Marine Fisheries Review (2014)


Harbor porpoise, Phocoena phocoena vomerina, in Cook Inlet, Alaska, are managed as part of the Gulf of Alaska (GOA) stock. It is not known if this population is distinct from porpoise in the GOA stock found outside Cook Inlet. No long-term dedicated studies of harbor porpoise have occurred in Cook Inlet. The objective here is to provide a summary of occurrence in Cook Inlet derived from archaeological data, anecdotal reports, and systematic surveys. Maps were created for each dataset. For 1,500 years, Alutiiq Eskimo subsistence societies occupied lower Cook Inlet until abandoning the region around 600 A.D. During that time, harbor porpoise exploitation increased and eventually made up over one-third of the faunal remains by number at midden sites. The Dena’ina and Chugach Alutiiq continued porpoise hunting into the period of early contact in the late 1700’s, after which there is no mention of continued exploitation. Harbor porpoise were rarely mentioned in expedition accounts collected by naturalists in the late 1800’s and early 1900’s.

Beginning in 1958, pelagic fur seal, Callorhinus ursinus, investigators collected cetacean sightings in Alaska waters when seals were not present. However, none of the harbor porpoise sightings occurred in Cook Inlet. With the exception of one net entanglement in upper Cook Inlet in 1956, sightings and strandings (including fisheries bycatch) were not reported in the inlet until the mid-1970’s. Interactions with fisheries factored in a quarter of the stranded animals recovered in Cook Inlet.

Systematic surveys of bird and marine mammal populations increased during the 1970’s and continued sporadically to the present day. One dedicated harbor porpoise aerial survey conducted in August 1991 estimated the population at 136 (CV = 63.2%), but this survey did not include the shoreline and many of the bays throughout Cook Inlet. An uncorrected abundance of 249 (CV = 60.7%) in June 1998 was based on offshore sightings obtained during beluga whale, Delphinapterus leucas, aerial surveys. The largest abundance estimate, 428 harbor porpoise (95% C.I. 26–830), was obtained during vessel surveys designed to count seabirds in lower Cook Inlet during the summer of 1993. Harbor porpoise sighting rates, abundance, and density estimates often were limited by survey area, effort, research plat-form, and study design. Therefore, each of these estimates is likely biased downward.

In the last decade the region has seen expansion of the Port of Anchorage, proposals to build a bridge crossing Knik Arm, plans to develop mining operations and supporting infrastructure, hydrokinetic energy generation proposals, oil and gas seismic exploration, and water quality effects from urban areas. The overall effect on harbor porpoise within the confines of Cook Inlet cannot be fully determined until we understand the genetic and demographic population structure of this highly mobile and cryptic species.