First Recorded Neonate Tiger Shark Could Indicate Local Birthing Area
The first recorded sighting of a newborn tiger shark (Galeocerdo cuvier) at Cocos Island in the Eastern Tropical Pacific has led scientists to speculate that the region may potentially be a birthing area for pregnant female tiger sharks.
The tiger shark neonate (less than 28 days old) was detected by baited remote underwater video stations (BRUVS), a network of underwater cameras designed to continuously record important habitats around the world in order to better inform and develop protection measures. The study was part of a research collaboration between scientists from the Ciencias del Mar y Limnología of the University of Costa Rica (CIMAR) and Cocos Island National Park.
Cocos Island is located approximately 550km southwest of Costa Rica and widely recognised as one of the best places in the world for scuba diving, for those that don't mind the 36-hour voyage to get there. As an isolated outpost of extreme biodiversity, it is frequented by at least 14 different species of shark, most famously its huge schools of scalloped hammerheads.
Tiger sharks are a circumglobal, temperate and tropical water shark, commonly found in shallow waters close to shore. Despite regular encounters, like many other shark species, little is known about their mating and reproductive habits. Although adult sharks are not generally observed to provide parental care to their offspring, studies have shown that live-bearing species – and their manta ray cousins – give birth in 'nurseries', areas where there is protection, a plentiful source of food, and fewer challenges to survival than the open ocean.
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There is some evidence that areas around Hawai'i, the Galápagos Islands and the Bahamas are used by tiger sharks as parturation – or 'pupping' – habitats, but there has been no previous indication of similar behaviour at Cocos Island, and this is the first baby tiger shark sighting taken from more than 400 BRUVs deployments over the past five years.
It's possible that the presence of a single baby shark near Cocos is just an isolated incident, however, the cameras have also recorded multiple female tiger sharks with heavily distended abdomens in the area, suggesting that they may be in the late stages of pregnancy.
While neither the neonate sighting nor the potentially pregnant females confirm that the area is used on a regular basis as a nursery, given the island's remote location and the unlikely proposition of a baby shark swimming long distances, the sighting almost certainly confirms that a female tiger shark gave birth near Cocos Island.
One speculative possibility for the new sighting is that Cocos Island has only recently become a nursing ground for tiger sharks. The report states that tiger sharks were first recorded around Cocos as late as 2008, since when the population has grown and is now regularly sighted throughout the year. Changing ocean conditions, redistribution of prey and human activities such as fishing can cause species to change their ranges, and Cocos Island provides a convenient mid-ocean respite for pregnant females, who would otherwise be forced to swim more than 500km to the closest mainland shore, or the Galápagos Islands, some 700km in the other direction.
Avi Klapfer of the Undersea Hunter Group, which reported the discovery on its Facebook page, said: 'Indeed this is a very exciting sighting, though it's the only one that we have seen. It does reflect on healthy environments and possibly a shift in nursing ground from nearshore mainland to the island, yet we will need to wait for more evidence of young sharks at Cocos before we call it a definite change.'
Although the sighting of the baby tiger shark does not confirm that Cocos is now, or has ever been, a tiger shark nursery, it clearly has implications for the continued management and possible expansion of the surrounding Marine Protected Area. With global shark populations in severe decline, identifying mating, pupping, and nursery habitats for sharks is more important than ever, and with massive, predatory fishing fleets active in the Eastern Tropical Pacific, protection of the Cocos-Galápagos Swimway, a 120,000 sq km migratory corridor between the two marine reserves, is essential.
The report on which this article is based, 'First record of a potential neonate tiger shark (Galeocerdo cuvier) at a remote oceanic island in the Eastern Tropical Pacific', by Marta Cambra, Sergio Madrigal-Mora, Isaac Chinchilla, Geiner Golfín-Duarte, Christopher G. Lowe, Mario Espinoza is available at doi.org/10.1111/jfb.14774