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Impact of bycatch fish species on important exploited species

The contract is aimed at an evaluation of the impact of various bycatch fish species on the survival of the important exploited species during the first year of life. Although there is a clear ultimate connection with management issues the research carried out covered only aspects of data collection and primary analysis. The results obtained enable extension of existing multispecies assessment models to incorporate the effects of other predator species and may cast new light on recruitment processes.

The research was directly linked to another project aimed at an evaluation of the food composition of 5 commercially important predator species and therefore did not require extra research vessel effort. In total 25 000 stomachs of bycatch species were collected. A priority was set and only stomachs of 12 000 grey gurnard and 4000 rays were selected for analysis.

The results indicate that the food of grey gurnards consists largely of a variety of commercially important species, particularly gadoids and sandeels. The different ray species vary significantly in the size at which they shift from feeding mainly on crustaceans to fish. The extent to which the rays feed on commercially important species is difficult to evaluate, because only a small component of the fish found in stomachs could be identified to the species level. More detailed analyses of the data are required to solve this problem.

On the basis of the results obtained and estimated biomass figures from the literature, it is concluded that both grey gurnard and starry ray consume large quantities of juvenile fish. Other ray species appear to be relatively less important. However, a final evaluation will only be possible when these data are incorporated in multispecies assessment models.

Reported by

Netherlands Institute for Fisheries Research
1,Haringkade PO Box 68
1970 AB Ijmuiden
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