Pacific angelshark
Encyclopedia
The Pacific angelshark (Squatina californica) is a species of angel shark
, family Squatinidae, found in the eastern Pacific Ocean
from Alaska
to the Gulf of California
, and from Ecuador
to Chile
, although those in the Gulf of California and southeastern Pacific may in fact be separate species. The Pacific angelshark inhabits shallow, coastal waters on sandy flats, usually near rocky reef
s, kelp forest
s, or other underwater features. This species resembles other angel sharks in appearance, with a flattened body and greatly enlarged pectoral and pelvic fins. Characteristic features of this shark include a pair of cone-shaped barbel
s on its snout, angular pectoral fins, and a brown or gray dorsal coloration with many small dark markings. It attains a maximum length of 1.5 m (4.9 ft).
An ambush predator
, Pacific angelsharks conceal themselves on the sea floor and wait for approaching prey, primarily bony fishes and squid
. Prey are targeted visually and, with a quick upward thrust of the head, snatched in protrusible jaws. Individual sharks actively choose ideal ambush sites, where they remain for several days before moving on to a new one. This species is more active at night than during the day, when it stays buried in sediment and seldom moves. Reproduction is aplacental viviparous, meaning that the embryo
s hatch inside the mother's uterus
and are sustained by a yolk sac
until birth. Females give birth to an average of six young every spring
.
Pacific angelsharks are not dangerous to humans unless provoked, in which case their bite can cause a painful injury. They are valued for their meat and are captured by commercial
and recreational fishers
across their range. A targeted gillnet
fishery for this species began off Santa Barbara, California
in 1976 and ended in 1994, after overfishing
and new regulations led to its near-collapse. This species is now mainly fished in Mexican
waters. The International Union for Conservation of Nature (IUCN) has assessed this species as Near Threatened
, as the Californian population is largely protected and recovering, while the impact of Mexican fisheries is unknown.
, the first Curator of Ichthyology
at the California Academy of Sciences
. He gave it the specific epithet californica, as the originally-described specimen was caught off San Francisco. Locally, this species may also be referred to as angel shark, California angel shark, or monkfish.
The Chilean angelshark
(Squatina armata) of the southeastern Pacific was synonymized
with this species by Kato, Springer and Wagner in 1967, but was later tentatively recognized as a separate species again by Leonard Compagno
. The taxonomic status of angel sharks in the southeastern Pacific – whether they are S. californica, S. armata, or if there is more than one Squatina species in the region – remains unresolved. The angel sharks inhabiting the Gulf of California may also represent a different species, as they mature at a much smaller size than those from the rest of their range.
A phylogenetic study based on mitochondrial DNA
, published by Björn Stelbrink and colleagues in 2010, reported that the sister species of the Pacific angelshark is the sand devil
(S. dumeril) of the western North Atlantic. The two species are estimated to have diverged approximately 6.1 Ma, close to when the Isthmus of Panama
first began to form. The authors also found that Pacific angelsharks from the Gulf of California differed genetically from those elsewhere, though they were equivocal as to whether this represented a species-level distinction.
. It may also occur from Ecuador to the southern tip of Chile (see taxonomic uncertainty above). This bottom-dwelling shark prefers habitats with soft, flat bottoms close to shore, such as estuaries and bay
s, and are often found near rocky reef
s, submarine canyon
s, and kelp forest
s. On occasion, they have been seen swimming 15 – above the sea floor. Off California, the Pacific angelshark is most common at a depth of 3 –, but has been reported from as deep as 205 m (672.6 ft).
A number of genetically discrete subpopulations
have been identified across the northern range of the Pacific angelshark. Several subpopulations exist along the coast from Point Conception
northward to Alaska. In the Southern California Bight
, there are at least three separate subpopulations off the mainland and northern and southern Channel Islands
. The subpopulation along the Pacific coast of Baja California
are distinct from those in the Gulf of California. These subpopulations have diverged from one another over time because Pacific angelsharks do not undertake long migratory
movements outside of their preferred home areas, and deep waters serve as effective geographical barriers to population mixing. Heterozygosity, a measure of genetic diversity
, is higher in the Pacific angelshark than in other shark species that have been examined.
. Unlike in rays, its five pairs of gill slit
s are located on the sides of the head rather than underneath, and the expanded anterior lobes of its pectoral fins are separate rather than fused to the head. The eyes are located on top of the head, with the spiracle
s behind. There are folds of skin without triangular lobes on the sides of head. The mouth is very wide and placed terminally (at the front of the snout); a pair of cone-shaped barbels
with spoon-like tips are located above. There are 9 tooth rows on either side of the upper jaw and 10 tooth rows on either side of the lower jaw, with toothless gaps at the middle of both jaws. Each tooth has a broad base and a single narrow, smooth-edged cusp.
The pectoral and pelvic fins are broad and angular with pointed tips. The two dorsal fin
s are located far back on the body, and there is no anal fin. The lower lobe of the caudal fin is larger than the upper. A row of small thorns runs down the middle of the back and tail; thorns are also present on the snout and over the eyes. As the shark ages, the thorns decrease in size and may disappear. The dorsal coloration is gray, brown, or reddish brown with scattered dark markings: large blotches surrounded by a ring of tiny spots in adults, and pairs of ocelli
in juveniles. The underside is white, extending to the margins of the pectoral and pelvic fins. This species measures up to 1.5 m (59.1 in) long and weighs up to 27 kg (59.5 lb).
(Carcharodon carcharias) and the broadnose sevengill shark
(Notorynchus cepedianus), and the northern elephant seal
(Mirounga angustirostris) are known to consume Pacific angelsharks. Known parasites of this species include the copepod
Trebius latifurcatus, which infests the skin, the myxosporidian Chloromyxum levigatum, which infests the gall bladder, and the tapeworm Paraberrapex manifestus, which infests the spiral valve
intestine
. The leech
Branchellion lobata may be attached around this shark's cloaca
, inside the intestine, and even inside the uterus
and on developing embryos.
, croakers
, flatfish
es, damselfish
es, mackerel
s, and sardine
s. During the winter and early spring, spawning squid are extremely abundant and become the primary source of food. In the southern Gulf of California, the most important prey species are, in descending order, the mackerel Decapterus macrosoma, the toadfish Porichthys analis, the lizardfish Synodus evermann, the soldierfish Myripristis leiognathus, and the shrimp Sicyonia penicillata. At Catalina Island
, this species feeds mainly on the blacksmith
(Chromis punctipinnis) and the queenfish (Seriphus politus). Adults and juveniles have broadly similar diets.
Individual sharks actively choose sites that will give them the best ambush success. They prefer junctions of sandy and rocky substrates near reefs, which are used by many fishes for shelter, usually orienting themselves either toward or parallel to nearby vertical structures. They also tend to face upslope, which may facilitate burying via falling sediment, bring more fish swimming downstream from the reef, and/or ease targeting by silhouetting prey against the sunlight.
Once settled at a successful site, a Pacific angelshark may remain there for up to ten days, re-burying itself on or near the same spot after every strike. As the local prey eventually learn to avoid the stationary predator, the shark will periodically shift to a new site several kilometers away at night. One study off Santa Catalina Island found that, over 13–25 hours, nine sharks together used only 1.5 km2 (0.6 mi2) of space. A later, longer-term study found that the sharks' sporadic position changes covered as much as 75 km (46.6 mi) over three months, almost circling the island. Single individuals swam up to 7.3 km (4.5 mi) in a single night.
The Pacific angelshark is primarily a visual hunter; experiments in nature show that they will strike at fish-shaped targets without any additional electrical, chemical, vibrational, or behavioral cues. At night, they are guided by the bioluminescence
of plankton
ic dinoflagellate
s and ostracod
s disturbed by moving prey. This species' visual system is attuned to the wavelength
s of light emitted by these plankton
ic organisms, showing the importance of night hunting. Pacific angelsharks are more likely to strike at prey approaching from the front than from the sides or back. It usually waits until the prey approaches to within 15 cm (5.9 in), as its attack is significantly less accurate beyond this distance. The strike is a stereotyped behavior
in which the shark presses the forward lobes of its pectoral fins against the bottom and thrusts its head upwards at up to a 90° angle. Its mouth forms a tube when opened, creating a suction force, while its jaws protude forward to secure the prey between sharp teeth. During the strike, the eyes are rolled backward into the head for protection. The entire strike is often completed in under a tenth of a second.
(on the left side), though some have two; the oviduct
s are often filled with yolk, which has been speculated to be from unfertilized eggs being resorbed. Young embryos 35 mm (1.4 in) long have translucent skin, protruding eyes, and exposed gill filament
s. Spots of pigment
have developed when the embryo is 70 mm (2.8 in) long, and the first row of teeth have appeared when the embryo is 110 mm (4.3 in) long. By the time the embryo is 150 mm (5.9 in) long, the mouth has migrated to a terminal position and the color pattern has fully developed; the external yolk sac begins to shrink as the yolk is transferred to an internal yolk sac, which holds it until it can be transferred to the intestine for digestion
. The internal yolk sac is fully resorbed before birth; if the pup is released prematurely, it does not feed until this process is complete.
Off Santa Barbara, birthing takes place from March to June after a gestation period
of ten months, and the females mate
again shortly afterward. The average litter size is 6 with a range of 1–11 (rarely 13); there is no correlation between female size and number of offspring. The young are born in water 55 – deep, probably to protect them from predators. Pacific angelshark embryos grow at 45 mm (1.8 in) per month when young, slowing down to 10 mm (0.393700787401575 in) per month just before birth, and are born at a length of 25 –. Newborn pups in captivity grow at a rate of around 14 cm (5.5 in) per year, while adults in the wild grow at around 2 cm (0.78740157480315 in) per year. Both sexes mature at 90 – long, corresponding to an age of 8–13 years. Gulf of California sharks, which may be another species, mature at 78 cm (2.6 ft) long for males and 85 cm (2.8 ft) long for females. About 20% of newborns survive to maturity. The maximum lifespan has been estimated at 25–35 years. Unlike other sharks, the growth rings on the vertebrae of this species are deposited in proportion to the shark's size rather than yearly, making age determination difficult.
and to a lesser extent off California (see below); the meat is considered excellent and is sold fresh or frozen. This species is captured in limited numbers by recreational fishers
using hook-and-line, spears, or even by hand, particularly off southern California. It is also taken as bycatch
in shrimp
trawls operating in the Gulf of California, and processed into fishmeal. The capacity of this species to withstand a focused fishing effort is limited, due to its low rates of reproduction and movement.
In 1976, the commercial gillnet fishery for the California halibut
(Paralichthys californicus), operating off Santa Barbara, expanded to include the Pacific angelshark as well. The sharks had become valuable due to their promotion as a substitute for the seasonally available common thresher shark (Alopias vulpinus), and the development of new processing techniques. Around 50% of the shark was used, while the skin
, cartilage
, and offal
were discarded. In the 1980s, rising demand led to the introduction of gillnets with a medium-sized mesh, designed specifically for this species. Fishery landings increased from a dressed (post-processing) weight of 148 kg (326.3 lb) in 1977, to 117000 kg (257,940.8 lb) in 1983, to 277000 kg (610,680.5 lb) in 1984. The fishery peaked in 1985 and 1986, when 550,000 kg (1.2 million lbs) were taken annually, making this species the number one shark fished off California. This level of exploitation was unsustainable, and despite a minimum size limit imposed in 1986, catches fell to 112000 kg (246,917.7 lb) in 1990.
In 1991, the use of gillnets in nearshore Californian waters was banned by a voter initiative (Proposition 132); the restricted area included much of the Pacific angelshark's habitat and reduced fishing pressure on the species. As a result, Pacific angelshark landings dropped further to 10000 kg (22,046.2 lb) dressed in 1994, when the central Californian halibut/angel shark fishery was closed completely, and have remained low since. The decline of the Californian fishery led to the industry shifting to Mexico, where gillnet pangas (artisanal fishing vessel
s) targeting this species now meet most of the angel shark demand in California. The International Union for Conservation of Nature (IUCN) has assessed this species as Near Threatened
; Pacific angelshark numbers off California appear to be increasing and demographic modeling suggests the stock is healthy. However, the impact of the intense, unregulated Mexican fishery on the global population is yet undetermined. There is continuing interest in California for a resumption of the commercial fishery, though conservation concerns have thus far taken precedence.
Angel shark
The angel sharks are an unusual genus of sharks with flattened bodies and broad pectoral fins that give them a strong resemblance to rays. The more than 16 known species are in the genus Squatina, the only genus in its family, Squatinidae, and order Squatiniformes. They occur worldwide in temperate...
, family Squatinidae, found in the eastern Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
from Alaska
Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...
to the 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...
, and from Ecuador
Ecuador
Ecuador , officially the Republic of Ecuador is a representative democratic republic in South America, bordered by Colombia on the north, Peru on the east and south, and by the Pacific Ocean to the west. It is one of only two countries in South America, along with Chile, that do not have a border...
to 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...
, although those in the Gulf of California and southeastern Pacific may in fact be separate species. The Pacific angelshark inhabits shallow, coastal waters on sandy flats, usually near rocky reef
Reef
In nautical terminology, a reef is a rock, sandbar, or other feature lying beneath the surface of the water ....
s, kelp forest
Kelp forest
Kelp forests are underwater areas with a high density of kelp. They are recognized as one of the most productive and dynamic ecosystems on Earth. Smaller areas of anchored kelp are called kelp beds....
s, or other underwater features. This species resembles other angel sharks in appearance, with a flattened body and greatly enlarged pectoral and pelvic fins. Characteristic features of this shark include a pair of cone-shaped barbel
Barbel (anatomy)
A barbel on a fish is a slender, whiskerlike tactile organ near the mouth. Fish that have barbels include the catfish, the carp, the goatfish, sturgeon, the zebrafish and some species of shark...
s on its snout, angular pectoral fins, and a brown or gray dorsal coloration with many small dark markings. It attains a maximum length of 1.5 m (4.9 ft).
An ambush predator
Ambush predator
Ambush predators or sit-and-wait predators are carnivorous animals that capture prey by stealth or cunning, not by speed or necessarily by strength. These organisms usually hide motionless and wait for prey to come within striking distance. They are often camouflaged, and may be solitary...
, Pacific angelsharks conceal themselves on the sea floor and wait for approaching prey, primarily bony fishes and 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...
. Prey are targeted visually and, with a quick upward thrust of the head, snatched in protrusible jaws. Individual sharks actively choose ideal ambush sites, where they remain for several days before moving on to a new one. This species is more active at night than during the day, when it stays buried in sediment and seldom moves. Reproduction is aplacental viviparous, meaning that the embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
s hatch inside the mother's uterus
Uterus
The uterus or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species...
and are sustained by a yolk sac
Yolk sac
The yolk sac is a membranous sac attached to an embryo, providing early nourishment in the form of yolk in bony fishes, sharks, reptiles, birds, and primitive mammals...
until birth. Females give birth to an average of six young every spring
Spring (season)
Spring is one of the four temperate seasons, the transition period between winter and summer. Spring and "springtime" refer to the season, and broadly to ideas of rebirth, renewal and regrowth. The specific definition of the exact timing of "spring" varies according to local climate, cultures and...
.
Pacific angelsharks are not dangerous to humans unless provoked, in which case their bite can cause a painful injury. They are valued for their meat and are captured by 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 recreational fishers
Recreational fishing
Recreational fishing, also called sport fishing, is fishing for pleasure or competition. It can be contrasted with commercial fishing, which is fishing for profit, or subsistence fishing, which is fishing for survival....
across their range. A targeted 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...
fishery for this species began off Santa Barbara, California
Santa Barbara, California
Santa Barbara is the county seat of Santa Barbara County, California, United States. Situated on an east-west trending section of coastline, the longest such section on the West Coast of the United States, the city lies between the steeply-rising Santa Ynez Mountains and the Pacific Ocean...
in 1976 and ended in 1994, after overfishing
Overfishing
Overfishing occurs when fishing activities reduce fish stocks below an acceptable level. This can occur in any body of water from a pond to the oceans....
and new regulations led to its near-collapse. This species is now mainly fished in Mexican
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...
waters. The International Union for Conservation of Nature (IUCN) has assessed this species as Near Threatened
Near Threatened
Near Threatened is a conservation status assigned to species or lower taxa that may be considered threatened with extinction in the near future, although it does not currently qualify for the threatened status...
, as the Californian population is largely protected and recovering, while the impact of Mexican fisheries is unknown.
Taxonomy and phylogeny
The Pacific angelshark was first scientifically described in 1859 by William Orville AyresWilliam Orville Ayres
William Orville Ayres was an American physician and ichthyologist. Born in Connecticut, he studied to become a doctor at Yale University School of Medicine....
, the first Curator of Ichthyology
Ichthyology
Ichthyology is the branch of zoology devoted to the study of fish. This includes skeletal fish , cartilaginous fish , and jawless fish...
at the California Academy of Sciences
California Academy of Sciences
The California Academy of Sciences is among the largest museums of natural history in the world. The academy began in 1853 as a learned society and still carries out a large amount of original research, with exhibits and education becoming significant endeavors of the museum during the twentieth...
. He gave it the specific epithet californica, as the originally-described specimen was caught off San Francisco. Locally, this species may also be referred to as angel shark, California angel shark, or monkfish.
The Chilean angelshark
Chilean angelshark
The Chilean angelshark, Squatina armata, is an angel shark of the family Squatinidae found in the subtropical waters of Chile. Its length is up to 1.03 m, although the holotype is lost.Reproduction is ovoviviparous.-References:...
(Squatina armata) of the southeastern Pacific was synonymized
Synonym (taxonomy)
In scientific nomenclature, a synonym is a scientific name that is or was used for a taxon of organisms that also goes by a different scientific name. For example, Linnaeus was the first to give a scientific name to the Norway spruce, which he called Pinus abies...
with this species by Kato, Springer and Wagner in 1967, but was later tentatively recognized as a separate species again by Leonard Compagno
Leonard Compagno
Leonard Joseph Victor Compagno is an international authority on shark taxonomy and the author of many scientific papers and books on the subject, best known of which is his 1984 catalogue of shark species produced for the Food and Agriculture Organization of the United Nations.-Career:*Ph.D,...
. The taxonomic status of angel sharks in the southeastern Pacific – whether they are S. californica, S. armata, or if there is more than one Squatina species in the region – remains unresolved. The angel sharks inhabiting the Gulf of California may also represent a different species, as they mature at a much smaller size than those from the rest of their range.
A phylogenetic study based on mitochondrial DNA
Mitochondrial DNA
Mitochondrial DNA is the DNA located in organelles called mitochondria, structures within eukaryotic cells that convert the chemical energy from food into a form that cells can use, adenosine triphosphate...
, published by Björn Stelbrink and colleagues in 2010, reported that the sister species of the Pacific angelshark is the sand devil
Sand devil
The sand devil or Atlantic angel shark, Squatina dumeril, is an angel shark of the family Squatinidae found in the outer continental shelf of the western Atlantic between latitudes 43°N and 9°N...
(S. dumeril) of the western North Atlantic. The two species are estimated to have diverged approximately 6.1 Ma, close to when the Isthmus of Panama
Isthmus of Panama
The Isthmus of Panama, also historically known as the Isthmus of Darien, is the narrow strip of land that lies between the Caribbean Sea and the Pacific Ocean, linking North and South America. It contains the country of Panama and the Panama Canal...
first began to form. The authors also found that Pacific angelsharks from the Gulf of California differed genetically from those elsewhere, though they were equivocal as to whether this represented a species-level distinction.
Distribution and habitat
Pacific angelsharks are found in cold to warm-temperate waters from the southeastern corner of Alaska to the Gulf of California, including the entire Baja peninsula, and are most common off central and southern CaliforniaCalifornia
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...
. It may also occur from Ecuador to the southern tip of Chile (see taxonomic uncertainty above). This bottom-dwelling shark prefers habitats with soft, flat bottoms close to shore, such as estuaries and bay
Bay
A bay is an area of water mostly surrounded by land. Bays generally have calmer waters than the surrounding sea, due to the surrounding land blocking some waves and often reducing winds. Bays also exist as an inlet in a lake or pond. A large bay may be called a gulf, a sea, a sound, or a bight...
s, and are often found near rocky reef
Reef
In nautical terminology, a reef is a rock, sandbar, or other feature lying beneath the surface of the water ....
s, submarine canyon
Submarine canyon
A submarine canyon is a steep-sided valley on the sea floor of the continental slope. Many submarine canyons are found as extensions to large rivers; however there are some that have no such association. Canyons cutting the continental slopes have been found at depths greater than 2 km below sea...
s, and kelp forest
Kelp forest
Kelp forests are underwater areas with a high density of kelp. They are recognized as one of the most productive and dynamic ecosystems on Earth. Smaller areas of anchored kelp are called kelp beds....
s. On occasion, they have been seen swimming 15 – above the sea floor. Off California, the Pacific angelshark is most common at a depth of 3 –, but has been reported from as deep as 205 m (672.6 ft).
A number of genetically discrete subpopulations
Evolutionary Significant Unit
An Evolutionarily Significant Unit is a population of organisms that is considered distinct for purposes of conservation. Delineating ESUs is important when considering conservation action.This term can apply to any species, subspecies, geographic race, or population...
have been identified across the northern range of the Pacific angelshark. Several subpopulations exist along the coast from Point Conception
Point Conception
Point Conception is a headland along the Pacific coast of U.S. state of California, located in southwestern Santa Barbara County. It is the point where the Santa Barbara Channel meets the Pacific Ocean, and as the corner between the mostly north-south trending portion of coast to the north and the...
northward to Alaska. In the Southern California Bight
Southern California Bight
The Southern California Bight includes coastal southern California, the Channel Islands and part of the Pacific Ocean.Within the Southern California bight lie the traditional territories of the Chumash and the Gabrieliño. These two cultures are considered the epitome of hunter-gatherer complexity...
, there are at least three separate subpopulations off the mainland and northern and southern Channel Islands
Channel Islands
The Channel Islands are an archipelago of British Crown Dependencies in the English Channel, off the French coast of Normandy. They include two separate bailiwicks: the Bailiwick of Guernsey and the Bailiwick of Jersey...
. The subpopulation along the Pacific coast of Baja California
Baja California
Baja California officially Estado Libre y Soberano de Baja California is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. It is both the northernmost and westernmost state of Mexico. Before becoming a state in 1953, the area was known as the North...
are distinct from those in the Gulf of California. These subpopulations have diverged from one another over time because Pacific angelsharks do not undertake long migratory
Fish migration
Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousands of kilometres...
movements outside of their preferred home areas, and deep waters serve as effective geographical barriers to population mixing. Heterozygosity, a measure of genetic diversity
Genetic diversity
Genetic diversity, the level of biodiversity, refers to the total number of genetic characteristics in the genetic makeup of a species. It is distinguished from genetic variability, which describes the tendency of genetic characteristics to vary....
, is higher in the Pacific angelshark than in other shark species that have been examined.
Description
With its flattened body and wing-like pectoral fins, the Pacific angelshark superficially resembles a rayBatoidea
Batoidea is a superorder of cartilaginous fish commonly known as rays and skates, containing more than 500 described species in thirteen families...
. Unlike in rays, its five pairs of gill slit
Gill slit
Gill slits are individual openings to gills, i.e., multiple gill arches, which lack a single outer cover. Such gills are characteristic of Cartilaginous fish such as sharks, rays, sawfish, and guitarfish. Most of these have five pairs, but a few species have 6 or 7 pairs...
s are located on the sides of the head rather than underneath, and the expanded anterior lobes of its pectoral fins are separate rather than fused to the head. The eyes are located on top of the head, with the spiracle
Spiracle
Spiracles are openings on the surface of some animals that usually lead to respiratory systems.-Vertebrates:The spiracle is a small hole behind each eye that opens to the mouth in some fishes. In the primitive jawless fish the first gill opening immediately behind the mouth is essentially similar...
s behind. There are folds of skin without triangular lobes on the sides of head. The mouth is very wide and placed terminally (at the front of the snout); a pair of cone-shaped barbels
Barbel (anatomy)
A barbel on a fish is a slender, whiskerlike tactile organ near the mouth. Fish that have barbels include the catfish, the carp, the goatfish, sturgeon, the zebrafish and some species of shark...
with spoon-like tips are located above. There are 9 tooth rows on either side of the upper jaw and 10 tooth rows on either side of the lower jaw, with toothless gaps at the middle of both jaws. Each tooth has a broad base and a single narrow, smooth-edged cusp.
The pectoral and pelvic fins are broad and angular with pointed tips. The two dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
s are located far back on the body, and there is no anal fin. The lower lobe of the caudal fin is larger than the upper. A row of small thorns runs down the middle of the back and tail; thorns are also present on the snout and over the eyes. As the shark ages, the thorns decrease in size and may disappear. The dorsal coloration is gray, brown, or reddish brown with scattered dark markings: large blotches surrounded by a ring of tiny spots in adults, and pairs of ocelli
Eyespot (mimicry)
An eyespot is an eye-like marking. They are found on butterflies, reptiles, birds and fish. In members of the Felidae family , the white circular markings on the backs of the ears are termed ocelli, and they are functionally similar to eyespots in other animals.Eyespots may be a form of...
in juveniles. The underside is white, extending to the margins of the pectoral and pelvic fins. This species measures up to 1.5 m (59.1 in) long and weighs up to 27 kg (59.5 lb).
Biology and ecology
During the day, Pacific angelsharks are almost never seen in the open, instead resting motionless on the sea floor buried under a thin layer of sediment that disguises their outlines. At night some individuals remain motionless, waiting for prey, while others may be encountered on the bottom unburied or actively swimming. Large sharks, including the great white sharkGreat white shark
The great white shark, scientific name Carcharodon carcharias, also known as the great white, white pointer, white shark, or white death, is a large lamniform shark found in coastal surface waters in all major oceans. It is known for its size, with the largest individuals known to have approached...
(Carcharodon carcharias) and the broadnose sevengill shark
Broadnose sevengill shark
The broadnose sevengill shark is the only extant member of the genus Notorynchus, in the family Hexanchidae. It is recognizable because of its seven gill slits, while most shark species have five gill slits, with the exception of the members of the order Hexanchiformes and the sixgill sawshark.The...
(Notorynchus cepedianus), and the northern elephant seal
Northern Elephant Seal
The northern elephant seal is one of two species of elephant seal . It is a member of the family Phocidae . Elephant seals derive their name from their great size and from the male's large proboscis, which is used in making extraordinarily loud roaring noises, especially during the mating...
(Mirounga angustirostris) are known to consume Pacific angelsharks. Known parasites of this species include the copepod
Copepod
Copepods are a group of small crustaceans found in the sea and nearly every freshwater habitat. Some species are planktonic , some are benthic , and some continental species may live in limno-terrestrial habitats and other wet terrestrial places, such as swamps, under leaf fall in wet forests,...
Trebius latifurcatus, which infests the skin, the myxosporidian Chloromyxum levigatum, which infests the gall bladder, and the tapeworm Paraberrapex manifestus, which infests the spiral valve
Spiral valve
A spiral valve is the lower portion of the intestine of some sharks, rays, skates and bichirs. A modification of the ileum, the spiral valve is internally twisted or coiled to increase the surface area of the intestine, to increase nutrient absorption....
intestine
Intestine
In human anatomy, the intestine is the segment of the alimentary canal extending from the pyloric sphincter of the stomach to the anus and, in humans and other mammals, consists of two segments, the small intestine and the large intestine...
. The leech
Leech
Leeches are segmented worms that belong to the phylum Annelida and comprise the subclass Hirudinea. Like other oligochaetes such as earthworms, leeches share a clitellum and are hermaphrodites. Nevertheless, they differ from other oligochaetes in significant ways...
Branchellion lobata may be attached around this shark's cloaca
Cloaca
In zoological anatomy, a cloaca is the posterior opening that serves as the only such opening for the intestinal, reproductive, and urinary tracts of certain animal species...
, inside the intestine, and even inside the uterus
Uterus
The uterus or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species...
and on developing embryos.
Feeding
A sedentary ambush predator, the Pacific angelshark feeds mainly on bony fishes, including kelp bassKelp Bass
The Kelp Bass , sometimes referred to as the Calico Bass , is a species of marine fish found in the north-eastern Pacific Ocean from Baja California, Mexico, to Washington, USA...
, croakers
Sciaenidae
Sciaenidae is a family of fish commonly called drums, croakers, or hardheads for the repetitive throbbing or drumming sounds they make...
, flatfish
Flatfish
The flatfish are an order of ray-finned fish, also called the Heterosomata, sometimes classified as a suborder of Perciformes. In many species, both eyes lie on one side of the head, one or the other migrating through and around the head during development...
es, damselfish
Damselfish
Damselfish comprise the family Pomacentridae except those of the genera Amphiprion and Premnas. They can grow up to long. While most are marine, a few species inhabit the lower stretches of rivers in freshwater. Damselfish usually have bright colors. in tropical coral reefs, and many of those are...
es, mackerel
Mackerel
Mackerel is a common name applied to a number of different species of fish, mostly, but not exclusively, from the family Scombridae. They may be found in all tropical and temperate seas. Most live offshore in the oceanic environment but a few, like the Spanish mackerel , enter bays and can be...
s, and sardine
Sardine
Sardines, or pilchards, are several types of small, oily fish related to herrings, family Clupeidae. Sardines are named after the Mediterranean island of Sardinia, around which they were once abundant....
s. During the winter and early spring, spawning squid are extremely abundant and become the primary source of food. In the southern Gulf of California, the most important prey species are, in descending order, the mackerel Decapterus macrosoma, the toadfish Porichthys analis, the lizardfish Synodus evermann, the soldierfish Myripristis leiognathus, and the shrimp Sicyonia penicillata. At Catalina Island
Santa Catalina Island, California
Santa Catalina Island, often called Catalina Island, or just Catalina, is a rocky island off the coast of the U.S. state of California. The island is long and across at its greatest width. The island is located about south-southwest of Los Angeles, California. The highest point on the island is...
, this species feeds mainly on the blacksmith
Chromis punctipinnis
The blacksmith is a fish native to the eastern Pacific Ocean. Its range is from Monterey Bay, California, to central Baja California, Mexico. The blacksmith reaches a maximum size of 25 cm and is dark blue.The blacksmith is symbiotic with the senorita fish...
(Chromis punctipinnis) and the queenfish (Seriphus politus). Adults and juveniles have broadly similar diets.
Individual sharks actively choose sites that will give them the best ambush success. They prefer junctions of sandy and rocky substrates near reefs, which are used by many fishes for shelter, usually orienting themselves either toward or parallel to nearby vertical structures. They also tend to face upslope, which may facilitate burying via falling sediment, bring more fish swimming downstream from the reef, and/or ease targeting by silhouetting prey against the sunlight.
Once settled at a successful site, a Pacific angelshark may remain there for up to ten days, re-burying itself on or near the same spot after every strike. As the local prey eventually learn to avoid the stationary predator, the shark will periodically shift to a new site several kilometers away at night. One study off Santa Catalina Island found that, over 13–25 hours, nine sharks together used only 1.5 km2 (0.6 mi2) of space. A later, longer-term study found that the sharks' sporadic position changes covered as much as 75 km (46.6 mi) over three months, almost circling the island. Single individuals swam up to 7.3 km (4.5 mi) in a single night.
The Pacific angelshark is primarily a visual hunter; experiments in nature show that they will strike at fish-shaped targets without any additional electrical, chemical, vibrational, or behavioral cues. At night, they are guided by the bioluminescence
Bioluminescence
Bioluminescence is the production and emission of light by a living organism. Its name is a hybrid word, originating from the Greek bios for "living" and the Latin lumen "light". Bioluminescence is a naturally occurring form of chemiluminescence where energy is released by a chemical reaction in...
of plankton
Plankton
Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...
ic dinoflagellate
Dinoflagellate
The dinoflagellates are a large group of flagellate protists. Most are marine plankton, but they are common in fresh water habitats as well. Their populations are distributed depending on temperature, salinity, or depth...
s and ostracod
Ostracod
Ostracoda is a class of the Crustacea, sometimes known as the seed shrimp because of their appearance. Some 65,000 species have been identified, grouped into several orders....
s disturbed by moving prey. This species' visual system is attuned to the wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
s of light emitted by these plankton
Plankton
Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...
ic organisms, showing the importance of night hunting. Pacific angelsharks are more likely to strike at prey approaching from the front than from the sides or back. It usually waits until the prey approaches to within 15 cm (5.9 in), as its attack is significantly less accurate beyond this distance. The strike is a stereotyped behavior
Stereotypy
A stereotypy is a repetitive or ritualistic movement, posture, or utterance, found in people with mental retardation, autism spectrum disorders, tardive dyskinesia and stereotypic movement disorder. Stereotypies may be simple movements such as body rocking, or complex, such as self-caressing,...
in which the shark presses the forward lobes of its pectoral fins against the bottom and thrusts its head upwards at up to a 90° angle. Its mouth forms a tube when opened, creating a suction force, while its jaws protude forward to secure the prey between sharp teeth. During the strike, the eyes are rolled backward into the head for protection. The entire strike is often completed in under a tenth of a second.
Life history
The Pacific angelshark is aplacental viviparous with the unborn young nourished by a yolk sac; reproduction occurs on an annual cycle. Most females have a single functional ovaryOvary
The ovary is an ovum-producing reproductive organ, often found in pairs as part of the vertebrate female reproductive system. Ovaries in anatomically female individuals are analogous to testes in anatomically male individuals, in that they are both gonads and endocrine glands.-Human anatomy:Ovaries...
(on the left side), though some have two; the oviduct
Oviduct
In non-mammalian vertebrates, the passageway from the ovaries to the outside of the body is known as the oviduct. The eggs travel along the oviduct. These eggs will either be fertilized by sperm to become a zygote, or will degenerate in the body...
s are often filled with yolk, which has been speculated to be from unfertilized eggs being resorbed. Young embryos 35 mm (1.4 in) long have translucent skin, protruding eyes, and exposed gill filament
Gill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...
s. Spots of pigment
Pigment
A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...
have developed when the embryo is 70 mm (2.8 in) long, and the first row of teeth have appeared when the embryo is 110 mm (4.3 in) long. By the time the embryo is 150 mm (5.9 in) long, the mouth has migrated to a terminal position and the color pattern has fully developed; the external yolk sac begins to shrink as the yolk is transferred to an internal yolk sac, which holds it until it can be transferred to the intestine for digestion
Digestion
Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream, for instance. Digestion is a form of catabolism: a breakdown of large food molecules to smaller ones....
. The internal yolk sac is fully resorbed before birth; if the pup is released prematurely, it does not feed until this process is complete.
Off Santa Barbara, birthing takes place from March to June after a gestation period
Gestation period
For mammals the gestation period is the time in which a fetus develops, beginning with fertilization and ending at birth. The duration of this period varies between species.-Duration:...
of ten months, and the females mate
Mating
In biology, mating is the pairing of opposite-sex or hermaphroditic organisms for copulation. In social animals, it also includes the raising of their offspring. Copulation is the union of the sex organs of two sexually reproducing animals for insemination and subsequent internal fertilization...
again shortly afterward. The average litter size is 6 with a range of 1–11 (rarely 13); there is no correlation between female size and number of offspring. The young are born in water 55 – deep, probably to protect them from predators. Pacific angelshark embryos grow at 45 mm (1.8 in) per month when young, slowing down to 10 mm (0.393700787401575 in) per month just before birth, and are born at a length of 25 –. Newborn pups in captivity grow at a rate of around 14 cm (5.5 in) per year, while adults in the wild grow at around 2 cm (0.78740157480315 in) per year. Both sexes mature at 90 – long, corresponding to an age of 8–13 years. Gulf of California sharks, which may be another species, mature at 78 cm (2.6 ft) long for males and 85 cm (2.8 ft) long for females. About 20% of newborns survive to maturity. The maximum lifespan has been estimated at 25–35 years. Unlike other sharks, the growth rings on the vertebrae of this species are deposited in proportion to the shark's size rather than yearly, making age determination difficult.
Human interactions
Although usually sedate and approachable underwater, Pacific angelsharks are quick to bite if touched, captured, or otherwise provoked, and can inflict severe lacerations. Commercial fisheries for this species exist off Baja CaliforniaBaja California
Baja California officially Estado Libre y Soberano de Baja California is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. It is both the northernmost and westernmost state of Mexico. Before becoming a state in 1953, the area was known as the North...
and to a lesser extent off California (see below); the meat is considered excellent and is sold fresh or frozen. This species is captured in limited numbers by recreational fishers
Recreational fishing
Recreational fishing, also called sport fishing, is fishing for pleasure or competition. It can be contrasted with commercial fishing, which is fishing for profit, or subsistence fishing, which is fishing for survival....
using hook-and-line, spears, or even by hand, particularly off southern California. It is also taken as bycatch
Bycatch
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...
in shrimp
Shrimp
Shrimp are swimming, decapod crustaceans classified in the infraorder Caridea, found widely around the world in both fresh and salt water. Adult shrimp are filter feeding benthic animals living close to the bottom. They can live in schools and can swim rapidly backwards. Shrimp are an important...
trawls operating in the Gulf of California, and processed into fishmeal. The capacity of this species to withstand a focused fishing effort is limited, due to its low rates of reproduction and movement.
In 1976, the commercial gillnet fishery for the California halibut
California halibut
The California halibut or California flounder, Paralichthys californicus, is a large-tooth flounder native to the waters of the Pacific Coast of North America from the Quillayute River in Washington to Magdalena Bay in Baja California. It feeds near shore and is free swimming. It typically weighs...
(Paralichthys californicus), operating off Santa Barbara, expanded to include the Pacific angelshark as well. The sharks had become valuable due to their promotion as a substitute for the seasonally available common thresher shark (Alopias vulpinus), and the development of new processing techniques. Around 50% of the shark was used, while the skin
Skin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...
, cartilage
Cartilage
Cartilage is a flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...
, and offal
Offal
Offal , also called, especially in the United States, variety meats or organ meats, refers to the internal organs and entrails of a butchered animal. The word does not refer to a particular list of edible organs, which varies by culture and region, but includes most internal organs other than...
were discarded. In the 1980s, rising demand led to the introduction of gillnets with a medium-sized mesh, designed specifically for this species. Fishery landings increased from a dressed (post-processing) weight of 148 kg (326.3 lb) in 1977, to 117000 kg (257,940.8 lb) in 1983, to 277000 kg (610,680.5 lb) in 1984. The fishery peaked in 1985 and 1986, when 550,000 kg (1.2 million lbs) were taken annually, making this species the number one shark fished off California. This level of exploitation was unsustainable, and despite a minimum size limit imposed in 1986, catches fell to 112000 kg (246,917.7 lb) in 1990.
In 1991, the use of gillnets in nearshore Californian waters was banned by a voter initiative (Proposition 132); the restricted area included much of the Pacific angelshark's habitat and reduced fishing pressure on the species. As a result, Pacific angelshark landings dropped further to 10000 kg (22,046.2 lb) dressed in 1994, when the central Californian halibut/angel shark fishery was closed completely, and have remained low since. The decline of the Californian fishery led to the industry shifting to Mexico, where gillnet pangas (artisanal fishing vessel
Traditional fishing boats
Traditionally, many different kinds of boats have been used as fishing boats to catch fish in the sea, or on a lake or river. Even today, many traditional fishing boats are still in use. According to the United Nations Food and Agriculture Organization , at the end of 2004, the world fishing fleet...
s) targeting this species now meet most of the angel shark demand in California. The International Union for Conservation of Nature (IUCN) has assessed this species as Near Threatened
Near Threatened
Near Threatened is a conservation status assigned to species or lower taxa that may be considered threatened with extinction in the near future, although it does not currently qualify for the threatened status...
; Pacific angelshark numbers off California appear to be increasing and demographic modeling suggests the stock is healthy. However, the impact of the intense, unregulated Mexican fishery on the global population is yet undetermined. There is continuing interest in California for a resumption of the commercial fishery, though conservation concerns have thus far taken precedence.