Marine Life & Conservation Blogs
Creature Feature – Megamouth Shark
A rare and mysterious species, the Megamouth Shark Megachasma pelagios was first sighted when one had gotten entangled in a sea anchor (Oceana, 2023), and hauled up by fishermen on-board a navy ship in 1976 (Black, 2014). The Megamouth Shark is distributed worldwide in tropical to temperate latitudes, can be found in costal to open ocean (epipelagic to bathypelagic), and is a filter feeder, like that of the Whale, and Basking Shark (Oceana, 2023).
Upon its first discovery, this genus of shark generated its own taxonomy, Order Lamniformes (mackerel sharks), and belongs to the family Megachasmidae (megamouth sharks) (Oceana, 2023). Currently this shark is listed as least concern on the IUCN Red List, with the most recent assessment of species health being in 2018 (IUCN Red List, 2023). The Megamouth Shark can be found resident in countries such as Australia, Sri Lanka, Vietnam, South Africa, and China, with the current population number of sharks being unknown due to their rare sightings, and lack of research (IUCN Red List, 2023).
A large species of shark, reaching weights of up to 2700 pounds (1215kg), and approximately 16 feet in length (5m), this species has only been observed within the wild a few times, with less than 60 individual sharks having been known by scientists to of ever been captured or observed (Oceana, 2023). The smallest of the three species of filter-feeding sharks, this shark derived its name from its remarkably large, circular mouth (Oceana, 2023). From what little research has been carried out on the species, from the rare few sightings these sharks have been observed residing near to the surface, in depths of up to 15,000 feet (4600m) (Oceana, 2023).
It is believed that Megamouth sharks only come near to the surface at night, spending the majority of their lives in the dark (Oceana, 2023). They are filter feeders that swim through the ocean with their mouths open capturing food resources, such as plankton (Oceana, 2023). The inside of their mouths contain light producing organs, believed to be used for attracting pelagic crustaceans and other prey (Oceana, 2023).
With commercial fisheries pushing to deeper depths to discover new species to market as food, more and more large deep sea creatures are being discovered (Oceana, 2023). Like other species of shark, megamouths mate via internal fertilization, giving birth to a small number of live young (Oceana, 2023). The adult shark does not connect to their live young through a placenta, and instead the mother provides an unfertilized egg during gestation (Oceana, 2023). Once born, the megamouth shark immediately becomes a filter feeder (Oceana, 2023). There is a huge lack in species behavioral ecology, and richness, and so electronic tagging studies and further research is needed in order to better understand, and to conserve this species (Watanabe & Papastamatiou, 2019).
SCIENTIFIC NAME: Megachasma pelagios
FAMILY: Megachasmidae
MAXIMUM SIZE: Up to 5.5 meters (18 feet) in length
DIET: Filter feeds for plankton, but also consumes deep water fish
DISTRIBUTION: Widespread distribution in tropical and temperate waters worldwide
HABITAT: Ocean-going. Surface to deep waters – 1,000m.
CONSERVATION STATUS:
Due to its elusive nature and rare sightings, little is known about its population size or trends. It is occasionally caught as bycatch in fishing gear, but there are no known directed fisheries for this species.
Banner image – Wikimedia Commons | GordonMakryllos
References:
- Black, R. (2014) A forgotten fossil megamouth gets a name. National Geographic. Available at: https://www.nationalgeographic.com/science/article/a-forgotten-fossil-megamouth-gets-a-name. Accessed: 21st March 2023.
- IUCN Red List. (2023) Megamouth Shark. IUCN Red List. Available: https://www.iucnredlist.org/species/39338/124402302#taxonomy. Accessed: 21st March 2023.
- (2023) Megamouth Shark. Oceana. Available at: https://oceana.org/marine-life/megamouth-shark/. Accessed: 21st February 2023.
- Watanabe, YY, Papastamatiou, YP. (2019) Distribution, body size and biology of the megamouth shark Megachasma pelagios. J Fish Biol. 95: 992– 998. https://doi.org/10.1111/jfb.14007
This month’s Creature Feature has a guest writer – Jodie Moore
Marine Life & Conservation Blogs
Creature Feature: Dusky Shark
In this series, the Shark Trust will be sharing amazing facts about different species of sharks and what you can do to help protect them.
This month we’re taking a look at the Dusky Shark, a highly migratory species with a particularly slow growth rate and late age at maturity.
Dusky sharks are one of the largest species within the Carcharhinus genus, generally measuring 3 metres total length but able to reach up to 4.2 metres. They are grey to grey-brown on their dorsal side and their fins usually have dusky margins, with the darkest tips on the caudal fin.
Dusky Sharks can often be confused with other species of the Carcharhinus genus, particularly the Galapagos Shark (Carcharhinus galapagensis). They have very similar external morphology, so it can be easier to ID to species level by taking location into account as the two species occupy very different ecological niches – Galapagos Sharks prefer offshore seamounts and islets, whilst duskies prefer continental margins.
Hybridisation:
A 2019 study found that Dusky Sharks are hybridising with Galapagos Sharks on the Eastern Tropical Pacific (Pazmiño et al., 2019). Hybridisation is when an animal breeds with an individual of another species to produce offspring (a hybrid). Hybrids are often infertile, but this study found that the hybrids were able to produce second generation hybrids!
Long distance swimmers:
Dusky sharks are highly mobile species, undertaking long migrations to stay in warm waters throughout the winter. In the Northern Hemisphere, they head towards the poles in the summer and return southwards towards the equator in winter. The longest distance recorded was 2000 nautical miles!
Very slow to mature and reproduce:
The Dusky Shark are both targeted and caught as bycatch globally. We already know that elasmobranchs are inherently slow reproducers which means that they are heavily impacted by overfishing; it takes them so long to recover that they cannot keep up with the rate at which they are being fished. Dusky Sharks are particularly slow to reproduce – females are only ready to start breeding at roughly 20 years old, their gestation periods can last up to 22 months, and they only give birth every two to three years. This makes duskies one of the most vulnerable of all shark species.
The Dusky Shark is now listed on Appendix II of the Convention on the Conservation of Migratory Species (CMS), but further action is required to protect this important species.
Scientific Name: Carcharhinus obscurus
Family: Carcharhinidae
Maximum Size: 420cm (Total Length)
Diet: Bony fishes, cephalopods, can also eat crustaceans, and small sharks, skates and rays
Distribution: Patchy distribution in tropical and warm temperate seas; Atlantic, Indo-Pacific and Mediterranean.
Habitat: Ranges from inshore waters out to the edge of the continental shelf.
Conservation status: Endangered.
For more great shark information and conservation visit the Shark Trust Website
Images: Andy Murch
Diana A. Pazmiño, Lynne van Herderden, Colin A. Simpfendorfer, Claudia Junge, Stephen C. Donnellan, E. Mauricio Hoyos-Padilla, Clinton A.J. Duffy, Charlie Huveneers, Bronwyn M. Gillanders, Paul A. Butcher, Gregory E. Maes. (2019). Introgressive hybridisation between two widespread sharks in the east Pacific region, Molecular Phylogenetics and Evolution 136(119-127), https://doi.org/10.1016/j.ympev.2019.04.013.
Marine Life & Conservation Blogs
Creature Feature: Undulate Ray
In this series, the Shark Trust will be sharing amazing facts about different species of sharks and what you can do to help protect them.
This month we’re looking at the Undulate Ray. Easily identified by its beautiful, ornate pattern, the Undulate Ray gets its name from the undulating patterns of lines and spots on its dorsal side.
This skate is usually found on sandy or muddy sea floors, down to about 200 m deep, although it is more commonly found shallower. They can grow up to 90 cm total length. Depending on the size of the individual, their diet can range from shrimps to crabs.
Although sometimes called the Undulate Ray, this is actually a species of skate, meaning that, as all true skates do, they lay eggs. The eggs are contained in keratin eggcases – the same material that our hair and nails are made up of! These eggcases are also commonly called mermaid’s purses and can be found washed up on beaches all around the UK. If you find one, be sure to take a picture and upload your find to the Great Eggcase Hunt – the Shark Trust’s flagship citizen science project.
It is worth noting that on the south coasts, these eggcases can be confused with those of the Spotted Ray, especially as they look very similar and the ranges overlap, so we sometimes informally refer to them as ‘Spundulates’.
Scientific Name: Raja undulata
Family: Rajidae
Maximum Size: 90cm (total length)
Diet: shrimps and crabs
Distribution: found around the eastern Atlantic and in the Mediterranean Sea.
Habitat: shelf waters down to 200m deep.
Conservation Status : As a commercially exploited species, the Undulate Ray is a recovering species in some areas. The good thing is that they have some of the most comprehensive management measures of almost any elasmobranch species, with both minimum and maximum landing sizes as well as a closed season. Additionally, targeting is entirely prohibited in some areas. They are also often caught as bycatch in various fisheries – in some areas they can be landed whilst in others they must be discarded.
IUCN Red List Status: Endangered
For more great shark information and conservation visit the Shark Trust Website
Image Credits: Banner – Sheila Openshaw; Illustration – Marc Dando
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