Temporal Population Genetic Structure of Yellow Perch Spawning Groups in the Lower Great Lakes

This study tested the hypothesis that the genetic composition of Yellow Perch Perca flavescens spawning groups at specific sites remained consistent among years or age-cohorts; this likely would influence spatial population structure and be important for delineating management units. Previous studies identified that spawning groups genetically differed among locations across fine geographic scales, but it was unknown whether these patterns persisted from year to year. We analyzed 15 nuclear DNA microsatellite loci from Yellow Perch spawning at six Lake Erie locations in 2009 in reference to two out-groups spawning in Lakes St. Clair and Ontario. Results were compared with a prior study of samples from the same locations that had been collected in various years, ranging from 2001 to 2005. We evaluated consistency for two of the spawning groups across multiple birth-year-cohorts. Results indicated that the levels of genetic diversity were similar across all spawning groups and years. All eight spawning groups genetically differed from one other, with their allelic compositions varying between the two sampling periods. Some variation occurred among individual sampling years and birth-cohorts, with the 2003 cohort being the most distinctive. Sampling groups contained relatively high proportions of full siblings (mean D 18.5%, ranging to 75% for the 2001 birth-cohort spawning at the eastern Lake Erie site), yet inbreeding appeared relatively low. Differences at sampling sites over time did not appear to reflect genetic drift but may instead suggest that spawning groups reproduce in slightly different locations from year to year or perhaps within a given season; this merits examination. Spatial and temporal patterns may reflect kin-group structuring and differential reproductive success, in which strong year-classes dominate spawning groups and impact genetic structure. The designation and application of management units (MUs) is a widely used approach to monitor and manage sustainable harvesting of populations in given areas (Begg et al. 1999; Schwartz et al. 2007), which may need to be adjusted via adaptive management for future conditions (Kocovsky et al. 2013; Shelton 2014). However, MUs that are based primarily on geography often are not biologically relevant (Waples and Gaggiotti 2006; Palsboll et al. 2007), and their mismatch can lead to reduced genetic diversity, productivity, and population size (Reiss et al. 2009). Genetic data provide a powerful tool to delineate stock structure, identify unique genetic variation and potential local adaptations, and may be used to help focus action at a biologically relevant scale (Pracheil et al. 2012; Rice et al. 2012; Allendorf et al. 2013). The Yellow Perch Perca flavescens (family Percidae) is a popular sport and commercial fishery species, whose geographic distribution extends across much of the northeast and central regions of North America (summarized by SepulvedaVillet and Stepien 2012; Stepien et al., in press). Its greatest abundances, most extensive habitats, and largest fisheries cooccur in the lower Laurentian Great Lakes, especially in Lake Erie, whose population levels have undergone frequent and poorly understood fluctuations (Scott and Crossman 1973; Hubbs and Lagler 2004; Kocovsky et al. 2013). Notably, *Corresponding author: [email protected] Present address: Department of Biology, University of Louisiana at Lafayette, 300 East St. Mary Boulevard, Lafayette, Louisiana 70506, USA. Received October 28, 2013; accepted October 22, 2014 211 Transactions of the American Fisheries Society 144:211–226, 2015 ! American Fisheries Society 2015 ISSN: 0002-8487 print / 1548-8659 online DOI: 10.1080/00028487.2014.982260 D ow nl oa de d by [U ni ve rs ity o f T ol ed o] , [ C ar ol A . S te pi en ] a t 1 3: 35 0 3 Fe br ua ry 2 01 5 Yellow Perch population sizes declined in the lower Great Lakes over the 1960s through 1985, which is attributed to a combination of exploitation, poor water quality, and changes in prey species (Henderson and Nepszy 1989; Tyson and Knight 2001). In response to improved management and habitat conditions, the Yellow Perch has undergone a shallow recovery in Lake Erie from 1985 to the present, averaging »180 million individuals and ranging from 43 million to 501 million per year since 1990 (Munawar et al. 2005; YPTG 2014). Lake Erie Yellow Perch are managed under the jurisdiction of the Great Lake Fishery Commission’s Lake Erie Committee, with recommendations from the Yellow Perch Task Group, which employs an MU framework to set annual quotas. In recent years, the fishery has been dominated by a few large year-classes (particularly 2003 and 2007), followed by poorer recruitment in subsequent cohorts (YPTG 2014). Understanding the temporal and spatial genetic stock structure (Ryan et al. 2003) that underlies these population fluctuations may provide important information for maintaining the fishery. Studies of spawning behavior coupled to genetic data comprise a powerful approach to identify reproductive groups and discern population structure. Yellow Perch undergo short migrations in late spring to early summer, aggregating to spawn on shallow reef complexes in lacustrine systems or slow-moving tributaries, where females drape egg masses that are fertilized by two to five males (Scott and Crossman 1973; Carlander 1997; Jansen et al. 2009). It is believed that Yellow Perch return to specific reproductive sites (Aalto and Newsome 1990; Carlander 1997; Craig 2000), which is supported by genetic data (Sepulveda-Villet and Stepien 2011, 2012; Stepien et al., in press) and tagging data (Clady 1977; Rawson 1980; MacGregor and Witzel 1987; Ontario Ministry of Natural Resources 2011). Aalto and Newsome (1990) removed Yellow Perch egg masses from given spawning sites, which led to fewer fish returning to those locations than to control sites in subsequent years, suggesting that they returned to the same spawning areas year after year (potentially their natal location). Yellow Perch spawning groups located just a few kilometers apart (17 km) in central Lake Erie were found to diverge from one another in genetic and morphological compositions (Kocovsky et al. 2013). Reproductive groups of Yellow Perch have been shown to be genetically differentiated, suggesting that they likely congregate in natal groups at specific spawning locations (Sepulveda-Villet and Stepien 2012; Sullivan and Stepien 2014). It is hypothesized that imprinting occurs during the early life history of Yellow Perch and of the related European Perch Perca fluviatilis, with their highly developed olfactory systems used to detect natal spawning sites and/or the pheromones of neighbors and relatives (Horrall 1981; Gerlach et al. 2001; Stepien et al., in press). Although Yellow Perch may spawn together with a specific group (believed to be their natal group), their exact spawning locations may vary somewhat from year to year. Notably, Bergek and Olsson (2009) compared spawning aggregations of European Perch caught at four different locations in Lake Erken in Sweden, consistently finding significant genetic differentiation among the samples. However, the local spawning groups also genetically differed from year to year when sampled at the same locations (Bergek and Olsson 2009). Sepulveda-Villet and Stepien (2011) analyzed Yellow Perch spawning groups in Lake Erie using 15 nuclear microsatellite loci, finding consistent levels of genetic diversity among spawning groups and that nearly all groups were distinguishable by allelic composition and frequencies. However, the sampling design was limited since each spawning group was sampled just once and different collection years were used. That experimental design may have confounded the interpretation of spatial versus temporal patterns. The present study thus investigates whether Yellow Perch genetic composition remains consistent among collection years and age-cohorts at specific spawning sites, which may influence spatial population structure and be important for defining MUs.