Spinetail Devil Ray: The Ocean’s Endangered Acrobat

The spinetail devil ray is a large, migratory species belonging to the same family as manta rays. These filter-feeders are known for their impressive size and acrobatic displays, yet their vast range and pelagic nature make them a difficult species to study. Inhabiting tropical and subtropical waters around the globe, they are a compelling example of the unique life that exists beneath the waves.

Physical Description and Identification

The spinetail devil ray possesses a broad, diamond-shaped body, with a wingspan that can reach up to 3.5 meters (11.5 feet). Its dorsal (top) side is a dark, slate blue to black color, often with a thick black band that stretches between the eyes. This darker coloration contrasts with its bright white underside, a pattern known as countershading that helps it blend into its environment.

Its common name is derived from two distinct features. The “devil” portion of its name comes from the two prominent cephalic fins on its head, which look like horns when unfurled for feeding. The “spinetail” name refers to a small, serrated spine at the base of its long tail, which is an identifying characteristic.

A spinetail devil ray is distinguished from its larger cousin, the manta ray, by its mouth. A spinetail devil ray has a subterminal mouth on the underside of its head, whereas a manta ray has a wide, terminal mouth at the very front. Spinetail devil rays are also smaller than the giant manta ray, which can achieve a wingspan of over 7 meters.

Global Habitat and Behavior

The spinetail devil ray has a circumglobal distribution in the tropical, subtropical, and warm temperate waters of every ocean. It is a pelagic species, inhabiting the open ocean rather than coastal areas. While it spends most of its time in the upper ocean layers, it has been recorded diving to depths of over 1,000 meters. These rays undertake long-distance migrations, with recorded movements up to 1,800 kilometers, driven by seasonal shifts in water temperature and food availability.

As a filter-feeder, its diet consists mainly of tiny organisms like krill, copepods, and crustacean larvae. Using its cephalic fins, it directs water into its mouth, where specialized gill plates filter out the food. Feeding often occurs at night when plankton migrates closer to the surface. While they can be solitary, these rays often form large schools for feeding and reproduction.

One of the most spectacular behaviors exhibited by the spinetail devil ray is breaching. The ray will propel itself entirely out of the water in a breathtaking acrobatic leap before crashing back to the surface. Scientists theorize this may be a form of communication, a method to dislodge parasites, or simply play.

Reproduction and Life Cycle

The spinetail devil ray’s slow reproductive strategy contributes to its vulnerability. The species is ovoviviparous, where eggs develop and hatch within the female’s body, leading to the birth of a live pup. The embryo initially receives nourishment from a yolk sac before absorbing a nutrient-rich uterine fluid from the mother.

Gestation is believed to last approximately one year, a significant investment of time and energy for the female. A female gives birth to a single, large pup per reproductive cycle, though on rare occasions, two have been recorded. Newborns are already quite large, with a disc width of about 90 to 160 centimeters.

The reproductive cycle can be long, with females resting for one to two years between pregnancies. This low reproductive rate means that populations are slow to recover from declines.

Conservation Status and Human Interaction

The spinetail devil ray is currently listed as “Endangered” on the IUCN Red List of Threatened Species, with a decreasing population trend. The global population size is unknown, but regional populations appear to be fragmented and have experienced steep declines.

The most significant threat is being caught as bycatch in fishing operations. Driftnets, purse seines, and longlines used to target other commercial species like tuna frequently entangle and kill these rays. In some regions, they are also targeted directly for their gill plates, which are valued in some Asian markets for use in a health tonic. Other pressures include plastic pollution and strikes from boats.

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