PARENT SESSION
Oral Session # 39: Limnology I: Ecosystems, Eutrophication, and Restoration.
Presiding: KL Cottingham
Wednesday, August 6. 8:00 AM to 11:30 AM, SITCC Meeting Room 101.
A field-test of the unimodal relationship between fish growth and macrophyte cover in lakes.
Spence Cheruvelil, Kendra*,1, Nate, Nancy1, 2, Soranno, Patricia1, Bremigan, Mary1, 1 Michigan State University, East Lansing, MI, spencek1@msu.edu2 Wisconsin Department of Natural Resources, Madison, WI
ABSTRACT- Macrophytes serve a dual role for fish in lakes. They provide a substrate for macroinvertebrate populations, which are the primary food source for many young fish, and they provide refuge from predators. Therefore, many foodweb interactions among fish are mediated by macrophytes. Since the influential paper by Crowder and Cooper in 1982, the idea accepted by both researchers and fisheries managers is that there is an optimal intermediate macrophyte cover for fish growth and foraging in lakes. Some small-scale experimental studies of largemouth bass and bluegill have found that bass foraging success is poor at high levels of macrophyte cover. In addition, although many southern U.S. reservoir studies have shown that macrophyte cover >10% promotes young-of-year bass abundance, moderate cover levels (40-60%) have been correlated with poor growth and low piscivory, and overall variability has been quite high. This high variability, and the fact that few whole-lake tests of this relationship have been conducted in north temperature lakes, has resulted in no clearly defined optimal range of macrophyte cover for bass and bluegill growth. Therefore, we performed a field test of this idea using 39 lakes in Michigan, U.S. We sampled macrophyte cover at the whole-lake scale in 2001 and 2002 (range of cover = 18-84%), and we assessed fish growth by calculating length at age for largemouth bass and bluegill using existing datasets from the MI Department of Natural Resources collected in the 1990s. Relationships between fish growth for each age class and macrophyte cover were analyzed for the 39 lakes using nonlinear and linear regression. We did not find strong evidence to support the idea of an optimal intermediate macrophyte cover for largemouth bass or bluegill growth rates. However, we did find that for bluegill ages 5-8, there were significant negative relationships between growth and macrophyte cover.
Key words: fish growth, macrophyte cover, lakes