The Use of Satellite Tags to Inform the Stock Assessment of a Data-Poor Species: Estimating Vertical Availability of Spiny Dogfish in the Gulf of Alaska

The Use of Satellite Tags to Inform the Stock Assessment of a Data-Poor Species: Estimating Vertical Availability of Spiny Dogfish in the Gulf of Alaska

Peter-John F. Hulson, Cindy A. Tribuzio, and Karson Coutre

The Use of Satellite Tags to Inform the Stock Assessment of a Data-Poor Species: Estimating Vertical Availability of Spiny Dogfish in the Gulf of AlaskaThis is part of Assessing and Managing Data-Limited Fish Stocks
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Description

In Alaska, harvest specifications for many data-poor stocks are determined by using the product of estimated biomass from the Alaska Fisheries Science Center bottom trawl survey and a pre-specified fishing mortality rate. For Pacific spiny dogfish in the Gulf of Alaska the bottom trawl survey biomass estimates are highly variable. In this study we used pop-up satellite archival tag data to estimate the vertical availability of spiny dogfish to the bottom trawl survey (the proportion of time spent under the headrope of the bottom trawl during survey operating hours) with the underlying goal of determining if the biomass estimates for this species from the bottom trawl survey can be improved. We estimated the vertical availability with two methods: one that assumed the bottom depth was the maximum depth recorded by the pop-up satellite tag in a 24-hour period, and the other that used the uncertainty in mean daily location estimates provided by a geolocation model to obtain bathymetric bottom depths around the mean daily location to compare with the depths recorded by the satellite pop-up tags. Using the satellite pop-up tag data, we determined that the estimated vertical availability to the bottom trawl of spiny dogfish (that were either tagged or recovered in the Gulf of Alaska during the survey months) from the first method was 0.6, and from the second method was 0.03. Taken together, the availability of spiny dogfish to the bottom trawl survey in the Gulf of Alaska can be quite small, which suggests that the biomass estimates from the bottom trawl survey are likely underestimated.

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