DEPOSITION AND PERSISTENCE OF BEACHCAST SEABIRD CARCASSES

Following a massive wreck of guillemots (Uria aalge) in late winter an d spring of 1993, We monitored the deposition and subsequent disappear ance of 398 beachcast guillemot carcasses on two beaches in Resurrecti on Bay, Alaska, during a 100 day period. Deposition of carcasses decli ned logarithmically with time after the original event. Since fresh ca rcasses were more likely to be removed between counts than older carca sses, persistence rates increased logarithmically over time. Scavengin g appeared to be the primary cause of carcass removal, followed by bur ial in beach debris and sand. Along-shore transport was negligible. We present an equation which estimates the number of carcasses deposited at time zero from beach surveys conducted some time later, using non- linear persistence rates that are a function of time. We use depositio n rates to model the accumulation of beached carcasses, accounting for further deposition subsequent to the original event. Finally, we pres ent a general method for extrapolating from a single count the number of carcasses cumulatively deposited on surveyed beaches, and discuss h ow our results can be used to assess the magnitude of mass seabird mor tality events from beach surveys.