A research project in the USA, which follows the behavior of albacore tuna by using archival tags, found that these beautiful fish dive to depths as deep as 350 meters.
The 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 Fisherman’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 that 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. 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. However 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 poorly known.
Since the start of the project, 197 tags have been deployed, mostly off the southern and central California coast. To date, 4 archival tags have been recovered, three of which were recovered during the first week of July, 2004 by sportfishing vessels operating out of San Diego. The longest time at liberty 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 liberty 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 10° Celsius (50° 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 feed.
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 meters (1,150 feet) in temperatures reaching 7° C (45°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. A reward of $500 is offered for return of a tagged fish
Source: SWFSC / NOAA/NMFS