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Physics Press Release 05-187 How Hot Tuna (and Some Sharks) Stay Warm Specialized muscles generate heat and swimming power Red muscle temperature of laminid sharks is greater than that of the surr ounding water. Lamnid sharks maintain an elevated temperature in the red muscle near the backbone.
Credit and Larger Version October 27, 2005 Scientists now have direct evidence that the north Pacific salmon shark m aintains its red muscle (RM) at 68-86 degrees Fahrenheit , much warme r than the 47 F water in which it lives. The elevated muscle temperature presumably helps the salmon shark survive the cold waters of the north Pacific and take advantage of the abundant food supply there. The heat a lso appears to factor into the fish's impressive swimming ability. During what some would say was a better-than-average day at work, Robert Shadwick of the Scripps Institution of Oceanography and his colleagues w ent salmon shark fishing in the Gulf of Alaska. After catching specimens over 7-feet long and weighing more than 300 pounds, the researchers mea sured temperatures throughout the sharks' bodies and tested the mechanic al power of RM samples. National Science Foundation (NSF) program manager, Ione Hunt von Herbing said, "Knowing specific details about the anatomy and physiology of salm on sharks provides key insight into their ability to produce such power and speed during swimming. The knowledge could translate into better des igns for underwater vehicles." The study was funded by NSF's integrative organismal biology program. Salmon sharks are lamnids, a group of sharks that also includes the mako and great white. Numerous studies have shown that lamnid sharks and tuna s share many anatomical and physiological specializations that endow the m with their impressive swimming power and speed. In contrast to other f ish where the RM is near the skin, the RM of these sharks and tunas is n ear the backbone. Even though the ancestors of bony tuna and cartilagino us sharks diverged more than 400 million years ago, selection pressure f or high-performance swimming in each group seems to have occurred indepe ndently about 50 million years ago. Throughout its life, a salmon shark never stops swimming because it will sink. The body heat generated from continuous swimming elevates the RM t emperature, which in turn, warms the surrounding white muscle and allows the shark to survive the frigid waters of the north Pacific. If a shark stops swimming, it could die from cold exposure.
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