New insights into the summer distribution of basking sharks (Cetorhinus maximus) in the northeast Atlantic

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Stasiuleviciute, Edita
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University College Cork
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Basking sharks, Cetorhinus maximus, have undergone widespread historic exploitation in the northeast Atlantic and are of conservation concern. A greater knowledge on their spatial and temporal habitat use in response to environmental conditions is required to better inform subsequent monitoring and management strategies. Several efforts to describe the occurrence and distribution of basking sharks have been already made, however nothing at large spatial scales. Sighting information on basking sharks was derived from three aerial survey programmes which covered extensive inshore and offshore waters within the northeast Atlantic. The occurrence of basking sharks in the area was highly seasonal, with individuals predominately observed during the summer months (May-August). Hotspots of occurrence were within the coastal waters off the south and west of Ireland, whereas areas such as southwest of England and west of Scotland, previously considered to be hotpots for basking sharks, were not aggregation sites during summer months, suggesting a seasonal change in distribution. Based on satellite-derived environmental variables and climate indices, this study revealed that distribution of basking sharks was associated with (1) lower chl-a concentrations (< 2.27 mg/m³), (2) shallow coastal waters which are most likely important summer feeding grounds; and (3) positive North Atlantic Oscillation (NAO) winter index, most likely through association with prey species. Sea surface temperature (SST) had no significant effect on the distribution of basking sharks. This study provided new insights into the seasonal occurrence of basking sharks on a large scale within the northeast Atlantic. The results produced here could be incorporated into future management frameworks for assessing the threat and conservation needs for this regionally protected species, as well as providing guidance for future research efforts.
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Baskin shark , Ecology , Aerial surveys
Stasiuleviciute, E. 2022. New insights into the summer distribution of basking sharks (Cetorhinus maximus) in the northeast Atlantic. MRes Thesis, University College Cork.
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