LINE TRANSECT ESTIMATES OF SHORT-TAILED SHEARWATER PUFFINUS TENUIROSTRIS MORTALITY IN THE SOUTH-EASTERN BERING SEA, 1997–1999

• Main Authors: K. David Hyrenbach, Cheryl L. Baduini, George L. Hunt, G. L. Line, Short-tailed Shearwater
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2000
• Subjects: Bering Sea; Puffinus tenuirostris
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.172.1352; http://www.marineornithology.org/PDF/29_1/29_1_3.pdf

Puffinus tenuirostris mortality in the south-eastern Bering Sea, 1997–1999. Marine Ornithology 29: 11–18. During 1997, hundreds of thousands of Short-tailed Shearwaters Puffinus tenuirostris starved to death in the Bering Sea. We surveyed the distribution and abundance of floating carcasses during a cruise between 27 August–12 September, and estimated that over 95 000 carcasses were afloat within three survey grids covering approximately 52 400 km 2. We repeatedly surveyed the same areas during two subsequent cruises in 1998 and 1999, and used standard population sampling techniques to evaluate the background levels of shearwater mortality during additional years when a die-off did not occur. The mortality event we observed in 1997 was unusual due to its extent and magnitude. During the die-off, dead shearwaters were sighted within all three survey grids. Conversely, we only encountered carcasses at one of these sites in 1998. Moreover, carcass densities in 1997 were at least one order of magnitude higher than those recorded during the following year. Surveys of seabird mortality at sea can account for floating carcasses before they are lost through advection and scavenging. Therefore, vessel-based surveys are likely to improve the accuracy of seabird mortality estimates based solely on counts of beach-cast carcasses. Here we describe the use of line transects to estimate seabird mortality at sea, and offer suggestions to standardize future surveys. Standardized