Basking Sharks Go Wide and Deep

Basking sharks are heavily exploited from the shark–finning industry. The damage is compounded by the fact we know so little about their distribution in the sea. As a copepod mass-consuming filter-feeder, they follow and seek out their preferred prey. Previously, only 11 basking sharks have been tagged. None of which ventured passed the continental shelf into deep water. Mauvis Gore and colleagues provide the first evidence of the longest distance and deepest dives of a transatlantic migrating basking shark.

Image copyright Chris Gotschalk, Wikipedia Commons.

Using satellite tags, Gore and colleagues tracked 2 basking sharks from the Isle of Man in the United Kingdom. One shark was boring and stayed near the shelf, traveling north-south in shallow water. We won’t talk about this lame-o. The other shark broke all the rules though. Before these researchers lucked out with this shark, the previous migratory record for Cetorhinus maximus, the basking shark, was 3,421km and depth record was 904m (off of New Zealand). Supershark reported in this paper traveled nearly 3 times farther at 9589km in 81 days of tagging (~118km/day) and dove to a deepest recorded depth of 1,264m! Way to go supershark!

What does a plankton-filtering shark do at such depths? At times, she would spent 12 or more hours at depths of 800-1000m. This suggests the shark was foraging and consuming prey in the deep sea. The authors note that mesopelagic copepods do occur around these depths. Note also on the map above that the basking shark seemed to (more or less) bee-line to the Labrador Sea. Gore and colleagues note that chlorophyll concentrations from satellite imagery, used to track primary productivity from phytoplankton blooms, were high in that region. The question still remains whether this regular migratory behavior for this shark. Other individuals have been observed migrating north-south along the both sides of Atlantic, though rarely venturing off the continental shelf into deep water.
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Gore, M.A., Rowat, D., Hall, J., Gell, F.R., Ormond, R.F. (2008). Transatlantic migration and deep mid-ocean diving by basking shark. Biology Letters, 4(4), 395-398. DOI: 10.1098/rsbl.2008.0147