Impact of lobster size on catches and prediction of commercial spiny lobster landings in Brazil

Abstract

On the Brazilian continental shelf, red spiny lobsters, Panulirus argus (Latreille, 1804) constitute a separate population with two distinct stocks, one in shallow waters (<50 m) and one in deeper waters (50-100 m). Stocks are highly exploited, especially undersized animals (≤75 mm CL) and older individuals. The observed decline in spiny lobster landings over the past two decades is believed to be due to overfishing in shallow waters, since over half the harvested lobsters are below the minimum legal size (75 mm CL), with a length at first capture of 61 mm CL. Spawning lobsters in deeper waters measure 96 mm CL at first capture; this coincides with the size class (90-99 mm CL) with the greatest reproductive potential. Furthermore, the capture of berried females and older lobsters (>135 mm CL) from deeper waters increases the risk of low recruitment and fishing collapse. The observed change in fishing patterns appears to be the consequence of increased fishing mortality (F) among pre-recruits. This is possibly the main cause of the large fluctuations observed in landings, although other factors, such as the interplay between environmental conditions and recruitment abundance, may have to be considered. Our results show that increasing the minimum legal size of red lobsters is likely to improve total landings in the long term, provided appropriate and tightly enforced control measures are designed and implemented.