Angel shark - Squatina squatina

The angel shark is one of the most strongly flattened shark species. Its body structure is consistently adapted to a life close to the seabed. Its anatomy differs markedly from that of streamlined pelagic sharks and in many respects resembles rays, without sharing their evolutionary lineage.

Flattened body and disc-like shape

The trunk of the angel shark is strongly dorsoventrally flattened. The pectoral fins and head form a broad, almost rectangular body disc. This shape increases the contact area on the seabed and enables the animal to lie flat in the sediment. The transition between head, pectoral fins and trunk is seamless; clearly defined shoulder regions are absent.

The tail is noticeably narrower compared to the forebody region. It bears two dorsal fins, which are positioned relatively far back. An anal fin is completely absent.

Head structure and sensory organs

The head is broad and short. The eyes are on the upper surface and protrude slightly. Directly behind them are large spiracles. These serve to take in water for respiration while the animal lies motionless in the sediment. This prevents sand or silt from entering the gills via the mouth.

The nostrils are positioned at the front of the head and are equipped with conspicuous skin flaps. These skin appendages direct water flow towards the olfactory organs and improve the chemical detection of bottom-dwelling prey.

Mouth position and dentition

The mouth is located on the underside of the head and is relatively large. The mouth slit extends far back, allowing rapid and wide opening. This anatomy is adapted for the sudden capture of prey passing by.

The teeth are small, pointed and arranged in multiple rows. They are not suited for cutting but for securely holding slippery prey. A pronounced tooth replacement ensures that damaged teeth are continuously replaced.

Pectoral fins and locomotion mechanics

The very large pectoral fins are laterally fused to the head. They serve less for active swimming than for stabilising on the substrate. Short forward movements are produced by powerful tail strokes, while the pectoral fins control the bodys position.

When striking prey, the body is thrust explosively upwards. This movement results from a combination of tail power and a sudden straightening of the front part of the body.

Skin structure and camouflage

The skin of the angelshark is covered with small placoid scales that feel rough. The dorsal surface bears numerous irregular spots and speckles in shades of brown, grey and sand. This pattern varies individually and allows an almost perfect camouflage on sandy or muddy substrate.

The underside is noticeably lighter in colour and mostly uniformly whitish. Colour changes like those seen in some ray species are not known.

Internal anatomy and skeletal features

Like all sharks, the angelshark has a cartilaginous skeleton. In the shoulder girdle and the area of the pectoral fins this is particularly broad to stabilise the large body surface. The vertebral column is less flexible in the anterior body region than in pelagic sharks, which suits its benthic lifestyle.

The gill openings are located on the sides of the body, not on the underside. This position allows sufficient respiration via the spiracles even when the body is partially buried.

The angelshark was historically widespread across much of the north-eastern Atlantic. Its present occurrence is highly fragmented and restricted to a few remnant areas. Changes in the use of nearshore habitats have had a lasting effect on the distribution pattern of this species.

Historical distribution range

Originally, the distribution stretched from southern Scandinavia across the North Sea and the English Channel along the Atlantic coasts of Western Europe. The entire Mediterranean, as well as parts of the Black Sea, were also part of its natural range.

The angelshark was long regarded in these regions as a regularly occurring bottom-dwelling shark. Historical catch records and scientific reports attest to its former abundance in nearshore shelf areas.

Current distribution

Today stable populations exist only in a few regions. These include mainly parts of the western Mediterranean as well as isolated stretches of coast in the eastern Atlantic. Particularly during the winter months around the Canary Islands it can be observed very reliably. In the North Sea, the English Channel and large parts of the central Mediterranean the species is considered locally extinct.

Observations mainly come from remote or less intensively fished areas. The distribution is highly fragmented and restricted to isolated populations.

Typical habitats

The angelshark inhabits predominantly shallow to mid-depth coastal waters. It favours sandy or muddy seabeds, where it buries itself during the day or lies flat on the substrate. Hard bottoms such as rocky reefs are used much less frequently.

Most records come from depths between five and one hundred metres. In some cases, individuals have been recorded at considerably greater depths, indicating a degree of ecological flexibility.

Habitat association and site fidelity

The angelshark shows a strong fidelity to suitable substrate types. Shallow shelf areas with fine-grained sediment play a central role. Within these habitats, the species often uses the same areas over extended periods.

This site fidelity increases vulnerability to local disturbances. Changes to the seabed caused by bottom trawling or construction activities directly affect the suitability of the habitat.

Importance of nearshore zones

Coastal areas are of particular importance for Squatina squatina. They provide suitable sediments, stable temperature conditions and adequate cover. The close association with these zones explains why the species suffers particularly from human use of coastal waters.

The angelshark exhibits a distinctly bottom-oriented lifestyle. Behaviour, feeding and reproduction are closely linked to its anatomical adaptations for life on sandy and muddy seabeds.

Behaviour

The angelshark lives mostly motionless on the seafloor. During the day it usually lies flat buried in the sediment so that only the eyes and spiracles remain visible. This resting period serves both to conserve energy and as camouflage.

Its main activity shifts to dusk and night. During these periods the angelshark more frequently leaves its resting places and moves slowly along the seabed. Movement is mainly by crawling or gliding with short, deliberate tail beats.

Its behaviour is strongly site-attached. Individual animals use the same areas for extended periods, provided sediment structure and low levels of disturbance are maintained.

Feeding strategy and prey range

The angelshark is a specialised ambush predator. It waits motionless until potential prey comes into close proximity. Prey capture occurs via an extremely rapid strike in which the mouth is suddenly opened, creating suction.

The diet mainly consists of bottom-dwelling bony fishes such as flatfish as well as smaller sharks and rays. Crustaceans are also occasionally taken but play a subordinate role. Prey is not torn apart but swallowed whole.

Hunting is limited to short distances. Longer pursuits do not occur. This strategy is energetically efficient and adapted to the shark’s limited swimming ability.

Reproductive biology

The angelshark is ovoviviparous. The embryos develop inside the female from yolk-rich eggs. A placenta is not formed. The young hatch before birth and are born live.

Litter size is usually between seven and twenty-five pups. The newborns are fully developed and immediately independent. There is no parental care.

Reproduction probably does not occur annually. The species is characterised by long development times, late attainment of sexual maturity and low reproductive rates.

Reproductive habitats and behaviour

Births preferably occur in shallow coastal areas with fine-grained sediments. These areas provide protection from larger predators and suitable conditions for the first months of life.

Juveniles occupy similar habitats to adults but are more frequently found in very shallow zones. The species’ strong dependence on specific breeding areas makes it particularly vulnerable to coastal disturbances.

The angelshark is among the most endangered shark species in Europe. Within a few decades large parts of its original population have disappeared. Today only a few isolated remnant populations remain. The causes are almost entirely due to human impacts on coastal ecosystems.

Overfishing and bycatch

The greatest threat to the angelshark is unintentional capture in fisheries. Because of its bottom-dwelling lifestyle it is particularly prone to being caught in bottom trawls, gillnets and longlines. These fishing gears are non-selective and catch the angelshark even where it is not targeted.

Historically the angelshark was deliberately exploited in many regions. Its meat, skin and liver oil had economic significance. With the industrialisation of fisheries, fishing pressure increased sharply. Even small additional losses still have severe consequences today, because the species grows slowly and produces only a few offspring.

Habitat loss in coastal areas

The angelshark depends on sandy and muddy seabeds in coastal areas. These habitats are among the most altered zones of the seas. Bottom trawl fisheries destroy the top layer of sediment and thus the structure of the seabed.

Added to these are coastal development, harbour expansion, dredging and pollution. Such interventions lead to a permanent deterioration of suitable habitats for shelter and reproduction. In many regions these habitats have been completely lost.

Climate change as an increasing stressor

Recent studies show that rising water temperatures affect the behaviour of the angelshark. In key refuge areas, significantly fewer females were observed in traditional mating zones during unusually warm years.

Pregnant females are particularly sensitive to temperature. When thermal thresholds are exceeded, they avoid shallow coastal areas. This can lead to temporal and spatial shifts in reproduction, further reducing reproductive success.

Low reproductive rate and biological vulnerability

The angelshark reaches sexual maturity late and produces only a limited number of fully developed young. Reproductive intervals are long. This combination means that populations recover very slowly even under favourable conditions.

Local populations are therefore particularly sensitive to additional losses. Just a few years of elevated mortality can be enough to permanently deplete a region.

Current conservation status

The angelshark is listed as Critically Endangered on the IUCN Red List. It is considered extinct in large parts of its former range. Within the European Union, the species is fully protected.

Capture, landing, trade and possession are prohibited. Bycatch must be released alive where possible. In addition, the angelshark is listed in several international agreements for the protection of migratory species and marine biodiversity.

Regional conservation measures and protected areas

One of the last more stable populations is found around the Canary Islands. There, special protection programmes have been established that combine research, monitoring and legal measures. The angelshark is under strict national protection there.

Rediscovery and conservation projects are also underway in certain regions of the Mediterranean and the northeast Atlantic. These focus on surveying the remaining animals, protecting sensitive habitats and cooperating with fisheries.

Importance of research and implementation

Despite comprehensive legal regulations, practical implementation remains a key challenge. Illegal catches, inadequate controls and a lack of data hinder protection. Long-term success depends on consistent fisheries management, habitat protection and international cooperation.

The angelshark is today regarded as an indicator species for the condition of coastal marine ecosystems. Its protection is closely tied to the preservation of these sensitive habitats.