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    Preliminary analyses of data collected during experimental phases of the 1994/95 and 1995/96 Antarctic crab fishing seasons

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    Document Number:
    WG-FSA-96/34
    Author(s):
    Watters, G.
    Agenda Item(s)
    Abstract

    Data collected from the FN American Champion during Phases 1 and 2 of the experimental crab fishery were analyzed with generalized additive models and depletion estimators. Results from the generalized additive models show that the density of fishable P. spinosissima is highest off the northern coast of South Georgia and at depths between about 100 and 300 fathoms. The Phase 1 results suggest that it would not be appropriate to extrapolate local estimates of abundance to the whole of Subarea 48.3 solely on the basis of depth-specific seabed area; extrapolations must consider location. Linear models fit to CPUE and cumulative catch data from the Phase 2 depletion experiments did not have significant, negative slopes. The insignificant regressions were probably a result of inter-haul variability in CPUE and crab movement and suggested that depletion estimators will not be appropriate tools for estimating local abundances of P. spinosissima. Approximately 6000 crabs were tagged and released during Phase 2. Four of the tagged crabs were recovered, and these crabs were at liberty for about 1 to 5 weeks. The recaptured crabs moved at rates between 0.08 and 0.25 n. mi./day. Mark-recapture estimates of standing stock and density were made for the area around Phase 2's third depletion square. The assumptions of the mark-recapture model were probably violated, but attempts were made to account for biased sampling of recaptured crabs and the movement of crabs away from their release sites. Density estimates from the mark-recapture data were on the order of 50,000-100,000 crabs/n. mi2, and there was a lot of uncertainty associated with these estimates. In general, the experimental harvest regime was successfU1. The regime provided important information about crab distribution and facilitated evaluation of local depletion estimators for use in stock assessment, but the WG-FSA may wish to re-evaluate the design of Phase 2.

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