EXTREME TEMPORAL VARIATION IN HARBOR SEAL (PHOCA VITULINA RICHARDSI) NUMBERS IN GLACIER BAY, A GLACIAL FJORD IN SOUTHEAST ALASKA

As part of a four-year project to determine a minimal population estimate (sum of maximal counts) for harbor seals in Alaska, the National Marine Mammal Laboratory, National Marine Fisheries Service (NMFS) extensively surveyed southeast Alaska in September 1993. The NMFS will base management decisions on the minimal population estimate derived from that survey. During the September 1993 survey, only 500 seals were counted in Johns Hopkins Inlet and only 1,086 were found at haulouts throughout Glacier Bay; three weeks earlier 4,500 seals were counted in Johns Hopkins Inlet alone. A large underestimate of seals in Glacier Bay could bias the estimate of seal numbers throughout southeast Alaska, unless they were detected in adjacent areas. We documented the decrease in seals on haulouts between August and September 1993 by comparing the Johns Hopkins portion of the NMFS September 1993 survey to a survey conducted in the fjord in August of the same year, and by comparing results of the September 1993 surveys of all haulouts in Glacier Bay (including Johns Hopkins Inlet) to two baywide surveys completed in August 1992 and 1994. The data suggest that more than half of the 6,000 seals found in Glacier Bay in August were not detected in the bay, or within a 60-km radius of the bay, during the September 1993 survey.