Basking sharks can grow up to 12m in length and are known to frequent Irish waters and coastal marine habitats each summer. Currently listed as endangered on the IUCN Red List of Threatened Species, the species is usually sighted in Irish coastal waters from May to September to feed on plankton. Until recently, researchers believed that the sharks would either migrate to warmer oceans during the winter months or cross the Atlantic.
However, according to reporting by the Donegal Daily, a team of scientists from Queen’s University Belfast and Canada’s Western University has now found evidence of some individuals staying around Ireland’s coast in winter where they remained below the surface. By attaching archival satellite tags to four basking sharks, the team was able to record water temperature, depth and location of the sharks for six months. The tags showed that two sharks migrated to Africa in winter, while the other two remained in near the Irish coastline.
“Our findings challenge the idea of temperature as the main reason for winter dispersal from Ireland. Likewise, further evidence of individual basking sharks occupying Irish coastal waters year-round has significant implications for national and European conservation efforts. Previously we understood basking sharks departed Irish coastal waters for more southern latitudes in the Autumn in response to falling water temperatures in the north east Atlantic,” said Dr Emmett Johnston, first author on the study.
Interestingly, the sharks that stayed in Irish waters during winter, were not registered on the surface for long periods of time and primarily swam in depths of 60 to 100m. The individuals in Africa dove to depths of up to 600m, making them experience colder temperatures than the individuals remaining in Ireland. This suggests that the sharks don’t solely migrate to find warmer waters.
The new findings highlight the importance of deep water habitats for the species which need to be further researched and considered for future conservation measures.
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Photography courtesy of Pexels.
