Spatial Distributions Of Lake Erie Walleye

Author : Mark R. DuFour
Publisher :
ISBN 13 :
Total Pages : 163 pages
Book Rating : 4.:/5 (17 download)

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Download or read book Hydroacoustic Quantification of Lake Erie Walleye (Sander Vitreus) Distribution and Abundance written by Mark R. DuFour and published by . This book was released on 2017 with total page 163 pages. Available in PDF, EPUB and Kindle. Book excerpt: This work was motivated to improve understanding of Lake Erie walleye (Sander vitreus) distribution and abundance. Lake Erie walleye are large migratory fish that are ecologically and economically important within the Great Lakes region. The population is monitored partly through a fishery independent gill net survey carried out by the Ohio Department of Natural Resources - Division of Wildlife (ODNRDOW). However, high variation in annual CPUE has interfered with this survey's ability to identify changes in walleye abundance. Therefore, the ODNR-DOW was interested in the potential of coupling hydroacoustic sampling with the existing gill net survey to quantify Lake Erie walleye distribution and abundance. In this dissertation I address four major questions that helped optimally couple hydroacoustic and gill net surveys. In Chapter 1, I evaluated the impact of beam compensation on surveyed target strength (TS) data. I found that using an intermediate beam compensation (18 dB), greater than conventionally suggested (6 dB), provided a higher quantity of TS data with minimal impact on TS data quality. Increased beam compensation led to higher encounter rates and more TS data per fish, which ultimately provided a better characterization of the low density walleye population. In Chapter 2, I evaluated the influence of vessel size and day-night period on the availability of the walleye population to a hydroacoustic survey. I found that walleye were less likely to avoid smaller sampling vessels, but the vessel size effect decreased with depth. Also, during the fall period of the gill net survey, walleye were more available to hydroacoustic sampling at night. Finally, although vessel size and day-night sampling period are important logistical consideration, capturing spatial distributions across the survey should be prioritized in future surveys. In Chapter 3, I compared gill net catch-per-unit-effort (CPUE) and hydroacoustic abundance estimates from across a large survey area with varied environmental conditions. I found that the relationship between gill net CPUE and abundance changed across the survey along environmental gradients. This indicated that sub-optimal catchability and gear efficiency in the gill net survey limits its ability to quantify changes in abundance, and adding a hydroacoustic component to this survey would be beneficial. In Chapter 4, I developed a method to infer species composition of the hydroacoustic data while addressing many apportionment challenges, such as: limited and variable species composition data, subjective threshold decisions, and uncertainty in mean TS estimates. This method improved species composition estimates, propagated uncertainty from both sampling methods, and eliminated subjective threshold decisions. Distribution estimates corresponded with known patterns of walleye movements and ecology, while survey-wide estimates were comparable to independent estimates based on annual stock assessments. Using the methods outlined here in, hydroacoustics could be successfully coupled with the existing ODNR-DOW gill net survey to improve quantification of Lake Erie walleye distribution and abundance.