Marine Life & Conservation Blogs
Creature Feature: Whale 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.
On 30th August it’s International Whale Shark Day! So to celebrate this month’s creature feature is all about the largest fish in the ocean… the Whale Shark!
The biggest shark in the ocean. The biggest fish in the ocean. The Whale Shark lives up to its name. Reaching a whopping 18m in length (potentially more). This is a legendary and beautiful shark.
They are unmistakable. Apart from their size, these filter-feeders have a beautiful patterning on their back. They have a checkerboard of white or yellowish spots on a grey, blue or brown back. It is often compared to a starry sky. In fact. In Madagascar they are known as “marokintana” for “many stars”.
Each Whale Shark’s pattern is unique. Amazingly, software used to identify star clusters from images of space has been adapted to identify individual Whale Sharks!
These sharks are highly migratory. Including journeys of 13,000km (made one way only) over 37 months. Which falls short of the most migratory shark, the Blue Shark. Tagging has revealed that there are regular ‘aggregation sites’. Here, Whale Sharks come together in huge numbers. Several hundred Whale Sharks may come together. To feed at annual, seasonal or lunar fish and invertebrate spawning events. The huge numbers of plankton at these events are consumed by suction. Whale Sharks can hang vertically and feed by sucking and gulping in water which is filtered through gill rakers.
Despite everything we know about them. And tagging studies. We still don’t know where Whale Shark’s pupping or nursery grounds are! We do know they are viviparous, giving birth to live young. Giving birth to up to 300 young.
Although they are protected by international agreements such as CITES and CMS. Unfortunately, Whale Sharks are endangered. They’ve been overfished in many areas for meat. Currently, the tourism industry for this species is booming. If you’re lucky enough to be able to go and see Whale Sharks – then why take a look at our guide for ecotourism.
Finally, if you want to support this majestic creature why not adopt a Whale Shark?
SCIENTIFIC NAME: Rhincodon typus
FAMILY: Rhincodontidae
MAXIMUM SIZE: 17m – 21m
DIET: Plankton
DISTRIBUTION: Circumglobal, all tropical and warm seas except the Mediterranean
HABITAT: Open ocean to close inshore off beaches
CONSERVATION STATUS:
Banner Image – © Paul Cowell | Shutterstock
In-text Images – © Frogfish Photography
For more amazing facts about sharks and what you can do to help the Shark Trust protect them visit the Shark Trust website 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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