Quantifying pursuit diving seabirds' associations with fine-scale physical features in a high tidal energy environment

The rapid increase in the number of tidal stream turbine arrays will create novel and unprecedented levels of anthropogenic activity within habitats characterized by horizontal current speeds exceeding 2 ms−1. However, the potential impacts on pursuit‐diving seabirds exploiting these tidal stream environments remain largely unknown. Identifying similarities between the fine‐scale physical features (100s of metres) suitable for array installations, and those associated with foraging pursuit‐diving seabirds, could identify which species are most vulnerable to either collisions with moving components, or displacement from these installations. A combination of vessel‐based observational surveys, Finite Volume Community Ocean Model outputs and hydroacoustic seabed surveys provided concurrent measures of foraging distributions and physical characteristics at a fine temporal (15 min) and spatial (500 m) resolution across a tidal stream environment suitable for array installations, during both breeding and non‐breeding seasons. These data sets were then used to test for associations between foraging pursuit‐diving seabirds (Atlantic puffins Fratercula arctica, black guillemots Cepphus grylle, common guillemots Uria aalge, European shags Phalacrocorax aristotelis) and physical features. These species were associated with areas of fast horizontal currents, slow horizontal currents, high turbulence, downward vertical currents and also hard–rough seabeds. The identity and strength of associations differed among species, and also within species between seasons, indicative of interspecific and intraspecific variations in habitat use. However, Atlantic puffins were associated particularly strongly with areas of fast horizontal currents during breeding seasons, and European shags with areas of rough–hard seabeds and downward vertical currents during non‐breeding seasons. Synthesis and applications. Atlantic puffins’ strong association with fast horizontal current speeds indicates that they are particularly likely to interact with installations during breeding seasons. Any post‐installation monitoring and mitigation measures should therefore focus on this species and season. The multi‐species associations with high turbulence and downward vertical currents, which often coincide with fast horizontal current speeds, also highlight useful pre‐installation mitigation measures via the omission of devices from these areas, reducing the overall likelihood of interactions. Environmental impact assessments (EIA) generally involve once‐a‐month surveys across 2‐year periods. However, the approaches used in this study show that more focussed surveys can greatly benefit management strategies aiming to reduce the likelihood of negative impacts by facilitating the development of targeted mitigation measures. It is therefore recommended that these approaches contribute towards EIA within development sites.

Quantifying pursuit-diving seabirds’ associations with fine-scale physical features in tidal streamenvironments

Acknowledgements James J. Waggitt was funded by a NERC Case studentship supported by OpenHydro Ltd and Marine Scotland Science (NE/J500148/1). Vessel-based transects were funded by a NERC (NE/J004340/1) and a Scottish National Heritage (SNH) grant. FVCOM modelling was funded by a NERC grant (NE/J004316/1). Marine Scotland Science provided time on the FRV Alba-na-Mara as part as the Marine Collaboration Research Forum (MarCRF). The bathymetry data used in hydrodynamic models (HI 1122 Sanday Sound to Westray Firth) was collected by the Maritime & Coastguard Agency (MCA) as part of the UK Civil Hydrography Programme. We wish to thank Christina Bristow, Matthew Finn and Jennifer Norris at the European Marine Energy Centre (EMEC); Marianna Chimienti, Ciaran Cronin, Tim Sykes and Stuart Thomas for performing vessel-based transects; Marine Scotland Science staff Eric Armstrong, Ian Davies, Mike Robertson, Robert Watret and Michael Stewart for their assistance; Shaun Fraser, Pauline Goulet, Alex Robbins, Helen Wade and Jared Wilson for invaluable discussions; Thomas Cornulier, Alex Douglas, James Grecian and Samantha Patrick for their help with statistical analysis; and Gavin Siriwardena, Leigh Torres, Mark Whittingham and Russell Wynn for their constructive comments on earlier versions of this manuscript.

Predictable hydrodynamic conditions explain temporal variations in the density of benthic foraging seabirds in a tidal stream environment

Tidal stream turbines could have several direct impacts upon pursuit-diving seabirds foraging within tidal stream environments (mean horizontal current speeds > 2 ms−1), including collisions and displacement. Understanding how foraging seabirds respond to temporally variable but predictable hydrodynamic conditions immediately around devices could identify when interactions between seabirds and devices are most likely to occur; information which would quantify the magnitude of potential impacts, and also facilitate the development of suitable mitigation measures. This study uses shore-based observational surveys and Finite Volume Community Ocean Model outputs to test whether temporally predictable hydrodynamic conditions (horizontal current speeds, water elevation, turbulence) influenced the density of foraging black guillemots Cepphus grylle and European shags Phalacrocorax aristotelis in a tidal stream environment in Orkney, United Kingdom, during the breeding season. These species are particularly vulnerable to interactions with devices due to their tendency to exploit benthic and epi-benthic prey on or near the seabed. The density of both species decreased as a function of horizontal current speeds, whereas the density of black guillemots also decreased as a function of water elevation. These relationships could be linked to higher energetic costs of dives in particularly fast horizontal current speeds (>3 ms−1) and deeper water. Therefore, interactions between these species and moving components seem unlikely at particularly high horizontal current speeds. Combining this information, with that on the rotation rates of moving components at lower horizontal current speeds, could be used to assess collision risk in this site during breeding seasons. It is also likely that moderating any device operation during both lowest water elevation and lowest horizontal current speeds could reduce the risk of collisions for these species in this site during this season. The approaches used in this study could have useful applications within Environmental Impact Assessments, and should be considered when assessing and mitigating negative impacts from specific devices within development sites.

Breeding populations of seabirds in California, 1989-1991. Volume I - population estimates

In 1989-1991, the U.S. Fish and Wildlife Service surveyed breeding populations of seabirds on the entire California coast. This study was sponsored by the Minerals Management Service in relation to outer continental shelf oil and gas leasing. At 483 nesting sites (excluding terns and skimmers in southern California), we estimated 643,307 breeding birds of 21 seabird species including: 410 Fork-tailed Storm-petrel (Oceanodroma furcata); 12,551 Leach's Storm-petrel (O. leucorhoa); 7,209 Ashy Storm-petrel (O. homochroa); 274 Black Storm-petrel (O. melania); 11,916 Brown Pelican (Pelecanus occidentalis); 10,037 Double-crested Cormorant (Phalacrocorax auritus); 83,394 Brandt's Cormorant (P. penicillatus); 14,345 Pelagic Cormorant (P. pelagicus); 888 Black Oystercatcher (Haemotopus bachmani); 4,764 California Gull (Larus californicus); 61,760 Western Gull (L. occidentalis); 2,838 Caspian Tern (Sterna caspia) (excluding southern California); 3,550 Forster's Tern (S. forsteri) (excluding southern California); 272 Least Tern (S. albifrons) (excluding southern California); 351,336 Common Murre (Uria aalge); 15,470 Pigeon Guillemot (Cepphus columba); 1,821 Marbled Murrelet (Brachyramphus marmoratus); 1,760 Xantus' Murrelet (Endomychura hypoleuca); 56,562 Cassin's Auklet (Ptychoramphus aleuticus); 1,769 Rhinoceros Auklet (Cerorhinca monocerata); and 276 Tufted Puffin (Fratercula cirrhata). The inland, historical or hybrid breeding status of American White Pelican (P. erythrorynchus), American Oystercatcher (H. palliatus), Heermann's Gull (L. heermanni), Ring-billed Gull (L. delawarensis), Glaucous-winged Gull (L. glaucescens) and Black Tern (Chlidonias niger) are discussed. Estimates for Gull-billed Tern (S. nilotica), Royal Tern (S. maxima), Elegant Tern (S. elegans) and Black Skimmer (Rhynchops niger) will be included in the final draft of this report. Overall numbers were slightly lower than reported in 1975-1980 surveys (summarized in Sowls et al. 1980. Catalog of California seabird colonies. U.S. Dept. Int., Fish Wildl. Serv., Biol. Serv. Prog., FWS/OBS 37/80). Recent declines were found or suspected for Fork-tailed Storm-petrel, Leach's Storm-petrel, White Pelican, Black Tern, Caspian Tern, Least Tern, Common Murre and Marbled Murrelet. Recent increases were found or suspected for Brown Pelican, Double-crested cormorant, California Gull, Western Gull, Forster's Tern and Rhinoceros Auklet. Similar numbers were found for other species or trends could not be determined without additional surveys, studies and/or more in-depth comparisons with previous surveys. The status of terns and skimmers in southern California has not yet been finalized.