Research Document - 2014/045

Reproductive Status of the American Lobster in Southwest Nova Scotia and the Bay of Fundy (Lobster Fishing Areas 34-38)

By J. Gaudette, M.J. Tremblay, A.M. Silva, C. Denton, and D.S. Pezzack

Abstract

The historical reproductive status of the American lobster, Homarus americanus, for Lobster Fishing Areas (LFAs) 34-38 was examined in the form of size-at-onset-maturity, egg production indices and other aspects of lobster reproduction (size structure, sex ratio, proportion of ovigerous females, mating success). A significant downward shift in size-at-onset-maturity was observed when comparing an unpublished dataset between 1978-79 and 2011 from North Head Grand Manan (LFA 38). A re-estimate of size-at-50%-maturity (SoM50) for 1978-79 indicates it was 99 mm carapace length (CL) rather than the published estimate of 108.1 mm CL.  The estimate for 2011 indicated a decline of approximately 7 mm to 92.5 mm. This shift was consistent with the observation that sizes of smallest ovigerous females have gradually declined over past 30-year in the Bay of Fundy and Southwest Nova Scotia. The sea sampling time-series have shown a dramatic increase of lobster over time and, combined with the shift in SoM50, the reproductive potential has increased dramatically in the Bay of Fundy. There is no clear trend in LFA 34. Reproductive potential of large females has slightly declined over time but was largely compensated by the increased potential of the smaller size group. Despite the overall increase in the egg production potential in the Bay of Fundy, observed egg production calculated from ovigerous females catch rates and fecundity-at-size only increased slightly or was steady when comparing the initial five-year of the time series to the past five years for the Bay of Fundy areas. The discrepancy between the two indices may be related to lower mating rates among mature females in recent years in comparison to 1978-79. Observed mating success had a positive size-dependent relationship among mature females and, thus, the contribution of small sizes females (i.e. below SoM50) to observed egg production was substantially lower than their reproductive potential. In LFA 34, the observed egg production indices were variable but showed no upward trend. This work suggests that increasing the minimum legal size would not have a significant effect on increasing egg production unless the increase is substantial. Instead, it may be more effective to protect larger females that appear more successful at mating. In addition, protecting large males may contribute to increased egg production as there are indications based on mating success and proportion of ovigerous females that sperm limitation may be occurring in within LFAs 34-38.

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