Seasonal variation in growth and mortality of larval Syacium gunteri (Piscis: Paralichthyidae) in the southern Gulf of Mexico (1992 and 1993)

Abstract

The seasonal variation in growth and mortality of Syacium gunteri larvae in the southern Gulf of Mexico was analyzed. Plankton samples, as well as temperature and salinity measurements were obtained during eight cruises in 1992 and 1993. Larval growth was estimated based on daily marks on sagitta otoliths, using the Laird-Gompertz model since it yielded the best hatching size (HS) estimates. Mean daily growth (MDG) and HS showed a cyclical variation pattern. In both years the highest values were recorded in spring (1992, MDG = 0.19 mm d^–1 and HS = 1.47 mm; 1993, MDG = 0.23 mm d^–1 and HS = 1.58 mm) and the lowest in winter (1992, MDG = 0.14 mm d^–1 and HS = 1.08 mm; 1993, MDG = 0.15 mm d^–1 and HS = 1.21 mm). The variation pattern of these parameters was directly and closely related to that of temperature. The mortality rate ranged from 0.05 to 0.26, also with a cyclical pattern, but contrary to that of growth and temperature. Cyclical patterns are not well documented for tropical and subtropical areas, such as the southern Gulf of Mexico, where fish spawn throughout the year and spring may be considered the beginning of the cycle, with spring cohorts showing the highest growth rates and those of winter the lowest. The greater change in temperature that occurs from winter to spring may be the factor triggering these events.