Characterizing Pacific halibut movement and habitat in a Marine Protected Area using net squared displacement analysis methods

We characterized small-scale movement patterns and habitat of acoustic-tagged adult (68 to 220 cm total length) female Pacific halibut during summer and fall in Glacier Bay National Park, Alaska, a marine protected area (MPA). We used net squared displacement ana lysis methods to identify 2 movement states, characterize individual dispersal patterns, and relate habitat variables to movement scales. Movement states identified for 32 of 43 halibut consisted of (1) a non-dispersive ‘residential’ movement state (n = 27 fish), where movement was restricted to an average movement radius of 401.3 m (95% CI 312.2−515.9 m) over a median observation period of 58 d, and (2) a ‘dispersive’ movement state (n = 15 fish), where movements of up to 18 km occurred over a median observation period of 27 d. Some fish (n = 10) exhibited both movement states. Individual fish demonstrated primarily non-random dispersal patterns including home range (n = 17), site fidelity (return to previously occupied locations following forays, n = 6), and shifted home ranges (n = 5). However, we also observed a random dispersal pattern (n = 4) with an estimated mean ± SE diffusion rate of 0.9 ± 0.05 km2 d−1. Home range size increased with depth but not fish size. Home range locations were associated with heterogeneous habitat, intermediate tidal velocities, and depths <100 m. Observations of non-dispersive movement patterns, relatively small home ranges, and site fidelity for adult females suggest that MPAs such as Glacier Bay may have utility for conservation of Pacific halibut broodstock.