Abstract
During the 1990s, Buzzards Bay supported a commercially viable American lobster fishery within Lobster Management Area-2 (LMA-2). Lobster landings and employment of commercial lobstermen in LMA-2 have since decreased substantially, concurrent with declines in abundance and inshore postlarval settlement. These changes occurred during a period of significant warming in southern New England, with coastal waters progressively characterized by thermal ranges affecting the physiology of all life stages. In addition to affecting the development and survival of pelagic larvae and newly settled juveniles, rising ocean temperatures redistribute adults towards cooler offshore waters during the critical time of larval release. The observed offshore shift in the distribution of egg-bearing females is characterized using kernel density estimation and impacts on larval delivery to Buzzards Bay are examined by simulating larval transport with a coupled biophysical individual-based model driven by realistic hindcasts of oceanographic conditions. Simulation results are discussed in the context of stated objectives, with considerable attention given to the observed redistribution of egg-bearing females and consequences on simulated larval transport. There is a clear relationship between rising June-July bottom temperatures in Buzzards Bay and the redistribution of egg-bearing females to offshore waters. The probability of settlement in Buzzards Bay is almost entirely dependent on spawning stock biomass, inferred using data from the southern New England region of statewide spring trawl surveys, and is less related to the redistribution of egg-bearing females. This study also identifies nursery habitat in Buzzards Bay most likely to be colonized and considers the thermal suitability of the Bay for newly settled juveniles. Model predictions suggest greater settlement potential along east-bay nursery habitat, but validation of predictions based on the density of early benthic phase lobsters from diver-based suction sampling was limited by few sites, low densities, and high variability. A downward trend in the thermal suitability of Buzzards Bay is present from the mid-1990s to 2017 and may threaten prolonged juvenile survival in the upper Bay. Finally, simulation results are compared to field observations of Buzzards Bay larval abundance collected at six stations in the summers of 2006 and 2007 (Milligan, 2010), as well as 2017 and 2018 (current study). Field observations of stage I larval abundance generally reflect model predictions and are consistent with the observed redistribution of egg-bearing females. Postlarval abundance in Buzzards Bay shows a drastic decline from 2006-2007 to 2017-2018 at the six stations sampled.