Tumbes Round Stingray

Urobatis tumbesensis is a small round stingray that lives on the bottom in the eastern Pacific, from Colombia to Peru ^[1],[2]. It was described in 1979 as a new species from the coast of Peru ^[3]. Its global category is Vulnerable ^[4]. In northern Peru it has been seen in the shallows of Los Órganos, resting in caves and crevices on mixed ground of sand, rock and seaweed ^[5].

The genus name, Urobatis, joins two Greek words: oura, tail, and batis, ray ^[2]. The species was described in 1979 in the genus Urolophus, family Urolophidae ^[3]. Today it is placed in the genus Urobatis, family Urotrygonidae ^[6]. That family was split from Urolophidae in 1996, and its species live in the eastern Pacific and the western Atlantic ^[1].

The upper side of the disc is brown, with dark and pale wavy lines and white spots the size of the eye; the underside ranges from brownish to white, pink or cream, usually darker at the edges, and towards the rear of the disc and the pelvic fins it shows a network of pale spots on a darker ground ^[1]. The upper side of the disc or the tail carries visible dermal denticles, tubercles or thorns, a feature it shares within the genus only with the western Atlantic Urobatis jamaicensis; they have not yet developed in newborns and are hard to see in juveniles ^[1].

Before 2015, 5 species of the genus were recognised in the eastern Pacific; that year a sixth, Urobatis pardalis, was described from the Pacific coast of Costa Rica, and it differs from Urobatis tumbesensis in having no denticles or tubercles on the upper side of the disc ^[1].

Similar species

• Urobatis halleri: Its disc is bare above, without denticles or tubercles, and its pattern is dominated by spots smaller than the eye; it has also been recorded in Peru, at Isla Lobos de Tierra and at Los Órganos ^[1],[7],[5].

It lives in the eastern Pacific, between Colombia to the north and Peru to the south, which mark the limits of its range ^[1]. It appears in the updated checklist of cartilaginous fishes of the Peruvian sea, based on its original description and on the 2001 annotated catalogue of Peruvian marine fishes ^[7].

It is a tropical bottom fish recorded both in the sea and in brackish water; it uses shallow coastal water, estuaries and mangroves, and reaches depths of at least 20 m ^[2],[6]. At Los Órganos it was recorded between 1 and 6 m, on mixed ground of sand, rock, reefs built by the polychaete Phragmatopoma and seaweeds such as Caulerpa or Ulva ^[5].

The largest length FishBase records for the species is 34.5 cm total length ^[2].

Among the 7 individuals sampled at Los Órganos the ratio of males to females was 1 to 1.3, not a significant difference; the males were above the 30 cm total-length size at maturity given in the literature, while for the females it could not be told whether they were mature, because their size at maturity is unknown ^[5].

At Los Órganos, apart from the eagle rays, which were swimming, every ray recorded on the morning surveys was motionless, fully or partly buried in sand; Urobatis tumbesensis turned up in mixed habitat, inside caves or crevices ^[5]. There it shares the shore zone with 7 other batoid species, among them Urotrygon chilensis, Zapteryx xyster, Narcine entemedor and Urobatis halleri ^[5].

It hosts parasites: in 1999 a new tetraphyllidean tapeworm was described from specimens taken in coastal waters of Ecuador, and the genus Pararhinebothroides was erected for it ^[8]. A later study, with new material from the Gulf of Guayaquil, concluded that this genus is not valid and moved the tapeworm to the genus Anthocephalum ^[9].

Its global category is Vulnerable ^[4]. The assessment, dated 24 February 2020, lists it under criteria A2cd ^[2].

FishBase estimates low resilience for it, with a minimum population doubling time of 4.5 to 14 years, and a high vulnerability to fishing, 55 out of 100 ^[2]. A review of the elasmobranchs endemic to South America lists it among them, with a range from Colombia to Peru ^[10].

The Los Órganos study notes that these vulnerable species need research before management plans can be drawn up, and proposes finding out whether that stretch of shore works as a gestation area and whether it qualifies as an Important Shark and Ray Area ^[5].

In 2016, 2017 and 2019, 20 field trips were made in the coastal zone of Los Órganos, Piura, snorkelling along transects of about 3 km at 1 to 6 m depth and only in the mornings, because from midday conditions such as strong wind lower visibility; 7 Urobatis tumbesensis were recorded ^[5]. In that work it turned up in caves and crevices of the mixed ground, while other rays, such as Urotrygon chilensis, were on sandy bottoms ^[5].