A Tag and Release Program for the Hawaiian Seamount Yellowfin and Bigeye Tuna Handline and Troll Fisheries

The project addresses issues of tuna movement and exploitation that are fundamental to resolving concerns over fishery interaction and gear conflict currently before the Council. This tagging project was prompted by local concerns related to a productive offshore handline fishery for yellowfin and bigeye tuna that concentrates fishing effort on the Cross Seamount located approximately 150 nautical miles southwest of Kona, Hawaii.

The objectives of the project are to investigate retention rates of tuna on the Cross Seamount, movement and exploitation patterns of tuna in relation to domestic fisheries and interaction between surface and longline fishing gear. The PFRP tagging project also supports a collaborative biological investigation of the Inter-American Tropical Tuna Commission that is an age validation study for bigeye tuna using oxy- tetracycline mark and recapture methodologies. The results from this tagging project may later be useful in planning a larger scale mark and recapture program to address broader issues of movement and interaction for the north central Pacific region. Field operations for the current seamount tagging project will continue through 1997 and preliminary analysis of the data has begun.

Principal Investigator:

Dr. Kim Holland
Hawaii Institute of Marine Biology (HIMB)
University of Hawaii at Manoa
Coconut Island
P.O. Box 1346
Kaneohe, Hawaii 96744
Phone (808) 236-7410/533-4110
FAX (808) 236-7443
email: kholland@hawaii.edu

Progress Report - September 1997

Study area and fishing grounds

The Cross Seamount, located at approximately 18 40' N latitude and 158 10' W longitude, is the primary fishing ground of the Hawaii based offshore handline fishery. Weather monitoring buoys that are set and maintained by NOAA in the outer Hawaii EEZ are also exploited by the handline vessels. These buoys have in effect become highly productive fish aggregators and can account for large catches of yellowfin and bigeye tuna and other pelagic species. Longline vessels also operate in waters adjacent to the buoys and at times directly over the Cross Seamount. Catch rates can be very high creating ideal locations from which to base tagging operations.

Tag releases and recoveries

All tagging effort for this project concentrates on bigeye and yellowfin tuna. A total of 4859 tuna have been tagged by the program as of September 3, 1997 consisting of 3399 bigeye (69.9%) and 1460 yellowfin (30.1%). The majority of the releases have been made at the Cross Seamount and weather buoy 2. A total of 294 recoveries have been made as of September 3, 1997 consisting of 176 bigeye and 118 yellowfin for an overall recovery rate of 6.1%.

Selected tuna were injected with a measured quantity of oxy-tetracycline in support of an age validation study for bigeye tuna, before being tagged and released. The OTC is completely harmless to the fish and to the edible quality of the flesh, but the chemical deposits an invisible layer on all bony structures at the time of injection. The OTC layer will be clearly visible under UV light allowing scientists to ascertain whether growth lines evident in the bones after tagging do or do not correspond to daily growth rings, like the annual growth rings in a tree trunk. This work is necessary before accurate daily age estimates of bigeye tuna can be made which are crucial for effective management of the stocks. The otoliths (ear bones) of these fish must be retrieved for this work to be completed with an accurate date of recapture. Over 100 OTC injected bigeye have been recaptured and analysis of the otoliths is ongoing. The tables below list tag releases and recaptures for OTC and non-OTC injected fish by location.

Recovery discussion and summary

Most of the recaptures have been made at the point of release or have indicated some movement between the seamount and offshore weather buoys. Of the recaptures made from locations away from the point of release, many them have come from Fish Aggregation Devices (FADs) anchored close to the main Hawaiian islands of Kauai, Molokai, Oahu and Hawaii. However some recaptures have been taken by daytime handline gear from areas where tuna are known to aggregate. These areas, known as koas by the Hawaiians are fished with baited handlines either during the day (palu ahi gear) or at night (ika shibi gear). Most of the recoveries have been made using handline gear from the offshore handline fishery. However, 13 recoveries have been reported from longliners and 5 have been taken with troll gear. One notable long- distance recapture was for a yellowfin tuna tagged on the Cross Seamount in November 1996 and recaptured by a purse seine vessel off the coast of Baja Mexico in July 1997.

Tag reporting and recovery mechanisms

Two colors of plastic dart tags are in use by the program with all tags inserted at the base of the second dorsal fin. Orange tags denote regular program releases for which the project needs the tag number, catch date, location, area, gear type and fork length of the fish. Green tags indicate that the fish was injected with OTC for the age validation study. The same data and the entire head or the otoliths of these fish should be retained in support of the age study on bigeye tuna. Rewards are offered for all tag recoveries.

Fisherman can report tag recaptures by calling the toll free number of 1-800-588-8066 (USA only). A recorded message provides details of tag recapture procedures and rewards. Otherwise, tags and recapture information can be sent to: Hawaii Tuna Tagging Project, c/o Hawaii Institute of Marine Biology, P.O. Box 1346, Kaneohe, Hawaii, 96744, USA or E-mail can be sent to Dr. Kim Holland, kholland@hawaii.edu

In light of the longevity and highly migratory nature of bigeye and yellowfin tuna it is possible that some fish tagged by this program will be recovered by vessels throughout the Pacific basin. Your cooperation is requested in assisting tag and otolith returns from this program.

Tag and Release Maps for Yellowfin and Bigeye Tuna

Tag and Release Map for Yellowfin Tuna

Tag and Release Map for Bigeye Tuna

This page updated August 15, 2006