Population structure, sex ratio and growth of the seabob shrimp Xiphopenaeuskroyeri (Decapoda, Penaeidae) from coastal waters of southern Brazil.

Raphael Grabowski,Sabrina Morilhas Simões,Antonio Castilho

doi:10.3897/zookeys.457.6682

Abstract

This study evaluated the growth and population structure of Xiphopenaeus kroyeri in Babitonga Bay, southern Brazil. Monthly trawls were conducted from July 2010 through June 2011, using a shrimp boat outfitted with double-rig nets, at depths from 5 to 17 m. Differences from the expected 0.5 sex ratio were determined by applying a Binomial test. A von Bertalanffy growth model was used to estimate the individual growth, and longevity was calculated using its inverted formula. A total of 4,007 individuals were measured, including 1,106 juveniles (sexually immature) and 2,901 adults. Females predominated in the larger size classes. Males and females showed asymptotic lengths of 27.7 mm and 31.4 mm, growth constants of 0.0086 and 0.0070 per day, and longevities of 538 and 661 days, respectively. The predominance of females in larger size classes is the general rule in species of Penaeidae. The paradigm of latitudinal-effect does not appear to apply to seabob shrimp on the southern Brazilian coast, perhaps because of the small proportion of larger individuals, the occurrence of cryptic species, or the intense fishing pressure in this region. The longevity values are within the general range for species of Penaeidae. The higher estimates for longevity in populations at lower latitudes may have occurred because of the growth constants observed at these locations, resulting in overestimation of this parameter.

Highlights

The impact of shrimp fisheries in tropical regions is comparable to impacts on the world’s most intensively exploited temperate continental-shelf ecosystems
Information about population biology can be important for understanding the life cycle of intensively fished species such as the seabob shrimp Xiphopenaeus kroyeri (Heller)
The present study evaluated the population biology of X. kroyeri in the Babitonga Bay region, focusing on the sex ratio at different times of the year, juvenile recruitment, growth rates, and longevity of males and females

Summary

Introduction

The impact of shrimp fisheries in tropical regions is comparable to impacts on the world’s most intensively exploited temperate continental-shelf ecosystems. Information about population biology can be important for understanding the life cycle of intensively fished species such as the seabob shrimp Xiphopenaeus kroyeri (Heller). This information can be developed from measurements of the size-class distribution, sex ratio, modal progression, growth, and longevity at spatial and temporal scales (Gab-Alla et al 1990, Nakagaki and Pinheiro 1999). Of the several species targeted by artisanal fishermen in southern Brazil, the seabob shrimp is one of the most important, and is among the top ten penaeid species caught worldwide (Gillett 2008, Silva et al 2013). This species is overexploited in southeastern and southern Brazil (Vasconcellos et al 2007, Almeida et al 2012)

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Results

Conclusion