Diel variation in the catchability of rose shrimp, Parapenaeus longirostris, and associated species from a bottom trawl survey off the portuguese south coast

Sonderblohm, Carlos

http://hdl.handle.net/10400.1/3082

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Authors

Sonderblohm, Carlos

Advisor(s)

Fonseca, Paulo

Erzini, Karim

Abstract(s)

An experimental crustacean bottom trawling survey targeting the deep-water rose shrimp Parapenaeus longirostris was carried out off the south of Portugal over five 24-hour cycles. Although circadian bias in the catch rates for this fishery has been reported, no conclusive study had been carried out until now. Catch per unit effort oscillated with the time of the day. Total catches, both in numbers and weight considerably higher in daytime than at night, suggesting that the 24-hour light cycle strongly influences catchability of rose shrimp. The rose shrimp, shows a clear shift in abundance from daytime to night hours, with catches decreasing sharply at dusk and, then increasing significantly at dawn. Overall, the most captured fish species: european hake, Merluccius merluccius; monkfish, Lophius budegassa; european conger, Conger conger; and great forkbeard, Phycis blennoides; present the same trend, although less marked. The exceptions are: silver scabbardfish, Lepidopus caudatus; blue Whiting, Micromesistius poutassou; tongue sole, Symphurus nigrescens; atlantic mackarel Scomber scombrus and silver cod, Gadiculus argenteus; whose catches were higher in the night hours. Understanding, the circadian variability in catches of highly valuable commercial species such as the deep-water rose shrimp may contribute to an improved management, by allowing a better control of fishing effort and more efficient use of technical measures