Porpoises of the Phocoena genus are marine mammals that inhabit various coastal and offshore waters around the world. These cetaceans, a group that includes whales and dolphins, are often elusive, making them a subject of ongoing scientific study. Understanding the unique characteristics, behaviors, and challenges faced by Phocoena species is important for their continued survival in marine ecosystems.
Identifying Porpoises: Distinguishing Features
Porpoises within the Phocoena genus exhibit several physical traits that set them apart from their dolphin relatives. Unlike dolphins, which typically possess conical, pointed teeth, porpoises have spade-shaped teeth. Their body shape tends to be more stocky and robust, contrasting with the generally leaner and longer appearance of dolphins.
Their dorsal fins differ; Phocoena species have a low, triangular dorsal fin, as opposed to the more curved or hooked dorsal fins of most dolphins. They also lack the prominent, elongated beak of many dolphins, instead featuring a more rounded head and blunt jaws. The genus Phocoena includes four species: the spectacled porpoise (Phocoena dioptrica), the harbor porpoise (Phocoena phocoena), the vaquita (Phocoena sinus), and Burmeister’s porpoise (Phocoena spinipinnis).
Habitats and Diets
Phocoena porpoises are typically found in cooler coastal waters, estuaries, and even rivers, though some species like the spectacled porpoise can be more oceanic. The harbor porpoise inhabits temperate and subarctic regions across the North Atlantic, North Pacific, and the Black Sea. Burmeister’s porpoise is found along the coast of South America. The vaquita is unique in its warm-water habitat, being endemic to the northern Gulf of California.
Their diet primarily consists of fish, squid, and crustaceans. Harbor porpoises feed mostly on small schooling fish. Vaquitas also consume fish, squid, and crustaceans, and may use passive sound to locate their prey in their turbid habitat.
Life and Social Behavior
Reproductive patterns within the Phocoena genus involve seasonal breeding. Harbor porpoises typically mate from June to September, and after a 10 to 11-month gestation period, a single calf is born between May and early August. Females can calve annually. Porpoises reach sexual maturity early and grow rapidly, contributing to a shorter overall lifespan, typically around 20 years in the wild.
The social behavior of Phocoena species is still being researched, but they are generally observed alone or in small groups, often consisting of one to three individuals. Larger aggregations, such as groups of up to 150 Burmeister’s porpoises, are occasionally seen, but these are thought to be temporary gatherings. These animals utilize echolocation, emitting high-frequency ultrasonic signals in a narrow sound beam to navigate, hunt for prey, and detect obstacles underwater. This biosonar system, with its high peak frequency around 130 kHz, allows them to detect small objects like net mesh and tiny fish.
Conservation Status and Threats
Phocoena species face threats, leading to varying conservation statuses across the genus. Entanglement in fishing gear, particularly gillnets, is a leading cause of death and injury for porpoises globally. An estimated 300,000 marine mammals, including porpoises, become entangled annually. The critically endangered vaquita (Phocoena sinus) is an example, with its population plummeting from over 200 individuals in 2008 to fewer than 30 by 2016, primarily due to bycatch in illegal gillnets set for totoaba fish. By May 2024, only 8 vaquitas were identified, making them the world’s most endangered marine mammal.
Beyond bycatch, habitat degradation, pollution, and climate change also pose risks. Chemical and plastic pollution can be ingested by porpoises, causing harm, while noise pollution from human activities like shipping and offshore wind farm construction can disrupt their echolocation and normal behavior. Climate change impacts, such as rising sea temperatures, are projected to affect over 70% of marine mammal habitats by 2050, influencing porpoise distribution and prey availability. Conservation efforts include gillnet bans, increased enforcement against illegal fishing, and the development of alternative, low-impact fishing gear. While a 2017 initiative to capture vaquitas for temporary protection was suspended due to risks, genetic studies suggest the remaining vaquita population still has enough diversity for recovery if bycatch can be prevented.