Pleuragramma antarcticum (Pisces, Nototheniidae) as Food for Other Fishes

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1 Polar Biol (1985) 4: Springer-Verlag 1985 Pleuragramma antarcticum (Pisces, Nototheniidae) as Food for Other Fishes in McMurdo Sound, Antarctica J. T. Ea~man Department of Zoology, Ohio University, Athens, OH , USA Received 2 November 1984; accepted 18 March 1985 Summary. Nine species of not0thenioid fishes were captured near the southern limit of their range in ice covered McMurdo Sound, Antarctica. Stomach contents were examined using an occurrence method. Fishes were present in the diets of 8 of 9 species; Dissostichus mawsoni and Gymnodraco acuticeps were predominantly piscivorous. Pleuragramma antarcticum was the most common prey fish consumed, being present in stomachs of 4 of 8 species. Pleuragramma was also partially piscivorous (22%) as well as cannibalistic (13%). As evidenced by their presence in the stomach contents of other fishes, all life history stages from 20 mm SL postlarvae to 160 mm SL adult Pleuragramma were represented under the ice of the Sound. Pleuragramma was also a major food item for Weddell seals, birds and possibly invertebrates. As a widely distributed species in the pelagic zone, Pleuragramma may be an ecological substitute for euphausiids in the food web of the Sound. Introduction Until recently Antarctic fishes of the endemic suborder Notothenioidei have been a poorly understood component of the Antarctic marine ecosystem (Knox 1970; Laws 1977). However since the FIBEX cruise in 1981, the importance of this group in the ecosystem has become increasingly evident (e.g., Kock 1982). Whereas the traditional krill based food web is short, including phytoplankton, krill, seals and whales, it is now recognized that the food web is more complex and includes many more levels of organisms (Siegfried et al. 1985). The Antarctic silverfish, Pleuragramma antarcticum Boulenger (1902), is one of the few pelagic neutrally buoyant notothenioids (DeVries and Eastman 1978). It is the dominant fish in both the Ross (DeWitt 1970) and Weddell Seas (Hubold 1984, 1985 a). Furthermore, Pleuragramma may be the key species in the midwater ecosystem of the Antarctic shelf (Hubold 1984), an area where krill are sparse (Hempel 1985). Although Pleuragramma have been observed shoaling and feeding beneath the ice along the Antarctic Peninsula (Daniels 1982; Daniels and Lipps 1982), we know nothing about their biology under the fast ice adjacent to the major ice shelves. Since ice cover severely limits the methods that may be used to collect midwater fishes, I resolved this difficulty by sampling Pleuraoramma from the stomach contents of other fishes that were more easily captured through the ice of McMurdo Sound adjacent to the Ross Ice Shelf. In this paper I will deduce aspects of the biology of Pleuragramma from its presence in the diets of some of a sample of eight other notothenioids. This study also provides general information on the feeding ecology of notothenioids in McMurdo Sound. Materials and Methods The Collection Site in McMurdo Sound This research was conducted near the U.S. McMurdo Station (77 50'S, 'E) at Cape Armitage on Ross Island in the southwestern Ross Sea. Fishes were collected in McMurdo Sound, a 72 km by 81 km body of water between Ross Island and the Antarctic mainland. The Sound is over 1000 m deep and is covered by a 2-3 m thick layer of annual sea ice for about 10 months a year (Littlepage 1965). In 1978, the primary year of this study, the annual ice had persisted for three years and reached a thickness of 4.5 m. With the exception of water under major ice shelves, this collection of fishes is from the coldest and most southern extent of the range of notothenioids. McMurdo Sound seawater at depths of m is characterized by nearly constant mean annual temperature (-1.87 C; SD = 0.09) and salinity (34.70%o; SD = 0.29) (Littlepage 1965). Furthermore there is no vertical thermostratification and dissolved oxygen is high ( % saturation) throughout the year (Littlepage 1965). Collecting sites in McMurdo Sound were holes drilled in the annual fast ice over various water depths. All these sites were on the eutrophic east side of the Sound within 5 km of McMurdo Station. At the time of year the collection was made, this area was devoid of euphausiids. At depths of m, sponges and their asteroid and nudibranch predators dominated the epifaunal community (Dayton et al. 1974). The east side of the Sound was also characterized by infaunal communities at least as dense as those of any other benthic assemblage in the world (Dayton and Oliver 1977). The substrate was volcanic rubble, and pre-

2 156 vailing currents on the east side of the Sound were generally southerly with a yearly mean velocity of 11.9 cm/s (Littlepage 1965). Plankton in the water column was therefore carried from open water to under the annual ice and eventually under the Ross Ice Shelf. Collecting sites were km from the edge of the annual ice in November, Collection of Fishes A trailer mounted, diesel powered auger was used to drill 107 cm dia holes through the ice. Small wooden huts, used as fishing stations, were periodically moved to holes over 40, 70, 100, 200 and 550 m water depths in the Sound. All holes were within an area of a few km 2, and the sample of fishes was therefore geographically homogeneous. I collected 276 specimens representing 9 species (Fig. 1). All specimens were adults measuring mm SL. Most benthic (Trematomus nicolal T. bernacchii, T. centronotus and T. hansoni) and benthopelagic (T. loennbergff) species were taken in conical, wire mesh bottom traps. The traps were baited with beef, attached to the cable of an oceanographic winch and lowered in place to remain for h. The traps in which T. loennbergii were captured attracted large numbers of the scavenging amphipod Orchomene plebs. Therefore the proportion of this item in the diet may be unreliably high. Using unbalted Mepps lures, I hand jigged cryopelagic Pagothenia borchgrevinki from immediately beneath the platelet ice over water 550 m deep. Gymnodraco acuticeps were captured in a similar fashion near the bottom in water 30-50m deep. Large (82-148cm SL; kg), pelagic Dissostichus mawsoni were caught on a set line fished at m. Raymond (1975) and Eastman and DeVries (1981) described this procedure. As it was difficult to collect pelagic Pleuragramma antarcticum through the ice, specimens of this species were taken from the stomachs of Dissostichus. My sample encompassed all notothenioids regularly inhabiting McMurdo Sound with the exception of these rare species: the nototheniids Aethotaxis mitopteryx, Trematomus lepidorhinus, T. newnesi, the harpagiferid Histiodraco velifer and a few species of channichthyids. Other notothenioids, especially channichthyids, harpagiferids and bathydraconids, are present in the adjacent Ross Sea (De- Witt and Tyler 1960; Iwami and Abe 1981). It is not known whether significant numbers of these species enter the Sound as heavy ice cover has precluded systematic trawling. I collected most species during November, 1978, and they therefore comprised a temporally homogeneous sample. Dissostichus were collected in October-December, 1978, 1979 and Pleuragramma were taken from stomachs of Dissostichus in November, 1978 and Dietary Analysis While in the field I analyzed stomach contents subsequent to anatomical work, consequently a quantitative analysis was not attempted. After sorting into major taxa and preserving representative samples for reference, I used an occurrence method to enumerate stomach contents. This entailed counting the number of stomachs containing one or more of each food item, and then expressing this number as a percentage of the total number of stomachs. Although this method does not give an indication of the importance of various food groups, it does describe the homogeneity with which various species select their diet and the extent to which these species may or may not behave as a single feeding unit (Bowen 1983). This method was therefore consistent with the major goal of my study: a qualitative examination of the presence of Pleuragramma in the diet of 8 other species that were vertically separated in the water column. Results Although all species lack swim bladders,- evolutionary alterations in buoyancy (Eastman and DeVries 1981, 1982; Eastman 1985; DeVries and Eastman 1978, 1981) have facilitated vertical partitioning of resources in the water column. The results of this dietary study sustained the observation that there are four ecological or buoyancy types among the fishes of McMurdo Sound (Eastman and DeVries 1982). Thus cryopelagic and pelagic species with reduced or neutral buoyancy (Fig. 1, top row) fed exclusively on nektonic organisms. For example, cryopelagic Pagothenia borchgrevinki fed in the platelet ice and in the water beneath the ice on small (2-3 mm) copepods and amphipods. Dissostichus mawsoni, the largest Antarctic fish, was a neutrally buoyant midwater predator that ate primarily fishes and mysids in McMurdo Sound. Pleuragramma antarcticum, also neutrally buoyant, was a shoaling midwater species that ate copepods, mysids and other fishes. The most important finding of this research was that fishes, especially Pleuragramma, were of wide occurrence in the diets of other McMurdo Sound fishes (Table 1). Fishes were a dietary item in 8 of the 9 species, and 2 of these 8 species, Dissostichus and Gymnodraco, were predominantly piscivorous. Pleuragramma was the most common prey species consumed, being present in the stomach contents of 4 of 8 species, including Pleuragramma. This is the first report of both piscivory (22%) and of cannibalism (13 /0) in Pleuragramma. Included as prey were larger individuals as well as postlarvae. For example, a 145 mm SL Pleuragramma had a 45 mm SL Pleuragramma in its stomach. Study of the diets of McMurdo Sound fishes produced the following insights into the biology of Pleuragramma in the Sound. All life history stages from postlarvae to 160 mm SL adults were present. Adults were consumed by Dissostichus. Postlarvae (20-25 mm SL) were found in the stomachs of Gymnodraco and other Pleuragramma. Assuming that hatching occurred at 6 mm, and that the daily growth rate in summer was 0.2 mm (Keller 1983), these specimens had grown to this size in the previous year and were therefore members of age class 1 (Hubold 1985a). It is possible that Pleuragramma spawn under the ice or near the edge of the annual ice, with the postlarvae being carried under the ice by the southerly currents in the Sound. As evidenced by its presence in the diet of cryopelagic, pelagic and benthic species (Table 1), Pleuragramma lived throughout the water column over bottom depths of m. Dietary diversity was low in all 9 species, possibly a consequence of the use of a high taxonomic level for prey identification. Numbers of major taxa consumed ranged from 3-6 with a mean of 4.2. Most of the fishes were trophic generalists confined to primarily benthic habitats (Fig. 1, middle and bottom rows). Trematomus bernacchii, T. centronotus and T. hansoni were, for example, typical benthic species that fed primarily on errant polychaetes. Trematomus nicolai was a shallow water benthic species that preyed on actively moving organisms, some of which may have been captured in the water column. Its large dorsally directed eyes indicated that vision was

3 157.(O -R H~.R,,~ < 2'?.-.; ~ ~ o ".: ~,.::. ~ l, '.\L 7; :_Y,,,,,+x ~ Hy 2",,..:,, x,?:,~,!??? "i?!...x [[ii!iiii~iii? +:>, "2", ~ o ~2J2 o d o 722 OoO ~! i! I I i i i!!! \%\ \\.. -R, %\~, - %\\ -=,. 7. %%\ : ; -.v..) : %\~ :.) %\\ : ::*~N ) : %% (,OC i~;" )OC DO' )OC % (30' )OC,l%, :..:.. i r t r i i r r i %\\ ii!i!i!!!!iiiiil ~ ~ :? x!x: ~ ~ o } 0 I l l l i LIILWIIIt:.:-! i! o.--'g" e~ U 0 o ~ ~ ~E '",7 o E < g "~ D Fig. 1. Diets by percentage frequency of occurrence for nine species of notothenioid fishes from McMurdo Sound, Antarctica

4 158 Table 1. Fishes in the diet of McMurdo Sound vertebrates. Unless otherwise indicated, numbers are percentage frequency of occurrence in the total diet Prey species 2 = Predator species Fishes Pagothenia borchgrevinki 6 Dissostichus mawsoni 71 Pleuragramma antarcticum 13 Gymnodraco acuticeps 29 Trernatomus nicolai Trematomus loennbergii Trematomus bernacchii Zrematomus centronotus Trematomus hansoni Mammals Leptonychotes weddelli 11 Leptonychotes weddelli 93 Birds Pygoscelis adeliae Catharacta maccormicki Fishes 39% of diet by volume; 90% of these are small Pleuragramma Pleuragramma most common fish eaten Eastman (1985) 97 Dearborn (1965b) 93 Testa et al. (1985) Emison (1968) Young (1963) probably important in capturing small nektonic prey. I do not, however, consider T. nicolai to be cryopelagic as suggested by Andriashev (1970). Although Andriashev reported that fingerlings of this species clung to the vertical underwater faces of icebergs, it is the seeking of food and refuge in the platelet ice that characterize cyropelagic species. In McMurdo Sound adult T. nicolai did not fulfill these requirements. Furthermore, as indicated by measurements of buoyancy (Wt in seawater/wt in air x Eastman and DeVries 1982), T. nicolai were relatively heavy (3.13% ), significantly heavier than cryopelagic Pagothenia borchgrevinki (2.75%_+0.078; t = 3.206, P<0.01; Eastman, personal observation). Although the gammarid Orchomene plebs was the dominant amphipod in McMurdo Sound (Rakusa-Suszczewski 1982), it was the primary amphipod in the diets of only Pagothenia borchgrevinki, Trematomus bernacchii, T. loennbergii and Dissostichus mawsoni. Orchomene plebs were extremely abundant near the bottom where they commonly scavenged in baited fish traps set for benthopelagic T. loennbergii. It may be that the amphipod component of the diet of this species was artificially high and did not reflect the normal proportion of 0. plebs in the diet. Benthic gammarids are frequently found in shallow water plankton samples (Hurley 1969). This appears to be true for O. plebs in McMurdo Sound as it was the primary amphipod in the diet of cryopelagic Pagothenia borchgrevinki. Hyperiid amphipods, which are usually pelagic (Hurley 1969), were the only amphipods consumed by Gymnodraco acuticeps and the predominant amphipods in the diets of Trematomus nicolai and T. centronotus. Hyperiids were second in occurrence to O. plebs in the stomachs of Pagothenia borchgrevinki. Discussion Research on the feeding ecology of notothenioid fishes has been largely confined to species from West Antarctica, especially the Antarctic Peninsula and the Subantarctic islands. The studies of Targett (1981) and Daniels (1982) represent recent contributions in this area as well as summarizing previous work. Recent research has also emphasized the importance of krill in the diets of many species (Permitin and Tarverdiyeva 1978; Moreno 1980). There has been little research on the dietary habits of notothenioids from East Antarctica. Among the few contributions are those of Arnaud and Hureau (1966); Hureau (1970); DeWitt and Hopkins (1977) and Williams (1985). Furthermore, there is little data on notothenioids feeding under ice or in habitats largely devoid of euphausiids. The diets of McMurdo Sound species are similar to those reported by other workers. Errant polychaetes predominate in the diets of most benthic species including T. bernacchii, T. centronotus and T. hansoni. This was also the case in Hureau's (1970) study of T. bernacchii and T. hansoni in Ad~lie Land and in Dearborn's (19~65~0 study of T. bernacchii in McMurdo Sound.

5 159 As can be seen from Table 1, Pleuragramma are present in the diet of nearly all fishes that either live in the water column or rise from the bottom to feed in the water, the only exception being Trematomus nicolai. In some locations Pleuragramma may live and occasionally feed near the bottom. For example, Hubold (1985 b) reports that in the Weddell Sea Pleuragramma are captured in bottom trawls and that the stomachs sometimes contain sand. Pleuraoramma are also an important component of the diet of other McMurdo Sound vertebrates feeding in the pelagic zone. These include Weddell seals (Dearborn 1965 b; Testa et al. 1985), Ad61ie penguins (Emison 1968) and the South Polar skua (Young 1963). Emison (1968) noted that Ad61ie penguins can live and successfully rear chicks in areas nearly devoid of euphausiids if the water is rich in Pleuraoramma. I have observed Pleuragramma entangled in the tentacles of jellyfish in McMurdo Sound. Other workers have reported Pleuragramma in the diets of a wide variety of organisms in locations other than McMurdo Sound. Among these organisms are asteriid starfish (Dearborn 1977), crabeater seals (Schultz 1945), whales (Andriashev 1965) and Gentoo penguins (Volkman et al. 1980). Larval Pleuraoramma are subject to significant predation by larval channichthyids in the Weddell Sea (Hubold 1985 a). Although Pleuragramma exhibit some dietary plasticity, with variation in the proportion of dominant prey groups, recent studies indicate that they feed almost exclusively in the pelagic zone. In the Ross Sea Pleuraoramma eat copepods and adult euphausiids, with copepods dominant by number and euphausiids dominant by weight (DeWitt and Hopkins 1977). Near the Antarctic Peninsula euphausiids are most important in the diet by both number and volume (Daniels 1982). In the northern part of the Weddell Sea small Pleuraoramma consume copepods, polychaetes and chaetognaths (Kellermann and Koch 1984). In the southern and eastern Weddell Sea the most abundant food items in the diet by number are copepods, gastropods and euphausiids, with euphausiids dominant by weight (Hubold 1985 b). In Prydz Bay, East Antarctica, copepods and larval euphausiids are the most important dietary items by weight (Williams 1985). Fishes are present in the diet of Pleuraoramma only as incidental items (Hubold 1985 b; Williams 1985). DeWitt (1970) speculated that, through predation, Pleuragramma might influence the distribution and abundance of juveniles of other midwater notothenioids in the Ross Sea. However, his dietary analysis (DeWitt and Hopkins 1977) showed that Pleuragramma in the Ross Sea eat copepods and euphausiids, not fishes. In McMurdo Sound, on the other hand, fishes are 22% of the diet by occurrence, including 13% cannibalism. This is a striking departure from the diet in other locations and probably indicates that the pelagic zone of McMurdo Sound is an extreme biotope, not comparable to the open waters of the Ross Sea, Weddell Sea or Prydz Bay. Under cover of heavy sea ice, with the attendant reduction in productivity and in the absence of euphausiids, Pleuragramma augment their diet of mysids and copepods with piscivory, including cannibalism. Cannibalism may be necessary for survival of Pleuragramma in McMurdo Sound. As Pleuragramma are the dominant fish in the Ross Sea (DeWitt 1970) adjacent to McMurdo Sound and since they are present in the diets of an array of species in the Sound, they are probably also the dominant fish in ice covered McMurdo Sound. As a widely distributed species in the pelagic zone, they serve as food for other vertebrates and invertebrates. They may be an ecological substitute for euphausiids in an area where this group is sparse. The vital role of Pleuragramma should be recognized in future food web studies in McMurdo Sound. Acknowledgements. This research was supported by NSF grants DPP and DPP and by funds from the Ohio University College of Osteopathic Medicine. For assistance in the field I thank Art DeVries, Wayne Van Voorhies, Bob Boyd, Fred Whoriskey, Joe Schrag, Scott O'Grady, Jeff Turner, Martha Wolfe and Beth Marks. The manuscript was improved by comments from Gerd Hubold and two anonymous referees. References Andriashev AP (1965) A general review of the Antarctic fish fauna. In: Oye P van, Mieghem J van (eds) Biogeography and ecology in Antarctica. Monogr Biol, vol XV. Junk, The Hague, pp Andriashev AP (1970) Cryopelagic fishes of the Arctic and the Antarctic and their significance in polar ecosystems. In: Holdgate MW (ed) Antarctic ecology, vol 1. Academic Press, London, pp Arnaud P, Hureau J-C (1966) R6gime alimentaire de trois T616ost6ens Nototheniidae antarctiques (Terre Ad~lie). Bull Inst Oceanogr (Monaco) 66:1-24 Boulenger GA (1902) Pisces. In: Report on the collections of natural history made in the Antarctic regions during the voyage of the "Southern Cross". British Museum (Natural History), London, pp Bowen SH (1983) Quantitative description of the diet. In: Nielsen LA, Johnson DL (eds) Fisheries techniques. American Fisheries Society, Bethesda, Maryland, pp Daniels RA (1982) Feeding ecology of some fishes of the Antarctic Peninsula. Fish Bull 80: Daniels RA, Lipps JH (1982) Distribution and ecology of fishes of the Antarctic Peninsula. J Biogeogr 9:1-9 Dayton PK, Oliver JS (1977) Antarctic soft-bottom benthos in oligotrophic and eutrophic environments. Science 197:55-58 Dayton PK, Robilliard GA, Paine RT, Dayton LB (1974) Biological accomodation in the benthic community at McMurdo Sound, Antarctica. Ecol Monogr 44: Dearborn JH (1965 a) Ecological and faunistic investigations of the marine benthos at McMurdo Sound, Antarctica. PhD Dissertation, Stanford University Dearborn JH (1965 b) Food of Weddell seals at McMurdo Sound, Antarctica. J Mammal 46:37-43 Dearborn JH (1977) Foods and feeding characteristics of Antarctic asteroids and ophiuroids. In: Llano GA (ed) Adaptations within Antarctic ecosystems. Proc 3rd SCAR Symp Antarct Biol. Smithsonian Institution, Washington, pp DeVries AL, Eastman JT (1978) Lipid sacs as a buoyancy adaptation in an Antarctic fish. Nature (London) 271: DeVries AL, Eastman JT (1981) Physiology and ecology of notothenioid fishes of the Ross Sea. J R Soc NZ 11: DeWitt HH (1970) The character of the midwater fish fauna of the

6 160 Ross Sea, Antarctica. In: Holdgate MW (ed) Antarctic ecology, vol 1. Academic Press, London, pp DeWitt HH, Hopkins TL (1977) Aspects of the diet of the Antarctic silverfish, Pleuragramma antarcticum. In: Llano GA (ed) Adaptations within Antarctic ecosystems. Proc 3rd SCAR Syrup Antarct Biol. Smithsonian Institution, Washington, pp DeWitt HH, Tyler JC (1960) Fishes of the Stanford Antarctic Biological Research Program, Stanford Ichthyol Bull 7: Eastman JT (1985) The evolution of neutrally buoyant notothenioid fishes: their specializations and potential interactions in the Antarctic marine food web. In: Siegfried RW, Condy PR, Laws RM (eds) Antarctic nutrient cycles and food webs. Proc 4th SCAR Syrup Antarct Biol. Springer, Berlin (in press) Eastman JT, DeVries AL (1981) Buoyancy adaptations in a swim-bladderless Antarctic fish. J Morphol 167: Eastman JT, DeVries AL (1982) Buoyancy studies of notothenioid fishes in McMurdo Sound, Antarctica. Copeia 1982: Emison WB (1968) Feeding preferences of the Ad61ie penguin at Cape Crozier, Ross Island. In: Austin OL (ed) Antarctic bird studies. Antarct Res Ser, vol 12. American Geophysical Union, Washington, pp Hempel G (1985) Marine food chains in the Antarctic. In: Siegfried RW, Condy PR, Laws RM (eds) Antarctic nutrient cycles and food webs. Proc 4th SCAR Symp Antarct Biol. Springer, Berlin (in press) Hubold G (1984) Spatial distribution of Pleuragramma antarcticum (Pisces: Nototheniidae) near the Filchner- and Larsen Ice Shelves (Weddell Sea/Antarctica). Polar Biol 3: Hubold G (1985 a) Aspects of the early life history of the high Antarctic fish Pleuragramma antarcticum. In: Siegfried RW, Condy PR, Laws RM (eds) Antarctic nutrient cycles and food webs. Proc 4th SCAR Symp Antarct Biol. Springer, Berlin (in press) Hubold G (1985 b) Stomach contents of the Antarctic silverfish Pleuragramma antarcticum from the southern and eastern Weddell Sea (Antarctica). Polar Biol (in press) Hureau J-C (1970) Biologic compar6e de quelques Poissons antarctiques (Nototheniidae). Bull Inst Oceanogr (Monaco) 68:1-244 Hurley DE (1969) Amphipoda Hyperiidea. Antarctic map folio series, folio 11. American Geographical Society, New York, pp Iwami T, Abe T (1981) The collection of the fishes trawled in the Ross Sea. Antarct Rec (Tokyo) 71: Keller R (1983) Contributions to the early life history of Pleuragramma antarcticum Boul (Pisces, Nototheniidae) in the Weddell Sea. Meeresforschung 30:10-24 Kellermann A, Kock K-H (1984) Postlarval and juvenile notothenioids (Pisces, Perciformes) in the Southern Scotia Sea and Northern Weddell Sea during FIBEX Meeresforschung 30:82-93 Knox GA (1970) Antarctic marine ecosystems. In: Holdgate MW (ed) Antarctic ecology, vol 1. Academic Press, London, pp Kock K-H (1982) Fische aus RMT 8- und Krillschwimmschleppnetzf~ingen w~ihrend FIBEX Arch Fischereiwiss 33: Laws RM (1977) The significance of vertebrates in the Antarctic marine ecosystem. In: Llano GA (ed) Adaptations within Antarctic ecosystems. Proc 3rd SCAR Symp Antarct Biol. Smithsonian Institution, Washington, pp Littlepage JL (1965) Oceanographic investigations in McMurdo Sound, Antarctica. In: Llano GA (ed) Biology of the Antarctic seas II. Antarct Res Ser, vol 5. American Geophysical Union, Washington, pp 1-37 Moreno CA (1980) Observations on food and reproduction in Trematomus bernacchii (Pisces: Nototheniidae) from the Palmer Archipelago, Antarctica. Copeia 1980: Permitin YY, Tarverdiyeva MI (1978) Feeding of fishes of the families Nototheniidae and Chaenichthyidae in the South Orkney Islands. Sov J Mar Biol 4: Rakusa-Suszczewski S (1982) The biology and metabolism of Orchomene plebs (Hurley 1965) (Amphipoda: Gammaridea) from McMurdo Sound, Ross Sea, Antarctica. Polar Biol 1:47-54 Raymond JA (1975) Fishing for Antarctica's largest fish, the Antarctic cod. Mar Technol Soc J 9:32-35 Schultz LP (1945) Fishes of the United States Antarctic Service Expedition Proc Am Philos Soc 89:298 Siegfried RW, Condy PR, Laws RM (1985) Antarctic nutrient cycles and food webs. Proc 4th SCAR Syrnp Antarct Biol. Springer, Berlin (in press) Targett TE (1981) Trophic ecology and structure of coastal Antarctic fish communities. Mar Ecol Prog Set 4: Testa JW, Siniff DB, Ross M J, Winter JD (1985) Dynamics of Weddell seal-antarctic cod interactions in McMurdo Sound, Antarctica. In: Siegfried RW, Condy PR, Laws RM (eds) Antarctic nutrient cycles and food webs. Proc 4th SCAR Syrup Antarct Biol. Springer, Berlin (in press) Volkman NJ, Presler P, Trivelpiece W (1980) Diets of pygoscelid penguins at King George Island, Antarctica. Condor 82: Williams R (1985) Trophic relationships between pelagic fishes and euphausiids in Antarctic waters. In: Siegfried RW, Condy PR, Laws RM (eds) Antarctic nutrient cycles and food webs. Proc 4th SCAR Symp Antarct Biol. Springer, Berlin (in press) Young EC (1963) Feeding habits of the South Polar Skua Catharacta maccormicki. Ibis 105: