Sicklefin Lemon Shark

Negaprion acutidens (Rüppell, 1837)

syn. Apeionodon acutidens, Aprionodon acutidens, Aprionodon acutidens queenslandicus, Carcharias acutidens, Carcharias forskalii, Carcharias munzingeri +6 more

3.8 m3-92 mCITES IIDangerousEndangered

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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.

Why it's threatened

Agriculture & aquaculture

Subsistence/artisinal aquaculture · Industrial aquaculture

Biological resource use

Intentional use: (subsistence/small scale) [harvest] · Unintentional effects: (subsistence/small scale) [harvest] · Unintentional effects: (large scale) [harvest]

Climate change & severe weather

Habitat shifting & alteration

The Sharptooth Lemon Shark is caught throughout much of its range in industrial and small-scale longline, gillnet, trawl, and handline fisheries that occur in coastal waters, including around coral reefs and mangrove habitats. It is retained for the meat and fins where possible. There is little data available on the capture of this species in fisheries of island nations in the Pacific Ocean where the species show little trend in population size. Throughout the coastal waters of Asia, it is caught in gillnets, longlines, trawls and handlines and landed. However, in recent years it has rarely been reported in surveys of landings sites. For example, Winter et al. (2020) reported a single individual in landings at Muncar in Indonesia in a 9 month period in 2017–2018. Similar levels of paucity of catch are reported in Thailand (Arunrugstichai et al. 2018), Philippines (Bureau of Fisheries and Aquatic Resources 2017) and Sri Lanka (Dissanayake 2005). In the Arabian Seas region, there is little species-specific data on Sharptooth Lemon Shark catch but generally, carcharhinids there are susceptible to and caught in a variety of fishing gear types, particularly gillnets and longlines, as well as trawl nets (which generally capture smaller individuals and species). Fisheries in the region have experienced increased demand for sharks since the 1970s due to the shark fin trade and as a result, effort is increasing in traditional shark fisheries in many areas (Bonfil 2003, Henderson et al. 2007, Jabado et al. 2015). Simultaneously, there has been a significant increase in coastal fishing effort and power in some parts of the Arabian Seas region leading to a reduction in the number of shark catches (e.g., De Silva 2006, Spaet and Berumen 2015). For example, in the Red Sea, the number of traditional boats operating more than tripled from about 3,100 to 10,000 between 1988 and 2006 (Bruckner et al. 2011).

In Australia, this species is caught in coastal gillnet, longline, and trawl fisheries in northern waters. For example, Harry et al. (2011) reported that it made up 0.3% of the gillnet catch (in numbers) in Queensland. It is taken in the North Prawn Fishery, with estimates of fishing mortality below those that would lead to population decline (Zhou and Griffiths 2008). It is also captured in small amounts in the North Territory Offshore Net and Line Fishery, Northern Territory Barramundi Fishery, and Western Australia Kimberley Gillnet and Barramundi Fishery (Simpfendorfer et al. 2019). The Sharptooth Lemon Shark was identified as a minor component of the large and prevalent Illegal, Unreported and Unregulated fishing (IUU) in northern Australian waters during the early 2000s (Field et al. 2009, Marshall 2011). However, the IUU fishing has declined significantly since 2006 due to increased border surveillance, international agreements, and possibly increased fuel prices and reduction in target shark species (Field et al. 2009, Haward and Bergin 2016).

The reliance of the Sharptooth Lemon Shark on coral reefs makes it susceptible to declines in habitat quality. Global climate change has already resulted in large-scale coral bleaching events with increasing frequency causing worldwide reef degradation. Almost all warm-water coral reefs are projected to suffer significant losses of area and local extinctions, even if global warming is limited to 1.5ºC (IPCC Report, 2019). Destructive fishing practices in some nations (e.g. dynamite fishing) (McManus 1997) and declining water quality (MacNeil et al. 2019) have also led to the decline in coral reef habitat.

The reliance of this species on mangrove habitats, especially as pupping and nursery grounds makes them susceptible to declines in habitat quality. The extent of mangrove habitat has declined markedly, with 20-35% of areas lost during the last half of the 20th century (Polidoro et al. 2010) as a result of coastal development for urbanisation, aquaculture and agriculture, timber harvesting sand resource extraction (Goldberg et al. 2020).

Threat classification from the IUCN Red List.