Cetacean bycatch - AbsoluteAstronomy.com

Cetacean bycatch is the incidental capture

By-catch

The term “bycatch” is usually used for fish caught unintentionally in a fishery while intending to catch other fish. It may however also indicate untargeted catch in other forms of animal harvesting or collecting...

of non-target cetacean species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

by fisheries

Fishery

Generally, a fishery is an entity engaged in raising or harvesting fish which is determined by some authority to be a fishery. According to the FAO, a fishery is typically defined in terms of the "people involved, species or type of fish, area of water or seabed, method of fishing, class of boats,...

. Species which are seriously affected by this include dolphin

Dolphin

Dolphins are marine mammals that are closely related to whales and porpoises. There are almost forty species of dolphin in 17 genera. They vary in size from and , up to and . They are found worldwide, mostly in the shallower seas of the continental shelves, and are carnivores, mostly eating...

s, porpoise

Porpoise

Porpoises are small cetaceans of the family Phocoenidae; they are related to whales and dolphins. They are distinct from dolphins, although the word "porpoise" has been used to refer to any small dolphin, especially by sailors and fishermen...

s, and whale

Whale

Whale is the common name for various marine mammals of the order Cetacea. The term whale sometimes refers to all cetaceans, but more often it excludes dolphins and porpoises, which belong to suborder Odontoceti . This suborder also includes the sperm whale, killer whale, pilot whale, and beluga...

s. Bycatch

Bycatch

can be caused by entanglement in fishing net

Fishing net

A fishing net or fishnet is a net that is used for fishing. Fishing nets are meshes usually formed by knotting a relatively thin thread. Modern nets are usually made of artificial polyamides like nylon, although nets of organic polyamides such as wool or silk thread were common until recently and...

s and lines

Fishing line

A fishing line is a cord used or made for angling. Important parameters of a fishing line are its length, material, and weight...

, or direct capture by hooks

Fish hook

A fish hook is a device for catching fish either by impaling them in the mouth or, more rarely, by snagging the body of the fish. Fish hooks have been employed for centuries by fishermen to catch fresh and saltwater fish. In 2005, the fish hook was chosen by Forbes as one of the top twenty tools...

or in trawl nets

Trawling

Trawling is a method of fishing that involves pulling a fishing net through the water behind one or more boats. The net that is used for trawling is called a trawl....

.

Cetacean bycatch is increasing in intensity and frequency. This is a trend that is likely to continue because of increasing human population growth and demand for marine food sources, as well as industrialization of fisheries which are expanding into new areas. These fisheries come into direct and indirect contact with cetaceans. An example of direct contact is the physical contact of cetaceans with fishing net

Fishing net

s. Indirect contact is through marine trophic pathways where fisheries are severely reducing fish stocks that cetaceans rely on for food. In some fisheries, cetaceans are captured as bycatch but then retained because of their value as food or bait

Bait fish

Bait fish are small fish caught for use as bait to attract large predatory fish, particularly game fish. Species used are typically those that are common and breed rapidly, making them easy to catch and in regular supply. Examples of marine bait fish are anchovies, halfbeaks such as ballyhoo, and...

. In this fashion, cetaceans can become a target of fisheries.

Bycatch trends

Generally cetacean bycatch is on the increase. Most of the world’s cetacean bycatch

Bycatch

occurs in gillnet

Gillnet

Gillnetting is a common fishing method used by commercial and artisanal fishermen of all the oceans and in some freshwater and estuary areas. The gillnet also is used by fisheries scientists to monitor fish populations. Because gillnets can be so effective their use is closely monitored and...

fisheries. The mean annual bycatch in the U.S. alone from 1990–1999 was 6,215 marine mammals, with dolphins and porpoises being the primary cetaceans caught in gillnets. A study by Read et al. estimated global bycatch through observation of U.S. fisheries and came to the conclusion that an annual estimate of 653,365 marine mammals, comprising 307,753 cetaceans and 345,611 pinniped

Pinniped

Pinnipeds or fin-footed mammals are a widely distributed and diverse group of semiaquatic marine mammals comprising the families Odobenidae , Otariidae , and Phocidae .-Overview: Pinnipeds are typically sleek-bodied and barrel-shaped...

s were caught from 1990–1994.

While gillnets are a principal concern, other types of nets also pose a problem: trawl nets

Trawling

Trawling is a method of fishing that involves pulling a fishing net through the water behind one or more boats. The net that is used for trawling is called a trawl....

, purse seines, beach seines, longline gear, and driftnets. Driftnets are known for high rates of bycatch and they affect all cetaceans and other marine species. They are fatal for small toothed whale

Toothed whale

The toothed whales form a suborder of the cetaceans, including sperm whales, beaked whales, dolphins, and others. As the name suggests, the suborder is characterized by the presence of teeth rather than the baleen of other whales.-Anatomy:Toothed whales have a single blowhole on the top of the head...

s (Odontocetes) and sperm whale

Sperm Whale

The sperm whale, Physeter macrocephalus, is a marine mammal species, order Cetacea, a toothed whale having the largest brain of any animal. The name comes from the milky-white waxy substance, spermaceti, found in the animal's head. The sperm whale is the only living member of genus Physeter...

s, as well as other marine mammals and fish such as shark

Shark

Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....

s, sea birds and sea turtle

Sea turtle

Sea turtles are marine reptiles that inhabit all of the world's oceans except the Arctic.-Distribution:...

s. Many fisheries routinely use driftnets exceeding the EU size limit of 2.5 km/boat. This illegal drift-netting is a major issue, especially in important feeding and breeding grounds for cetaceans.
However, the tuna industry has achieved successes in reversing cetacean bycatch trends. International recognition of the problem of cetacean bycatch in tuna fishing led to the Agreement on the International Dolphin Conservation Program in 1999 and overall there has been a dramatic reduction in death rates. In particular, dolphin bycatch in tuna fishing in the East Tropical Pacific has dropped from 500,000 per year in 1970 to 100,000 per year in 1990 to 3,000 per year in 1999 to 1,000 per year in 2006.

Cetaceans at risk

Bycatch is recognized as a primary threat to all cetaceans. The following cetaceans are at high risk for entanglement in gillnet

Gillnet

Atlantic humpback dolphins

The Atlantic humpback dolphin (Sousa teuszii) is endemic to West Africa. Several stocks have been identified with numbers ranging from tens to a few hundred. Abundance estimates are lacking. Gaps in the species range and hence distribution is evident. Bycatch is only documented in a few West African countries. Surveys and evaluations need to be conducted to determine the presence/ absence of humpback dolphins in their historical range. Conservation measures need to be implemented to save this species. Because many people live off the sea, it is not feasible to have complete gillnet closures. Some areas may be designated as off-limits to gillnet fisheries. Eco-tourism may be implemented successfully because of high species diversity

Species diversity

Species diversity is an index that incorporates the number of species in an area and also their relative abundance. It is a more comprehensive value than species richness....

Baleen whales

Baleen whale

The Baleen whales, also called whalebone whales or great whales, form the Mysticeti, one of two suborders of the Cetacea . Baleen whales are characterized by having baleen plates for filtering food from water, rather than having teeth. This distinguishes them from the other suborder of cetaceans,...

s, Mysticeti, are often taken in gill-nets and in fisheries that use vertical lines to mark traps and pots. Large cetaceans such as humpback and right whales may carry off gear after entanglement. This explains the large scars borne by whales along the U.S. Atlantic coast. Analyses show that 50-70% of Gulf of Maine

Gulf of Maine

The Gulf of Maine is a large gulf of the Atlantic Ocean on the east coast of North America.It is delineated by Cape Cod at the eastern tip of Massachusetts in the southwest and Cape Sable at the southern tip of Nova Scotia in the northeast. It includes the entire coastlines of the U.S...

humpback whales, Megaptera novaeangliae, and North Atlantic Right Whale

North Atlantic Right Whale

The North Atlantic right whale which means "good, or true, whale of the ice") is a baleen whale, one of three right whale species belonging to the genus Eubalaena, formerly classified as a single species. With only 400 in existence, North Atlantic right whales are among the most endangered whales...

, Eubalaena glacialis, have been entangled at least once in their lifetime. The North Atlantic right whale is one of the most endangered large cetaceans and only 300-350 individuals remain. Minke Whales, Balaenoptera acutorostrata, are also at risk.

Burmeister’s porpoises

The Burmeister's porpoise

Burmeister's Porpoise

Burmeister's Porpoise is a species of porpoise endemic to the coast of South America. It was first described by Hermann Burmeister, for whom the species is named, in 1865...

(Phocoena spinipinnis) is one of three cetaceans that are most often bycaught in Peru

Peru

Peru , officially the Republic of Peru , is a country in western South America. It is bordered on the north by Ecuador and Colombia, on the east by Brazil, on the southeast by Bolivia, on the south by Chile, and on the west by the Pacific Ocean....

and Chile

Chile

Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...

. Several thousand porpoises are caught each year in Peru alone. Bycatch is a frequent occurrence for this species because of the inability to detect them in the water. Surveys have shown that bycatch remains a concern in that area today and it is unknown whether or not the population is declining. Data, conservation measures and awareness are lacking. These porpoises are cryptic

Crypsis

In ecology, crypsis is the ability of an organism to avoid observation or detection by other organisms. It may be either a predation strategy or an antipredator adaptation, and methods include camouflage, nocturnality, subterranean lifestyle, transparency, and mimicry...

making surveying a challenge . It is also difficult to estimate bycatch because the sale of porpoise meat is no longer available at markets.

Commerson’s dolphins

The expanding trawl fisheries devastated the Commerson's dolphin

Commerson's Dolphin

Commerson's Dolphin is one of four dolphins in the Cephalorhynchus genus. The species has also the common names Skunk Dolphin, Piebald Dolphin and Panda Dolphin...

(Cephalorhynchus commersonii) populations in Patagonia

Patagonia

Patagonia is a region located in Argentina and Chile, integrating the southernmost section of the Andes mountains to the southwest towards the Pacific ocean and from the east of the cordillera to the valleys it follows south through Colorado River towards Carmen de Patagones in the Atlantic Ocean...

. Trawl fisheries greatly expanded for twenty years until they crashed in 1997. Pelagic

Pelagic zone

Any water in a sea or lake that is not close to the bottom or near to the shore can be said to be in the pelagic zone. The word pelagic comes from the Greek πέλαγος or pélagos, which means "open sea". The pelagic zone can be thought of in terms of an imaginary cylinder or water column that goes...

squid

Squid

Squid are cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two, usually longer, tentacles...

fisheries took over which use pelagic trawls that are harmful to dusky, short-beaked common dolphins, and Commerson’s dolphins. There are approximately 21,000 Commerson’s dolphins remaining today. Two stocks have been identified in the population but genetic

Genetics

Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....

information and bycatch levels are unknown. With anchovy

Anchovy

Anchovies are a family of small, common salt-water forage fish. There are 144 species in 17 genera, found in the Atlantic, Indian, and Pacific Oceans. Anchovies are usually classified as an oily fish.-Description:...

fisheries expanding, it is imperative to assess the Commerson’s dolphin population before these fisheries grow. The seasonal operation of in-shore gillnet fisheries are known to involve bycatch of cetaceans. Presently, there are no known estimates of gillnet bycatch. The bycatch problem in Argentina

Argentina

Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...

is political in nature. Improvements in fishing technology, awareness, and a large scale survey of Commerson’s dolphin populations and the impact of bycatch is essential.

La Plata dolphins

The La Plata

La Plata Dolphin

The La Plata Dolphin or Franciscana is found in coastal Atlantic waters of southeastern South America. Taxonomically it is a member of the river dolphin group and the only one that actually lives in the ocean and saltwater estuaries, rather than inhabiting exclusively freshwater...

or Franciscana dolphin (Pontoporia blainvillei) is the most threatened small cetacean in the southwest Atlantic Ocean

Atlantic Ocean

The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...

due to bycatch. They are only found in the coastal waters of Argentina

Argentina

, Brazil

Brazil

Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...

, and Uruguay

Uruguay

Uruguay ,officially the Oriental Republic of Uruguay,sometimes the Eastern Republic of Uruguay; ) is a country in the southeastern part of South America. It is home to some 3.5 million people, of whom 1.8 million live in the capital Montevideo and its metropolitan area...

. This species has been divided into four ranges (FMU’s: Franciscana Management Units) for management and conservation purposes. These populations are genetically different. Mortality rates are 1.6% for FMU 4 and 3.3% for FMU 3 but it is unknown whether these estimates are accurate. Aerial survey

Aerial survey

Aerial survey is a geomatics method of collecting information by using aerial photography, LiDAR or from remote sensing imagery using other bands of the electromagnetic spectrum, such as infrared, gamma, or ultraviolet. It can also refer to the chart or map made by analysing a region from the air...

s have proven inconclusive so far as to the population numbers of franciscanas. To rectify this situation, more surveys are needed as well as political commitment, awareness campaigns and bycatch mitigation techniques.

Harbour porpoises

There is substantial incidental catches in fishing operations. Often, the Harbour Porpoise

Harbour Porpoise

The harbour porpoise is one of six species of porpoise. It is one of the smallest marine mammals. As its name implies, it stays close to coastal areas or river estuaries, and as such, is the most familiar porpoise to whale watchers. This porpoise often ventures up rivers, and has been seen...

(Phocoena phocoena) is killed by incidental by-catch (10, 11, 12). Gillnets pose a serious threat to the harbour porpoise as they are extremely susceptible to entanglement. A study by Caswell et al. in the western North Atlantic combined the mean annual rate of increase of the harbour porpoise with the uncertainty of incidental mortality and population size. It was found that the incidental mortality exceeds critical values and therefore by-catch is a significant threat to the harbour porpoise. Harbour porpoises become entangled in nets due to their inability to detect the nets before collision. In 2001, 80 harbour porpoises were killed in salmon

Salmon

Salmon is the common name for several species of fish in the family Salmonidae. Several other fish in the same family are called trout; the difference is often said to be that salmon migrate and trout are resident, but this distinction does not strictly hold true...

gillnet fisheries in British Columbia

British Columbia

British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...

, Canada

Canada

Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

Hector's and Maui's dolphins

In New Zealand

New Zealand

New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...

, these dolphins have a high rate of entanglement. Hector's dolphin

Hector's Dolphin

Hector's dolphin is the best-known of the four dolphins in the genus Cephalorhynchus and is found only in New Zealand. At about 1.4 m in length, it is one of the smallest cetaceans....

(Cephalorhynchus hectori) is endemic to the coastal waters New Zealand and there are about 7,400 in abundance. A small population of Hector’s dolphins is isolated on the west coast of the island and have been declared a subspecies called Maui's Dolphin

Maui's dolphin

Maui's dolphin is the world's smallest known species of dolphin. They are a sub-species of the Hector's dolphin....

. Maui's dolphins (Cephalofhynchus hectori maui) are often caught in set nets and pair trawlers

Pair trawling

Pair trawling is a fishing activity carried out by two boats, with one towing each warp . As the mouth of the net is kept open by the lateral pull of the individual vessels, otter boards are not required...

resulting in less than 100 left in the wild. For protection, a section of the dolphin’s range on the west coast has been closed to gillnet fisheries.

Indo-Pacific humpback and bottlenose dolphins

Drift

Drift net

Drift netting is a fishing technique where nets, called drift nets, are allowed to float freely at the surface of a sea or lake. Usually a drift net is a gill net with floats attached to a rope along the top of the net, and weights attached to another rope along the foot of the net to keep the net...

and bottom-set gillnet

Gillnet

s are the biggest conservation threat to these dolphins in the Indian Ocean

Indian Ocean

The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...

. There have only been assessments in some areas, such as Zanzibar

Zanzibar

Zanzibar ,Persian: زنگبار, from suffix bār: "coast" and Zangi: "bruin" ; is a semi-autonomous part of Tanzania, in East Africa. It comprises the Zanzibar Archipelago in the Indian Ocean, off the coast of the mainland, and consists of numerous small islands and two large ones: Unguja , and Pemba...

. Hunting, until 1996, reduced the population and contributed to its decline. Now hunting has been replaced with eco-tourism. It was estimated in 2001 that there are 161 bottlenose dolphins (Tursiops aduncus)] and 71 Indo-Pacific Humpback Dolphin

Humpback dolphin

Humpback dolphins are members of the genus Sousa. These dolphins are characterized by the conspicuous humps and elongated dorsal fins found on the back of adult members of the species...

(Sousa chinensis) that are left based on photo-identification mark-recapture techniques. A study on bycatch revealed over 160 incidences of bycatch since 2000. Approximately 30% of bycatch is in drift and bottom-set gillnets. Mortality is about 8% and 5.6% for bottlenose and humpback dolphins respectfully . The mitigation of bycatch is imperative for these species and eco-tourism.

Irrawaddy dolphins

Based on a survey in 2001, fewer than 70 Irrawaddy dolphin

Irrawaddy dolphin

The Irrawaddy dolphin is a euryhaline species of oceanic dolphin found in discontinuous subpopulations near sea coasts and in estuaries and rivers in parts of the Bay of Bengal and Southeast Asia.-Etymology and taxonomic history:...

s (Orcaella brevirostris) left in the upper region of the Malampaya Sound in the Philippines

Philippines

The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...

and 69 individuals in the Mekong River. They have been severely impacted by lift nets, and crab gear and they are critically endangered. It is estimated that mortality from bycatch may be greater than 4.5% in Malampaya Sound and 5.8% in the Mekong River. The population is declining dramatically. Current bycatch levels are unsustainable and bycatch reduction measures as well as long-term systematic monitoring are urgently required. The elimination of gillnets from areas of high use is needed and economic incentives need to be provided to the local people.

Spinner and Fraser’s dolphins

In the Philippines

Philippines

, tuna

Tuna

Tuna is a salt water fish from the family Scombridae, mostly in the genus Thunnus. Tuna are fast swimmers, and some species are capable of speeds of . Unlike most fish, which have white flesh, the muscle tissue of tuna ranges from pink to dark red. The red coloration derives from myoglobin, an...

driftnet fisheries have a substantial impact on the populations. One tuna fishery alone kills 400 Spinner Dolphin

Spinner Dolphin

The Spinner Dolphin is a small dolphin found in off-shore tropical waters around the world. It is famous for its acrobatic displays in which they spin longitudinally along their axis as they leap through the air.-Taxonomy:...

(Stenella longirostris) and Fraser's dolphin

Fraser's Dolphin

Fraser's Dolphin or Sarawak Dolphin is a cetacean in the family Delphinidae found in deep waters in the Pacific Ocean and to a lesser extent in the Indian and Atlantic Oceans.-Taxonomy:...

s (Lagenodelphis hosei) each year. Round-haul nets are an even greater concern with a bycatch of up to 3000 dolphins per year. Dolphins that are bycaught often end up as shark bait for longline fisheries. There is not enough data to conclude total bycatch for the Philippines. Initial assessment indicates that bycatch is not sustainable. Monitoring of dolphin populations and fisheries is urgently needed.

Yangtze River dolphins and finless porpoises

The Yangtze River or Baiji

Baiji

Baiji may refer to:* The Baiji or Yangtze River Dolphin * Baiji, Iraq, a city of northern Iraq.* "Baiji" is the pinyin Romanization for Baekje....

dolphin (Lipotes vexillifer) is the most endangered cetacean and is only found in the Yangtze River

Yangtze River

The Yangtze, Yangzi or Cháng Jiāng is the longest river in Asia, and the third-longest in the world. It flows for from the glaciers on the Tibetan Plateau in Qinghai eastward across southwest, central and eastern China before emptying into the East China Sea at Shanghai. It is also one of the...

, China

China

Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

. A survey conducted in 1997 found only thirteen dolphins. The Yangtze River finless porpoise

Finless Porpoise

The finless porpoise is one of six porpoise species. In the waters around Japan, at the northern end of its range, it is known as the sunameri . A freshwater population found in the Yangtze River in China is known locally as the jiangzhu or "river pig". There is a degree of taxonomic uncertainty...

(Neophocaena phocaenoides asiaeorientalis) also lives in the Yangtze River. Abundance has declined and there are fewer than 2000 dolphins left. This may be due, in part, to the construction of the Three Gorges Dam

Three Gorges Dam

The Three Gorges Dam is a hydroelectric dam that spans the Yangtze River by the town of Sandouping, located in the Yiling District of Yichang, in Hubei province, China...

which covers a significant amount of the dolphin’s habitat. Both species are often subject to entanglement in gillnets.

Vaquita

The vaquita

Vaquita

The vaquita is a rare species of porpoise. It is endemic to the northern part of the Gulf of California. Estimates of the number of individuals alive range from 100 to 300. The word "vaquita" is Spanish for little cow...

(Phocoena sinus) is highly endangered and is endemic to the upper Gulf of California

Gulf of California

The Gulf of California is a body of water that separates the Baja California Peninsula from the Mexican mainland...

, Mexico

Mexico

The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...

. They are killed in both gillnets and trawl nets from commercial

Commercial fishing

Commercial fishing is the activity of catching fish and other seafood for commercial profit, mostly from wild fisheries. It provides a large quantity of food to many countries around the world, but those who practice it as an industry must often pursue fish far into the ocean under adverse conditions...

and artisanal fishing

Artisan fishing

Artisan fishing is a term used to describe small scale low-technology commercial or subsistence fishing practices. The term particularly applies to coastal or island ethnic groups using traditional techniques such as rod and tackle, arrows and harpoons, throw nets and drag nets, and traditional...

. There are presently less than 600 vaquitas left in the Gulf of California.

Acoustic deterrent devices

The use of acoustic alarms to mitigate by-catch and also to protect aquaculture sites has been proposed but has advantages and risks associated with the alarms.
Acoustic deterrent devices, or pinger

Pinger

Pinger may refer to:*Ping'er, fictional character in Dream of the Red Chamber*Methylenedioxymethamphetamine*Underwater locator beacon...

s, have reduced the number of cetaceans caught in gill nets. Harbour porpoises have been effectively excluded from bottom-set gill nets during many experiments for instance in the Gulf of Maine

Gulf of Maine

, along the Olympic Peninsula

Olympic Peninsula

The Olympic Peninsula is the large arm of land in western Washington state of the USA, that lies across Puget Sound from Seattle. It is bounded on the west by the Pacific Ocean, the north by the Strait of Juan de Fuca, and the east by Puget Sound. Cape Alava, the westernmost point in the contiguous...

, in the Bay of Fundy

Bay of Fundy

The Bay of Fundy is a bay on the Atlantic coast of North America, on the northeast end of the Gulf of Maine between the Canadian provinces of New Brunswick and Nova Scotia, with a small portion touching the U.S. state of Maine...

, and in the North Sea

North Sea

In the southwest, beyond the Straits of Dover, the North Sea becomes the English Channel connecting to the Atlantic Ocean. In the east, it connects to the Baltic Sea via the Skagerrak and Kattegat, narrow straits that separate Denmark from Norway and Sweden respectively...

. All of these studies show up to a 90% decrease in harbour porpoise bycatch. Pingers work because they produce a sound that is aversive (20; 15). There has been a recent re-evaluation of the potential of pingers and their use in other fisheries due to their growing success.
An experiment on the California

California

California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

drift gill net fishery demonstrated how acoustic pingers reduce marine mammal bycatch. It was shown that bycatch was significantly reduced for common dolphins and sea lion

Sea Lion

Sea lions are pinnipeds characterized by external ear-flaps, long fore-flippers, the ability to walk on all fours, and short thick hair. Together with the fur seal, they comprise the family Otariidae, or eared seals. There are six extant and one extinct species in five genera...

s. Bycatch rates were also lower for other cetacean species like the Northern right whale dolphin

Northern Right Whale Dolphin

The Northern right whale dolphin is a small and slender species of marine mammal found in the North Pacific Ocean. The Northern right whale dolphin travels in groups of up to 2000, often with other cetaceans, in deep waters of the North Pacific...

, Pacific white-sided dolphin

Pacific White-sided Dolphin

The Pacific White-sided Dolphin is a very active dolphin found in the cool to temperate waters of the North Pacific Ocean.-Taxonomy:...

, Risso’s dolphin and Dall's Porpoise

Dall's Porpoise

Dall's porpoise is a species of porpoise found on the North Pacific. It came to worldwide attention in the 1970s when it was disclosed for the first time to the public that salmon fishing trawls were killing a lot, thousands of Dall's porpoises and other cetaceans each year by accidentally...

. It is agreed upon that the more pingers on a net, the less bycatch. There was a 12-fold decrease in common dolphin entanglement using a net with 40 pingers.
However, the widespread use of pingers along coastlines effectively excludes cetaceans such as porpoises from prime habitat

Habitat

* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...

and resources. Cetaceans which are extremely sensitive to noise are effectively being driven from their preferred coastal habitats by the use of acoustic devices. In poorer quality habitat, harbour porpoises are subjected to increased competition for resources. This situation is recognized as range contraction which can be a result of climate change

Climate change

Climate change is a significant and lasting change in the statistical distribution of weather patterns over periods ranging from decades to millions of years. It may be a change in average weather conditions or the distribution of events around that average...

, anthropogenic activity, or population

Population dynamics of fisheries

A fishery is an area with an associated fish or aquatic population which is harvested for its commercial or recreational value. Fisheries can be wild or farmed. Population dynamics describes the ways in which a given population grows and shrinks over time, as controlled by birth, death, and...

decline. Large scale range contractions are considered indicative of impending extinction

Extinction

In biology and ecology, extinction is the end of an organism or of a group of organisms , normally a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point...

. A similar form of deterrent is noise pollution originating from vessel traffic.

Barium sulfate

A promising gillnet

Gillnet

that is effective in reducing bycatch for harbor porpoises contains barium sulfate

Barium sulfate

Barium sulfate is the inorganic compound with the chemical formula BaSO4. It is a white crystalline solid that is odorless and insoluble in water. It occurs as the mineral barite, which is the main commercial source of barium and materials prepared from it...

. These nets are detected at a greater distance than conventional nets because the barium sulfate reflects the echolocation

Echolocation

Echolocation may refer to:* Acoustic location, the general use of sound to locate objects* Animal echolocation, non-human animals emitting sound waves and listening to the echo in order to locate objects or navigate...

signal, and also renders the nets more visible. Barium sulfate makes the nets stiffer if it is added at high concentration. All three factors: echo reflectivity, stiffness, and visibility may be important in reducing bycatch. Fish takes in the Bay of Fundy

Bay of Fundy

were normal, except for haddock takes, which were down by 3-5%. The advantage of this approach is that it is passive and thus does not require batteries, and there is no “dinner bell” effect. The potential advantage of these nets is greatest in the artisanal fishery

Artisan fishing

. NOAA would like further testing to verify the effectiveness of the nets.

Fishing regulations and management

Management and regulation are lacking in many fisheries today. Management measures

Fisheries management

Fisheries management draws on fisheries science in order to find ways to protect fishery resources so sustainable exploitation is possible. Modern fisheries management is often referred to as a governmental system of appropriate management rules based on defined objectives and a mix of management...

are urgently needed to monitor fisheries (and illegal fisheries

Illegal, unreported and unregulated fishing

Illegal fishing takes place where vessels operate in violation of the laws of a fishery. This can apply to fisheries that are under the jurisdiction of a coastal state or to high seas fisheries regulated by regional organisations....

) to protect cetaceans. Efforts to document bycatch should focus on gill-net

Gillnet

fisheries because cetaceans are more likely to be caught in gill-nets. Conservation efforts should be directed to areas where marine mammal bycatch is high but where no infrastructure exists to assess the impact. There is a lack of reporting on a global scale of cetacean bycatch.

In the U.S. the Marine Mammal Protection Act

Marine Mammal Protection Act

The Marine Mammal Protection Act of 1972 was the first article of legislation to call specifically for an ecosystem approach to natural resource management and conservation. MMPA prohibits the taking of marine mammals, and enacts a moratorium on the import, export, and sale of any marine mammal,...

prohibits the use and sale of marine mammals captured by fisheries. Similar legislation prohibits the use and sale of marine mammals in other countries. A marine mammal mortality monitoring program for commercial fisheries occurs in the U.S. where “Take Reduction Teams” observe the extent of bycatch and then formulate strategies to reduce bycatch and Take Reduction Plans are put into place.

Temporary closure

Temporary closure of fisheries during the short period of the year when cetaceans are migrating through the area would decrease bycatch significantly.

Observers on boat

Observers

Fisheries observer

A fisheries observer is an independent specialist who serves on board commercial fishing vessels, or in fish processing plants and other platforms, and is employed by a fisheries observer program, either directly by a government agency or by a third party contractor. Observers spend anywhere from...

on boats should be present on fishing vessel

Fishing vessel

A fishing vessel is a boat or ship used to catch fish in the sea, or on a lake or river. Many different kinds of vessels are used in commercial, artisanal and recreational fishing....

s to spot cetaceans in the water so that they can be avoided.

Other Ways of Mitigating Bycatch

Implement gear technology (changes in fishing gear and practices) documented to mitigate problematic cetacean bycatch
Choose only fish that are caught using cetacean friendly fishing gear.
Buy food that has a “dolphin safe” label.
Read The sustainable seafood
Sustainable seafood
Sustainable seafood is seafood from either fished or farmed sources that can maintain or increase production in the future without jeopardizing the ecosystems from which it was acquired...

guide for information on seafood that is produced sustainably.
Volunteer locally.
Raise awareness for cetacean bycatch.

Fish caught in nets that are designed not to harm dolphins is marketed as "dolphin safe", though this label may not be truly indicative of the harm done to dolphins in that fishery.

External links

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