A major question of whether a large fishing closure as part of the Palau National Marine Sanctuary will benefit local fisheries is being investigated in Palau. The National Geographic Pristine Seas, the Palau International Coral Reef Center, the Palau National Marine Sanctuary Office have been collaborating on a state of the art tuna-tagging study in the waters of Palau over the past several weeks. Although tuna and marlin can move great distances, studies in Hawaii have shown they spawn in Hawaiian waters and spend nearly all their lives in Hawaii, so their protection likely benefits local fisheries. This ongoing study is being done to examine the long-term horizontal and vertical movements of yellowfin tuna and blue marlin in Palau using externally attached pop-up satellite archival tags (PSAT tags) to determine the residency, feeding behavior, and potentially spawning behavior of these species in and around Palau.
In August 2016, the team from the National Geographic Pristine Seas program worked with local Palauan fishermen to tag 1 yellowfin tuna (~ 40 lbs) and 5 blue marlins (150-350 lbs). In April of 2017, we again worked with Palauan fishermen to satellite tag 12 yellowfin tuna between 35 and 150 lbs, with 5 fish over 100 lbs. In addition, we tagged 2 blue marlin (150 and 250 lbs).
Satellite tagged Pacific blue marlin (198 cm fork length) prior to release (MinPAT-348A, located at base of dorsal fin).
Catching a blue marlin during August tagging trip.
Releasing tagged blue marlin.
Yellowfin tuna with satellite tag.
Preliminary examination of movement pattern of yellowfin tuna shows the fish swim near the surface during nighttime hours. During daylight hours, the fish make numerous deep dives with several excursions > 150 m. The optimal temperature range for yellowfin tuna is between 24 and 27°C, but dives to depths of ~ 200 m, likely in search of food, subjected the fish to temperatures of 10°C, requiring a quick return to the warmer upper water column to maintain homeostasis.
In comparison to yellowfin tuna, blue marlin depth preferences were shallower, with much of the time spent near the surface in waters > 29°C. Blue marlin spent nearly all it’s time on the surface during nighttime hours, but spent much of the day time between 30-60 m, but with several excursions to the surface.
The pelagic predator tagging team members (August 2016).
Examination of the movement patterns of yellowfin tuna and marlin around Palau will help determine how resident these species are and how important the sanctuary closure will therefore be to the local fisheries. Electronic tagging has emerged as a powerful tool to reduce the uncertainty in scientific knowledge of the movement of large open ocean fishes such as tuna and therefore inform better fisheries management. This study will help contribute to more informed management of the Palau National Marine Sanctuary and local Palauan fisheries.
[Press release from National Geographic Pristine Seas, University of Hawaii, Palau International Coral Reef Center, and Palau National Marine Sanctuary]