At-sea determination of female American lobster (Homarus americanus) mating activity: Patterns vs. expectations

• Spermatophore presence in the seminal receptacle was used to indicate mating activity.
• Mating activity by size class was compared to maturity data utilized in the stock assessment.
• More small females had mated than expected (based on maturity data) in Gulf of Maine regions.
• In Southern New England regions, fewer large females had mated than expected.
• Discrepancies from expected mating activity may affect stock assessment assumptions.

We examined female American lobsters (Homarus americanus) for evidence of mating activity in selected regions within Gulf of Maine (GOM) and Southern New England (SNE) waters. The presence of a spermatophore in their seminal receptacles was used as an indication of mating activity (spermatophore positive, “SP”). To determine if all presumably-mature females had mated, the proportion of females that were SP was compared to the size-at-maturity data used in the Atlantic States Marine Fisheries Commission (ASMFC) American Lobster Stock Assessment. A total of 1696 females were examined, and in all regions >75% of these females were SP. In most regions, more presumably-immature females (based on pre-existing maturity data) were SP than expected, while in the two SNE regions (Rhode Island) there were more presumably-mature females lacking sperm than expected. We suggest that due to the depleted condition of the SNE lobster stock, the discrepancy between expected maturity and mating activity in SNE females warrants further attention. Additionally, our data suggest that there is a need to re-examine lobster size-at-maturity throughout the GOM lobster stock. It appears as if either the maturity schedules have recently shifted, or sexually immature females are regularly mating in many regions.