Marine Scotland

Understanding how seals use the water column in tidally energetic areas

November 30, 2017 by No Comments

Midpoint locations of each harbour seal dive (in red) overlaid on the high resolution bathymetry data

Midpoint locations of each harbour seal dive (in red) overlaid on the high resolution bathymetry data

As the tidal renewable industry continues to grow, increasing our understanding of the way that marine mammals use tidally energetic areas is of particular importance. This is a particular issue as there is increasing evidence that tidal energetic areas can be important foraging areas for marine mammals, therefore understanding how marine mammals use the water column is required to improve assessments of the risk of collision between seals and tidal turbines in highly energetic areas.

Building on work undertaken in a previous project which developed an improved collision risk modelling approach, utilising the most up to date information available on how seals (specifically harbour seals) use tidally active areas, this report presents a specific case study on how harbour (Phoca vitulina) and grey seals (Halichoerus grypus) use the water column within the Brims tidal energy lease area, located between Orkney and the north coast of Scotland. The Brims site is much deeper than the site used in the original work and so provides an opportunity to consider how this affects seals’ use of the water column.

Summarising the most up to date telemetry data from 20 seals tagged between 2010 and 2016, the report details the proportion of time seals spent at different depths in the water column, as well as the number of times seals passed through different water depths during foraging dives in the Brims site.

The work, undertaken by the Sea Mammal Research Unit (SMRU) at the University of St Andrews, is an important step in understanding how seals use the water in highly energetic areas which can be used to inform collision risk models on the risks posed between seals and tidal turbines.

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