Modeling the Influence of Directional Swimming Ability in American Lobster ( Homarus americanus ) Postlarvae on Settlement

Abstract

We developed a particle tracking model for the transport and dispersion of American lobster ( Homarus americanus ) larvae for the Gulf of Maine (GoM) that considers both passively drifting larval stages and their swimming ability during the postlarval (pre‐settlement) stage. The model takes into account two characteristics of the postlarval stage: directional swimming toward shallower regions and diel fluctuations of their swimming speed. Diffusivity (lateral mixing), based on surface GPS drifter observations, was also considered and used to validate this model. Numerical experiments, using the hydrodynamics predicted by the Gulf of Maine Operational Forecasting System (GoMOFS) model, were conducted to test the potential impact of postlarval swimming ability on successful settlement on suitable habitat (defined as regions shallower than 20 m). The results of this experiment showed that elevated swimming ability (18 cm/s) in postlarvae significantly improves settlement success compared to trials modeling postlarvae with a diminished swimming ability (7 cm/s), or no swimming ability (control) at all. In contrast, diel swimming behavior in postlarvae slightly decreased successful settlement. In addition, ocean drifter observations and numerical simulations consistently revealed that successful settlement decreases the further the initial release point of larvae is from the coast. Combined, these experiments indicate that both the swimming ability of postlarvae and the distance they are from shore when they hatch are critical factors that influence their potential to reach viable settlement locations in the GoM. These data also suggest that if the GoM continues to warm, and females move further offshore to avoid warmer inshore waters, the settlement success of their larvae may be compromised.

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