Lobster in a Changing Gulf of Maine: Investigating the Temporal Impact on Molting and the Fishing Fleet

We investigated the phenological and fisheries dynamics surrounding the spring molt of American lobster (Homarus americanus, Milne Edwards 1847) in the Gulf of Maine. We created a time series from Maine Department of Marine Resources Lobster Sea Sampling data using logistic models to estimate the timing and duration of the spring molt for eastern, central, and western regions of the Maine coast. These estimates revealed substantial inter-annual variability in the timing of the spring molt for all regions and that 2012 was indeed anomalously early relative to other years. Each region experienced significantly different molt timing for any given year, indicating that there are spatially-distinct molting phenologies along the Maine coastline. Generalized Linear Models were constructed using the molting time series and hindcasted bottom temperatures from the Northeast Coastal Ocean Forecasting System using the Finite Volume Composite Ocean Model to analyze how nearshore and offshore bottom ocean temperatures might shape molting trends and differences. This analysis revealed that the influence of nearshore temperatures was significant in the eastern region only and the relationship between nearshore temperatures and the timing of the spring molt weakened from east to west.

Logistic models were also applied to Maine Department of Marine Resources Landings Program data to estimate and evaluate multiple landings-based proxies for the timing of the spring molt via the fishing fleet’s ability to synchronize with the lobster molting phenology. Newshell landings, as a percent of the annual weekly maximum, were identified as the best proxy, given relative difference from the annual in-situ estimates of spring molt timing and lower standard error values. The fleet’s ability to synchronize with variable spring molting phenology was assessed using a correlation analysis. This analysis revealed that both eastern and western fleets followed the same temporal patterns as the lobster molt timing in their region and the western fleet showed a poorer, more variable ability to absolutely synchronize their timing when compared to the eastern fleet.

Maine lobstermen were interviewed to investigate how they achieve an optimal synchrony, revealing the utilization of several environmental and non-environmental variables. General temperature, lunar and tidal phases, and Penobscot River discharge were fishermen-nominated variables tested using correlation analysis. These analyses showed that fishermen methodology and its association with spring molt timing were spatially variable. General temperatures displayed the same weakening association with spring molt from east to west; tidal phase was significant in the east only; and river discharge was significantly associated in the eastern and central regions. River discharge association with molting was also temporally variable, showing strongest significant positive relationships during April.

We discuss these investigations into the temporal and spatial dynamics of the spring lobster molt along the Maine coast and the fishery’s response to inter-annual variation, creating a baseline of information about the spring molt for Maine. We also discuss the degree to which the fleet is able to approximate and adapt to inter-annual variation in this phenology and some of the methods they have been using to accomplish this synchrony.