With it’s slim, silver-copper body, pointed snout, large eyes, and small fins, the shark captured by a small-scale commercial fisher looked like any other shark in the family Carcharhinidae, known as the requiem sharks. One of the largest and best-known families of sharks, these animals are medium-to-large, active predators that are known to be migratory and found in waters worldwide. They can sometimes be hard to tell apart since so many in this family look alike, so pardon the fisher for not being fully aware that the shark they had caught was the first night shark reported in Puerto Rico.
Officially known as the Commonwealth of Puerto Rico (Spanish for “rich port”), this Caribbean archipelago is an unincorporated territory of the United States. Known for its vibrant culture, majestic mountains, and pristine beaches, it consists of the main island, four small islands, and hundreds of cays and islets. The Caribbean is a known hot-spot for sharks, and Puerto Rico is slowly but surely making its mark as a “must see” shark research area. In fact, 14 species of carcharhinid sharks have been reported in Puerto Rico, although it may be an underestimation due to lack of monitoring and data reporting on the island. That a night shark (Carcharhinus signatus) was recorded here isn’t entirely surprising – their range is a large swath of the Western Atlantic Ocean (from Delaware to southern Brazil and Argentina), as well the Eastern Atlantic off Africa (think Senegal through the Democratic Republic of the Congo and even in northern Namibia). In fact, the species was first described from Cuba, and it’s English name is a translation from the Spanish name (tiburón de la noche) it was given by Cuban fishers because it was caught only at night. Fishers in Mexico call it ‘ojo verde’ (green eye) because of the ghostly color that stares up at them as they try to unhook them off their lines.
A coastal and semi-oceanic species observed along outer continental and insular shelves, they can go down to depths of 820 feet (250 meters) or deeper during the daytime, often ascending in the water column at night to about 98-164 ft (30-50 m) deep; here they feed on mainly small fish and squid. Night sharks are known to form schools, but only one adult female night shark was recovered from a depth of 1,082 ft (330 m). She was entangled in hook and line gear used in the deep-water snapper and grouper fishery here, making it the first confirmed sighting for Puerto Rico. The only evidence she left behind? Photos, a description of the shark’s appearance and a small tissue sample preserved in 90% alcohol was passed on to scientists Dr. Michelle Schärer-Umpierre and Glorimar Franqui-Rivera.
“At first, when I received the evidence of a previously unreported species of shark in our waters, I was thrilled. After an extensive literature search, my motivation grew, but with the genetics lab results, the option of a validated report finally became a realization,” explains Schärer-Umpierre. “It’s a delightful prospect to be working with Puerto Rican partners to generate proof to reveal the island’s elasmobranch biodiversity following reports like the megamouth (Megachasma pelagios) in 2017, longfin mako (Isurus paucus) in 2020 and most recently, the night shark (Carcharhinus signatus).” The Boricua scientists published these findings in the Journal of the Marine Biological Association of the United Kingdom, detailing that DNA barcoding was used to confirm the photo identification of the shark captured. “[This finding increases] the shark species reported for [Puerto Rico] and [supports the night shark’s] range up to the Mona Passage in the eastern Caribbean Sea,” the authors stress in their article.
“Increasing the information available on the elasmobranchs in Puerto Rico is critical in revealing which threats are a priority to conserve threatened and endangered species (i.e. oceanic white tip, scalloped hammerhead, silky). However, we still have many challenges in generating scientifically valid data on which species require strict protection and which can provide opportunities for our coastal economies through dive tourism or managed fisheries,” says Schärer-Umpierre. “Putting sharks and rays on the map in the US Caribbean is crucial to be able to apply criteria to protect populations of migratory sharks that navigate along corridors near islands, deep water seamounts, and underwater mountain ranges, as well as for those that reproduce near the coast at river mouths, seagrasses, and mangroves, that are vulnerable nursery habitats requiring urgent conservation action.”
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