OCCURRENCE AND BIOLOGY OF THE DAGGERNOSE SHARK ISOGOMPHODON OXYRHYNCHUS(CHONDEICHTHYES: CARCHARHINIDAE) OFF THE MARANHAO COAST(BRAZIL)

摘要

The daggernose shark, Isogomphodon oxyrhynchus (Muller and Henle, l839) indabits shallow waters of the western Atlantic from Trinidad to northern Brazil Where it is abun- dant off the coast of the state of Maranhao, in the Sao Marcos and Cuma Bays and on shallow coastal banks. The distribution of the species has been associated with hot, hu- mid climates and highly turbid waters Where mangroves are the dominant system. The species enters bays during the dry season and moves to the shallow banks off the coast during the rainy season. This is probably due to the decreasing salinity Both juveniles and adults were caught throughout the year. Males are mature at l03 cm TL and females at ll5 cm TL. The females outnumbered males in the overall sample. Female length varied between 55 to l45 cm TL and male from 60 to l25 cm TL. Pregnant females accounted for 70/100 of samples collected in January (rainy season). They bore recently fertilized eggs or very small embryos. Non-pregnant adult females in this period showed heavy ovaries, indicating imminent mating. Pregnant females containing embryos as large as 37 cm TL were collected in November (dry season), suggesting that birth may occur at the beginning of the year, When rainfall starts. Gestation seems to develop from January to December. Variations in several organs related to both the rainy and dry seasons indi- cate a fairly defined cycle for the species. The maximum size of the litter was found to be seven embryos. Fecundity could not be related to female size. A resting break may take place between two successive cycles. Both the absence of migration and general traits of the Whole shark community confirm that the study area has important conservation value.