Harriet R. Huber

Trends and status of harbor seals in Washington State: 1978-1999

In the first half of the 20th century, harbor seal (Phoca vitulina richardsi) numbers were severely reduced in Washington state by a state-financed population control program. Seal numbers began to recover after the cessation of bounties in 1960 and passage of the Marine Mammal Protection Act (MMPA) in 1972. From 1978 to 1999, aerial surveys were flown at midday low tides during pupping season to determine the distribution and abundance of harbor seals in Washington. We used exponential and generalized logistic models to examine population trends and size relative to maximum net productivity level (MNPL) and carrying capacity (K). Observed harbor seal abundance has increased 3-fold since 1978, and estimated abundance has increased 7 to 10-fold since 1970. Under National Marine Fisheries Service (NMFS) management, Washington harbor seals are divided into 2 stocks: coastal and inland waters. The observed population size for 1999 is very close to the predicted Kfor both stocks. The current management philosophy for marine mammals that assumes a density-dependent response in population growth with MNPL > K/2 is supported by growth of harbor seal stocks in Washington waters.