Abundance and population structure of Plesionika narval (Fabricius, 1787) in the Northeastern Atlantic

Analysis of abundance and population structure of Plesionika narval was performed on data concerning 5,255 specimens obtained from 62 fishing sets carried out off the Madeira archipelago (Northeastern Atlantic) between 2004 and 2008 in a depth range from 101 to 350 m. Abundance ranged from 0.01 to 19.74 specimens-per-trap and significant differences were found between seasons, probably as a result of an increment of population in the spring during the recruitment season. The analysis of size distribution revealed that the carapace length (CL) ranged from 2.45 to 28.61 mm and that mean female size consistently exceeded that of males. Differences in mean CL were statistically significant between depth strata and seasons. Of the specimens sampled, 57.00% were males, 41.88% females and 1.42% undetermined. Sex ratio also differed significantly between seasons according to depth strata, consolidating the hypothesis of the existence of seasonal migrations related with the reproductive cycle of this species. Ovigerous females showed larger sizes and occurred all year around and remain in shallow waters in winter, summer and autumn and move to deeper waters in spring. The highest frequency of ovigerous females was recorded in summer, between 151 and 200 m deep supporting the hypothesis that spawning of this species occurs in shallow waters, especially in late summer.

Prospective study of the fishery of the shrimp Plesionika narval (Fabricius, 1787) in the Northeastern Atlantic

Several experimental surveys were carried out in the Northeastern Atlantic, Madeira archipelago from 1991 to 2008 to explore new fisheries resources. This study examined the selectivity of bottom and floating traps and the analysis of yield-per-recruit (YPR) and biomass-per-recruit (BPR) providing helpful insight to the management of the shrimp Plesionika narval. A total of 28,262 specimens were sampled and the analysis of length at first capture returned higher values when using floating traps indicating that these traps are more selective, exerting less pressure on the resource. The YPR and BPR analysis showed that the stock is under exploited for the studied area and suggests that the use of floating traps in the commercial fisheries of P. narval is recommended, which will allow a higher maximum allowable limit of exploitation and greater yield. The results suggest that P. narval has the potential to support a viable and sustainable fishery using floating traps.