Abstract
Little terns have recently begun to use the main bank of Scroby Sands as a nesting site, following the decline of the mainland North Denes colony within the Great
Yarmouth North Denes SPA. There is concern that breeding Little Tern Sternula albifrons may be at increased risk of collision with turbines at Scroby Sands offshore wind farm.
The objectives of this study were thus to:
• Assess the current density of Little Tern usage of Scroby Sands wind farm
• Use current density data for Little terns to inform collision risk modelling
• Assess why any increased usage of Scroby Sands wind farm by Little terns is occurring and whether this could affect collision risk.
Eight boat-based surveys over a route of 46 km incorporating 10.3 km within the wind farm, utilising snapshots for flying terns every 250 m (n=185) were performed approximately every two weeks from early May to mid August 2013. Recording of the distance of birds allowed Distance sampling to be used, which clearly showed a decline in detectability over 300 m for all tern species, with 200 m being a more realistic detection distance for Little Tern. The route also incorporated the previous sampling protocol adopted from 2002-2006 that included 12 one km long survey stations where all birds were recorded and a specifically designed surface tow net was used to sample the prey available to Little terns.
The key finding from prey sampling was evidence of the recovery of the Herring stock known to have been previously affected by pile-driving during construction of the wind farm. The peak density of young clupeids, mainly comprised of young-of-theyear Herring was around 0.38 individuals m-2 and thus best described as ‘moderate’. The trends in distribution and abundance of young clupeids mirrored previously described patterns. Namely, fish were concentrated around North Denes and nearby inshore sites and peaked in early June before declining. Incursion of YOY Sprat also occurred but in insufficient numbers to replace Herring including later in the season.