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Improvement of fish stock assessment by direct methods

The shortcomings of the acoustic and daily egg production (DEPM) methods of assessing fish stocks as applied to the Bay of Biscay anchovy have been identified and corrected. Both methods indicate similar trends in describing the fluctuations of the anchovy population in the period 1989 to 1992. The methodology of the acoustic surveys was found to be appropriate for the area and season of study. Statistical analyses and tests proved the sampling strategy for the DEPM are also appropriate. With respect to the consistency of the production estimates the jack knife technique was applied to the egg data collected during the 1992 survey. It showed that the daily production is well determined by the model.

An important series of observations on the environmental and meteorological conditions has been carried out during the surveys. Sexual maturity seems to require a certain temperature of sea water. The distribution of eggs as well as the vertical and horizontal distribution of the adult anchovy may be influenced by the different moves of the water masses. No correlation between temperature, salinity and spawning intensity is evident.

The genotypic and phenotypic characters of the Bay of Biscay anchovy have been thoroughly studied. 2 different groups seem to form the population although the results do not support the pure or discrete stock concept.

The study of the variability of sexual maturity in space and time was done by the observation on the gonosomatic index. The variation of maturity can be modelled by the combined influence of several variables (ie sea water surface, salinity and fish weight). The observations have made evident the existence of maturity waves, and a different timing of the maturation of large and small anchovy.

The relationship of meteorological and environmental conditions with respect to recruitment has been analyzed. Upwelling is the only factor that seems to be positively correlated with recruitment.

Reported by

Instituto Espanol de Oceanografia
240,Apartado de Correos
39080 Santander
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