Ageing methodologies of Lake Michigan alewife were evaluated as a precursor to growth and condition investigations of alewife stocks. Four commonly used aging tissues were evaluated including: otoliths, scales, vertebrae, and opercles. Otoliths were significantly more precise than other structures in all analyses. The accuracy of age determinations given by otoliths was corroborated through length frequency analysis. Total processing time was highest for scales. Whole otolith methodology was used to age alewives from Indiana, Michigan, and Wisconsin based on precision, accuracy, and time efficiency. A trend of higher median lengths and weights in young fish from the Green Bay, Wisconsin site was identified. Older fish grew faster in the main-lake sample sites near Pentwater, Michigan and Indiana waters. The Indiana population had the highest condition factor (K), while Wisconsin had the lowest, with Michigan in between. An overall temporal decline in condition of alewife was identified when compared with historical studies. This is a consideration that may influence salmonid stocking decisions because the alewife serves as their primary food. / Department of Biology

Investigations were made examining the relationships between gastropod species richness and abundance across 20 phosphate and 20 natural lakes in Central Florida. In additional to lake category, age of phosphate lakes was used to determine if phosphate lakes ever approximate natural lakes. Additional physical, chemical, and biological parameters, including chlorophyll a, Ca, secchi, phosphorous, conductance, fish predation, and recreational lake use were investigated in order to determine if they affected gastropods with lake age. Comparisons were also made between gastropod species richness and average abundance and two groups of dominant vegetation categories: Panicum, a structurally complex macrophyte, and Typha, a less structurally complex macrophyte. After phosphate mining operations are completed, Florida state regulations require the establishment of ecologically viable habitat (created lakes) which reflects the properties of regional natural lakes including vegetation structure, littoral zone, bank slope, and lake depth. The littoral zone is part of the mandated structure of the lake, and is of considerable importance to the uptake, storage, transformation and release of nutrients. Within the littoral zone, gastropods are a critical link in the food web with implications for the long term structure and function of a lake. They are known for their close associations with macrophytes and are common environmental indicators since they have limited mobility, high diversity, are well studied, are representative of their habitat type and have a widespread geographic range. They are also an important food sources for many predators in aquatic environments, include migratory waterfowl and game fish. Gastropod species richness and abundance data were collected via standard net sweep methodology. Abundance was presented in catch per unit effort, therefore all abundance data were averages. Initial comparisons between gastropod species richness and average abundance yielded no significant differences between natural and phosphate lakes. However, when age was applied as a covariate, there was a significant difference between lake age as a continuous variable in species richness comparisons. Additionally, categorical comparisons between lakes older or younger than 30 years indicated significantly higher species richness and average abundance of gastropods in lakes phosphate lakes older than 30 years. Physical and chemical properties of the lakes did not appear to influence gastropod populations between lakes of different ages. Fish predation interactions did not indicate any significant influence either. However, the presence of boat ramps did indicate a positive relationship between average gastropod abundance and species richness and recreational lake use. Littoral zone macrophyte comparisons between dominant vegetation Typha and Panicum indicated a significantly positive relationship between gastropod species richness and average abundance in older phosphate lakes dominated by the more structurally complex Panicum macrophytes. Confidence in the Typha and Panicum results was confounded by lack of access to younger, Typha dominated, phosphate lakes. An increase in sample size for younger Typha lakes, with additional site access, may further support these findings.

Upper Klamath Lake in southern Oregon has two species of lacustrine suckers, Lost River sucker Deltistes luxatus and shortnose sucker Chasmistes brevirostris that were historically abundant. Results of surveys performed in the mid-1980's indicated that populations of both species were declining and ageing with apparent recruitment failure in most years since 1970. In 1988 both species were listed as endangered species and high priority has been placed on investigating recruitment of Upper Klamath Lake suckers. Lapilli are the preferred otolith for ageing suckers. Lapilli form predictably on the day of hatch, have the most conservative morphology of the three otoliths, and deposit easily discernable increments that begin on the day of hatch and proceed daily, and grow in a predictable relationship with somatic growth. Ages estimated by otolith analysis and resulting hatch dates of young-of-the-year Lost River sucker and shortnose sucker were consistent annually and consistent with reported spawning period for suckers from Upper Klamath Lake. Otolith increment analysis is necessarily lethal, whereas scale circuli analysis is not lethal. My findings suggest that scale circuli count is an inefficient estimator of daily Daily age estimates for age in young-of-the-year Lost River sucker and shortnose sucker. any given circuli count varied by approximately 51 days in Lost River sucker and 30 days Additionally, my results do not accurately predict the size or age at in shortnose sucker. which scales are formed, thereby invalidating an assumption of age and growth models. Consequently, scale circuli analysis cannot be used to produce accurate estimates of age or growth for young-of-the-year Lost River sucker and shortnose sucker. Lost River sucker and shortnose sucker achieve a relatively large size by the autumn of their first year, consistent with other members of Catostomidae. Interspecific difference in growth rates was evident in each year with Lost River sucker exhibiting faster growth than shortnose sucker in each year. Abundance of young-of-the-year suckers does not appear to be strongly correlated to somatic growth rate, though hatch date and environmental parameters are highly correlated with abundance. In both Lost River sucker and shortnose sucker, in years with the highest abundance (1991 and 1993), the mean hatch dates of surviving fish were later than in years with the lowest abundance. Also, young-of-the-year Lost River sucker and shortnose sucker experienced wide environmental fluctuations in Upper Klamath Lake as seasonal limnological and climatic variation create a dynamic habitat for young suckers. Water temperature, precipitation, air temperature, and minimum lake elevation are all strongly correlated to abundance of young-of-the-year suckers. / Graduation date: 1999

Created lakes are an end product of phosphate mining in Florida. Beginning in 1975, Florida reclamation rules set criteria for phosphate created lakes aiming to approximate the structure of natural lakes, and emphasizing extensive littoral zones with both emergent and submersed vegetation. Lake development relative to lake age and design were examined for 22 phosphate lakes representing a 40-year age trajectory, utilizing water quality and benthic invertebrate communities from littoral and deep-water locations (Chapter 1). The relative importance of morphometry and lake age in the development of littoral plant communities was examined using multiple vegetation surveys throughout the year, in a separate investigation of 39 littoral locations from 13 lakes reflecting age and morphometry gradients (Chapter 2). The same littoral locations were used to investigate benthic community composition in relation to emergent and submersed plant habitats (depth of 0.5 m and 1.5 m respectively), water quality, sediment characteristics, morphometry and lake age (Chapter 3). Phosphate lakes >5.5m deep are warm monomictic water bodies, stratifying from April to October/November, and developing thermoclines at approximately 4 m. Shallow lakes (<5.5 m deep) are polymictic. Phosphate lakes become eutrophic or hypertrophic immediately after creation and remain so through time. Unlike reservoirs, they do not go through a trophic surge, which is an initial period of great productivity that declines as sediment nutrient storage is exhausted. Among the 22 sampled lakes, epilimnetic physical and chemical water quality variables (Secchi depth, chlorophyll a, turbidity, pH) did not differ along the age trajectory. Only specific conductance declined significantly, 10-20 years after lake creation, most probably due to bank stabilization. All water quality variables were within the range of natural lakes in the region, and were most similar to urban rather than suburban or rural natural lakes. Benthic invertebrate abundance (total, Chironomidae, Oligochaeta, invertebrates other than Chironomidae and Oligochaeta) and taxa richness displayed great variability with lake age and did not differ among decadal lake groups at any depths examined (1 m, deepest point). Invertebrate abundance did not differ between littoral and deep habitats, except for lakes >10 years old, where littoral abundance was greater than deep-water abundace, suggesting faster colonization of the littoral zone. Littoral taxa richness was greater than richness in deep-water, which was attributed to taxa other than Chironomidae and Oligochaeta. Deep-water and most littoral habitats were dominated by Chironomidae, whereas Oligochaeta were occasionally dominant in the littoral zone. Dissolved oxygen was the variable explaining most variance of both littoral abundance and richness. Littoral macrophyte communities in phosphate lakes differed from natural Florida lakes. Although most phosphate lakes developed emergent littoral zones, submersed vegetation was absent, with few exceptions of the non-indigenous Hydrilla verticillata. Plants clustered in groups reflecting their hydrological designations. Frequently encountered plants classified either in the obligate wetland plant group, characterized by Typha, and inhabiting mostly intermediate-age lakes or the facultative wetland plant group, characterized by Panicum repens. Most plants in the latter group were bimodally distributed in youngest and oldest lakes, whereas few plants were ubiquitous. Littoral plant community composition was determined by both lake morphology and age, but the relative influence of these two components was not clear. Littoral plant composition was a good predictor of lake development. Morphometric (slope) and sediment characteristics (organic content, particle size) did not differ between the two littoral depths examined (0.5 m and 1.5 m). Slope correlated moderately but significantly with lake age, and organic content was low in all samples. Total littoral benthic invertebrate abundance and its major component Chironomidae, started from low values at newly created lakes and remained low or increased unpredictably with time. Total, Chironomidae, Oligochaeta and Gastropoda abundances did not differ between the depths of 0.5 m and 1.5 m, whereas taxa richness and the abundance of invertebrates other than Chironomidae, Oligochaeta, and Gastropoda was greater at the shallower depth (0.5 m).The relative effect of lake morphology versus age on benthic invertebrate composition was not clear. Total and Chironomidae abundance increased with lake age at 0.5 m, and bank slope at 1.5 m. Both littoral invertebrate abundance and richness in phosphate lakes were lower than in a natural, mesotrophic, macrophyte-dominated lake in the region, characterized by great Oligochaeta densities.