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Case Study: Northern Gannets
Case Study: Northern Gannets

Context

The Northern Gannet is the largest breeding seabird in the North Atlantic Ocean. This species was a focus of this study because it is abundant in the mid-Atlantic in winter, during non-breeding periods. Previous studies conducted in Europe have also indicated a range of possible effects of offshore wind development on Northern Gannets, including collision mortality and displacement.

Download Mid-Atlantic Wildlife Studies: Distribution and Abundance of Wildlife along the Eastern Seaboard 2012-2014. This 32-page summary publication explores aspects of the mid-Atlantic ecosystem; describes our survey and analytical approaches; and presents a range of results, featuring several case studies on specific species or phenomena.

The Executive Summary for the technical report is also available here.

 

Take Home Messages

  • The broad-scale distribution and movements of Northern Gannets during winter may increase the likelihood that individuals would be in the vicinity of offshore wind developments repeatedly throughout the season.
  • Important foraging and habitat use areas appear to be defined by a wide variety of habitat characteristics. Construction and operations of offshore wind energy facilities, including associated vessel traffic, could potentially cause localized displacement anywhere in the study area, but this is most likely within about 30-40 km of shore where Northern Gannets were more abundant.
 

Background

Northern Gannets are long-lived and exhibit high adult survival. They begin breeding around five years of age. Females lay one egg per year; both parents raise the chick. In the Western Hemisphere, Northern Gannets breed at six colonies in southeastern Canada—three in the Gulf of St. Lawrence, Quebec, and three off the eastern and southern coasts of Newfoundland. They winter in Atlantic shelf waters from the Mid-Atlantic Bight to the northern Gulf of Mexico.

The Northern Gannet has a Conservation Status of Least Concern from the International Union for the Conservation of Nature, due to its relatively large population size and exceptionally large range. The North American breeding population, 27% of the global population, has experienced a healthy growth rate of 4.4% per year since 1984, although that appears to have slowed in recent years.

 

Distribution and Abundance

Winter distribution of Northern Gannets tracked via satellite telemetry (n=17; preliminary data).
Winter distribution of Northern Gannets tracked via satellite telemetry (n=17; preliminary data).
 
Predicted abundance of Northern Gannets for a given day in the winter of 2013-2014 (Nov.-Jan.) Models used observation data from boat-based surveys and remotely sensed environmental covariate data to predict abundance across the study area. The highest abundance of Northern Gannets was predicted to occur closer to shore in regions with high primary productivity.
Predicted abundance of Northern Gannets for a given day in the winter of 2013-2014 (Nov.-Jan.) Models used observation data from boat-based surveys and remotely sensed environmental covariate data to predict abundance across the study area. The highest abundance of Northern Gannets was predicted to occur closer to shore in regions with high primary productivity.
 

Behaviors and Habitat Use

Northern Gannet migration was highly asynchronous and widely dispersed across the continental shelf; they generally moved up the coast in March-April, often pausing in large bays. Birds typically left breeding colonies in September and either followed the coast or the shelf edge southward, arriving in the wintering area in November-December. Individuals roamed widely through the area in winter, showing low site fidelity.

Northern Gannets were most consistently observed in nearshore waters in our surveys, although telemetry data showed them regularly ranging as far as 50 km onto the continental shelf. The birds generally used habitat characterized by highly productive, shallower waters, with lower sea surface salinities, especially areas closer to shore and over fine sandy substrate.

 

Temporal Variation

Northern Gannets were observed from boat-based and digital aerial surveys year round, with the highest numbers observed between September and April.

Satellite tracked Northern Gannets first arrived in the mid-Atlantic in August, with peak arrival time around November, and they departed between February and May. A time variant kernel density model of satellite telemetry data was developed to improve our understanding of the species’ use of the landscape through time. The movement video generated from this model is shown here.

 

For More Information

For more information, see Chapters 12, 17, 22, 23, and 24 in the technical report.

Telemetry data were gathered as part of a longer-term study of Northern Gannets funded by multiple agencies and organizations.

Funders and collaborators for this effort are listed on the study methods page.

 

References

  • Chardine JW, Rail J-F, Wilhelm S (2013) Population dynamics of Northern Gannets in North America, 1984-2009. Journal of Field Ornithology 84:187-192 DOI: 10.1111/jofo.12017
  • Fifield DA, Montevecchi WA, Garthe S, Robertson GJ, Kubetzki U, Rail J-F (2014) Migratory tactics and wintering areas of Northern Gannets (Morus bassanus) in North America. Ornithological Monographs 79: 1-63
  • Furness RW, Wade HM, Masden EA (2013) Assessing vulnerability of marine bird populations to offshore wind farms. Journal of Environmental Management 119: 56–66. doi:10.1016/j.jenvman.2013.01.025
  • Garthe S, Benvenuti S, Montevecchi WA (2000) Pursuit-plunging by gannets. Proceedings of the Royal Society of London Series B - Biological Sciences 267:1717-1722
  • Montevecchi, WA (2007) Binary responses of Northern Gannets (Sula bassana) to changing food web and oceanographic conditions. Marine Ecology Progress Series 352:213-220
  • Mowbray, TB (2002) Northern Gannet (Morus bassanus). In The Birds of North America, No 693 (A Poole & F Gill, Eds.). The Birds of North America, Inc., Philadelphia, PA
  • Nelson JB (1978) The Gannet. T & AD Poyser, Berkhamsted, UK
  • Vanermen N, T Onkelinx, W Courtens, M Van de Walle, H Verstraete, EW.M Stienen (2015) Seabird avoidance and attraction at an offshore wind farm in the Belgian part of the North Sea. Hydrobiologia 756:51–61. doi: 10.1007/s10750-014-2088-x
 
Photo Credits: Header image © BRI-Jonathan Fiely; Maps © BRI
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