Aggregations and reproductive events of the narrownose smooth-hound shark (Mustelus schmitti) in relation to temperature and depth in coastal waters of the south-western Atlantic Ocean (38–42°S)

Abstract

Knowledge of environmental influence on reproductive dynamics in chondrichthyans is critical for effective management. The present study assessed the potential influences of temperature and depth on aggregations and reproductive events of the narrownose smooth-hound shark (Mustelus schmitti), using an analysis criterion based on the co-occurrence of different reproductive stages. Data were collected from 363 sample sites during six research surveys, covering an area of ~47 744 km2 along the coast (38–42°S, depth of <50 m). Aggregations of M. schmitti adults were mostly associated with the warmer spring surveys, with the aggregation sites being significantly warmer than those of non-aggregation. Evidence of pupping and ovulation was observed, almost simultaneously, during all spring surveys. However, the occurrence of these reproductive events showed a clear interannual variability pattern that was significantly explained by water temperature. Particularly, the occurrence of ovulation was associated with temperatures above 16–17°C. These results suggest that M. schmitti adults may follow the warming gradient along the environment and, thus, they aggregate in shallow and productive waters during the course of spring. Their reproductive events could be induced by temperature increase. This scenario suggests that changes in the patterns of bottom temperature may be important drivers of the reproductive dynamics of M. schmitti.