Sicklefin Lemon Shark

The Sicklefin Lemon Shark (Negaprion acutidens), also known as the Sharptooth Lemon Shark, is a species of requiem shark within the family Carcharhinidae, prevalent in the tropical waters of the Indo-Pacific region. It bears close resemblance to the Lemon Shark (N. brevirostris) found in the Americas, with both species exhibiting robust bodies, broad heads, and paired dorsal fins of similar proportions, complemented by a yellow-tinged hue. The distinguishing feature of the sicklefin lemon shark is its characteristically falcate fins. Adults can attain lengths up to 3.8 meters (12 feet) and are typically found in shallow waters, not exceeding 92 meters (302 feet) in depth, across diverse environments ranging from mangrove estuaries to coral reefs.

As a slow-moving predator primarily preying on bony fish, the sicklefin lemon shark is notably sedentary, often residing in familiar locations year-round. Like other species in its family, it is viviparous, with females bearing a maximum of 13 offspring biennially after a gestation period of 10–11 months. Despite its potential danger to humans and a tendency to respond assertively when provoked, this shark generally exhibits caution, retreating under non-threatening conditions. The International Union for Conservation of Nature (IUCN) has classified this species as Endangered, due to its limited reproductive capacity and restricted movement, which hamper population recovery. Overexploitation for meat, fins, and liver oil, primarily in 🇮🇳 India and Southeast Asia, has led to severe population declines or local extinctions.

The geographic range of the sicklefin lemon shark extends from 🇿🇦 South Africa through the 🌊 Red Sea, including island nations such as 🇲🇺 Mauritius, 🇸🇨 Seychelles, and 🇲🇬 Madagascar, eastward along the 🇮🇳 Indian subcontinent to Southeast Asia, and as far as 🇹🇼 Taiwan, the 🇵🇭 Philippines, 🇵🇬 New Guinea, and northern 🇦🇺 Australia. This species is also present throughout many Pacific islands, including 🇳🇨 New Caledonia (🇫🇷 Overseas France), Palau, and 🇫🇯 Fiji, among others. Genetic studies indicate significant differentiation between populations, suggesting minimal interregional mixing.

Inhabiting coastal continental and insular shelves, they are found from the intertidal zone to depths of 92 meters (302 feet), often in bays, estuaries, lagoons, and sandy flats. Occasionally, they may enter open waters, as depicted in the 1971 documentary "Blue Water, White Death." Juveniles are commonly observed on reef flats or in mangrove shallows, sometimes venturing into seagrass-free zones.

Morphologically, the sicklefin lemon shark is characterized by a stout body, broad head, and rounded snout, with small eyes and absent spiracles. It has unique dental features, including 13 to 16 tooth rows on each jaw side, and large, serrated cusps on the upper teeth. The dorsal, pectoral, and pelvic fins exhibit pronounced falcation. The species' dermal denticles overlap and are distinguished by three to five horizontal ridges.

Primarily sedentary, sicklefin lemon sharks are often seen calmly near the seafloor or motionless, capable of self-ventilation unlike most requiem sharks. They demonstrate limited territorial range, as evidenced in studies in the 🇸🇨 Seychelles and 🇵🇫 French Polynesia, with some individuals exhibiting residency behavior.

The sicklefin lemon shark's diet predominantly comprises bottom-dwelling teleosts but also occasionally includes cephalopods and crustaceans. Older sharks may consume larger prey, such as stingrays. They are susceptible to predation by larger shark species and host a variety of parasites. Observations have documented interactions with bluestreak cleaner wrasses, highlighting their symbiotic cleaning behavior.

In terms of reproduction, this shark exhibits viviparity, with females giving birth to one to 13 pups biennially after a 10–11 month gestation. While there is limited evidence of philopatry, birthing and breeding seasons vary by region.

Despite several reports of unprovoked attacks on humans, the sicklefin lemon shark is regarded as potentially hazardous, owing to its size and defensive nature when threatened. Nevertheless, it generally avoids human interaction. The species is a popular subject in ecotourism and adapts well to captivity.

The IUCN's global Endangered status for the sicklefin lemon shark reflects its vulnerability due to overfishing and habitat loss. In Southeast Asia, this is exacerbated by unregulated fisheries and environmental degradation, leading to its rarity in regions like 🇮🇳 India and 🇹🇭 Thailand. Conversely, the species is less targeted in 🇦🇺 Australia, where it is designated as Least Concern.