Virginia Institute of Marine Science
We employed ultrasonic transmitters to follow (for up to 48 h) the horizontal and vertical movements of five juvenile (6.8-18.7 kg estimated body mass) bluefin tuna (Thunnus thynnus) in the western North Atlantic (off the eastern shore of Virginia). Our objective was to document the fishes' behavior and distribution in relation to oceanographic conditions and thus begin to address issues that currently limit population assessments based on aerial surveys. Estimation of the trends in adult and juvenile Atlantic bluefin tuna abundance by aerial surveys, and other fishery-independent measures, is considered a priority. Juvenile bluefin tuna spent the majority of their time over the continental shelf in relatively shallow water (generally less then 40 m deep). Fish used the entire water column in spite of relatively steep vertical thermal gradients (approximate to24degreesC at the surface and approximate to12degreesC at 40 m depth), but spent the majority of their time (approximate to90%) above 15 m and in water warmer then 20degreesC, Mean swimming speeds ranged from 2.8 to 3.3 knots, and total distance covered from 152 to 289 km (82-156 nmi). Because fish generally remained within relatively confined areas, net displacement was only 7.7-52.7 km (4.1-28.4 nmi). Horizontal movements were not correlated with sea surface temperature. We propose that it is unlikely that juvenile bluefin tuna in this area can detect minor horizontal temperature gradients (generally less then 0.5degreesC/km) because of the steep vertical temperature gradients (up to approximate to0.6degreesC/m) they experience during their regular vertical movements. In contrast, water clarity did appear to influence behavior because the fish remained in the intermediate water mass between the turbid and phytoplankton-rich plume exiting Chesapeake Bay (and similar coastal waters) and the clear oligotrophic water east of the continental shelf.
Yellowfin Tuna; Katsuwonus-Pelamis; Hawaiian-Islands; Pelagic Fishes; Skipjack Tuna; Acute-Hypoxia; Albacares; Temperature; Ocean; Bight
Brill, Richard; Lutcavage, Molly; Metzger, Greg; Bushnell, Peter; Arendt, Michael D.; Lucy, Jon; Watson, Cheryl; and Foley, David, Horizontal And Vertical Movements Of Juvenile Bluefin Tuna (Thunnus Thynnus), In Relation To Oceanographic Conditions Of The Western North Atlantic, Determined With Ultrasonic Telemetry (2002). Fishery Bulletin, 100(2), 155-167.