Northern Gannet: Delayed Impact
Photograph by Brian Skerry, National Geographic
A northern gannet coasts on the water. Among the 102 species of birds harmed in the wake of the Deepwater Horizon explosion and oil spill, this long-distance migrating bird, known by the scientific name Morus bassanus,
suffered the highest levels of oil damage. New research indicates much
greater impact on immature birds than traditional counting methods would
suggest, with long-term effects that remain to be seen.
"Seabirds
are among the most obvious and immediate indicators of wildlife and
environmental damage during marine pollution events," said William
Montevecchi of Memorial University, Newfoundland, Canada. He led a
study published in Biology Letters, a journal of the Royal
Society, that took advantage of advances in tracking technology to focus
on the northern gannet, the largest seabird that breeds in the North
Atlantic, and the only species of solely Canadian origin to be
significantly affected by the spill. Using bird-borne global location
sensors (GLS) and satellite tags to assess migration patterns, the
researchers concluded the gannet population saw a much higher level of "oiling" than traditional assessment methods—bird "banding" or body counts—would suggest.
The
Memorial University scientists extrapolated from GLS and satellite tags
that the number of gannets of all age classes that winter in the Gulf
of Mexico was 118,633 birds, more than double the number (54,905)
estimated by traditional banding techniques.
In addition, the
study authors stated that researchers traditionally assess seabird
mortality by counting dead and dying animals along coasts, so they see
only a fraction of those affected.
Most mature gannets had already
returned to their breeding colonies in Canada before the Gulf spill in
April, but the study concluded more than 50,000 immature gannets were in
the Gulf during the spill and suffered oil-related mortality. The
long-term effects of those gannet deaths will not show up until those
birds would have reached sexual maturity—at about five or six years of
age.
—Barbara Mulligan