Grey Reef Shark

The grey reef shark (Carcharhinus amblyrhynchos), occasionally misspelled as amblyrhynchus or amblyrhinchos, is a prominent species within the family Carcharhinidae, often visible throughout the Indo-Pacific region. This species is prevalent from Easter Island to 🇿🇦 South Africa and is frequently observed in proximity to the drop-offs of coral reefs in shallow waters. Morphologically, the grey reef shark exhibits a classic "reef shark" silhouette, featuring a broad, rounded snout and prominent eyes. Key distinguishing features include a plain or white-tipped first dorsal fin, dark fin tips, a broad black margin on the tail fin, and an absence of ridges between the dorsal fins. Most individuals reach a length of approximately 1.88 meters (6.2 feet).

The dorsal coloration is grey, often with a bronze hue, transitioning to white ventrally. The caudal fin is marked by a distinctive black band encompassing its rear margin. Fins exhibit dusky to black tips, and individuals from the undefined may display a narrow white tip on the first dorsal fin, a trait not typically seen in Pacific populations. Prolonged exposure to shallow waters results in darkening of the sharks’ coloring. Typically, the grey reef shark measures up to 1.9 meters (6.2 feet), with the largest recorded specimen reaching 2.6 meters (8.5 feet) in length and 33.7 kilograms (74 pounds) in weight.

As swift and agile predators, grey reef sharks predominantly consume free-swimming bony fishes and cephalopods. Despite their moderate size, they exhibit aggressive behavior that often asserts dominance over other reef shark species. These sharks often establish a home range within a particular reef area, exhibiting social behaviors rather than territorial tendencies. Groups of five to twenty individuals are common near coral reef drop-offs during daylight, dispersing during the night for hunting activities. Female grey reef sharks may form groups in very shallow waters, potentially benefiting from the increased temperature for growth acceleration or embryonic development. They are viviparous, with mothers providing nourishment to embryos via a placental connection, resulting in litters of one to six pups biennially.

The grey reef shark is notable for being the first species recorded to display a threat behavior, an action indicating readiness to attack. This involves a characteristic "hunched" posture, drooping pectoral fins, and a pronounced side-to-side swimming pattern. Such displays are typically exhibited when approached or cornered by divers, serving as a warning signal. The species has been implicated in multiple human interactions and should be approached with due caution, especially when exhibiting threat displays. Fishing pressures and their low reproductive rates render the species vulnerable to population declines, prompting the International Union for Conservation of Nature to classify it as endangered.

Morphologically, the grey reef shark is streamlined with a moderately robust body, characterized by a long, blunt snout and considerable, round eyes. Dental formations consist of 13 or 14 teeth per jaw (commonly 14 in the upper jaw and 13 in the lower), with triangular, slant-cusped upper teeth and narrower, erect-cusped lower teeth. The tooth serrations are more pronounced on the upper jaw. The first dorsal fin is medium-sized, with no connecting ridge to the second dorsal fin, and the pectoral fins are falcate in shape.

This species is indigenous to both the 🇮🇳 Indian and 🌊 Pacific Oceans. Within the 🌊 Indian Ocean, its range extends from 🇿🇦 South Africa to 🇮🇳 India, including 🇲🇬 Madagascar, nearby islands, the 🌊 Red Sea, and the 🇲🇻 Maldives. In the 🌊 Pacific Ocean, its distribution spans from Southern 🇨🇳 China to northern 🇦🇺 Australia and 🇳🇿 New Zealand, encompassing regions such as the Gulf of Thailand, the 🇵🇭 Philippines, and 🇮🇩 Indonesia. Reports also place this species among numerous Pacific islands.

Primarily a coastal, shallow-water species, grey reef sharks inhabit depths under 60 meters (200 feet), though occasional dives to 1,000 meters (3,300 feet) have been recorded. They are typically associated with continental and insular shelves, favoring the leeward aspects of coral reefs displaying clear waters and complex topography. Frequently, they are found near drop-offs at reef peripheries or within reef channels subjected to substantial currents and infrequently within lagoons. Occasionally, they may migrate several kilometers into the open ocean.

Their diet predominantly includes bony fishes, with cephalopods and crustaceans comprising secondary food sources. Larger sharks tend towards a higher intake of cephalopods. These predators exhibit sophisticated hunting methods, capable of pinning shoals against reef structures. Large hunting groups, such as the one documented at Fakarava Atoll in 🇵🇫 French Polynesia, underscore their prowess. Their acute olfactory capabilities allow detection of tuna extract in minuscule concentrations. Feeding frenzies may ensue in the presence of substantial prey, resulting in intra-species predation.

In terms of reproductive behaviors, males engage in biting to secure females during copulation. The viviparous nature results in a placental connection following yolk sac depletion, with each female operating with a single functional ovary and two functional uteri. Births of one to four pups occur every other year, with litter size correlating with maternal dimensions and gestational periods estimated between 9 to 14 months. Their lifespan extends at least 25 years.

Grey reef sharks maintain a high activity level continuously, with peak activity levels observed nocturnally. Initial curiosity towards divers is typical, yet it wanes with repeated exposure, though aggression may increase when food is present or in open water situations. Documented attacks on humans, especially spear fishers, suggest incidental motivations linked to proximity to prey. This species exhibits defensive aggression when pursued or cornered, recommending immediate cautious withdrawal if a threat display occurs. Caution is advised against photography during displays due to potential provocation. Though modest in size, these sharks can cause considerable harm, demonstrated in research settings where submersible equipment suffered damage. Historical records indicate 13 attacks (unprovoked and provoked) involving this species, none of which resulted in fatalities as of the last report in 2008 by the International Shark Attack File.