Food Web Constraints on Chinook Salmon Recruitment in a Large Lake Michigan Tributary.

Natural reproduction of Chinook salmon now supplies half of all recruits to the Lake Michigan sport fishery but may vary greatly due to environmental variability and biotic interactions in tributary nursery areas. From 2004 to 2007, I evaluated the relative effect of predation by stocked sport fish species on Chinook salmon recruitment variability in the Muskegon River, a large Lake Michigan tributary. Together, walleye and brown trout annually consumed from 17 to 47% of available Chinook salmon parr. Although brown trout consumed large quantities of Chinook parr, I found that hatchery trout dominated walleye diets. Walleye were size-selective for small hatchery trout but prey size was independent of predator size. In general, walleye showed neutral selection for prey species although they positively selected for rainbow trout and selected against Chinook parr in some years. Brown trout consumed smaller-than-average Chinook salmon parr although prey size was also independent of predator size. Chinook parr were positively selected as prey by brown trout but only in April when parr were < 40 mm in length. The presence of alternate prey significantly influenced walleye predation on Chinook salmon parr while brown trout appeared to be limited by Chinook size. I developed a functional response model using a Type-II curve for walleyes and a Type-I curve for brown trout to varying abundances of prey. Brown trout had the greatest impact on Chinook salmon recruitment based on their feeding behavior and consumption rates. Management efforts to reduce brown trout abundance via stocking could increase short-term survival of Chinook salmon parr by up to 31%. To assess long-term predation effects on Chinook recruitment from the Muskegon River, I used a stage-based matrix model (RAMAS Stage) parameterized with empirically-derived estimates of Chinook salmon growth, survival, abundance and fecundity. I simulated variable fry-to-smolt survival rates using 26 theoretical predator regimes and compared the results to baseline (i.e. observed) values. Only scenarios that involved removal of brown trout significantly increased long-term Chinook salmon recruitment. Based on the results of my dissertation research, I recommend elimination of brown trout stocking in all tributaries that produce Chinook salmon parr.Ph.D.Natural Resources and EnvironmentUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/75804/1/damonkr_1.pd

Influence of Predation Mortality on Survival of Chinook Salmon Parr in a Lake Michigan Tributary

Predation mortality among Chinook salmon Oncorhynchus tshawytscha parr can act at small spatiotemporal scales and cause variability in parr survival and potential recruitment. We analyzed predator diets and multiplied per capita consumption rates by predator population estimates to evaluate the relative effect of predation by stocked sport fishes on the variability in survival of Chinook salmon parr in the Muskegon River, Michigan, from 2004 to 2007. Brown trout Salmo trutta were a major predator of Chinook salmon parr, consuming from 15% to 34% of the total number available, while walleyes Sander vitreus consumed from 0.2% to 15%. Walleyes also consumed large quantities of brown trout and rainbow trout O. mykiss. Brown trout predation on Chinook salmon parr was largely dependent on parr size, while walleye predation was buffered by the availability of rainbow trout and brown trout. Predation mortality appeared to be responsible for a more than three‐fold difference in the survival of Chinook salmon parr in the Muskegon River. The vulnerability of Chinook salmon parr to predation appeared to be controlled by parr growth rates, brown trout stocking dates, and the number of brown trout stocked. Fishery regulations to manipulate piscivore abundance may lead to higher survival and lower variability in the survival of Chinook salmon parr.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141027/1/tafs0147.pd

Alewife planktivory controls the abundance of two invasive predatory cladocerans in Lake Michigan

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74873/1/j.1365-2427.2007.01728.x.pd

Sampling a Littoral Fish Assemblage: Comparison of Small-Mesh Fyke Netting and Boat Electrofishing

We compared small-mesh (4-mm) fyke netting and boat electrofishing for sampling a littoral fish assemblage in Muskegon Lake, Michigan. We hypothesized that fyke netting selects for small-bodied fishes and electrofishing selects for large-bodied fishes. Three sites were sampled during May (2004 and 2005), July (2005 only), and September (2004 and 2005). We found that the species composition of captured fish differed considerably between fyke netting and electrofishing based on nonmetric multidimensional scaling (NMDS). Species strongly associated with fyke netting (based on NMDS and relative abundance) included the brook silverside Labidesthes sicculus, banded killifish Fundulus diaphanus, round goby Neogobius melanostomus, mimic shiner Notropis volucellus, and bluntnose minnow Pimephales notatus, whereas species associated with electrofishing included the Chinook salmon Oncorhynchus tshawytscha, catostomids (Moxostoma spp. and Catostomus spp.), freshwater drum Aplodinotus grunniens, walleye Sander vitreus, gizzard shad Dorosoma cepedianum, and common carp Cyprinus carpio. The total length of fish captured by electrofishing was 12.8 cm (95% confidence interval ¼ 5.5– 17.2 cm) greater than that of fish captured by fyke netting. Size selectivity of the gears contributed to differences in species composition of the fish captured, supporting our initial hypothesis. Thus, small-mesh fyke nets and boat electrofishers provided complementary information on a littoral fish assemblage. Our results support use of multiple gear types in monitoring and research surveys of fish assemblages. Copyright by the American Fisheries Society 2007, Originally published in the North American Journal of Fisheries Management 27: 825-831, 2007