CCAMLR Scier~ce,Vol. 8 (2001): 119-132

VARIATIONS IN CONDITION INDICES OF ICEFISH AT SOUTH GEORGIA FROM 1972 TO 1997

I. Everson %3 British Antarctic Survey Natural Environment Research Council High Cross, Madingley Road Cambridge CB3 OET, United Kingdom Email - [email protected]

K.-H. Kock Institut fur Seefischerei Bundesforschungsanstalt fur Fischerei Palmaille 9, D-2267 Hamburg, Germany

Abstract

Mackerel icefish (Cllanzpsocephal[~sgzrnnnvi) are widespread on the South Georgia shelf, Antarctica, and have been fished commercially since the early 1970s. They are known to feed predominantly on . An index of condition which uses the ratio of the measured total mass to the estimated mass is shown to provide a good indicator of local krill density. The index is likely to be little affected by the reproductive cycle unless there is high krill availability during the months around the spawning time, and even then the effect is much less than the highest observed values. The condition index responds rapidly to changes in krill density and therefore can provide indications of short-term variations in krill availability. Condition index provides a useful proxy for krill density and is likely to be of considerable value in interpreting the results from ecosystein assessments such as that in progress under the auspices of CCAMLR.

Le poisson des glaces (Cl~nn1psoce~1zal~~sglri~riari) est une espece courante sur le plateau de GPorgie du Sud, en Antarctique, et fait l'objet de pi.che commerciale depuis le dPbut des ann6es 70. I1 se nourrit principaleinent de krill. Un indice de condition reposant sur le rapport ei~trele poids total mesurP et le poids estim6 constitue un bon indicateur de la densite locale de krill. I1 est peu probable qu'il soit affect6 par le cycle reproductif B moins que le krill soit particulierement abondant les mois entourant le frai, et m@medans ce cas, l'effet serait beaucoup moins important que les valeurs les plus Plev6es observkes. L'indice de condition, du fait qu'il repond rapidement aux changements de densite du krill, donne une indication des variations court terme de l'abondance du krill disponible. I1 peut illustrer la densite du krill et devrait @tredes plus utiles pour interpreter les rPsultats des Pvaluations de 1'Pcosysti.me en cours sous les auspices de la CCAMLR.

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Resumen

El draco rayado (Chnrirpsocepl~nl~rsglulr1ar.i) se encuentra distribuido ampliamente en la plataforma de Georgia del Sur (Antirtida), y su explotacibn comercial cornenz6 a Everson and Kock

principios de la decada de 10s setenta. El kril es el coniponente principal de su dieta y se ha cncontrado que el indice de condicici~idado por la proporcidn de la masa total medida con respecto a la lnasa estimada es un buen indicador de la densidad local de kril. El indice varia muy poco en funcion del ciclo reproductor, salvo que haya una gran abundancia de kril dura~ite10s meses cercanos a la 6poca de desove, y aitn asi, el efecto es mucho inenor que 10s valores in&ximosobservados. Los cambios en la densidad de kril afectan riipidainente a1 indice de condicion y por lo tanto este puede indicar variaciones de la disponibilidad de kril a corto plazo. El indice de condicion es un sustituto viable para la densidad de kril y tiene gran potential en la interpretacion de 10s resultados de las evaluaciones del ecosistema que se efectuanbajo 10s auspicios de la CCRVMA.

Keywords: ~iiackerelicefish, C. plrzizari, condition, krill, ecosystem interaction, CCAMLR

INTRODUCTION in the months leading up to spawning, at which time they may account for 20% of the total mass Mackerel icefish (C1zni1ipsocep1~nli~sgtlnnnui) are (Kock, 1992; Everson et al., 1996). Arising from widespread in CCAMLR Subarea 48.3 ill water up this, we envisage two scenarios whereby the total to 400 m deep. Since 1970 they have been subject to mass of the fish may vary as a result of changes in a commercial fishery of varying intensity, in peak feeding conditions. years yielding a total catch of over 100 000 tonnes (Kock, 1992). They feed predominantly on Antarctic Good followed by poor feeding conditions. krill (E~rplzazisinsiiycvbn), (Kock et al., 1994) which Initially the stomach contents would decrease itself is subject to commercial fishing. Trophic leading to a reduction in total mass. If the poor interactions between icefish and krill are thus of feeding conditions continue, then there is likely particular interest due to the complexities of to be an effect on the body fat deposits and also applying an ecosystesn approacl~to management a reduction in the musculature. as required by the Convention for the Conservation of Antarctic Marine Living Resources. Poor followed by good feeding conditions. Initially the stomach is likely to be empty, or An index of condition of C. gz~ni~nriderived by nearly so, and, if the poor feeding conditions comparing measured mass to an estimated 'average' have been prolonged, the musculature will also mass has been show11 to be related to the amount of have a below-average mass. An improvement krill available to C. gi~i~izariin the sampled region in feeding conditions will result in an increase (Everson et al., 1997). That study used the gutted in stomach mass and some time later, if inass of fish, from a series of research vessel surveys favourable conditions continue, total lipid and to South Georgia, to derive the conditior~index. body muscle, as some of the energy is converted Data from commercial vessels are available for to structural protein. many months going back to the start of the fishery, although the sampling of such catches included the We recognise that this is a very simplified view, total length and total mass but not the gutted mass however it is based on tl~eextensive review by of fish. If a condition index using total mass can be Love (1988)of the effects of different feeding regimes demonstrated to provide a reliable indicator of krill on fish that are being used in aquaculture and also availability then this information might be used to information reported to us by Frolkina (pers. comm. provide a much more extensive view of the status reported in Anon., 1998). The scenarios outlined of fish and krill since the early 1970s. above take no account of any variation in gonad mass and are cos~sequentlyonly appropriate for The gutted mass of fish comprises the total immature fish. The gonad mass, as part of the total mass of bone, body musculature, fins and spinal but not gutted mass, brings an added level of chord. All of these can vary but, for this study, we complexity that is dependent on the reproductive assume that the greatest variation is likely to be cycle. Thus, as the gonads approach spawning present in the mass of the body ~nusculature.Total coi~ditionthe total mass is likely to increase although mass is the gutted mass plus the mass of the viscera the gutted mass may remain more or less stable. and gonads. The Inass of the viscera will vary mostly due to the amount of food contained in the Arising from this, we expect a condition index stomach and energy stored as fat deposits in the using total mass to respond quickly to changes in body cavity (Frolkina, pers. comm.). In addition, feeding status but be subject to a greater degree of the gonads of sexually mature fish increase in size variation arising from cl~angesin stomach coi~tents. Condition indices of mackerel icefish at South Georgia

One using gutted mass is likely to respond with a relationships using only those records for which slight time delay and have a lower variance with both W,, and W,, had been measured. The same respect to one using total mass. analytical procedures as used in Everson et al. (1997), a least-squares regression on the log-transformed In this study we have sought to determine L,, W,, and W,,, were used. The resultant length-to- whether a condition index derived from total mass mass relationships were used to derive an estimated can provide indications of krill status in a similar mass for each fish ( and K,,). Two condition manner to one using gutted mass and from it indices were calculated: C,, a gutted mass condition determine when good and poor feeding conditions index and C,, a total mass condition index for each were present in the past. of the 'i' fish:

MATERIALS AND METHODS

Data were collected from the following sources: and (i) research vessel surveys by Germany, UK and the USA, details of which are given in Everson et al. (1997); All the data for this part of the study came (ii) research vessel surveys by Argentinian from research vessel surveys and consequently scientists (Marschoff et al., 1994, 1995, 1996, are restricted to nine separate months (eight as 1997); described in Everson et al. (1997) and a further survey in September 1997). (iii) commercial fishing activities by Russian vessels between 1972 and 1991 (unpublished Gutted mass was not available from the datasets data provided by VNIRO, Moscow, collated from the commercial fishery and for these only C, and checked by Institut fur Seefischerei, Hamburg, Germany); and could be determined. For this analysis a new length-to-mass relationship was calculated using (iv) commercial fishing and research vessel data data from all the sources. This much larger dataset from Polish vessels from 1977 (unpublished contained a large number of fish which were data provided by Sea Fisheries Institute, measured and weighed at sea. Inconsistencies in Gdynia, Poland). data from smaller fish in some samples forced us to consider only those fish greater than or equal in The data were divided into two groups total length to 30 cm. This group is composed of geographically: South Georgia for hauls between sexually mature fish (Everson et al., 1996). 34"W and 40°W, and Shag Rocks for hauls between 40°W and 44"W. The series of data have been Information on krill status was derived from grouped by month, beginning in August 1972 and two sources: extending to September 1997, although not all months over that period were sampled. (i) direct estimates of krill density from acoustic surveys (Brierley et al., 1999); and Data were loaded into a central database. In some instances total length was not recorded and (ii) indirect estimates of krill status as indicated for those records it was estimated from the by species dependent on krill and monitored standard length using the relationship: by the CCAMLR Ecosystem Monitoring Program (CEMP) (SC-CAMLR, 1995). Lf = (1.1017 * Standard Length) + 0.611 (11 = 1 247, r2 = 0.992). Statistical analyses were undertaken using Minitab. This relationship was derived from all records that contained values for both the total and standard length. RESULTS

The database included a measured total (Wi,) Length-to-mass Relationships and gutted mass (W,:,)for each fish. The condition index analyses were undertaken in stages. The first A number of total length (L,) to mass relationsl~ips part entailed determinil~gaverage length-to-mass were derived and these are summarised below. Everson and Kock

Records from fish where both total mass and krill survey. These are plotted in Figure 2. Under gutted mass had been measured: good feeding conditions icefish will eventually reach satiation, whereas when krill are scarce fish males (N = 1 246): feed more on the hyperiid amphipod Tlzernisfo total mass = 0.001294 LIiJ6 gntldichaudii and also tend to eat less overall (Kock (r2= 0.984) et al., 1994). Arising from these considerations we would expect the relationship between krill gutted mass = 0.001137 Lt ?-'" density and condition index to be asymptotic, (v2 = 0.988) rather than linear. A least-squares regression on the log-transformed data gave the following females (N = 1 421): relationship: total mass = 0.001243 L, 347 (v2 = 0.980) Ln C, = -0.1182 + 0.0439*(Ln(Kvilldensity)) (v2 = 0.713). gutted mass = 0.001256 L, 343 (v2 = 0.986). Although these conclusions are based on data from relatively few months, they do indicate a strong Records from fish where only total mass had functional relationship between the icefish C, and been measured and which were 30 cm or greater in krill density. We conclude from this that condition total length: index is following food availability with a short, of the order of a month or less, response time. males: total mass = 0.001322.L,"J5 (N = 5 453; r2 = 0.896) Temporal Variation in Condition Index females: Relationship to Icefish Reproductive Cycle total mass = 0.001003.LtXs2 (N = 8 277; v2 = 0.869). The gonadosomatic index (GSI), the ratio of gonad mass to total mass expressed as a percentage increases, in the case of female Antarctic fish, to Comparison of C, with C, over 20% in the months leading up to spawning. Such an increase in gonad mass would increase the The results, plotted separately for male and total mass and consequently C, immediately prior female fish, are shown in Figure 1 and have a fairly to spawning. Taking a generalised notothei~iid tight distribution around the line where C,s equals cycle described by Everson (1984) as a standard C,. The product moment correlation coefficients because the equivalent information is unavailable were 0.951 for males and 0.898 for females, both of for C. giin~~clri,we estimate a theoretical condition which were significant at the 1% level. index using GSI to estimate gonad mass. During the resting phase, because the ovary contains While we would expect C, and C, to be correlated, vitellogenous oocytes, the GSI remains at around a very close relationship would not be expected The resting testis is much smaller but still due to differences in response times to changes in 3.5%. feeding conditions. Variation between C, and C, accounts for around 1% of the body mass. A can be due to a variety of additional causes such as theoretical condition cycle would consequently be measurement error and natural variation between as in Table 1. From this analysis it is apparent that individual fish, but since the trend is clearly present, the gonad mass will contribute less than 5% to C, in we feel that the total mass cortdition index has all except the two months prior to spawning. similar validity to that derived from gutted mass Depending on locality, that will mean that except and reported earlier (Everson et al., 1997) for for the months of March, April, May and possibly providing an indicator of krill availability to February, C, will be little affected by the spawning icefisli. cycle. We have investigated this by plotting C, and the Comparison of Condition Index results are shown in Figure 3. The spawning season to Krill Density in April aid May (months 4 and 5) is iiot clearly apparent from an inspection of tlie monthly C, for A series of krill density estimates reported two reasons. Firstly, because the GSI makes only a by Brierley et al., (1999) was compared wit11 C, small contribution to C, except prior to spawning obtained from fish caught in the same month as the (Table 1)and, secondly, because there were relatively Condition indices of mackerel icefish at Soutl~Georgia

Table 1: Theoretical changes in total mass condition index caused by seasonal variation in the gonadosomatic index (GSI). The calculations assume that during the restin phase, the first seven months since last spawning, the GSI is l'%,kr males and 354% for females.

Months Since Male GSI Male C, Female GSI Female C, Last Spawning 1-7 1 1 .OO 3.5-4 1 .00 8 2 1.01 5 1.01 9 3 1.02 6 1.02 10 5 1.04 8 1.04

few samples around the spawning season. The It is unfortunate that there are relatively few important point here is that gonad mass appears to periods when samples were available simultaneously be having little influence on the variation in C, from both localities, but in spite of this there are through most of the year. several obvious inconsistencies. There are several periods, indicated in boldface type, for which the C, is normal in one area but low in the other. There Annual Variation are also some instances of low C, at both South Georgia and Shag Rocks; these are indicated by The mean indices during the first part of the year underscore in the list above. Such a difference is tend to be greater than unity, an indication that not unexpected because, although South Georgia more fish are actively feeding during this period and Shag Rocks are separated geographically by than during the latter part of the winter as noted by only a narrow region of deep water, the degree of Frolkina (pers. comm. reported in Anon., 1998). separation means that there are likely to be different feeding regimes for C. gu~znari(Kock et al., 1994). Of the months for which sampling is Between-season Variation available, 40°/o of those on the South Georgia shelf and 35% of those on the Shag Rocks shelf had C, Information from 13 731 C. gziizizari sampled in significantly less than one. 65 months on the South Georgia shelf and 2 160 sampled in 20 months from the Shag Rocks shelf were used in the analysis. The C, and 95% confidence Short-term Variation limits were plotted sequentially by month in Figure 4. The mean values fluctuate although not Looking at the results sequentially month by in an apparently regular manner. month, rather than as a longer-term picture, further features emerge. A good example is around the Periods during which the C, was significantly period 1977 to 1983 plotted in Figure 5, where there less than one and assumed to indicate poor feeding is good temporal coverage. In some periods there conditions at South Georgia and/or at Shag Rocks is a sequence of values following a clear trend. Good occurred during the following months: examples of rising trends are over the periods January to May 1978 and from November 1978 to South Georgia: Shag Rocks: March 1979. Declining trends are seen from February Aug-Oct 72 July + Sept 72 to May 1977 and October 1977 to January 1978. Nov 77 + Jan 78 No sample Thus, the general trend that is apparent in Figure 3, Nov 78 No sample and noted in Anon. (1998), is subject to a large degree Dec 80-Jan 81 No sample of variation from year to year. No sample (Feb 81 normal) April + June 81 Nov 82 No sample The evidence from Figure 2 indicates that Nov 83-Jan 84 No sample the changes shown in Figure 5 are responses Nov-Dec 85 Oct-Nov 85 to changing krill density. When there has been No sample Jan 87 a rapid change, such as between January and Sept 87 No sample February and between November and December June 90-Jan 91 Normal in the same year, we infer that there has been a Jan-March 94 Normal sudden change in krill density and consequently Sept 97 Sept 97 the feeding status of icefish. Everson and Kock

Table 2: Comparison of icefish condition indices (C,) during thesummermontl~swith Me CEMP indices for land- based species that are dependent on krill. The condition indices are the mean value for all sexually mature fish. FUSE =fur seal; GEPE = gentoo penguin; MAPE = ; trip = foraging trip duration; surv = pup survival; meal = meal size and S = breeding success.

Year ct FUSE CEPE MAPE Nov Dec Jan Feb Mar Trip Surv Meal S Meal S

Comparison of Condition Index average fur seal pup weight in 1973, a year when with Fur Seal and Penguin Indices there were no reports of krill scarcity, to that on the same calendar date in 1978 showed that in the The ecosystem approach to management is 1977/78 season the growth rates were running central to the aims of CCAMLR. Much work has almost a month later, as shown in Figure 6. An been done on the functional relationships between alternative comparison is that on the same date the fur seals, macaroni and gentoo penguins monitored pups were 1.4 kg lighter despite having been born as part of CEMP and reported in SC-CAMLR (1997). on the same calendar date (Bonner et al., 1978). It is beyond the scope of the present paper to The apparent return of favourable krill conditions consider all parameters in detail, so we focus 0x1 in February and March 1978, as indicated by the characteristics related directly to the diet of each of icefish C,, occurred too late or else was of insufficient the three species. These are fur seal foraging trip magnitude to change the situation since the gentoo duration and pup survival, gentoo and macaroni penguins and black-browed albatrosses had very penguin meal size and breeding success, all of which low chick survival rates during that season. Poor are considered to have a close affinity to local krill feeding conditions for gentoo penguins may have availability (Reid et al., 1999). These parameters persisted locally; one of the authors (K.-H. Kock) are considered to be integrating over the period December to March over the approximate range of found dead penguins on the shore of Cumberland 50 to 100 km from the breeding site. The foraging Bay, South Georgia, in March 1978. In 1978/79, trip and diet parameters integrate over these same when penguin breeding success was normal, the scales but in periods of two to five days, whereas icefish Ci was low in November but close to one in pup survival and penguin breeding success are December, suggesting that the penguins had not single values integrating over the whole period been unduly affected by poor conditions early in (SC-CAMLR, 1989, Table 4). For this analysis the the season followed by more favourable feeding CEMP indices have been scored as +l if the mean conditions later. value for the season is greater than the upper 95% confidence limit for the mean of all values, 0 if it During the 1990/91 and 1993/94 seasons all lies within the confidence interval and -1 if it is CEMP parameters, with the exception of macaroni lower than the lower 95% confidence limit. These penguin breeding success, indicated poor feeding results are summarised in Table 2. conditions. At South Georgia the icefish C, over the same period was also low, indicating a scarcity of During the 1977/78 season, breeding success, krill. By contrast, the icefish Ci in both these seasons the only parameter reported at that time for at Shag Rocks was close to one. The Shag Rocks both penguin species, was extremely low and this shelf is at the extreme range for macaroni penguins coincides with a low icefish condition index for during the breeding season (Trathan et al., 1998) November 1977 and January 1978. Comparing the and it is therefore possible that this species could Condition indices of mackerel icefish at Soutli Georgia

just obtain sufficient food to provision chicks by of long-term status, whether it has been a 'good' or feeding at the limit of its foraging range. Such a 'poor' krill season, but also some insight into within- spatial separation would require greater energy season changes. From this it is clear that 'good' and expenditure by the parent bird, a situation which 'poor' krill status are not j~stseasonal categories, could adversely affect the meal size delivered to but need to be considered on a smaller timescale. the chick without affecting chick survival. Gentoo Thus, there can be quite rapid (of the order of a penguins, and to a lesser extent fur seals, are more month) changes in krill status within a region. In restricted in their foraging range during the breeding this paper we suggest that such changes have a rapid season and hence are more likely to be affected by effect on icefish condition. Such rapid responses local krill scarcity. may be seen by looking at small temporal scale subsets of the CEMP data but, since these are integrating over periods which are greater than the DISCUSSION timescale over which krill status changes, the signal as summarised in a 'seasonal mean value' An analysis of condition indices needs to take can provide equivocal answers. account of the key components that make up the index. An index based on total mass is likely to It has become the practice to develop combined vary due to the size of the gonad, the amount of food standardised indices (CSI) of the CEMP data in the stomach and the mass of the musculature. (SC-CAMLR, 1997). These have the advantage that they provide a graphical form that clearly indicates Consideration of the reproductive cycle and its when there has been a 'poor' krill season. However, effects on the condition index led us to conclude their utility does not go beyond this because they that outside the period (possibly) from February to do not take account of the response functions of the May gonad mass has little effect on the index. CEMP parameters to changes in the krill status. 111 Consequently, periods when the condition index determining these response functions, note should is down to 0.9 or up to 1.1 can be largely attributed also be taken of the interdependence of the different to the status of the body musculature, liver size parameters. For example, penguin arrival weight, and stomach fullness. The liver mass, as noted by a parameter that is thought to be dependent on Everson et al. (1997), varies from around 1 to 4'10 of feeding status in winter, almost certainly has an the body mass. Arising from this it is only likely to effect on breeding success. have a minor effect (less than 2%) on a total mass condition index. In developing an ecosystem assessment using these various indices it is clear that there are inter- The gutted mass condition index is well correlated dependencies which need to be considered. with the total mass index, indicating that a large Investigating the way in which these different part of the variation is occurring due to changes in components interact and their resultant responses the musculature. Love (1988) has demonstrated that will provide a greater insight into understanding for cod (Gndus morhzin) periods of starvation can the system and eventually an ecosystem assess- lead to emaciation, although under such conditions ment of value in providing advice for resource some of the weight loss is compensated for by the management. uptake of water.

The results from the initial parts of this study ACKNOWLEDGEMENTS comparing icefish condition with krill density indicates a strong relationship between the two The data used in this paper came from many factors as shown in Figure 2. For such a situation sources and we gratefully acknowledge the to be present, it is necessary that the icefish hard work undertaken by colleagues, most of condition index responds to change at least as whom are unknown to us, working on research rapidly as the rate of change in krill density. There vessels and commercial trawlers. We thank the were no krill density estimates during 1977 and AtlantNIRO Research Institute of Kaliningrad, 1978, so we infer that the changes in condition index Russia, Prof. Josef Sosinski of Sea Fisheries Institute, indicate changes in krill density. Gdynia, Poland, and Dr Enrique Marschoff of the Instituto Antartico Argentino for making their datasets available. We gratefully acknowledge CONCLUSIONS support provided by Institut fur Seefischerei, Hamburg, Germany, for the work collating and Using the condition indices gives a much more checking the Russian data, and to the Government extensive dataset that provides indications not only of South Georgia and the South Sandwich Islands Everson and Kock for financial support in preparing the Polish data. Marschoff, E.R., B. Prenski, B. Gonz5lez, C. Remaggi We also thank two referees, Drs Frolkina and and C. Balestrini. 1994. Preliminary results of Pakhomov, for useful comments which have the Dr Edt~ardo L. Holmberg 1994 cruise to improved the clarity of the paper. Finally, we Subareas 48.3 and 48.2. Document WG-FSA- thank all our colleagues who have worked with 94/29. CCAMLR, Hobart, Australia: 70 pp. us on research cruises and in particular Graeme Parkes (MRAG Americas), Jacek Szlakowski and Marschoff, E.R., B. Gonzalez, A. Madirolas, Dzinek Cielniaszek (Poland), Suni Wilhelms J. Calcagno, G. Tossol~ottoand C. Balestrini. (Germany), Tony North and the late Martin White 1995. Results of Dr Ed~iardo L. Hol~nberg (BAS). This study was supported by the Dynamics 1995 fish survey in Subarea 48.3. Document and Management of Ocean Ecosystems core-funded WG-FSA-95/35. CCAMLR, Hobart, Australia: science program at BAS. 39 PP.

Marschoff, E.R., B. Gonzalez, J. Calagno, REFERENCES G. Shandikov, F. Lbpez, A. Madirolas and R. Reta. 1996. Results of Dr Edi~ardoL. Holmberg Anon. 1998. Reference Book on Fish Clzenlical and 1996 fish survey in Subarea 48.3. Document Processing Techizology Properties for Sea and Ocean WG-FSA-96/27. CCAMLR, Hobart, Australia: Species. VNIRO, Moscow. (In Russian). 25 PP.

Bonner, W.N., I. Everson and P.A. Prince. 1978. A Marschoff, E.R., B. Gonzalez, J. Calcagno and shortage of krill, Ez~phausia superba, around B. Prenski. 1997. Results of Dr Edz~ardoL. South Georgia. ICES C, CM 1/22: 4 pp. Holmberg 1997 fish survey in Subarea 48.3. Document WC-FSA-97/47. CCAMLR, Hobart, Brierley, A.S., J.L. Watkins, C. Goss, M.T. Wilkinson Australia. and I. Everson. 1999. Acoustic estimates of krill density at South Georgia, 1981 to 1998. Reid, K., K.E. Barlow, J.P. Croxall and R.I. Taylor. CCAMLR Science. 6: 47-57. 1999. Predicting changes in the Antarctic krill Et~phausiastlperbn population at South Georgia. Everson, I. 1984. Fish biology. In: Laws, R.M. (Ed.). Mar. Biol., 135: 647-652. Aiztarctic Ecology. Academic Press, London: 491-532. SC-CAMLR. 1989. Report of the Working Group for the CCAMLR Ecosystem Monitoring Program. Everson, I., K.-H. Kock and G. Parkes. 1996. In: Report of the Eighth Meeting of the Scientific Ovarian development associated with first Colnnzittee (SC-CAMLR-VllI),Annex 7. CCAMLR, maturity in three Antarctic channichthyid Hobart, Australia: 297-347. species. 1. Fish Biol., 49 (5): 1019-1026. SC-CAMLR. 1995. Report of the Working Group Everson, I., K.-H. Kock and G. Parkes. 1997. for the CCAMLR Ecosystem Monitoring Program. Interannual variation in condition of the In: Report of tlze Fourteetztlz Meeting of the mackerel icefish. J. Fish Biol., 51 (1): 146-154. Scientific Conznzittee (SC-CAMLR-XIV),Annex 4. CCAMLR, Hobart, Australia: 105-253. Kock, K.-H. 1992. Antarctic Fish and Fisheries. Cambridge University Press, Cambridge: 359 pp. SC-CAMLR. 1997. Report of the Working Group for the CCAMLR Ecosystem Monitoring Program. Kock, K.-H., S. Wilhelms, I. Everson and J. Groger. In: Report of the Sixteentlz Meeting ofthe Scientific 1994. Variations in the diet composition and Conzniittee (SC-CAMLR-XVI), Annex 4. CCAMLR, feeding intensity of mackerel icefish (Clzampso- Hobart, Australia: 125-238. cephaltls gllnnori) at South Georgia (Antarctica). Mar. Ecol. Prog. Ser., 108 (1-2): 43-57. Trathan, P.N., E.J. Murphy, J.P. Croxall and I. Everson. 1998. Use of at-sea distribution data Love, R.M. 1988. The food fishes. Their intrinsic to derive potential foraging ranges of macaroni variation an practical implications. Farrand penguins during the breeding season. Mar. Ecol. Press, London. Prog. Ser., 169: 263-275. Condition indices of mackerel icefish at South Georgia

Total mass condition index

Total mass condition index

Figure 1: Scatter plot of mean monthly values for C, plotted against the total mass. Everson and Kock

Krill density (g m-')

Figure 2: CI~nmpsocephnlt~sguiznnvi C, plotted against krill density from acoustic surveys during the same month (krill data from Brierley et al., 1999).

/*Male 1

Calendar month

Figure 3: Mean C, plotted by month. The normal spawning period is during April and May, months 4 and 5 respectively. Condition indices of mackerel icefish at South Georgia

0.7 , I I I I I I 1970 1975 1980 1985 1990 1995 2000

Year

Year

Figure 4: Monthly mean Ct and error bars (2x SE) for all the data from (a) South Georgia and (b) Shag Rocks. Everson and Kock

South Georgia

Year

Figure 5: Plots of monthly mean C, for the period 1975 to 1953.

Days since 30 January

Figure 6: Fur seal pup growth during two seasons, from Bonner et al. (1978). Condition indices of mackerel icefish at South Georgia

Liste des tableaux

Tableau 1: Changements theoriques de l'indice de condition du poids total causes par la variation saisonniPre de l'indice gonadosomatique (GSI). Les calculs presument que pendant la phase de repos, les sept mois qui suivent la derniPre ponte, le GSI est de 1% pour les msles et de 3,54'%1pour les femelles.

Tableau 2: Comparaison des indices de condition (Ct)pendant les mois d'ete, et des indices du CEMP pour les espPces terrestres qui dependent du krill. Les indices de condition sont repr6sentes par la valeur moyeni~ede tous les poissons sexuellelnent matures. Les chiffres donnes entre parenthsses correspondent aux Pchantillons de moins de 30 poissons. FUSE = otarie; GEPE = manchot papou; MAPE = gorfou macaroni; trip = duree de la sortie alimentaire; surv = survie des jeunes; meal = taille du repas et S = succ6s de la reproduction.

Liste des figures

Figure 1: Diagramme de dispersion des valeurs mel~suellesmoyennes de Ct par rapport au poids total.

Figure 2: Diagramme de Clzarnpsocepllnltls giintznri C, par rapport ?ila densite de krill provenant des campagnes d'evaluation acoustiques menPes en un m@memois (donnees de krill de Brierley et al., 1999).

Figure 3: Ct moyen par mois. La ponte a normalement lieu pendant les mois d'avril et de mai (mois 4 et 5 respectivement).

Figure 4: C, moyen mensuel et barres d'erreur (2x SE) pour toutes les dollnees (a) de Georgie du Sud et (b) des ilots Shag.

Figure 5: Diagrammes de C, moyen mensuel pour la periode de 1975 i 1983.

Figure 6: Croissance des juveniles d'otaries en deux saisons, selon Bonner et al. (1978).

Ta6n. 1 Teope~HYec~EiekI'3MeHeHHR HHneKCa @M~HO~O~H~~CKO~OCOCTO2HMR no o6mebi MaCCe, Bbl3BaHHbIe C~~OHHO~~H3MeHYHBOCTbK) rOHaAOCOMaTlIqeCKOr0 ElHAeKCa (GSI).B paCYeTaX IlpkiHPiMaeTCSI, YTO B0 BpeMR nepHOAa nOKOR (nep~bte7 MeCRqeB nOCne H~P~CT~)GSI COCTaBnReT 1% BAR CZiMqOB II 3.5-4% GJlR CaMOK.

'a6n. 2 CpaBHeHPIe kiHAeKC0B @M'~~~O~O~MY~CKO~OCOCTORHIISI JI~ARHO~~ pb16b1 (C,) B0 BpeMH JleTHPlX MeCRueB C MHAeKCaMM CEMP 3aBMCRIQHX OT KpMnZ Ha3eMHbIX XIIIIJHMKOB. ~PHBO~HTCRCpeAHee 3HaqeHMe HHAeKCOB @M?~IO~O~MY~CKO~OCOCTORHHH BnSI nceB nonoo0'3penoB pb16h1. UM@P~IB CKO~K~X oTHOC5ITCSI K ~bl60p~a~< 30 ph16. FUSE = MOpCKHe KOTIIKki, GEPE = IIanyaCCKEfe KIIIHrBKHbI, MAPE = '3OJlOTOBOJIOCbIe nklHfBHHbl, trip = IIpOAOnXHTeAbHOCTb IIOXOAa '3a n~meB,SUSV = BbIXMRaeMOCTh noToMcroa, meal = 06aeM nprn~m~ae~oii?a O~HH pa3 nmqn m S = penpony~~m~~brbiycnex.

PHC.2: C, Chan1psoceyha1~i.sgi4lltl~i-i no CpaBHeHHK, C IInOTHOCTbK) KpMJlR 3a TOT XeMeCXQ KIO BKYCTMYeCKMM CbeMKaM (~ZlHHbleno KpWIK, - 1.13 Brierly et al., 1999).

Pcrc. 3: Cpen~eeC, no ~ec~ua~.06bl~~brii nep~on ~epec~a - anpenb H M~B(C~~TB~TCTB~HHO 4 n 5 ~ecxu)

PBC.4: Cpe~~e~ec~~~breC, 1.r 0~~~6~14(2x SE) fin% ocex na~~brxno (a) Klm~oii reoprcln 11 (b)c~ana~ mar.

PIIC.6: POCT WeHKOB MOpCKOrO KOTllKa B0 BpeMIl ABYX Ce3OHOR, no Banner et al. (1978). Everson and Kock

Lista de las tablas

Tabla 1: Cambios teoricos en el indice de condicion de la masa total causados por la variacion estacional del indice gonadosomBtico (GSI). Los calculos suponell que durante la fase de descanso (10s siete meses posteriores a1 ultimo desove) el GSI es de 1% para 10s machos y de 3,5-4% para las hembras.

Tabla 2: Comparacion entre 10s indices de condicio11 del draco rayado (C,) durante 10s meses de verano y 10s indices del CEMP para las especies depredadoras de kril que se reproducen en tierra. Los indices de condicion representan el valor promedio de todos 10s peces que han alcanzado la madurez sexual. Las cifras entre parPntesis corresponden a muestras de menos de 30 peces. FUSE = lob0 fin0 antartico; GEPE = pingiiino papila; MAPE = pingiiino macaroni; trip = duration del viaje de alimentacion; surv = supervivencia del cachorro; meal = porcion de aliment0 S = 6xito reproductor.

Lista de las figuras

Figura 1: Diagrama de dispersion de 10s valores del promedio mensual de Ct en funcion de la masa total.

Figura 2: C, de Cl~nn~psoceplznlusgtlnrznri en funcion de la densidad de kril de las prospecciones acusticas realizadas en un mismo mes (datos de kril de Brierley et al., 1999).

Figura 3: Promedio de C, por mes. El period0 normal de desove ocurre en abril y mayo (meses 4 y 5 respectivamente).

Figura 4: Promedio mensual de C, e ii~tervalosdel error (2x SE) para todos 10s datos de (a) Georgia del Sur y (b) Rocas Cormoran.

Figura 5: GrBficos del promedio lnensual de C, desde 1975 hasta 1983.

Figura 6: Crecimiento de cacl~orrosde lob0 fino durante dos temporadas, de Bonner et al. (1978).