Spatial and temporal dynamics of larval American lobsters Homarus americanus H. Milne Edwards, 1837 (Decapoda: Astacidea: Nephropidae) in a rapidly declining stock

Abstract

The southern New England (SNE) stock of the American lobster (Homarus americanus H. Milne Edwards, 1837), previously supporting one of the largest fisheries in the region, has declined significantly since the late 1990s and is now severely depleted. This decline has largely been attributed to environmental changes and recruitment failure, suggesting there is a recruitment bottleneck. Nearshore coastal nursery habitats, subject to recent ocean warming trends, have experienced drastic reductions in adult and recruit populations. Lack of contemporary larval abundance data nevertheless poses challenges for evaluating a prospective bottleneck. We resurveyed larval lobster abundance and distribution at sites in Rhode Island originally sampled from 1989–1995 during a period of high lobster abundance, to assess prospective early life-history bottlenecks and determine the environmental drivers of nearshore larval dynamics. Neuston net tows were conducted during the summers of 2021 and 2022 to sample larvae. Larval presence and abundance, environmental drivers, and spatial distribution were investigated with generalized linear models. Seasonal postlarval abundance (post larvae (PL) days 1,000 m−2 per season) was also calculated for comparison to historical estimates. Sea surface temperatures were the strongest predictor of larval and postlarval presence and abundance, with factors such as wind and sampling station accounting for variations in spatial distribution. Mean integrated seasonal postlarval supply for 2021 and 2022 was 22 PL days 1,000 m−2 per season, representing a stark reduction compared with estimates from the 1990s (mean of 611 PL days 1,000 m−2 per season). Despite this decline, larval arrival and timing remained similar across studies, indicating unchanged phenology. Current postlarval production coincided with observed reductions in overall spawning stock biomass, indicating that low spawning stock may cap larval supply, ultimately leading to low recruitment. These results emphasize the importance of monitoring early life history to inform the management of the SNE lobster stock.