Special Status Species
SPECIAL STATUS SPECIES: Harbor porpoise (Phocoena phocoena)
Harbor porpoise Photo: NOAA Common name: Harbor porpoise
Scientific name: Phocoena phocoena
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Range Habitat Movements
Abundance Natural History Threats
Conservation Research Gaps Recommended Actions
References Resources

Listing Status
Endangered Species Act (?)
Status: Not listed

California Endangered Species Act (?)
Status: Not listed

Marine Mammal Protection Act (?)
Status: San Francisco-Russian River: Non-strategic stock
Status: Monterey Bay: Non-strategic stock
Status: Morro Bay: Non-strategic stock
Stock Assessment: Updated at least every three years 1

The World Conservation Union (IUCN) (?)
Status: Vulnerable (world-wide)

Convention on International Trade in Endangered Species (CITES) (?)
  Appendix II

Geographic Range
General: This species is limited to temperate and sub-polar waters in the northern hemisphere (Figure 1). It is rarely found in water warmer than 17C.2 In the Pacific, harbor porpoise are found along the coast of western North America from Pt. Conception, California to Alaska and across the Aleutian chain to Kamchatka and Japan. Based on significant genetic differences and density discontinuities identified from aerial surveys, the population along the California coast was split into 4 stocks .1,3 Those stocks are: (1) the Morro Bay stock from Point Conception to Point Sur; (2) the Monterey Bay stock from Point Sur to Pigeon Point; (3) the San Francisco-Russian River stock from Pigeon Point to Point Arena; and (4) the Northern California-Southern Oregon stock from Point Arena to Cape Blanco, Oregon (Figure 2).
Harbor porpoise distribution map
Figure 1. Global distribution of the harbor porpoise.
MBNMS: Three of the stocks in California have ranges that overlap the boundaries of the MBNMS (Figure 2). The Morro Bay stock occurs in the southern portion of the Sanctuary between Cambria and Point Sur. The entire Monterey Bay stock occurs in Sanctuary waters. The San Francisco-Russian River stock occurs in the northern portion of the MBNMS between Pigeon Point and Marin County.
Geographic range of harbor porpoise along California coast
Figure 2. Geographic range of the harbor porpoise stocks along the California coast. The shaded area represents harbor porpoise habitat (0-200 m) along the U.S. west coast. The Morro Bay, Monterey Bay, and San Francisco-Russian River stocks are found in waters of the MBNMS.32
General: Harbor porpoise are found in coastal and inland habitats including bays, estuaries, and harbors. Recent aerial surveys used to estimate harbor porpoise abundance in California waters found that only 8% of the observed individuals occurred in waters between 90 m - 200 m deep and most of those individuals were sighted north of the Russian River-San Francisco stock region.4 Other surveys in various locations along the California coast have found that harbor porpoise abundance declined sharply in waters deeper than 60 m and 110 m.5,6
MBNMS: Within Monterey Bay, California, harbor porpoise concentrations are greater north of the submarine canyon, with frequent sightings off Sunset Beach and north of La Selva Beach.7 Two other areas of high abundance in the Sanctuary are the southern Monterey Bay (off of the former Fort Ord) and near the mouth of San Francisco Bay.8
Migration and Movements
General: Harbor porpoise are present year-round along the coast of central and northern California. Unlike harbor porpoises in the Atlantic Ocean, those in the Pacific show no evidence of migration or extensive movements. Genetic data show evidence of population structure along the California coast indicating limited dispersal between stocks.3 Genetic data also suggest that breeding males move greater distances than breeding females.3 Regional differences in pollutant residues support the conclusion that harbor porpoises along the CA coast remain in a single region for extended periods of time if not their entire lives.9
MBNMS: Harbor porpoises inhabit regions of MBNMS year-round, but details on their movements and behavior within this area are not well understood. Genetic studies showed that harbor porpoises from the Monterey Bay stock were statistically distinguishable from those in other stocks.3 Low variance in pollutant ratios from animals collected in the Monterey Bay suggest that the animals were collected from a resident population.9 Both these findings suggests that few individuals are moving between the Monterey Bay stock and the adjacent stocks.
General: The most recent abundance estimate for California waters of approximately 24,000 harbor porpoise was made based on aerial surveys in 1999 and 2002.4 This estimate is very similar to the prior estimate for the 1997-1999 survey period.10 Abundance of this species is highest in northern California and decreases to the south with the lowest abundances observed in the southernmost stock.10 Higher densities have been found during the summer and fall, but movement out of the study area (e.g., into deeper water) or reduced sighting ability in larger winter swells may be the cause of this pattern.5 Harbor porpoise typically travel in small groups, avoid boats, and show little of their bodies above water. This combination of behavioral traits makes harbor porpoise difficult to observe in the field, especially in rough seas.6
MBNMS: Aerial surveys between 1986 and 1995 showed an apparent declining trend in abundance of harbor porpoise in central California (Figure 3), but this decline was correlated with changing ocean temperatures, suggesting movement of animals rather than a true population decline.11,12 Subsequently, the abundance of harbor porpoise in central California was estimated to be higher in 1997 and 1999 than in any survey since 1986 (Figure 3).10 It is unclear how much of this increase may reflect a true population increase and how much may be related to a redistribution of animals in and around the study area in response to changing oceanographic conditions.12 Estimates of stock size, based on aerial surveys from 1999 and 2002, are: 8,521 for the San Francisco-Russian River stock; 1,613 for the Monterey Bay stock; and 1,656 for the Morro Bay stock.4 These numbers are slightly higher than those made for 1997-1999, but the increases were not statistically significant.
Aerial survery abundance map
Figure 3. Aerial survey estimates of abundance for the Monterey Bay stock of harbor porpoise, 1988-2002. Error bars represent lower and upper 95% confidence intervals. Solid line represents a linear regression of the natural logarithm of abundance over time. The slope of this regression is not statistically significant (p = 0.64).32
Natural History
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General: Entanglement in fishing gear: Harbor porpoise are extremely vulnerable to entanglement in gillnets, but they may also become entangled in other types of fishing gear and aquaculture pens. Estimates of harbor porpoise mortality in the set gillnet fishery along the California coast ranged between 144 to 622 animals for the four-year period between 1995 and 1998.19 Harbor porpoise mortality was estimated to be 128, 26, 3, and 16 animals in this fishery in 1999, 2000, 2001, and 2002, respectively.20,21,22,23 The threat posed by the set gill net fishery was dramatically reduced in 2002 by a prohibition on the use of gillnets in waters shallower than 60 fathoms in central California (for more details see "Research and Conservation" below).1 During the summer of 2004, 36 harbor porpoise stranded along the central California coast. It appears that a number of the animals died from fishery interactions, but the responsible fishery had not yet been identified.8

Boat traffic: Harbor porpoise are known to move away from all types of boats including motorized watercraft, sailboats and kayaks. It is possible that increasing concentration of boat traffic in prime foraging locations could lead to abandonment of those areas.

Pollution (e.g., chemical pollution, oil pollution, marine debris): Any increase in offshore oil and gas development would increase both the potential of an oil or chemical spill and the amount of shipping traffic in and adjacent to harbor porpoise habitat. Harbor porpoise along the California coast have measurable loads of chemical pollutants including organochlorides (e.g., PCBs, DDT) and heavy metals.9 The impact of these pollutants on the health and reproduction of these animals is not well understood. Some harbor porpoise have stranded with plastic and other marine debris in their digestive system.24

Acoustic disturbance (e.g., noise from ships, aircraft, research boats, and military and industrial activities): Harbor porpoise are sensitive to sounds including low frequency noise from wind-turbines and high frequency noise from acoustic deterrent devices.25,26 There is concern about the potential negative impacts of active-sonar on marine mammals, specifically the low frequency (100-500 Hz) and mid-frequency (2.8-3.3 kHz) active sonar used in military activities by the U.S. and other nations.27 The impact of seismic testing for geological mapping and oil and gas exploration is also unknown.

Declining prey resources: This could result from either natural prey population fluctuations or commercial harvest of prey species. Schooling fishes and crustaceans are often used for human consumption or as feed in mariculture facilities.

MBNMS: No threats are unique to the MBNMS
Conservation and Research

Harbor porpoises in California are not listed under the Endangered Species Act (ESA). The Marine Mammal Protection Act (MMPA) protects them from take and importation. None of the stocks discussed in this report are considered "depleted" or "strategic stocks" at this time under the MMPA. However, if the annual human-caused mortality of harbor porpoise increases slightly to 11 in the Monterey Bay, or 7 in the Morro Bay stocks, then the stock would be considered strategic.1 Under the MMPA, the National Marine Fisheries Service (NMFS) is responsible for management and conservation of the harbor porpoise in U.S. waters.

As required under the MMPA, NMFS updates the Stock Assessment Reports for all marine mammal stocks at least every three years. Current Stock Assessment Reports are available on the NOAA Office of Protected Resources website. Currently, researchers with the NMFS assess the status of harbor porpoise stocks by monitoring population size and determining causes of death and serious injury:

Harbor Porpoise Aerial Surveys (Principal Investigator: Karin Forney, Southwest Fisheries Science Center (SWFSC)). The purposes of the aerial surveys are: (1) to estimate abundance and trends of harbor porpoise stocks in central and northern California and (2) to conduct habitat studies of harbor porpoise in central California. Surveys occur in the summer/autumn every 2-5 years. The last full-scale survey was completed in 2002 and the next one is planned for 2006 or 2007.8 Additional abundance, distribution and habitat data have been collected several times per year since 2001 during fine-scale aerial surveys for leatherback turtles and harbor porpoise from about the mouth of San Francisco Bay to Point Lobos.8

Marine Mammal Health and Stranding Response Program Network (Southwest Regional Stranding Coordinator: Joe Cordaro, NMFS/SWFSC). The network consists of volunteer groups that respond to marine mammal strandings in different parts of the southwest region. Samples from stranded animals provide information on biological parameters, including age, length, reproductive condition, contaminant loads, stock discreteness, types of parasites or diseases, and cause of death. In addition to collecting data from stranded animals, this program assesses health trends, correlates health with available data on physical, chemical, environmental, and biological parameters, and coordinates effective responses to unusual mortality events.

MBNMS: Beach COMBERS - Coastal Ocean Mammal and Bird Education and Research Surveys (Project Leader: Hannah Nevins, Moss Landing Marine Laboratories). In 1997 the MBNMS began a beach survey program using trained volunteers to survey beached marine birds and mammals monthly at selected sections of beaches throughout the Monterey Bay area. Currently, the program monitors 45 km of beaches in the MBNMS. The program is a collaborative project between MLML, MBNMS, and other state and research institutions, with the specific goal of using deposition of beach cast carcasses as an index of the health of the sanctuary. The Marine Mammal Health and Stranding Response Program Network is notified of all stranded or dead cetaceans so that data can be collected and the cause of the stranding event determined.<
General: The California Department of Fish and Game (CDFG) is not required to have research and monitoring programs for harbor porpoise because this species is not listed as threatened or endangered under the California Endangered Species Act. However, when one or more state-managed fisheries negatively impact a species protected under the MMPA, NMFS (the lead management agency) works with CDFG to address the problem. The recent closure of the state-managed halibut/angel shark set gillnet fishery, intended to reduce incidental take of sea otters, is expected to help harbor porpoise stocks as well. A permanent closure inshore of 60 fathoms (~110 m) was implemented by CDFG in September of 2002 and extends from Pt. Reyes in Marin county (38N) to Pt. Arguello in northern Santa Barbara county (3435'N). Given that over 90% of the harbor porpoise in California occurs in waters less than 90m, this closure is expected to eliminate the risk of entanglement in set gillnets from almost all harbor porpoise habitat in the MBNMS.4
Research Gaps
  • Supplement existing aerial survey effort by NMFS to determine the seasonal changes in distribution and abundance of harbor porpoise and to identify the location of important foraging habitat in the MBNMS. Coastal waters out to 200 m should be surveyed throughout the longitudinal extent of the Sanctuary at least once per season (most of the recent distribution and abundance data was collected in the summer/fall and in the central and northern portions of the MBNMS).
  • Determine the impacts of various types of acoustic disturbance that occur in the MBNMS, including noise from ships, boats, aircraft, and research, military and industrial activities.
  • Continue studies of stock structure in central California, particularly to refine the location of stock boundaries. Use biopsies to determine the genetic variability within and between the three stocks. Telemetry studies are needed to assess daily and seasonal movements and measure rates of inter-area exchange.
Recommended Actions
General: No general actions are recommended because these three harbor porpoise stocks are limited in geographic distribution to waters in and around the MBNMS.<
  • Support the continued closure of set gillnets in waters less than 100 m in the MBNMS.28
  • Support efforts by NMFS and CDFG to document levels of incidental take in various fisheries in the MBNMS. Encourage enactment of regulations to minimize this source of mortality.28
  • If acoustic disturbances are found to negatively impact harbor porpoise, work to minimize those activities in the MBNMS.29,30
  • Improve water quality by reducing entry of chemical pollutants (e.g., DDT, PCBs, heavy metal, oil) and marine debris into Sanctuary waters through resource management and education outreach programs.31
  • Discourage offshore mariculture projects in the MBNMS. Offshore mariculture could negatively impact harbor porpoise in three ways:
    1. entanglement in netting and lines;28
    2. competition for food - schooling crustaceans and fish are often harvested to feed to farmed fish; and
    3. habitat degradation - declining water quality and increasing parasite load.
Cited References
1. Carretta JV, Forney KA, Muto MM, Barlow J, Baker J, Lowry M (2004) U.S. Pacific Marine Mammal Stock Assessments: 2003. NOAA Technical Memorandum NMFS-SWFSC-358, U.S. Department of Commerce."
2. Read AJ (1999) Harbour porpoise Phocoena phocoena (Linnaeus, 1758). In: Ridgway SH, Harrison R (eds) Handbook of Marine Mammals, Volume 6. Academic Press, San Diego, CA, p 323-355.
3. Chivers SJ, Dizon AE, Gearin PJ, Robertson KM (2002) Small-scale population structure of eastern North Pacific harbour porpoises (Phocoena phocoena) indicated by molecular genetic analyses. Journal of Cetacean Research and Management 4:111-122.
4. Carretta JV, Forney KA (2004) Preliminary estimates of harbor porpoise abundance in California from 1999 and 2002 aerial surveys. Administrative Report LJ-O4-01, Southwest Fisheries Science Center, National Marine Fisheries Service, La Jolla, CA.
5. Carretta JV, Taylor BL, Chivers SJ (2001) Abundance and depth distribution of harbor porpoise (Phocoena phocoena) in northern California determined from a 1995 ship survey. Fishery Bulletin 99:29-39.
6. Barlow J (1988) Harbor porpoise, Phocoena phocoena, abundance estimation for California, Oregon, and Washington: I. Ship surveys. Fishery Bulletin 86:417-432.
7. Byrd B (1997) Abundance, distribution, food habits, and prey availability of the harbor porpoise (Phocoena phocoena) in northern Monterey Bay, California. M.S. Thesis, California State University, Stanislaus, through Moss Landing Marine Laboratories.
8. Karin Forney, NMFS-SWFSC, Personal Communication
9. Calambokidis J, Barlow J (1991) Chlorinated hydrocarbon concentrations and their use for describing population discreteness in harbor porpoises from Washington, Oregon, and California. In: Reynolds JE, Odell DK (eds) Marine mammal strandings in the United States: proceedings of the Second Marine Mammal Stranding Workshop; 3-5 December 1987, Miami, Florida. NOAA Technical Report-NMFS 98:101-110.
10. Carretta JV (2003) Preliminary estimates of harbor porpoise abundance in California from 1997 and 1999 aerial surveys, Administrative Report LJ-O3-04, Southwest Fisheries Science Center, National Marine Fisheries Service, La Jolla, CA.
11. Forney KA (1995) A decline in the abundance of harbor porpoise, Phocoena phocoena, in nearshore waters off California, 1968-93. U S National Marine Fisheries Service Fishery Bulletin 93:741-784.
12. Forney KA (1999) Trends in harbor porpoise abundance off central California 1986-95: evidence for interannual changes in distribution? Journal of Cetacean Research and Management 1:73-80.
13. Rice DW (1998) Marine mammals of the world: systematics and distribution. Society for Marine Mammalogy Special Publication No. 4.
14. Jones RE (1981) Food habits of smaller marine mammals from northern California. Proceedings of the California Academy of Science 42:409-433.
15. Sekiguchi K (1995) Occurrence, behavior and feeding habits of harbor porpoises (Phocoena phocoena) at Pajaro Dunes, Monterey Bay, California. Aquatic Mammals 21:91-103.
16. Toperoff AK (1997) Diet of Harbor Porpoise (P. phocoena) using stomach contents and stable isotope analyses. M.S. Thesis, California State University, San Jose through Moss Landing Marine Laboratories.
17. Stuart LJ, Morejohn GV (1980) Developmental patterns in osteology and external morphology in Phocoena phocoena. Report of the International Whaling Commission:133-137.
18. COSEWIC (2003) COSEWIC assessment and update status report on the harbour porpoise Phocoena phocoena (Pacific Ocean population) in Canada. Committee on the Status of Endangered Wildlife in Canada, Ottawa.
19. Forney KA, Benson SR, Cameron GA (2001) Central California gillnet effort and bycatch of sensitive species, 1990-1998. p 141-160 In: McIvin EF, Parrish J (eds) Seabird Bycatch: Trends, Roadblocks, and Solutions. University of Alaska Sea Grant AK-SG-01-01, Fairbanks, Alaska.
20. Cameron GA, Forney KA (2000) Preliminary Estimates of Cetacean Mortality in California/Oregon Gillnet Fisheries for 1999, Paper SC/52/O24 presented to the International Whaling Commission (unpublished). 12p.
21. Carretta JV (2001) Preliminary estimates of cetacean mortality in California gillnet fisheries for 2000, Paper SC/53/SM9 presented to the International Whaling Commission (unpublished). 21p.
22. Carretta JV (2002) Preliminary estimates of cetacean mortality in California gillnet fisheries for 2001, Paper SC/54/SM12 presented to the International Whaling Commission (unpublished). 22p.
23. Carretta JV, Chivers SJ (2003) Preliminary estimates of marine mammal mortality and biological sampling of cetaceans in California gillnet fisheries for 2002, Paper SC/55/SM3 presented to the International Whaling Commission (unpublished). 21p.
24. Baird RW, Hooker SK (2000) Ingestion of plastic and unusual prey by a juvenile harbour porpoise. Marine Pollution Bulletin 40: 719-720.
25. Koschinski S, Culik BM, Henriksen OD, Tregenza N, Ellis G, Jansen C, Kathe G (2003) Behavioural reactions of free-ranging porpoises and seals to the noise of a simulated 2 MW windpower generator. Marine Ecology Progress Series 265:263-273.
26. Gearin PJ, Gosho ME, Laake JL, Cooke L, DeLong RL, Hughes KM (2000) Experimental testing of acoustic alarms (pingers) to reduce bycatch of harbour porpoise, Phocoena phocoena, in the state of Washington. Journal of Cetacean Research & Management 2:1-9.
27. National Research Council (2005) Marine Mammal Populations and Ocean Noise: Determining When Noise Causes Biologically Significant Effects. Committee on Characterizing Biologically Significant Marine Mammal Behavior. National Academies Press, Washington, DC. 142 pages.
28. Addressed in part by JMPR Wildlife Disturbance Issues - Marine Mammal, Seabird and Turtle Disturbance Action Plan: Commercial Harvest Related Disturbance Strategy. Joint Management Plan Review (JMPR). Proposed Action Plans. Draft report. Monterey Bay National Marine Sanctuary.
29. Addressed in part by JMPR Wildlife Disturbance Issues - Marine Mammal, Seabird and Turtle Disturbance Action Plan: Low Flying Aircraft Disturbance Strategy. Joint Management Plan Review (JMPR). Proposed Action Plans. Draft report. Monterey Bay National Marine Sanctuary.
30.Addressed in part by JMPR Wildlife Disturbance Issues - Marine Mammal, Seabird and Turtle Disturbance Action Plan: Acoustic Disturbance Strategy. Joint Management Plan Review (JMPR). Proposed Action Plans. Draft report. Monterey Bay National Marine Sanctuary.
31. Addressed in part by JMPR Wildlife Disturbance Issues - Marine Mammal, Seabird and Turtle Disturbance Action Plan: Marine Debris Strategy. Joint Management Plan Review (JMPR). Proposed Action Plans. Draft report. Monterey Bay National Marine Sanctuary.
32. Carretta JV, Forney KA, Muto MM, Barlow J, Baker J, Hanson B, Lowry M (2005) U.S. Pacific Marine Mammal Stock Assessments: 2004. NOAA Technical Memorandum NMFS-SWFSC-375, U.S. Department of Commerce.
References and Resources
Click here for images, reports, and links to other websites for this species.

Acknowledgement of Reviewers
Thank you to Karin Forney (NMFS-SWFSC) for reviewing this report and providing helpful comments and corrections.

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