Do Commercial Fishery CPUE Data Reflect Stock Dynamics of the Baltic Herring?

Do Commercial Fishery CPUE Data Reflect Stock Dynamics of the Baltic Herring?

Tiit Raid, Ahto Järvik, Leili Järv, and Olavi Kaljuste

Do Commercial Fishery CPUE Data Reflect Stock Dynamics of the Baltic Herring?This is part of Fisheries Assessment and Management in Data-Limited Situations
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Description

Herring are important commercial fisheries of the Baltic Sea. The structure and dynamics of Baltic herring stocks has been monitored thoroughly since international management started in the mid-1970s but management has not always been successful, particularly during periods of rapid change. Shortcomings in certain assessment data are a concern and the difficulty of obtaining appropriate biological samples from the huge and extremely heterogeneous herring stocks is a problem. Another problem is the lack of good tuning data for age-structured analyses. Presently the results of an annual International Acoustic Survey are used for tuning in extended survivors analysis (XSA). A critical shortcoming is that the acoustic survey does not cover several key areas of herring distribution. Therefore, there is a need for alternative or supplementary data to minimize effects of biased acoustic results. CPUE (catch per unit effort) in commercial trawl fishery may be a potential source of additional data. In theory, the CPUE should be proportional to the stock size so changes in CPUE, adjusted for gear efficiency, could provide, at low cost, supplementary information on stock trends. The CPUE data collected from the Estonian pelagic trawl and pound net fishery (a small part of the larger Baltic herring fishery) show good accordance with the results of VPA estimates of separate stock units in 1990-2000s. Further exploration of commercial CPUE as a stock status index would be reasonable.

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