Photo byPer Berggren
Harbor porpoise are small cetaceans, being only about as long as a woman is tall. They are shy animals and are most often seen in small groups of two or three. They live near-shore throughout their range, which extends throughout cold temperate waters of the northern hemisphere. Because they prefer coastal habitats, harbor porpoise are particularly vulnerable to being caught in gillnets and fishing traps and have been extirpated from several areas within their range. Off the west coast of the US and Canada, which is the area of interest for our studies, harbor porpoise are essentially continuously distributed from Point Conception, CA to Barrow, AK.
We have used both mitochondrial and nuclear DNA markers to ask whether there is evidence of population structure among harbor porpoise living off the coasts of CA, OR and WA. That is, is there evidence of limited dispersal between groups such that they are functionally independent or essentially reproductively isolated? Our analyses of the genetic data indicate that, yes, there is limited dispersal (Chivers et al., 2002). These results in conjunction with what is known about their distribution and abundance (Forney 1999) were used to redefine the management units used for assessing status (Carretta et al., 2004).There are now six management units of harbor porpoise recognized off the coasts of CA, OR and WA. Additional genetic data are being analyzed and tracking studies are being conducted to help us better understand the population structure and movement patterns of harbor porpoise.
Carretta, J., K. Forney, M. Muto, J. Barlow, J. Baker, B. Hanson, and M. Lowry. 2004. US Marine Mammal Stock Assessments: 2004. NOAA-TM-NMFS-SWFSC-375. 323pp.
Chivers, S. J., A. E. Dizon, P. Gearin, and K. M. Robertson. 2002. Small-scale population structure of eastern North Pacific harbor porpoise, Phoceona phocoena, indicated by molecular genetic analyses. Journal of Cetacean Research and Management 4(2):111-122.
Forney, K. A. 1999. The abundance of California harbor porpoise estimated from 1993-97 aerial line-transect surveys. NOAA, NMFS, Southwest Fisheries Science Center Administrative Report LJ-00-02.