Harbour Porpoise populations throughout the range continue to be threatened by incidental mortality through bye catch in many fisheries. In north America alone bottom set gill nets catch hundreds of porpoises yearly. Chemical and noise pollution may also threaten this species.
Harbour porpoises are found in the temperate waters of the northern hemisphere. They inhabit coastal waters with a depth of less than 150 meters. Their common name is derived from their regular appearance in bays and harbours. Many populations of harbour porpoises are migratory.
During the spring of 1999, at least 162 harbour porpoise mortalities have been recorded along the eastern US seaboard, from North Carolina to Maine. This number of mortalities is over three times that recorded for 1998 and well above the previous record of 103 recorded mortalities in 1977. The largest number of mortalities were recorded in North Carolina (51 animals), with 25 recorded in Virginia, 19 in Maryland and 43 in Massachusetts. Observations on the dead harbour porpoises reveal that they appear to have very thin blubber layers (suggesting that they may be unhealthy) and some animals clearly carry net marks on their bodies, indicative of death by entanglement in fishing gear. Certain countries have afforded harbour porpoises special status. In Atlantic Canada, harbour porpoises are listed as threatened by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC). Northwest Atlantic harbour porpoises are currently designated as a strategic stock under the U.S. Marine Mammal Protection Act (MMPA) because current levels of killing exceed the estimated Potential Biological Removal (PBR) level for the population.
Harbour porpoises are listed in the IUCN Red List of Threatened Species as "Vulnerable" throughout their range. CITES lists the species as "Appendix 2".