Habitats used by shortnose sturgeon in two Massachusetts rivers, with notes on estuarine Atlantic sturgeon: A hierarchical approach

Biotelemetry of shortnose sturgeon Acipenser brevirostrum and Atlantic stur geon A. oxyrinchus oxyrinchus was used to study fish uses of habitat in sev eral hierarchical classes in the Connecticut and Merrimack rivers. Hierarch ical classes were geomorphological region (straight river run, run with an island, and river curve), river cross section (channel or shoal), and micro habitat (water depth, bottom current, substrate, and illumination). Coastal wandering juvenile Atlantic sturgeon were summer visitors to the Merrimack River, where they used a narrow range of habitat on all spatial scales, e. g., run-with-island, the channel portion of the cross section, and sand sub strate. Shortnose sturgeon, year-round residents in both rivers, showed gre at individual variation in habitat use, and all ages selected a broad range of habitats on all spatial scales. However, shortnose sturgeon in both riv ers preferred curves with sand or cobble substrate and avoided runs regardl ess of substrate. Individuals used channel or shoal at rates ranging from 0 to 100% on a weekly time scale in an unpredictable manner. Connecticut Riv er shortnose sturgeon increased their use of curves, channels (deep water), and sand substrate in the fall. This strategy may conserve energy because these conditions usually reflect slow water velocity. Winter habitat select ion continued the fall pattern, but was less variable because habitat affin ity was highest among wintering fish. Documenting individual fish use of la rge-scale habitat revealed habitat relationships that would not have been d iscovered if only fish use of microhabitat had been studied.