Graduate Student: Todd Kittel Adviser: Brian Sloss
Impoundments on large rivers fragment and impede fish populations, especially potamodromous fish such as lake sturgeon (Acipenser fulvescens). Fragmentation can result in numerous viability concerns regarding genetic and demographic issues. The remnant Menominee River lake sturgeon populations are the second largest conglomerate in Lake Michigan. River-locked populations spawn below White Rapids (WR) and Grand Rapids (GR) dams while the parental lake-run population spawns below the Menominee Dam (MD). The WR population maintains annual spawning runs (≈200 fish/year) and successful recruitment. The GR population is smaller and maintains annual spawning runs with successful recruitment albeit possibly sporadic. These populations likely have small numbers of spawning fish dominating a given year’s reproductive effort potentially resulting in the majority of offspring being related. Small, isolated populations lose genetic diversity through genetic drift and inbreeding. Compounded by lake sturgeon life-history (late maturity, intermittent spawning, and polygamous), loss of genetic diversity threatens short-term productivity and long-term viability.
There are two objectives of this study: (1) characterize population structure and the distribution of genetic variation within and among river reaches and estimate gene flow between thereby assessing the effects of fragmentation and (2) determine the impact of fragmentation and small population size on viability and sustainability by assessing valuable life-history measures of the river-locked Menominee River populations. A total of 678 lake sturgeon (33.2-162.2 cm TL) were captured during the 2005 spawning season (44d) via electrofishing and gill netting. Length, weight, girth, sex, and a tissue sample were taken from each fish and then tagged with a passive integrated transponder (PIT tag) for recapture identification. Population estimates were calculated using the Schnabel method. Drift nets were deployed to collect larval sturgeon. Microsatellite genotyping was performed on 12 standardized loci. The distribution of genetic variation was assessed through levels of heterozygosity, allelic richness, genic differentiation, and F-statistics. Connectivity between populations was assessed through estimates of genetic and observed migration rates. To evaluate life-history characteristics, offspring were assigned to known spawners based on a maximum likelihood approach. We estimated the effective population size/effective number of breeders and minimum baseline spawning population sizes. Differential success among spawners and the coefficient of relatedness among sequential cohorts was assessed through coefficients of relatedness for all larval fish. A low number of sampled larvae in 2005 (0 and 87 for WR and GR, respectively) may limit these analyses. Efforts to identify other potential spawning sites are planned to increase the number of larvae collected in 2006. Additional samples of age +1 individuals and larvae (2006 spawning season) as well as archived spine samples taken in 1978 (WR) and 2001 (MD) will be added. Evaluating these remnant lake sturgeon populations will assist efforts to conserve genetic diversity and long-term viability of Menominee River populations as well as address immediate management concerns regarding fish passage.
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