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Spirit Lake, IA, United States

Meerbeek J.R.,22 252nd Avenue | Hawkins K.A.,22 252nd Avenue
North American Journal of Fisheries Management | Year: 2013

The primary assumption of using back-calculated length-at-age (BCL) methods to estimate fish growth is that the body length and hard-part radius relationship is linear. Therefore, standardized techniques are required for BCL methods to be comparable over time. Recent studies have found that unsectioned dorsal spines of Sander spp. improve efficiency and provide accurate age estimates. We evaluated a simple, standardized method of using unsectioned Walleye S. vitreus (N = 162) dorsal spines to estimate age and BCL (direct-proportion and Fraser-Lee methods) by comparing these estimates with those of a sectioned spine technique. We validated the technique by comparing observed growth (measured via a mark-recapture study) with BCL growth estimated via sectioned and unsectioned techniques. The time required to process, prepare, view and perform BCL for each of the two techniques was also compared. Both reader age estimates and exact reader agreement rates were significantly better using the sectioned spine technique. Age frequencies varied significantly among readers and techniques as differences ranged up to 8 years. No difference was detected among the slopes of the back-calculation methods among techniques, but there were significant differences in the mean BCL estimates for ages < 10 years old. The relationships between observed growth and growth estimated via BCL methods were significant; however, BCL methods significantly overestimated Walleye growth. Total processing time for the unsectioned technique was significantly less, but based on our poor ability to replicate ages, we do not suggest the use of our standardized unsectioned spine technique to estimate the age or BCL older Walleye. In addition, no BCL method accurately estimated annual growth regardless of technique or reader experience. We conclude that more research is necessary to validate dorsal spine-based BCL estimates on Walleye populations. Once validated, further research evaluating new or modifying our technique for unsectioned Walleye spines needs to be explored. © 2013 Copyright Taylor and Francis Group, LLC. Source

Meerbeek J.R.,22 252nd Avenue | Larscheid J.G.,22 252nd Avenue | Hawkins M.J.,22 252nd Avenue | Scholten G.D.,22 252nd Avenue
North American Journal of Fisheries Management | Year: 2013

We evaluated the effects of fish length, fish sex, and number of days posttagging on retention of large-format, soft visible implant (VI) alphanumeric tags that were injected underneath the clear tissue on the lower mandible of Walleyes Sander vitreus. We also evaluated whether the direction of insertion or the application of surgical-grade tissue adhesive to the tag incision site would affect tag retention. Adult Walleyes were collected with gill nets from natural lakes in Iowa during spring and then were transported to a hatchery, where they were measured, sexed, and tagged. One worker injected 752 Walleyes (mean TL = 21.8 in; SE = 0.16) with two identical VI tags; each side (left and right) of the lower mandible received one tag. Incisions were dried with a cloth, and tissue adhesive was applied to one of the two tag injection sites. Walleyes were released back into the lake and were recaptured with gill nets and by anglers. Of the 129 Walleyes recaptured up to 5 years posttagging, 80 fish (62%) had retained both tags and the remaining 49 fish had retained one of the tags. Retention adjusted for fish that lost both tags (n = 8; probability = 0.09) was 58% (80 of 137). Tag retention was significantly related to fish size at the time of tagging, as smaller fish lost more tags. Consequently, males (mean TL = 20.5 in; SE = 0.39) were more likely to lose tags than females (mean TL = 24.3 in; SE = 0.26). Insertion direction, adhesive application, or the number of days posttagging at recapture did not influence VI tag retention. We recommend that in studies requiring high tag retention in Walleyes, the injection of large-format, soft VI tags into the clear tissue underneath the mandible should not be considered. © 2013 Copyright Taylor and Francis Group, LLC. Source

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