Effect of lobster size variation on catches on the continental shelf off Ceará, Brazil

Abstract

In this study we evaluate to what extent variation in length class composition of P. argus at two depth ranges (1- 10 m and 30-50 m) is reflected in the overall biomass and how this affects the management of spiny lobster resources on the continental shelf off Ceará. Lobster catches consisted mainly of large juveniles (42-50 mm CL) and pre-recruits (50-73 mm CL) in shallow waters, and of adults (80-109 mm CL) at intermediate depth (30-50 m). Based on selectivity curves, the size at first capture (L50) in shallow waters was 12% smaller than the minimum legal size (MLS). A 13% or a 21% increase would be required to reach the current MLS (75 mm CL) or the ideal MLS (80 mm CL), respectively. In contrast, at intermediate depth L50 was greater than the MLS. Pre-recruits (50-73 mm CL) comprised 86% of catches (98% of the mean biomass) in shallow waters and 26.1% (55% of the mean biomass) at intermediate depth. If the L50 for shallow waters were raised to the current MLS or the ideal MLS, the biomass would increase by 79 and 84%, respectively.