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Pop-Off Satellite Archival Tags to Chronicle the Survival and Movements of Blue Sharks Following Release from Longline Gear
Progress Reports (PDF): FY
2004, FY 2003,
FY 2002, FY
Compared to bony fishes, sharks are susceptible to overexploitation since they generally mature at a late age, have low fecunditites, long gestation periods, and are long lived (4, 5, 6). Blue sharks are also probably the widest ranging shark species. They appear to make extensive and complex migrations, but movement patterns across seasons are not well documented. Because blue sharks are both ubiquitous and highly vagile, effective resource management, equitable resource allocations, and the population assessments upon which these are based, depend on a thorough understanding of long term horizontal movement patterns. Data on movement patterns of pelagic fishes have traditionally been obtained either by analysis of catch statistics, tag and release studies, and direct observation of the movements of individuals carrying ultrasonic (usually depth sensitive) transmitters. Although all three methods can be effective, all have limitations in the quality of data that can be obtained.
Recent advances in electronic data storage technology have made it possible to construct devices that allow the long term (months to years) recording of detailed records of the vertical and horizontal movements of fishes. These "archival" tags are carried inside the fish and record data on geographical position, ambient light levels, swimming depth and temperature (internal and external). Further design refinements have also made it possible for fine-scale environmental and daily geolocation data to be downloaded via satellites with "pop-off" satellite archival tags (PSATs). These PSAT tags are released from the fish at a specified period and/or threshold depth, allowing for immediate access to recorded time-series data.
During the course of this three year project, researchers plan to attach PSATs on up to 50 blue sharks captured and released from commercial longline gear. Researchers anticipate the majority of sharks to be tagged on dedicated longline cruises aboard the NMFS research vessel Townsend Cromwell and while onboard commercial longline vessels. Researchers will attach hook timers to longline droppers to record the duration of hooking prior to subsequent release. Researchers hope to have tags equipped with a "safety valve" feature to insure that collected data are not lost. This will consist of a glass link that will crush at a precisely specified depth. That is, if the fish sinks and dies, at about 800 m (before the float implodes), the glass link will break and allow the tag to float to the surface.
Project researchers' plan to use PSATs to study the horizontal and vertical movements, and distribution of blue shark is intended to provide critical knowledge in three areas:
Year 1 funding for this project received November 2000.
Dr. Michael Musyl
National Marine Fisheries Service
Kewalo Research Facility
1125-B Ala Moana Blvd.
Honolulu, Hawaii 96814 USA
Phone (808) 592-8305
FAX (808) 592-8300
Dr. Richard Brill
Virginia Cooperative Marine Education and Research (CMER)
Virginia Institute of Marine Science
Gloucester Point, VA 23062 USA
Phone (804) 684-7773
This page updated August 22, 2006