Polar Biol (2004) 27: 637–650 DOI 10.1007/s00300-004-0632-2 REVIEW Joseph Donnelly Æ Joseph J. Torres Tracey T. Sutton Æ Christina Simoniello Fishes of the eastern Ross Sea, Antarctica Received: 26 November 2003 / Revised: 16 April 2004 / Accepted: 20 April 2004 / Published online: 16 June 2004 Ó Springer-Verlag 2004 Abstract Antarctic fishes were sampled with 41 midwater in Antarctica is dominated by a few fish families and 6 benthic trawls during the 1999–2000 austral (Bathylagidae, Gonostomatidae, Myctophidae and summer in the eastern Ross Sea. The oceanic pelagic Paralepididae) with faunal diversity decreasing south assemblage (0–1,000 m) contained Electrona antarctica, from the Antarctic Polar Front to the continent (Ever- Gymnoscopelus opisthopterus, Bathylagus antarcticus, son 1984; Kock 1992; Kellermann 1996). South of the Cyclothone kobayashii and Notolepis coatsi. These were Polar Front, the majority of meso- and bathypelagic replaced over the shelf by notothenioids, primarily Ple- fishes have circum-Antarctic distributions (McGinnis uragramma antarcticum. Pelagic biomass was low and 1982; Gon and Heemstra 1990). Taken collectively, the concentrated below 500 m. The demersal assemblage fishes are significant contributors to the pelagic biomass was characteristic of East Antarctica and included seven and are important trophic elements, both as predators species each of Artedidraconidae, Bathydraconidae and and prey (Rowedder 1979; Hopkins and Torres 1989; Channichthyidae, ten species of Nototheniidae, and Lancraft et al. 1989, 1991; Duhamel 1998). Over the three species each of Rajidae and Zoarcidae. Common continental slope and shelf, notothenioids dominate the species were Trematomus eulepidotus (36.5%), T. scotti ichthyofauna (DeWitt 1970). Most members of this (32.0%), Prionodraco evansii (4.9%), T. loennbergii group are primarily benthic as adults but some species (4.7%) and Chaenodraco wilsoni (4.3%). Diversity indi- have become pelagic to varying degrees (Andriashev ces were highest for tows from 450 to 517 m (H¢=1.90– 1970; Eastman 1991, 1993). Larval and juvenile noto- 2.35). Benthic biomass ranged from 0.7 to 3.5 t kmÀ2.It thenioids are part of the coastal pelagic ecosystem and was generally higher in tows from 450 to 517 m (0.9– some species occur to a lesser extent in oceanic waters 2.0 t kmÀ2) although the highest biomass occurred at an (Kellermann and Kock 1984; Kellermann and Slo´- inner-shelf station (238 m) due to large catches of sarczyk 1984; Williams 1985; Tabeta and Komaki 1986). T. eulepidotus, T. scotti and P. evansii. The only wholly pelagic notothenioid genus known to occur regularly in oceanic waters as an adult is Diss- ostichus (Andriashev 1964; Yukhov 1971; Kock 1992). Studies on the composition and distribution of Introduction coastal assemblages led to the zoogeographic classifica- tion of Antarctic fish into East Antarctic and West Pelagic and demersal fish assemblages are an important Antarctic Provinces (see reviews by Andriashev 1965, part of coastal marine ecosystems. The offshore pelagial 1987; DeWitt 1971). More recently, Kock (1992) pro- posed a modified classification scheme with the intent of incorporating both the oceanic and coastal fish fauna. In J. Donnelly (&) Æ J. J. Torres Æ C. Simoniello College of Marine Science, his scheme, the West Antarctic Province (as well as the University of South Florida, South Georgia Province of the Glacial Subregion and all 140 7th Avenue South, St Petersburg, of the Kerguelen Subregion) is designated the Seasonal FL 33701, USA Pack-Ice Zone, and the East Antarctic Province is des- E-mail: [email protected] ignated the High-Antarctic Zone. For either scheme, Tel.: +1-727-5531648 Fax: +1-727-5531189 data on species distribution and abundance provide the basis for characterizing regional assemblages and T. T. Sutton Harbor Branch Oceanographic Institution, delineating zoogeographic boundaries. 5600 US 1 North, Ft. Pierce, Over the past two decades, our understanding of FL 34946, USA Antarctic fish biology and ecology has steadily increased 638 through new literature on pelagic and benthic ichthyo- knots for all MOCNESS, Tucker and bottom tows. fauna (Daniels and Lipps 1982; Kock et al. 1984; Midwater tows with the fish trawl were done at 3.0–3.4 Hubold and Ekau 1987; Williams 1988; Ekau 1990; knots. Sampling took place in three different coastal Hureau et al. 1990; Piatkowski et al. 1990; White and zones: (1) offshore, water depths >2,500 m; (2) con- Piatkowski 1993; Zimmerman 1997; Duhamel 1998; tinental slope, water depths 500–2,000 m; and (3) Eastman and Hubold 1999; Vacchi et al. 1999; Ruhl continental shelf, water depths £ 500 m. Ice cover et al. 2003) and new species (DeWitt and Hureau 1979; varied from 2/10 to 10/10 within each zone Stein and Tomkins 1989; Miya 1994; Sko´ra 1995; throughout the sampling period. Balushkin and Eakin 1998; Eakin and Balushkin 1998, Fresh specimens were identified, counted, and mea- 2000; Eakin and Eastman 1998; Balushkin 1999; sured, then either preserved in 10% formalin or frozen. Eastman and Eakin 1999; Chernova and Eastman 2001). When not determined directly after capture, wet weight However, except for range information on Dissostichus was calculated from length-weight regressions or esti- mawsoni (Andriashev 1964; Yukhov 1971), there are no mated from preserved specimen weights (assuming a fish data from the eastern Ross Sea region. This area is 20% loss from fresh weight). In cases where large far removed from any permanent scientific research numbers of individuals were collected, a sub-sample was stations and has high year-round ice cover (Gloersen kept and the remainder weighed, measured, and dis- et al. 1992), making ichthyological sampling quite carded. Species identifications were based on taxonomic difficult. Regardless of the zoogeographical scheme or keys in Gon and Heemstra (1990), supplemented with terminology one chooses, the eastern Ross Sea area is works by Miya (1994), Schneppenheim et al. (1994), one of potential faunal transition and, in the words of Balushkin and Eakin (1998), Eastman and Eakin (1999, Andriashev (1987), has been ‘‘mare incognito’’ for fishes. 2000), and La Mesa et al. (2002). Integrated abundance (number m-2) for each species in the water column was calculated as number per vol- Materials and methods ume filtered multiplied by the vertical range (in meters) of the tow, then summing all tows vertically. Integrated As part of the Antarctic pack-ice seal (APIS) study biomass (g WW mÀ2) was calculated following the within the eastern Ross Sea, (68–79°S, 128–179°W), we same protocol. This procedure was used for the 0–500 conducted midwater and benthic trawling on board the and 0–1,000 m depth ranges for zone 1 and the 0–500 m RVIB Nathaniel B. Palmer during the 1999–2000 depth range for zones 2 and 3. For bottom tows, inte- austral summer (NBP99-09, December 1999–February grated abundance and biomass for each species was 2000). Midwater sampling was done using three dif- determined by dividing the number or weight value by ferent trawls: (1) a 4-m2 mouth area, five-net MOC- each tow’s swept area (km2). Swept area was estimated NESS trawl with 4-mm mesh nets and 1-mm-mesh by multiplying towing speed (in knots, where 1 cod-end bags; (2) a 9-m2 mouth area Tucker trawl knot=1,850.7 m hÀ1) · time on bottom (in hours) · with a 4-mm-mesh main net tapering to a 1-mm-mesh effective mouth width (in meters) (Sparre et al. 1989). tail section and terminating in a jug-type cod-end with Following Eastman and Hubold (1999), we considered a 1-mm mesh liner; and (3) a 14-m footrope-length species numerically dominant if they comprised ‡5% of balloon fish trawl (Pierce and Mahmoudi 2001) with a the catch. Diversity (H¢, Shannon and Weaver 1949), 9 m effective mouth width and 3 m height. The net evenness (J¢, Pielou 1966) and species’ richness (SR, consisted of a 10-cm-mesh front section, a 5-cm-mesh Margalef 1958) indices were calculated for all bottom mid-section and terminating in a 3.8-cm-mesh end trawls. Hydrographic data were collected from CTD section fitted with a 0.6-cm-mesh liner. The net was casts taken near our trawling locations. spread using two 1.2·1.8 m steel ‘‘V’’ doors and fish- ing depth limited by adjusting the towing point on the yoke. Half-meter, 163-m-mesh plankton nets were Results nested inside the MOCNESS and Tucker nets (any fish collected were added to the totals for the main net). General overview Volume filtered was estimated using both TSK dial- type flowmeters (MOCNESS and Tucker nets) and Temperature profiles within each zone showed little General Oceanics torpedo-type flowmeters (nested variability (Jacobs et al. 2002). Representative CTD plankton nets). No flow volumes were recorded for the traces of temperature for the three zones are shown in fish trawl. MOCNESS tows were over both 0–500 and Fig. 1. For zone 1, a roughly isothermal surface layer 0–1,000 m depth ranges; Tucker and pelagic fish trawls with temperatures of À1.4 to À1.8°C extended to be- were towed obliquely over 0–500 m. Trawling depth tween 50 and 150 m. Temperatures increased rapidly for both the Tucker and fish trawls was estimated over the next 200 m, reaching a maximum of 1.6–1.8°C, from the amount of wire out and wire angle and re- then gradually decreased with depth to approximately corded with a time-depth recorder. Benthic sampling 1.5°C at 500 m and 1.0°C at 1,000 m. For zone 2, the was done using the fish trawl with bottom time rang- only significant changes were a deepening of the surface ing from 10 to 15 min.