Animal Diversity Web

Diversity

The genus Phocoena can be found in the order Cetacea, family Phocoenidae, and is comprised of 4 species (Fajardo-Mellor et al. 2006). These four species include Phocoeana phocoena, Phocoena sinus, Phocoena spinipinnis, and Phocoena dipotrica. There have also been three subspecies recognized including P. phocoeana phocoena, P. phocoena vomerine, and P. phocoeana relicta (Fajardo-Mellor et al. 2006). These subspecies were found in the Atlantic, Pacific, and the Black sea respectively (Fajardo-Mellor et al. 2006).

Looking at Phocoena phocoena (Harbor Porpoise), these mammals primarily feed on fish, however, in some areas they also prey on squid and crustaceans ("Harbor Porpoise: Phocoena phocoena" 2009). They feed near the sea bottom at depths less than 200m and can also forage near the surface ("Harbor Porpoise: Phocoena phocoena" 2009). Generally, these harbor porpoises feed independently but some have been observed collaborating to herd fish near the surface. It is possible that they use the surface of the ocean as a wall as they herd them from the bottom to feed ("Harbor Porpoise: Phocoena phocoena" 2009). Some behavior of this species shows that they tend to reside in one area for extended periods of time, however, they also have onshore/offshore migrations ("Harbor Porpoise: Phocoena phocoena" 2009). They have also been known to be able to dive up to 220m. Physiologically, these porpoises have thick blubber for thermoregulation and are normally found in small groups of 1-3 animals ("Harbor Porpoise: Phocoena phocoena" 2009).

The Phocoena sinus (Vaquita) inhabits an area of around 4000km2 near the west coast of the upper gulf of California ("V - Vaquita: Phocoena sinus" 2009). This region is incredibly turbid which may be a quiet strategy used to avoid predators. Similar to Phocoena phocoena, its prey primarily consists of demeseral/benthic fish, squid, and crustaceans and it is possible that passive sound is used to find their prey ("V - Vaquita: Phocoena sinus" 2009). Much of the social organization is unknown with estimated mean school sizes to be around 2 with records of up to 8 or 10 individuals reported ("V - Vaquita: Phocoena sinus" 2009). An important behavior is their group aggregation. Compared to the other species, the vaquita have larger dorsal fins (vascularized), flippers, and flukes ("V - Vaquita: Phocoena sinus" 2009). Additionally they have large arteriole vessels with a plexus of thin walled veins. These characteristics could be adaptations to the extreme temperatures in the waters of the Upper Gulf of California ("V - Vaquita: Phocoena sinus" 2009).

The Phocoena spinipinnis (Burmeisters porpoise) is primarily found by coastal waters 100-1000m from shore and from depths between 5-25m ("Burmeister's Porpoise: Phocoena spinipinnis" 2009). These porpoises consume primarily fish, shrimp, and squid. They have an unobtrusive swimming behavior that makes it difficult to spot this species. These porpoises seem to be in group sizes between 2-8 individuals and can occasionally aggregate in larger groups (the largest sighting being of 150 individuals) however, the frequency and reasoning behind this is still unknown ("Burmeister's Porpoise: Phocoena spinipinnis" 2009).

The Phocoena dipotrica (Spectacled porpoise) does not have many observations on feeding behavior. In terms of its social behavior, sighting have found pods consisting of between 1-5 animals ("Spectacled Porpoise: Phocoena dioptrica" 2009). However, there is not much known about the social behavior, sounds, and other associations with this species. Like the Burmeisters porpoise they seem to have unobtrusive swimming behavior that make them difficult to spot at sea ("Spectacled Porpoise: Phocoena dioptrica" 2009). ("Burmeister's Porpoise: Phocoena spinipinnis", 2009; Fajardo-Mellor, et al., 2006; "Harbor Porpoise: Phocoena phocoena", 2009; "Spectacled Porpoise: Phocoena dioptrica", 2009; "V - Vaquita: Phocoena sinus", 2009)

Geographic Range

The four species of the genus Phocoena are found in different areas around the globe. Phocoena phocoena, the harbor porpoise, is found throughout the coastal waters of the North Pacific, North Atlantic, and the Black Sea ("Harbor Porpoise: Phocoena phocoena" 2009). Although these porpoises tend to reside within these areas for long periods of time, they also have onshore/offshore migrations. Within this they tend to move parallel to the coast and this may be in response to changes/movements in prey populations or to avoid ice during the winter ("Harbor Porpoise: Phocoena phocoena" 2009). Phocoena sinus inhabits narrow habitats and has limited distributions that make it one of the rarest marine mammal species ("V - Vaquita: Phocoena sinus" 2009). Sightings have found that the distribution of the vaquita is limited year-round to a small portion in the upper Gulf of California ("V - Vaquita: Phocoena sinus" 2009). Phocoena spinipinnis is found by the west coast of South America ("Burmeister's Porpoise: Phocoena spinipinnis" 2009). This species ranges from the northmost point from Paita (northern Peru), along the Peruvian and Chilean coasts, Argentina, Uruguay, and Brazil. There is still more research needed to look at the geographic boundaries of these animals, however, it has been proposed that the range of these porpoises is continuous from Paita to the La Plata River Basin by Argentina to Uruguay and Brazil ("Burmeister's Porpoise: Phocoena spinipinnis" 2009). Finally, Phocoena dipotrica is found in cool temperate, subantarctic, and Antarctic waters. The sightings have been widely distributed ranging from Uruguay, to Patagonia, to South Georgia, to Kerguelen, to the Auckland islands, Tasmania, and Heard island. These porpoises are also known to enter estuaries and channels ("Spectacled Porpoise: Phocoena dioptrica" 2009). ("Burmeister's Porpoise: Phocoena spinipinnis", 2009; "Harbor Porpoise: Phocoena phocoena", 2009; "Spectacled Porpoise: Phocoena dioptrica", 2009; "V - Vaquita: Phocoena sinus", 2009)

• Biogeographic Regions
• antarctica
• atlantic ocean
• pacific ocean

Habitat

The four species found in the genus Phocoena have different habitat preferences. Phocoena phocoena has several important habitats including the North Sea, Gulf of Maine, US west coast, and Alaska ("Harbor Porpoise: Phocoena phocoena" 2009). These porpoises have a depth range of up to 200m where they forage part of the time. The other part of the time they tend to forage on the surface and can also use the surface as a back wall to push prey toward from deeper depths ("Harbor Porpoise: Phocoena phocoena" 2009). The Phocoena sinus (vaquita) has a very small habitat in the upper Gulf of California. This area has a lot of turbid waters which could be an important part of its strategy to avoid predators present in clearer waters. Phocoena spinipinnis is mainly found in coastal waters throughout its geographic range and can be at depths between 5-25m ("Burmeister's Porpoise: Phocoena spinipinnis" 2009). There have also been sightings of them farther offshore (up to 50km) diving at depths between 30-60m ("Burmeister's Porpoise: Phocoena spinipinnis" 2009). There is still a lot that is unknown about the foraging strategies of these porpoises. Finally, with Phocoena dioptrica, there is very little information on its foraging behavior, habitat (although it seems to be found in cooler areas), and diving behavior (they have been seen to dive but depths are not widely known yet) ("Spectacled Porpoise: Phocoena dioptrica" 2009). ("Burmeister's Porpoise: Phocoena spinipinnis", 2009; "Harbor Porpoise: Phocoena phocoena", 2009; "Spectacled Porpoise: Phocoena dioptrica", 2009; "V - Vaquita: Phocoena sinus", 2009)

• Habitat Regions
• saltwater or marine

• Aquatic Biomes
• pelagic
• benthic
• coastal

Systematic and Taxonomic History

There has been a lot of contention between morphological and molecular data with the phylogeny (Fajardo-Mellor et al. 2006). Phocoenids were recognized as a family with three genera including the Neophocaena, Phocoena, and Phocoenoids. Previously, Barnes in 1985 used osteological characters to group Phocoenoides and Phocoena dioptrica in the same clade and assigned Phocoena dioptrica to a new different genus called Phocoena. Phocoenidae was also divided into two subfamilies Phoconoidinae, which had Phocoeena dalli and Australophocaena dioptrica with Salumiphocaena stocktoni and Piscolithax, and the other subfamily Phocoeninae which contained Neophocaena and Phocoena (Fajardo-Mellor et al. 2006). This was the previous classification until Rosel analyzed molecular sequences in 1995 and found no support for the two subfamilies previously identified. What Rosel and colleagues in 1995 found was that Neophocaena was basal to all phocoenids and that there was a separation between northern species including Phocoena phocoena and Phocoenoides dalli and southern species including Phocoena dioptrica, Phocoena sinus, and Phocoena spinipinnis (Fajardo-Mellor et al. 2006). Thus, there was a change in organization as Phocoena dioptrica was reassigned to its original genus Phocoena (Fajardo-Mellor et al. 2006). While this may be the current conclusion, there is still a large debate around morphological and molecular data relative to the phylogeny.

A more recent study by Fajarhdo-Mellor and colleagues in 2006 has agreed that Neophocaena is the most basal group and most related to the genus Phocoena. Within the genus Phocoena, however, there seems to be a slight difference between the 1995 study in that P. dipotrica is more closely related to the northern species Ph. dalli and P. phocoena. Within this P. phocoena and Ph. dalli have remained sister taxa which is a remained similarity, although the more recent study found that the bootstrap is relatively low (Fajardo-Mellor et al. 2006). (Fajardo-Mellor, et al., 2006)

• Synonyms

  • Australophocaena

• Synapomorphies

  • premaxillary prominence
  • fusion of three or more cervical vertebrae
  • trabeculate anterior sac
  • vestibular sac enclosed by an intrinsic muscle
  • vestibular sacs with deep transverse folds

Physical Description

The species of porpoises within this genus have many similar morphological features. These mammals are small and does not exceed a body length of 250cm (Read 2018). Alongside this smaller body size, these mammals also have smaller appendages (Read 2018). In contrast to delphinids, they do not have an external rostrum or beak (Read 2018). All porpoises seem to retain traits from its juvenile development into adult morphology (paedomorphosis) (Read 2018). In addition to the short rostrum, they have defining traits including large and rounded braincases and delayed fusion of cranial sutures (Read 2018). Species of phocoenids, removing the Phocoena dalli, have small raised protuberances known as epidermal tubercles (Read 2018). These are found on the leading edge of the dorsal fin and are most well defined in the Phocoeana spinipinnis. In terms of the morphology of pigments, this tends to vary amidst the species within this genus. What can be found more often than not is darker pigmentation around the eyes, a bridle which is a “system of stripes extending from the eye and blowhole to the apex of the melon”, and there is the general morphological pattern of countershading which is found in many marine mammals and odontocetes (Read 2018). In Phocoena dipotrica, there is a morphological pattern found with pigmentation around the eye as they tend to have a well-developed dark eye patch encircled by a narrow white line (Read 2018).

In addition to those general traits in the genus, there are specific morphological traits that differ by species. Phocoena sinus is the smallest of all the porpoises with females being approximately 140.6cm and males measuring smaller on average to about 134.9cm ("V - Vaquita: Phocoena sinus" 2009). Additionally, compared to other porpoises, the vaquita have larger flippers and a taller and more falcate dorsal fin ("V - Vaquita: Phocoena sinus" 2009). The most defining pigmentation found on these species are the black eye ring and lip patches ("V - Vaquita: Phocoena sinus" 2009). Their skull structures also suggest they have a broader and shorter rostrum compared to other species in this genus ("V - Vaquita: Phocoena sinus" 2009). Phocoena phocoena is highly identifiable by its triangular-shaped dorsal fin and this species also has a rotund shape to limit heat loss ("Harbor Porpoise: Phocoena phocoena" 2009). When looking at Phocoena spinipinnis, in addition to its tubercles, a diagnostic trait of the dorsal fin is that it is far back on its body, triangular, and canted backwards ("Harbor Porpoise: Phocoena phocoena" 2009). In terms of pigmentation, this species tends to be dark gray, lead gray or sometimes have a brownish hew with light gray to white portions around the abdomen ("Harbor Porpoise: Phocoena phocoena" 2009). It also has a well defined eye patch with a light gray or white halo, and this eye patch can reach the lip patch ("Harbor Porpoise: Phocoena phocoena" 2009). They also have stripes on its flipper and abdominal region ("Harbor Porpoise: Phocoena phocoena" 2009). Finally, the Phocoena dioptrica has distinctive pigmentation with juveniles having dark gray dorsal sides and light gray ventral sides with dark gray/brown streaks ("Spectacled Porpoise: Phocoena dioptrica" 2009). This pigmentation changes in adults which have black dorsal surfaces and a contrasting white ventral region. Additionally, males in this species have a striking large dorsal fin ("Spectacled Porpoise: Phocoena dioptrica" 2009). ("Burmeister's Porpoise: Phocoena spinipinnis", 2009; "Harbor Porpoise: Phocoena phocoena", 2009; Read, 2018; "Spectacled Porpoise: Phocoena dioptrica", 2009; "V - Vaquita: Phocoena sinus", 2009)

• Other Physical Features
• endothermic
• bilateral symmetry

• Sexual Dimorphism
• female larger

Reproduction

There is not much known about the mating systems in the genus Phocoena. What is known about Phocoena phocoena in this genus is that they tend to have more promiscuous mating systems. With this, there is also a lot of sperm competition as the males produce large quantities of sperm, likely in order to mate with several females ( "Harbor Porpoise: Phocoena phocoena" 2009) . ("Harbor Porpoise: Phocoena phocoena", 2009)

• Mating System
• polygynandrous (promiscuous)

In general, porpoises tend to reach sexual maturity early and grow rapidly (Read 2018). Most porpoises have a gestation period of approximately 10-11 months (Read 2018). However, this in addition to pregnancy rates or lactation periods are not known in Phocoena dioptrica (Read 2018). In Phocoena phocoena, they have a calving season that usually occurs between May-August, and this is followed by mating which occurs approximately 1.5 months after calving ("Harbor Porpoise: Phocoena phocoena" 2009). They have a longer gestation period of about 10.5 months and are weaned before they turn one, although some are capable of getting some solid food at a few months old ("Harbor Porpoise: Phocoena phocoena" 2009). They can become sexually mature between 3-4 years old but are not fully physically mature until they are around 5 for males and 7 for females ("Harbor Porpoise: Phocoena phocoena" 2009). Phocoena sinus (vaquitas) have a small sample size and thus not too much information is known. However there are estimates that mature females range from the ages 3-6 and they are usually sexually mature at age 3 giving birth at age 4 ("V - Vaquita: Phocoena sinus" 2009). Additionally, unlike the harbor porpoises, vaquitas may not be annual reproducers ("V - Vaquita: Phocoena sinus" 2009). For Phocoena spinipinnis, a study in Peru found the average length of sexual maturity in females is around 154.8cm and 159.9cm for males ("Burmeister's Porpoise: Phocoena spinipinnis" 2009). They also found that the mating season likely occurs between December-March, but there can still be successful mating outside of these seasons ("Burmeister's Porpoise: Phocoena spinipinnis" 2009). There is still much research that needs to be done on reproduction in genus Phocoena. ("Burmeister's Porpoise: Phocoena spinipinnis", 2009; "Harbor Porpoise: Phocoena phocoena", 2009; Read, 2018; "Spectacled Porpoise: Phocoena dioptrica", 2009; "V - Vaquita: Phocoena sinus", 2009)

• Key Reproductive Features
• seasonal breeding
• year-round breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual

There is a lack of information on the parental investment found in the Phocoena genus. What is common within this genus and eutherian mammals is that maternal investment is characterized by the gestation period wherein the young is provided nutrition by the mother in the uterus, the period of lactation post-birth, and the mixed feeding period where both milk and more solid foods are provided for the young (Langer 2008). (Langer, 2008)

• Parental Investment
• female parental care

Lifespan/Longevity

Phocoenids generally have a shorter life-span of approximately 20 years in the wild (Read 2018). These porpoises tend to reach sexual maturity early and grow rapidly (Read 2018). Additionally, they have a demanding reproductive schedule which goes in tandem with their shorter life-span (Read 2018). Aside from information from the wild, there is not much known about porpoises in captivity. (Read, 2018)

Behavior

The behavior of porpoises is limited but growing with increasing amounts of research on the species within this genus. Porpoises consist of motile species which exhibit natatorial locomotion adapted for swimming (Read 2018). While the social behavior of the species in this genus are still largely unknown, they can be found alone or in small groups. On some rarer occasions, they can form much larger aggregations, but these are likely more temporary and within these groups, there is often a mother-calf pair found (Read 2018). Additionally, the society these porpoises live in may follow fission-fusion associations whereby there is an incredibly dynamic composition and associations within the social group. Within fission-fusion associations, individuals can fuse or diverge from these social groups (Read 2018). One of the long-term associations known is between the lactating female and the dependent calf which generally lasts no longer than 2 years (Read 2018). Additionally, porpoises are generally shy (not including the Dall's porpoise) and they seldom leap out of the water(Read 2018). Typically, when they emerge, they will exhibit a rolling behavior before submerging again for a long period of time. On calm days, they may lay by the surface for a slightly longer period of time before submerging again (Read 2018). (Read, 2018)

• Key Behaviors
• natatorial
• motile
• solitary
• social

Communication and Perception

While individuals in this genus do travel in groups and seem to have socializing behavior, there is still much that is unknown about the communication and perception of mammals in the genus Phocoena (Read 2018). Delphinids which are social tend to use clicks for the purposes of echolocation as well as whistles to communicate (Sørensen et al. 2018). However, when looking at Phocoena phocoena, research by Sørensen and colleagues in 2018 has shown that they produce only the narrow-band high-frequency (NBHF) clicks. These types of clicks are not necessarily well-suited for communication purposes however, they may still utilize sound within their limited social interaction. During these interactions they seem to utilize two categories of sound featuring high-repetition rate click trains (Sørensen et al. 2018). Additionally, when hunting vaquitas tend to use passive sound as opposed to echolocation when trying to detect their prey ("V - Vaquita: Phocoena sinus" 2009). (Read, 2018; Sørensen, et al., 2018; "V - Vaquita: Phocoena sinus", 2009)

• Perception Channels
• tactile
• acoustic
• echolocation
• chemical

Food Habits

The species within this group are relatively small which means that they are required to feed more often (Read 2018). When feeding, there is little evidence to suggest that they do this in groups. Currently, what we know indicates that these mammals usually forage individually. Some of the species that live in more coastal regions such as the harbor and Burmeister's porpoise primarily forage for pelagic (herring, anchovy, capelin, etc) fish and supplement this diet with demersal fish. Contrarily, the Dall's porpoise primarily forage for mesopelagic fish and squid (Read 2018). (Read, 2018)

• Primary Diet
• carnivore
  • piscivore
  • molluscivore

• Foraging Behavior
• stores or caches food

Predation

There is still much that is unknown about anti-predator adaptations. However, similar to many marine mammals, some of these species appear to exhibit countershading morphology as a form of disruptive coloration to break up the body line so they are more difficult to detect if seen from above or below (Read 2018). Additionally, the spectacled porpoise is suspected to have predators including the killer whales (Orcinus orca), leopard seals (Hydrurga leptonyx), and sharks. Further research is required for more generalized information for this genus ("Spectacled Porpoise: Phocoena dioptrica" 2009). (Read, 2018; "Spectacled Porpoise: Phocoena dioptrica", 2009)

• Anti-predator Adaptations
• cryptic

• Known Predators

  • Orcinus orca
  • Hydrurga leptonyx
  • Sharks

Ecosystem Roles

The species in this genus generally forages on pelagic, demersal, mesopelagic fish, and squid. Considering this, they could play a role as a top-down predator for the populations of these prey species (Read 2018).

Additionally, there have been several different parasites detected with the Burmeister's porpoise ("Burmeister's Porpoise: Phocoena spinipinnis" 2009). In cranial sinuses and the inner ear of Burmeister porpoises that measure over 125cm (length) have had the nematode Stenurus australis tightly packed. The length of the porpoises with these nematodes may indicate that they begin infestation possibly when solid food starts to be ingested. In lower amounts but in the same location, the campulid trematode Nasitrema globicephalae has also been found. In populations within Argentina, the Stenurus minor was found in the cranial sinuses as well as tympanic bulla of these porpoises. The lungs can also be infected with nematodes which include the Pseudalius inflexus and Halocercus sp.. In the gastrointestinal tract, trematodes including Synthesium tursionis, Pholeter gastrophylus, and Braunina cordiformis were found. Nematodes including the Anisakis typica, Anisakis simplex, and Pseudoterranova sp. as well as the acantocephalan Polymorphus cetaceum have also been found in the gastrointestinal tract. In addition to all of this, there have been parasitic crustaceans in the genus Isocyamus which have been found in some porpoises from Peru and these whale lice were found in fresh wounds, mouth, genital slit, axillae, and the base angle of the dorsal fin. Beyond parasites, there has also been an ectocomensal barnacle, Xenobalanus globicipitis, which was found on the tips of the flippers, the dorsal fins, and on the flukes of these porpoises found in Peru ("Burmeister's Porpoise: Phocoena spinipinnis" 2009).

The spectacled porpoise tends to be incredibly attractive when dead to scavengers and predators ("Spectacled Porpoise: Phocoena dioptrica" 2009). The harbor porpoise in the North sea are affected by higher levels of mercury and have died due to diseases such as pneumonia ("Harbor Porpoise: Phocoena phocoena" 2009). Finally, vaquita's can have some unusual numbers of vertebrae digits and a pathological condition within their ovaries which is the calcification of corpora albicantia ("V - Vaquita: Phocoena sinus" 2009). ("Burmeister's Porpoise: Phocoena spinipinnis", 2009; "Harbor Porpoise: Phocoena phocoena", 2009; Read, 2018; "Spectacled Porpoise: Phocoena dioptrica", 2009; "V - Vaquita: Phocoena sinus", 2009)

• Ecosystem Impact
• parasite

Economic Importance for Humans: Positive

While there is presently not much known about the positive economic importance for humans from this species, historically, Harbor and Dall's porpoises were hunted for the utilization of the blubber and meat (Read 2018). Currently, species such as the vaquita have garnered public concern for protection ("V - Vaquita: Phocoena sinus" 2009). (Read, 2018; "V - Vaquita: Phocoena sinus", 2009)

• Positive Impacts
• food
• body parts are source of valuable material

Economic Importance for Humans: Negative

There are no known adverse effects of the genus Phocoena on humans.

Conservation Status

The conservation status for the species within the genus Phocoena varies from those that are low concern with unknown population, and those that are near threatened, and those that are critically endangered such as the vaquita ("Phocoena" n.d.). According to Read and colleagues, some of the main issues that threaten these species are bycatch from gill net fisheries, habitat degradation and destruction, marine noise pollution, and historic instances of hunting. The biggest issue of concern, however, is bycatch in these gill net fisheries. This is a threat that affects all species of the genus as many of them are caught, with as many as 7000 killed in the North sea between 1994-1998 (Read 2018). While the consequences of such large-scale bycatch has not been thoroughly investigated, it is likely to have led to the depletion of populations. In order to combat this, vessels engaged in these activities have to be equipped with acoustic alarms to ward these species off before fishing (Read 2018). These activities have had a drastic effect on vaquitas in particular which have been driven to the brink of extinction. They are bycatch illegal gill nets set to catch totaba (large sea bass) in an illegal trade system (Read 2018). ("Phocoena", n.d.; Read, 2018)

• IUCN Red List [Link]

  Not Evaluated

Contributors

Ayaka Paul (author), Colorado State University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

References

2009. Burmeister's Porpoise: Phocoena spinipinnis. Encyclopedia of Marine Mammals (Second Edition), 2: 163-167. Accessed September 20, 2021 at https://www.sciencedirect.com/science/article/pii/B9780123735539000432.

2009. Harbor Porpoise: Phocoena phocoena. Encyclopedia of Marine Mammals (Second Edition), 2: 530-533. Accessed September 20, 2021 at https://www.sciencedirect.com/science/article/pii/B9780123735539001255.

n.d.. "Phocoena" (On-line). IUCN Red List. Accessed December 10, 2021 at https://www.iucnredlist.org/search?query=Phocoena&searchType=species.

2009. Spectacled Porpoise: Phocoena dioptrica. Encyclopedia of Marine Mammals (Second Edition), 2: 1087-1091. Accessed September 20, 2021 at https://www.sciencedirect.com/science/article/pii/B9780123735539002479#!.

2009. V - Vaquita: Phocoena sinus. Encyclopedia of Marine Mammals (Second Edition), 2: 1196-1200. Accessed September 20, 2021 at https://www.sciencedirect.com/science/article/pii/B9780123735539002741.

Fajardo-Mellor, L., A. Berta, R. Brownell Jr., C. Boy, G. P.. 2006. THE PHYLOGENETIC RELATIONSHIPS AND BIOGEOGRAPHY OF TRUE PORPOISES (MAMMALIA: PHOCOENIDAE) BASED ON MORPHOLOGICAL DATA. Marine Mammal Science, 22/4: 910-932. Accessed September 20, 2021 at https://onlinelibrary-wiley-com.ezproxy2.library.colostate.edu/doi/full/10.1111/j.1748-7692.2006.00080.x.

Langer, P. 2008. The phases of maternal investment in eutherian mammals. Science Direct, 111/2: 148-162. Accessed October 21, 2021 at https://doi.org/10.1016/j.zool.2007.06.007.

Read, A. 2018. Porpoises, Overview. Pp. 770-772 in B Würsig, K Kovacs, J Thewissen, eds. Encyclopedia of Marine Mammals, Vol. n/a, 3 Edition. Online: Academic Press. Accessed October 19, 2021 at https://doi.org/10.1016/B978-0-12-804327-1.00205-3.

Sørensen, P., D. Wisniewska, J. Teilmann, P. Madsen. 2018. Click communication in wild harbour porpoises (Phocoena phocoena). Scientific Reports, 8: 9702. Accessed December 10, 2021 at 10.1038/s41598-018-28022-8.