Recruitment of Bluegill and Yellow Perch in Nebraska Sandhills Lakes: Integrating Multiple Life Stages

Bluegill Lepomis macrochirus and yellow perch Perca flavescens are important, native sport fishes to Nebraska Sandhills lakes. Recruitment dynamics of the fish populations within a given community will ultimately structure the fish communities. I conducted a multiple life-stage investigation of bluegill and yellow perch recruitment in Nebraska Sandhills lakes. I focused on four topics, 1) the effect of climate on year-class strength of multiple populations broadly across a series of Nebraska Sandhills lakes, 2) larval prey selection and match- mismatch regulation of recruitment, 3) age-0 dynamics and the potential effect of abiotic and biotic variables on recruitment, and, 4) potential predation by yellow perch on age-0 bluegill. Results from this study contribute to the understanding of ecology of bluegill and yellow perch and management related to recruitment. I collected adult population samples of bluegill and yellow perch from several Sandhills lakes and estimated ages using sagittal otoliths. Residuals from catch-curves were used to assess the relation between climatological variables and year-class strength. Recruitment was relatively consistent for both species (no missing year classes detected) and asynchronous. The lack of synchrony in yellow perch and bluegill population year-class strength suggests that climate does not act similarly broadly across a series of Nebraska Sandhills lakes and that individual variability among lakes is equally or more important in influencing year-class strength for these two species in the Nebraska Sandhills ecoregion. I did find support for the concept of climate influence on bluegill and yellow perch recruitment. Spring temperature, precipitation, and winter severity appeared to be the most supported metrics governing recruitment of these species. Food availability is believed to regulate fish recruitment, both directly and indirectly. The availability of zooplankton, especially to newly hatched larvae, is thought to be particularly crucial. I examined stomach contents of larval bluegill and yellow perch larvae in Pelican Lake and Cameron Lake for two years. I also determined zooplankton availability from environmental samples and calculated prey selection using Chesson’s alpha. In addition, I investigated potential match-mismatch regulation of recruitment. Copepod nauplii and Bosmina spp. were commonly used by bluegill and copepods were commonly used by yellow perch. There were abundant zooplankton populations available for consumption. Matches in larval bluegill and yellow perch abundance and zooplankton abundance were detected in all years; exact matches were common. No mismatches in predator and prey production were observed. It is unknown if relatively large mismatches may lead to decreased recruitment for these two fish species. No predation by age-0 yellow perch on age-0 bluegill was observed, even though yellow perch hatched two months prior to bluegill. Given that zooplankton were abundant and well-timed to larval fish abundance over the time span of this study, the match-mismatch hypothesis alone may not fully account for observed recruitment variability in the populations that I studied. Recruitment dynamics of fish populations ultimately structure fish communities and may be regulated by abiotic and biotic factors both directly and indirectly. I documented age-0 dynamics of bluegill and yellow perch for four years in Pelican Lake and two years in Cameron Lake. I indexed larval densities, abundance of juveniles in the fall, abundance of the same cohorts the following spring, and abundance of age-2 bluegill and age-1 yellow perch to investigate recruitment to the adult population. Age was estimated for larval fishes using sagittal otoliths to determine hatching date. I also assembled an environmental dataset including temporal trends in zooplankton, benthic macroinvertebrates, vegetation coverage, and physical and biological water quality parameters. Peak larval densities of bluegill and yellow perch were variable although it appeared that recruitment was relatively consistent as some individuals of each cohort survived to recruit to the adult populations each year. A single peak in larval bluegill abundance was observed in most years, which is a finding contrary to the long-held assumption of multiple spawning bouts within a season. The bluegill spawning season was protracted, as previously reported, lasting approximately 2 months and the timing of hatch was relatively similar each year. Growth of later-hatched bluegill was faster than that of their earlier-hatched counterparts in most years. In addition, growth of late-hatched bluegill was correlated to catch of juveniles in the fall, suggesting that these fish may contribute more to eventual recruitment. No evidence of size-selective overwinter mortality was detected for bluegill. The yellow perch spawning season was truncated, a finding consistent with previous research. There was some evidence of size-selective overwinter mortality of yellow perch in only one instance. My estimates of larval density for both species were a poor predictor of later season catches or recruitment to the adult population. My exploratory analyses indicated that temperature, winter severity, and growth rates may be important determinants of survival and ultimate recruitment to the adult population. Seasonal food habits of adult yellow perch were investigated in West Long Lake. Benthic macroinvertebrates were a primary diet item. Specifically, chironomids, amphipods, and odonates were common diet items. Predation on age-0 bluegill was observed in the fall, and increased predation in the winter suggested potential ability of yellow perch to affect recruitment of bluegill. My study provides some of the first ecosystem-wide information on the dynamics of age-0 bluegill and yellow perch. I found, over the years examined, that no single factor appears to affect bluegill and yellow perch recruitment. Instead, a suite of factors, interacting in complex ways may ultimately govern the recruitment of these species. My results should be interpreted with caution as they are based on four years of data collection and the addition of more years of observation in this ongoing project may improve our ability to determine abiotic and biotic factors that influence recruitment of these two important species