Pristiophorus schroederiBahamas saw shark

Geographic Range

Bahamas sawsharks (Pristiophorus schroederi) are found in the waters of the western central Atlantic Ocean, off the coast of eastern Florida, Cuba and the Bahamas. Heupel (2006) suggests they are also found in the Gulf of Mexico. (AquaMaps, 2010; Heupel, 2006; Kiraly, et al., 2003)

Habitat

Bahamas sawsharks usually reside in coastal saltwater habitats, on continental slopes. They live at depths ranging from 400 to 1,000 m below the surface, but they are most commonly captured in the depth range of about 440 to 640 m. They may use sediments or the oceanic substrates found at these depths. (Ebert, et al., 2013; Heupel, 2006; Kiraly, et al., 2003)

  • Range depth
    400 to 1000 m
    1312.34 to 3280.84 ft

Physical Description

Bahamas sawsharks are brownish grey, characterized by bilateral symmetry with a flattened head and body with a long and thin saw-like rostrum. The largest adult reported was 81 cm, but Thompson and Springer state that they can reach a maximum length of 86.5 cm. Castro (2011) stated that the holotype for this species, a female, measured 38.5 cm, but it is unclear if this is a typical length for an adult. Average adult lengths have not been reported. These sharks are around 30 cm at birth.

Bahamas sawsharks have rostra approximately one-third the length of their entire body, and it is lined with smooth, elongated sharp teeth called denticles. These denticles are not actually teeth, but instead adapted dermal spines. A pair of barbels are located halfway down the rostrum, with 13 to 14 teeth on each side in front of the barbels (towards the tip of the rostrum), and 9 to 10 towards the body. Castro (2011) reported that bahamas sawsharks have small, cone-shaped teeth with a total of 36 teeth in their upper jaws and 32 in their lower jaws.

Bahamas sawsharks are mostly cartilaginous. Their exterior consists of 5 lateral gill slits and two dorsal fins of equal size and shape. There are no anal fins, but there are large pectoral fins.

Females are normally larger than males, but no measurements comparing sexes have been reported. (Berkovitz and Shellis, 2017; Castro, 2011; De Iuliis and Pulerà, 2019; Heupel, 2006; Keyes, 1982; Kiraly, et al., 2003; "Sharks, Skates, Rays, and Chimeras", 1965; Springer and Bullis, 1960)

  • Sexual Dimorphism
  • female larger
  • Range length
    86.5 (high) cm
    34.06 (high) in

Development

Bahamas sawsharks are ovoviviparous, meaning they hatch from eggs while still inside their mother. Before hatching, young depend entirely on the yolk within their eggs. Although gestation periods have not been reported for this species, other sawshark species have reported gestation ranges of 12 to 15 months. During the embryonic stage, their denticles are mostly covered in a layer of skin, most likely to protect mothers from impalement. As embryos develop, their teeth are first folded back and then begin to straighten, mineralize, and harden. This keeps mothers protected from sharp denticles, and once she gives birth, the babies will almost be fit for survival.

Bahamas sharks average 30 cm long at birth. Like all sharks, sawsharks experience indeterminate growth. However, exact rates of growth have not been reported. (Berkovitz and Shellis, 2017; Dulvy and Reynolds, 1997; Springer and Bullis, 1960; Welten, et al., 2015)

Reproduction

Mating has not been described for Bahamas sawsharks. The serrated rostra that sawsharks have are suspected to play a role in mating rituals. Research suggests that larger male sawsharks may use them to fight one another during breeding season. It is unknown what type of mating system these sawsharks practice. Like all sharks, fertilization is internal, through the use of male claspers. (Roy, et al., 2000; "Sharks, Skates, Rays, and Chimeras", 1965)

Bahamas sawsharks are ovoviviparous, meaning the eggs hatch inside the parent and live birth occurs. Although the gestational period has not been reported for this species, other sawsharks have gestation periods of 12 to 15 months. These sharks are seasonal breeders, but due to their presumed long gestation period, they only reproduce every 2 years.

Numbers of offspring in a brood vary from 3 to 22 across all sawshark species, so Bahamas sawsharks are likely within this range. A nonscientific web source noted that young sawsharks (species unlisted) stay with their mother for 2 years, but no scientific sources corroborate this find. It is unclear whether or not this age range corresponds to the age of sexual maturity for males and females. (Ebert, et al., 2013; Springer and Bullis, 1960)

  • Breeding interval
    Sawsharks are thought to breed every 2 years
  • Breeding season
    Unknown, but thought to be seasonal

Female sawsharks are ovoviviparous, and keep their eggs internally for 12 to 15 months before young are born. Eggs are not fed by their mothers internally, but instead depend on yolk already within their eggs. Male sawsharks provide no parental investment beyond the act of mating. A nonscientific web source noted that young sawsharks (species unlisted) stay with their mothers for 2 years, but no scientific sources have corroborated this find. (Dulvy and Reynolds, 1997; Helmenstine, 2019)

Lifespan/Longevity

The longevity of Bahamas sawsharks is still unknown, but Walker (2016) report that common sawsharks Pristiophorus cirratus can live up to 15 years. It is suspected that Bahamas sawsharks have a similar lifespan. These sharks are not kept in captivity. (Helmenstine, 2019; Walker, 2016)

Behavior

There is not much known about this species. Like all sawsharks, this species is natorial and motile, and thought to be fairly sedentary. They have been captured at depths up to 1000m, along the oceanic substrate. They likely use their sawlike mouths to look for prey in the substrate, and some authors suggest that males use the saws to battle one another. Sawsharks are thought to be solitary but can form schools. A nonscientific web source noted that young sawsharks (species unlisted) stay with their mother for 2 years, but no scientific sources corroborate this find, nor were the behaviors associated with this care described. (Helmenstine, 2019; Nevatte, 2015)

Home Range

Home range and territory sizes have not been reported for Bahamas sawsharks. Ceccarelli et al. (2014) state that sharks in coastal areas are considered sedentary (as compared to other marine fish). Known home ranges for coastal sharks are less than 100 square km; it is suspected that Bahamas sawsharks also have a relatively small range. (Ceccarelli, et al., 2014)

Communication and Perception

Bahamas sawsharks, like other sawsharks, use the barbels on their rostra as their sense of touch. This is most likely a way of feeling the ocean floor and searching for prey. They also use electrical signals in order to communicate and may even be used to shock their prey. Their sense of sight is also used to communicate and search for prey. Shark eyes are reported to be specialized to detect motion in water.

Sharks are known to have a strong sense of smell, which plays a major role in locating prey.

Like all sharks, they have ampullae of Lorenzini, concentrated in their heads and rostra, that serve as electroreceptors. Like all fish, these sawsharks have lateral lines that help them perceive their environment. These lateral lines run along the sides of their bodies and sense vibrations in the water. ("Sharks, Skates, Rays, and Chimeras", 1965; Springer and Bullis, 1960)

Food Habits

Bahamas sawsharks are strictly carnivorous. They feed on small fish, crustaceans, or other organisms that they find close to the ocean floor. They use their barbels to detect prey sources and will side-swipe their prey with their rostra to kill it. Diet studies have not been conducted to further elucidate predator-prey relationships. (Nevatte, 2015; Raoult, et al., 2015)

  • Animal Foods
  • fish
  • aquatic crustaceans

Predation

Predators of Bahamas sawsharks likely include larger sharks (suspected, not reported) and humans (Homo sapiens). Humans capture them rarely as bycatch in deepwater trawling efforts.

Sawsharks have natural brown or greyish tones to help them blend into their surroundings to hide from predators. (Heupel, 2006)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Bahamas sawsharks are thought to prey on smaller, sediment-dwelling organisms near the bottom of the ocean. They may serve as prey for larger sharks. Due to the rarity in collection of this species, parasites have not been reported. Other species in the genus host tapeworms. McKenzie and Caira (1998) and Lisnerova et al. (2020) discuss the role of myxozoan parasites in the sawshark family. (Heupel, 2006; Lisnerova, et al., 2020; McKenzie and Caira, 1998)

Economic Importance for Humans: Positive

There are no known positive economic impacts of Bahamas sawsharks on humans. They are a rare bycatch and have no role in commercial fisheries. (Heupel, 2006)

Economic Importance for Humans: Negative

Bahamas sawsharks have no negative economic impacts on humans.

Conservation Status

Bahamas sawsharks are listed as "Data Deficient" on the IUCN Red List. They have "no special status" on CITES, the US Federal list, and state of Michigan list. Castro (2011) reports that these sawsharks are listed as "protected" in Florida, despite having never been collected in the immediate vicinity of Florida coasts.

Further investigation into this listing revealed that the Florida Fish and Wildlife Conservation Commission listed sawsharks, sawfish, and a few rays and sharks as prohibited from harvesting in 1992. However, the harvesting prohibition was removed for sawsharks in 1998. Castro (2011) reported that sawsharks were originally - and erroneously - listed because they look similar to sawfish, a species group that does warrant protection in Florida.

Due to their rarity in capture and non-interest in commercial fisheries, no conservation measures are in place. Their location at great depths provides some natural protection from humans. As they are data deficient, the logical next step to conserving these sawsharks would be to gain a better understanding of their natural history. (Castro, 2011; Florida Fish and Wildlife Conservation Commission, 2020)

Contributors

Bobbi Lowe (author), Radford University, Lauren Burroughs (editor), Radford University, Logan Platt (editor), Radford University, Karen Powers (editor), Radford University, Galen Burrell (editor).

Glossary

Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

World Map

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.

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.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

electric

uses electric signals to communicate

female parental care

parental care is carried out by females

fertilization

union of egg and spermatozoan

indeterminate growth

Animals with indeterminate growth continue to grow throughout their lives.

internal fertilization

fertilization takes place within the female's body

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

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.

piscivore

an animal that mainly eats fish

saltwater or marine

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

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

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

solitary

lives alone

tactile

uses touch to communicate

vibrations

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

visual

uses sight to communicate

References

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