ARCHIVAL TAGGING:

A long-term Archival Tagging Project was undertaken in 2001 by the Southwest Fisheries Science Center of the National Marine Fisheries Service in cooperation with the American Fishermen’s Research Foundation to study the migratory patterns of juvenile (3 to 5 years old) North Pacific albacore (Thunnus alalunga). The project is structured as a five-year program and entails tagging approximately 100 fish in each of the years 2001-2005 for a total of 500 tags deployed by the end of 2005.

The archival tags are sophisticated, small electronic data-logging devices that record depth, water temperature, internal temperature of the fish, and ambient light levels for a period up to four years. The tags are cylindrical and are roughly 3 inches long and 1 inch in diameter with an 8-inch stalk connected at one end. The tags are surgically implanted in the abdominal cavity of the fish with the stalk protruding outside.  (Watch this wmv video of surgical installation of a tag.)

To date over 24,000 albacore have been tagged with conventional dart tags and 1,245 of these have been recovered.

Light level readings are used to determine the geographic position of the fish. The tags provide a detailed history of the fish’s vertical and horizontal movements in addition to the physical details of their oceanic environment during the period at liberty.

These aspects of the biology of juvenile albacore are poorly understood. It is known from previous tagging studies that juveniles make long-range migrations in the north Pacific between Japan and the west coast of North America prior to becoming sexually mature — but the timing, extent, and routes of these migrations are poorly understood. The vertical distribution and extent to which oceanographic conditions influence juvenile albacore horizontal distributions and behavior is also not well known.

Since the start of the project, tags have been deployed mostly off the southern and central California coast. Of the tags thus far recovered, he longest time at sea was 367 days and the greatest net movement between the release and recovery locations was 206 nm. Analysis of the light levels for one fish at sea for nearly a year indicates that the fish moved extensively throughout the waters off southern California and Baja California, moving north into waters off Point Conception in the late summer and south into the area offshore of Bahia Magdalena in the winter.

Depth and temperature records recorded by the tags show a pattern of repetitive diving by the fish between the surface and depths greater than 150 m (492 feet) throughout the day, with nights spent in the upper 40 m (130 feet). Individual dives routinely exceeded 30 minutes into waters as cold as 10º Celsius (50º Fahrenheit). Stomach contents of the recovered fish included a mixture of mesopelagic animals — including myctophids and pelagic red crabs — as well as anchovies and sardines, suggesting that they were feeding on the deep scattering layer as well as surface feeding.

These are the first detailed records of north Pacific albacore behavior from the eastern Pacific. The repetitive diving below the thermocline into waters as deep as 350 m (1,150 feet) in temperatures reaching 7º C (45º F) was unexpected for these small, warm-bodied fish. The fish from which data were collected did not undertake trans-Pacific migrations; however, north-south movements off the coasts of California and Baja California were extensive.

As more tags are returned, the data are expected to provide new insights into the North Pacific albacore stock structure and the habitat use patterns of these juvenile fish, which are essential to developing accurate population assessments.

Tuna tags

Two types of tuna tags

The American Fishermen’s Research Foundation has information on the archival tagging program at afrf.org/tagging

During 2005, two fishing vessels took technicians from the National Marine Fisheries Service on trips off the Oregon coast to tag about 150 albacore tuna. The WFOA encourages people to be on the lookout for tags on fish caught in any region of the North Pacific.

There is a $500 reward for fish recovered with archival tags — details are available through the Southwest Fisheries Science Center.

The first tag in the program was recovered in October 2003 after about three months. Another 14 were recoverd off San Diego by recreational fishermen. Two were recovered off the coast of Oregon. AFRF paid the the $500 reward for the recovery of each tag, and data was assimilated at the NMFS/NOAA Southwest Fisheries Science Center in LaJolla, California.

The tags cost $2000 each and are surgically implanted into the albacore.

Project Goals:

  • Develop field procedures for applying tags that maximize survival of tagged fish
  • Document details of North Pacific albacore biology that are currently only generally understood
  • Determine exact migration routes of juvenile fish (3-4 year old)
  • Determine time/temperature/depth characteristics of migrating fish
  • Incorporate retrieved data into future stock assessment models

AFRF agreed to provide matching funds of up to $75,000 for this project in conjunction with a bidding process that will be conducted by NMFS for the deployment of another 100 or more tags over the next few years. The NMFS awarded funding in the amount of $235,000 for the program. NMFS then selected the vessels to deploy 55 tags in 2002 and another 55 in 2003.

The scientists recommended that because of the high stress on the fish, low impact methods must be used to capture fish for the highest chance of survival. They recommend bait pole methods and other hand line techniques where the vessel is nearly stopped at the time of hooking. A NMFS technician is onboard and complete the procedure.