Abstract
This is the first study to evaluate in broad spatiotemporal scales the growth parameters and population structure of Rimapenaeus constrictus, a barely damaged species composing the bycatch from shrimp fishing in the Western Atlantic. The abundance and size-class frequency distribution, growth, longevity and sex ratio were evaluated from monthly samples obtained in the northern littoral of São Paulo state from Jan/1998 to Jun/2003. We measured 5,812 individuals in which the sex ratio was skewed toward females; this was more evident in size classes greater than 10 mm in CL (carapace length) (binomial test, p<0.05). We selected 16 growth cohorts of females, and 8 of males, the majority consisting of younger individual cohorts excluded from the fisheries closure period. Growth estimates resulted in a CL∞ of 17.42 mm, a growth coefficient of 0.008 and a longevity of 579 days (1.60 year) for females, as well as a CL∞ of 16.3 mm, a growth coefficient of 0.01 and a longevity of 425 days (1.17 year) for males. Our results provide information of incontestable relevance to our knowledge of fishing management. We therefore strongly recommend that the fisheries closure period be changed to protect this species' recruitment period and consequently its adult individuals.
Highlights
Crustacean fisheries production has been declining throughout the southeastern Brazilian Coast, mainly in the Ubatuba region, which within a10-year period (2005-2015) has shown a 64% of reduction in biomass landings (Instituto de Pesca, São Paulo: www.pesca.sp.gov.br)
Species with no economic value, such as Rimapenaeus constrictus (Stimpson, 1874), are protected by the fisheries closure period as well, since the bycatch and economically important species are not being captured during this period
The northern coast of São Paulo state is strongly influenced by two other water masses, each showing specific characteristics and distinct models of distribution between summer and winter: Coastal Water (AC: high temperature (>20o C) and low salinity [20o C) and high salinity [>36]) (Castro-Filho et al 1987)
Summary
Crustacean fisheries production has been declining throughout the southeastern Brazilian Coast, mainly in the Ubatuba region, which within a10-year period (2005-2015) has shown a 64% of reduction in biomass landings (Instituto de Pesca, São Paulo: www.pesca.sp.gov.br). In Brazilian Southeastern coast, the use of motor boats for shrimp trawling from March 1st to May 31st is forbidden by the Brazilian Institute of Environment and Natural Renewable Resources (IBAMA 2016). During this season (the fisheries closure period), fishermen are prohibited from using such gear to capture economically marketable shrimp species or to transport, stock or commercialize these animals. This measure aims to protect their regular population structure, reproduction and recruitment period (normative instruction available at: www.ibama.gov.br). Species with no economic value (bycatch), such as Rimapenaeus constrictus (Stimpson, 1874), are protected by the fisheries closure period as well, since the bycatch and economically important species are not being captured during this period
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