Lesser spotted dogfish (also called the small-spotted catshark) and its egg case by Jack O’Donovan Trá
This Easter why not head to your nearest beach and take part in a shark eggcase hunt! You can follow The Ray Project for ideas and tips on how to collect and identify your egg cases. Once you have found your eggs and correctly identified them using an eggcase identification guide, make sure to log your findings on The Ray Projects website.
Sharks, skates and rays (elasmobranchs) reproduce in a number of different ways. Some give birth to live young (viviparous), others have eggs that hatch internally before the young are born (ovoviviparous), which means the baby sharks feed off a yolk sac rather than a placenta attached to the mother. And some species lay their eggs and their young develop and hatch out as fully-formed miniature sharks and skates (oviparous).
Some examples of egg-laying sharks in Irish waters are the lesser spotted dogfish (also called the small-spotted catshark), bullhuss and the blackmouth catshark.
Shark eggs come in all different shapes and sizes. Sharks found in Irish waters lay eggs that have a leathery pouch to protect the embryo while it’s developing and curly tendrils at the end. These tendrils are used to attach the egg to seaweed or coral so they are anchored and can’t drift away in the ocean currents.
Different shark species’ eggs take different lengths of time to hatch. Some only take a few months while others can take over a year. The same species of eggs will also vary in size depending on the mother’s geographical location. Species in the Mediterranean and the Atlantic will have subtle differences.
Rays do not lay eggs, only true skates do. This can be confusing as thornback rays lay eggs and we can find their egg cases along Irish beaches. In fact, Thornback ‘rays’ are actually skates.
Confusing names can happen a lot in the animal kingdom (Killer ‘whales’ are not actually whales; they are the world’s largest species of dolphin) and elasmobranchs are no exception.
Skate eggs look quite different to shark eggs. They have the same leathery protective capsule for the baby to develop within but instead of curly tendrils, they have horns protruding from the corners of the capsule. This also helps the mother to wedge her eggs safely between rocks or in the substrate.
This blog was written by Grace Carr, Marine Policy Officer at the Irish Wildlife Trust, a partner of the Fair Seas campaign.
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We also welcome you to join us in Cork on 8th June, where we are hosting our inaugural World Ocean Day conference. We are bringing ocean advocates, government, industry and key stakeholders together to map out the next steps for Marine Protected Areas (MPAs) in Irish waters.
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