Reproductive Success of Founders In a Slimy Sculpin Reintroduction Program

Slimy sculpin (Cottus cognatus) are a small, benthic, freshwater fish species native to southeastern Minnesota. Recent conservation efforts of the Minnesota Department of Natural Resources included reintroducing sculpin to rehabilitate native fish fauna in historically degraded streams. Prior research examined overall ancestry, changes in genetic diversity, and fitness in reintroduced sculpin populations up to two generations after stocking. We conducted new introductions to examine initial dynamics in survival and reproduction and how they affect genetic diversity. Three streams were stocked in the fall of 2008 with 100 translocated individuals from two source streams. Fin clip samples were taken from all stocked individuals and samples from their offspring were collected after the next two spawning seasons. Parentage analysis of offspring using 12 microsatellite loci was performed to determine the reproductive success of founders and retention of genetic diversity in the offspring. In the first year following stocking, 20-36 founders contributed at least one offspring across the three streams. By the second year, essentially the reproductive lifetime of these short-lived species, the total number of founders remained at 20 in one stream but increased to 44 and 51 in the other two streams. Skewed sex ratios (1.5:1 – 4.0:1 females to males) and high variation in reproductive success among individuals lowered the effective number of founders. Of the alleles present in the stocked fish at each stream, 11-32% were not detected in the offspring. These findings can guide the number of fish stocked to achieve founder number or genetic diversity goals in these reintroduced populations.