Experiments on the chance of escape by lobsters of genus Panulirus , caught by double-entrance traps

Abstract

Research is an important evaluation tool for use in the management of fish stocks. Oral reports obtained by the authors with continued and  widespread complaints by those involved in the production chain, from fishermen to exporters, about fixing the mesh size of traps intended for lobster  fishing and lack of access to technical advice which determined this size, justified the present study. The database for this research work was obtained at  a lobster outlet located on Redonda Beach, Icapuí county, Ceará State in the period from July to August, 2010. The main lobster landing sites are the  beaches of Ponta Grossa, Redonda and Peroba, on the same county. Out of a total 208 collected individuals, 60 belonged to species  Panulirus laevi- cauda , of which 30 were females and 30 males, and 148 belonged to species  Panulirus argus , of which 64 were females and 84 males. The fishing trips  were performed by artisanal sailing boats which operated with 30 to 60 cangalhas (two-entrance traps) per vessel. The pertinent information included:  i) number of individuals per species and sex; ii) carapace length, in cm (distance between the anterior margin of the carapace, in the slot formed by  rostral thorns until its rear end); iii) number of the grid and the trap’s correspondent mesh size, in cm The average sizes of the grid were as follows: 5.3  ± 0.88 cm (CV females; 5.12 ± 0.95 (CV male); 6.63 ± 1.62 (V female); 7.18 ± 1.93 cm (V male). The smallest mesh used was the same for the two lobster  species, namely 4.1 cm, but the maximum ones differed: 6.4 cm for both sexes of  P. laevicauda , and 9.1 cm for females and 12.5 cm for males of  P. argus .  Taking one same mesh size of mesh for both species, the males showed carapace lengths bigger than females. The larger the size of the mesh, minor was  the variation between species for both females and males. In the case of females, there was a reversal from 6 cm of the screen, in which CV has become  greater. Females of both species showed greater variation than males until the mesh size of 5 cm. From 5 cm, males showed greater variation than fe- males. For mesh size of 4.5 cm, red lobsters had the average length of the cephalothorax (CC) for both sexes of 7.7 cm, thus close to the 7.5 cm legal size.