Abstract
AbstractAtka Mackerel Pleurogrammus monopterygius is the most abundant commercially exploited groundfish in the Aleutian Islands, Alaska. It is also the predominant prey of the endangered Steller sea lion Eumetopias jubatus in the Aleutians Islands range. In 1992, trawl exclusion zones (TEZs) that ranged from 10 to 20 nautical miles were established around rookeries to protect Steller sea lion prey abundance. This study examined the efficacy of the TEZs by estimating the movement and local abundance (10–20 nautical miles) of Atka Mackerel inside and outside of these zones using an integrated tagging model that incorporated independent data for tagging survival, recruitment, and tag reporting rates. Atka Mackerel were tagged, released, and recovered from 2000 to 2006 at four Aleutian Island locales, from both inside and outside of the TEZs. Atka Mackerel local abundance and their movement patterns across these harvest boundaries were estimated for all the study areas inside and outside the TEZs, and local exploitation rate by the fishery was calculated for each area open to fishing outside the TEZ boundary. In areas with high Atka Mackerel abundance and little movement from inside to outside the protection zones (e.g., Seguam Pass and Kiska Island), the TEZs were expected to work well to preserve the prey field for Steller sea lions. In areas of low Atka Mackerel abundance and frequent movement from the inside to the outside of the protection zone (e.g., Amchitka Island), the TEZs were expected to be less effective. Our study indicated that TEZs can be effective for preserving prey fields of Atka Mackerel for Steller sea lions, but each study area needs to be carefully evaluated in order to understand area‐specific variations in abundance and movement patterns.Received October 21, 2014; accepted December 16, 2015
Highlights
Groundfish stocks in Alaska are managed at large spatial scales; important ecological interactions such as predation, spawning, and habitat selection occur on a local scale
In 1992, trawl exclusion zones (TEZs) that ranged from 10 to 20 nautical miles were established around rookeries to protect Steller sea lion prey abundance
This study examined the efficacy of the TEZs by estimating the movement and local abundance (10–20 nautical miles) of Atka Mackerel inside and outside of these zones using an integrated tagging model that incorporated independent data for tagging survival, recruitment, and tag reporting rates
Summary
Groundfish stocks in Alaska are managed at large spatial scales; important ecological interactions such as predation, spawning, and habitat selection occur on a local scale. To estimate the abundance at other locales in the Aleutian Islands, this study expanded the previous work by McDermott et al (2005) and examined the small-scale abundance, movement, and local exploitation rate of Atka Mackerel in relation to the TEZs in four areas of known Atka Mackerel population centers in the Aleutian Islands (Figure 1). The objectives were to (1) use tag–release and recovery methods to estimate local abundance and movement inside and outside the TEZs at four sites in the central and western Aleutian Islands, (2) expand the integrated maximum likelihood tagging model used in previous studies (McDermott et al 2005) to include Atka Mackerel recruitment, and (3) estimate local exploitation rates at all four study sites
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