Date of Award

8-2013

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Ecology and Environmental Sciences

Advisor

Gayle Zydlewski

Second Committee Member

Michael Kinnison

Third Committee Member

Kate Beard-Tisdale

Abstract

Shortnose sturgeon (Acipenser brevirostrum) is a species of fish known to utilize three distinct habitats seasonally for spawning, foraging, and wintering. They are also federally endangered as defined by the Endangered Species Act, mandating that any habitats deemed necessary for their survival and recovery be classified as “critical habitat”. Documenting both habitat use and population status is crucial to setting management strategies and goals.

Physical characteristics of habitat used by shortnose sturgeon in the Penobscot River, Maine over four winters, their influences on shortnose sturgeon wintering behavior, and the annual size of the wintering population in the Penobscot were the focus of this research. Wintering, a refuge behavior exhibited by shortnose sturgeon, is most pronounced in northern populations and characterized by an aggregation of all individuals in a river into one or a few dense groups. Though wintering behavior has been documented in many northern sturgeon rivers, the characteristics that sturgeon base their wintering habitat selection on are not fully understood. Annual shortnose sturgeon arrival and departure patterns were documented using acoustic telemetry of previously tagged individuals.

Wintering aggregations of sturgeon were documented and counted at sample locations using a Dual IDentification SONar (DIDSON). Counts and documented areas were used to calculate densities at sampled locations in and around wintering habitat. Sample locations and densities were entered into a Geographic Information Systems (GIS) program and used to estimate densities throughout winter habitat using spatial interpolation. Resulting density estimates were used to calculate a population estimate for each sample day using two spatial interpolation methods. The effects of different sampling layouts and spatial interpolation methods were tested and validated on a simulated wintering shortnose sturgeon population.

Shortnose sturgeon were documented wintering in a single aggregation each year, at river kilometer (rkm) 36.5 during winters of 2008 - 2010, and at rkm 42 during winter 2011. Aggregation and departure rates and timing varied each year, and did not correlate with changes in either river temperature or flow. Wintering site depths were similar for the initial three years, but different from the wintering site used in 2011, and similar to those reported at wintering sites in other rivers. Substrate was predominately coarse gravel, slightly larger than sand-sized substrate reported for wintering sites of other rivers, though this may be a result of differences in sampling technique.

Population estimates were successfully calculated for each sample day using two spatial interpolation methods: inverse distance weighting (IDW), and kriging. Based on the results of simulation analyses, the optimal population estimate for each day was selected, then the optimal estimate for each year was selected. Annual population estimates ranged from 539 (426 - 652 95% CI) individuals in 2008 to 1186 (887 - 1485 95% Cl) in 2010, and were similar or slightly lower than those generated using independent mark-recapture sampling methods and robust design population modeling. Thus, the population estimation method used in this study is an effective and efficient way to estimate the number of wintering shortnose sturgeon in the Penobscot River, and can be adapted to other wintering shortnose sturgeon populations, or species that aggregate and demonstrate limited movement for an extended period of time.

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