Abstract
BackgroundPacific cod (Gadus macrocephalus) is an ecologically important species that supports a valuable commercial fishery throughout Alaska waters. Although its life history includes seasonal movement for spawning and feeding, little is known about its movement ecology. Here, we present results from the first study to use pop-up satellite archival tags (PSATs) to track the within-year movements of Pacific cod to understand their potential seasonal movement patterns within the Aleutian Islands. This study was part of a cooperative research project; tagging was conducted onboard commercial vessels during the winter fishing season while Pacific cod were aggregated to spawn in the central Aleutian Islands.ResultsOf the 36 PSATs deployed, we were able to obtain movement data from 13 Pacific cod that were at liberty between 60 and 360 days. We determined that three tagged Pacific cod were predated on by marine mammals and three were recaptured by the commercial fishery. Geolocation models were produced for four migrating individuals. Eight Pacific cod moved to a productive foraging ground near Seguam Island located 64 to 344 km from their release site and presumed spawning ground within a few weeks of their release. These movements indicate that some Pacific cod in the Aleutian Islands undergo seasonal migration. Three Pacific cod remained near their release locations (within 50 km) for more than 75 days suggesting the existence of partial migration in the population. Two Pacific cod undertook larger movements (378 and 394 km) during which they swam over deep passes and crossed several management boundaries highlighting the potential connectedness of Pacific cod throughout the Aleutian Islands.ConclusionsThis study provided important initial insights into the seasonal movement patterns of Pacific cod in the Aleutian Islands. Most tracked Pacific cod (77%) undertook migrations in the middle of March (64–394 km) from their winter spawning areas to summer foraging areas, but a few individuals remained in their capture location suggesting a partial migration strategy. Their ability to cross deep passes that were previously seen as potential barriers to movement has expanded our understanding of population connectivity.
Highlights
Pacific cod (Gadus macrocephalus) is an ecologically important species that supports a valuable commercial fishery throughout Alaska waters
This average fork length was the same as a random sample of Pacific cod that were landed at the fish plant in Adak, Alaska, during the study period ( x = 81.2; range = 49 to 114 cm; n = 429), indicating that the Pacific cod that were tagged and released likely came from the same part of the population that was being caught by the fishery
Out of the 100 maturity samples taken at the plant, only 6 Pacific cod were immature and they were all less than 66 cm
Summary
Pacific cod (Gadus macrocephalus) is an ecologically important species that supports a valuable commercial fishery throughout Alaska waters. This study was part of a cooperative research project; tagging was conducted onboard commercial vessels during the winter fishing season while Pacific cod were aggregated to spawn in the central Aleutian Islands. It is a highly productive area and supports a large abundance of several economically important fish species such as Pacific ocean perch (Sebastes alutus), Atka mackerel (Pleurogrammus monopterygius), and Pacific cod (Gadus macrocephalus) [3, 4]. Genetic work has shown strong support for significant differences between Bering Sea and Aleutian Islands cod, as well as the possibility for additional differentiation within spawning stocks found along the Aleutian Archipelago [5, 6]. In Alaska, Pacific cod is currently managed as three separate stocks: Gulf of Alaska, Aleutian Islands, and Bering Sea
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