Spatial ecology of flapper skate (<i>Dipturus intermedius – Dipturus batis complex</i>) and spurdog (<i>Squalus acanthias</i>) in relation to the Loch Sunart to the Sound of Jura Marine Protected Area and Loch Etive

Background

Elasmobranchs (sharks, skates and rays) have the potential for high mobility. However, where they show certain types of behaviour such as residency or site fidelity, Marine Protected Areas (MPAs) can be a valid option for their conservation. Such behaviour has been identified in the flapper skate (Dipturus intermedius), resulting in the Loch Sunart to the Sound of Jura MPA being established for this species. One aim of this project was to better understand how the skate use the MPA using an array of acoustic sensors in the Firth of Lorn and Sound of Mull (the Firth of Lorn acoustic array). The project also set out to explore the spatial behaviour of spurdog (Squalus acanthias) in Loch Etive, a sea loch that is connected to and lies adjacent to the MPA. In both cases, tagging technologies including acoustic and archival tags were used.

Main findings

Flapper skate (Dipturus intermedius)

Tagged females displayed higher occupancy in the Firth of Lorn than males. The average number of days females remained in the Firth of Lorn over the course of the project (13 months) was 85, whereas for males it was 31. Four female skate were detected for over 200 days each. Only two males were detected for longer than 50 days. Skate mostly remain in water depths between 100 – 150 m over summer months (March – August) with some individuals having a larger depth range over winter months (September – February).

Spurdog (Squalus acanthias)

Both sexes have high residency in Loch Etive. 95% of tagged spurdog were detected in the loch for more than 250 days. Only male spurdog were tagged in the Firth of Lorn. They moved away between August and November, returning in November and remaining in the Firth of Lorn over winter. None of these were detected in Loch Etive. There was very limited evidence of females from the loch moving into the Firth of Lorn with 2 spurdog being detected in the Firth of Lorn. Where the movements of male and female spurdog could be compared, there were no discernible differences between the sexes.