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Creature Feature: Dusky Shark

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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.

The Shark Trust is the leading UK-based shark conservation charity. The team works globally to safeguard the future of sharks, and their close cousins, the skates and rays. Engaging with a global network of scientists, policymakers, conservation professionals, businesses and supporters, to further shark conservation. Established in 1997 to provide a voice for UK sharks, the Shark Trust has an ever-growing number of passionate supporters. And together we're creating positive change for sharks around the world. Want to join us and help protect sharks around the world? Click here! www.sharktrust.org

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The Ocean Cleanup to Complete 100th Extraction Live from the Great Pacific Garbage Patch

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the ocean cleanup
  • The Ocean Cleanup marks 100th extraction of plastic pollution from the Pacific Ocean by livestreaming entire cleaning operation from start to finish.
  • Occasion brings together supporters, partners, donors and followers as the project readies its cleanup technology for scale-up.
  • Founder and CEO Boyan Slat to provide insight on the plans ahead.

The Ocean Cleanup is set to reach a milestone of 100 plastic extractions from the Great Pacific Garbage Patch.

Extraction #100, scheduled for 28 or 29 May 2024, will be the first ever to be livestreamed direct from the Pacific Ocean, allowing supporters and partners around the world to see up close how the organization has removed over 385,000 kilograms (nearly 850,000 lbs) of plastic from the GPGP so far – more than double the bare weight of the Statue of Liberty.

the ocean cleanup

The mission of The Ocean Cleanup is to rid the oceans of plastic. To do this, the non-profit project employs a dual strategy: cleaning up legacy floating plastic in the Great Pacific Garbage Patch (the world’s largest accumulation of floating plastic), while stopping the flow of plastic from the world’s most polluting rivers.

The Ocean Cleanup captured its first plastic (the first ‘extraction’) in the GPGP in 2019 with System 001, following years of trials and testing with a variety of concepts. Through System 002 and now the larger and more efficient System 03, the organization has consistently improved and optimized operations, and is now preparing to extract plastic trash from the GPGP for the 100th time.

the ocean cleanup

Extraction #100 will be an interactive broadcast showing the entire extraction procedure live and in detail, with insight provided by representatives from across The Ocean Cleanup and partners contributing to the operations.

This is an important milestone in a key year for The Ocean Cleanup.’ said Boyan Slat, Founder and CEO of The Ocean Cleanup. ‘We’ve come a long way since our first extraction in 2019. During the 2024 season, with System 03, we aim to demonstrate that we are ready to scale up, and with it, confine the Great Pacific Garbage Patch to the history books.

the ocean cleanup

The livestream will be hosted on The Ocean Cleanup’s YouTube channel and via X. Monitor @theoceancleanup for confirmed timings.

www.theoceancleanup.com

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Marine Life & Conservation Blogs

Book Review: Plankton

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Plankton: A Worldwide Guide by Tom Jackson and Jennifer Parker

This is a book that jumps off the shelf at you. The striking front cover demands that you pick it up and delve further, even if you may not have known you wanted to learn more about the most diminutive life in our ocean, plankton!

Small it might be. Much of the imagery in the book has been taken under huge magnification. Revealing stunning beauty and diversity in each scoop of “soup”. There is lots to learn. Initial chapters include interesting facts about the different vertical zones they inhabit, from sunlight to midnight (the darkest and deepest areas). I loved finding out more about the stunning show that divers oft encounter on night dives – bioluminescence.

The black water images are wonderful. So this is a book you can have as a coffee table book to dip in and our of. But, these tiny organisms are also vital to our very survival and that of all the marine life we love. They provide half the oxygen produced on our planet. They are also responsible for regulating the planets climate. And for a shark lover like me – they are food for charismatic sharks and rays like the Basking Shark and Manta Ray, along with a huge number of other species. This book contains great insight into their biology, life cycles, migration, and how the changes in currents and sea temperatures affects them.

This is a book that is both beautiful and packed with information about possibly the most important group of organisms on our planet. Anyone interested in the ocean should have it one their shelves.

What the publisher says:

Plankton are the unsung heroes of planet Earth. Passive drifters through the world’s seas, oceans, and freshwater environments, most are invisible or very small, but some are longer than a whale. They are the global ocean’s foundation food, supporting almost all oceanic life, and they are also vitally important for land-based plants, animals, and other organisms. Plankton provides an incomparable look at these remarkable creatures, opening a window on the elegance and grace of microscopic marine life.

This engaging book reveals the amazing diversity of plankton, how they belong to a wide range of living groups, and how their ecology, lifestyles, and adaptations have evolved to suit an enormous range of conditions. It looks at plankton life cycles, the different ways plankton feed and grow, and the vast range of strategies they use for reproduction. It tracks where, how, and why plankton drift through the water; shares perspectives on migrations and population explosions or “blooms” and why they happen; and discusses the life-sustaining role of plankton in numerous intertwined food webs throughout the world.

Beautifully illustrated, Plankton sheds critical light on how global warming, pollution, diminishing resources, and overexploitation will adversely impact planktonic life, and how these effects will reverberate to every corner of our planet.

About the Authors:

Tom Jackson is a science writer whose many popular books include Strange Animals and Genetics in MinutesJennifer Parker is a zoology and conservation writer and the author of several books. Andrew Hirst is a leading expert on plankton whose research has taken him around the world, from the Antarctic to Greenland and the Great Barrier Reef.

Book Details

Publisher: Princeton University Press

Hardcover

Price: £25

ISBN: 9780691255996

Published: 9th April, 2024

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