Haller's Round Ray

The round stingray has a nearly round pectoral fin disc usually colored brown or grayish brown above, with pale yellow spots or reticulations. Some individuals are plain or black. The underside is white to yellowish. The tail is short and stout, with a long, thick, serrated stinging spine. The teeth are small and diamond-shaped, and sexually dimorphic in that the central teeth of males are erect, sharply pointed, and curved inward. They attain a maximum pectoral fin disc width of 25 cm in males and 31 cm in females. The tail spine is periodically shed and replaced; for most of the year round stingrays have only one spine, but at the beginning of July small secondary spines begin to appear. The number of rays with secondary spines increases to a peak around September and October, then declines as the primary spines fall off and are replaced. The replacement process is complete by December.

This species is endemic to the eastern North Pacific Ocean, from Humboldt Bay in northern California south to Panama. It is most common around southern California and the Baja Peninsula. They inhabit tropical to warm-temperate waters close to shore, usually less than 15 m deep, although they have been reported to a depth of at least 91 m. This species favors soft-bottomed habitats such as mud or sand, often with abundant eelgrass, which they use for camouflage. They also occur around rocky reefs. Round stingrays prefer temperatures above 10 °C (50 °F); the adults are more tolerant of temperature changes than juveniles. They are most abundant in the coastal and bay waters of southern California from spring to fall. In winter, they move to deeper water where the temperature is more stable. Round stingrays have been observed congregating near the warm seawater effluent released by coastal electric generators, which may replicate the conditions of estuary environments.

In nature, round stingrays strongly segregate by age and sex, with the females staying in water deeper than 14 m and males and juveniles in shallower habitat. The juveniles feed on polychaete worms and small benthic crabs until they are 14 cm across. As they mature, their diet shifts towards bivalve molluscs. Round stingrays are daytime foragers that are most active in the warm temperatures of summer and fall. Using their pectoral disc and mouths, they dig large pits to uncover buried prey. The digging of these pits plays an ecologically important role, as they also uncover prey for smaller fish. In the northern part of its range, round stingrays are preyed upon by the northern elephant seal and the giant sea bass. Other predators include large sharks. Numerous parasites are known for the round stingray, comprising 40 species in approximately 19 families. External parasites include copepods and leeches, while 16 species of tapeworms are known from its digestive system, including Phyllobothrium hallericola n. sp. and Acanthobothrium olseni. Additional parasites that may be found in this ray's spiral valve intestine include Eimeria chollaensis sp. nov. and Rhinebothrium spp. As with other stingrays, the round stingray reproduces through aplacental viviparity, bearing litters of 1–6 young with an average of 2–3. The litter size increases with female size. …