Abstract Xiphopenaeus kroyeri (Heller, 1862) is the third most common species caught by fishing boats in the state of São Paulo, Brazil and production of this shrimp in the Cananéia region located on the southern coast of this state ranks second in the nation. The aim of this study was to investigate the temporal variation of the total biomass and size of X. kroyeri and analyze this variation against environmental factors in order to suggest some information about the best periods to fish this species. Samples were caught monthly from four sampling stations in Cananéia between July 2012 and June 2014 using a fishing boat equipped with otter-trawl nets. Temperature and salinity were monitored using a multiparameter probe, and sediment samples were also taken using a Van Veen-type gripper for particle size analysis. The shrimp were weighed, quantified, and carapace length was measured (mm). In general, the highest total biomass values were recorded when the fishery was closed in the southeast and south regions, and the highest catch of smaller individuals was also observed during this period. In contrast, in November 2013 the fishing is permitted and high biomass composed of large individuals was observed. The monthly biomass showed a positive relationship with sediment texture, because this species prefers very fine sediments to burrow as a defense against predators.

ResumoFoi investigada a dinâmica populacional de Acetes americanus, enfocando a razão sexual, crescimento dos indivíduos, longevidade, recrutamento e a relação da abundância com dos fatores ambientais na região de Macaé, a qual é fortemente influenciada pela ressurgência costeira. Foram realizadas coletas de julho de 2010 a junho de 2011, em dois pontos (5 m e 15 m), utilizando uma rede otter trawl. Cerca de 19.500 indivíduos foram capturados com predominância de fêmeas (77,15%) e essas foram maiores que os machos indicando dimorfismo sexual. Houve inversão do paradigma latitudinal, onde os camarões apresentaram maiores tamanhos e longevidade quando comparados a outras regiões de maiores latitudes e isso provavelmente se deve às baixas temperaturas e alta produtividade primária. Apesar de não apresentar correlação estatística entre a abundância e os fatores ambientais, a espécie foi mais abundante em temperaturas próximas aos 20,0º C e nos meses com alta concentração de clorofila-a. Devido às características peculiares da região, os espécimens de A. americanus apresentarem diferenças em relação a tamanho e longevidade quando comparados aos indivíduos amostrados em outros estudos realizados na plataforma continental do sudeste brasileiro.

AbstractThe population dynamics of Acetes americanus was investigated, focusing on the sex ratio, individual growth, longevity, recruitment and relationship between abundance and environmental factors in the region of Macaé, strongly influenced by coastal upwelling. Otter trawl net samplings were performed from July 2010 to June 2011 at two points (5 m and 15 m). Nearly 19,500 specimens, predominantly females (77.15%), were captured. Their sizes, larger than that of males, indicated sexual dimorphism. Shrimps at lower latitudes present larger sizes and longer longevity than those from higher latitudes. This difference is probably due to low temperatures and high primary productivity. Though no statistical correlation was found between abundance and environmental factors, the species was more abundant in temperatures closer to 20.0º C and in months with high chlorophyll-a levels. Due to the peculiar characteristics of this region, A. americanusshowed greater differences in size and longevity than individuals sampled in other studies undertaken in the continental shelf of Southeast Brazil.