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Atlantic sturgeon () is a long-lived, estuarinedependent, anadromous fish. They were once a valuable and abundant resource along North America’s east coast. Habitat degradation, direct harvesting, and by-catch resulted in substantial declines in Atlantic sturgeon stock. In 2012 a segment of Atlantic sturgeon (New York Bight distinct population segment) was listed as a U.S. endangered species. Monitoring changes in sturgeon population is often done by sampling juvenile populations because juvenile sturgeons stay in their natal reproductive habitat for two to six years before migrating as mixed stocks along Atlantic coastal areas. The New York State Department of Environmental Conservation monitors juvenile sturgeon abundance in the tidal portion of the Hudson River. The data (sturgeon.csv) used in this problem are from 2006 to 2015, including counts of juvenile sturgeons caught (CATCH), effort (Effort), water chemistry (dissolved oxygen (DO), conductivity (COND), salinity (SALINITY)), tidal stage (STide), distance to salt front (DTSF), and sampling month (MON) and year (YEAR).

(a) Use Poisson regression to model the changes in sturgeon abundance over time (year, i.e., Catch ~ YEAR) using effort as the offset.

(b) Use GAM to explore the nature of the temporal trend, after the effects of other factors (e.g., temperature, salinity, distance to salt front) are accounted for.

(c) Revise the Poisson regression model based on GAM output and check if overdispersion is a problem.