Connectivity of Lobster Populations in the Coastal Gulf of Maine

Example of model output
Example of model output: number of postlarvae/km2 summed over all days from June through September in one settlement season. The highest abundances are shown in red; dark blue denotes low numbers.
Project Summary:

This project is a synthesis and modeling study designed to quantify the relationships (“connections”) between egg hatching patterns and young lobster settlement patterns within the Gulf of Maine.

Location:

Gulf of Maine, Modeling project, 2003-2007

Significance

This interdisciplinary study combines known biological data about lobster reproduction, larval development and settlement with physical parameters including water temperature, currents, bathymetry, and meteorology to describe how local populations of lobsters are connected across a large area such as the Gulf of Maine. The study found that, with a few notable exceptions, most coastal lobster populations are derived from larvae that were produced within 1 or 2 lobster management zones.

  • Lewis Incze, Aquatic Systems Group, University of Southern Maine
  • Huijie Xue, School of Marine Sciences, University of Maine
  • Nicholas Wolff, Aquatic Systems Group, University of Southern Maine,
  • Danya Xu, School of Marine Sciences, University of Maine
  • Carl Wilson, Maine Department of Marine Resources
  • Robert Steneck, Darling Marine Center, University of Maine
  • Rick Wahle, Bigelow Laboratory for Ocean Sciences
  • Neal Pettigrew, School of Marine Sciences, University of Maine
  • Yong Chen, School of Marine Sciences, University of Maine
  • U.S. NOAA (National Oceanic and Atmospheric Administration’s) Center for Sponsored Coastal Ocean Research, and the Census of Marine Life Gulf of Maine Area Program
Project Detail:

The lobster (Homarus americanus) fishery is currently the most lucrative fishery in coastal Gulf of Maine. The recent trend of steadily increasing annual catches has been met with nervous enthusiasm. Not enough is known about lobster larvae transport, settlement, and survival dynamics to predict whether the current abundance of the stock will continue, or for how long. As such, there is intense interest in elucidating the factors that drive patterns of lobster larvae settlement. Our objective was to understand the degree to which settlement in different parts of the coast is driven by distant versus local egg production, and how this varies from year to year.

To this end we combined a coupled biophysical model of the Gulf of Maine region with the best available biological data on lobsters (current population, reproduction, and larval development, etc.) to explore the dynamics of larval production and settlement in the Gulf of Maine. The biophysical model we used is the operational model of the Gulf of Maine Ocean Observing System, which is based on the Princeton Ocean Model. We coupled this model with data from an ongoing modeling study of the benthic population headed by Yong Chen (one of the scientists on this project) in order to complete the life cycle from egg production back to the adult stock.

Before we could model lobster larvae as they were transported around the Gulf, we had to estimate how many were being hatched every day everywhere along the coast. This required a large effort to represent, to the best of our ability, the spatial and temporal distribution of hatching, something that had never been done before.

Our primary goal was to use the computational capacity of the model to calculate the connectivity of the population along the coast. The model generated over 7 million larval data points a year. This is important for understanding basic population processes as well as managing heavily exploited populations because it reveals how egg-producing regions are connected to settlement regions. Egg producing regions can change over time, and a model allows you to examine how population changes in part of the coast would affect recruitment in that and other parts of the Gulf. In this study, we held the egg production patterns constant and observed how interannual variations in the currents affected settlement patterns. The abundance and patterns of planktonic stages calculated by the model agree quite well with field observations, and the flow fields agree qualitatively with satellite-tracked drifter trajectories and with current measurements made at GoMOOS (Gulf of Maine Ocean Observing System) buoys.

While it is true that the strong currents in the Gulf of Maine mean that larvae can get transported long distances and thus come from almost anywhere, the model showed relatively high levels of self-recruitment within most lobster management zones. A large proportion of settlement comes from larvae which originated within the same zone. All areas are connected to some extent to other “upstream” areas, but most of the larvae come from within 1-2 zones. A few zones depend strongly on upstream sources of larvae because the zones are in high “flow-through” areas, may have low egg production themselves, and are downstream of high egg production areas. These patterns change over time, so one cannot view as satisfactory a fixed (single model) idea of the population dynamics.

Publications:

Incze, L.S., R.A. Wahle, N. Wolff, C. Wilson, R. Steneck, E. Annis, P. Lawton, H. Xue, and Y. Chen. 2007. Early life history and a modeling framework for lobster populations in the Gulf of Maine. Journal of Crustacean Biology 26(4): 555-564

Incze, L., H. Xue, N. Wolff, D. Xu, C. Wilson, R. Steneck, R. Wahle, P. Lawton, N. Pettigrew, and Y. Chen. 2010. Connectivity of lobster (Homarus americanus) populations in the coastal Gulf of Maine: part II. Coupled biophysical dynamics. Fisheries Oceanography 19(1): 1–20 PDF

Xue, H., L.S. Incze, D. Xu, N. Wolff and N. Pettigrew. 2008. Connectivity of lobster populations in the coastal Gulf of Maine. Part I: Circulation and larval transport potential. Ecological modeling 210: 193-211 PDF