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Introduction

Elusive, shy, cryptic. These are all terms that have all been used to describe the harbor porpoise, the second smallest cetacean (only the Vaquita is smaller) in the world. At only 5-5.5 feet long and 135-170 lbs, they are robust, with a blunt face that does not have a beak or rostrum like you would see on most dolphin species. Their dorsal fin is also different from their dolphin cousins in that it is more triangular in shape compared to the more curved or falcate dorsal fin of dolphins. Harbor porpoise coloration is dark grey/brown that fades to intermediate shades of grey on the sides, with a white belly. They have dark grey chin patch on the underside of their chin, and dark lines going from their pectoral fin to their mouth. These markings are not as striking as other species, and so there has been little attempt to individually ID harbor porpoises, until recently. Pacific Mammal Research, along with colleagues at the Marine Mammal Center have been using their scars and pigmentation patterns (along with dorsal fin shape/markings) to ID individuals, showing that it can be done, and other organizations are starting their own ID projects now as well. This will help us to learn so much more about this species, especially their little known social behavior.

Distribution

Harbor porpoises are found in northern temperate and subarctic waters, as well as in Arctic coastal and offshore waters. They are not found in the southern hemisphere at all. As their name may suggest, they prefer coastal areas, and are more commonly seen in bays, estuaries, harbors, and fjords that are less than 650 feet deep (although some animals have been known to spend time in much deeper offshore waters).

In terms of range, harbor porpoises in the North Atlantic can be seen from from western Greenland to North Carolina, U.S.A., and from the Berents Sea to parts of West Africa. In the North Pacific, they’re found from Japan north up to the Chukchi Sea, and Central California to the Beaufort Sea. Because of their extensive range, harbor porpoise populations are typically split into different “stocks” based on their geographic locations and, if known, their genetic relatedness. Here in the U.S. Salish Sea, harbor porpoises are part of the Washington Inland Waters stock.

Prey & Behavior

Being small themselves it makes sense that harbor porpoises generally feed on small fish and squid (usually less than 30cm) that they swallow whole (no chewing or ripping!).  They feed on a variety of prey, but here in the Salish Sea some of their top prey are Pacific herring, Pacific hake, Northern anchovy and Walleye Pollock (these are also common in many other populations throughout their range). They will also occasionally eat squid. But we still have more to learn about their diet as we recently documented that they capture large salmon, and down in San Francisco Bay, CA they eat large American shad. Harbor porpoises have a high metabolism and need to have consistent food sources. If they are already nutritionally stressed or sick, they can starve in as little as 3 days, so getting the caloric intake is very important! They need to eat up to 10% of their body weight a day, so it might make sense for an individual to try and catch one large fish, packed with a lot of calories, rather than chasing around hundreds of smaller fish.

This may also be more important for females who may be lactating and/or pregnant (requiring significantly more calories) every year. The risk comes in that these large fish can get stuck in their throat, causing their goosebeak (that separates the trachea from the esophagus) to become dislodged and causing them to asphyxiate (i.e. choke). We recently found that the vast majority of porpoises found asphyxiated on large fish were female (over 92%), and about 87% of those were reproductively active. This could have large implications for a population if reproductively active females are being disproportionately taken out of a population; more research is needed! 

They become sexually mature at about 3-4 years of age, gestation is about 11 months and they lactate for 8-12 months.  Their life span can be as little as 8 and as long as 24 years, but is more likely around 14-15 years. Harbor porpoises are quite elusive, at least compared to other porpoise and dolphin species, and we know little about their behavior.  They live in smaller groups of 1-3, but are seen in groups up to 10, and occasionally in large aggregations of 100+ (we don’t know why these aggregations happen). In some places they migrate seasonally, in others they don’t, we still know little about their movements, especially here in the Salish Sea. They don’t generally approach boats, don’t bow-ride, and their surfacing is very low key (not splashy). It is thought, because of these behaviors in combination with the fact that they don’t have whistles and other vocalizations that are for communication (at least that we know of), that harbor porpoises are not social. However recent research has countered that argument. We have observed them wake riding. Communicative signals have been found in their vocalizations. Cooperative group foraging (with specialized roles) has been documented. It is likely that they are social, the question is what that looks like. Their social structure will look different than their dolphin cousins, but that doesn’t mean it doesn’t exist! The thought that they are asocial is likely more due to the fact that past research has not been focused on this species, and thus researchers have not been out there to document these behaviors. Long-term research is important – the more we observe, the more we learn about this intelligent, enigmatic species and their social, reproductive and foraging behaviors.

Status

Harbor porpoises are protected by the Marine Mammal Protection Act and by CITES Appendix II throughout their range. There are thought to be approximately 7-800,000 harbor porpoises worldwide, and here in the Washington Inland Waters stock there are thought to be around 11,000.

Harbor porpoises are considered a species of least concern by the IUCN except in the Black Sea and Baltic Sea. These populations are listed as Endangered, and Critically Endangered, respectively. It has been shown that there are genetic differences between Black Sea harbor porpoises and other populations, and they also show some physiological and phenotypic differences. This makes sense when you look at the geography of these areas, which are quite isolated and may be difficult to access thus limiting genetic mixing. The Black Sea population became separated from other harbor porpoise populations during the post-glacial warming of the Mediterranean Sea. Unfortunately harbor porpoises were hunted to near extinction in these regions between the 1930s and 1980s, resulting in ~90% population decline. It is no wonder, then, that the populations are struggling here.

The Black Sea harbor porpoise is darker with a smaller skull. Photo: BSC/TUDAV.

Threats

  • Entanglement & Bycatch: This is probably one of the main sources of mortality for harbor porpoises worldwide. They feed on many of the forage fish and schooling fish that commercial fishermen target, and are particularly susceptible to bycatch in gillnets, trawls, and herring weirs due to their small size.
  • Disease: Harbor porpoises are susceptible to disease like all marine mammals, but recent research has shown that there are certain fungal pathogens and infections that may infect them more than we realized, frequently showing up in necropsies of dead porpoises that appear otherwise healthy. This is an ongoing area of research, but we do know that disease and infection with pathogens is a threat to this species.
  • Dedicated Hunts: As mentioned previously, in some areas of the world harbor porpoises have been hunted for their meat and blubber, and this was historically a huge threat for their population numbers. We don’t hear of this happening much today, but it might still occur in areas where commercial whaling is still allowed.
  • Pollution: Like all marine mammals, harbor porpoises are at risk from marine debris and pollution. They live their entire lives in the ocean, often in coastal and highly populated areas with lots of potential for exposure to pollutants.
  • Predation: Harbor porpoises are often targeted by mammal-eating killer whales in various parts of the world, including here in Washington, and are a main source of prey for the large delphinids. Another risk of predation comes from a less well-known, and slightly bizarre, scenario: grey seals! in parts of the UK and Scotland, intentional killing and in some cases predation of harbor porpoises by grey seals has been documented by researchers. Although we do not know the extent of this it seems it may happen with some regularity.

Fun Facts

  • The name porpoise actually comes from the Latin for pig, porcus. Phocoena also means “pig” or “pig fish”. Sometimes harbor porpoises are called “puffing pigs” due to this name and the sound they make when they surface.
  • They vocalize in the ultrasonic range, which means we as humans didn’t even know that they WERE vocalizing until our technology caught up and we could “see” their clicks on our hydrophone and computer equipment!
  • Although you might not think it, harbor porpoises have actually been shown to be extremely intelligent. There are a few animals that have managed to survive in captivity, and they were able to demonstrate tricks, remember commands, follow instructions, and in general showed a high level of comprehension and memory when trained.

cindy.elliser@pacmam.org

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