Sensitivity of fish density estimates to standard analytical procedures applied to Great Lakes hydroacoustic data

Kočovský, Patrick M.; Rudstam, Lars G.; Yule, Daniel L.; Warner, David M.; Schaner, Ted; Pientka, Bernie; Deller, John W.; Waterfield, Holly A.; Witzel, Larry D.; Sullivan, Patrick J.

doi:10.1016/j.jglr.2013.09.002

Cited by 19 publications

(21 citation statements)

References 27 publications

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“…), including Rainbow Smelt Osmerus mordax , which are the dominant forage fish in the Central and East basins (Kocovsky et al. ; Thomas et al. ) and are known to exhibit DVM to track preferred light regimes (Appenzeller and Leggett ).…”

Section: Discussionmentioning

confidence: 99%

Vertical Habitat Use by Adult Walleyes Conflicts with Expectations from Fishery‐Independent Surveys

et al. 2019

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Stock assessments of Walleyes Sander vitreus in Lake Erie rely on a combination of suspended and bottom overnight gill-net surveys to provide population and demographic information. However, the assumption that Walleyes undertake diel vertical migrations and become available to the suspended gill nets at night has never been validated. To understand how vertical habitat use affects the availability of Walleyes to fishery-independent surveys, we compared individual behaviors observed by means of acoustic depth telemetry tags (20 individuals; 2013-2016) with catches in paired suspended and bottom gill-net sets (273 paired sets; 2013-2016) used by management agencies. In contrast to our expectations and observations in other lakes, the mean depths for Walleyes most often occurred in the lower one-half to one-third of the water column, and at lake depths <25 m the fish tended to be close to the bottom. The relationship between fish and lake depth was dependent on year and season. At lake depths >15 m, Walleyes were found at shallower depths during stratified periods (i.e., summer) than during unstratified periods (autumn). They were also found at shallower depths in 2015 and 2016 than in 2013 and 2014. In paired autumn gill-net surveys, (1) the overall proportion of Walleye catch was nearly equal in suspended and bottom gill nets and (2) the proportion of the catch in suspended gill nets declined with fish length. The pattern of decline was dependent on how deep the suspended net was fished and the year in which the data were collected. These results provide evidence that the suspended gill-net surveys currently being used to assess Walleye demographics in Lake Erie are biased toward the capture small Walleyes, while bottom nets are biased toward the capture of large ones. Future telemetry investigations will be needed to understand whether these biases reflect differences in the depth of habitat between small and large Walleyes. GORMAN ET AL.

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Section: Discussionmentioning

confidence: 99%

Vertical Habitat Use by Adult Walleyes Conflicts with Expectations from Fishery‐Independent Surveys

et al. 2019

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“…In addition, TS estimates are highly variable (McClatchie et al 1996), therefore, at times estimates may be based on both sparse and variable data. Conventional data analysis methods (Rudstam et al 2009;Parker-Setter et al 2009;Kocovsky et al 2013) restrict data to a subset of high quality (i.e., accurate and precise) TS estimates collected near the acoustic beam axis, within the 3 dB beam width (i.e., 6 dB two-way beam width; Simmonds 1984;Simmonds and MacLennan 2005). While the practice of limiting data quantity is intended to ensure quality, the net effect may reduce accuracy and precision of population level estimates due to small sample size, especially when fish are sparsely distributed.…”

Section: Introductionmentioning

confidence: 99%

Sparse targets in hydroacoustic surveys: Balancing quantity and quality of in situ target strength data

et al. 2017

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Hydroacoustic sampling of low-density fish in shallow water can lead to low sample sizes of naturally variable target strength (TS) estimates, resulting in both sparse and variable data. Increasing maximum beam compensation (BC) beyond conventional values (i.e., 3 dB beam width) can recover more targets during data analysis; however, data quality decreases near the acoustic beam edges. We identified the optimal balance between data quantity and quality with increasing BC using a standard sphere calibration, and we quantified the effect of BC on fish track variability, size structure, and density estimates of Lake Erie walleye (Sander vitreus). Standard sphere mean TS estimates were consistent with theoretical values (-39.6 dB) up to 18-dB BC, while estimates decreased at greater BC values. Natural sources (i.e., residual and mean TS) dominated total fish track variation, while contributions from measurement related error (i.e., number of single echo detections (SEDs) and BC) were proportionally low. Increasing BC led to more fish encounters and SEDs per fish, while stability in size structure and density were observed at intermediate values (e.g., 18 dB). Detection of medium to large fish (i.e., age-2+ walleye) benefited most from increasing BC, as proportional changes in size structure and density were greatest in these size categories. Therefore, when TS data are sparse and variable, increasing BC to an optimal value (here 18 dB) will maximize the TS data quantity while limiting lower-quality data near the beam edges.

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“…; Kocovsky et al. ). Analytical decisions made during data analysis include determining cell sizes, single target detection settings, how to group targets, and how best to estimate density or biomass of the target species of interest, among others.…”

Section: Summary Of the Hydroacoustic Protocol Settings Used To Genermentioning

confidence: 98%

Hydroacoustic Data‐Analysis Recommendations to Quantify Prey‐Fish Abundance in Shallow, Target‐Rich Ecosystems

Dillon

Conroy

Ludsin

2019

N American J Fish Manag

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Standardized sampling methods can benefit fisheries management by facilitating a comparison of fish abundance estimates within and among ecosystems. Towards developing an improved standardized hydroacoustic method for estimating prey-fish abundance and target strength in small (surface areas <15 km 2 ), shallow (maximum depths <20 m), freshwater ecosystems (e.g., north-temperate reservoirs), we evaluated how the incorporation of several recommended hydroacoustic data-analysis procedures from the Great Lakes Standard Operating Procedures (GLSOP) into an existing hydroacoustic protocol used in north-temperate reservoirs influenced estimates of prey-fish abundance. To facilitate our evaluation, we conducted hydroacoustic surveys in four Ohio reservoirs during August 2016 and then compared prey-fish abundance estimates generated from the existing Ohio Department of Natural Resources, Division of Wildlife reservoir protocol with those that included three GLSOP recommendations separately and in combination. The three recommendations were (1) removal of background noise, (2) use of a lower maximum beam compensation (MBC) setting, and (3) application of the Sawada index (N v ) to identify and replace biased, in situ, cell-specific target strengths. Our analyses showed that the removal of background noise (À0.1% to 0% change) and application of N v (À7.8% to 0% change) had little substantive effect. However, decreasing the MBC from 12 to 6 dB significantly reduced prey-fish abundance estimates (4.1% to 16.1% decrease). When we simultaneously applied all three GLSOP recommendations, estimated prey-fish abundance consistently decreased (À8.8 to À16.0%) across reservoirs. Collectively, our findings suggest the need for incorporation of several GLSOP data-analysis procedures into protocols developed for shallow, target-rich ecosystems, such as Ohio reservoirs. By doing so, more precise estimates of fish abundance can be generated to the benefit of fisheries management.

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Sensitivity of fish density estimates to standard analytical procedures applied to Great Lakes hydroacoustic data

Cited by 19 publications

References 27 publications

Vertical Habitat Use by Adult Walleyes Conflicts with Expectations from Fishery‐Independent Surveys

Vertical Habitat Use by Adult Walleyes Conflicts with Expectations from Fishery‐Independent Surveys

Sparse targets in hydroacoustic surveys: Balancing quantity and quality of in situ target strength data

Hydroacoustic Data‐Analysis Recommendations to Quantify Prey‐Fish Abundance in Shallow, Target‐Rich Ecosystems

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