Abstract

Previous fecundity estimates for king mackerel assumed a determinate spawning pattern, but recent evidence for king mackerel and similar species indicates that they are indeterminate spawners, with the possibility of multiple spawning events over a protracted (months long) reproductive season. Our objective was to estimate the batch fecundity and the spawning frequency needed for an indeterminate fecundity approach. We found regional and temporal differences in batch fecundity. Batch fecundity was lower in east Florida (Atlantic) than NW Florida (NE Gulf of Mexico). This regional difference was largely attributed to the low oocyte density of females sampled from the early portion of a bi-modal spawning season in the Atlantic, a pattern not seen in the Gulf. Mean spawning fractions by region and year ranged from 7.1 to 11.5%. However, our finding that 88% of the histologically assessed fecundity samples contained both old and more recent post-ovulatory follicles suggests that spawning fractions are much higher, and thus spawning is occurring more frequently than estimates made by observing females with visibly hydrated ovaries. Estimates of annual fecundity could not be determined due to difficulties in spawning frequency estimation; improved estimates would require histological calibration and expanded spatio-temporal sampling. For stock assessment purposes, we ultimately had to assume that batch fecundity was an adequate metric to estimate reproductive potential for the population model. Due to limited sample sizes, the assessment advice was to apply a single batch fecundity function covering both the Gulf and Atlantic management units in southeastern U.S. waters.

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