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Rhinobatos annulatusLesser guitarfish

By mila garelle-essam

Geographic Range

Lesser guitarfish (Rhinobatos annulatus) are native to coastal areas in the Atlantic and Indian Oceans. They live primarily along the coast of southern Africa, including waters surrounding Namibia, Angola, and South Africa. However, observations of lesser guitarfish are not always accurate, as they can be confused with other species in the family Rhinobatidae. (Schulman and Hanessian, 2013)

Habitat

Lesser guitarfish are a marine neritic species, meaning that they prefer habitats in shallow waters, along coastlines and out to the edges of continental shelves. They also inhabit sheltered bays and estuaries. Lesser guitarfish spend much of their time on the ocean floor, often in sandy areas that are beneficial for hiding and raising young. (Froese and Pauly, 2021; Muller and Henle, 2019; Schulman and Hanessian, 2013)

  • Range depth
    75 to 0 m
    246.06 to 0.00 ft

Physical Description

Lesser guitarfish have flat, wide bodies, similar to other ray species (superorder Batoidea). Their flat profile and sandy-beige coloring allow them to camouflage on sandy ocean floors. Mature males reach an average length of around 58 cm, while mature females reach an average length of around 65 cm. (Rossouw, 2014)

  • Sexual Dimorphism
  • female larger
  • Range length
    23 to 140 cm
    9.06 to 55.12 in

Development

There is limited information regarding the growth and development of lesser guitarfish. A closely related and more researched species, shovelnose guitarfish (Rhinobatos productus), display indeterminate growth and a 1:1 sex ratio. It is possible that lesser guitarfish develop similarly. (Rossouw, 1984; Timmons and Bray, 1997)

Reproduction

There is limited information regarding the mating systems of lesser guitarfish. In summer, lesser guitarfish move into shallower waters to mate. Mating generally occurs close to shore in the surf zone. It is suspected that lesser guitarfish are monogamous within a mating season. (Rossouw, 2014)

Female lesser guitarfish reach sexual maturity at 3 years old, followed by an average of 4 years of reproduction. Lesser guitarfish are ovoviviparous, meaning young develop from eggs, but hatch within their mother. Females gestate eggs for 10 months, after which they give birth to live young. Young are born in summer, in litters that range from 2 to 10 individuals. (Rossouw, 2014)

  • Breeding interval
    Lesser guitarfish breed once yearly, during summer.
  • Breeding season
    April to June
  • Range number of offspring
    2 to 10
  • Average gestation period
    10 months
  • Average time to independence
    1 years
  • Average age at sexual or reproductive maturity (female)
    3 years

There is limited information regarding parental investment in lesser guitarfish. Females carry developing eggs inside their bodies, but no further parental investment has been observed. (Rossouw, 2014)

  • Parental Investment
  • female parental care
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female

Lifespan/Longevity

The maximum reported lifespan for lesser guitarfish in the wild is 7 years. Their lifespans are often limited by predation and fishing practices. There is no information regarding the lifespan of lesser guitarfish in captivity. (Rossouw, 2014)

  • Range lifespan
    Status: wild
    5 to 7 years

Behavior

Lesser guitarfish are primarily solitary. They occasionally move around to hunt, but mostly spend their time partially buried in sand on the seafloor. (Gledhill, et al., 2020; Harris, 2010)

Home Range

There is limited information regarding home ranges of lesser guitarfish. Individuals are not known to defend a specific territory. (Rossouw, 2014)

Communication and Perception

Lesser guitarfish are capable of detecting prey on the seafloor, even when their prey is covered by sediment. However, there is limited information regarding the specific senses that lesser guitarfish rely on to find prey. It is likely that lesser guitarfish find prey using electroreceptors called ampullae of Lorenzini, which detect electric signals that living organisms emit. Lesser guitarfish live on the seafloor in relatively shallow, well-lit areas. Their eyes are located dorsally, which suggests they rely on eyesight to detect potential predators swimming above them. (Harris, 2010)

Food Habits

Lesser guitarfish hunt for prey submerged or partially submerged in sediment on the seafloor. They primarily eat molluscs, marine worms, and non-insect arthropods. Lesser guitarfish trap their prey between their mouths and the seafloor. They will also stir up sediment to uncover submerged prey. (Harris, 2010; Muller and Henle, 2019)

  • Animal Foods
  • mollusks
  • aquatic crustaceans
  • other marine invertebrates

Predation

Humans (Homo sapiens) are the main predator of lesser guitarfish. Because lesser guitarfish hide in sediment on the seafloor to avoid predation, fishing trawls that drag the seafloor often catch them. Lesser guitarfish are harmed by both intended catch and bycatch. Lesser guitarfish have coloration that camouflages them with their environment and helps them avoid many natural predators. (Gledhill, et al., 2020)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Lesser guitarfish consume molluscs, marine worms, and non-insect arthropods, which impacts food webs in the areas they inhabit. Several parasitic species have been reported using lesser guitarfish as hosts, including Trichodina rhinobatae, Neoheterocotyle robii, Pseudoleptobothrium christisoni, Echinobothrium dougbermani, and Gnathia pantherina. (Harris, 2010)

Commensal/Parasitic Species
  • Trichodina rhinobatae
  • Neoheterocotyle robii
  • Pseudoleptobothrium christisoni
  • Echinobothrium dougbermani
  • Gnathia pantherina

Economic Importance for Humans: Positive

Lesser guitarfish are part of the fishing industry, and are a food source for human populations (Harris, 2010; Rossouw, 2014)

  • Positive Impacts
  • food

Economic Importance for Humans: Negative

There are no known negative impacts of lesser guitarfish on humans.

Conservation Status

Lesser guitarfish are listed as "vulnerable" on the IUCN Red List and have no special status in the CITES appendices. They are likely threatened by unsustainable fishing practices. Populations appear to be stable currently, though there are no records of direct population surveys for lesser guitarfish. Researchers use angler catch limits as an indication of population health. Lesser guitarfish are not listed on the U.S. Federal list or State of Michigan list because their range does not extend to waters around North America. (Gledhill, et al., 2020)

Contributors

mila garelle-essam (author), Colorado State University, Galen Burrell (editor), Special Projects.

Glossary

Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

World Map

acoustic

uses sound to communicate

benthic

Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

brackish water

areas with salty water, usually in coastal marshes and estuaries.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

electric

uses electric signals to communicate

female parental care

parental care is carried out by females

food

A substance that provides both nutrients and energy to a living thing.

indeterminate growth

Animals with indeterminate growth continue to grow throughout their lives.

molluscivore

eats mollusks, members of Phylum Mollusca

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

ovoviviparous

reproduction in which eggs develop within the maternal body without additional nourishment from the parent and hatch within the parent or immediately after laying.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

vibrations

movements of a hard surface that are produced by animals as signals to others

visual

uses sight to communicate

References

Froese, R., D. Pauly. 2021. "Acroteriobatus annulatus" (On-line). World Register of Marine Species. Accessed February 21, 2022 at https://www.marinespecies.org/aphia.php?p=taxdetails&id=871953.

Gabsi, Z. 2008. New record of sugeon fish from Oman with notes on some uncommon rays. French Society of Icthyology, 32(4): 355-358.

Gledhill, K., R. Leslie, H. Winker. 2020. Lesser Guitarfish. IUCN Red List of Threatened Species, 3.1: 1-4.

Harris, S. 2010. An assessment of the role of the sand shark Rhinobatos annulatus as a predator in Langebaan Lagoon. South African Journal of Marine Science, 7: 153-159.

Moore, A. 2017. Are guitarfishes the next sawfishes? Extinction risk and an urgent call for conservation action. Endangered Species Research, 34: 75-88.

Muller, , Henle. 2019. "Acroteriobatus annulatus (Müller & Henle, 1841)" (On-line). Fish Base. Accessed February 21, 2022 at https://www.fishbase.se/summary/Rhinobatos-annulatus.html.

Rossouw, G. 1984. Age and growth of the sand shark, Rhinobatos annulatus, in Algoa Bay, South Africa. Journal of Fish Biology, 25(2): 213-222.

Rossouw, G. 2014. Maturity, spermatogenesis and seasonal reproductive cycle of male Rhinobatos annulatus (Muller & Henle,1841) from Algoa Bay, South Africa, and a novel description for sperm release from the spermatocyst. african Zoology, 49(1): 128-136.

Schulman, A., N. Hanessian. 2013. Two New Species of Echinobothrium (Cestoda: Diphyllidea) from Batoids off South Africa. Department of Ecology and Evolutionary Biology, 80: 22-32.

Timmons, M., R. Bray. 1997. Age, growth, and sexual maturity of shovelnose guitarfish, Rhinobatos productus. Fishery Bulletin, 95: 349-359.

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