Song S. Qian
Christine M Mayer
Christopher Vandergoot
Mark R. DuFour
2020
<div id="abstracts" class="Abstracts u-font-serif"><div id="abs0010" class="abstract author"><div id="abst0010"><p id="spar0080">Abundance estimates facilitate successful fisheries management. Fisheries agencies often monitor abundance through fishery independent standardized protocols generating relative measures such as catch-per-unit-effort (CPUE), where CPUE is assumed proportional to true abundance. Unfortunately, this assumption is rarely met as fish behavior and environmental conditions influence catchability and sample gear efficiency. We used paired gillnet and hydroacoustic samples and a catchability equation (<span class="math"><span id="MathJax-Element-1-Frame" class="MathJax_SVG" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><msub is="true"><mi is="true">U</mi><mi is="true">i</mi></msub><mtext is="true"></mtext><mo is="true">=</mo><mtext is="true"></mtext><mi is="true">q</mi><msubsup is="true"><mi is="true">N</mi><mi is="true">i</mi><mi is="true">&#x3B2;</mi></msubsup></math>"><span class="MJX_Assistive_MathML">U<sub>i</sub>=qN<sub>i</sub><sup>β</sup></span></span></span>) to assess the correspondence between gillnet CPUE (<span class="math"><span id="MathJax-Element-2-Frame" class="MathJax_SVG" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><msub is="true"><mi is="true">U</mi><mi is="true">i</mi></msub></math>"><span class="MJX_Assistive_MathML">U<sub>i</sub></span></span></span>) and hydroacoustic abundance estimates (<span class="math"><span id="MathJax-Element-3-Frame" class="MathJax_SVG" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><msub is="true"><mi is="true">N</mi><mi is="true">i</mi></msub></math>"><span class="MJX_Assistive_MathML">N<sub>i</sub></span></span></span>). We found that gill nets were hyperstable (i.e., β < 1) and efficiency declined along environmental gradients. These gradients, such as increased depths, and decreased turbidity and water temperatures, likely influenced fish behavior, and encounter and gear saturation rates. As a result, catchability declined with increasing abundance qacross survey regions. Finally, simulations showed that catchability gradients and variable migratory patterns can contribute to annual variation in CPUE indices regardless of changes in abundance. Surveys plagued by varying catchability could benefit from coupling with hydroacoustics, a sample gear less subject to gear efficiency and catchability issues.</p></div></div></div><ul id="issue-navigation" class="issue-navigation u-margin-s-bottom u-bg-grey1"></ul>
application/pdf
10.1016/j.fishres.2018.11.009
en
Elsevier
Evaluating catchability in a large-scale gillnet survey using hydroacoustics: Making the case for coupled surveys
article