http://journals.cambridge.org Downloaded: 11 Dec 2013 IP address: 203.156.207.249 Antarctic Science 7 (4): 351-356 zyxwvutsr (1995) zyxwvut Interpopulation relationships in two species of Antarctic fish Notothenia rossii and Champsocephalus gunnari from the Kerguelen Islands: an allozyme study GUY DUHAMEL', CATHERINE OZOUF-COSTAZ1, GHlSLAlNE CATTANEO-BERREBP zy and PATRICK B ERRE B I2 zyxwv 'Museum national d'histoire naturelle, Laboratoire d'ichtyologie g6nkrale et appliquke, 43 rue Cuvier, 75231 Paris Cedex 05, France Wniversitk Monpellier zyxwvuts 11, Laboratoire Gdnome et Populations, CNRS URA 1493, case 063, place zyxw E. Bataillon, 34095 MontpeNier Cedex 05, France Abstract: zyxwvutsrq Enzymatic polymorphism was used to detect variability within Notothenia rossii from two sites on the Kerguelen Plateau and Champsocephalus gunnari from the same sites and the South Orkney Islands. No polymorphism was found in the second species and it was low but not statistically significant in the first. This apparent homogeneity does not substantiate suggestions from other results that the populations can be separated, especially in the case of C. gunnari. Other approaches will be necessary to solve definitively the question of population separation. Received 9 January 1995, accepted 30 May 1995 Key words: Champsocephalus gunnari, Notothenia rossii, Kerguelen Plateau, population separation, enzymatic polymorphism, electrophoresis Introduction The Kerguelen Plateau, the largest shelf in the Southern Ocean, is located in the Indian sector and has a north-west/ south-east orientation. It nearly reaches the Antarctic continental shelf in its southern extent. The Kerguelen Islands in the north (49"s) and Heard and McDonald islands (53"s) are the only islands to emerge from the shelf. Among the 61 fish species known to inhabit the shelf, diversity is low with only 19 endemic (Duhamel 1993). Of these, the order Notothenioidei dominates both in number of species (58%) and in biomass. Four species of this group have been exploited during the last 25 years, mainly off the Kerguelen Islands on the shelf break and the surrounding banks. Seven banks (named Skif, Shell, Coral, Aurora, Discovery, Pike and Zapadnaia) occur at various distances and depths (Fig. 1). They are populated by most of the species found on the shelves, but whether or not the populations are isolated from those on the shelves has not been resolved. Because of their relative proximity exchanges between the peri-insular and bank fish within each species cannot be precluded. For instance, a semi-pelagic behaviour could facilitate migration of shelf fish towards the ocean and the banks for trophic or reproductive reasons, or a population could disperse geographically during the larval stage. zyxwvut For Champsocephalus gunnari and Notothenia rossii, elucidating whether or not the bank and peri-insular shelf populations are separated would help both our understanding of their biological cycles whilst also increasing our knowledge of the stock dynamics of these two heavily exploited species. C. gunnari, of the family Channichthyidae, is the most abundant species on the Kerguelen Shelf. Analyses of length/frequency distributions of this species for the whole area have been analysed for over 25 years (Duhamel1987a, 1991, 1993, Gerasimchuck 1993). The data reveal an apparently distinctive demographic structure for the species with cyclic appearances of size groups identified as cohorts or age classes. These cohorts are often characteristic of individual islands and banks. An icefish group on the Skif Bank, 225 km south-west of the Kerguelen peri-insular shelf, never shows any common length distributions with the Kerguelen peri-insular group (Duhamel1987a). This lack of common population features suggests that individuals from both sites are reproductively isolated. Furthermore, the existence of a spawning ground specific to Skif Bank and bathymetrically isolated from that of the islands, and where fish spawn at different times (Duhamel 1987b), shows that the brood stock from both groups do not spawn at the same time. Observations made on the shelf of Heard and McDonald islands and its related banks (R.Williams, personal communication 1992) have shown the same phenomenon. It has previously been shown from analysis of morphological and meristic characters (Kock 1981, Gubsch 1982, Sosinski 1985), from parasite infestation rate (Siege1 1980) and from differences in biological characteristics (Kock 1992) that populations from the Atlantic sector of the Southern Ocean (i.e. South Georgia, South Orkney Islands, South Shetland Islands and Bouvet Island) are distinct from the populations of the Indian sector. The aim of our study is to determine whether distinct populations of C. gunnari also exist in various parts of the Kerguelen Plateau. Population genetics methods will test for the existence of an independent population on the Skif Bank. 35 1