Raja eglanteria

Geographic Range

Clearnose skates range along the Atlantic coast of the United States from Massachusetts to southern Florida, as well as in the eastern and northern Gulf of Mexico, from mid-Florida to eastern Texas (22-48°N, 59-91°W). They are rarely found north of Cape Cod, MA.

• Biogeographic Regions
• nearctic nearctic
  • native native
• atlantic ocean atlantic ocean
  • native native

Habitat

Clearnose skates live in saltwater bays and estuaries on the coastal sea floor, preferring soft, sandy, near shore substrates. They are typically found in inshore waters less than 100 m deep, but they have been found at depths of up to 330 m. They prefer water temperatures between 5-27°C (most commonly 9-21°C), and salinities of 12-35 ppt. These skates vary their habitat use and depth by season, mainly to remain within their preferred temperature range, but also depending on their activity (breeding versus feeding).

• Habitat Regions
• temperate temperate
• saltwater or marine saltwater or marine

• Aquatic Biomes
• benthic benthic
• coastal coastal
• brackish water brackish water

• Other Habitat Features
• estuarine estuarine

Physical Description

Clearnose skates are a relatively small species of skate, with a maximum recorded length of 84 cm. Together, the head, pectoral fins, and trunk form a broad disc shaped like a flattened spade; the maximum recorded disc width is 48 cm. Individuals in southern parts of the range tend to be smaller. Two dorsal fins are present, separated by a short gap. A single continuous row of stout thorns (33-39 thorns in adults, 14-19 in small juveniles) is present along the midline of the back, extending from the shoulders to the first dorsal fin near the tip of the tail. Smaller thorns are present on the orbital rims and on each shoulder. There are one to three thorns present between the dorsal fins, and at least one row of stout thorns along the lower edges of the tail. The dorsal surface is covered in tooth-like denticles. The outline of the snout is sharply angled, close to 90 degrees. The dorsal surface is brownish to grayish in color and the pectoral fins are marked with dark spots, blotches, and/or bars. A characteristic feature of this species is a translucent space on each side of the snout. The ventral surface is white to cream-colored and free of markings; it is smooth in young individuals and bears a band of spicules along the anterior margins; females may have ventral patches of prickles as well. No geographic or seasonal variation in pigmentation has been reported. These skates have 46-54 teeth in rows set in their upper jaws and 48 teeth in their lower jaws. Males have sharper teeth, set in a different pattern, as well as various dermal spines, to aid in mating. Males are also distinguished by the presence of a pair of claspers (external copulatory organs).

• Other Physical Features
• ectothermic ectothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• sexes shaped differently

Development

Development has been studied in great detail for this species. Ova are typically released in pairs, likely one from each ovary. Ova enter a common ostium, then separate again so that each can travel down one of the two oviducts, where they are fertilized. An egg case begins to form before ovulation occurs. Egg cases are, on average, 3.7-4.7 cm wide and 6.4-7.7 cm long. Egg cases have a horn at each of their four corners, each horn with a small groove (respiratory canal) at the base of its lateral edge. Once ova are fertilized, egg case formation is completed. One to thirteen days after fertilization, eggs are deposited. During days one through four after oviposition, a fertilized egg begins cleavage and expansion of the blastodisc. The neural tube and embryonic axis form between days 4 and 7. Pharyngeal pouches and gill filaments develop between days 10 and 28. Respiratory pores in the egg case are unplugged between days 25 and 28, at which time the water is moved through the egg case with continuous tail beats from a developing embryo. During weeks four through seven, fins expand and external filaments transition to internal gills. Epidermal pigmentation develops and yolk absorbtion is completed during weeks 8 through 12. The yolk is absorbed during this time as well. Young hatch around week 12, fully formed and completely independent.

Reproduction

In captivity, females have been observed slightly arching their backs, raising their tails, and raising and lowering the posterior margins of both pectoral fins while positioned directly in front of a male. This behavior appears to be an attempt to gain a male's attention, but is not always successful and does not seem to be necessary for the initiation of mating behavior.

A male will approach a female from behind, then bite onto the trailing edge of one of her pectoral fins, holding on with his jaws, as well as with his spines (two sets of dorsal dermal spines, malar spines found lateral to the eye, and alar spines found in rows over the distal portions of each pectoral fin). A male and female have been observed in this position for one to four hours before beginning copulation. To begin copulation, a male then rotates his pelvis underneath a female's tail and pelvic fin, and inserts one clasper into her cloaca. This is a slow process, taking up to an hour to complete. If the male is attached to her right pectoral fin, the right clasper is inserted. If he is attached to her left pectoral fin, he inserts the left clasper. No preference has been documented between initial attachment to the right or left pectoral fin. Once inserted, the clasper expands distally, anchoring it in place. Sperm pass into storage glands, known alternatively as shell glands, oviductal glands, or nidamental glands. Sperm remains viable for up to three months.

• Mating System
• polygynandrous (promiscuous) polygynandrous (promiscuous)

Clearnose skates are oviparous, and their breeding season is heavily influenced by water temperatures; the optimal water temperature for breeding is 16-22°C. Therefore, different geographical populations may breed at different times. Clearnose skates living near the western coast of Florida breed from December to mid-May. Females mature at 4-6 years of age, while males mature at 2-4 years of age (47-58 cm total length for both sexes). Females store sperm and have been observed producing fertilized eggs up to five weeks following copulation. Sperm are thought to remain viable for up to three months.

During oviposition, a female slightly arches her back while contracting the posterior lobes of the pelvic fins ventrally. After shaking the pelvic region from side to side, a single egg is expelled. The second egg is laid several minutes to several hours later. This pelvic shaking often partially buries the egg in the substrate, and sticky material on tendrils at the posterior end of the egg case helps to anchor it. Females lay 23-25 pairs of eggs per season. The total incubation/developmental period for pairs of eggs is about 96 days if the eggs are laid early in the season, but can be as short as 62 days for eggs laid toward the end of the season. Young skates emerge from the egg case at the ruptured anterior end, between the two anterior horns. They are fully formed and independent upon hatching, measuring 13.0-15.0 cm long and 8.4-10.5 cm wide.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
  • internal internal
• oviparous oviparous
• sperm-storing sperm-storing
• delayed fertilization delayed fertilization

Offspring are fully independent upon hatching; no parental care has been documented after oviposition.

• Parental Investment
• no parental involvement

Lifespan/Longevity

Clearnose skates have a lifespan of 5 years or more.

Behavior

Clearnose skates use a form of benthic locomotion called "true punting", which is somewhat unusual among benthic elasmobranchs. In order to move, they first dig their bilobed pelvic fins into substrate, then retract them caudally, while keeping the body still otherwise. Through this method of locomotion, Clearnose skates are able to perform detailed maneuvers along the substrate, aiding in location and detection of prey while causing little water disturbance, which could alert prey and predators alike. They may also swim in the water column, using a motion that is intermediate between pectoral fin undulation and oscillation.

• Key Behaviors
• natatorial natatorial
• diurnal diurnal
• nocturnal nocturnal
• motile motile
• migratory migratory
• solitary solitary

Home Range

These skates move between spawning and feeding areas, typically within a range of 200 km. Northern populations appear to migrate south and into deeper waters during autumn months, returning during the spring.

Communication and Perception

Clearnose skates have a mechanosensory lateral line system used for detecting water movements. This system is comprised of neuromast receptor organs, composed of hair cells and support cells, which are covered by a gelatinous cupula. Drag from the movement of water displaces the cupula, causing sensory information to be sent to processing centers in the hindbrain. The positioning of the neuromasts helps these animals to detect water movements from currents, predators, prey, or conspecific individuals. They are also electrosensitive, using specialized organs (Ampullae of Lorenzini) to detect electrical signals, while also using electrical discharges socially to communicate.

Clearnose skates have low-profile, dorsally positioned eyes. The position of their eyes allows them to bury in the substrate while keeping the eyes uncovered; they are able to see 360° around their dorsal surfaces. Light can also be perceived through their patches of translucent rostral tissue.

• Communication Channels
• visual visual
• tactile tactile
• electric electric

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• vibrations vibrations
• chemical chemical
• electric electric

Food Habits

Clearnose skates are carnivorous, feeding on decapod crustaceans, bivalves, polychaetes, squids, shrimp, crabs, and fishes. In particular, larger individuals tend to feed preferentially on squid, depending on location and season.

• Primary Diet
• carnivore carnivore
  • piscivore piscivore
  • eats non-insect arthropods
  • molluscivore molluscivore

• Animal Foods
• fish
• mollusks
• aquatic or marine worms
• aquatic crustaceans

Predation

Embryonic clearnose skates both produce (through tail movements related to respiration) and detect (from potential predators) electrical signals. If an embryo senses electrical signals produced by a potential predator, it will halt its tail movements, in order to avoid detection. Once hatched, their elaborate pupillary structures and distinct dorsal markings provide excellent camouflage from predators. Nevertheless, these skates may be prey to other carnivorous fishes, as well as gastropods (as embryos).

• Anti-predator Adaptations
• cryptic cryptic

Ecosystem Roles

In addition to their ecosystem roles as predators of benthic organisms and prey to larger vertebrates, clearnose skates may serve as hosts to a number of parasites.

Economic Importance for Humans: Positive

Although clearnose skates can be used for food, they are not typically fished and are not considered to be economically important.

• Positive Impacts
• food food

Economic Importance for Humans: Negative

Clearnose skates pose no significant threats to humans, although injury is possible if direct contact with a skate's thorns occurs.

Conservation Status

This species is currently listed as a species of least concern by the IUCN and has no special status on the U.S. Federal List, CITES, or the State of Michigan list. Clearnose skates remain common despite being frequently caught by fishermen as bycatch.

Additional Links

Encyclopedia of Life

Contributors

Molly Miller (author), Indiana University-Purdue University Fort Wayne, Mark Jordan (editor), Indiana University-Purdue University Fort Wayne, Jeremy Wright (editor), University of Michigan-Ann Arbor.

References

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