Catch and Effort Analysis with Uncertain Stock and Effort Dynamics: Southern Bluefin Tuna Longline
R. Campbell
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Description
Of interest in recent years has been how best to construct annual indices of stock abundance for the southern bluefin tuna (SBT) stock which adequately account for the spatial and temporal dynamics of the fishery. This fishery has been characterized by a continuous decline in the size of the spawning stock since the 1960s, the introduction of restrictive catch quotas in the mid-1980s with concomitant reductions in the spatial distribution of effort, and a recovery in the abundance of juveniles during the 1990s. In particular, the spatial and temporal distribution of the fishing effort for SBT has declined appreciably since the mid-1980s and this has resulted in a problem in the use of catch and effort data to calculate indices of SBT abundance. Basically there are no data to assess the present state of the stock in large areas in which the stock was fished historically. Investigations of the spatial distribution of fishing effort also indicate the possibility of increased spatial targeting of localized regions of higher catch rates. Nevertheless, due to the lack of fishery independent indices of abundance, many aspects of the underlying stock and effort dynamics remain uncertain. In order to account for these present uncertainties, a range of models, based on various hypotheses of the underlying stock and effort dynamics, have been developed for estimation of the CPUE-based annual indices of stock abundance.
Item details
- Item number: AK-SG-98-01d
- Year: 1998
- DOI: https://doi.org/10.4027/fsam.1998.04
