Marine Life & Conservation Blogs
Creature Feature: Great White 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 supreme apex predator is perfectly adapted to their environment. With a large torpedo shaped body and powerful tail they’re truly built for speed. At top speed they can reach up to 25mph.
White Sharks belong to a group of sharks (known as the mackerel sharks) who have a remarkable adaptation that enables them to retain warmth. This makes them much more efficient hunters.
Sharks lose a lot of heat through their gills, where blood vessels are exposed to the cooler water. To minimise heat loss mackerel sharks have a network of tiny capillaries which act as a heat exchange system (known as a rete mirabile). Blood vessels carrying warm deoxygenated blood to the gills pass alongside cold oxygenated blood going to the body. As they pass in opposite directions heat is exchanged and returned to the muscles.
Amazingly the body temperature of mackerel sharks can be 10°C higher than the surrounding water.
White Sharks vary in colour (from olive to brown or grey) with a white underbelly, which is what is thought to have given them their name. This counter shading acts as camouflage. Concealed from above and below, they’re able to sneak up on unsuspecting prey.
When turned on their back, White Sharks enter a trance-like state known as tonic immobility. It’s thought that being upside down disorientates them, causing this unusual response. The behaviour could be related to mating but nobody knows for sure.
In some cases Orca have figured out how to use this to their advantage. Off the coast of California they’ve been seen preying on White Sharks, pinning them upside down. Unable to respond, the shark suffocates and is then eaten.
As a top predator White Sharks play a key role in keeping our oceans healthy. They do this by keeping other populations in check and preying on the sick and old. This prevents the spread of disease and helps to improve the gene pool.
Scientists estimate that White Sharks can live 70 years or more. Making them one of the longest-living sharks!
- SCIENTIFIC NAME: Carcharodon carcharias
- FAMILY: Lamnidae (Mackerel Sharks)
- MAXIMUM SIZE: 6m
- DIET: They have a varied diet including, fish, sharks, rays, sea mammals and birds. They’re also opportunistic feeders and will scavenge on dead whales.
- DISTRIBUTION: Widespread but mostly found in temperate seas. Hot spots include: South Africa, Australia, New Zealand, Northeast US, California and the Pacific coast of Mexico.
- HABITAT: Shallow and coastal waters. They also travel across the open ocean, at depths of 0-300m. Commonly aggregate around rocky reefs near colonies of seals, sea lions, and walruses.
- CONSERVATION STATUS: Vulnerable
Love White Sharks? Find out more about this mighty ocean predator and support vital White Shark research by adopting a White Shark today by clicking here.
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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