Ecologia reprodutiva de Lutjanidae no litoral norte de Bahia, Brasil: contribuçoes ao manejo sustentável da pesca artesanal

Abstract

The snappers, Lutjanidae, are the most important group of reef fishes caught by the artisanal fleet in the northeast coast of Brazil. These long-live and demersal fishes began to be most exploited during the 50s and 60s in order to diversify the decreasing lobster and tuna fisheries. Here, I provide new insights upon the reproductive ecology of specifically on lane snapper (Lutjanus synagris (Linnaeus, 1758)), vermillion snapper (Rhomboplites aurorubens, (Cuvier, 1829)) and silk snapper (Lutjanus vivanus, (Cuvier, 1828)), three of the 10 target species of Lutjanidae family in the northern coast of Bahia and the impacts of artisanal fisheries. First, I described some population parameters, such as sex ratio (SR), length-weight (WRL), condition factor (K) and spatial distribution in the sample area. I found that the sex ratio was skewed to female in lane snapper and to male in the other species in length greater than 30 cm. I also found sexual segregation in the Lutjanus genus, a first signal of transitory spawning aggregation strategy. In the Rhomboplites genus, I do not found differences in your special distribution, a evidence of resident spawning aggregation strategy. Then I examined the length-weight relationship, I found a negative allometric population relationship, indicating that small individuals had different conditions than larger ones, suggesting invest in the increasing in size than weight. Also, I found that the condition factor was the principal factor of aggregation in the sample area. After this, I described the reproductive female ecology of these three species, through a comprehensive assessment of their temporality and reproductive strategies, based on modern histology protocols and image analysis. In particular, I sought to predict the impacts of fishing on this assemblage and describe not only their reproductive potential and reproductive temporality, but generate information applicable and viable to resource management.

The lifetime scale of temporality was estimated with the length at 50% maturity (vermillion snapper 16 cm, lane and silk snapper: 18 cm) and the annual scale was described using the gonadossomatic index (GSI) and histological methods. The prevalence of spawning capable females and the GSI values indicate that these species have a protracted spawning season that span from August to April (Lutjanus) and October to April (Rhomboplites). Comparisons with morphological methods were made and indicated that this method was not accurate to describe the reproductive cycle of these species. To describe the annual cycle of the silk snapper, was needed a validation run through the annual frequency distribution the diameter of oocytes in vitellogenesis and the number of oocytes in development (NDO) and the relative number of oocytes in development (NDOr), because the use of the phases of gonadal development was not applicable, for each month were composed of 50% or more females in spawning capable phase. Histologically, the gonads of Lutjanidae showed all the different stages of oocyte development found in pelagic spawning species, including migratory nucleis, coalescence and hydration. Three stages of post-ovulatory follicles (recent, intermediate and old) and two stages of atresia (alpha and beta) were well differentiated, and cystic structures of hydrated follicles, nematodes and cestodes parasites were found.

In the intrasazonal scale, I found that the mean spawning fraction ranged from 0,18 (silk snapper, with a batch interval of 4,6 days) to 0,27 (lane and vermillion snapper, with a batch interval of 3,4 days. This is approximately equivalent to a individual spawning time of two months. The recruitment strategy during the spawning period was presented for the first time: asynchronous at the beginning of the reproductive station (lane and vermillion snapper) and synchronous during the spawning period (assemblage). The type of fecundity was determined by stereological analyses. The results showed that these species are batch spawners with indeterminate fecundity that presents asynchronous oocyte development. The principal maternal influences in the egg production were length and weight, indicating that females with better condition to produce more eggs. Moreover, the principal temporal relationship with the fecundity were moon phases and season according to the rhythm of the rain. The annual fecundity of the assemblage was between 1 to 19 millions of eggs (lane and vermillion snapper) and from 34 to 55 millions of hydrated eggs, which defines this assemblage as high fecundity, but, this fact, per se, do not contribute to higher resilience against the exploitation.

In Brazil, the only single specie of Lutjanidae family (L. purpureus) has a policy of protection, and according to my results, management measures to the species study in the North of the Bahia are discussed. I find that the annual distribution of spawning peak of Lutjanidae coincides with the peaks warmest warms in the Northeast cost of Brazil, as well as the most richest and best conditions for the larva assessment. Therefore, I propose the better management alternative of this resource should be the delimitation of biological rest periods. Finally I also considered that the geographical and temporal effort made by the standard boat, follows a pattern, that varies very little and is based on the knowledge acquired over generations of fishermen. The result of this work together with the fishermen´s knowledge should be integrated to define closed seasons in order to protect different stages of spawning capable phases and female condition, and the livelihoods of fishermen.