Martin J. Jennings

Cumulative Effects of Incremental Shoreline Habitat Modification on Fish Assemblages in North Temperate Lakes

Abstract To evaluate effects of habitat modification at different spatial scales, we assessed species richness and tolerance of fish assemblages in littoral zones of 17 Wisconsin lakes with extensive residential and recreational development, and compared fish associations among site-specific and lakewide conditions. Samples consisted of combined DC electrofishing and seining. Stations were randomly selected within strata defined by type of shoreline erosion control structure, including retaining walls, rock riprap, and no structure. Habitat characteristics differed among the site types. Species richness at the site level was greatest in complex habitat (riprap) regardless of fish assemblage structure. However, more effort was required to achieve complete sampling of fish species present in sites without erosion control structures. This result may be related to homogeneity of habitat among sites altered by manmade structures. We used an analysis of covariance (ANCOVA) to compare site level habitat effects ...

Is Littoral Habitat Affected by Residential Development and Land Use in Watersheds of Wisconsin Lakes

ABSTRACT We measured differences in nearshore littoral zone habitat among lakes with different amounts of residential development and different patterns of watershed land use. Sampling stations were located at randomly selected sites within the nearshore littoral zone of limnologically similar lakes. An index of development density (based on counts of residential structures) and watershed cover types detected by satellite imagery summarized human influence in the riparian zone and watershed. To compare effects of development at local sites to effects of cumulative development density (structures/km shoreline), we used analysis of covariance. Quantity of woody debris, emergent vegetation and floating vegetation decreased at developed sites and in lakes with greater cumulative lakeshore development density. Littoral sediments contained more fine particles at developed sites and in lakes with greater development density. Sediment composition, quantity of vegetation, and woody debris were weakly associated with differences in watershed land use. Cumulative changes to watersheds and riparian zones are associated with measurable differences in littoral habitat that may not be detectable at smaller scales. For effective conservation, regulatory programs should consider the cumulative effects of development and land use on aquatic systems.

Effect of Population Size Structure on Reproductive Investment of Male Bluegill

Abstract Although a goal of fisheries management is to understand factors affecting the growth rate and size structure of exploited populations, the relation between growth rates and variation in reproductive behaviors in Lepomis species has received little attention. Allocation of energy to reproductive functions (e.g., gonadal maturation, gamete production, nesting and spawning activities, and brood defense) negatively affects growth rate and, ultimately, maximum body size. To assess how social factors influence energy allocation, we manipulated population size structure of male bluegills L. macrochirus in experimental ponds and evaluated individual reproductive behavior and testes development. We predicted that smaller parental males would invest less in reproduction in the presence of larger parental males than they would in their absence. Observations were consistent with this prediction; smaller parental males had smaller testes and nested less frequently in the presence of larger males than in thei...

Survival, Growth, and Tag Retention in Age-0 Muskellunge Implanted with Passive Integrated Transponders

Abstract Mark–recapture studies are an important component of fisheries research and management. Underlying assumptions of such studies include minimal tag loss and negligible effects on the behavior, fitness, and survival of tagged individuals. Passive integrated transponder (PIT) tags are becoming increasingly commonplace, largely because of their small size, ease of implantation, longevity, and reportedly high rates of retention. We evaluated tag retention and survival and growth effects on age-0 muskellunge Esox masquinongy marked with PIT tags at two implantation sites, the peritoneal cavity and the dorsal musculature, during overwinter trials in Illinois and Wisconsin. For both trials, no significant differences in survival (88.0–89.8%), relative daily growth (0.0006–0.00062 mm·mm−1·d−1), or tag retention (99.5–99.8%) were observed among the two implantation groups and a control group. Survival and tag retention were also similar between trials. Our findings suggest that PIT tags implanted either in...

Seasonal Variation in Fish Assemblage Structure and Habitat Structure in the Nearshore Littoral Zone of Wisconsin Lakes

Abstract To evaluate whether fish abundance, fish habitat, and fish–habitat associations vary across seasons in nearshore littoral zones of five northern Wisconsin lakes, we assessed fish abundances and quantified habitat characteristics in littoral zones across three seasons (spring, summer, and fall) during 1996. Seasonal responses of the fish community in the nearshore littoral zone were taxa specific and guild specific. In the nearshore littoral zone, species richness and the abundance of pumpkinseeds Lepomis gibbosus, rock bass Ambloplites rupestris, yellow perch Perca flavescens, and centrarchids differed significantly across seasons. Some habitat characteristics, including mean water depth, maximum water depth, percent floating vegetation, and percent submersed vegetation, also differed significantly among seasons. Analysis of covariance indicated that changes in fish abundance for the three species coincided with variation in habitat characteristics in the nearshore littoral zone. Significant inte...

A Comparison of Fish and Aquatic Plant Assemblages to Assess Ecological Health of Small Wisconsin Lakes

ABSTRACT Biological monitoring uses assemblage structure to assess condition of ecological systems. Taxa that effectively integrate impacts within the system of interest are useful for biological monitoring, whereas taxa that do not demonstrate predictable responses can provide ambiguous or misleading indicators. We compared the effectiveness of aquatic plant and fish assemblages for biological monitoring in 16 small lakes (< 80 ha). The lakes were limnologically similar but differed in extent of lakeshore development and type of watershed land-cover. Linear regression analysis revealed that the quality of the aquatic plant community declined with increasing lakeshore development (number of dwellings per km of shoreline), which is the primary source of impacts within this group of northern Wisconsin lakes. As lakeshore development increased, we observed a decrease in the Floristic Quality Index (FQI) of a lake, number of plant species per lake, number of highly intolerant plant species per lake, and the species richness and frequency of occurrence of floating vegetation. Conversely, fish species richness, centrarchid species richness, number of small benthic fish species, intolerant fish species richness and the proportion of the total catch of intolerant and vegetative-dwelling fish were not related to lakeshore development. These results indicate that, within the range of conditions observed, aquatic plant communities are more sensitive to lakeshore development than fish communities. Neither aquatic plant species composition nor fish assemblage variables were correlated with watershed land cover types; however all the watersheds were relatively small and undisturbed. In small lakes with few fish species, aquatic plants can be used as biological indicators for monitoring ecological conditions.

Conservation Genetics of Lake Superior Brook Trout: Issues, Questions, and Directions

Abstract Parallel efforts by several genetic research groups have tackled common themes relating to management concerns about and recent rehabilitation opportunities for coaster brook trout Salvelinus fontinalis in Lake Superior. The questions that have been addressed include the evolutionary and genetic status of coaster brook trout, the degree of relatedness among coaster populations and their relationship to riverine tributary brook trout populations, and the role and effectiveness of stocking in maintaining and restoring coasters to Lake Superior. Congruent genetic results indicate that coasters are an ecotype (life history variant) rather than an evolutionarily significant unit or genetically distinct strain. Regional structure exists among brook trout stocks, coasters being produced from local populations. Introgression of hatchery genes into wild populations appears to vary regionally and may relate to local population size, habitat integrity, and anthropogenic pressures. Tracking the genetic diver...

Implementation of Genetic Conservation Practices in a Muskellunge Propagation and Stocking Program

Conservation of genetic resources is a challenging issue for agencies managing popular sport fishes. To address the ongoing potential for genetic risks, we developed a comprehensive set of recommendations to conserve genetic diversity of muskellunge (Esox masquinongy) in Wisconsin, and evaluated the extent to which the recommendations can be implemented. Although some details are specific to Wisconsins muskellunge propagation program, many of the practical issues affecting implementation are applicable to other species and production systems. We developed guidelines to restrict future broodstock collection operations to lakes with natural reproduction and to develop a set of brood lakes to use on a rotational basis within regional stock boundaries, but implementation will require considering lakes with variable stocking histories. Maintaining an effective population size sufficient to minimize the risk of losing alleles requires limiting broodstock collection to large lakes. Recommendations to better app...

Genetic identity of brook trout in Lake Superior south shore streams: Potential for genetic monitoring of stocking and rehabilitation efforts

Abstract Rehabilitation of migratory (“coaster”) brook trout Salvelinus fontinalis along Lake Superiors south shore is a topic of high interest among resource stakeholders and management agencies. Proposed strategies for rehabilitation of this brook trout life history variant in Wisconsin include supplemental stocking, watershed management, habitat rehabilitation, harvest regulations, or a combination thereof. In an effort to evaluate the success of coaster brook trout rehabilitation efforts, we collected genetic data from four populations of interest (Whittlesey Creek, Bois Brule River, Bark River, and Graveyard Creek) and the hatchery sources used in the Whittlesey Creek supplementation experiment. We characterized the genetic diversity of 30 individuals from each of four populations using 13 microsatellite DNA loci. Levels of genetic variation were consistent with those in similar studies conducted throughout the basin. Significant genetic variation among the populations was observed, enabling adequat...

Evaluation of Supplemental Walleye Stocking in Northern Wisconsin Lakes

Abstract Supplemental stocking of walleye Sander vitreus is an important component of fishery management programs in North America. We conducted an experimental study in 23 northern Wisconsin lakes over a 4-year period to assess differences in year-class strength with and without supplemental stocking. These study lakes all hosted walleye fisheries targeting mixed-recruitment populations (i.e., ones with both natural reproduction and supplemental stocking). We tested for differences in catch per effort (CPE) between stocked and nonstocked years using a general linear mixed model. Catch per effort of age-0 walleyes was 2.3 greater per shoreline mile when lakes were stocked, suggesting that stocking increases year-class strength by about 0.13 age-0 walleyes/ acre. Catch per effort values approximated a Poisson distribution, most lakes showing low CPE of age-0 walleyes whether or not they were stocked. Stocked fingerlings were marked with oxytetracycline as fry to determine the percent contribution of stocke...