CCAMLR Scieilce, Vol. 8 (2001): 133-146 AGE-LENGTH COMPOSITION OF MACKEREL ICEFISH (CHAMPSOCEPHALUS GUNNARI, PERCIFORMES, NOTOTHENIOIDEI, CHANNICHTHYIDAE) FROM DIFFERENT PARTS OF THE SOUTH GEORGIA SHELF G.A. Frolkina AtlantNIRO 5 Dmitry Donskoy Street Kaliningrad 236000, Russia Email - atlantQbaltnet.ru Abstract Biostatistical data obtained by Soviet research and commercial vessels from 1970 to 1991 have been used to determine tlne age-length composition of mackerel icefish (Chnnzpsoceplzalus g~~izllnrl)from different parts of the South Georgia area. An analysis of the spatial distribution of C. giirzrznri size and age groups over the eastern, northern, western and soutlnern parts of tlne shelf, and near Shag Rocks, revealed a similar age-leingtl~composition for young fish inhabiting areas to the west of the island and near Shag Rocks. Differences were observed between those t~7ogroups and the easterin group. The larger number of mature fish in the west is related to the migration of maturing individuals from the eastern and western parts of the area. It is implied that part of tlne western group migrates towards Shag Rocks at the age of 2-3 years. It has been found that, by number, recruits represent the largest part of tlne population, whether a fishery is operating or not. As a result of this, as well as the species' ability to live not only in off- bottom, but also in pelagic waters, an earlier age of sexual maturity compared to other nototheniids, and favourable oceanographic conditions, the C. g~lrliznrl stock could potentially recover quickly from declines in stock size and inay become abundant in the area, as has bee11 demonstrated on several occasions in the 1970s and 1980s. Les donnees biologiques des statistiques des navires sovietiques de recherche et de commerce de 1970 a 1991 ont servi a determiner la composition dge-longueur du poisson des glaces (Cl~nrrzpsoceplzal~~sgtinnnri) de divers secteurs adjacents B la Gkorgie du Sud. Une analyse de la repartition spatiale des groupes de tailles et d'dges de C. gllrznnri sur les secteurs est, nord, ouest et sud du plateau, ainsi qu'a proximit6 des ilots Shag revele la similarit6 de la composition dges-longueurs des juvkniles de poissons frequentant l'ouest de l'ile et les alentours des ilots Sliag, mais des differences entre ces deux groupes et le groupe de l'est. La proportion importante de poissons matures 5 l'ouest est like a la migration des individus matures des rkgions est et ouest. I1 semble qu'une partie du groupe de l'ouest inigre vers les ilots Shag 2i l'bge de 2-3 ans. De plus, en nombre, les recrues reprksentent la plus grande partie de la population, qu'une p@cheriesoit en activit6 ou non. En consi.quence, et si l'on considere par ailleurs la capacite de l'espece de vivre non seulement en eaux proches du fond, mais aussi en eaux pelagiques, sa inaturitk sexuelle 5 un 2ge moins klev6 que d'autres notot116niides, et les conditions ocPanographiques favorables, le stock de C.guntznrl pourrait recuperer rapidement des dkcimations du stock et devenir abondant dans la region comme cela a kte dkmontre a plusieurs reprises dans les annkes 70 et 80. Anx H3yYeHHrl pa3MepHO-BO3paCTHOrO COCTaBa Ll(yK0BHfl~0fi~~~OK~OBKII (C~LZI?IPSO- cephalzu g~l117CIri)Ha pa3JIllYHbIX YYaCTKaX pafio~aFOXHOG re~prkikiHCIlOJIb30BaHb1 ~MOCTZITMCTIIY~CKH~MaTepHanbl HOlICKOBblX I? npOMbICnOBbIX pefic0B COBeTCKHX CyAOB 3a nepuon 1970- 199 1 rr. A~anM'3npocTpaHcTseHHoro pacnpeneneaarr pawepHo- BO~~~CTH~IXrpynn C. gur~nuriHa BocToKe, ceeepe, 3anane, tore urenb+a ocTpoBa m y CKan mar BblXBlIJI CXOACTHO pa3~ep~0-~03pa~T~0fiCTPYKTYPbI B nepBbIe rOAb1 SKkl3HI.I Memny pb160fi, 06u~am1~eiiK ?anany OT ocTpoBa Ir y wan LUar, 11 oTnmwe ~TMXABYX rpynnIlponoK OT BOCTOYHOG. 1;onbrrree KonauecTeo nono~ospenofipb16b1 ~a sana~e CB27aHO C ~Il~palJHefiCWna CO'3peBLUEiX oco6eG C BOCTOYHOrO &l 3alTaAHOrO YYaCTKOB. Ilpe~nonarae~c~,YTO YacTb 3anan~oErpynnrrpoerw pb16bl MctrpnpyeT K cKanaM UIar Ha BTOPOM-TpeTheM rOny XM'3H11. O~H~PYX~HO,YTO, YkiCneHHO, ~a~60JIhUlyK)YaCTh nOnyJlRI@lki COCTaBnReT IIOnOnHeHMe, He'3aBHCMMO OT HaJlMYllR MnIl OTCyTCTBIiX np~Mh1CJla.Gnaronap~ 3TOMy, a TaKZKe CIIOCO~HOCTI~Bllna 061.1~a~hHe TOnbKO B ~PCI~OHH~IX,HO II B nenarwiecKt3x Boaax, 6onee paHHeMy nonoBoMy co3peeaHmo no CpaBHeHEiK) C flpyrllMI.1 HOTOTeHileBblMM ki 6~ar0IIpkiX~~h1~OKeaHOJIOT1iYeCKI.IM ycnonmxM 3anac C. gu~rirariMomey 661~1PO BOCCI aHanJIkiBal ~C>IPI UOCI 111 a1 b UMCOKOI~ YllCneHHOCTlI B 3TOM pafi~~e,LIT0 HeOHHOKpaTHO CJIyLIaJIOCb B 1970-e I< 1980-e ronh1. Resumen Se utilizaron 10s datos de bioestadistica obtenidos de las investigaciones soviPticas y de 10s barcos de pesca comercial de ese pais desde 1970 hasta 1991 para determinar la composici6n de talla-edad del draco rayado (Clini?~psocepl~al~~sgl~izilnri) de varias regiones de Georgia del Sur. El analisis de la distribucion espacial por talla y edad de las poblaciones de C. glliirinri de las regiones este, norte, oeste y sur de la plataforma y cerca de las rocas Cormoran, demostr6 una siil-rilitud entre la composici6n de talla-edad de 10s peces juver~ilesque habitan en las regiones a1 oeste de la isla y cerca de las rocas Cormoran, y una diferencia entre estas dos poblaciones y la del este. La mayor abundancia de peces maduros adultos en la poblacion del oeste se relaciona con la migraci6n de peces juvei-riles del este y oeste de la zona. Se supone que parte de la poblaci6n del oeste inigra hacia las rocas Cormoran a 10s 2 o 3 aiios. Se observ6 que 10s reclutas representan la mayor proporci6i-r en nuinero de la poblacion, independienteinente de la explotaci6i-r. Debido a esto, a la capacidad de la especie para habitar tanto cerca del lecho n-rarino como en aguas pelagicas, a la temprai-ra madurez sexual de la especie en relacion a otros nototPnidos, y a las condiciones oceanogr6ficas favorables, el stock de C. giliziinri tiene ~111gran potei-rcial de recuperacion de las dismin~~cionesdel tamaiio de la poblacion, e incluso de alcanzar una gran abundancia en la zona. Esto ya ha sido demostrado en varias ocasiones durante las dPcadas del 70 y 80. Keywords: C. glrirrinrr, length-age composition, juveniles, immature and mature fish, CCAMLR INTRODUCTION of C. giiiznmi. Studies carried out by scientists from different countries will enable the development of Mackerel icefish (C. yzinnavi) has been, and a long-term strategy for managing C. gu~znnvistocks continues to be, one of the most important com- in the South Georgia area which take into account mercial species in waters around South Georgia. the ecological characteristics of this species. A number of papers on the ecology of C. gl~nizari have been published (e.g. Permitin, 1982, 1987; Efremenko, 1982; Lubimova, 1980, 1987; Shust, MATERIAL AND METHODS 1987, 1998). The most detailed information on C. gilnnavi has been provided by I<ock (1979,1981) The materials used in this study were collected and Sosinski (1981). These articles, however, lack during research cruises conducted from 1970 to information on the species' life history, e.g. the 1991. Supplementary data on C. guiznari were taken spatial distribution of various size-age classes of from commercial fishing vessels of the USSR C. gtiiiiz~~vion the shelf. In particular, this relates to Northern and Southern Fleets. the size composition of C. gzi11izavi off Shag Rocks. Materials collected by AtlantNIRO from 1970 to In addition, we analysed the results of six 1991 allowed us to study the spatial distribution of pelagic and seven bottom trawl surveys carried out different size-age classes in considerable detail. by AtlantNIRO around South Georgia from 1984 to 1991. These surveys covered the area outside the We have analysed and summarised all the island's territorial waters, i.e. mainly beyond the data available to us in order to determine the 100 m isobath. distributional and biological characteristics of C. guiiizavi. We hope the results of our work will Pelagic trawl survey methods are described in help explain a number of features of this species' Frolkina et al. (1998). biology. For bottom trawl surveys, a HEK-4 bottom CCAMLR scientists are currently giving a great trawl was used, which had been considerably deal of attention to various aspects of the ecology modified to prevent snagging on hard bottoms. Age-length conipositiol~of mackerel icefish from the South Georgia shelf The trawl mouth was 18-25 m wide and 7-8 m RESULTS high. The trawl had a small-mesh liner with 10 mm meshes in the codend. History of Commercial Fishing for C. gz~rzizcrri Bottom trawl surveys were carried out using the same design as pelagic surveys, i.e. stratified C. guniiari was first caught commercially in the shallow waters of Shag Rocks by Soviet vessels random sampling. Depth strata selected were 100- in November-December 1970. The total catch 200 m, 201-300 m and 301-500 m. Trawl stations was approximately 10 000 tonnes for that period were selected by a random number generator with (SC-CAMLR, 1993), giving a catch per unit effort one trawl station for each 80-100 miles2, with no of 55.6 tonnes/vessel/ day. In 1971/72 this species, less than three stations per stratum. Hauls were together with Psetldoclzaenichthys georgiaizus, was only made during daylight hours to prevent bias occasionally taken in the northern and northeast- caused by diurnal vertical migrations. The trawl ern regions of the South Georgia shelf, yielding was towed at 3-3.5 knots for 30 minutes. Catch- catches at the rate of approximately 40 tonnes/ ability was assumed to be 100%. vessel/day in various months.