Thresher shark characteristics, habitat, reproduction, nutrition

The thresher shark (Alopias vulpinus) is a cartilaginous fish (Chondrichthyes class), representative of the Lamniformes order and of the Alopiidae family. This species has several common names, the most striking of which are whip shark or coludo shark..

This species is considered to be an oceanodrome, since it makes migrations in the ocean, moving either towards spawning areas or different feeding areas that are due to changes in marine conditions and availability of resources..

The migrations of these sharks do not occur between different geographical areas. Because of this, different subpopulations around the world appear to be genetically isolated..

Although they are large animals and show a certain degree of intimidation, they are docile and harmless to man. However, its enormous dimensions can cause great damage to fishing nets..

It is a cosmopolitan species in temperate and subtropical waters, and even goes deep into tropical latitudes. In addition to this, they have a marked tolerance to cold water, for which it has been pointed out on several occasions that it may be a species with regional endothermy.

Temperate coastal waters appear to be preferred for spawning. Females that do so in the Mediterranean region are above the average number of offspring of the species.

The common thresher shark uses its elongated dorsal fin to produce thrust and immobilize its prey when feeding. The main idea is that they stun their prey with a blow of the fin and then consume them.

Article index

• 1 General characteristics
  • 1.1 Coloring
• 2 Habitat and distribution
• 3 Taxonomy
• 4 Playback
• 5 Nutrition
  • 5.1 Hunting strategy and natural predators
• 6 Conservation
• 7 References

General characteristics

Thresher sharks are large and their length can vary depending on sex. The maximum lengths recorded range between 5.7 meters for females and 4.2 meters for males..

However, in nature sightings of specimens with sizes above 4.5 meters are rare, perhaps due to overfishing of individuals with large sizes. The weight of these sharks can exceed 340 kilograms.

The most outstanding characteristic of this species and the other two species of the genus Alopias, is that they have a heteroclose caudal fin with a disproportionately long, strap-shaped dorsal lobe. This lobe approaches the length of the trunk of the body to the base of the tail fin..

Despite being large animals, they have relatively small eyes, the pectoral fins are curved and narrow and have a defined white patch on the base of the same.

Alopias vulpinus It has similar teeth in both jaws, these are relatively small, with smooth edges and a wide base. The teeth do not have secondary cuspids. The hemimandibles are separated by small diastemas and have more than 18 rows of teeth in each jaw.

Coloration

The coloration of these sharks is variable. Dorsally they have a grayish-blue or grayish-brown coloration that extends from the snout to the tail fin. This coloration decreases in intensity towards the sides, being contrastingly white on the ventral surface..

The ventral white coloration extends over the pectoral and pelvic fins. There may be some black scores on the dorsal fin, pectoral fins, and pelvics. In the following video you can see the morphology of this species:

Habitat and distribution

Alopias vulpinus is the most common species of genus Alopias. It practically has a global distribution within a limited latitudinal range that encompasses the tropical and subtropical regions. The depth range covered by this species goes from 0 to 650 meters, being usual to observe them from the surface to a depth of 360 meters..

It has been recorded on both sides and hemispheres of the Pacific, Atlantic, and Indian Oceans and throughout the entire Mediterranean Sea, the Adriatic Sea, the Caribbean, among others..

Although it is a species that occupies a great diversity of environments throughout the areas where it is distributed, it is more frequent to observe it near the continental and insular coasts up to about 50 miles from the coast. Juveniles are more common on the coast and bays for a few years after birth..

In some places, such as the northeast of the Indian Ocean, there is a certain segregation in the distribution of the sexes, both spatially and in the depth where they are located within the water column..

These sharks have a predominantly diurnal activity, during which time they are active hunters. They are less active at night and swim at relatively constant depths..

Taxonomy

The three recognized species of the genus Alopias they are easily distinguishable from each other and form a monophyletic group within the Alopiidae family. The shape of the teeth and the dental formula are defining characteristics within the genus..

Evidence found in the analysis of allozymes as genetic markers indicated that there could be a fourth undescribed species. However, genetic analyzes using mitochondrial markers from various populations around the world discarded this hypothesis..

Reproduction

This species is ovoviviparous. Mating occurs in mid to late summer. The maturation age of females varies between 3 and 9 years and 3 to 7 years for males. These sharks can live up to 24 years.

The calves are born in spring in most ranges, yet pregnant calves and females can still be recorded throughout the year in the Indian Ocean..

The embryos feed on the yolk sac initially and on other infertile eggs that the female produces in order to feed them, this being known as oophagia (consumption of eggs). A healthy female can give birth between 2 and 4 young per reproductive cycle on average.

The gestation period lasts for nine months. However, the number of fetuses depends on the size of the parent female. For example, there are records of a female who was sighted with 7 fetuses.

Normally, each female only has two young, each of which develops in one of the oviducts and generally corresponds to a male and a female. Despite this, the reproductive rates of the species turn out to be low, since it appears to be regulated by the oophageal practices of the fetuses..

The length of the young at birth is quite variable, they can measure between 1.1 to almost 1.6 meters in total length.

Nutrition

These sharks have a broad diet that includes juvenile pelagic fish that vary by geographic location. There are more than 20 species that have been reported in the stomach contents of these fish.

However, fish such as mackerel (genus Scomber), bluefish, herring (Clupleidae), needlefish, sardines, lancetfish, lanternfish (Myctophidae), as well as anchovies (Eugralis Y Anchovy) and hake.

On the other hand, it also preys on mollusks such as squid, octopus and various pelagic crustaceans, including shrimp and crabs. Additionally, but less frequently, they are capable of capturing seabirds, which rest on the surface of the water..

The fish species that are most important in their diet are Eugralis mordax, Merluccius productus, Scomber japonicus Y Savdinops sagax. Within invertebrates, squids are common, such as Doryteuthis opalescens and the red pelagic crabPleuroncodes planipes). 

Hunting strategy and natural predators

The hunting strategy of Alopias vulpinus it is particularly conspicuous within this group of cartilaginous fish. Initially, it was argued that the upper lobe of the tail fin should have a role in foraging activities.

These sharks use their tails as a hunting tool whose purpose is to stun or confuse the fish on which they feed. In addition to this, it has been observed that through the movements of their tail they organize the movements of the schools in some direction that facilitates the subsequent capture of individuals..

Among the predators of these large sharks are killer whales (Orcinos orca) in some localities like New Zealand. The orcas that inhabit New Zealand appear to feed on a great diversity of elasmobranchs that inhabit this region, including approximately 10 species that include a A. vulpinus. In the following video you can see how this species uses its tail to hunt:

Conservation

This species is categorized in a global context as vulnerable according to the IUCN due to strong declines in this species throughout its range of distribution. A synergy of factors including its slow reproductive cycle, directed fisheries and bycatch are causes of risk for the species.

Due to the wide distribution of this species, regional categorizations have been made on its conservation status. It is considered a near threatened species in the central and eastern Pacific and vulnerable in the northwest and central western Atlantic, as well as in the Mediterranean Sea. For the Indian Ocean, there is poor data.

This species is mainly valued for its meat and some soft parts such as the liver, as well as the skin and the fins. It is generally marketed fresh, dry salted, smoked or frozen. Many catches are made accidentally due to fishing for pelagic osteitic species.

In some locations in the central Pacific, the populations of these fish have decreased between 60 and 80%..

On the other hand, there is also a high incidence of this species in sport fishing. This thresher shark is also listed in Appendix II of CITES. Currently the species is protected under international agreements, due to its migratory characteristics.

References

1. Aalbers, S. A., Bernal, D., & Sepulveda, C. A. (2010). The functional role of the caudal fin in the feeding ecology of the common thresher shark Alopias vulpinus. Journal of Fish Biology, 76(7), 1863-1868.
2. Bernal, D., & Sepulveda, C. A. (2005). Evidence for temperature elevation in the aerobic swimming musculature of the common thresher shark, Alopias vulpinus. Copeia, 2005(1), 146-151.
3. Cartamil, D., Wegner, N. C., Aalbers, S., Sepulveda, C. A., Baquero, A., & Graham, J. B. (2010). Diel movement patterns and habitat preferences of the common thresher shark (Alopias vulpinus) in the Southern California Bight. Marine and Freshwater Research, 61(5), 596-604.
4. Eitner, B.J. 1995. Systematics of the Genus Alopias (Lamniformes: Alopiidae) with evidence for the existence of an unrecognized species. Copeia 3: 562-571.
5. Goldman, K.J., Baum, J., Cailliet, G.M., Cortés, E., Kohin, S., Macías, D., Megalofonou, P., Perez, M., Soldo, A. & Trejo, T. 2009. Alopias vulpinus. The IUCN Red List of Threatened Species 2009: e.T39339A10205317. http://dx.doi.org/10.2305/IUCN.UK.2009-2.RLTS.T39339A10205317.en. Downloaded on 27 November 2019.
6. Moreno, J. A., Parajúa, J. I., & Morón, J. U. L. I. O. (1989). Reproductive biology and phenology of Alopias vulpinus (Bonnaterre, 1788) (Squaliformes: Alopiidae) in the north-eastern Atlantic and western Mediterranean. Scientia Marina, 53(1), 37-46.
7. Preti, A. N. T. O. N. E. L. L. A., Smith, S. E., & Ramon, D. A. (2001). Feeding habits of the common thresher shark (Alopias vulpinus) sampled from the California-based drift gill net fishery, 1998-1999. California Cooperative Oceanic Fisheries Investigations Report, 145-152.
8. Visser, I. N. (2005). First observations of feeding on thresher (Alopias vulpinus) and hammerhead (Sphyrna zygaena) sharks by killer whales (Orcinus orca) specializing on elasmobranch prey. Aquatic Mammals, 31(1), 83-88.