Spring Bluefin Blitz Ends NC Tagging Season on a High Note
 After a relatively disappointing January in North Carolina, with only three fish tagged, we'd hung up our tagging gear for the season. However, rumors of abundant fish off Hatteras were too much to resist. We dusted off the gear and were out on the water on the last day of March.
March may go out like a lamb, but the bluefin tuna were feeding like lions that day! The action was red hot, with over 20 knock-downs. We ended the day with 10 fish tagged, all in the 120-160 lb range.
A couple days later we were out on the water again, with an equally successful and exciting expedition. Nine additional fish were released with archival tags, bringing our 2-day total to 19.
This large school of 160-lb fish has been expected. It's a comparatively abundant cohort of fish that's provided a visible spike in the recreational fishing survey data over the last several years. The fish are now 6 years old and will undoubtedly provide numerous heart-racing thrills to anglers in the mid-Atlantic and New England this summer as they continue to migrate north.
Importantly, if an industry effort to lower the size for commercial sale from 73 inches to 65 inches is successful, these fish will be eligible to the commercial fishery this summer as well, which would provide increased competition with the recreational fishery and reduce the percentage of this cohort that will reach maturity and spawn. Allowing more of these fish to mature and contribute to the next generation would be wise for the future of Atlantic bluefin tuna and the fisheries that target them. The National Marine Fisheries Service will announce the 2009 regulations in mid-May.
Visit our blog for more NC highlights.
 Respirometry, Respirometry, and More Respirometry!!!
What's been keeping the team at the Tuna Research and Conservation Center (TRCC) in Monterey, CA busy lately? You guessed it – respirometry! Respirometry is a method to measure our captive bluefin tunas' rate of oxygen consumption, which is a very good indicator of their metabolic rate. And, how do we measure the rate of oxygen consumption of these very large, powerful, and fast bluefin tunas? In a respirometer, of course!
We capture an individual fish by hand from one of the main TRCC tanks and transport it via a water-filled sling to a special tank called a respirometer. Once in the chamber, the fish swims against a current generated by a propeller – kind of like a treadmill! The chamber is sealed for ten minutes at a time, during which we measure the rate of decline of oxygen concentration in the water. We then do a bit of number crunching and end up with an estimate of the fish’s metabolic rate. The beauty of the respirometer is that we can regulate factors such as water speed and temperature to determine their influence on the fish’s metabolic rate.
We’ve been doing these studies here for a long time, but we’re particularly excited about the experiments this year because the fish are carrying tags that measure heart rate. Dr. Tim Clark and his colleagues in Australia developed the tags, and we have been collaborating with them for the past two years. Our preliminary results are exceptional and suggest that heart rate can also be used as a proxy for metabolic rate – potentially allowing us to estimate the metabolism of tunas in the wild!
Our flume studies have taught us many things about the physiology of bluefin tuna. Better understanding their metabolism gives us insights into foraging ecology of wild bluefin and feeding efficiency of bluefin tuna in aquaculture operations. This information has many applications, including discerning feeding in electronic tag data and determining the optimal holding temperature for aquaculture operations.
Visit our blog to view video of a fish swimming in the respirometer.
Data Highlight: A satellite tag deployed on a 57-inch bluefin tuna in France in August 2007 popped up 3 months later just 175 miles from the release site. The track included an excursion into Algerian waters. |
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Tags Out
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Data In
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Atlantic
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1025
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500
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Pacific
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612
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324
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