Sicklefin devil ray

Mobula tarapacana is a devil ray of the family Mobulidae, in the order Myliobatiformes ^[1]. It is one of the five mobulid species recorded off Peru ^[2], and it appears in the checklist of Peruvian chondrichthyans under the English name Chilean devil ray ^[3]. It is an oceanic animal: individuals fitted with satellite transmitters in the central North Atlantic dived to almost 2000 m ^[4]. Its global category on the IUCN Red List is Critically Endangered ^[5].

Philippi described it in 1892 as Cephaloptera tarapacana, and it is now accepted within the genus Mobula; WoRMS lists Mobula coilloti, from 1960, and Mobula formosana, from 1962, as later synonyms ^[1]. The checklist of Peruvian chondrichthyans gives its English name as Chilean devil ray, and a study at Isla del Coco, in Costa Rica, uses the same name ^[3],[6].

It is a large mobulid. In Sri Lankan landings, the rays measured had a disc width of 98 to 326 cm, with females between 132 and 326 cm and mature males between 212 and 314 cm, although those figures include pups ^[7]. In catches from the Bohol Sea, in the Philippines, the rays measured ranged from 179 to 279 cm ^[8].

It belongs to the group of large mobulids, which is recognised by a slit-shaped spiracle on the upper surface of the pectoral fins ^[9]. The filter plates of its gills have heart-shaped lobes covered in conical denticles, and the lobes of neighbouring plates can be joined by connective tissue ^[9].

Telling mobulids apart at a landing site is difficult: in Peru, the official IMARPE records attributed all catches to Mobula thurstoni until 2012, and misidentifications still bias the catch data ^[2].

Similar species

• Mobula mobular: Mobula mobular has smooth, rectangular lobes on its gill filter, whereas Mobula tarapacana has heart-shaped lobes covered in denticles; this is an internal feature that requires examining the gill arch ^[9].
• Mobula birostris: Mobula birostris is much larger, with females of 180 to 478 cm disc width in Sri Lanka, and its filter lobes are rectangular rather than heart-shaped ^[7],[9].
• Mobula thurstoni: Mobula thurstoni has the same kind of filter, with heart-shaped lobes and denticles, so that feature does not separate them; size helps, though with overlap: in Sri Lanka the females of Mobula thurstoni measured 72 to 168 cm disc width and those of Mobula tarapacana 132 to 326 cm ^[9],[7].

The studies available on the species come from the central North Atlantic ^[4], the Indian Ocean ^[7], the Bohol Sea in the western Pacific ^[10] and the eastern tropical Pacific ^[6].

Off Peru it appears in the checklist of chondrichthyans, which relies on the catalogue of marine fishes by Chirichigno and Cornejo ^[3]. It is one of the five mobulid species recorded in the country, together with Mobula birostris, Mobula mobular, Mobula munkiana and Mobula thurstoni ^[2].

It is an open-sea species: the 15 individuals tagged in the Azores stayed in oceanic waters throughout the tracking, which lasted up to 9 months ^[4]. At Isla del Coco, between 2010 and 2019, this species and Mobula birostris, counted as a single group, were recorded in about 57 % of the dives of a submersible ^[6].

In Sri Lankan landings, 3 pups of this species were recorded, of 117, 132 and 149 cm disc width, and the smallest pregnant females measured 304 and 326 cm ^[7]. In the Bohol Sea, the females measured were between 195 and 242 cm and the males between 200 and 279 cm ^[10].

It is one of the deepest-diving marine animals: among the 15 individuals fitted with satellite transmitters in the Azores, those tagged in 2011 reached daily maximum depths of 1736 to 1896 m, in water of 3.6 to 4.4 °C, and descended at speeds of up to 6 m per second ^[4]. Earlier studies had concluded that the heat exchangers in the skull probably warm the species' brain ^[4].

It is a filter feeder that also takes larger prey. In the Bohol Sea, the krill Euphausia diomedeae occurred in 18 of the 22 stomachs examined, and others held copepods, a squid and fish remains ^[10]. DNA analysis of the stomachs of 24 rays from the same sea detected 3 fish taxonomic units (OTUs) in this species, against 14 in Mobula birostris ^[8].

There were more deep dives by day (28) than at night (21), and the stepwise ascents are consistent with a search for fish or squid in dense layers at that depth; the authors caution that direct confirmation is needed ^[4].

Its global category on the IUCN Red List is Critically Endangered ^[5].

All mobulids have been listed in Appendices I and II of the Convention on Migratory Species since 2014 and in Appendix II of CITES since 2016 ^[2]. In Peru, Mobula birostris has had special protection since 2016, which prohibits catching, retaining and selling it; in 2024 the Ministry of Production extended protection to all mobulids with a rule scheduled for January 2025, although fishing communities have voiced concern about their livelihoods and enforcement is uncertain ^[2].

Official statistics do not separate it: between 2000 and 2023 IMARPE reported about 7445 t of mobulids, and the species-level data name only Mobula mobular, Mobula munkiana and Mobula thurstoni, plus an unspecified group ^[2].

Outside Peru there are better figures. In Sri Lankan markets, annual landings of this species were estimated, with a model, at between 4867 individuals in 2019 and 13966 in 2013, and the mean width of landed rays fell by about 2.4 cm per year ^[7].

In Peru mobulids are retained mainly for their meat, fresh or dried, with no sign of a gill-plate trade, and in the Lambayeque region the meat is used in traditional cooking ^[2].

In Sri Lanka, where this species is the second most landed after Mobula mobular, its fresh meat was the most valued in the markets of Negombo and Chilaw ^[7].

In the Peruvian literature consulted the species appears only in the checklist of the Peruvian sea's chondrichthyans ^[3], and at the 6 ports of Tumbes and Piura where 257 mobulids were measured between April 2017 and February 2019 the species identified were Mobula mobular, Mobula thurstoni, Mobula munkiana and Mobula birostris ^[2].