Date of Award
Master of Science
Walleye (Sander vitreus) culture for maintenance stocking in lakes has always been fraught with challenges. Their propensity to cannibalize at an early age and their reluctance to accept a prepared diet make the production of advanced fingerlings extremely costly. Hatchery reared walleye fingerlings are extremely vulnerable to predation when stocked into impoundments with established fish populations. This study was conducted to determine if fish culturists could increase walleye survival by exposing summer fingerlings to fish predators and/or providing experience with piscivory before being stocked for recreational angling. Tank studies were conducted to minimize environmental variation among experimental treatments and replicates. In 2005, 5 treatment groups were tested, including a group that was allowed to feed on zooplankton only, a group that was habituated to feed, a group that was exposed to a fish predator, a group that was given an opportunity to prey on fish, and a group that was exposed to a fish predator and given an opportunity to prey on fish. In 2006, the feed habituated group was lost to disease, but a feed habituated group that was given experience avoiding fish predators and opportunity to forage on fish prey and a feed habituated group that was given opportunity to forage on fish prey were added. Walleye fingerlings from the 5 treatment groups in 2005 were placed in tanks with cover and a 250 mm largemouth bass as a predator. Walleye survival was measured after 24 hours; no significant differences in survival were detected among treatment groups in 2005. In 2006, 10 walleye fingerlings from each of the 6 treatment groups were added to tanks fitted with a cedar reef for cover and two 250 mm largemouth bass. Fingerling walleye survival was highest in the feed habituated prey exposed group and the feed habituated predator and prey exposed group after 14 days; higher survival in these groups may have been due to their larger initial size. Pond studies were also conducted in 2005 and 2006 to evaluate differences in survival among treatment groups under conditions that more closely resemble environments into which fingerling walleye are stocked. Twelve 0.4-hectare ponds were prepared by placing 15 adult bluegill (~200 mm total length) and 5 adult largemouth bass (~300 mm total length) into each pond along with a 6.5 m cedar reef for cover. Survival of fingerling walleye in ponds was measured on days 3, 7, 15, 30, 60, 90, and 120 post-stocking. Pond and tank trials indicated no apparent post-stocking increase in survival for walleye fingerlings that were given prior exposure to predators or fish prey. Additionally, a multiple batch tagging / marking procedure was needed to separate walleye fingerling groups in ponds and tanks. Visible Implant Elastomer (VIE) tags and liquid nitrogen freeze brands were chosen and retention rates were determined for fingerling walleye, as little published information on retention rates for these techniques was available. VIE tags were lost steadily over time (41.67% retention at 270 days), while freeze branding showed much better retention (87.88% retention at 270 days).
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