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    Escapement of elephant seal prey in the Heard Island fishery for Dissostichus eleginoides

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    Document Number:
    WG-EMM-97/42
    Author(s):
    Slip, D., Constable, A.J., de la Mare, W.K., Williams, R.
    Agenda Item(s)
    Abstract

    The Patagonian toothfish, Dissostichus eleginoides, has been reported as prey of Elephant seals in the Heard Island region. A question was raised at SC-CAMLR-XV concerning what affect the fishery for toothfish in Division 58.5.2 might have on the abundance of the age classes of toothfish preyed on by these seals. This paper provides an updated analysis of the age of toothfish taken by Elephant seals at Heard Island and uses the generalised yield model (Constable & de la Mare, 1996) to examine the level of escapement of fish preyed on by these seals under the current Total Allowable Catch of 3800 tonnes.
    Of 21 otoliths found in Elephant Seal stomachs at Heard Island that have previously been identified as being from Dissostichus eleginoides, 18 were from one stomach and, of these, only 7 could be reliably identified as being from toothfish. There appeared to be three pairs among the seven identified otoliths, based on the similarities of size and erosion state. Estimates of age were obtained from these otoliths. The importance of Dissostichus eleginoides as prey of the Elephant seals at Heard Island is unclear given the small number of otoliths that are of sufficient quality to be identified reliably and related to a specific size class of fish. However, it seems that toothfish in the age range of 2-6 years are likely to be vulnerable, to some extent, to predation by Elephant seals.
    The evaluation of escapement of young fish (ages 2-6 years old) under the current catch limit of 3800 tonnes in the trawl fishery in Division 58.5.2 indicates that escapement in biomass is more than 85%, well above the 75% level adopted by CCAMLR for other prey species such as for krill, Euphausia superba, generally and icefish, Champsocephalus gunnari, at Heard Island.

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