The mackerel icefish (Champsocephalus gunnari) is a prominent member of the coastal fish fauna of the Seasonal Pack-ice Zone and the islands north of it. Separated into a number of stocks, its distribution ranges from the Scotia Arc region, namely South Georgia, in the Atlantic Ocean sector to the Kerguelen-Heard Plateau in the Indian Ocean sector. Mackerel icefish have been heavily exploited since the beginning of the 1970's with reported annual catches exceeding 50- 100 000 tomes in some years.
Champsocephalus gunnari has many characteristics typical of Antarctic fish species with respect to life history characteristics, such as egg size, fecundity and growth. These fall well within the range of other sympatric red-blooded notothenioids: Eggs are large and yolky. Egg diameter, egg production per gram body weight, and growth performance at South Georgia and the Kerguelen Islands was comparable to similar sized nototheniids and channichthyids. Stocks of C. gunnari have a number of biological characteristics in common, such as feeding mode and food, early life history, and growth in the first years of life. However, stocks in Sub-Antarctic waters differ in reproductive characteristics, such as length and age at first spawning, natural mortality and life expectancy from those on more southerly grounds. They may grow to more than 60cm and may become 13-15 years old. However, in the vicinity of South Georgia and the Kerguelen Islands, fish apparently do not exhaust this growth potential fully. Their ability to reproduce at an early age coupled with a comparatively high fecundity and growth performance may mean that the stocks of C. gunnari in Sub-Antarctic waters have far more resilience and a greater capacity to rebuild than species with the slower reproductive rates common in other notothenioids.
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Abstract:
Scientific observation under the auspices of the CCAMLR Scheme of International Scientific Observatio was conducted onboard the Chilean longliner 'Puerto Ballena' fishing for Patagonian toothfish (Dissostichus eleginoides) in Subarea 48.3 from March to May 1996. Details of the cruise are provided. Biological investigations incorporated length, sex, maturity and weight measurements of D. eleginoides, the estimation of the finfish by-catch, the estimation of a conversion factor of product to fresh weight for D. eleginoides and the assessment of incidental mortality of seabirds associated with the longline operations. The catch of D. eleginoides was mainly comprised of specimens of 70-130 cm whith the proportion of females in the catch exceeding those of males in fish larger than 1 10 cm. Length at sexual maturity and length at first spawning differed considerably between males and females with males becoming mature at a much smaller length. Black-browed albatrosses and white-chinned petrels were the most abundant species in the vicinity of the vessel when longlines were set. About 44 % of the longlines were set during daylight hours. Consequently, black-browed albatrosses made up a considerable portion of the seabird by-catch. A by-catch of 159 dead seabirds was reported by the scientific observer and the crew with black-browed albatrosses and white-chinned petrels forming the bulk of the by-catch. In addition a number of albatrosses, giant petrels and white-chinned petrels were hooked alive during hauling and released alive. Sperm whales and Orcas were the most common marine mammals observed in the vicinity of the vessel. Orcas in some cases caused a considerable loss of fishes from the lines.
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Abstract:
In anticipation of the development of a new fishery for the oceanic squid Martialia hyadesi in the Scotia Sea a revision is presented of annual consumption of the species by higher predators and a brief review is provided of information about the life cycle and distribution obtained from research fishing and commercial catches. The species is consumed by seabirds, seals and whales and the most reliable data are from seabirds because comprehensive sampling can be carried out during the breeding season. A conservative estimate for total annual consumption by higher predators in the Scotia Sea is 245,000 tonnes compared with an upper estimate of 550,000 tonnes if less reliable data are included. M. hyadesi spawns in winter/spring, probably has a two year life cycle and, in common with other ommastrephids, is semelparous. It is proposed that the timing and catches of the fishery should be highly conservative and set with regard to the timing of breeding and consumption rates of the most sensitive of the dependent species. Most predators that have been studied consume M. hyadesi during the first year of its life cycle. Fishing on M. hyadesi after the chick-rearing season of the most sensitive predator (grey-headed albatross) would minimise competition locally and ensure that the fishery only exploited the stock after escapement from most higher predator species. It would also allow monitoring of predation on the stock prior to the fishing season as a form of pre-recruit assessment. Closing the fishery before recruitment of the next generation would ensure availability of prey for higher predators for the following chick rearing season. Preliminary data from a squid jigger undertaking research fishing around South Georgia in June 1996, under the auspices of CCAMLR, provide the basis for assessing realistic potential catch rates.
Abstract:
Observations on abundance of by-catch fishes were made during fishing operations for krill Euphausia superba Dana conducted by the Ukrainian trawler Grigory Kovtun in the vicinity of South Georgia (May to July, 1992), the Polish trawler Lepus on the fishing grounds of South Orkney Islands and South Georgia (March to May, 1993), and by the Japanese fishing vessels No.3 and No.5 Chiyo Maru in the South Georgia area (July to August, 1992) and Niitaka Maru to the north of the South Shetland Islands (January to February, 1994) to determine the proportion of juvenile fish forms in krill concentrations. In the South Orkney Islands area, eight hauls were subjected to analysis and there was no by-catch of juvenile notothenioids at all in the samples collected. In the area around South Georgia, six notothenioid species including one unidentified bathydraconid fish were found as by-catch juveniles during three surveys by different countries. Among the six species, Lepidonotothen larseni was the most abundant in the Polish and Japanese by-catch samples, and its estimated value of an arithmetic mean was 11541 ind./t krill and 34588 ind./t krill respectively. In the Ukrainian sample, most of by-catch juveniles were referred to Champsocephalus gunnari and L. larseni, and its arithmetic mean was 78523076 ind./t krill and 60352790 ind./t krill respectively. Thirteen species including four mesopelagic fish species were found in krill catches of 25 of 99 examined net hauls made in the South Shetland Islands area. Also among by-catch fish from this area, juvenile L. larseni was the most abundant and its arithmetic mean was 10247 ind./t krill. In all the three areas, a relatively low by-catch of the family Myctophidae was observed. Abundance of by-catch fish could have depended on the density of krill concentration. The large incidental catch of juvenile fish occurred in hauls with the relatively low krill CPUE, and fish by-catch was not found or rare in hauls for krill swarms of higher density.
Abstract:
One of the non-solved problems in krill exploitation has been the by-catch of fish larvae that use (or co-occurred) the krill swarms as their habitat. The detection of this problem started together with the massive antarctic krill exploitation during the 80's. There has been recognized several fish species whose larvae develop within the krill swarms, nevertheless, few have been the quantitative evaluations that give evidences that this technological interaction, is affecting the recovery of over-exploited populations or that commercial or noncommercial populations are diminishing.