lCES CM 1997/EE:16

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Tidal regime and the early life history patterns of flounders.

John SeIden Burke ~., Masahiro Ueno 2' lzumi Kinoshita 2 , Donald E. Hoss! and

Masaru Tanaka 3

1) National Marine Fisheries Service, Beaufort Laboratory, Beaufort NC 28516,

U.S.A.

2) Fisheries Research Station, Kyoto University, Maizuru, Kyoto 625, Japan.

3) Division of Appl{ed Biosciences, Kyoto University, Kyoto 611, Japan.

*Corresponding author, ernail- jburke@hatteras.bea.nmfs.gov, Fax 919-728-8784.

Abstract: Behavior and distribution of flounders of the genusParalieh:hys appear to differ among systems that differ in tidalregime. Field sampling and laboratory experiments were eonducted inJapan in areas that experience weak.and_strong tides and in NorthCarolina, USA, where the tide is relatively strong. Patternsobserved in North Carolina appear to correspond to those observedin areas with a strong tide in Japan. Laboratory experimentsindicated that wild flounder from strongly tidal systems had anendogenous rhythm of activity in phase with the tidal regime. Incontrast wild flounder larvae captured in the system with a weaktide and laboratory reared larvae did not. During immigration tonurseries, flounders in areas with strong tides exhibit verticalmigration and distribute by tidal stream transport'while floundersin the system with a weak tide remained near the bottom regardlessof tidal stage. These patterns of distribution result in differentsettlement patterns. In strongly tidal systems flounder nurseriesare eoneentrated in the shallows and shift with the tide. Insystems with a weak tide nurseries extend. seaward into deeperhabitats. variability in reeruitment, among systems differing intidal regimes, might be expected if the immigration and settlementperiod is eritieal to the establishment of year elass strength.

Key words: flounder, reeruitment, rhythmie behavior, settlementdistribution, tidal migration.

1. IntroductionReeent work suggests that the late larval and early juvenile

stages of marine species may be important in generating variationin reeruitment in some stocks (Miller et al 1991, Bradford 1992).Species that spend much of life in the oceans but have a lifehistory that includes the use of estuarine or shallow coastalhabitat as nursery areas may be particularly vulnerable during thelate larval stage. Many of these species spend most of the larvalperiod at sea and settle as late larvae in eoastal nurseries where ~they will spend the early juvenile phase. Coastal.nurseries maybe entered by tidal stream transport a mechanism that can providerapid inshore transport. This transport mechanism has beenobserved in a wide variety of speeies that utilize inshorenurseries including both flatfish and roundfish (Weinstein, 1975),eels (Wippelhauser and MeCleave, 1988), and crabs (Olmi, 1994).

The potential importance of geographie and seasonalvariability in tidal regime to species that utilize tidal eurrentfor transport to or retention in estuaries has been recognized(Power, 1997). Species that utilize tidal stream transport maylive in systems with weak or strong tides. Examples of pairs ofsystems that differ in tidal regime hut share species that mayexhibit tidal stream transport include the Northwest Atlantic andGulf oE Mexico, The North Sea and Baltic Sea, and the Sea of Japanand East China Sea. To investigate how tidal regime might affectbehavior and distribution of flounder, a joint American andJapanese research effort has focused a comparative study onimmigration and settla~ent of flounders of the genus Paraliehthys.We compare field distributions and behavior of flounder from

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American and Japanese study areas that differ in tidal regime. Ourresults indicate that tidal regime influences behavior ofimmigrating larvae and consequently the distribution of settledjuveniles.

2. Materials and Methods2.1 Study sites

Laboratory and field work was conducted at two areas in Japan.The primary study area in Japan was Yura Bay (Burke et al., 1997)located in the western part of Wakasa Bay on the shores of the Seaof Japan (Fig. 1). Tidal range is slight (mean 0.3 m at springtide) and aSYmmetrical due to the similarity in amplitude of thediurnal and semidiurnal tides in the bay (Fig. 2). Cyclical tidalcurrents in the area are not clearly apparent and currents greaterthan 0.2 rn/sec. are rare. The other study site Yanagihamma(Amarullah et al., 1991), a protected beach, was located on theIsland of Kyushu facing the East China Sea (Fig. 1). Like the YuraBay site the tide at Yanagihamma is aSYmmetrical but in contrastthe tidal range is about 3 m so that tidal flats are developed.

The U. S. study area (Burke et al. 1997), located" in thenortheüstern pürt of Onslow BüY (üpproximately 34~ N), includesnearshore waters, Beaufort Inlet and the Newport River Estuary(Fig. 3). The tide is symmetrical with a maximum range of about" 1

m. Maximum tidal currents of about 1 rn/sec have been recorded atBeaufort Inlet and are progressively damped up estuary (Klavens,1983) .

2.2 Vertical distribution samplingSampling for vertieal distribution of Japanese flounder

(Paralichthys oliyaceus)and the American flounders (ParaliebthySdentatus, ..E.... letbostigma, and..E.... albigutta) was eondueted duringpeak immigration pericds in Beaufort Inlet (February and March1995, 1997) and YuraBay (April and May 1994 and 1995). Allsampling was eondueted after dark and eonsisted of aseries ofobservations, each ineluding a hydrographie east for depth profilesof salinity and temperature and a set of iehthyoplankton 'sainplestaken with opening and elosing gear to sampie middepth and bottom(for details see Burke et al., 1997). On each sampie date portionof the flood and ebb tide were sampled. Sampies were preserved inalcohol, the fish removed and identified to species. Developmentalstage (Minami, 1982; Goto et al., 1989) and length of each'flounderwas determined and the eateh standardized to the number/100 m' fromcounts of flowmeters mounted in all nets.

To eompare the vertieal distribution of flounder between floodand ebb stages of thetide, two by" two contingeney tables werüused. Our null hypothesis was that no association existed between'vertical position of flounder and tidal stage. For each studyarea, all eateh data for eaeh tidal stage/vertieal positioncombination was pooled and the number of individuals caught atmiddepth and at the bottom during ebb tides eompared to thoseeatehes for flood tides (Chi-Square, p=O.05).

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2.3 Benthic distribution sampling. Beam trawl surveys were conducted at all three sites. The

Yura Bay study site was sampled with a 1.6 m beam trawl forrecently settled Japanese flounder during April-June in both 1994and 1995. Sampling was conducted in the bay (3-30 m)from the RVRvokuyo-maru, and in the surfzone «1-2 m) and within the YuraRiver Estuary «1-3 m)from a small boat and by towing the trawl bymanpower in the shallows. Yanagihama was sampled in May 1996 witha beam trawl, push net and quadrat-nets (Senta et ale i 1990).Sampling was conducted around the turn of the tide (ebb-flood) todetermine distribution of Japanese flounder relative to the shiftof the tide.

At the Beaufort Inlet study site sampling was conducted in1995 and 1996 and 1997 in February and March with a 2 m beam trawl.A variety of depths were systematically sampled in Onslow Bay (15-3m) and the Newport estuary «1-2 m). The surf zone was also sampledusing methods similar to those employed at Yura Bay.

2.4 Activity pattern experimentsActivity pattern experiments were conducted at the three sites

with wild caught flounder. In addition both lab reared summerflounder and Japanese flounder were tested. Experiments consistedof monitoring uctivity of flounder in an experimental apparatus(Fig'~ 4) for 24-72 hrs at constant temperature in the dark.Flounders collected from the wild· were introduced into' theapparatus as soon as possible «12 hrs) at the salinity andtemperature of capture and activity recorded. Activity of G-Hstage; lab reared summer flounder (raised at the BeaufortLaboratory using standard methodsfor rearing Japanese flounder)and Japanese flounder (raised at the Kyoto University FisheriesResearch Station) was also recorded on video tape. Video tapeswere reviewed at regular intervals and an index of activity, themaximum number of flounder swimming in the chamber simultaneouslyduring a five minute period, was used to quantify activity of eachgroup of flounder.

3 Resu1ts3.1 Vertical distribution

In Yura Bay discrete depth sampling indicated that Japaneseflounder tended to be concentrated near the bottom (Fig. 5)Highest mean density occurred at the bottom regardless of tidalstage and bottom sampies accounted for 81% of the total catch.Analysis of the contingency table indicated that there was noassociation between tidal stage and position in the water column(Chi-sq. p>O.OS). A wide range of developmental stages were~aught during vertical distribution sampling in Yura Bay (Fig. 6)and a large percentage of the catch consisted of presettlementstages of development (stages C-F).

Sampling in Beaufort Inlet indicated that abundance anddistribution of American paralichthyids varied with tidal stage.On the five sampie dates highest· densities of flounders weresampled at the bot tom during ebb tide and in the water columnduring flood (Fig. 5). Our analysis indicated that position in. the

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water column was dependent on tidal stage (Chi-sq, p< 0.001). Theshift in distribution and abundance of flounders appeared to beclosely associated with the shift in tidal stage; however, theincrease in relative abundance of flounders in the water columnappeared to occur around slack tide and preceded the rise insalinity which follows the onset of flood tide. The size and rangeof development of flounders sampled at Beaufort Inlet- was narrowand though the relative prcportion of a given stage varied amongthe - three species of Paral i.;;;htbys present, the catch of all threespecies consisted of the se:tlement stages G, H, I stage (Fig.6).

3.2 Benthic" distributionBeam trawl surveys of Yura Bay, the surfzone and the Yura

River indicated that 'settlement occurred primarily in the bay atdepths shallower than 10 m. Length frequency, developmental stagecomposition and CPUE from systematically sampled depths in the bayand in the surf zone during months of peak settlement (April andMay) in 1995 all indicate that peak settlement occurred around the5 m contour.

Beam trawl surveys in the vicinity of Beaufort Inlet andwithin the Newport River Estuary indicated that settlement occurredwithin the estuary. Though flounders were captured both in OnslowBay and in the 3urf zone during the immigration period (February­March) their densities were low and all flounders were transforminglarvae. On the final sampie date in both these habitats afterimmigration had concluded, flounders were absent. In contrastdensities of flounder within the estuary were high and consisted ofa mix of transforming larvae and completely settled juveniles.

Japanese flounder catches at Yanagihama showed that flounderresponded strongly to the flooding tide. Quadrat-net trap catchshowed that flounder followed the flooding tide onto the tidal flatwhere they could be captured in water a few centimeters deep.

3.3 Activity pattern experimentsvideo records from laboratory experiments showed that wild

flounders from Yanagihama and Beaufort Inlet had a regular patternof activity while laboratory reared flounders and wild Japaneseflounders from Yura Bay had no clear pattern of activity. Periodicactivity with peak frequency of about 12 h was generally correlatedwith the time of ebb tide (Fig. 7).

4. DiscussionThe observed vertical distributions of flounder larvae and the

settlement distributions of late larvae and early juveniles can beexplained by two factors i.e., larval behavior and patterns ofwater circulation. Our observations indicate that flounderbehavior is flexible and that recruitment mechanisms anddistribution will vary relative to the tidal regime in which theyare entrained.

Our laboratory experiments and field sampling indicate that insystems with a relatively strong tidal signal flounder develop atidal rhythm of activity. Results of activity experimentsgenerally support the model of Boehlert and Mundy (1988) whichproposes that stimuli associated with tidal flux act as a zeitgeber

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and superimposes a circa tidal rhythm upon an existing circadianrhythm (Gibson, 1976). Thus tidal stream transport appears theresult of development of an endogenous tidal rhythm which may allowlarvae to move rapidly inshore and enter estuaries against netseaward flow.

At Yura Bay where the tidal signal was weak, laboratoryexperiment and field distribution of flounder indicates that tidalstream transport is not utilized. The presence of earlydevelopmental stages (Fig. 6) within the nursery area of Yura Bayindicates that flounder larvae in this system can be passivelytransported to nursery areas by currents. Episodic events that maycause inflow of offshore water to the Bay are probably important torecruitment to the nursery ground. The apparent concentration ofJapanese flounder near the bottom (Fig. 5) suggests that currentsthere may be important to inshore transport.

The different mechanisms of inshore transport appear toinfluence patterns of settlement. Early juvenile flounders inOnslow Bay appear to be restricted to shallow estuarine habitat.Similarly Japanese flounder, in strongly tidal systems, settle inthe shallows and the nursery shifts with the tide (Subayantoet ale1993, Tanaka et ale 1989). In contrast settlement in Yura Bay wasmore diffuse with the main settlement area in relatively deepwater. This pattern has been reported from other nursery areaswith weak tides to the south (Furuta, 1996) and north (Kato, 1996)of Yura Bay. It appears that in systems where the tide provides apredictable means of rapid transport flounder migrate to and settlein the shallows. In systems with a weak tide such as the Sea ofJapan, flounder rely on an, apparently more variable means oftransport and consequently distribution of nursery grounds is morevariable.

The coherence of the tidal signal during the immigration periodcould influence year to year and geographie variability inrecruitment to nursery areas. Differences observed in endogenousbehavior of flounders from systems that differ in tidal regimeindicate that the strength of the tidal signal is important todevelopment of tidal stream transport. In systems such as the SeaofJapan the tidal signal may be too weak or may be easily maskedpreventing development of rhythmic behavior with a tidal period.Animals entrained in a tidal rhythm could be transported in thewrong direction when the normal pattern of flow associated with' thetide is disrupted by episodic events such as storms~ We wouldpredict that among systems varying in tidal regime the greater thecoherence of the tidal signal the lower the variability inrecruitment attributable to inshore migration.

AcknowledgmentsThis work was supported by the US/Japan Cooperative ResearchProgram sponsored by the Japan Society for the Promotion ofSciences and the National Science Foundation under agreement no.INT-9315541. Any opinion, finding, conclusions or recommendationsexpressed in this publication are those of the authors and do notnecessarily reflect the views of the National Science Foundation.

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References

Amarullah, M.H., Subayanto, Noichi,T., Shigemitsu, K., Tamamoto Y.and Senta T., 1991. Settlement of larval Japanese flounderParalichthys olivaceus along Yanagiharna Beach, Nagasaki Prefecture.Bull. Fac. Fish. Nagasaki Univ., 70: 7-12.

Boehlert, G.M. and Mundy, 1988. Roles of behavioral and physicalfactors in larval and juvenile fish recruitment to estuarinenursery areas. Am. Fish. Soe. Symp., 3: 261-281.

Bradford, M.J., 1992. Preeision of reeruitment predietions fromearly li fe stages of marine fishes. Fish. Bull., 90:.439-453.

Burke,J.S., Ueno, M., Tanaka, Y., Walsh, H., Maeda, T., Kinoshita,I., Seikai,T., Hoss,D.E., and Tanaka, M., 1997. The influence ofenvironmental factors on early life history patterns of flounders.J. Sea Res. in press.

Furuta, S., 1996. . Predation on juvenile Japanese f10under(Paralichthys oliyaceus) by diurnal piseivorous fish: fieldobservations and laboratory experiments. In: Y. Watanabe, Y.Yamashita and Y. Oozeki (eds), Survival Strategies in Early LifeStages of Marine Resourees. Balkema, Rotterdam, Netherlands, pp.285-296.

Gibson, R.N., 1976. Comparative' studies on the rhythrns of juvenileflatfish. In: P.J. DeCoursey (ed), Biologieal Rhythms in the MarineEnvironment. Univ. South Carolina Press, Columbia, SC: pp. 199-214.

Goto, T., Sudo, H., Tomiyama, M. and Tanaka, M., 1989. Settleingperiod of larvae and juveniles of Japanese flounder Paralichthysoliyaceus in Shijiki Bay, Hirado Island. Bull. Jap. Soe. Sei.Fish., 55: 9-16.

Kato, K., 1996. Study on resourees, eeology, management andaquaeulture of Japanese flounder, Paraljchthys oliyaeeus, off theeoast of Nigata Prefecture. Natl. Res. Inst. Aquacult., 2: 105­114.

Klavens, A.S., 1983. Tidal hydrodynamies and sediment transport inBeaufort Inlet, North Carolina. NOAA Tech. Rpt. 100: '1-119.

Miller, J.M., Burke, J.S. and Fitzhugh, G.R., 1991. Early lifehistory patterns of Atlantie North American flatfish: likely (andunlikely) faetors controlling recruitment. Neth. J. Sea Res., 27:261-275.

Minami, T., 1982. The earIy Iife history of a flounder paralichthysoljyaceus. Bull. Jap. Soc. Sci. Fish., 48: 1581-1588.

Olmi, E.J., 1994. Vertical migration of blue. crab'Callinectes

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saQidus megalopae: implieations for transport in estuaries. Mar.Eeo. Prog. Ser., 113: 39-54.

Power, J.H., 1997. Time and tide wait for no animal: Seasonal andregional opportunities for tidal stream transport or retention.Estuaries, 20: 312-318.

Senta, T., Sakamoto, F., Noiehi, T. And Kanbara, T., 1990. The R-Hpush net and quadrat-net for studying distribution patterns ofjuvenile flatfishes along the beaeh. Bull. Fae. Fish. NagasakiUniv., 68: 35-41.

Subayanto, Hirata, I. and Senta T., 1993. Larval settlement ofJapanese flounder on sandy beaehes of the Yatsushiro Sea, Japan.Bull. Jap. Soe. Sei. Fish., 59: 1121-1128. ..

Tanaka M., Goto T., Tomiyama, M., Sudo, H. and Azuma, -M., 1989.Lunar-phased immigration and settlement of metamorphosing Japaneseflounder larvae into the nearshore nursery ground. Rapp. P.-v.Reun.Cons. Int. Explor. Mer., 191: 303-310.

Weinstein, M.P., Weiss, S.L., Hodson, R.G., and Gerry, L.R., 1980.Retention of three taxa of postlarval fishes in an intensivelyflushed tidal estuary, Cape Fear River, North Carolina. Fish.Bull., 78: 419-436.

Wippelhauser, G.S. and MeCleave, J.D., 1988. Rhythmie aetivity ofmigrating juvenile Ameriean eels Anguilla rostrata. J. Mar. Biol.Assoe. U.K., 68: 81-91.

Figures

Figure 1. Maps showing the geographie loeation of Yura Bay and ..Yanagihama Beaeh.

Figure 2. Examples of predieted tidal heights for Yura Bay,Yanagihama Beaeh, and Onslow Bay.

Figure 3. Map showing study area at Onslow Bay ineluding theBeaufort Inlet and Ne\vport River Estuary.

Figure 4. Experimental apparatus used J..n endogenous rhythmobservations.

Figure 5. Mean flounder catch at mid depth and bottom for floodand ebb stages of the tide at Yura Bay and Onslow

Figure 6. Developmental stage eomposition of Japanese flounder andthree species of American flounder caught during verticaldistribution sampling just seaward of nursery grounds.

Figure 7. Example of results from laboratory aetivity patternexperiments eondueted in the dark at eonstant temperature with wildsouthern flounder, Paralichthys lethostigma. Aetivity is plottedwith predieted tidal height for the loeation of eapture.

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