Effects of EVOS on abundances and reproduction of Murre colonies, near PWS, coastal Kenai and Alaska Peninsulas, and Kodiak Island (1989-1991).

We surveyed murres (Uria spp.) annually from 1989 through 1991 at breeding
colonies within the trajectory of the oil to determine whether numbers had declined and to
evaluate the effects of oil on nesting phenology and reproductive success, following the 1989
Exxon Valdez oil spill (EVOS). The colonies we surveyed contained the majority of the estimated
200,000 murres attending colonies in the affected area, and we found reduced numbers at all
study colonies following the spill. In addition, nesting was delayed and productivity rates
were far below normal following the spill. In contrast, numbers of murres did not decline and
reproductive parameters were normal at 2 colonies we surveyed outside the trajectory.
The only indication of recovery since the spill was a slight increase in reproductive success at
monitored colonies in 1991. The most likely cause of reduced numbers of murres at cliffs
following the oil spill was direct mortality from the oil. Since breeding murres were
congregating near colonies at the time of the spill, most murres killed were probably
experienced breeders. We concluded that reduced densities and skewed age structures were
the most likely causes of abnormal breeding after the spill.