Ewan Wakefield

University of Glasgow

The Distribution and Ecology of Seabirds in the Sub-Polar Frontal Zone of the Northwest Atlantic

Summary

This cruise aims to survey and sample of seabirds in the Northwest Atlantic to examine multiple aspects of their ecology. In addition, complimentary studies on physical oceanography, nutrient dynamics and cetaceans will be undertaken.

Background

Breeding seabirds are a familiar sight in coastal areas but pelagic species, such as shearwaters and fulmars, spend most of their time far out at sea. Typically, they travel 100s to 1000s of km from their colonies to provision their offspring and may migrate across oceans during non-breeding periods. Until recently this made them enigmatic but the development of bird-borne tracking devices is now providing incredible insights into their movements and behaviour. Nonetheless, many fundamental aspects of their ecology (diet, niche partitioning, etc.) remain poorly understood.

This is of concern for a number of reasons: Firstly, pelagic seabirds may be major consumers of mesotrophic organisms in many areas of the world’s oceans, thereby exerting top-down control of pelagic ecosystems. Moreover, recent studies on functionally homologous cetaceans suggest an intriguing possibility - that by rapidly resupplying nutrients (and particularly iron) within the photic zone, seabirds enhance primary production within oceanic waters, mediating carbon drawdown. Similarly, due to their wide ranging movements, they may provide important links between disparate marine ecosystems, such as those on and off-shelf or in different hemispheres.

Secondly, shearwaters and other large petrels rely on the wind in order to fly efficiently. This constrains them to follow least-cost pathways defined by large-scale wind patterns, much in the same way as traditional sailing ships. There is emerging evidence that climate change may alter these wind patterns, potentially impacting seabirds in either positively or negatively. In turn, this could disrupt their provision of the ecosystem services alluded above.

Finally, negative impacts from human activities, such as fisheries and the introduction of invasive species to breeding colonies, mean that as many as 40% of seabird species may become functionally extinct by 2100. There is therefore an urgent need to identify areas used most frequently by seabirds so that potentially harmful human activities can be mitigated.

Early seabird biologists worked largely from ships, piecing together data on distribution, movement and diet, often through lethal sampling of birds. There followed a shift to colony-based studies, and latterly to remote observation using bird-borne devices. Since the pioneering days, surprisingly few studies have been carried out at sea in the deep Atlantic, despite the fact that the area is bounded by large seabird colonies and some of the world’s most developed countries. A recent meta-analysis of tracking data by BirdLife International and others has identified a potentially important hotspot of seabird diversity and abundance in the deep Northwest Atlantic. It has been suggested that this area, which lies in the vicinity of the sub-polar front, south of the Charlie Gibbs Fracture Zone (CGFZ), should be designated as a High Seas Marine Protected Area but more data are needed to confirm its importance.

Context

Expedition DY080 is being undertaken as part of the NERC-funded project Seabirds and wind - the consequences of extreme prey taxis in a changing climate.  

This project has five broad objectives:

• to estimate the distribution, movements and behaviour of key seabird populations during breeding and non-breeding stages and determine the dependence of these processes on movement constraints and habitat;
• to quantify temporal variation in habitat use within species and niche partitioning between them;
• to predict how wind-mediated seabird movement corridors are likely to change under future climate change scenarios and estimate how this will affect the ecosystem functions performed by seabirds;
• to estimate nutrient recycling and transport within and between marine ecosystems by seabirds; and
• to facilitate the conservation of seabirds and other higher marine predators by identifying potential High Seas Marine Protected Areas.

The study focuses on four morphologically similar speceis: Cory's shearwaters (Calonectris diomedea), northern fulmars (Fulmarus glacialis), great shearwaters (Ardenna gravis) and sooty shearwaters (Ardenna grisea).

During the project, these species will be tracked using gelocation and time-depth loggers deployed at their colonies. In addition, we intend to track the latter two species at higher resolution using satellite tags deployed on birds caught at sea. This will allow simultaneous observation of individual birds, seabird communities, and the environment in which they forage.

Expedition Aims

• To estimate the distribution, abundance and behaviour of seabirds and cetaceans in a study area centred on the sub-polar front, south of the Charlie Gibbs Fracture Zone (CGFZ), and to survey these species en route to and from the study area.
• To develop non-lethal methods of catching seabirds at sea.
• To estimate the diet, stable isotope and contaminant loading, faecal nutrient content and moult status of seabirds within the study area.
• To determine the comparative habitat use of great and sooty shearwaters on and off the Canadian continental shelf and the timing of their movements between these areas.
• To map the location of major frontal features and nutrient regimes within the study area.
• To estimate the vertical distribution and biomass of mesopelagic nekton within the study area.
• To conduct in vitro phytoplankton incubation experiments to estimate rates of nutrient cycling within the study area.

Participating institutes: The University of Glasgow, Environment Canada, the Sea Mammal Research Unit, the University of Manitoba, the University of Rhode Island, the University of Coiumbra, GEOMAR, CEFAS, the Royal Society for the Protection of Birds.

The cruise blog can be accessed here