Pseudobatos leucorhynchus

Pseudobatos leucorhynchus is a guitarfish of the family Rhinobatidae, in the order Rhinopristiformes ^[1]. It lives in tropical coastal waters of the eastern Pacific over soft, sandy bottoms ^[2]. The 2015 checklist of Peruvian chondrichthyans includes it, with a record from Tumbes ^[3]. In the Colombian Pacific, 286 specimens caught incidentally between 2001 and 2007 were studied ^[2]. Its global category on the IUCN Red List is Vulnerable ^[4].

It has the flattened, elongated body typical of guitarfishes. The back is dark grey, sometimes with pale spots; the snout is very pale and translucent, and the underside is white ^[2].

In the Colombian Pacific females measured 20.0 to 76.0 cm total length and males 22.5 to 64.3 cm; these maximum sizes exceeded the 62.5 and 63 cm cited earlier for the tropical eastern Pacific ^[2]. In bycatch from Ecuador, by contrast, the 1024 fish sampled spanned 20.5 cm up to 106.0 cm, with females growing larger than males ^[5].

In the checklist of Peruvian chondrichthyans it is listed as Rhinobatos leucorhynchus in the family Rhinobatidae, where the list also includes Rhinobatos glaucostigma and Rhinobatos planiceps ^[3].

It is a tropical eastern Pacific species, distributed from the Gulf of California to the Galápagos Islands ^[2]. FishBase gives it from Mazatlán, in Mexico, to Ecuador, including the Galápagos ^[6].

It inhabits tropical coastal waters and estuaries with soft, sandy bottoms ^[2]. In the Colombian Pacific the specimens were obtained in the central shrimp fishing zone, between 5°05' N and 2°31' N ^[2]. That sample contained no juveniles, which the authors read as a spatial separation between life stages: neonates and juveniles would be closer to shore, in shallow water and estuaries ^[2].

It is viviparous. In the Colombian Pacific the median size at maturity was 48.5 cm total length in females and 51.2 cm in males; the smallest mature female measured 44 cm and the smallest male with signs of maturity, 42 cm ^[2]. Each female carried 1 to 6 embryos, averaging 3.45 with 4 as the most frequent value, and larger mothers had more eggs and more embryos ^[2]. The young would be born at 19 to 19.5 cm total length ^[2].

Among adults the sex ratio was 2.4 females per male, whereas among embryos it was 1:1, so the authors propose that the sexes segregate in space after birth ^[2]. In that sample the reproductive cycle could not be defined, but a reproductive season between June and September is inferred and births would begin around August ^[2].

In Ecuador 1024 specimens (458 males and 566 females) were sampled between April 2013 and January 2015; half the females were mature at 57.8 cm and half the males at 60.9 cm, and females already carried young at 65.1 cm ^[5]. There the litter was 1 to 7 embryos, birth occurs at 20 to 26 cm, the ovarian cycle lasted about 6 months, gestation 5 to 6 months, and 2 ovulation peaks were seen, from May to June and from November to December ^[5]. Embryos of different sizes were found all year round, which indicates an asynchronous cycle ^[5].

It is a specialised benthic predator. Of 211 stomachs examined in the Colombian Pacific (147 from females and 64 from males), 18.0 % were empty and 30 prey types were found; shrimps, especially Trachypenaeus sp., were the main food, at 52.0 % of the index of relative importance ^[2]. Niche breadth was 0.06, a value that indicates a specialised diet ^[2].

The diets of males and females differ: females eat more fish, among them the toadfish Porichthys margaritatus, and males more crustaceans and mantis shrimps ^[2]. The authors conclude that it takes its food from the sandy-muddy bottoms where it lives and does not chase fish in midwater ^[2].

Its global category on the IUCN Red List is Vulnerable ^[4].

Although there is no fishery directed at it, its presence in nearshore estuarine habitats and shallow water makes it vulnerable to trawling, and the dorsal fins of the largest individuals are traded ^[2]. It is caught regularly as bycatch in shrimp fishing, both small-scale and industrial, in the Colombian Pacific ^[2]. The authors consider that, given its biological characteristics and its commercial importance, it needs management attention ^[2].

In the Colombian Pacific it is taken incidentally in industrial and small-scale shrimp trawling; its meat is sold locally and the dorsal fins of the largest individuals are traded, although its commercial value is not high ^[2]. In Ecuador the specimens studied in the 2015 research arrived as bycatch of commercial fisheries on the Pacific coast ^[5].

Very little has been published about this ray in Peru: the updated checklist of chondrichthyans, from 2015, includes it with a record from Tumbes taken from the 2001 catalogue of Chirichigno and Cornejo, without further site detail ^[3]. The literature consulted describes it as a trawl catch on soft bottoms of coastal waters, not as a reef species to look for underwater ^[2].