Common names
Spinytail Round Ray., Panamic Stingray.
Binomial
Urotrygon aspidura.
Synonyms
Urolophus aspidurus.
Identification
A medium-sized round stingray with a sub-circular disc that is wider than long; width 1.1 x length. Snout obtusely angular. Snout tip extended, especially in adult males. Tip pointed; acutely angular. Anterior margins of disc straight to mildly concave, apices broadly rounded. Disc smooth. Described as having thorns on tail only, but the animal shown on this page (and others examined on the internet) have large thorns from nape to caudal fin. Pelvic fins narrowly triangular with slightly convex posterior margins, length sub-equal to width.
Eyes very small; orbit length 0.16-0.2 x snout length. Mouth strongly arched. Nasal curtain short and skirt-shaped. Nostrils oval.
Tail long and slender-based. Lateral skin folds usually absent. Tail length 56-59% of total length. Caudal sting long and slender, origin at mid-tail. Upper caudal lobe much shorter than lower lobe; 18-21% of total length. Posterior margin of caudal fin narrowly pointed.
Colour
Dorsum uniformly tan to dark brown; unmarked. Upper edge of spiracle pale. Thorns on midline may appear paler or yellowish. Tail brown above, pale laterally. Ventrum pale. Caudal sting pale. Caudal fin with a dark median stripe.
Size
Maximum total length at least 42cm. Length at birth unknown.
Conservation Status
NEAR THREATENED
The Spinytail Round Ray (Urotrygon aspidura) is a bycatch component of commercial shrimp trawl fisheries throughout its range. It is generally discarded, but may be retained for bait or ground into fishmeal. The Spinytail Round Ray has a very early age-at-maturity (2.3 years) which affords it some resilience to fishing mortality. Throughout most of its range, fishing pressure is intense, but populations in some areas appear to be fairly stable, e.g. in Colombia.
Habitat
Sub-tropical to warm-temperate seas. Found on sandy or muddy substrates in shallow bays and slopes from 5-100m.
Distribution
Eastern Pacific. Found from Mazatlan in the Sea of Cortez, Mexico, to Punta Negra in Northern Peru.
Reproduction
Aplacental viviparous. Females mature at 2.3yrs. Poorly known.
Diet
Diet unknown. Probably small crustaceans, mollusks, and fishes.
Behavior
Unknown. One animal observed resting in a depression in the sand (probably excavated by a larger ray) at 21m.
Reaction to divers
The only spinytail round ray that I have encountered, bolted immediately.
Diving logistics
According to fishermen, the spinytail round ray is fairly common in Panama Bay but there is no diving infrastructure in that area and the visibility is very poor.
I encountered this species at 20m depth near Playa Ocotal in northern Costa Rica. Sightings are rare but images of this species exist from the same area so this may be a good place to look for them.
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Similar species
Rogers Round Ray Quite similar but distinguishable by a few scattered dark spots on disc.
Dwarf Round Ray Similarly shaped but without thorns on midline.