PFRP Home > Biology Projects List

Pop-Off Satellite Archival Tags to Chronicle the Survival and Movements of Blue Sharks Following Release from Longline Gear

Related PFRP projects:
Developing Biochemical and Physiological Predictors of Long Term Survival in Released Blue Sharks and Sea Turtles

Evaluating Biochemical and Physiological Predictors of Long Term Survival in Released Pacific Blue Marlin Tagged with Pop-up Satellite Archival Transmitters (PSATs)

Modeling the Eco-physiology of Pelagic Fishes and Sharks with Archival and Pop-up Satellite Archival Tags (PSATs)

Progress Reports (PDF): FY 2004, FY 2003, FY 2002, FY 2001

Project Overview
Blue shark (Prionace glauca) is the most commonly caught species during commercial longline operations in the Pacific(¹⁾. As many as 150,000 sharks are captured per year⁽²⁾. Blue shark are incidental by-catch and are often discarded after removal of their fins to satisfy increasing demand primarily from the Asian market. There has been a dramatic increase in the numbers of blue sharks finned by the Hawaii-based longline fishery; from 977 sharks in 1992 to 58,444 sharks in 1998⁽³⁾. As a result, blue shark by-catch and finning practices have emerged as important fisheries management issues. Shark finning, and the commercial by-catch of sharks in general, are also coming under intense scrutiny by several non-governmental environmental organizations (NGOs).

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:

1. Daily horizontal and vertical movement patterns, depth distribution, and effects of oceanographic conditions on the vulnerability of blue sharks to longline fishing gear.
2. The survival rates of blue sharks captured and released from commercial longline gear.
3. Stock identification, dispersal, and possible fishery interactions.

Year 1 funding for this project received November 2000.

Footnotes:
(1) Bigelowe, K.A., C.H. Boggs and X. He, 1999. Environmental effects on swordfish and blue shark catch rates in the U.S. North Pacific longline fishery. Fisheries Oceanography 8:178-198.
(2) Ito, R.Y., 1995. Annual report of the 1994 Hawaii-based longline fishery. NOAA, NMFS, SWFSC Honolulu Laboratory Administrative Report H-95-08.
(3) McCoy, M.A. and H. Ishihara, 1999. The socioeconomic importance of sharks in the U.S. flag areas of the western and central North Pacific. NOAA, NMFS, SWR Administrative Report AR-SWR-99-01.
⁽⁴⁾ Graves, J.E., B.E. Luckhurst and E.D. Prince, 1999. An evaluation of pop-up satellite tag technology to estimate post-release of blue marlin (Makaira nigricans). ICATT, SCRS Report 99/97.
⁽⁵⁾ Smith, S.E., W.D. Au and C. Show, 1998. Intrinsic rebound potentials for 26 species of Pacific sharks. Marine and Freshwater Research 49:663-678.
⁽⁶⁾ Castro, J.I., C.M. Woodley and R.L. Brudek, 1999. A preliminary evaluation of the status of sharks species. FAO Fisheries Technical Paper No. 380, Rome. 72 pp.

Project Investigators: