Lesser guitarfish
Acroteriobatus annulatus
Also known as the ‘sand shark’, this distinctive angular fish is actually a ray. Lesser guitarfish prefer sandy bottom environments and are common in very shallow waters – even in the surf zone. This makes them a popular species in catch-and-release angling competitions.
IDENTIFICATION
Elongated body with a flattened head and triangular snout. Rounded, ‘wing-like’ pectoral fins, and two triangular dorsal fins located on the tail behind the pelvic region. Like all rays, the mouth and gill openings are located on the underside (ventral side) of the body, and eyes on the dorsal side (atop their heads). Spiracles located just behind the eyes. Sandy brown or tan colouration, with darker brown spots (on individuals found in KwaZulu-Natal) or white spots with brown centres (on individuals found in the rest of southern Africa). Snout almost translucent.
SPECIAL BEHAVIOUR
The lesser guitarfish is perfectly camouflaged to its sandy surroundings and can quickly disappear by partially burying itself in the sediment.
REPRODUCTION
It is thought that lesser guitarfish move into shallower waters in summer to mate and reproduce, close to the surf zone. Reproduction is aplacental viviparous, meaning that the young are nourished via yolk sac, developing in a thin egg capsule inside the mother’s body. The egg hatches in the uterus and the young are born shortly afterwards. Female lesser guitarfish can have litters of 2 to 10 pups following a gestation period of 10 months. Reproduction occurs annually, with adults becoming sexually mature around 3 years.
HABITAT AND GEOGRAPHICAL RANGE
Lesser guitarfish occur inshore in shallow, sandy bottom environments from the shoreline to depths of 75 m. Habitats include estuaries, enclosed bays, lagoons and the surf zone. They are endemic to southern Africa, occurring from central Namibia in the west to northern KwaZulu-Natal in the east. However, it should be noted that observations of lesser guitarfish can be inaccurate due to easy confusion with other guitarfish species (such as the bluntnose guitarfish, Acroteriobatus blochii, in Namibia).
DIET DESCRIPTION
Lesser guitarfish feed on benthic invertebrates such as small crustaceans, sand mussels and polychaete worms.
THREATS
The lesser guitarfish is primarily caught as by-catch in trawl, beach seine and gillnet fisheries. They may also be targeted to a lesser extent by artisanal fisheries, with their meat retained for local consumption and fins traded internationally. They are also targeted by small, recreational catch-and-release angling competitions.
RELATIONSHIP WITH HUMANS
Lesser guitarfish are relatively harmless to humans. Their close proximity to the shoreline, especially during the summer months, can bring them into contact with people frequently, however, they are quick to disappear in the face of disturbance or threat. An additional consequence of their preference for shallow waters is that they are sometimes caught incidentally by shore anglers.
CONSERVATION
Recreational anglers in South Africa are restricted to a maximum of 10 individuals per day (although enforcement of this measure is an ongoing problem). Lesser guitarfish may also benefit from a number of protected areas that occur throughout their range.
FUN FACTS
Lesser guitarfish are the fish equivalent of a metal detector! They use their highly tuned sixth sense – electroreception – to find marine invertebrates buried in the sand.
Lesser guitarfish are also masters of stealth. Not only can they blend in seamlessly with their environment, they can also move in the blink of an eye! When threatened, the lesser guitarfish puts on a burst of speed, leaving a plume of sand and silt in its wake.
REFERENCES
Pollom, R., Da Silva, C., Gledhill, K., Leslie, R., McCord, M.E. & Winker, H. 2020. Acroteriobatus annulatus. The IUCN Red List of Threatened Species 2020: e. T60163A124446397
The South African Association for Marine Biological Research (SAAMBR). Fact Sheet: Lesser Guitarfish
