Pacific smalltail shark

Carcharhinus cerdale is a small, slender shark of the family Carcharhinidae that lives in the coastal waters of the American Pacific ^[1],[2]. The 1984 FAO shark catalogue treated it as a synonym of the Atlantic smalltail shark, Carcharhinus porosus, and in 2011 it was again recognised as a separate Pacific species; that is why much of the literature, the Peruvian included, still calls it Carcharhinus porosus ^[2],[3],[4]. The global IUCN Red List classifies it as Critically Endangered ^[5].

The FAO shark catalogue, which still lumped the Atlantic and Pacific populations into a single species, describes a grey, slim shark under 1.5 m long, with a moderately long, pointed snout, large round eyes, short and inconspicuous labial furrows and no ridge between the two dorsal fins ^[2]. The first dorsal is large and sickle-shaped; the second is medium-sized and rather low and begins over the middle of the anal-fin base or slightly behind it, and the anal fin is deeply notched; the pectorals are small and falcate ^[2].

It usually has 14 to 15 rows of teeth in each half of the jaws; the upper ones carry narrow, tall and strongly serrated cusps ^[2]. It is grey above and pale below; the tips of the pectoral, dorsal and caudal fins are often dark but carry no striking marks, and the pale flank band is barely visible ^[2]. That description mixes specimens from both oceans, so not every feature in it need hold for the Pacific animal ^[2],[3].

Similar species

• Carcharhinus porosus: They are so alike that they were treated as one species for decades; since the split, the checklist of Colombian elasmobranchs keeps Carcharhinus porosus for the Caribbean and recognises Carcharhinus cerdale as the valid Pacific species, so in Peruvian waters the second name is the right one ^[3],[2].

In the eastern Pacific it ranges from the Gulf of California to Peru, without reaching the oceanic islands ^[2]. It appears in the checklist of chondrichthyans of Mexico's Pacific coast ^[6], in that of the Colombian Pacific, backed by museum specimens ^[3], and in the list of Peruvian sharks, where it is named Carcharhinus porosus ^[4].

According to the FAO catalogue, which pooled data from both oceans, it is a tropical shark of the continental shelf that lives near the bottom, from the shoreline down to at least 36 m, and favours muddy bottoms and estuaries ^[2]. On the Colombian Pacific coast, where it was recorded as Carcharhinus porosus, it turned up in the nets of a single shrimp trawler sampled each October, whose hauls averaged 11.6 to 31.0 m deep depending on the year ^[7].

It is viviparous with a yolk-sac placenta and gives birth to 2 to 7 pups; the FAO catalogue credits it with a maximum length that probably does not exceed 150 cm and a size at birth of 31 to 40 cm ^[2]. These figures were put together when the Atlantic and Pacific populations were considered one species, so they should be applied to Carcharhinus cerdale with caution ^[2],[3].

In shrimp trawls on the Colombian Pacific coast, the individuals caught averaged between 37.6 and 41.0 cm in total length in the sampling years in which the species appeared, from 1995 to 2004 ^[7].

It is a harmless shark that feeds mainly on fish: the FAO catalogue lists sardines, sea catfishes, croakers, jacks, grunts and small sharks, young hammerheads among them, as well as shrimp ^[2].

As of 2016 there were no published studies of its diet in the tropical eastern Pacific, so an analysis of trawl fishing in Colombia had to use for it a trophic level of 4.1 taken from an estimate published in 1999 ^[7]. In a stable-isotope study of 7 shark species from the Colombian Pacific, this one among them, the species' feeding areas overlapped in coastal habitats ^[8].

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

In the monitoring of a single shrimp trawler on the Colombian Pacific coast, its catch per fishing hour fell from 0.24 in 1995 to 0.01 in 2001; it rose to 0.17 in 2003, was 0.02 in 2004, and none were caught in 2007 ^[7].

Between 2016 and 2018, 689 sharks landed by small-scale fishers in northern Chocó, Colombia, were sequenced, and only 5 turned out to belong to this species ^[9]. Sharks there usually reach port without heads or fins, which is why DNA is needed to find out which species are being caught ^[9].

In Peru, Ministerial Resolution 209-2001-PE sets a minimum catch length of 150 cm for the species of the genus Carcharhinus, and the 2016 analysis of the Peruvian shark fishery applies it to this species as well, which it lists as Carcharhinus porosus ^[10].

Not medical advice. For a sting, a poisoning or an allergy, seek medical care.

A study of mercury in sharks confiscated at the port of Buenaventura, on Colombia's Pacific coast, measured total mercury in fins and muscle of 7 species, this one included ^[8]. About 24 % of the muscle samples exceeded the recommended international limits for human consumption, mostly in Alopias pelagicus and Sphyrna lewini ^[8].

The FAO catalogue records it as an incidental longline catch throughout its range, used fresh, frozen or dried and salted for human consumption; oil was extracted from the liver and the carcasses went into fishmeal ^[2].

In Peru it appears, as Carcharhinus porosus, among the 18 shark species with recorded landings; from 1996 to 2010, six species made up 98 % of what was landed and the other 12, this one among them, only 2 % together ^[10]. There it is known by the name «cazón» ^[11]. In Colombia sharks are caught for human consumption and their fins are exported illegally; this species was among the sharks seized at the port of Buenaventura that a 2021 study analysed ^[8].

Its range reaches Peru ^[2]. The 2015 updated checklist of Peruvian chondrichthyans includes it under the name Carcharhinus porosus, based on the 2001 catalogue of marine fishes and the 2014 national plan of action for sharks ^[4], and the 2016 analysis of Peru's shark fishery counts it among the 18 species with recorded landings, with species-level data from 1996 to 2010 ^[10]. None of these sources names particular places or recent sightings in the country ^[4],[10].