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    Assessments of by-catch in trawl fisheries at Heard and MacDonald Islands

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    de la Mare, W.K., Williams, R., Constable, A.
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    This paper provides an assessment of the long-term annual yield for three species caught as by-catch in the commercial trawl fisheries in the Heard Island area (Statistical SubArea 58.5.2): Channichthys rhinoceratus, Lepidonotothen squamifrons and skates (Bathyraja spp.). These assessments were undertaken with the aim of examining the potential for the commercial trawl fisheries to significantly affect the spawning biomass of these stocks in the longer term. The long-term annual yield for each of the three species were estimated using the generalised yield model developed for WG-FSA, based on survey data obtained from the region in 1990-1993. Values for missing input parameters were obtained from the literature. The second part of the analysis examined the amount of each species caught in the commercial operations, the nature of the trawl operations in which they were caught and the effectiveness of current by-catch provisions in CCAMLR to ensure the status of these species is not affected by these fisheries. The estimates of long term annual yields for Channichthys rhinoceratus, Lepidonotothen squamifrons and skates were 69-97 tonnes (average 80 t), 7-91 1 tonnes (average 325 t) and 50-210 tonnes (average 120 t) respectively. Notably, the by-catch in 1997 did not exceed the lowest estimates of yield for each species. The results indicate that the current commercial trawl fisheries around Heard Island are unlikely to be negatively affecting these stocks. Notably, the large majority of infringements of the 5% by-catch rule in CCAMLR were caused by very small amounts of by-catch. This occurs, especially in prospecting mode, when the catch of target species is low, and hence the amount of by-catch necessary to trigger the 5% rule is also very low. Most infringements were caused by less than l00kg of by-catch. While the basic role of the by-catch provisions is to protect the by-catch species from over-exploitation combined with protection them from being targetted by commercial operations, the current 5% by-catch rule excludes many areas from prospecting. In order to enable prospecting for commercial aggregations of icefish or toothfish while protecting the by-catch species from excessive fishing effort, the by-catch rule could be modified for the Heard Island area to allow catches of by-catch species of up to 100 kg in any one haul. However, if this level is exceeded by any one of the by-catch species then the 5% rule should be enforced.