Greg G. Sass

Fish Community and Food Web Responses to a Whole-lake Removal of Coarse Woody Habitat

Abstract As lakeshores are developed, property owners often thin the riparian forest and remove older logs or fallen limbs from the adjacent littoral zone. This practice alters fish habitat and produces unknown ecosystem changes. To assess potential effects on fish communities and food web interactions, we removed more than 75% of the coarse woody habitat (CWH) from the treatment basin of Little Rock Lake, Wisconsin, while leaving the reference basin unaltered. Prior to CWH removal, the food webs in both basins were similar and dominated by aquatic prey. After CWH removal, largemouth bass (Micropterus salmoides) in the treatment basin consumed less fish, ate more terrestrial prey, and grew more slowly relative to the population in the reference basin. Yellow perch (Perca flavescens) in the treatment basin declined to extremely low densities as a consequence of predation and little or no recruitment. In contrast, perch in the reference basin were replenished by several successful cohorts produced in consec...

Prospects for Fishery-Induced Collapse of Invasive Asian Carp in the Illinois River

ABSTRACT Invasive Asian Carp are threatening to enter Lake Michigan through the Chicago Area Waterway System, with potentially serious consequences for Great Lakes food webs. Alongside efforts to keep these fishes from entering Lake Michigan with electric barriers, the state of Illinois initiated a fishing program aimed at reducing their densities through intensive commercial exploitation on the Illinois River. In this study, we explore prospects for the “collapse” of Asian Carp in the Illinois River through intensive fishing. Based on a meta-analysis of demographic data, we developed a dynamic simulation model to compare the performance of existing and alternative removal strategies for the Illinois River. Our model projections suggest that Asian Carp in the Illinois River are unlikely to collapse if existing harvest rates are kept below 0.7 or fishing continues to be size selective (targeting only fish >500 mm or <500 mm) or species selective (targeting mostly Bighead Carp), although their biomasses cou...

The role of density dependence in growth patterns of ceded territory walleye populations of northern Wisconsin: Effects of changing management regimes

Abstract We assessed density-related changes in growth of walleye Sander vitreus in the ceded territory of northern Wisconsin from 1977 to 1999. We used asymptotic length (L ∞), growth rate near t 0 (ω), and body condition as measures of walleye growth to determine the relationship between growth and density. Among lakes, there was weak evidence of density-dependent growth: Adult density explained only 0–6% of the variability in the growth metrics. Within lakes, growth was density dependent, L ∞, ω, and body condition of walleyes changing with density for 69, 28, and 62% of the populations examined, respectively. Our results suggest that walleye growth was density dependent within individual lakes. However, growth was not coherently density dependent among lakes, which was possibly due to inherent differences in the productivity, surface area, forage base, landscape position, species composition, and management regime of lakes in the ceded territory. Densities of adult walleyes averaged 8.3 fish/ha and di...

Effects of Water Hardness on Size and Hatching Success of Silver Carp Eggs

Abstract Eggs of silver carp Hypophthalmichthys molitrix absorb water after release from the female, causing them to become turgid and to increase substantially in size. The volume of water that diffuses within an egg is most likely determined by (1) the difference in ionic concentration between the egg and the water that surrounds it and (2) the elasticity of the egg membrane. Prior observations suggest that silver carp eggs may swell and burst in soft waters. If water hardness affects silver carp reproductive success in nonnative ecosystems, this abiotic factor could limit silver carp distribution or abundance. In this study, we tested the effect of water hardness on silver carp egg enlargement and hatching success. Groups of newly fertilized silver carp eggs were placed in water at one of five nominal water hardness levels (50, 100, 150, 200, or 250 mg/L as CaCO3) for 1 h to harden (absorb water after fertilization). Egg groups were then placed in separate incubation vessels housed in two recirculation...

Inland Fisheries Habitat Management: Lessons Learned from Wildlife Ecology and a Proposal for Change

The habitat concept in inland fisheries has been less studied than wildlife ecology. Since 1950, the cumulative number of publications about “freshwater or inland habitat and fisheries management” has been 60%–95% less than those considering “habitat and wildlife management.” The number of publications about “marine, river, and stream habitat and fisheries management” has also generally exceeded those for “lake habitat and fisheries management.” We provide a perspective comparing inland fish and wildlife habitat management systems and highlight lessons from wildlife ecology that could benefit inland fisheries. We reason that wildlife habitat management has become widespread and accepted because humans share habitats with wildlife and positive/negative responses to habitat restorations/loss are directly observable. We recommend that inland fisheries habitat studies and restorations include opportunities for humans to directly observe the ecological benefits of such practices. To support aquatic habitat man...