Benthic habitat mapping of Cardigan Bay, in relation to the distribution of the bottlenose dolphin

Hannah Vallin BSc (Hons) Zoology, Aberystwyth University

The distribution and behaviour of many marine organisms such the bottlenose dolphin Tursiops truncatus, are influenced by the benthic habitat features, environmental factors and affinities between species of their surrounding habitats. Cardigan Bay along the west coast of Wales is a thriving marine environment. Benthic habitat mapping of the seabed allows assumptions to be made between particular behaviours such as foraging and feeding in relation to varying bathymetric characteristics on a fine-scale environment. In addition to studying the bathymetric layout along Cardigan Bay the extent of the daily oscillating tidal changes were also investigated. The purpose of this was to see if the spring or neap and ebb or flood of a tide had any effect on the behaviour and activity level of T.  truncatus. Data was collected over a three month summer period whilst onboard a research vessel. Cetacean sightings data were collected, recording exact locations and behaviours of T.  truncatus.  Following dedicated transect routes from New Quay to Ynys-Lochtyn, using specialised equipment, the boats own echo-sounder readings and Global Positioning System were used to continuously collect and calculate depth readings to create a 3-D visual image of the sea floor indicating any bathymetric features. T. truncatus spent the majority of observational time foraging with over 79% of individuals displaying this behaviour, and were observed most frequently around New Quay and Ynys Lochtyn headlands as well as within New Quay bay. Benthic mapping of the area gave rise to two particular features of interest just off New Quay headland, indicating regions of greater depths and steeper gradients, displaying gully features. However, these features do not indicate any association with increased foraging or feeding behaviour. The ebb and flood variation of diurnal tides have a strong influence on the occurrence of T. truncatus displaying foraging and feeding behaviours within Cardigan Bay. However, there is no significant difference between the monthly spring and neap tidal oscillations, and effects on the foraging and feeding behaviour of T. truncatus.  There was also no significant difference between the tidal cycle and leaping and milling behaviour of T. truncatus. Throughout the survey period a high abundance of cetaceans within this coastal region were observed, the findings and bathymetric features supports the need for the continued conservation for T. truncatus within their home range of Cardigan Bay.

Key words: Bottlenose dolphin (Tursiops truncatus), bathymetric features, Cardigan Bay, tidal cycles, foraging, feeding.

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