| Pacific electric ray | ||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
 |
||||||||||||||||
| Conservation status | ||||||||||||||||
| Scientific classification | ||||||||||||||||
|
||||||||||||||||
| Binomial name | ||||||||||||||||
| Torpedo californica Ayres, 1855 |
||||||||||||||||
 Range of the Pacific electric ray
|
The Pacific electric ray, Torpedo californica, is a species of ray, family Torpedinidae, and the only electric ray endemic to the western coast of the United States. It is a solitary, nocturnal predator of bony fishes, which it subdues using pulses of electricity. Care should be exercised around this species, as it has been known to act aggressively towards divers if provoked and its electric shock can knock down a grown person. Pacific electric rays are of significance to molecular biology as a model organism for studies on acetylcholine receptors and other proteins, which are abundant in the cells of its electric organs.
Contents |
Taxonomy
This species was originally described by William Orville Ayres in 1855 as Torpedo californica, and subsequently placed in the genus Tetronarce by Theodore Gill in 1861. It was returned to its original name after Tetronarce was synonymized with Torpedo as a subgenus. The species name californica comes from the U.S. state where it was first discovered. Other common names include the California torpedo ray, torpedo ray, and electric ray.[2]
Distribution and habitat
The Pacific electric ray occurs in the northeastern Pacific Ocean, from the Magdalena and Sebastian Vizcaino Bays in Baja California to the Dixon Entrance in northern British Columbia, possibly with one or more discrete populations north of Point Conception.[2][3] Electric rays off the coasts of Peru, Chile, and Japan may be of this species, but this has yet to be determined.[4]
They are generally found over sandy bottoms, around rocky reefs, and near kelp beds. Along the coast of California they are most often found at depths of 3-30 m, but off Baja they are most commonly observed at depths of 100-200 m. A Pacific electric ray has been videotaped 17 km west of Point Pinos, Monterey County, swimming at a depth of 10 m over water 3,000 m deep; this and other observations suggest that these fish periodically move offshore into an epipelagic habitat. They prefer temperatures of 50-55 degrees F.[2]
Description
A soft, flabby-bodied ray, the Pacific electric ray has an oval pectoral fin disc with a pair of visible kidney-shaped electric organs. The tail is short and stocky with a large caudal fin. There are two dorsal fins, the first nearly twice the size of the second. The teeth are small, with a single smooth-edged cusp, numbering 25-28 in the upper jaw and 19-26 in the lower. The skin is smooth, devoid of dermal denticles or papillae. It is a uniform dark gray to bluish or brown above, sometimes with small black spots, and lighter below.[2] The females are larger and slower-growing than males; males grow to a maximum length of 92 cm and females 137 cm.[5] They weigh up to 41 kg.[3]
Biology and ecology
The Pacific electric ray is a solitary, nomadic fish that can remain suspended in the water column with very little effort. They have few predators due to their large size and formidable electrical defenses.[4] The Cooper's nutmeg snail (Cancellaria cooperi) is a specialized suctorial parasite of the Pacific electric ray, and possibly of other bottom-dwelling fishes such as the Pacific angelshark (Squatina californica). The snails are attracted to the chemicals contained in the ray's surface mucus; they make small cuts on the ventral surface of the ray and feed on blood through their proboscis.[6]
Feeding
Pacific electric rays feed mainly on bony fishes, including anchovies, hake, herring, mackerel, flatfishes, and kelp bass, but will also take invertebrates such as cephalopods.[2] A 124-cm female has been seen consuming a silver salmon (Onchorhynchus kisutch) nearly half her length.[7] Nighttime seine net sampling conducted at the surface of Monterey Bay have captured Pacific electric rays in surprising numbers, suggesting that they rose upwards to feed on small fishes.[8]
Observations at the rocky Naples Reef near Santa Barbara, California, show that Pacific electric rays forage actively over the reef at night, when many reef fishes descend from the water column and become quiescent about a meter above the bottom. When a prey fish enters range, the ray lunges forward and folds the anterior and lateral margins of its pectoral fins over it. It then envelops the prey further by making short kicks with its tail, sometimes performing somersaults and/or barrel rolls, while incapacitating it with electric shocks. The stunned fish is then passed to the weak but flexible mouth with undulations of the disc, and swallowed head-first. One instance of a 75-cm female Pacific electric ray capturing and ingesting a 20-cm jack mackerel (Trachurus symmetricus) took no more than 10 seconds. During the day, the Pacific electric ray moves to the sandy flats adjacent to the reef and partially buries itself, ambushing close-by prey by suddenly lunging its head upwards and simultaneously delivering an electric shock.[7]
Studies of Pacific electric rays off the Palos Verdes Peninsula in southern California show that when attacking fish, the rays discharge up to 414 direct current electric pulses, averaging 5 ms long each, at a maximum rate of 308 pulses per second. The maximum voltage was measured at 45 V for one individual. The ray also continues to generate pulses at a reduced rate after the initial attack, regardless of whether it was successful. There was no relationship between the amplitude of the discharges and the size of the individual; the rate of the pulses increased with water temperature.[9] Their power output can be one kilowatt in a large individual, due to low internal resistance. At night or in turbid water where their vision is limited, the Pacific electric ray may rely on picking up electrical cues with their ampullae of Lorenzini to locate prey.[4] They have been documented attacking artificially generated electric fields and conductive metal electrodes.[9]
Life history
Like other electric rays, the Pacific electric ray is ovoviviparous, with the embryos initially supported by a yolk sac, and then by uterine fluid enriched with mucus, fat, or protein, secreted by specialized structures on the uterine wall of the mother. There is no definite breeding season, but the males are believed to be capable of reproducing every year and the females every other year. Litters range between 17-20, with the young measuring 18-23 cm long. The young double their size in their first year, growing up to 25 cm longer.[4]
Male Pacific electric rays reach maturity at 7 years of age and a length of 64.5 cm, while females reach maturity at 9 years of age and a length of 73.1 cm. Their lifespan is estimated to be at least 16 years and possibly as much as 24 years. The population growth rate of the Pacific electric ray is apparently higher than most other elasmobranch species, with a doubling time of 11.2-13 years.[5]
Human interactions
The electric shock generated by the Pacific electric ray is enough to knock down an adult human. They should be treated with caution, especially at night when they are active and have been known to swim directly at divers with their mouths open if confronted or harassed. There are no confirmed fatalities due to this species, but it may have been involved in several suspicious, unexplained fatal diving accidents.[2] This species does not fare well in captivity.[3]
Electric rays, including the Pacific electric ray, are used as model organisms for molecular biology research because of the high natural abundance of some proteins in their electrical organs, notably acetylcholinesterase and nicotinic acetylcholine receptor. The characterization of the ACh receptor of the Pacific electric ray and its subsequent applications (such as in the pathophysiology of the disease myasthenia gravis) are considered some of the most important successes in molecular neurobiology, and a model approach for other studies.[10] There is a small commercial fishery for this species in southern California for biological and medical research. This ray is also taken as by-catch in trawls and gillnets, and by recreational fishers, but is of no value.[4] These activities appear to have little impact on its population and it is assessed as of Least Concern by the IUCN Red List.[1]
References
- ^ a b Neer (2000). Torpedo californica. 2006 IUCN Red List of Threatened Species. IUCN 2006. Retrieved on May 12, 2006.
- ^ a b c d e f Ebert, D.A. (2003). Sharks, Rays, and Chimaeras of California. University of California Press. ISBN 0520234847.
- ^ a b c "Torpedo californica". FishBase. Ed. Ranier Froese and Daniel Pauly. November 2008 version. N.p.: FishBase, 2008.
- ^ a b c d e Tough, S. Biological Profiles: Pacific Electric Ray. Florida Museum of Natural History Ichthyology Department. Retrieved on November 23, 2008.
- ^ a b Neer, J.A. and Cailliet, G.M. (2007). "Aspects of the Life History of the Pacific Electric Ray, Torpedo californica (Ayres)". Copeia 2001 (3): 842–847. doi:.
- ^ O'Sullivan, J.B., McConnaughey, R.R. and Huber, M.E. (June 1987). "A blood-sucking snail: the Cooper's nutmeg, Cancellaria cooperi Gabb, parasitizes the California electric ray, Torpedo californica Ayres". The Biological Bulletin 172: 362–366. doi:.
- ^ a b Bray, R.N. and Hixon, M.A. (April 21, 1978). "Night-Shocker: Predatory Behavior of the Pacific Electric Ray (Torpedo californica)". Science, New Series 200 (4339): 333–334.
- ^ Allen, J.G., Pondella, D.J. and Horn, M.H. (2006). The Ecology of Marine Fishes: California and Adjacent Waters. University of California Press. ISBN 0520246535.
- ^ a b Lowe, C.G., Bray, R.N. and Nelson, D.R. (1994). "Feeding and associated electrical behavior of the Pacific electric ray Torpedo californica in the field". Marine Biology 120: 161–169.
- ^ Scandalios, J.G. and Wright, T.R.F. (1991). Advances in Genetics. Academic Press. ISBN 0120176297.
This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
