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Images: Clues in Shark Vertebrae Reveal Where They've Been

Basking sharks, the world’s second-largest fish, have become endangered. To devise effective strategies to protect the sharks, scientists are striving to gain basic knowledge about where they live, mate and give birth. (Greg Skomal, Massachusetts Division of Marine Fisheries)

A professional harpoonist, Captain Bill Chaprales aboard the fishing vessel Ezyduzit out of Sandwich, Mass., tags a basking shark with a device that will record where the shark swims for up to a year before the tag pops off and transmits the data back to scientists on shore. See video below. (Li Ling Hamady, MIT/WHOI Joint Program)

Data from basking sharks tagged off the coast of Massachusetts showed that the sharks migrated beyond their previously known ranges (red shading), with some going across the equator as far as Brazil (dotted lines). (Skomal et al, Current Biology, 2009)

MIT/WHOI graduate student Li Ling Hamady reveals clues to sharks' lifestyles by studying vertebrae from sharks that have stranded and died. (Li Ling Hamady, MIT/WHOI Joint Program)

A thin section cut from a shark vertebra shows distinct alternating light and dark layers of tissue, laid down sequentially over a shark’s lifetime. Similar to tree rings, the layers may preserve a chemical record of environmental conditions the shark was exposed to and reveal its habits and habitats. (Li Ling Hamady, MIT/WHOI Joint Program)

Different areas of the ocean have different ratios of carbon and nitrogen isotopes. As sharks forage through these isotopically distinct habitats, they can absorb the isotopic signatures of local prey, giving scientists a natural “tag” to track their movements. In this map, color variations represent different ratios of nitrogen isotopes (15N/14N) in the ocean. (Kelton McMahon, WHOI)

Scientists are also looking for the chemical signature of a “bomb spike” lingering in the backbones of basking sharks to learn more about the sharks’ largely unknown lifestyle. Levels of radioactive carbon-14 in the atmosphere spiked in the late 1950s and early 1960s because of nuclear weapons testing. 14C levels in both the Northern (dark gray) and Southern (light gray) Hemispheres nearly doubled from historical levels until the 1963 Limited Test Ban Treaty prohibited testing in the atmosphere. (Based on GNUPLOT 4.2 patchlevel 2)