Community Research and Development Information Service - CORDIS

Evaluation of the influence of vertical dynamics on catchability of cod (Gadus morhua L.)

A statistical method was developed to determine the way that individual cod use their vertical environment. This method uses depth time-series to estimate empirical cumulative density functions of the difference between tag-measured and 24h maximum depths. The purpose of this analysis has been to develop an operational method to quantify the vertical distribution of cod, enabling to assess the probability of catch for an individual cod at a known location when gear opening and trawling depth are known. For acoustic surveys the method can aid to assess the probability that an individual cod is in the acoustic dead zone.

The vertical range above maximum depth for which capture probability was 0.5 was used as a reference for system comparison, and ranged between 1.5 m in the Baltic and 84.9 m in the Barents Sea. This methodology allows in principal to estimate the capture probability for a cod when positioning of the gears known, both in the case of trawls or acoustic devices. Considering individuals that do not differ behaviourally, the aforementioned probabilities translate directly to the fractions of the population, which are accessible to a trawl or acoustic survey.


David RIGHTON, (Project Coordinator)
Tel.: +44-0150-2562244
Fax: +44-0150-2513865
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