Tidal upwellings as critical habitats for shearwaters in the Bay of Fundy
Many seabirds undertake dramatic migrations, traveling thousands (or tens of thousands) of kilometers between their summer breeding grounds and over-winter foraging sites, but little is known about the stop-over sites where these birds forage to replenish energy reserves between long-distance trips. Around Grand Manan Island, tidal currents form strong and predictable upwelling regions where seabirds and marine mammals forage. Great and Sooty shearwaters, two of the most abundant summer seabirds in Atlantic Canada, make heavy use of these upwelling systems, particularly in August prior to migration. This provides us with a rare opportunity to study shearwaters outside of their breeding season.
Since 2005 we have been studying the diets, movements, habitat use and migrations of shearwaters around Grand Manan Island. From small boats, we use throw nets to capture birds at sea allowing us to measure, weigh and sample more than 300 individuals over the past 6 years. Blood and feather samples are used in bio-chemical analyses of stable isotopes and fatty acids to decipher their diets, which consist primarily of krill, herring, mackerel and squid. Satellite transmitters have allowed us to track individuals, revealing foraging “hotspots” at tidal upwellings in the Bay of Fundy and documenting long-distance migration routes to their breeding grounds in the southern hemisphere (the longest recorded track was over 47,000 km during 209 days!). Visit these links to see tracks from shearwaters tagged around Grand Manan: 2006, 2007, 2008, and 2009.
Seabirds are widely regarded as important indicators of marine ecosystem health. Through yearly sampling, we are using dietary analysis to investigate changes in shearwater diets, which can indicate changes in the prey base in Fundy tidal upwelling ecosystems. We have already observed a shift in shearwater diets from herring and krill (2005-2006) to squid and krill (2007-2009), and we plan to continue monitoring shearwater diets over the next 5 to 10 years. Measures of body condition, studies of stress hormones, and analysis of hematology (blood cell counts and diseases) also form part of our annual monitoring program to investigate changes in the “health” of shearwaters that use tidal upwelling sites around Grand Manan.