12.028

� Corresponding author. Tel.: +351 292200400; fax.: +351 292200411.

E-mail address: [email protected] (G.M. Menezes).

Deep-Sea Research II 56 (2009) 2683–2704


et al., 2002b). Instead of an autochthonous-derived energy, someevidences suggest that these stocks are mainly supported by anadvected energy supply of zooplankton and micronekton (Dowerand Mackas, 1996; Fock et al., 2002a; Pusch et al., 2004). Studieson the diets of demersal fish species at Great Meteor Seamountfound that their interaction with vertically migrating mesopelagicfauna plays a significant role in the maintenance of these stocks(Fock et al., 2002b), in agreement with the sound-scattering layer(SSL) interception hypothesis (Isaacs and Schwartzlose, 1965).

In recent years, seamount fish fauna and invertebrate com-munities have received increasing research interest for scientific,conservation and economic reasons. They are important fishinggrounds for both demersal and pelagic fisheries, but also areasof increased biodiversity and greater densities of filter feederswith high conservation importance, such as deep-water corals andsponges. Seamounts have been targeted by commercial fishingdue to the occurrence of large aggregations of some fish species inmid- and deep-water. For instance, orange roughy (Hoplostethus

atlanticus) and other economically valuable fish species (e.g., Beryx

splendens, Epigonus telescopus) have been found to form densereproductive and feeding aggregations at seamounts and havebeen heavily exploited in several oceans (Rogers, 1994; Vinni-chenko, 1997b; Clark et al., 2004; Tracey et al., 2004).

Increasing fishing activities at seamounts and the complexityof biological and ecological traits of their exploited fish popula-tions (e.g., recruitment mechanisms, resilience, longevity) haveraised concerns on the human impacts on this biota (Rogers, 1994;Koslow, 1997). A number of seamount fish populations havealready been depleted, and the long-term impacts of suchactivities on the seamount habitats and benthic organisms remainunquantifiable (Vinnichenko, 1997b; Clark et al, 2004).

The Azores and Madeira archipelagos, like most of the oceanicislands, are surrounded by oligotrophic waters, and have steepslopes and narrow shelves. In general, exploitable fishingresources are therefore smaller, deeper, more vulnerable tooverfishing, and most of the fishing is done on seamount-likefeatures. Seamounts are common topographic features in theAzores area. Recently Morato et al. (2008) mapped and described63 large, and 332 small seamount-like features in the whole EEZof the Azores. In Madeira, seamounts are less numerous,comprising only about five large features.

Over the period 1979–1982, several scientific longline surveyswere carried out in the Madeira archipelago, including Seineseamount, by the former National Institute for Fisheries Research(INIP) using the R/V ‘‘Noruega’’ (INIP, 1980; Leite, 1983). Thesesurveys aimed to evaluate and support the development of thefishery for black-scabbard fish (Aphanopus carbo), and also tostudy the oceanographic conditions of the region.

In the 1980s, Seine seamount was already exploited bylongliners targeting demersal fishes and also by traditional pole-and-line tuna fleets. In general, fishing activities at Sedlo andSeine are almost unknown. Sedlo seamount has not been acommon demersal fishing ground for the Azorean fishing fleetsprobably because it is relatively deep, limiting the occurrence ofmost traditional target species. The few records of fishing nearSedlo seamount refer to surface-longliners targeting swordfish(Santos et al., 2009). In 2002, exploratory trawl fishing, targetingorange roughy (H. atlanticus), took place at Sedlo seamount and15 fish species were recorded for the first time in the Azores area(Menezes et al., in prep.). This was the first time a bottom trawlwas used in the Azores, and most of the new species recordedare not catchable by baited fishing gears (the gears used incommercial fishing and fish sampling surveys in region). Trawlingon island slopes and seamount features is difficult due to the steepslopes and rough nature of the seabed; therefore, longlines havebeen used in most studies of demersal and deep-water fish

assemblages in the Atlantic archipelagos and at their neighbour-ing seamounts (Uiblein et al., 1996, 1999; Menezes, 2003;Menezes et al., 2006).

Seamount fish fauna have been described in several studies,but few works have included species taken below 600 m (Traceyet al., 2004). Comparisons of fish assemblages between sea-mounts, or between seamounts and neighbouring areas (islandsand continental slopes), are still scarce.

In this study, we characterize and compare the structure andspatial distribution of the demersal fish fauna of Seine (Seine) andSedlo (Sedlo) seamounts down to 2000 m water depth, based onlongline fishing surveys carried out under the OASIS project.Patterns of abundance and distribution of the fish fauna of theSedlo and Seine seamounts, over such a wide depth range, areimportant to infer the spatial dynamics of these species and mayhave implications for conservation and management, or forplanning future monitoring survey programs in similar areas.Results are discussed at a regional scale and compared withprevious studies made in the Azores and Madeira archipelagos.

1.1. Study areas

The two investigated seamounts are located in the NorthAtlantic near the Portuguese archipelagos of the Azores andMadeira (Figs. 1 and 2). Sedlo seamount rises from a depth ofabout 2000 m. The depth of the eastern and shallowest summit isabout 750 m below the winter mixed-depth layer (Bashmachni-kov et al., 2009), with an approximate planar area of about 43 km2

at the 800-m depth contour. Seine seamount rises from a depth ofabout 4000 m. The shallowest depth is about 160 m, and theapproximate area at the 200-m depth contour is about 20 km2.

At Sedlo and Seine seamounts, the North Atlantic CentralWater (NACW) forms the shallower water mass down to600–700 m. Below, the Mediterranean Water (MW) occupies alayer from 700 to 1100–1400 m. The Labrador Sea Water (LSW)predominates below 1500 m, and the North Atlantic Deep Water(NADW) distributes lower than 2500 m. At Sedlo (from 700 to1000–1200 m), traces of other water masses can also beidentified: the SubArctic Intermediate Water (SAIW), the LabradorSea Water (found below the NACW) and the Antarctic Inter-mediate Water (AAIW). Slow currents dominate the LSW andthe NADW and spread to the south and east, while the MWoutflow spreads to the west at around 1000 m depth, and shoulddistribute deeper and have a strong influence at Seine seamount(Bashmachnikov et al., 2009).

Both seamounts are located in an area of some oceanographiccomplexity, influenced by the Azores current (AzC) or the NorthAzores Flow (NAzF), with this probably having a great influence atSedlo. These flows are linked to the Gulf Stream and are subject tohigh seasonal changes in their dynamics.

2. Material and methods

2.1. Fish surveys

The longline investigations at both seamounts were carried outby the R/V ‘‘Arquipelago’’ (25 m long). The Seine seamount surveytook place in July 2003, while the cruise survey to Sedlo seamountwas made in two missions, the first in October 2003 and thesecond in September 2004.

Fish populations were sampled through several longlinestations in a depth-stratified sampling design by intervals of50 m. In all surveys we used a transect strategy where acontinuous length of gear was deployed in a single fishing

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G.M. Menezes et al. / Deep-Sea Research II 56 (2009) 2683–27042684


operation. Transects were roughly set down the seamount flanks,which made the fishing effort (no of hooks) to be allocatedproportionally to the size of each depth stratum.

2.2. Sampling gears and fishing operations

At each seamount two different longline arrays (LLA and LLB,see Fig. 3) were deployed in a total of eight fishing operations:four shallower sets from the summit to about 1300 m depth, andfour deeper sets between 800 and 2000 m. In total, eight stations(four for each longline type) were sampled at each seamount(Table 1).

Both longlines consisted of several units (mainline units or‘‘quarter-skate’’ units), arranged in wood cages (‘‘skates’’). Twodifferent longlines were used to avoid gear and fishing losses indeepest areas. Large deep-water sharks and other species withsharp teeth (e.g., A. carbo) dominate in deeper waters and in thesecircumstances the nylon branch-lines may be easily cut. For thisreason the hook sizes must be larger and tied differently.Changing the main-lines’ orientation (from horizontal to vertical)and using a smaller number of large hooks decreased the contactof the gear with the seabed and also decreased the risks of havingan excessive weight to be hauled from very deep-waters.

Longline A (Fig. 3)—This longline (hereafter referred to as LLA)is identical to the one often used in the commercial fishery in the

Azores and has been the standard gear used in other demersal fishsurveys carried out in the Madeira and Azores archipelagos(Menezes et al., 2006). Each mainline unit is disposed in each ofthe four skate sides (‘‘quarter-skate’’), and is attached to eachother when the gear is being deployed. The mainline is connectedto the main-rope and a floating buoy through a tying rope with asnap swivel at the edge, which is laid down every two mainlineunits. In between two successive floating buoys, a stone (approx.71 kg) is connected to the mainline also every two mainline units.The hooks used in LLA were J-type hooks (gape of 12 mm), baitedwith chopped-salted sardine. The upper hooks near the buoysshould lie, on average, between 10 and 20 m off the bottomdepending on currents, deploying velocity or depth.

Longline B (Fig. 4)—This gear (hereafter referred to as LLB),which was used in the deeper sets, has a different disposition ofmainline. In this case, the mainline units are not linked to eachother but are attached separately by tying each rope to themain-rope staying in a vertical position. Each mainline unit had 10J-type hooks (gape of 18 mm), attached to the branch-line by asteel twisted brass fixture (‘‘belisqueiro’’—length 728 cm), andthe hooks were baited alternating with chopped-salted sardine,squid and shrimp. Both gears minimize the risk of gear loss in thetypically rugged bottoms of the areas surveyed, and provideeffective fishing of benthic and benthopelagic species.

In all surveys, the LLA was normally deployed one hour beforesunrise, and line retrieval usually started three hours later. Due to

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Fig. 1. The Azores archipelago and the Sedlo seamount location, with indication of the longline sampling transects (PAL—Princesa Alice Bank).

G.M. Menezes et al. / Deep-Sea Research II 56 (2009) 2683–2704 2685

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Fig. 2. The Madeira archipelago and the Seine seamount location with indication of the longline sampling transects.

Table 1Summary characteristics of the surveyed stations over the Sedlo and Seine seamounts under the OASIS project.

Smt Station code Date Position start Position end Depth (m) Effort (no. hooks)

Lat. (N) Long. (W) Lat. (N) Long. (W) Start End

Sedlo seamount Sedlo(1)O03 21/10/03 40121.710 26135.550 40118.890 26137.890 742 1160 2568

Sedlo(1)V04 16/09/04 40116.010 26139.330 40113.960 26142.180 762 1257 2940

Sedlo(2)V04 15/09/04 40116.430 26139.030 40114.460 26139.030 757 1222 1776

Sedlo(3)V04 14/09/04 40116.350 26138.860 40116.450 26135.790 757 1300 2044

SedloP(1)V04 15/09/04 40112.490 26139.240 40115.040 26138.890 958 2011 427

SedloP(3)V04 14/09/04 40115.520 26133.470 40116.040 26136.600 1106 1948 496

SedloP(4)O03 22/10/03 40122.740 26133.750 40119.820 26137.180 814 1903 910

SedloP(5)O03 23/10/03 40120.540 26132.790 40121.390 26150.110 874 1071 508

Seine seamount Seine(1)V03 13/07/03 33149.020 14121.160 33152.250 14121.860 199 1287 2567

Seine(2)V03 14/07/03 33147.630 14120.960 33147.940 14117.850 185 1241 2673

Seine(3)V03 15/07/03 33145.930 14121.270 33142.000 14120.330 180 1154 3186

Seine(4)V03 16/07/03 33147.340 14122.430 33146.610 14127.410 201 1229 3052

SeineP(5)V03 17/07/03 33151.720 14121.900 33153.440 14122.110 767 2000 452

SeineP(6)V03 17/07/03 33143.050 14120.670 33140.570 14119.860 840 2100 432

SeineP(7)V03 18/07/03 33146.940 14135.610 33146.350 14129.270 939 2094 544

SeineP(8)V03 18/07/03 33147.860 14118.570 33148.110 14116.430 767 1993 429


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Fig. 3. Schematic representation of the ‘‘stone-buoy’’ horizontal Longline A (LLA) used down to the 1300 m depth.

Fig. 4. Schematic representation of the vertical Longline B (LLB) used in the 751–2000-m depth interval.



operational reasons, in deeper sets (LLB) the line was deployed atdifferent times of the day, and the soak time varied between fourand nine hours.

2.3. Sampling effort

The effective fishing effort (those hooks that fish effectively)by station and depth stratum was calculated by subtracting theestimated missing hooks (lost or tangled hooks) from theestimated total number of hooks deployed. These estimationswere obtained through hook counting and sampling during gearretrieval (one observer counts and classifies the hooks as baited,unbaited, with fish or lost). Because the number of hooks in each‘‘quarter-skate’’ may vary, the total number of hooks deployed isestimated from an average of hooks per ‘‘quarter-skates’’.

The allocation of fishing effort by depth was dependent on thelocal topography and local slope. At Seine seamount the estimatedtotal number of hooks released was 13,425 for LLA and 1950 forLLB, and the estimated effective fishing effort applied was 11,478and 1857 hooks, respectively. At Sedlo seamount the estimatedtotal number of hooks released was 11,594 for LLA and 2700 forLLB, and the estimated effective fishing effort applied was 9328and 2341 hooks, respectively (Table 1). At both seamounts someportions (mainline units) were entangled or lost due to the ruggedbottom, resulting in zero fishing effort in some depth strata(missing values).

2.4. Biological sampling and fish data

All fishes caught were sorted and identified to the lowesttaxonomic level possible (usually species), counted, weighed andmeasured. The nomenclature and other auxiliary information onspecies follow Compagno (1984a, 1984b), Whitehead et al. (1984,1986), Santos et al. (1997) and FishBase (Froese and Pauly, 2005).More detailed biological sampling was conducted on somespecies, and the biological material collected was preserved tobe analysed for studies of trophic pathways, fish genetics,reproduction or growth.

2.5. Analytical methods

Because the species richness is almost always underestimatedin any sampling, and varies with the fishing methods used, speciesarea curves were constructed, following the jack-knife procedureimplemented in the PC-ORD ver. 4.25 (McCune and Mefford,1999), to estimate the maximum number of existing speciessusceptible to be caught in each area with the longlines used, inorder to evaluate the adequacy of sub-sampling.

To study the general depth distribution patterns of abundanceand biomass for each seamount, the total catch per unit effort(CPUE) by depth strata was calculated following Eq. (1), for eachlongline type (for numbers and weight-no. Ind./1000 hooks andkg/1000 hooks).

CPUE ¼ Catch ðno: Ind: or kgÞhooks� 1000 (1)

To characterize the vertical structure of the demersal fishassemblages of Sedlo and Seine we used the hierarchicalunweighted pair group method using arithmetic averages(UPGMA) cluster analysis (using PRIMER v.5) separately for eachseamount based on a triangular matrix of Bray–Curtis similaritycoefficients following Field et al. (1982).

Due to the small number of samples, the species catch data andthe fishing effort from the two longline types were pooled andaggregated in 100-m depth intervals. In this way two samples/species catch rates matrices were built and analysed. A few

uncommon samples/strata observations were excludedfrom the pooled matrix because they distorted excessively theresulting display. In general these observations only includeone unusual fish species in the catch, or most of the hookswere lost. The excluded observations were (strata/station code):24/SEDLO(3)V04, 25/SEDLOP(4)O03, 36/SEDLOP(4)O03 and35/SEINEP(7)V03.

The catches of Scomber colias below the 300 m depth wereexcluded from all analyses because on many occasions this speciesis caught in the water column during descent and/or ascentof the longline; hence allocation to any specific depth strata isimpossible.

Similarity, permutation tests (ANOSIM, po5%; Clarke andWarwick, 2001) implemented in the PRIMER v.5 software packagewere run to test the null hypothesis that there were no differencesbetween groups of samples as a function of (1) longline type(LLA and LLB) and (2) location (differences between fishassemblages of Seine and Sedlo seamounts at comparable depthintervals for each longline type). In ANOSIM, an R statistic iscalculated, and a permutation test is used to analyse whether theR statistic is significantly different from zero. The R statistic, whichfalls between 0 and 1, reflects the rank similarities within andbetween sites, and can be seen as a comparative measure of thedegree of separation of sites. The R value is approximatelyzero when similarities between and within sites are the sameon average.

The SIMPER procedure of the PRIMER software was applied toidentify characteristic species that most contribute to thesimilarities within sites or discriminate between sites or betweenthe two longline types used at comparable depths (Clarke andWarwick, 2001).

The relation of the biotic similarity matrix with the environ-mental data of each seamount was analysed with the BIO-ENVprocedure (Clarke and Ainsworth, 1993) also implemented inPRIMER v.5. This analysis consists of choosing a subset ofenvironmental variables that provides the best match with thebiotic similarity matrices. The strength of agreement between thebiotic and abiotic samples similarity matrices was determined bythe Spearman rank correlation coefficient. The environmentaldissimilarity matrices used in the BIO-ENV analysis were basedon normalized Euclidean distances (Clarke and Warwick, 2001).Environmental data were obtained from a calibrated CTD(Sea-Bird SBE 19plus) at several pre-defined stations over theseamounts and in adjacent areas to 2000 m depth. Average valuesper 50- and per 100-m depth intervals for temperature, O2,salinity and chlorophyll a were calculated and assumed equal forall stations sampled at each seamount.

3. Results

3.1. Species composition and catch patterns

Considering all the samples and gear types (i.e., LonglineA—LLA and B—LLB), a total of 22 different species were caught atSedlo seamount. Of these, 11 were teleosts, 9 elasmobranchs and2 holocephalids (Table 2). Among the eight families of teleostspecies identified, Moridae were best represented with threespecies, while among the four families of elasmobranch species,Dalatiidae were best represented with five species.

At Seine seamount a total of 41 different species were caught:28 teleosts, 12 elasmobranchs and 1 holocephalid (Table 3).Among the 18 families of teleost species identified, the Moridaedominated with five species, while among the five elasmobranchfamilies the Dalatiidae were best represented with six species.

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The species curve analyses for each longline type andseamount show that the fish species susceptible to being caughtare reasonably represented. For Sedlo seamount the jack-knifeprocedure estimated 18 species for LLA and 27 for LLB, while forSeine seamount the estimated number of species amounted to 42for LLA and 27 for LLB. The observed number of species caught atthe two seamounts corresponds to about 80% and 70% of theestimated number of species caught by LLA and LLB, respectively,meaning that only a few additional species can be expected with ahigher longline sampling effort.

At Sedlo seamount, the alfonsino (B. splendens) and thecardinal fish (E. telescopus) comprise about 52% and 22%,respectively, of the LLA catches in terms of numbers, and 33%and 39% in terms of weight, and were mainly due to the unusuallyhigh quantities of both species caught at station SEDLO(1)V04near the east summit of the seamount (Table 2). Between 800and 2000 m depth, the species Centrophorus squamosus, Mora

moro, Centroscymnus coelolepis and Etmopterus princeps compriseabout 78% of the number and 90% of the weight caught with theLLB (Table 2).

The species Trachurus picturatus and Helicolenus d. dactylop-

terus corresponded to about 56% of the specimens caught (33% in

weight) with the LLA at Seine seamount. With the LLB (800–2050-m depth interval), the species C. coelolepis, Synaphobranchus

kaupii, and M. moro made up more than 59% of the catches innumber and 59% in weight.

At Seine seamount, T. picturatus was the most caught speciesin terms of weight and number (234 kg and 560 individuals) atdepths o200 m, corresponding to about 60% of all catches interms of number (Fig. 6). In the 300–500-m depth interval H. d.

dactylopterus was the most frequent species, while between 701and 1300 m the catches were dominated by the M. moro and thedeep-water sharks Deania cf. calcea and Etmopterus pusillus. Thecatches of the LLB were dominated by the species M. moro, Deania

cf. calcea and A. carbo between the 701- and 1300-m depthinterval. The deep-water shark, C. coelolepis, is dominant below1300–2000 m depth, along with S. kaupii. The species Antimora

rostrata appears to be highly abundant below 1900 m depth atSeine seamount.

The species depth composition at the two seamountsreveals a continuous replacement of dominant speciesand some differences between longlines. At both seamounts,the deep-water sharks dominate in the deepest strata (Figs. 5and 6).

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Table 2Species catch data in number and weight obtained at Sedlo seamount by longline type.

Longline type Family Species code Common name Species Number (no. Ind.) Weight (kg)

Longline A Centrophoridae XAR Leafscale gulper shark Centrophorus squamosus 10 97.8

SAP1 Birdbeak dogfish Deania cf. calcea 21 56.6

Dalatiidae COL Portuguese dogfish Centroscymnus coelolepis 1 7.2

SAP3 Longnose velvet dogfish Centroselachus crepidater 3 2.5

LIX3 Great lanternshark Etmopterus princeps 6 5.8

Pseudotriakidae PSE False catsharks Pseudotriakis microdon 1 73

Berycidae ALF Alfonsino Beryx splendens 745 746.6

Epigonidae ESC Cardinalfish Epigonus telescopus 310 893.3

Moridae MMO1 North Atlantic codling Lepidion eques 1 1

MMO3 Eastern N. Atlantic codling Lepidion guentheri 3 4.5

MMO Common mora Mora moro 260 388

Phycidae ABR2 Greater forkbeard Phycis blennoides 1 2.3

Synaphobranchidae CGI Kaup’s arrowtooth eel Synaphobranchus kaupii 20 5.3

Trichiuridae EPR Black scabbardfish Aphanopus carbo 5 5.8

ESP1 Elongate frostfish Benthodesmus elongatus simonyi 21 4.3

Sub-total 1408 2293.8

Longline B Centrophoridae XAR Leafscale gulper shark Centrophorus squamosus 82 661.2

SAP1 Birdbeak dogfish Deania cf. calcea 7 20



CRY Shortnose velvet dogfish Centroscymnus cryptacanthus 1 3.1

LIX3 Great lanternshark Etmopterus princeps 24 24

LIX2 Smooth lanternshark Etmopterus pusillus 1 0.4

Hexanchidae HEX Bluntnose sixgill shark Hexanchus griseus 2 –

Pseudotriakidae PSE False catsharks Pseudotriakis microdon 1 –

Chimaeridae HAF Smalleyed rabbitfish Hydrolagus affinis 2 20.8

HMI Large-eyed rabbitfish Hydrolagus pallidus 1 –


Moridae MMO1 North Atlantic codling Lepidion eques 1 0.6


MMO Common mora Mora moro 55 33.7

Ophidiidae SPG Pudgy cuskeel Spectrunculus grandis 1 5.2

Scophthalmidae ARE Megrim Lepidorhombus whiffiagonis 1 2.6



Sub-total 255 1163.2

Total 1663 3457



3.2. Comparison between sampling methods and seamounts

Comparisons between the catches of the two longlines geartypes in the overlapping depth interval give significant differencesin the species caught (see Fig. 7). In general results give small R

statistic values (high similarities) but significant differences bothin Sedlo and in Seine seamounts (SedloLLB vs. SedloLLA: ANOSIMglobal R ¼ 0.276 p-level ¼ 0.3%; SeineLLB vs. SeineLLA: ANOSIM

global R ¼ 0.403 p-level ¼ 0.1%). The LLB appears to be moreefficient in catching those species with sharp teeth and large sizes(e.g., A. carbo, and several deep-water sharks) when comparedwith the catches of the LLA at the same depths (Fig. 7). In this casethe branch-lines to the hooks of the LLA appear to be easily cut.

Differences in the species composition between the twoseamounts (at those comparable depth intervals: 801–1200 mfor LLA and 801–2000 m for LLB samples, Fig. 8) appear not very

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Table 3Species catch data in number and weight obtained at Seine Seamount by longline type.

Longline type Family Species codes Common name Species Number (no. Ind.) Weight (kg)

Longline A Centrophoridae XAR Leafscale gulper shark Centrophorus squamosus 1 7.65


SAP2 Arrowhead dogfish Deania profundorum 11 28.65

Dalatiidae SAP3 Longnose velvet dogfish Centroselachus crepidater 2 5.22

CRY Shortnose velvet dogfish Centroscymnus cryptacanthus 1 6

LIX2 Smooth lanternshark Etmopterus pusillus 21 6.15

SQU Spined pygmy shark Squaliolus laticaudus 1 0.07

Rajidae RAI1 Thornback ray Raja clavata 7 10.44

Scyliorhinidae LET Blackmouth catshark Galeus melastomus 50 51.74

Berycidae IMP Alfonsino Beryx decadactylus 14 15.3

ALF Slendid alfonsino Beryx splendens 84 30.66

Carangidae CHI Blue jack mackerel Trachurus picturatus 560 234.72

Congridae CGR Conger eel Conger conger 15 39.25


Lotidae GDR Azores rockling Gaidropsarus granti 1 0.22

Macrouridae RAT2 Common Atlantic grenadier Malacocephalus laevi 11 2.46

Moridae GAD Gadella Gadella maraldi 1 0.12



MMO4 Black codling Physiculus dalwigki 1 0.75

Phycidae ABR2 Greater forkbeard Phycis blennoides 6 5.09

ABR1 forkbeard Phycis phycis 8 14.72

Polymixiidae SAL Stout beardfish Polymixia nobilis 4 1.33

Polyprionidae CHE Wreckfish Polyprion americanus 14 62.86

Scombridae CAV Atlantic chub mackerel Scomber colias 121 57.46

Scorpaenidae BAG Offshore rockfish Pontinus kuhlii 78 32.57

Sebastidae BCN Blackbelly rosefish Helicolenus d. dactylopterus 270 105.34

Serranidae ANT Swallowtail seaperch Anthias anthias 2 0.13


Tetraodontidae BAL Blunthead puffer Sphoeroides pachygaster 1 2.8


ESP1 Elongate frostfish Benthodesmus elongatus simonyi 8 3.53

ESP Silver scabbardfish Lepidopus caudatus 1 0.45

Triglidae CAB East Atlantic red gurnard Aspitrigla cuculus 10 4.31

Sub-total 1481 1030.4

Longline B Centrophoridae XAR Leafscale gulper shark Centrophorus squamosus 7 53.23


SAP2 Arrowhead dogfish Deania profundorum 1 0



CRY Shortnose velvet dogfish Centroscymnus cryptacanthus 7 28.94

LIX3 Great lanternshark Etmopterus princeps 2 2.05

Pseudotriakidae PSE False catsharks Pseudotriakis microdon 3 32.91

Chimaeridae HAF Smalleyed rabbitfish Hydrolagus affinis 1 13.02

Bramidae XAP2 Bigscale pomfret Taractichthys longipinnis 2 4.48

Macrouridae Coryphaenoides mediterraneus 1 0.93

Moridae MMO7 Blue antimora Antimora rostrata 5 8.76





Sub-total 135 501.22

Total 1616 1532



pronounced as indicated by the low values of the global R

statistics obtained (from the non-parametric ANOSIM).Despite the low R statistics, there are significant differences inthe specific catch composition between the two seamount at thedepth intervals considered (SedloLLA vs. SeineLLA: ANOSIMR ¼ 0.158 p-level ¼ 0.1%; SedloLLB vs. SeineLLB: ANOSIM R ¼ 0.179p-level ¼ 0.1%).

Considering the samples obtained with the LLA (Fig. 8), theSIMPER results (Table 1A, url) revealed that the species M. moro

accounts for more than 50% of the average similarity among thesamples at each seamount. The species that contribute mostto discrimination between the two seamounts are M. moro,B. splendens, Deania cf. calcea, S. kaupii and E. telescopus, with anaverage dissimilarity between the two seamounts of about 69%.The Seine samples were on average less heterogeneous(samples average similarity 49%) than the samples of the Sedloseamount (30%).

The SIMPER results on the similarity matrices of the LLBsamples (Table2A url) give low average similarities amongsamples at each seamount (25% for Sedlo and 20% for Seine).The average dissimilarity between the two seamounts isabout 86%. The species that contribute most to theobserved average dissimilarities were E. princeps and C. coelolepis

(Fig. 8).

3.3. Single-species depth distribution and size structure

Depth ranges of individual species for each seamount (poolingthe catches of each longline type) are shown in the Fig. 9A and B.It should be mentioned that the deeper and shallower distributionlimits of the species may be truncated by the maximum andminimum surveyed depths at each seamount, and results mayalso be less precise for those species with low abundances. As canbe seen, the species occurring in deep-waters tend to have widerdeep distribution ranges. The larger depth ranges were observedfor S. kaupii, C. squamosus or C. coelolepis.

For those species occurring at both seamounts and livingbelow 701 m (the minimum surveyed dept at Sedlo seamount), acomparison of their maximum depth of occurrence is plotted inFig. 10. To be comparable, only those species with adequatenumber of records and whose known distributions are well belowthe shallower bathymetric limit of Sedlo seamount were includedin this analysis. The selected species appear to distribute slightlydeeper at Seine seamount when compared with Sedlo, except thespecies C. squamosus whose maximum depth of occurrence wasnoted at Sedlo. The species E. princeps shows similar depthdistributions at both seamounts.

The summary statistics of length frequency distributions of allspecies caught at the two seamounts are presented in Tables 4

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Fig. 5. Relative frequency of the main species caught by depth strata and longline type at Sedlo seamount.



and 5. In general, for all species, the catches were dominated byadult fishes.

Considering those species present at both seamount areas,significant differences (Kolmogorov–Smirnov tests, K–S, po0.001;following Sokal and Rolf, 1995) were found in the lengthdistributions of B. splendens, E. telescopus and M. moro, whichtend to be larger at Sedlo seamount. No differences (K–S, p40.05)between the two seamounts were obtained for the lengthdistributions of the species S. kaupii, C. coelolepis, A. carbo andDeania cf. calcea.

The unusual catches of B. splendens and E. telescopus atstation SEDLO(1)V04 mainly comprised large specimens withadvanced gonad maturation stages (developing or spawning/mature gonads). In the case of E. telescopus, about 78% of the

specimens were in spawning condition, while in the caseof B. splendens about 60% of the observed gonads were in thepre-spawning stage.

There is an overall increase in mean body weight with depth(Fig. 11), followed by a decrease below 1800 m. At Sedlo seamount,the mean body weight increases with depth and for both longlinetypes, and the highest mean sizes were observed in the interval1101–1200 m. At Seine seamount the mean fish size from the LLBpeaks in the interval 1801–1900 m, while for the LLA the meansize increase is not so pronounced and the largest values wereobtained in the 701–1200-m depth interval. The observed depthtrends of the mean body weight at Sedlo and Seine were similar inthe interval 1300–2000 m, and in both cases, there is an abruptdecrease in the mean weight below 1800 m depth. The results also

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Fig. 6. Relative frequency of the main species caught by depth strata and longline type at Seine seamount.



show that the LLA tends to catch smaller fishes when comparedwith the LLB, as can be observed in those overlapping depth stratacovered by both gears (701–1300 m, Fig. 9). As shown before thesedifferences are mainly caused by higher catches of large deep-water sharks by the LLB when compared with the catchcomposition of the LLA.

3.4. Patterns of abundance, biomass and species richness

The geographical and depth-related variation in abundance,biomass indices for all species pooled by gear type is shown inFig. 12A–D. The average catch rates by depth strata at Sedlo variedfrom 20 to 243 Ind./1000 hooks and 129 to 318 kg/1000 hooks forLLA. For LLB values varied from 12 to 208 Ind./1000 hooks andfrom 129 to 975 kg/1000 hooks. At Seine catch rates varied from34 to 193 Ind./1000 hooks and from 37 to 164 kg/1000 hooks for

LLA. For LLB values varied from 10 to 173 Ind./1000 hooks and 26to 762 kg/1000 hooks. The depth profiles of overall abundance andbiomass indices based on the two longline types are variableand in some cases with no defined trends (Fig. 12A–D). Significantdecreasing trends with increasing depth are observed forabundance indices from catches with the LLA at both seamounts(SeineLLA, Abund.: rs ¼ �0.68; po0.05; SedloLLA, Abund.: rs ¼ �0.90;po0.05), for biomass and abundance indices obtained with LLB inSeine (SeineLLB, Abund.: rs ¼ �0.80; po0.05; SeineLLB, Biom.:rs ¼ �0.58; po0.05), and for the biomass at Sedlo obtained withLLB (SedloLLB, Biom.: rs ¼ �0.62; po0.05). A non-significantpositive trend was obtained at Seine seamount for the biomassindex derived from the LLA catches (SeineLLB, Biom.: rs ¼ �0.39;p40.05). Non-significant negative trends were also obtained atSedlo seamount for the biomass index derived from the LLA andabundance index arising from LLB catches (SedloLLB, Biom.:rs ¼ �0.70; p40.05, SedloLLB, Abund: rs ¼ �0.43; p40.05).

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Fig. 7. Pairwise comparison at comparable depths of the species-by-species catch rates obtained by the two types of longlines used at Seine and Sedlo seamounts.



Species richness by depth strata varies between 16 and 1 atSeine and between 12 and 1 at Sedlo seamount. The number ofspecies caught was higher at Seine due to the more speciousshallower depths covered (Fig. 13). Species richness decreasessignificantly with depth at the two seamounts, and, in general, thespecies richness at both seamounts is similar at coincident depthstrata (Seine: rs ¼ –0.82; po0.05; Sedlo: rs ¼ –0.71; po0.05)(Fig. 13). At Seine seamount two main discontinuities in speciesrichness can be distinguished: one in the depth interval701–800 m, and the other at 1300–1400 m. At Sedlo the mainspecies richness discontinuity is more or less coincident with theSeine discontinuity at about 1200–1300 m.

3.5. Multispecies distribution patterns

Cluster analysis showed a clear depth-aligned assemblagestructure at each seamount (Fig. 14A and B), when considering

the dendrogram clusters at 50–60% similarity levels. At Sedloseamount three main assemblages were distinguished (Fig. 14A):one cluster in the 700–800 m interval (SD1), a second clusterfrom 801 to 1200 m depth (SD2), and a third cluster from1301 to 2000 m (SD3). At Seine, four main clusters can beconsidered (Fig. 14B): a shallow slope cluster between 101and 400 m depth (SN1); an upper mid-slope cluster in theinterval 401–700 m (SN2), a deep mid-slope cluster in the701–1300 m interval (SN3) and a deep slope cluster from 1301to 2000 m depth (SN4). For Sedlo seamount the averagesimilarities within each group vary between 56% and 67%.The dissimilarity between SD2 and SD3 groups is about 79%.The species that contribute most to discrimination between SD2and SD3 clusters were E. princeps and C. coelolepis (dominantspecies in the SD3 cluster) and C. squamosus. B. splendens,most abundant in the SD1 cluster, and C. squamosus werethe main discriminating species between the SD1 and SD2assemblages. A complete dissimilarity with almost no species in

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Fig. 8. Pairwise comparison at comparable depths of species-by-species catch rates between the two seamounts.



common was obtained between the SD3 and SD1 (Fig. 15 andSIMPER results, Table A3 url).

At Seine seamount the average similarities for each mainassemblage considered vary between 45% for SN4 and 59% forSN2. The dissimilarity between the cluster combinations SN3/SN1and SN4/SN1 was 100%, with no species in common. Highdissimilarity values also were obtained among the other groupcombinations, reflecting a clear depth distribution patternof fish assemblages. Separation between the SN1 and SN2 clusterswas mainly due to the high abundance values of T. picturatus inthe SN1 cluster and higher abundances of H. d. dactylopterusand M. moro in the SN2 assemblage. M. moro, H. d. dactylopterus

and B. splendens are the main discriminating species be-tween the SN2 and SN3 clusters. Between the SN3 and SN4assemblages M. moro and Centrophorus coelolepis account for alarge proportion of the dissimilarity (Fig. 16 and SIMPER resultsTable A4 url).

The strength of agreement between the biotic and abioticsamples (dis)similarity matrices as given by the BIO-ENV analyseswas, in general, high. For Seine, the depth/temperature combina-tion gives the best matching values (0.85) with the bioticsimilarity matrix, and for Sedlo, the temperature alone and theoxygen/temperature combination gives the best matching valuesof about 0.88.

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Fig. 9. Individual bathymetric distribution range of the species caught at Sedlo seamount (A) and Seine seamount (B). Mean depth of occurrence and minimum and

maximum depths of occurrence, obtained from all surveys pooling the data from the two longline types used.



4. Discussion

We have described and quantified the vertical fish assemblagestructure of demersal and deep benthopelagic fishes occurringover Sedlo and Seine seamounts. We focus on species composi-tion, depth distribution, size structure and on the main ecologicalpatterns of abundance, mean body weight and species richness.

4.1. Species composition

For Seine seamount a total of 41 fish species from 24 differentfamilies were recorded, whereas at Sedlo a total of 30 species from18 different families were caught. When combining these datawith the trawl catches from Sedlo (Menezes et al., in prep.) andSeine (Christiansen et al., 2009), the number of species known tooccur at Sedlo seamount increases to 80 species in 42 different

families, corresponding to about 16% of all species recorded forthe Azores to date (Santos et al., 1997), and to 52 species in 34families at Seine seamount.

The knowledge of species composition and ecological featuresof any fish community is largely dependent on the samplingmethods used (Merrett et al., 1991a, b; Bjordal and Løkkeborg,1996; Albert and Bergstad, 1993). In this work, the surveyedichthyofauna was dominated by top predators and scavengingdemersal or benthopelagic fishes attracted to bait. The sizedistributions obtained also show that adult fishes tend todominate the longline catches, as was also observed elsewhere(e.g., Bjordal and Løkkeborg, 1996; Menezes, 2003).

Despite the low number of samples, the OASIS surveys cover abroad depth range (101–2000 m in Seine and 700–2200 m inSedlo) and allowed the catch of about 80% and 70% of theestimated theoretical maximum number of fish species occurringat Sedlo and Seine seamounts, (i.e., the fish assemblage suscep-tible to the longlines used in this study). Several sampling gearshave been used at Sedlo (e.g., longlines, trawl, video, traps), and todate the ichthyofauna of Sedlo and Seine is probably one of thebest known when compared with other North Atlantic seamounts.

At comparable depths, based on the species caught and thespecies lists from previous works (Menezes, 2003; Menezes et al.,2006; Uiblein et al., 1999), we can conclude the existence of highfaunistic affinities between Seine and Sedlo seamounts and to theneighbouring areas of the Azores and Madeira archipelagos, or theGreat Meteor Seamount. A detailed biogeographic description isout of the scope of the present work, but in general, the marinefauna of the Madeira and Azores islands and neighbouringseamounts have a mixture of species, with higher affinities tothe eastern Atlantic and the Mediterranean when compared withthe western or east northern areas of the Atlantic (Lloris et al.,1991; Santos et al., 1997; Gomes et al., 2001; Gaertner, 2000;Menezes et al., 2006).

From a total of 37 different species caught in the 800–2000-mdepth interval, 17 species occurred at both seamounts. Multi-variate statistical analysis suggests differences in fish assemblages

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Fig. 10. Maximum depth of occurrence of the main species caught, common to the

Sedlo and Seine seamounts.

Table 4Summary descriptive statistics of the length composition of the species caught at Sedlo seamount.

Species Common name Species code Number (no. Ind.) Length (cm)

Min. Mean Max. Mode S.D.

Centrophorus squamosus Leafscale gulper shark XAR 91 101 113.4 131 110 6.8

Deania cf. calcea Birdbeak dogfish SAP1 26 77 87.6 106 80 7.5

Centroscymnus coelolepis Portuguese dogfish COL 38 87 103.6 121 96 9.4

Centroselachus crepidater Longnose velvet dogfish SAP3 2 76 77.5 79 – 2.1

Centroscymnus cryptacanthus Shortnose velvet dogfish CRY 1 82 82 82 – –

Etmopterus princeps Great lanternshark LIX3 29 21 56.7 70 58 20.5

Etmopterus pusillus Smooth lanternshark LIX2 1 43 43 43 – –

Hexanchus griseus Bluntnose sixgill shark HEX 2 190 199.5 209 – 13.4

Pseudotriakis microdon False catsharks PSE 2 211 226 241 – 21.2

Hydrolagus affinis Smalleyed rabbitfish HAF 2 114 115.5 117 – 2.1

Hydrolagus mirabilis Large-eyed rabbitfish HMI 1 – – – – –

Epigonus telescopus Cardinalfish ESC 265 36 56.8 71 65 8.2

Lepidion eques North Atlantic codling MMO1 1 51 51 51 – –

Lepidion guentheri Eastern N. Atlantic codling MMO3 5 45 60.1 84 – 16.2

Mora moro Common mora MMO 245 35.5 52 69 51 6.5

Spectrunculus grandis Pudgy cuskeel SPG 1 88 88 88 – –

Lepidorhombus whiffiagonis Megrim ARE 1 78 78 78 – –

Synaphobranchus kaupii Kaup’s arrowtooth eel CGI 21 48 57.2 65 60 4.7

Beryx splendens Alfonsino ALF 296 29.5 36.4 42.5 37 2.4

Phycis blennoides Greater forkbeard ABR2 1 64 64 64 – –

Aphanopus carbo Black scabbardfish EPR 9 77 100.1 115 101 11.3

Benthodesmus elongatus simonyi Elongate frostfish ESP1 16 72 94.3 103 94 7.7



between the Sedlo and Seine seamounts (at comparable depths),but these results must be interpreted with care. Contrastsobtained may reflect differences in the relative abundance of the

species regardless the similarities of the taxa occurring inboth seamounts. On the other hand, the low number of repli-cates and the low diversity of the sites being compared may

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Table 5Summary descriptive statistics of the length composition of the species caught at Seine seamount.

Species Common name Species code Number (no. Ind.) Length (cm)

Min. Mean Max. Mode S.D.

Centrophorus squamosus Leafscale gulper shark XAR 8 109 113.1 119 113 3.5

Deania cf. calcea Birdbeak dogfish SAP1 61 77 89.7 112 86 8.1

Deania profundorum Arrowhead dogfish SAP2 11 60 84.4 101 – 12

Centroscymnus coelolepis Portuguese dogfish COL 32 85 102 116 109 8.3

Centroselachus crepidater Longnose velvet dogfish SAP3 7 58 70.1 80 80 9.4

Centroscymnus cryptacanthus Shortnose velvet dogfish CRY 8 77 91.5 110 – 13.3

Etmopterus princeps Great lanternshark LIX3 2 57 59 61 – 2.8

Etmopterus pusillus Smooth lanternshark LIX2 21 36.5 40.8 44.5 43 2.6

Squaliolus laticaudus Spined pygmy shark SQU 1 23.5 23.5 23.5 – –

Raja clavata Thornback ray RAI1 7 46 60.1 77 49 12.9

Galeus melastomus Blackmouth catshark LET 50 57 69.9 77 71 4.2

Pseudotriakis microdon False catsharks PSE 2 158 158.5 159 – 0.7

Hydrolagus affinis Smalleyed rabbitfish HAF 1 125 125 125 – –

Taractichthys longipinnis Bigscale pomfret XAP2 2 42.5 43.8 45 – 1.8

Beryx decadactylus Alfonsino IMP 14 26 34.8 47 28.5 6.4

Beryx splendens Slendid alfonsino ALF 82 20.5 25.1 34 24.5 3.2

Trachurus picturatus Blue jack mackerel CHI 558 22.5 33 40 32.5 2.6

Conger conger Conger eel CGR 15 60 93.6 156 81 32.7

Epigonus telescopus Cardinalfish ESC 14 38.5 45.9 54 54 4.7

Gaidropsarus granti Azores rockling GDR 1 30.5 30.5 30.5 – –

Malacocephalus laevi Common Atlantic grenadier RAT2 12 35 42 52 38.5 4.9

Gadella maraldi Gadella GAD 1 24 24 24 – –

Lepidion guentheri Eastern N. Atlantic codling MMO3 3 36 64 80 – 24.3

Mora moro Common mora MMO 102 32.5 48.7 65 53 6.1

Physiculus dalwigki Black codling MMO4 1 27.5 27.5 27.5 – –

Antimora rostrata Blue antimora MMO7 5 46 56 63 – 7

Phycis blennoides Greater forkbeard ABR2 6 29.5 41.3 75 36 16.8

Phycis phycis Forkbeard ABR1 8 42 51.6 61 51 5.5

Polymixia nobilis Stout beardfish SAL 3 19.5 25.8 30.5 – 5.7

Polyprion americanus Wreckfish CHE 14 59 61.5 71 61 3.3

Scomber colias Atlantic chub mackerel CAV 114 24.5 34.2 44 34 3.3

Pontinus kuhlii Offshore rockfish BAG 78 19.5 28.9 36.5 28.5 3.9

Helicolenus d. dactylopterus Blackbelly rosefish BCN 268 15 27.2 41 23.5 5.4

Anthias anthias Swallowtail seaperch ANT 2 16 16 16 16 –

Synaphobranchus kaupii Kaup’s arrowtooth eel CGI 37 35.5 57.5 73 65 8.2

Sphoeroides pachygaster Blunthead puffer BAL 1 45.5 45.5 45.5 – –

Aphanopus carbo Black scabbardfish EPR 11 94 105.8 115 106 6

Benthodesmus elongatus simonyi Elongate frostfish ESP1 8 102 109.3 114 107 3.9

Lepidopus caudatus Silver scabbardfish ESP 1 83 83 83 – –

Aspitrigla cuculus East Atlantic red gurnard CAB 9 30.5 33.6 40.5 33.5 2.9

Fig. 11. Depth profiles of the total mean fish weights for each seamount and longline type.



decrease the power of the one-way ANOSIM test (increasethe probability of Type II error) (Clarke and Warwick, 2001).In spite of the significant differences observed, the small

global R values obtained (0.16 for LLA and 0.18 for LLB), mayindicate that similarities between seamounts will be the same, onaverage.

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Fig. 12. Depth profiles of the overall relative abundance (no./hooks�1000) and relative biomass (kg/hooks�1000) indices obtained for each seamount and longline type:

(A) and (B) LLA; (C) and (D) LLB.

Fig. 13. Total number of species caught over Seine and Sedlo seamounts in each 100-m depth stratum.



The unusual and localized spawning aggregations ofB. splendens and E. telescopus on the Sedlo summit (stationSEDLO(1)V04), and the spawning aggregations of orange roughy(H. atlanticus), also found for the first time in the Azores watersover Sedlo (Melo and Menezes, 2002), suggest that this seamountmay be an important spawning area for commercially importantspecies in the region. Several authors have suggested a spawningseason for B. splendens during the summer/fall (e.g., Vinnichenko,1997a; Gonzalez et al., 2003), which appears to agree with ourresults (obtained in September). Menezes (2003) found otherspawning aggregations in November over the Nova HolandaSeamount in the Cape Verde archipelago. Mixed schools ofE. telescopus and B. splendens were also observed by Hareide andGarnes (2001) on the top of several seamounts at the Mid-AtlanticRidge (MAR). The results obtained in the OASIS Sedlo surveyconstitute the first unequivocal observation of reproductiveactivity of both species in the Azores area. Previous surveys andreproductive studies of B. splendens in the Azores were not

conclusive and did not reveal any defined seasonal pattern at apopulation level (e.g., Isidro, 1996; Menezes et al., 2001). For theNew Caledonia area Lehodey et al. (1997) proposed a complex lifecycle and reproductive strategy of B. splendens linked to thepredominant local gyre circulation system involving differentseamounts in the path. They proposed the existence of ‘‘vegetativezones’’ where juveniles grow until they reach maturity, andreproductive zones inhabited by mature individuals. In theAtlantic, the reproductive strategy of B. splendens and E. telescopus

remains poorly understood. For management purposes, whetherthese reproductive aggregations occur periodically in the area andhow long they persist should be further investigated.

4.2. General vertical ecological patterns

Abundance and biomass indices obtained at the two surveyedseamounts are slightly larger than those obtained on the Madeira

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Fig. 14. Dendrograms obtained from the cluster analyses for each seamount after averaging the samples to each 100-m depth strata intervals, and pooling the samples from

the two longline types: (A) Seine Smt and (B) Sedlo Smt.



(period 1995–1997) and Azores islands slopes (data fromMenezes, 2003) at comparable depths. These results may be asign of fishing depletion effects over the islands’ sloped areas, butmay also relate to the well-documented pattern of increasedconcentrations of several fish species over seamounts (Boehlertand Genin, 1987; Rogers, 1994; Koslow, 1997). Higher standingstocks (including demersal fishes) over seamounts appear to bemainly supported by advected energy supply instead of auto-chthonous energy sources (Boehlert and Genin, 1987; Fock et al.,2002a), but further research is needed to better quantify andunderstand seamount functioning.

No unequivocal depth trends with abundance andbiomass indices were obtained at both sites and overarchingconclusions are uncertain. With the exception of the positivebiomass depth trend at Seine obtained with the LLA, in general,we obtained decreasing trends of abundance and biomass indicesat Sedlo and Seine, both for the LLA and for the LLB catches.At Sedlo, decreasing biomass trends obtained with the LLA andabundance depth trend from LLB catches were not significant, aswell as the positive biomass depth trend obtained from LLAcatches at Seine. Overall, significant decreasing trends wereobserved previously in the Madeira, Azores and Cape Verdearchipelagos (Menezes, 2003; Menezes et al., 2006) and on othercontinental slope areas (e.g., Mauchline and Gordon, 1991;Merrett and Haedrich, 1997). Food supply to demersal deep-seafishes has been suggested to be affected by productivity inepi- and mesopelagic layers, and the decreasing trends arenormally related to the general reduction in the food availabilitydown the slope.

At coincident shallower depth intervals abundance andbiomass indices were, in general, higher at Sedlo than at Seine(both for LLA and for LLB catch rates), probably reflecting theusual South to North latitudinal increase of species abundance.However, it should be noted that the reproductive aggregations ofB. splendens and E. telescopus found at Sedlo at the depth interval700–1000 m largely contribute to these differences. The higherproductivity regime at Sedlo seamount region (Kiriakoulakis et al.,2009; Martin and Christiansen, 2009) may explain the higherdemersal standing stocks observed when compared with Seineand also the differences observed on the size structures of somespecies. Among the common species to both OASIS study sites,significant differences were found in the size structure ofB. splendens, E. telescopus and M. moro, which tend to be largerat Sedlo seamount. More highly productive areas are normallyreflected in greater abundance, biomass, or larger mean fishweights (Haedrich and Rowe, 1977; Merrett and Haedrich, 1997),and changes in fish community structure (Merret, 1987; Collinset al., 2005).

In deeper waters no clear latitudinal pattern can be assigned,but in some depth strata the observed relative abundance andbiomass indices were higher at Seine mainly due to the highcatches of C. coelolepis. At Sedlo the mean body weight peaks ataround 1200 m depth, while at Seine a steady increase with noclear discontinuities was found, but large values were obtained indeeper waters (between 1500 and 1800 m depth). At both sites anabrupt decrease in the mean body weight is observed below1800 m. The differences found in the depth profiles of mean bodyweight result from differences in species dominance, but also

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Fig. 15. Relative frequency (in terms of numbers) by species for each cluster shown in Fig. 14A for Sedlo seamount.



from differences in depth distribution of the species in each area,in particular, the distribution of large deep-water sharks (Deania

cf. calcea, C. squamosus or C. coelolepis). As shown, these speciestend to distribute slightly deeper at Seine than at Sedlo,explaining the larger mean body weight observed at Seine below1500 m. The distribution of these mid-slope dominating species(Hareide and Garnes, 2001; Iglesias and Munoz, 2001) may bephysiologically influenced by prevailing hydrographical condi-tions in each region. The influence of the Mediterranean Waterthat affects a wider depth range at Seine (Bashmachnikov et al.,2009) can, in part, explain the deeper occurrence of these andother species whose distribution may coincide with that of MW(see Fig. A1 url for differences in water temperatures, salinity andO2 concentrations between Seine and Sedlo). Differences in thedepth range of influence of the prevailing water masses affectinglocal depth profiles of temperature, salinities or O2 concentrations(or their combination) were found to explain significant differ-ences in the depth distribution of some co-occurring species inMadeira, Azores and Cape Verde (e.g., H. dactylopterus, Serranus

atricauda, Menezes, 2003).At Sedlo seamount transitions in the biomass and mean body

weight profiles around 1000–1200 m appear to be coincidentindependently of the gear used. The persistent transition around1000 m, also observed for different taxonomic groups in the NorthAtlantic slope waters (e.g., Mauchline and Gordon, 1991) and inthe Mediterranean (e.g., Stefanescu et al., 1993; D’Onghia et al.,2004), has been suggested as the boundary of the deep-sea fauna(Gordon and Duncan, 1985). In general, this transition zonecoincides with an increased abundance of large predatorybenthopelagic fish species (e.g., deep-water sharks; Menezeset al., 2006) and was suggested to be influenced by the increasedabundance of deep-mesopelagic prey (Mauchline and Gordon,

1985). Rogers (2000) relates the peaks of abundance and diversityto the upper and lower boundaries of oxygen-minimum zones,which in the Azores is more or less confined to between the lowerboundaries of the thermocline (at lower boundary of the NACW)at about 600–700 m, and lower limit of occurrence of theMediterranean Water at about 1000 m (Bashmachnikov et al.,2009). At both Seine and Sedlo clear diversity profile disconti-nuities occurred at 751 m and at 1200/1300 m, which again can beroughly associated with the boundaries of the MW and also withthe oxygen-minimum layers.

Small but similar values of diversity were observed at the twostudy sites within the expected core of distribution of theLabrador Sea Water (from 1400 to 2000 m depth), suggestingmore analogous and homogeneous environmental conditions indeeper waters.

4.3. Assemblage structure and dominance patterns

Discrete fish assemblages described in this work at bothseamounts were mainly structured by depth. The strength ofagreement obtained between the biotic and abiotic dissimilaritymatrices (as given by the BIO-ENV analysis) was high; depth,temperature and oxygen being the variables that mainly explainthe assemblage structures found.

Some species may occur at different depths due to ontogenichabitat shifts (related to differential feeding habits with age andsize), or have large depth range of distribution; thus speciesoccurrence may not be exclusive for any particular depthassemblage. Small individuals of most of the species were notcaught, and the assemblages described reflect only the distribu-tion of their adult stages. In general, the faunal zonation by depth

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Fig. 16. Relative frequency (in terms of numbers) by species for each cluster shown in Fig. 14B for Seine seamount.



found in this study for both sites were similar to those foundpreviously for Madeira and the Azores (Menezes, 2003; Menezeset al., 2006), and also resemble those found in the MediterraneanSea (D’Onghia et al., 2004) and southernmost part of the Mid-Atlantic Ridge (Hareide and Garnes, 2001).

The proposed large-scale assemblage patterns appear coherentwith the main vertical hydrographic structure, in particular theprevailing water mass distribution and boundaries known for thetwo study sites. Similar links between the vertical faunisticstructure and the prevailing water masses were also suggested forother areas (Fock et al., 2004; Williams et al., 2001) includingMadeira, Cape Verde and Azores islands slopes (Menezes, 2003;Menezes et al., 2006).

At the edge of the Seine plateau on the upper slope (101–700 mdepth) two main assemblages emerge from cluster analysis: onedown to the 200/300 m depth and the other in the 400–700-mdepth interval. The shallower assemblage at the top of Seineseamount is more diverse and its species composition is similar tothat found in the neritic areas of other seamounts in the Azores.Results obtained also agree with differences between the islandshelf habitats and the neritic seamount areas found previously inthe Azores and Cape Verde archipelagos. These differences relateto the absence of some species (e.g., Pagrus pagrus or Pagellus

acarne) that are abundant on the island shelves and to the highabundance of adult Trachurus picturatos and S. colias over theseamounts (Menezes et al., 2006). The differences in assemblagestructure between islands and seamounts are therefore morepronounced in the neritic layers, whereas in deeper slope waters,fish assemblages become more similar probably because of theoverall increase in environmental homogeneity and decrease inspecies diversity (Menezes et al., 2006).

Abundant T. picturatus (and S. colias), mainly at the edge of theseamount plateau, constitutes a ubiquitous species associationalso observed in other neritic areas of shallow seamounts (e.g., thePrincesa Alice Bank or the D. Joao de Castro Bank in the Azores;Menezes et al., 2006). Uiblein et al. (1999) also found this speciesassociation at Great Meteor Seamount, and suggested that thesespecies may show intense trophic interactions with the plateaudwellers during the day. Fock et al. (2002b) show that over theGreat Meteor plateau most populations distribute at the edge ofthe plateau, where the interception with the horizontally advectedsound-scattering layer organisms is increased (supporting the SSLinterception hypothesis; Isaacs and Schwartzlose, 1965).

Intermediate slope assemblages found at Seine (400–700 m)have also correspondence with the small cluster at 701–800 mobtained for Sedlo. Both clusters coincide with the core distribu-tion of the North Atlantic Central Water and are mainly composedof mesopelagic feeders, like B. splendens, E. telescopus, Benthodes-

mus elongatus or Galeus melastomus. Noticeable is the absenceof H. d. dactylopterus at Sedlo seamount, which is very abundant inthe Azores and is known to distribute deeper than 800 m(Menezes et al., 2006). The small available area of habitat atthese depths at Sedlo seamount may explain the absence, since nosignificant fishing pressure is known to occur in the zone.

The mid-slope assemblages (800–1200/1300 m), also coinci-dent at the two seamounts, appear well delineated by thecore distribution of the MW, but characteristic species differbetween the seamounts. At Sedlo the E. telescopus andC. squamosus dominate, while at Seine seamount the M. moro

and Deania cf. calcea are the most abundant species in thiscluster. All these species feed both in the benthopelagiclayer and at the bottom; however, it appears that at these depths,predators predominate at Sedlo and scavengers predominateat Seine.

Deeper assemblages (below 1300 m at Seine and below 1200 mat Sedlo) appear to coincide with the Labrador Sea Water. Fish

species present in deepest surveyed areas are similar; however,again the dominant species differ slightly between the twoseamount areas. At Seine, the scavenging species C. coelolepis

and S. kaupii (following Collins et al., 2005) appear to predominatein deeper assemblages, whereas at Sedlo at the same depths,C. coelolepis also occurs in high quantities, but species assumed tohave a more predatory behaviour, like E. princeps, were found tobe more abundant.

Collins et al. (2005) found differential intra- and interspecificdepth trends in body size of scavenging and non-scavenging deep-sea fishes in response to ecological causes related with the foodavailability across depth gradients. They suggest that the deep-water scavengers tend to have larger body sizes than predators asan ecological response, which favours their search ability to findrandomly distributed food items in less productive environments.The larger squaliform C. coelolepis, which is assumed to beprimarily a scavenger, is therefore expected to be more abundantin the less productive environment of Seine seamount. Thedifferences in dominance of functional groups in intermediateand deeper clusters could therefore be affected by the generalproductivity regimes between the two seamounts (Kiriakoulakiset al., 2009; Machın et al., 2009). Yet, there is still a need for moredetailed studies on the biology and ecological features of thedeep-water species caught, characteristics that are still largelyunknown. With the present data alone it is difficult to knowwhether the differential predominance of each species at the twoseamounts is a consequence of differences in food availability(linked to different productivity regimes), a latitudinal andvertical effect of the species distribution, or any fishing effectover Seine seamount. For example, the lower abundance ofC. squamosus at Seine may be an indication of fishing exploitation,given that this species is an important by-catch of the black-scabbard fish (A. carbo) fishery in the Madeiran and of-shoreseamounts of the archipelago. On the other hand, the speciesE. princeps is known to have a more northern distribution (Froeseand Pauly, 2005), and this may also justify the smaller quantitiesfound at Seine.

4.4. Further work

The scope of the present work was to describe the speciescomposition and to understand the way demersal fish speciesassemblages are distributed at the two surveyed seamounts.Further research is needed to better understand the main factorsinfluencing the differential bathymetric succession of speciesalong seamount depth gradients, and the main ecologicaldeterminants of differential species dominance patterns in deeperwaters. Physiological adaptation to the prevailing vertical hydro-logical conditions may explain the species distribution and thelarge-scale vertical assemblage structure found. However, furtherecological factors, like productivity patterns affecting the amountand quality of available food, appear to shape the abundance,diversity or dominance patterns of functional groups within thosemain assemblages and should be investigated further. In parti-cular, studies on trophic ecology and reproduction are stillscarce for most of the deep-water species and need to be madein each area.

Acknowledgements

This study was undertaken under the framework of OASIS—

Oceanic Seamounts: an integrated study project (Contract no:EVK3-CT-2002-00073-OASIS) funded by the European Union. Thestudy would not have been possible without extensive fieldassistance. We are grateful to Jose Branco, Pedro Cambraia Duarte,

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Telmo Morato, Ruth Higgins and all the crew members of the R/VArquipelago. Anonymous reviewers provided helpful comments.

Appendix A. Supplementary data

Supplementary data associated with this article can be foundin the online version at doi:10.1016/j.dsr2.2008.12.028.

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Author's personal copy - WordPress.com · 2013-12-16 · unquanti able ( Vinnichenko, 1997b; Clark et al, 2004). The Azores and Madeira archipelagos, like most of the oceanic islands,