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Antarctic•\.Peninsula

RACER: Ichthyoplankton abundance, species composition,and distribution in Gerlache Strait, Antarctica, October to

November 1989VALERIE I. LOEB, Moss Landing Marine Laboratories, Moss Landing, California 95039

The antarctic fish fauna is dominated by coastal formsassociated with continental and island shelf waters.

Prominent are numerous species representing families ofnotothenioid fish endemic to antarctic waters: Nototheniidae,Channichthyidae, Bathydraconidae, Artedidraconidae, andHarpagiferidae. Although the adults of most of these speciesare bottom dwelling and produce demersal eggs, the larvaeare pelagic (Loeb et al. in press; North 1991). Plankton surveysin the Antarctic Peninsula region have shown that these lar-vae are generally confined to shelf and slope waters. Althoughmost of the coastal and mesopelagic fish species reportedfrom this region have been represented in the samples, thelarvae of some known abundant species are rarely encoun-tered (Kellermann and Kock 1988; Kellermann 1989a). Thisdearth could result in part from retention of the larvae ofsome species within coastal spawning areas and the paucityof inshore sampling by the surveys. High primary productionand plankton biomass in coastal areas may also support ele-vated larval fish abundance relative to offshore waters (Loeb1991).

The detailed study in Gerlache Strait during 1989 by theresearch on antarctic coastal ecosystem rates (RACER) pro-gram (Huntley et al. 1990) makes it possible to examine the

. 17

16. -'V

63000' 6200' 61'00'W

Figure 1. RACER study area and station locations, 20 October-24November 1989. Numbers denote survey grid stations; A is the timeseries station.

importance of coastal environments to larval fish, includingaspects of abundance, composition, and retention innearshore waters.

Larval fish were obtained from vertically stratified multi-ple opening closing net and environmental sensing system(MOCNESS) samples collected in Gerlache Strait and adjacentBransfield Strait waters between 30 October and 24 Novem-ber 1989. Tows were made at stations arranged in a grid pat-tern across a 4,000-square-kilometer (km 2) survey area atapproximately 1-week intervals for a period of 1 month (figure1). Replicated tows were made at a time-series station (stationA) located in the eastern Gerlache Strait during three of thefour sampling intervals. Larval fish were sorted from 1,732samples resulting from 103 tows. Tow depths were to 290meters (m) or to within 40 m of the seafloor in shallowerwaters (Huntley et al. 1990). Combined sample data for thewhole water column are presented here. Abundance,expressed as numbers per 10 m 2 , was derived from thesummed sample abundance for each tow. Average values foreach of the 22 grid stations and for the replicated tows at sta-tion A are used to describe overall ichthyoplankton abun-dance and species composition during the study.

Only one of the 103 tows did not contain larval fish; theother tows had between 2 and 88 larvae and yielded a total of1,578 larvae. The overall averaged abundance of 19.0 larvaeper 10 m2 (table) is similar to that found in the northern Ger-lache Strait during the December 1986 RACER cruise (18.8 lar-vae per 10 m2 ; Loeb 1991). Nineteen larval fish taxa were rep-resented in the collections (table). Nineteen is a relativelylarge number of taxa, especially given the restricted samplingarea. Ichthyoplankton collections from a much greater area ofthe Antarctic Peninsula region during three spring (Octo-her-December) sampling periods by Kellermann (1989a)y ielded between 13 and 19 species and a cumulative total of4 species.

Three Nototheniid species, Lepidonotothen larseni,J'rematomus newnesi, and T. lepidorhinus, numerically domi-nated and constituted 84 percent of the total averaged abun-(lance. Two mesopelagic species, Bathylagus sp. (Bathylagi-Iae) and Electrona antarctica (Myctophidae), together repre-ented 8 percent of the total. The Channichthyiid Chionodracoastrospinosus was also relatively abundant (3 percent). Two

other channichthyids, Champsocephalus gunnari and Chiono-bathyscus dewitti, were collected. L. larseni, T. newnesi, C. ras-trospinosus, and E. antarctica typically are the dominantspecies in ichthyoplankton collections from the AntarcticPeninsula region during October-December (Kellermann andKock 1988; Kellermann 1989a,b). T. lepidorhinus, C. gunnari,

ANTARCTIC JOURNAL - REVIEW 1993177

634U

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a) Abundancemean no. 1Om-2

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Young fish abundance and composition in the RACERsamples collected in Gerlache Strait, October-November1989. Presence in the percent of the total 23 stations atwhich each species was collected.

Lepidonotothen larseni10.7457.63538100.0Trematomus newnesi3.7219.97 59982.6Trematomus lepidorhinus1.256.69 24265.2Electrona antarctica0.894.771956.5Bathylagussp. 0.653.514452.2

Chionodraco rastrospinosus 0.633.363447.8Bathydraconid #10.231.24726.1

Champsocephalus gunnari 0.160.88917.4Lepidonotothennudifrons0.120.661026.1Racovitzia glacialls0.070.37213.0

Artedidracoskottsbergi0.070.352126.1

Gobionotothen gibberifrons 0.040.221413.0Chionobathyscus dewitti0.030.1464.3Notolepis sp. 0.010.0428.7Harpagifer antarcticus<0.010.0428.7

Unidentified B<0.010.0214.3Unidentified A<0.01<0.0114.3Unidentified C <0.01<0.0114.3Bathydraconid #2<0.010.0114.3Pleuragramma antarcticus

(juvenile) 0.010.0514.3

Lepidonotothen kempi(juvenile) 0.010.0414.3

Damaged/unidentified0.33 23

Figure 2. Distribution patterns of four relatively abundant larval fishspecies in Gerlache Strait during October-November 1989.TOTAL 18.971,578

Number of stations 23Number of tows 103

and C. dewitti have been rare and Bathylagus sp. uncommonin previous collections. The relatively high abundance ofBathylagus sp. may in part result from sampling depth: previ-ous collections (Kellermann and Kock 1988; Kellermann1989a) were generally from tow depths less than or equal to200 m and substantial proportions of Bathylagus sp. in Ger-lache Strait were found to occur between 200 and 290 m (Loeb1992). Reported nearshore distributions of adult T. lepidorhi-nus (DeWitt, Heemstra, and Gon 1990) and inshore spawningmigrations by channichthyids (Kock and Kellermann 1991)suggest that proximity to coastal source areas may explaintheir elevated larval abundance in Gerlache Strait.

The more abundant species demonstrated extensive butcharacteristic distributions (table, figure 2). L. larseni was col-lected at all stations but was most abundant to the west anddownstream of a strong current flowing northeast along theaxis of Gerlache Strait (Amos, Jacobs, and Hu 1990; Niiler, Ille-man, and Hu 1990). T. newnesi was present at more than 80percent of the stations and was uniformly distributed acrossGerlache Strait. T. lepidorhinus was also widely distributedacross the Strait (present at 65 percent of stations) but was

more abundant in the north. Bathylagus sp. was distributed inthe eastern and downstream areas of the strait; it was collect-ed at about half of the stations. These differing distributionpatterns probably reflect an interaction of various parametersincluding bathymetry, the location of spawning areas, hydro-graphic features such as currents and gyrals, and larval verti-cal distribution patterns and behavior.

This work was supported by National Science Founda-tion grant OPP 91-17832. Thanks go to M. Huntley, E. Brinton,W. Nordhausen, and J. Lovett for their support and assistancein the sample collecting and processing.

References

Amos, A.F., S.S. Jacobs, and 1.-H. Hu. 1990. RACER: Hydrography ofthe surface waters during the spring bloom in the Gerlache Strait.Antarctic Journal of the U.S., 25(5), 131-134.

DeWitt, H.H., P.C. Heemstra, and 0. Gon. 1990. Nototheniidae. In 0.Gon and P.C. Heemstra (Eds.), Fishes of the southern ocean. Gra-hamstown: J.L.B. Smith Institute of Ichthyology.

Huntley, M.E., P. Niiler, 0. Holm-Hansen, M. Vernet, and E. Brinton.1990. RACER: An interdisciplinary study of spring bloom dynam-ics. Antarctic Journal of the U.S., 25(5), 126-128.

Kellermann, A. 1989a. The larval fish community in the zone of sea-sonal pack-ice cover and its seasonal and interannual variability.ArchivfilrFischerei Wissenschaft, 39(1), 89-109.

ANTARCTIC JOURNAL - REVIEW 1993178

Kellermann, A. 1989b. Catalogue of early life stages of antarcticnotothenioid fishes. BIOMASS Scientific Series, 10, 45-136.

Kellermann, A., and K.-H. Kock. 1988. Patterns of spatial and tempo-ral distribution and their variation in early life stages of antarcticfish in the Antarctic Peninsula region. In D. Sahrhage (Ed.),Antarctic ocean and resources variability. Berlin: Springer-Verlag.

Kock, K.-H., and A. Kellermann. 1991. Reproduction in antarcticnototheniold fish. Antarctic Science, 3(2), 125-150.

Loeb, V.J. 1991. Distribution and abundance of larval fishes collectedin the western Bransfield Strait region, 1986-87. Deep-SeaResearch, 38(8/9), 1251-1260.

Loeb, V.J. 1992. RACER: Composition and vertical distribution of lar-val fishes at a time-series station in Gerlache Strait, November1989. Antarctic Journal of the U.S., 27(5), 173-175.

Loeb, Vi., A.K. Kellermann, A.W. North, and M.G. White. In press.Antarctic larval fish assemblages: A review. Los Angeles CountyMuseum of Natural History Contributions in Science.

Niiler, P., J. Illeman, and 1.-H. Hu. 1990. RACER: Lagrangian drifterobservations of surface circulation in the Gerlache and Bransfieldstraits. Antarctic Journal of the U.S., 25(5), 134-138.

North, A.W. 1991. Review of the early life history of antarctic Notothe-nioid fish. In G. di Prisco, B. Maresca, and B. Tota (Eds.), Biology ofanta rctic fish. Berlin: Springer-Verlag.

RACER: Larval feeding ecology of three species of antarcticfishes (hevnidonotothen larseni, Trematomus newnesi, and T.

lepidorhinus) from Gerlache Strait, Antarctica, November 1989EDWARD A. LAMAN and VALERIE J. LOEB, Moss Landing Marine Laboratories, Moss Landing, California 95039

Relatively few studies have investigated the feeding ecolo-gy of antarctic larval fishes. Kellermann (1986, 1990)

reviewed the early biology and feeding habits of five speciesof notothenioid fishes from the Antarctic Peninsula regionand performed a detailed analysis of the seasonal and dielfeeding habits as well as food preferences of larval Lepidono-tothen (Nototheniops) larseni. North and Ward (1989)described the larval feeding habits of four fish species fromSouth Georgia (Trematomus hansoni, Harpagifer georgianus,Parachaen ich thys georgian us, Pseudochaen ich thys geor-gianus). North and Ward (1990) investigated the larval feed-ing ecology of Champsocephalus gunnari and other speciescollected from Cumberland East Bay; these species areimportant to the finfish industry at South Georgia. By con-trast, a cursory literature search for feeding studies of larvalfishes from tropical and temperate regions yielded more than3,000 references.

We present here the preliminary results from feedingstudies on larval fishes collected in Gerlache Strait duringNovember 1989 by the research on antarctic coastal ecosys-tem rates (RACER) program (Huntley et al. 1990). During thisprogram, vertically stratified MOCNESS (multiple opening-closing net environmental sensing system) tows were made atstations arranged in a grid pattern across a 4,000-square-kilo-meter (km2) survey area (see Loeb, Antarctic Journal, in thisissue). The survey was repeated at approximately 1-weekintervals for a period of 1 month. Replicated tows were madeat a time-series station (station A) located in the eastern Ger-lache Strait during three of the weekly sampling intervals. Thefeeding studies concentrate on three numerically dominantspecies in the samples: Lepidonotothen larseni, Trematomusnewnesi, and T. lepidorhinus (Loeb 1992; Loeb, Antarctic Jour-nal, in this issue). In addition to conventional feeding-habitanalysis, which involves recording feeding incidence and prey

identification, number, and volume, our studies includeaspects of larval fish nutritional condition and the ecologicalrole of yolk reserves. A new method will be used to evaluatefeeding success based on a combined analysis of yolk reservesand larval condition factor as defined by various morphomet-nc indices.

Kellermann (1990) noted long yolk resorption timesamong antarctic fish larvae relative to the larvae of temperateor boreal fish and hypothesized the importance of yolkreserves to enable the larvae to survive extended periods ofpoor food availability in the highly variable antarctic environ-ment. Kellermann (1990) also suggested that observed differ-ences in the incidence and size of yolk reserves of L. larsenilarvae may result from spatial and temporal variations in theplanktonic environment and early feeding success. The sam-pling coverage of the 1989 RACER program permits an exami-nation of variations in the rate of yolk utilization in conjunc-tion with feeding success within Gerlache Strait over a 1-month period.

Preliminary analyses of the yolk reserves were madeusing image analysis software (Image 1.37; National Instituteof Health) applied to larval fish displayed on a Macintosh IIcxcomputer screen via television microscopy. The initial mea-surements were taken as area from a lateral view of the yolkreserve. This was done by outlining the yolk, which is easilyvisible on the screen, and employing an area-estimation func-tion. The results for L. larseni and T. lepidorhinus are present-ed in the table. T. newnesi is not included here because noneof the 41 larvae examined had visible yolk remains. It must benoted that yolk utilization is a dynamic process and that all ofthe larvae so far examined were obtained at station A near theend of sampling period (19-22 November). The T. newnesi insamples collected 3 weeks earlier had obvious, and at timeslarge, yolk reserves.

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