The deployment of electronic tags that can record and archive data eliminates the need to track individual fish acoustically from a ship. The tags collect data on depth, light and external and internal temperature every two minutes. They also use sunrise and sunset data with sea surface temperature to compute a daily location, yielding tens of thousands of data points.
More than 15,000 days of archival data have been collected in the past five years, and records on individual fish span as much as 3.6 years. Previously, the longest duration scientists had followed large open-ocean fish and obtained similar types of data was six days.
The research team also deployed pop-up satellite tags. These tags, which are attached externally to the fish, detach and float to the surface at a pre-programmed date. Data on depth, temperature and location were stored on the tag during the mission and transmitted back to the lab via the Argos environmental satellite system. Pop-up tags were deployed in New England, North Carolina and in the Gulf of Mexico.
The researchers demonstrated that bluefin dive to remarkable depths, at times exceeding the 3,281-foot (1000-meter) pressure sensors in the tags. Data from the tags show that bluefin spend most of their time closer to the surface, in the top 984 feet (300 meters).
Bluefin also display a remarkable range of temperature preferences, from near-freezing waters when feeding (37 F or 2.8 C) to very warm temperatures when breeding (86 F or 29.5 C). The Atlantic bluefin is one of only a handful of warm-blooded fishes. Block and her colleagues demonstrated that bluefin maintain a high internal temperature, around 77 F to 80 F (25 C to 26 C) even when swimming in the most frigid waters.
The researchers also reported the first descriptions of what they believe to be breeding behavior in giant tunas. Most surprising is that the spawning period occupies a short
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Contact: Ken Peterson, Monterey Bay Aquarium
831-648-4922
Stanford University
16-Aug-2001