Angular Angelshark: Squatina guggenheim

Family: Squatinidae
Common name(s)

Angular Angelshark.

Identification

A small angelshark species with a relatively long head that protrudes forward of the pectoral fin margins. Barbells have unfringed, slightly spatulate tips. Nasal flaps weakly fringed. Spiracle to eye width less than 1.5 eye size. Broadly concave forehead between eyes. Paired thorns (enlarged denticles) present on snout, between eyes, and between spiracles. Median dorsal row of thorns present along length of back. Pectoral fins relatively small with pointed apexes.
Dorsal coloration tan or grey-brown with a dense covering of very small dark spots, and a few paired, larger dark spots. Vague ocelli on pectoral fins. Ventrum pale.

Size

Maximum size 95 cm (Ebert et al. 2013). Size at birth 25-30cm.

Habitat

Tropical and temperate sandy substrates often close to monumentation such as rocky reefs. Inshore and continental shelf. From 10m to at least 80m.

Distribution

Southwest Atlantic. Found from Rio De Janeiro in Brazil, southward to northern Patagonia in Argentina.

Conservation Status

ENDANGERED

The Angular Angelshark is threatened by being caught as bycatch in trawl and gillnet fisheries. Angel sharks lie motionless on the sea floor during the day but actively forage at night, and therefore they are highly susceptible to bottom-set gillnets that are set at night (Standora and Nelson 1977). The great increase of the annual angel shark catches in southern Brazil in 1992-1993 was due to a new fishery that targeted angel sharks specifically with bottom gillnets on the outer shelf (Klippel et al. 2005). Bottom gillnets were up to six times as effective as bottom trawls in terms of mean annual angel shark CPUE (Miranda and Vooren 2003, Vooren and Klippel 2005). After declines occurred as a result of trawl fisheries, the directed fishing with bottom gillnets was an additional threat to the Brazilian population of the Angular Angelshark.
Bottom trawling in Brazil targets an array of productive bony fishes, while elasmobranchs are caught as commercially valuable bycatch. Between 1985 and 2002, species such as the Angular Angelshark were overfished while the more productive species of fishes continue to sustain these fisheries (Miranda and Vooren 2003, Klippel et al. 2005).
An angel shark bottom gillnet fishery on the outer shelf commenced around 1990 and large amounts of angel shark were caught this way until 2004 when the species became protected in Brazil (Miranda and Vooren 2003).
Chiaramonte (1998) stated that the angel sharks were the second most important fish landed by the gillnet fleet of Puerto Quequen, Argentina.

Citation
Oddone, M., Awruch, C.A., Barreto, R., Charvet, P., Chiaramonte, G.E., Cuevas, J.M., Dolphine, P., Faria, V., Paesch, L., Rincon, G. & Vooren, C.M. 2019. Squatina guggenheimThe IUCN Red List of Threatened Species 2019: e.T130393378A130393975. https://dx.doi.org/10.2305/IUCN.UK.2019-1.RLTS.T130393378A130393975.en. Downloaded on 23 January 2021.

Reproduction

Like other squatinids, the angular angelshark is an aplacental viviparous species. 2-10 pups per litter. Pups develop in the uterus for the first four months before moving into the enlarged cloaca until born. Gestation period approximately 11 months. Reproductive cycle triennial.

Diet

Feeds on small demersal fishes and shrimps. The angular angelshark is an ambush predator that lays on the substrate partially covered by sand. When a fish swims within range, the angelshark explodes upwards from its concealment, mouth agape and clamps down on its prey.

Behavior

The angular angelshark remains motionless (waiting for prey to swim near its mouth) for long periods each day. Gravid females migrate into shallow water to give birth.

Reaction to divers

Easy to approach. Remains motionless, relying on camouflage. Will bolt if molested.

Diving logistics

The angular angelshark is rarely seen by divers but it is possible. I managed to track one down off the coast of Argentina near the town of Mar del Plata. Unfortunately, the southwest Atlantic is notoriously prone to storms so reaching offshore reefs where this species is most likely to be seen, is not particularly easy.
In November 2014, I waited three weeks for a 4hr window of opportunity, but did get to encounter this species in approximately 20m depth on a bank that was about 40 minutes from shore.

The best way to search for angelsharks is to swim along the edge of the reef, about 2m above the sand, in rocky or kelpy areas where the sharks have sand they can hide under and access to a good supply of fishes.
Although the shark will likely be buried under a fine covering of sand, their outline is often somewhat visible. Even if the outline of the angelshark is obscured, they always keep their eyes and spiracles exposed. After a few encounters, you should be able to pick out the signs of a shark’s presence more easily.
Once you have located a shark, with slow, non-aggressive movements, it is usually possible to settle down next to it and gently fan away most of the sand to get a better look. This does not distress the animal or significantly waste its energy because one or two pectoral fin flaps will completely cover it again. Be careful not to wave your hand too close to its mouth to avoid a demonstration of its incredibly fast bite reflex!

Similar species

Argentine Angelshark Distinguished by shorter head, lack of thorns along midline, and bolder pattern of tightly spaced dark spots that are slightly smaller than eye size.

Hidden Angelshark Distinguished by two pairs of more elaborate ocelli (eye-like markings) on pectoral fins. Ocelli consist of yellowish circles edged in black, with small black pupil-like centres.