Effects of Increasing Chinook Salmon Bag Limits on Alewife Abundance: Implications for Lake Michigan Management Goals

Abstract

AbstractTo predict effects of modifying the daily bag limit (DBL) on management of Chinook salmon Oncorhynchus tshawytscha and alewives Alosa pseudoharengus, we analyzed harvest and effort data collected from both charter and noncharter anglers during 1997–2005 in Michigan waters of Lake Michigan. Overall, the percent of anglers who caught the DBL of three Chinook salmon was low for charter (10.2%) and noncharter (3.3%) angler groups. However, during 1997–2005, the percent of anglers that caught their DBL increased from 3.3% to 26.5% for charter anglers and from 0.5% to 7.8% for noncharter anglers. To predict harvest under a higher DBL, we fit a discrete negative binomial distribution to the observed daily harvest distribution under the current DBL of three fish. We then used the fitted negative binomial to predict the daily harvest distribution under a DBL of five fish. Using this approach, the potential increase in the number of fish harvested with the higher DBL was minimal, but the additional harvest showed an increasing 1997–2005 trend from 315 to 7,301 fish for charter anglers and from 450 to 18,151 fish for noncharter anglers. There was a positive linear relationship between proportion of anglers harvesting the current DBL and harvest rates, which indicates that angler success is a function of Chinook salmon abundance. Using an age‐structured deterministic population model and the production‐conversion efficiency method, we estimated potential reduction in annual lakewide consumption of alewives by Chinook salmon resulting from a higher DBL. The reduction in consumption averaged 313 metric tons and increased from 28 (1997) to 935 metric tons (2005). We conclude that higher DBLs would have a relatively minor impact on lakewide forage fish abundance but would be more consistent with current management objectives.