Factors influencing the hooking mortality of walleyes caught by recreational anglers on Mille Lacs,

Abstract.-Recent implementation of size-based regulations in recreational fisheries for walleye Sander vitreus have led to more released walleyes and presumably to more losses of released fish. We conducted this study to estimate hooking mortality in Mille Lacs, Minnesota, and to determine factors that influence the survival of released walleyes. Volunteers and Minnesota Department of Natural Resources employees sampled walleyes with common angling methods in 2003 and 2004 on Mille Lacs (n ¼ 1,246). Simple hooking mortality rates ranged from 0% (95% confidence interval ¼ 0-1.8%; n ¼ 204) in May, when lake water temperatures were less than 208C, to 12.2% (9.2-15.9%; n ¼ 392) in the July-August period, when lake water temperatures were at least 208C. We used logistic regression within generalized linear or additive models to determine influential variables. Hooking mortality was most associated with water temperature, bleeding, fish length, hook location, and fish floating upon release. Mortality increased as the water warmed above 188C and was higher for fish that bled at temperatures less than 248C but similar for both bleeding and nonbleeding fishes at temperatures of 248C or more. Fish hooked in the throat or stomach died at higher rates than fish hooked in the jaw, inner mouth, or gills and those that were externally foul-hooked, especially when they were smaller. Although fish of medium length (300-600 mm) were more likely to be deep hooked, they died less frequently than walleyes of other lengths. Cutting the line did not significantly improve survival in deeply hooked fish. Mortality was similar between live bait jigs and live bait regular hooks. Most observed hooking mortality was caused by damage to major internal organs. Hooking mortality is minimized when anglers fish in cool water, use active fishing methods, and catch medium-length walleyes

Population Dynamics and Movement of a Burbot (Lota lota) in Western Lake Michigan and Green Bay

I estimated population statistics, movement, and potential yield of burbot (Lota lota) in Wisconsin waters of Green Bay and Lake Michigan. After decimation by the sea lamprey (Petromyzon marinus), burbot have rebounded in the lake and are an abundant piscivore in Green Bay. In summers 1987 and 1988 6730 burbot in Green Bay and 195 in northwestern Lake Michigan were tagged and released. Additional burbot (4008) were collected from September, 1986 through October, 1989 and used for aging and calculating length-weight relations. Mean back-calculated lengths at age, determined from whole otoliths, showed curvilinear growth, rapid at early ages and nearing an asymptote by age 16 (66 cm). Females grew faster than males after age 2, and overlap in size ranges of each age class was evident for both sexes after age 1. Growth in length was similar throughout the lake and bay, but length-weight relations differed (ln(W)=3.021 ln(L)-11.82, Green Bay and Lake Michigan East of Door County, Wisconsin; ln(W)=3.27 ln(L)-13.26, Lake Michigan south of Door County, Wisconsin). In Green Bay, smaller burbot (<40 cm) were found in waters averaging 11-13°c, and larger burbot were found in waters averaging 9-10°c. Most of the tagged burbot were caught in waters deeper than 15 m, and bloated when the nets were brought to the surface. Bloated burbot were deflated by puncturing the gas bladder with the tagging needle. Handling mortality was low in both years of tagging (1-3%). Tag loss was 7 to 11% annually. Tag returns (431) revealed movement from Green Bay to Lake Michigan, but no burbot tagged in the lake were recaptured in the bay. Twenty-seven percent of the recaptured burbot had moved from the tagging areas. Mortalities in Lake Michigan (A=.52, u=.17 -- east of Door County, Wisconsin; A=.46, u=.08 -- east of Milwaukee, Wisconsin area) were calculated from catch curve analysis and mark/recapture data; in Green Bay mortalities (A=.59, u=.26) were estimated solely from mark/recapture data. The estimated size of the catchable burbot population in the Wisconsin waters of Green Bay in 1988 was 181,407 (±70,908 SD), a density of 0.82 burbot/ha. Burbot were most abundant in areas north of sturgeon Bay, Wisconsin, as dense as 75 (59 to 95) burbot/ha. Burbot were recruited into the drop net, trap net, and large-mesh gill net fishery at age 5 in Lake Michigan and age 6 in Green Bay. Yield and potential yield were low for both Lake Michigan and Green Bay, less than half of what was recruited.University of Wisconsin Sea Gran

Reservoir Fish Escapement in North America: A Historical Review and Future Directions

Downstream escapement of fishes from reservoirs via release structures can represent a loss to populations comparable to natural and harvest mortality. Consequently, quantifying and managing fish escapement is a critical component of sustainable reservoir fish management. We reviewed existing literature to assess the state of knowledge of reservoir fish escapement and found 57 unique papers published from 1942 through 2021. Early studies of escapement sought to evaluate escapement by directly capturing fish below release structures. More recently, advances in technology have enabled more detailed studies on factors influencing escapement and the influence it has on regulating reservoir fisheries. Evaluations have occurred throughout North America, assessing escapement of 49 species through a number of different outlet structures. Annual escapement estimates ranged from 0-100% and escapement tended to be higher from spillways and surface release outlets compared to other outlets. Further, smaller bodied individuals tended to escape at higher rates than larger fish and escapement was generally positively related to reservoir discharge metrics. Sixteen papers assessed benefits of physical and non-physical barriers for reducing reservoir fish escapement and determined barriers were effective for retaining fish in reservoirs. We conclude by describing management options to address escapement as well as three pressing research needs that will broaden the existing knowledge base regarding fish escapement. In light of predicted changes in precipitation events and subsequent adaptations to reservoir management, quantifying and mitigating fish escapement will be a critical component of sustainable reservoir fish management in the future.This is the peer-reviewed version of the following article: Lewis, Madeline C., W. Robert Cope, Thomas P. Miles, Claire Rude, Richard E. Bruesewitz, Benjamin J. Dodd, Mark K. Flammang et al. "Reservoir Fish Escapement in North America: A Historical Review and Future Directions." North American Journal of Fisheries Management, which has been published in final form at DOI: 10.1002/nafm.10790. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving. Copyright 2022 American Fisheries Society. Posted with permission

Global patterns and drivers of ecosystem functioning in rivers and riparian zones

Abstract River ecosystems receive and process vast quantities of terrestrial organic carbon, the fate of which depends strongly on microbial activity. Variation in and controls of processing rates, however, are poorly characterized at the global scale. In response, we used a peer-sourced research network and a highly standardized carbon processing assay to conduct a global-scale field experiment in greater than 1000 river and riparian sites. We found that Earth’s biomes have distinct carbon processing signatures. Slow processing is evident across latitudes, whereas rapid rates are restricted to lower latitudes. Both the mean rate and variability decline with latitude, suggesting temperature constraints toward the poles and greater roles for other environmental drivers (e.g., nutrient loading) toward the equator. These results and data set the stage for unprecedented “next-generation biomonitoring” by establishing baselines to help quantify environmental impacts to the functioning of ecosystems at a global scale