AFSC/RACE/GAP/Nichol: Archival tag depth and temperature data from Pacific cod

Data from 250 recaptured (624 released) depth and temperature recording archival (data storage) tags attached to Pacific cod off Kodiak Island and in the eastern Bering Sea from 2001 to 2003, were used to describe the vertical movement patterns of Pacific cod. Three publications resulted from the research with subject matter including: 1) P. cod behavior as related to barotrauma; 2) P. cod vertical distribution as related to survey trawl catchability; 3) P. cod diel vertical migration. Please see publications for more detail.

To examine 1) P. cod behavior as related to barotrauma; 2) P. cod vertical distribution as related to survey trawl catchability; 3) P. cod diel vertical migration.

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Nichol, D.G. & Chilton, E.A. 2006. Recuperation and behavior of Pacific cod after barotrauma. ICES Journal of Marine Science 63: 83-94.

Nichol, D.G., Honkalehto, T. & Thompson, G.G. 2007. Proximity of Pacific cod to the seafloor: Using archival tags to estimate fish availability to research bottom trawls. Fisheries Research 86: 129-135.

Nichol, D.G., Kotwicki, S., and Zimmermann, M. 2013. Diel vertical migration of adult Pacific cod Gadus macrocephalus in Alaska. J. Fish Biol. 83: 170-189.

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: A total of 624 Pacific cod were tagged with electronic data storage tags off Kodiak Island in the Gulf of Alaska, and off Unimak Island in the eastern Bering Sea from 2001 to 2003. There were two release sites off Kodiak Island (inside Kupreanof Strait and near Ugak bay), and three release sites off Unimak Island (off Cape Sarichef, off Amak Island, and off Akun Island). Cod were initially captured with pots and hook and line gear at bottom depths ranging from 32 to 127 m near Unimak Island (Table 1). Pots were steel-framed with dimensions of 2.1 × 2.1 × 0.9 m or 2.3 × 2.3 × 1.2 m, and 4 × 4 cm to 6 × 6 cm stretched nylon mesh. Pots were “soaked” during both daylight and night-time hours from 5.2 - 22 h off Kodiak Island and from 3.8 - 102 h off Unimak Island. Both pots and hook and line gear were retrieved at minimum rate of 20 m min-1. Captured cod were transferred to a tank supplied with running sea-water and were retained in the tank only long enough to determine if they could maintain buoyancy near the bottom of the tank without apparent difficulty and if they lacked serious external damage.

Data storage tags were attached externally, beneath the anterior dorsal fin, using 0.5 mm stainless steel wire as described in Nichol and Somerton (2002). Cod were measured to the nearest centimeter total length (TL). Sizes of tagged cod ranged from 49 to 85 cm TL. Cod were released at the site of initial capture immediately after tagging.

Data storage tags, Lotek Wireless LTD-1100, recorded depth and temperature. The tags had a maximum recording depth of 600 m, with accuracy of + 1.5 m if fish remained in less than 150 m, + 3 m if fish exceeded 150 m, and + 6 m if fish exceeded 300 m. Water temperature was recorded with an accuracy of + 0.3 ¿C. Frequency of data recordings decreased with time at liberty, starting at 14 s intervals and decreasing to 30 min intervals after 341 days. The average recording interval for tags in this study was 13 min.

Tagged fish were captured in commercial trawl, pot, long-line and jig fisheries. A cash reward was provided as an incentive for returning tags. Capture information included latitude, longitude, depth, and date of capture. Specimen information included fish length, sex, and fish weight.