Flach 2008 Aspects of behavioral ecology

MARINE MAMMAL SCIENCE, 24(3): 503–515 (July 2008)C© 2008 by the Society for Marine MammalogyDOI: 10.1111/j.1748-7692.2008.00198.x

Aspects of behavioral ecology of Sotalia guianensisin Sepetiba Bay, southeast Brazil

LEONARDO FLACH

Projeto Boto Cinza,Rua Sta Terezinha, 531, Muriqui, 23870-000

Mangaratiba, Rio de Janeiro, Braziland

Whale Unit, Mammal Research Institute,University of Pretoria, c/o P.O. Box 61,

Cape Town 8000, South AfricaE-mail: [email protected]

PATRICIA A. FLACH

Projeto Boto Cinza,Rua Sta Terezinha, 531, Muriqui, 23870-000

Mangaratiba, Rio de Janeiro, Brazil

ADRIANO G. CHIARELLO

Programa de Pos-graduacao em Zoologia de Vertebrados,PUC-Minas, Avenida Dom Jose Gaspar 500, Predio 41,

Belo Horizonte, Brazil, 30.535-610

ABSTRACT

Boat-based surveys were conducted from August 2002 to July 2003 to study theactivity patterns, spatial pattern of area use, and group characteristics of Sotalia guia-nensis in Sepetiba Bay, southeast Brazil. Predetermined routes covered the entranceand interior of the bay, resulting in 210 dolphin sightings during 3,300 km totaleffort. Data on activity were collected using scan group sampling with instanta-neous recording after 5 min of observation. Dolphins were sighted more frequentlyin the entrance of the bay, where water is deeper, and salinity and transparency arehigher, than in the interior of the bay, where the environment is more influencedby freshwater inputs. Foraging and feeding were the most frequent activities, andoccurred predominantly between 0600 and 1000. Foraging and feeding peakedduring ebbing, low, and flooding tides, while socializing predominated at hightide. Mean group size was larger in the interior of the bay and when seabirds werepresent. Large aggregations containing >100 individuals of Sotalia guianensis seenyear-round indicate that Sepetiba Bay is an important area for this species in coastalBrazil.

Key words: activity pattern, Sotalia guianensis, habitat use, group size, Rio deJaneiro.

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504 MARINE MAMMAL SCIENCE, VOL. 24, NO. 3, 2008

Dolphin activity patterns can be influenced by time of day, season, water depth,bottom topography, tide flow, and human activities (Shane 1990). In addition, thedolphins’ responses to these ecological variables are somewhat unpredictable andcan differ depending on the habitat in which the animals are studied (Shane 1990).The study of activity patterns is important as this parameter is one of the primefactors directly influencing the group size and, indirectly, the social organization ofdolphins (Shane et al. 1986). Also, activity rhythms of animals reflect adaptationto seasonal and diurnal variations of environmental factors and are a result of acomplex compromise between optimal foraging/feeding time, social activities, andenvironmental constraints (Nielsen 1983).

Based on differing morphometry and genetics, the genus Sotalia has been dividedinto two species, the riverine species S. fluviatilis and the marine species S. guianensis(Monteiro-Filho et al. 2002, Cunha et al. 2005, Cabalero et al. 2007). S. guianensis isperhaps one of the most commonly observed and best studied coastal dolphins in thesouthwest Atlantic Ocean. The broad pattern of distribution of S. guianensis alongthe coasts of Central and South America is well known. Although many aspects ofits natural history, behavior, reproduction, geographic fidelity, and home range havebeen studied, few studies have been published (da Silva and Best 1996, Ramos et al.2000, Santos et al. 2001, Rosas and Monteiro-Filho 2002, Flores and Bazzalo 2004).Therefore, details of fine-scale spatial and temporal distribution, patterns of area use,and group characteristics are scarce in the literature.

Threats to S. guianensis from bycatch, chemical pollutants, and loss of importanthabitat (e.g., mangroves), are significant (Reeves et al. 2003). Thus, factors affectinghabitat use, activity, and social dynamics are critical for assessing their conservationand management status. The goals of this study were to: (1) investigate the spatialand temporal distribution pattern of S. guianensis population in southeast Brazil, (2)verify how activities and spatial area usage relate to environmental parameters, and(3) describe group characteristics of S. guianensis in the Sepetiba Bay region.

MATERIAL AND METHODS

Study Area

Sepetiba Bay is located in the southern part of Rio de Janeiro State (22◦54′–23◦04′,43◦36′–44◦02′W) spanning 526 km2 with an average depth of 8.0 m and dredgedchannels 20–30 m deep. In this study the bay was sectioned into two regions (entranceand interior) due to its environmental differences (Fig. 1). The northern portion isbordered by mountain chains and sand beaches separated by rocky shores. At thewestern part lies the entrance, with a number of islands, rocks, and the main connec-tion to the Atlantic Ocean. This area, influenced by open waters, has a sand and gravelsubstrate, high salinity, and high transparency. The eastern part (interior) has exten-sive mangrove areas with river drainage systems that contribute most of the mud andsilt substrate, as well as low salinity, transparency, and depths (Pessanha and Araujo2003) (Fig. 1). Despite its high number of habitats and species diversity, the baysuffers from increasing industrial outflows, port activities, losses of mangrove areas,and industrial fishing activities (Araujo and Azevedo 2001, Pessanha and Araujo2003).

Field Methods

Three months of pilot surveys were carried out to investigate the best samplingprotocols and to construct an ethogram (Table 1). Moreover, 64 h of total effort

FLACH ET AL.: SOTALIA BEHAVIOR 505

Figure 1. Distribution of sightings of Sotalia guianensis in Sepetiba Bay during winter (�)and summer (◦). The vertical line shows where the bay was divided into interior and entrancefor analysis purposes (see Methods). Map and GIS processing by Andre Hirsch.

(24 h searching for the animals and 40 h of direct observation) were used to train theobservers. After that, data were collected from 12 mo from August 2002 to July 2003.During this period, 78 survey days traversed 3,300 km (entrance: 1,873 km; interior:1,427 km) covering an area of 455 km2 (entrance: 205 km2; interior: 250 km2) andproduced 210 dolphin sightings during “good” sea state (Beaufort 0–3). Thus, wesampled on average 1 group/day (interior) to 4.3 groups/day (entrance). For these 210sightings, a total of 317 h of effort was spent, with 224 h searching for the dolphinsand 93 h in direct observation.

Two observers in a 7.5-m boat equipped with a 225-hp outboard engine conductedthe surveys. Line transects were established in order to cover the entire area of thebay and thus to assess different habitat characteristics used by the dolphins. Thesetransects were covered at an average speed of 12–15 km/h. Starting positions andtime of day were alternated randomly for each survey, and starting time of eachsurvey was recorded to register the number of hours spent searching for the dolphins

Table 1. Ethogram of S. guianensis in Sepetiba Bay.

Activity Definition

Forage-feed Surface behavior characterized by repeated, fast and arched dives,changing directions suddenly and concentrating in one location.

Social Some individuals of the group in physical contact, spending most of thetime at the surface with one another, rubbing, rolling, chasing, and alsodisplaying leaps, tail slaps, belly up, and other surface behavior.

Travel Moving steadily in one direction and showing body not arched, often inconstant speed and sometimes presenting porpoise and leaps.

Rest Slow movement at the surface, dorsal fin exposed, body little arched.Unknown Moving in various directions in one location, showing no surface behavior.


and in direct observation effort. When a group of dolphins was sighted the boatwas stopped and search effort suspended. Then a quick approach to the group wastaken to collect data on time, position, group size, group composition, and behavioractivity. The behavior activities were recorded using the scan group sampling withinstantaneous recording after 5 min of observation (Altmann 1974, Mann 1999).Associations between dolphins and marine birds such as frigates, Fregata magnificens,boobies, Sula leucogaster, and terns, Sterna sp., were recorded. After data collection wascomplete, the time was registered and the route was resumed from the point whereit was interrupted.

Definitions and Analysis

Each time a group of dolphins was detected, it was recorded as a sighting (af-ter Karczmarski 1999). Five categories of activity were distinguished (adapted fromShane 1990 and Karczmarski and Cockcroft 1999) (Table 1). Age categories wereclassified as neonate, calf, juvenile, and adult (see Shane 1990). The term “group”refers to dolphins that were detected visually by the observers forming one or severalsubgroups next to another and in an apparent association and engaged in similaractivities. The term “large aggregations” in this study refers to groups contain-ing >100 dolphins usually engaged in predominantly foraging/feeding or social-izing activities (see Norris and Dohl 1980, Norris and Schilt 1988). Environmen-tal parameters, including surface water temperature, turbidity, salinity, and depthwere measured for each sighting position using a thermometer, secchi disc, refrac-tometer, and fish finder, respectively. Tidal state (high, ebbing, low, flooding) wascategorized using a tidal chart, and spring and neap tides were considered for theanalysis. The high and low tides lasted 1 h each and the rest of the time was as-signed to flooding and ebbing tides. In order to estimate water depth availability,a nautical chart of Sepetiba Bay was divided into squares of 30′′ of latitude andlongitude, with water depth from each vertex (n = 442) used as a proxy of depthavailability.

Two seasons (winter and summer) were distinguished using the annual mean seasurface temperature (25.6◦C), an approach adopted from Karczmarski et al. (1999).In general sea surface temperatures were below the annual mean (25.6◦C) in winter(May–October) and above this value in summer (November–April) (see Results). TheMann-Whitney test was used to check for seasonal differences (winter vs. summer)in water parameters (depth, temperature, salinity, and turbidity) and in group size.The chi-square test was used to check if depth of dolphin sightings varied accordingto depth availability in the bay, as measured above, and also to contrast activityfrequency between seasons and time of day. All expected frequencies were calculatedproportional to sample effort. A statistical table (Rohlf and Sokal 1981) was usedto find the significance (P) for the chi-square test. The Kruskal-Wallis test was usedto check if water parameters differed among categories of activity (one test for eachwater parameter), and if group size differed among categories of activity.

RESULTS

Spatial Distribution and Environmental Parameters of Sightings

Sightings were more frequent (80.5%, n = 169) in the entrance of the bay than inthe interior (19.5%, n = 41) (chi-square with Yates correction: � 2 = 48.055, df = 1,


Table 2. Seasonal variation in water parameters collected during sightings of S. guianensisin Sepetiba Bay.

Season Depth (m) Temperature (◦C) Salinity (‰) Turbidity (m)

Winter 11.37 23.89 31.29 3.38Summer 11.4 26.71 30.82 3.06Mann-Whitney U 5348 938.5 4235 2412.5P 0.938 0 0.01 0.098

P < 0.001) (Fig. 1). This sighting frequency did not vary by seasons (� 2 = 0.469,df = 1, P = 0.493).

Sightings recorded in winter showed lower water temperature and higher watersalinity than summer sightings (Table 2). Sightings that occurred in the entrance ofthe bay, closer to the open ocean, were in deeper water of higher salinity and lessturbidity (higher Secchi values) than sightings in the interior of the bay (Table 3).The dolphins were recorded less frequently than expected at depths <6 m and morethan expected at depths >11 m (Fig. 2) (� 2 = 120.806, df = 3, P < 0.001).

Activity Patterns

The behavior observed most frequently was foraging/feeding (62.9% of sightings),followed by unknown (13.3%) and traveling (11.0%), while socializing (7.6%) andresting (5.2%) were the least frequently observed behaviors. This pattern of activitywas similar between areas (� 2 = 3.036, df = 4, P > 0.100) and between seasons (� 2 =4.445, df = 4, P > 0.100). Frequency of activities varied significantly according totime of the day (� 2 = 19.752, df = 8, P < 0.001): foraging/feeding peaked in earlymorning (0600–1000) while resting and social activities were more frequently seenin the afternoon (1400–1800) (Fig. 3).

Activity did not differ based on temperature [Kruskal-Wallis test: temperature(H = 1.734, df = 3, P = 0.629); salinity (H = 1.724, df = 3, P = 0.623); turbidity(H = 5.858, df = 3, P = 0.119), and water depth (H = 1.421, df = 3, P = 0.701)].However, significant differences were detected in relation to (spring) tides (� 2 =21.438, df = 3, P < 0.040), with higher frequency of foraging/feeding during low,flooding and ebbing tides, and higher frequency of socializing during high tides(Fig. 4).

Table 3. Differences between entrance and interior of the bay in water parameters collectedduring sightings of S. guianensis in Sepetiba Bay.

Area Depth (m) Temperature (◦C) Salinity (‰) Turbidity (m)

Entrance (205 km2) 12.14 25.48 31.35 3.29Interior (250 km2) 8.29 25.59 29.68 2.8Mann-Whitney U 1877 3122 1769 1609P 0 0.728 0 0.029


0

20

40

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80

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120

< 6 6 to < 11 11 to <16 ≥ 16

Fre

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Depth category (m)

Figure 2. Observed (�) and expected (�) frequency of sighting of S. guianensis by waterdepth at Sepetiva Bay. Expected frequencies were calculated proportionate to the bathymetry(see Methods).

Group Characteristics

Group size ranged from one to approximately 280 dolphins (mean = 30.2, SE =3.43, median = 12) and was significantly larger in the interior (70.9, SE = 13.2 dol-phins/group) than at the entrance of the bay (20.5, SE = 2.29 dolphins/group) (Mann-Whitney, U = 2,250, P < 0.0001). Group sizes were highly variable. Most groups(68%) contained between two and 20 dolphins (n = 142), while large aggregations

Figure 3. Percentage occurrence of main group activities of S. guianensis at Sepetiba Bayduring three time periods.


Figure 4. Group activity frequency of S. guianensis according to different spring tide typein Sepetiba Bay.

accounted for 7% of the sightings (n = 14) and were present year-round (Fig. 5).Group size did not vary significantly between seasons (Mann-Whitney, U = 5,358,P = 0.850) and changed little with behavior (Kruskal-Wallis, H = 7.587, df = 3,P = 0.056). Solitary dolphins were observed on only two occasions. Sea birds were ob-served in association with dolphins on 32 occasions. In the majority of these observedassociations with seabirds (n = 31) dolphins were feeding (in the remaining casethey were socializing). Dolphin groups with seabirds present were larger (mean =58.9, SE = 13.0, n = 32) than groups without birds (mean = 25.0, SE = 3.1, n =178) (Mann-Whitney, U = 1,570, P < 0.0001). Among seabirds, the most commonassociation was between dolphins and boobies (Sula leucogaster, 50.0%), followed byterns (Sterna sp., 15.6%) frigates (Fregata magnificens, 9.4%), or mixed birds association(terns/boobies, 15.6%) and (boobies/frigates, 9.4%).

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40

50

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6-10

11-1

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Figure 5. Frequency distribution of S. guianensis group size in Sepetiba Bay.


DISCUSSION

Spatial Distribution and Environmental Parameters of Sightings

This study shows that S. guianensis uses the entrance of the bay most often, wherewater is deeper, with higher salinity and transparency, clearly a result of strongerinfluence of open water. According to Araujo et al. (2002), these environmentalcharacteristics, together with a sea bottom relief of rocks and channels, allow higherfish diversity with little variability throughout the year in the entrance of SepetibaBay. This stable fish assemblage is perhaps the main reason for preference of S.guianensis for this part of the bay. The dolphins were observed more often than expectedin areas with depths over 11 m, showing an intense utilization of deep areas with steepbottom, within channels, and near rocks. A similar pattern of sightings concentratedin deeper waters is known for Guanabara Bay, Rio de Janeiro State (Azevedo et al.2007), although most other studies indicate that S. guianensis uses areas with depths<6 m (Lodi 2003, Flores and Bazzalo 2004, Daura-Jorge et al. 2005). Studies ofother species, such as bottlenose and humpback dolphins, also showed preferencesfor deep areas and channels, which might host a greater concentration of prey (Mazeand Wursig 1999, Jefferson 2000, Hastie et al. 2004). However, humpback dolphinsof South Africa and bottlenose dolphins of Argentine are confined to shallow watersand rock shores (Wursig and Wursig 1979, Karczmarski et al. 2000), indicating thatdolphins adapt to local conditions and thus depth preference is, perhaps, location-specific.

Activity Patterns

The high frequency of foraging/feeding activity observed in this study was alsoobserved by others authors working with other species and S. guianensis (Wursig andWursig 1980, Brager 1993, Karczmarski and Cockcroft 1999, Daura-Jorge et al.2005, Azevedo et al. 2007). Possible reasons include the mobility and size of smallcetaceans, such as S. guianensis and other small odontocete species, which must feedoften to fuel their high field metabolic rate (Costa and Williams 1999). Neitherthe entrance nor the interior was used preferentially by S. guianensis to engage inspecific activities, similar to what has been observed with this species at GuanabaraBay (Azevedo et al. 2007) and humpback dolphins in Hong Kong waters ( Jefferson2000). Nonetheless, S. guianensis used specific areas for given activities in southernBrazil (Daura-Jorge et al. 2005). The relatively small variation of sea surface watertemperature throughout the year (when compared to higher latitudes) and the smallfluctuation of prey abundance (Araujo et al. 2002, Pessanha and Araujo 2003), mightexplain the lack of seasonal differences in activity patterns in Sepetiba Bay, which isalso observed in Guanabara Bay (Azevedo et al. 2007). On the other hand, at Norte Bay(Santa Catarina State, Brazil), the southernmost limit of distribution of the species,higher fluctuations in sea surface temperature and food resources influenced activitypatterns of S. guianensis, which changed seasonally (Daura-Jorge et al. 2005). It isimportant to note, however, that in this study relatively large areas were comparedand microhabitats were not discriminated between the entrance and interior. Also,the groups of dolphins were not followed all day long, raising the possibility thatthe results could be different if such approaches were chosen. Therefore, the apparentabsence of seasonal and spatial variation in activity patterns at Sepetiba Bay shouldbe interpreted cautiously.


The early morning foraging/feeding activity peaks are similar to those reportedfor other S. guianensis and bottlenose dolphins (Hanson and Defran 1993, Bearziet al. 1999, Daura-Jorge et al. 2005, Azevedo et al. 2007). This probably relatesto the higher necessity of energy intake in early morning or to diel variation inprey activity/availability because food resource can be more active, concentrated,or accessible during certain times of the day or at certain points of the tidal cycle(Stevick et al. 2002). The decrease in light intensity at dusk and its increase at dawnserves as signals of change in biotic environmental conditions, which is reflected inthe behavior of fish (Hobson 1972, McFarland 1991). In this regard, it is possiblethat the prey of S. guianensis is more accessible and susceptible to being capturedduring the crepuscular transition, as observed for bottlenose dolphins in coastalCalifornia (Hanson and Defran 1993). On the other hand, the socializing and restingactivity were more frequent in the afternoon, indicating either that food resourceis less available or more difficult to capture during this time of day, as observedfor S. guianensis and bottlenose and humpback dolphins (Shane 1990, Brager 1993,Karczmarski and Cockcroft 1999, Azevedo et al. 2007).

In Sepetiba Bay water parameters such as depth, surface temperature, turbidity,and salinity did not affect the activity patterns of the dolphins. These variables areknown to influence the distribution and abundance of those fish species that are mostcommon in Sepetiba Bay (da Costa and Araujo 2002, Araujo et al. 2002, Pessanhaand Araujo 2003, Pessanha et al. 2003). Because distribution of cetaceans is oftenlinked with the distribution and abundance of their prey (Barros and Wells 1998)such variables may play a more important role in the spatial distribution of thedolphins than to their behavioral activities. Of all the environmental parameterstested, only the spring tides significantly influenced behavioral activities. The peaksof foraging/feeding activities were observed during low, flooding and ebbing tides,which according to local fisherman, correspond with movements of schooling fish inand out of the bay. Socializing activity was more frequent during high tides followingflood tides, indicating that dolphins may prefer to socialize during high slack water,and after feeding in more prey-rich tides. A similar sequence of behavior associatedwith the tidal cycle was also reported for bottlenose dolphins in the Adriatic Sea(Bearzi et al. 1999). In Guanabara Bay, however, the tidal cycle and depth did notaffect the behavioral activities of the dolphins (Azevedo et al. 2007).

Group Characteristics

The mean group size of S. guianensis in this study (30.2 individuals) is one of thelargest observed for the species, comparable only with group sizes in Paraty Bay (Riode Janeiro State, Brazil) (32.4 individuals) and Norte Bay (Santa Catarina State, Brazil)(29 individuals) (Lodi 2003, Daura-Jorge et al. 2005, Flores and Fontoura 2006). Moststudies of S. guianensis report mean group sizes ranging from 3 to 13 dolphins (DiBeneditto et al. 2001, Edwards and Schnell 2001, Azevedo et al. 2005, Spinelli et al.2006). According to Araujo and Azevedo (2001), Sepetiba and Paraty bays share thesame fish assemblages that form large schools and are distinct from other estuariesand bays of south and southeast Brazil. Apart from Sepetiba, large aggregations ofS. guianensis such as reported here, have been observed only in Paraty (Lodi 2003),perhaps reflecting similarities in the food base mentioned above. The dolphin groupsizes were larger during the interactions with seabirds (mostly boobies), which isprobably linked to large schools of fish that attracts both large groups of dolphins


and seabirds. The foraging/feeding behavior was the predominant activity observedduring such interactions. Similar results have been reported for dusky dolphins inNew Zealand (Markowitz et al. 2004).

The largest group sizes occurred during socializing and smallest during travelingactivities, although the difference was marginally significant. Similarly, as seen inbottlenose dolphins along the coast of the southern United States (Maze-Foley andWursig 2002, Shane 2004), the S. guianensis at Guanabara Bay also showed largestgroups during socializing activities (Azevedo et al. 2005). In contrast, in other areas(Lodi 2003, Daura-Jorge et al. 2005) the larger groups of S. guianensis were observedduring foraging/feeding. Clearly, activity pattern is one of the factors influencingthe group size of different species of dolphins, including S. guianensis. The lack ofsignificant seasonal changes in group size of dolphins corresponds with findings inother studies (Azevedo et al. 2005) and has also been observed for bottlenose dolphinsand humpback dolphins in Florida and Hong Kong, respectively (Irvine et al. 1981,Jefferson 2000). Findings from other sources are varied, however. In Paraty Bay andNorte Bay, for example, S. guianensis showed larger group size during the summer(Lodi 2003, Daura-Jorge et al. 2005) whereas, the largest group sizes elsewhereoccur during other seasons (Wursig 1978, Karczmarski et al. 1999). These variedresults suggest that seasonal variation of group size may be related to idiosyncrasiesof environmental constraints among habitats. The main findings reported here ongroup size and frequency of large aggregations set the Sepetiba population apartfrom the other populations already studied in Brazil. Another distinctive factor is thesize of this population, which is estimated to be between 739 and 2,196 individuals(Flach et al., in press), the largest population of the species thus far estimated for theBrazilian coast. These characteristics should stimulate further studies to understandbetter this population and help plan a conservation strategy for it.

ACKNOWLEDGMENTS

This work would not have been possible without the full financial support of the companyVALE, which is gratefully acknowledged. We wish to express our thanks to Leandro Quadros,Francisco Lafeta, Rubens Vianna, Felisbello Dalseco, Paulo Horta, and Tadeu Guerra for theirhelp during all aspects of this work. And our gratitude to the helpful research backgroundacquired from our colleagues Leszek Karczmarski, Paula Moreno, and Bernd Wursig at theMMRP-Texas A&M. This article was greatly improved by generous critiques and commentsfrom Dr. Leszek Karczmarski, Dr. Janet Mann, and anonymous reviewer. One of the au-thors (AGC) has a research grant (# PQ-301100/2005-5) from The Brazilian Science Council(CNPq).

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Received: 3 October 2006Accepted: 5 November 2007

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