Basking sharks are long-distance swimmers

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A team of scientists have tagged two basking sharks (Cetorhinus maximus) and found that they are capable of swimming further and deeper than previously thought.

The results of the tagging study by Mauvis Gore and coauthors are published in the latest issue of the journal Biology Letters.

The two sharks were tagged and released off the Isle of Man, with the data from the tags being transmitted via satellite.

The smaller shark remained in coastal waters within the continental shelf, but the larger shark traveled a horizontal distance of 9589 km in 81 days, eventually arriving just off the coastal waters of Newfoundland.

This distance is almost three times the current record of 3421 km (observed in New Zealand).

At the same time, the authors also discovered that the shark was diving deeper than previously thought, reaching a maximum depth of 1264 m (the previous maximum recorded depth is 750"1000 m).

The authors speculate that such long-distance migrations may be a normal feature of basking shark biology, citing recent studies that have shown other large shark species to undertake migrations of similar length (e.g. between South Africa and Australia).

The authors conclude: This conclusion has significant implications for the species conservation, especially given an estimate of an effective population size of only 8200 individuals globally and its IUCN status as Vulnerable.

Despite protective legislation, the numbers in the northeast Atlantic may show only limited recovery if mature adults are exposed to exploitation in other oceanic regions.

For more information, see the paper: Gore, MA, D Rowat, J Hall, FR Gell and RF Ormond (2008) Transatlantic migration and deep mid-ocean diving by basking shark. Biology Letters 4, pp. 395"398.