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Status of Stocks & Multispecies Assessment Program

Testing Electronic Tags for Light-based Geolocation of Alaska Groundfish

figure 3, archival tag
Figure 3.  Closeup of archival tag attached to mooring line.  The sensor stalk can be seen extending from the left end of the tag.  The twine and tape were part of the mooring line attachment.  For scale, the diameter of the tag is approximately 1 cm.  Photo by Olav Ormseth.

SSMA researchers are currently conducting a study to determine the utility of electronic archival tags (Fig. 3) for studying movement of Alaska groundfish. The initial work is being done on Pacific cod and, if successful, will be applied to other species such as skates.

These tags have light, depth, and temperature sensors and store data from these sensors at user-determined time intervals. When the tag is recovered, the light record can be used to obtain daily estimates of latitude and longitude for the tagged fish.

Lotek Wireless Inc. (Newfoundland, Canada) has developed a new type of tag that is smaller than previous models and uses an improved algorithm for estimating geographic position. Since these tags have not been tested in high latitudes, funds were obtained through a cooperative research grant to conduct a pilot study. This study is in two parts: 1) testing the position estimates provided by tags moored at a known, fixed location; 2) testing capture methods and tag implantation procedures on captive Pacific cod off Juneau, Alaska.

For Part 1, moorings were deployed during May 2009 in approximately 100-m water depth in Resurrection Bay, Alaska, (in the vicinity of Seward) and Captain's Bay outside of Unalaska in the eastern Aleutian Islands.

Two sets of tags, each with three depths intervals, were on each mooring location. After 4 days the first set of tags was recovered to ensure proper installation and equipment performance. A second set remained in place and will be recovered in October. These deployments were achieved with help from personnel of the Alaska SeaLife Center (Seward) and the University of Alaska Fairbanks (Unalaska).

Preliminary results from the Unalaska tags suggest that the tags might have difficulty detecting enough light at depths greater than 50 m. Therefore, additional tags were placed at shallow depths in Resurrection Bay (Seward) to provide a greater range of light intensity values. The tags in Seward were recovered in September 2009, but the data have not yet been analyzed. The Unalaska tags will be retrieved in October 2009.

For Part 2 of the study, the F/V Williwaw was chartered to capture live Pacific cod using pot gear in the vicinity of Juneau, Alaska. During 24-28 August 2009, five Pacific cod were captured and transferred to a laboratory tank at Auke Bay Laboratories. These fish are currently in a recovery period, and archival tags will be implanted in three of the five individuals in September 2009.

To reduce impacts on swimming ability and streamlining, the tags will be placed inside the body cavity. The tags have a sensor stalk approximately 10 cm long that extends out through the body wall and allows the recording of external light and temperature data. The fish will be kept in the live tanks for up to a year.

In addition to the tag testing, these fish will be part of a controlled study linking otolith microchemistry to water temperature and fish growth. This is being done in conjunction with Tom Helser of the AFSC Age and Growth Program.

By Olav Ormseth and Susanne McDermott

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