Is the spawning frequency dependent on female size? Empirical evidence in Sardinops sagax and Engraulis ringens off northern Chile

In this study, we review the relationship between female size and spawning frequency using information from Sardinops sagax and Engraulis ringens, two species which are important for the economy of countries located in the Humboldt Current System. We test the hypothesis that spawning frequency is positively related to female size using information for these two species in northern Chile. The data analyzed were obtained from four different sources: (a) reproductive information obtained from the application of the Daily Egg Production Method (DEPM) in E. ringens between 1992 and 2005; (b) adult reproductive parameters for different species of the genus Engraulis; (c) spawns counts for a brood stock of E. ringens reared in captivity; (c) results from an indirect method based on a gonadosomatic calibrated index developed for S. sagax utilizing data obtained from 1974 to 1996. An analysis of the 11-year DEPM data series for E. ringens suggest that the daily spawning fraction also increases with the average weight of mature anchovy females and that such relationship may also be described using an asymptotic model. A plot of the daily spawning fraction and average female weight data obtained from results of DEPM applications for different Engraulis species from around the world also showed a positive correlation, suggesting that this relationship may be valid for many species, even those located in different habitats. An analysis of the data obtained from the E. ringens brood experiments showed that the number of eggs spawned in the tank increased monthly as female age increased, even though the number of females decreased due to natural mortality. Results in S. sagax females showed that smaller females have shorter spawning periods and a lower spawning fraction; accordingly, bigger females spawned more frequently than smaller ones. The long term estimation (1974–1996) of spawning numbers in relation to S. sagax female size was well described by a sigmoid function.