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If you have any questions on the information presented, or require additional report data or attachments, please contact the Report Contact
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The BC Steelhead Harvest Analysis (SHA) is a province-wide mail survey of steelhead anglers which has been conducted annually since 1967, to obtain estimates of effort and catch stratified by stream and residency. This study reports the compilation and examination of information relating to the accuracy of the survey.
(Province Wide)
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Author: DeGisi, J.S.
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Old Reference Number: SK122
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Old Reference System: Skeena Fisheries Report
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Date Published: Jul 1999
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Report ID: 337
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Audience: Government and Public
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The BC Steelhead Harvest Analysis (SHA) is a province-wide mail survey of steelhead anglers which has been conducted annually since 1967, to obtain estimates of effort and catch stratified by stream and residency. This study reports the compilation and examination of information relating to the accuracy of the survey. Objectives were to assess the capability of available data to reveal the precision and bias of SHA estimates, and to summarize how SHA results compare to steelhead fishery catch and effort parameter estimates from other sources.
Precision of SHA estimates was examined by bootstrap re-sampling of questionnaire responses for approximately 45 fisheries between 1983 and 1995. Precision varied substantially among resident classes, in part due to the higher mail-out proportion applied for non-resident anglers. At a given parameter level, precision also varied substantially between fisheries. Relative precision was highest for estimates of the number of participating anglers, and lowest for catch parameters. Resulting 95% confidence interval widths ranged from approximately twice the estimate value for the lowest estimate values assessed, to roughly one-third the estimate value in the best case for the highest estimates examined.
Bias was assessed through reanalysis of follow-up contact data from 1978/79 and 1982/83, along with preliminary examination of results from an intensive study on the Thompson River in 1984. First-mailing upward bias due to nonresponse was estimated at 24% for number of anglers, 59% for number of successful anglers, and 29% for retained catch, for province-wide aggregate data from the 1978/79 study. In 1982/83, aggregate data from Region 1 re-contact similarly suggested first-mailing upward bias due to nonresponse of 24% for number of anglers but only 33% for number of successful anglers. Water-specific results for 14 fisheries reported in 1978/79 imply first-mailing upward bias due to nonresponse of 20% for number of anglers, 24% for angler days, 29% for retained catch and 27% for released catch, with high variability between fisheries in apparent bias. The Thompson River 1984 study matched individual anglers' field survey results against their SHA questionnaire responses, and suggested that positive recall bias occurs due to angler memory exaggeration of effort and catch as well as angler assignment of activity to the wrong time period. However, rigorous statistical analysis of this dataset is needed to alleviate censoring of the data and allow unbiased estimates of recall effects along with nonresponse bias.
Ninety-five stream-specific annual estimates of one or more steelhead fishery parameters were available from BC provincial and regional fishery reports of field studies. Comparisons from the province-wide dataset show mean upward discrepancy for SHA estimates relative to field results of 42% for number of anglers, 58% for angler days, 83% for retained catch and 109% for released catch. However, most field studies in this dataset have yielded fishery parameter estimates subject to unquantified but substantial downward bias; the data provide a poor basis for assessment of bias in SHA parameter estimates. Dean River field studies from the period 1972-95 show mean upward discrepancy for SHA estimates of 28% for number of anglers, 27% for angler days, 63% for retained catch and 94% for released catch. A restricted dataset of Dean River studies from 1985-95 displays mean upward discrepancy for SHA estimates of 35% for number of anglers, 21% for angler days, 41% for retained catch and 75% for released catch. Although the Dean River data provide approximately unbiased fishery parameter estimates, the comparative dataset probably provides a poor baseline for quantifying SHA bias. Dean River anglers and angler behavior are highly atypical relative to other BC steelhead anglers and fisheries, in terms of characteristics which are likely to affect both nonresponse and recall bias.
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Report Type
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Fish and Aquatic Habitat Information |
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Subject
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Fish Species - Steelhead - Oncorhynchus mykiss |
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Region - Thompson-Nicola |
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Region - Province Wide |
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Fish and Fish Habitat - Stock Assessment |
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Watershed Groups - 120 - Thompson |
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