26th June
Today is Angel Shark Day - a day to celebrate these magnificent, weird and wonderful animals. You could certainly be forgiven for not even realising that angel sharks are, indeed, true sharks. They are not rays! Yet, with their flattened body, bizarre fins and powerful tail like a shark, angel sharks almost look like a mix of all of their shark and ray cousins combined. In fact, many people have never even heard of angel sharks, but knowing about these unique animals may be absolutely critical to their survival! Angel sharks are some of the most threatened sharks on the planet today and raising awareness about their plight will be vital to gaining support for their conservation. So please allow me to introduce you to these unique little characters... Hopefully you will fall in love with them too and become a part of the movement to pull them back from the brink of extinction.
Abnormal Fins
The fins of angel sharks are very different to other types of sharks. Their pectoral fins have drastically changed, as they are expanded laterally and fused to the side of the head, they look like skate wings. Unlike most sharks, angel sharks do not have an anal fin. Whastmore, their "caudal" (tail) fin is unique. They are the only type of sharks where the upper lobe of the tail is smaller than the lower lobe. This has developed because it allows the angel shark to gain lift when it propels itself from the seafloor to catch its prey (Compagno, 1984).
Nocturnal Lives
Angel sharks are "nocturnal". This means they are more active at night. Angel sharks have remarkable senses that allow them to detect their prey in the dark. Like all sharks, angel sharks have a keen sense of smell and are able to detect minute electric fields - even the tiny charges generated by muscle contractions! They also have sensory barbels projecting from the face, near the mouth, which can be used to detect prey. Yet angel sharks do have excellent eye sight too! Some angel sharks have even adapted to using the light created by bioluminescent plankton to see their prey (Compagno, 1984, Ellis, 2020).
Global Distribution
Angel sharks live all over the world. They can be found in the Mediterranean, the black Sea, the Atlantic - in coastal areas from Norway to the Canary Islands and in the Pacific - from as far north as Alaska, through California, Ecuador and all the way down to Chile. They also live in the waters off Australia and Japan (Compagno, 1984).
Eggs on the Inside
Angel sharks are "ovoviviparous". This is also known as "aplacental viviparity". This means that eggs hatch inside before the female gives birth to live young after about 8 to 10 months of pregnancy. This is quite a common reproductive method amongst sharks (Compagno, 1984, Ellis, 2020).
Whilst a females can give birth to litters of 8 to 25 pups, they can only breed once every two years and only 20% of the young will survive to adulthood. They are therefore described as having "low fecundity", meaning they do not breed very quickly, so cannot boost their populations very quickly after significant declines (Ellis, 2020).
Large Size
Angel sharks are about 30 cm long when they are born, but they can grow to quite large sizes as adults! Most species are approximately 1.5 metres long, but the largest species - the Japanese angel shark Squatina japonica - can reach over 2 metres in length (Compagno, 1984).
Sharp Teeth
Angel sharks have very wide mouths and strong jaws, armed with long, needle-like teeth. Their nine rows of teeth on their upper jaw and 10 rows in their lower jaw, with a gap at the centre is perfect for catching their prey (Compagno, 1984, Ellis, 2020).
Harmless (to Humans)
Angel sharks pose no significant threat to humans. They have only been known to attack people when they were provoked or manhandled, at which point their large size and impressive teeth can cause injuries. But these incidents are few and far between.
Angel sharks much prefer to snack on fish, crustaceans, mollusks, squids and skates (Compagno, 1984, Ellis, 2020).
Ambush predators
Angel sharks are ambush predators. This means that they lie in wait for their prey to come close to them, at which point they strike with lightening speed. Angel sharks can lunge and catch their prey from their resting position in as little as a tenth of a second! Almost faster than your eyes can see (Compagno, 1984).
Angel sharks rely on being invisible for this strategy to work. This requires excellent camouflage and the ability to stay very still.
Some sharks need to keep moving to be able to breathe, but not the angel shark. Thanks to "spiracles" on the side of their head and strong muscles in their mouth to keep oxygenated water running over their gills, angel sharks can stay lying on the substrate indefinitely while they wait for prey to wander by (Compagno, 1984, Ellis, 2020).
Angel sharks will often find a hunting spot that they like - in a flat, sandy area between rocks, near to a reef or kelp forests - and keep hunting there for around 10 for a days before moving on to a new patch (Compagno, 1984, Ellis, 2020).
Risk of Extinction
Angel sharks are some of the most threatened sharks - they are ranked as the second most threatened family of elasmobranchs (sharks, skates and rays) in the world. The International Union for the Conservation of Nature (IUCN), lists 50% of the 23 species of angel sharks as either 'critically endangered' (CR), 'endangered' (EN) or 'vulnerable' (VU), which means they are at risk of being entirely wiped out in the wild! (Gordon, 2019, Ellis, 2020, Lawson, 2020).
Angel sharks have seriously declined across a lot of their range and have even been completely "extirpated" in some areas, meaning they have become locally extinct in certain places. These declines are thanks to their massive over exploitation in fisheries. As they live near to the coast, their habitats are also at risk of degradation from human activity; including coastal urbanisation, industrial runoff of pollutants, and disturbance by tourism and recreational activities (IUCN).
Knockouts
Angel sharks are absolutely beautiful. Every species has a completely unique pattern to their skin, made up of spots, flecks or marbling (Compagno, 1984, Ellis, 2020).
These markings are very important to help angel sharks recognise other members of their species. It's not all about looks though, their patterns are also vital to camouflage. As these sharks spend a lot of time resting on the substrate, amongst rocks, corals or sand, the colours and patterns make them more more cryptic to their prey. It also meakes in harder for larger predators to see them, so they don't become prey themselves (Compagno, 1984, Ellis, 2020).
Shallow Habitats
Angel sharks mostly live in shallow, temperate waters. Whilst they do undergo migrations, to stay within a comfortable temperature range as the seasons change, they still generally stick to areas near to the coastline. They come into especially shallow areas to give birth to their young (Compagno, 1984, Ellis, 2020).
It is their close proximity to the coastline that makes angel sharks so at risk to human interference, as many of their crucial habitats are near to urbanised areas or in regions where industrial fisheries are active (Lawson, 2020).
If you too are fascinated by angel sharks and want to be involved in their conservation, you can support the vital work of the Angel Shark Conservation Network, the Angel Shark Project and the Shark Trust.
References
Compagno LJV (1984). FAO species catalogue. Vol. 4. Sharks of the world. An annotated and illustrated catalogue of sharks species known to date. Part 1. Hexanchiformes to Lamniformes. FAO Fish Synopsis, 125:4, Part.1. Access online.
Ellis JR, Barker J, McCully Phillips SR, Meyers EKM, Heupel M (2020). Angel sharks (Squatinidae): A review of biological knowledge and exploitation. Journal of Fish Biology, 98:3, 592-621. Access online.
Gordon CA, Hood AR, Al Mabruk SAA, Barker J, Bartolí A., Ben Abdelhamid S, Bradai MN, Dulvy NK, Fortibuoni T, Giovos I, Jimenez Alvarado D, Meyers EKM, Morey G, Niedermuller S, Pauly A, Serena F and Vacchi M (2019). Mediterranean Angel Sharks: Regional Action Plan. The Shark Trust, United Kingdom. Access online.
Lawson JM, Pollom RA, Gordon CA, Barker J, Meyers EKM, Zidowitz H, Ellis JR, Bartoli A, Morey G, Fowler SL, Jimenez Alvarado D, Fordham SV, Sharp R, Hood AR & Dulvy NK (2020). Extinction risk and conservation of critically endangered angel sharks in the Eastern Atlantic and Mediterranean Sea, ICES Journal of Marine Science, 77: 12–29. Access online.
By Sophie A. Maycock for SharkSpeak
