Serendipitous re-sighting of a basking shark Cetorhinus maximus reveals inter-annual connectivity between American and European coastal hotspots.

Transatlantic stock mixing in basking sharks Cetorhinus maximus is supported by low genetic diversity in populations throughout the Atlantic Ocean. However, despite significant focus on the species' movements; >1500 individual sharks marked for recapture and >150 individuals equipped with remote tracking tags, only a single record of transatlantic movment has been previously recorded. Within this context, the seredipitous re-sighting of a female basking shark fitted with a satellite transmitter at Malin Head, Ireland 993 days later at Cape Cod, USA is noteworthy.

Latent power of basking sharks revealed by exceptional breaching events.

The fast swimming and associated breaching behaviour of endothermic mackerel sharks is well suited to the capture of agile prey. In contrast, the observed but rarely documented breaching capability of basking sharks is incongruous to their famously languid lifestyle as filter-feeding planktivores. Indeed, by analysing video footage and an animal-instrumented data logger, we found that basking sharks exhibit the same vertical velocity (approx. 5 m s-1) during breach events as the famously powerful predatory great white shark. We estimate that an 8-m, 2700-kg basking shark, recorded breaching at 5 m s-1 and accelerating at 0.4 m s-2, expended mechanical energy at a rate of 5.5 W kg-1; a mass-specific energetic cost comparable to that of the great white shark. The energy cost of such a breach is equivalent to around 1/17th of the daily standard metabolic cost for a basking shark, while the ratio is about half this for a great white shark. While breaches by basking sharks must serve a different function to white shark breaches, their similar breaching speeds questions our perception of the physiology of large filter-feeding fish.