RESEARCH ON LOBSTER AGE-SIZE RELATIONSHIPS: DEVELOPING REGIONALLY SPECIFIED GROWTH MODELS FROM META-ANALYSIS OF EXISTING DATA

Understanding growth of the American lobster is critical to our ability to manage this economically important fishery. However, modeling growth is challenging because lobsters cannot be easily aged and their growth is determined by temperature among other environmental factors. In this study I developed regional growth models for three oceanographically contrasting regions of the species range: southern New England, Gulf of Maine, and the Bay of Fundy. First, I developed a model of the molting process using empirical data on lobster sizes and growth from each region. Second, temperature was incorporated into the model to assess whether it was the main factor influencing differences in lobster growth among the regions. The temperature dependent model was also used to predict how lobsters would grow in a changing climate.

Considerable regional differences in lobster growth were evident. In southern New England, growth started the fastest, but because lobsters mature sooner in warmer water, growth slowed dramatically at a relatively small size. In contrast, in the Gulf of Maine and Bay of Fundy, growth started slower, but lobsters did not mature until a larger size and the subsequent decline in growth rate was less severe. Thus, although lobsters in southern New England, initially grow faster and reach harvestable size sooner, they do not grow as large as those in the north, because the onset of sexual maturity appears to inhibit growth more severely in the south.  

Regional differences in growth were not entirely explained when temperature was included in the model. But when using this model to make predictions, when the size of maturity was also reduced under warming temperature, as might be expected, the result was to decrease in growth rate at an earlier age.

Thus, while regionally-specified models have advanced our ability to account for regional differences in lobster growth, they have yet to adequately include the environmental factors that determine those differences.  Temperature surely plays an important role in the observed regional differences in growth rate, however, I cannot rule out other factors that may also be important, such as food availability, population density, or local adaptation.