When sharks are fished-out from coral reefs, fish body shapes change

Sounds kinda weird.. but studying nearly identical coral reef systems off Australia, my collaborators and I discovered something unusual on the reefs subjected to nearly exclusive fishing of sharks—fish with significantly smaller eyes and tails. This provides evidence of body shape changes in fish due to human-driven shark declines from overfishing.

For these reef fish, eye size is critical for detecting sharks, especially under low-light conditions, and tail size is important for escaping sharks with burst speed. Graphic: Hiram Henriquez and Alberto Cairo, University of Miami

In the study, our research team analyzed seven different fish species from two neighboring coral reef systems off the coast of northwestern Australia. The coral reef systems, known as the Rowley Shoals and the Scott Reefs, are each comprised of multiple atoll-like reefs, are nearly identical biologically and physically in all but one way— the coral reefs in Rowley Shoals are protected from fishing, while the coral reefs in the Scott Reefs have been subjected to nearly exclusive commercial shark fishing for centuries. Targeted shark fishing has intensified in the region in recent decades to fuel the demand of shark fin soup. As a result, shark populations have been decimated at the Scott Reefs, but remain healthy at the Rowley Shoals.

Our team collected 611 fish of seven different species across multiple sites from different coral reefs within the Rowley Shoals and the Scott Reefs. We then took photographs of each fish and digitally analyzed photographs, measuring body length, body width, eye area and tail area of each fish.

We found that at Scott Reefs, where shark populations have declined, the eyes of fishes that are normally prey for sharks were on average up to 46 percent smaller compared to the same sized fish of the same species on reefs at the Rowley Shoals where shark populations are healthy. The same pattern was true for fish tail sizes, with the overall size of fish tails being on average up to 40 percent smaller at the Scott Reefs compared to the Rowley Shoals. Interestingly, these patterns were consistent across seven fish species that vary in behavior, diet and trophic-guild.

Eye size is critical for detecting predators, especially under low-light conditions when many sharks usually hunt, and tail shape enables burst speed and rapid escape from sharks. So we believe that the removals of sharks by humans have potentially caused a reduction in the size of fish body parts that are otherwise normally important for detecting and avoiding sharks. It’s possible that the removal of sharks have lead to an evolutionary change in the fish.

The differences in fish body shapes measured between the two coral reef systems could also have consequences for energy flow throughout the ecosystem, ultimately impacting the food web. These results are particularly important since sharks are among the most threatened marine animals and the consequences of their global removals due to fishing is not well understood and has been a topic of significant speculation, debate and concern. However, these finding shed new light on  our understanding of the potential cascading effects the loss of sharks on marine ecosystems.

Source material Rosenstiel School of Marine & Atmospheric Science, University of Miami

Research paper: Hammerschlag N, Barley SC, Irschick DJ, Meeuwig JJ, Nelson ER, Meekan MG (2018) Predator declines and morphological changes in prey: evidence from coral reefs depleted of sharks. Marine Ecology Progress Series 586:127-139.

Originally posted 2018-08-16 00:49:39.

Top 25 Birds of Australasia

Australasia is renowned for their unique and unusual animals, and their birdlife is no exception. In Australasia you can see birds like Emus, Cassowaries and Logrunners. Australia and New Zealand are endemism hotspots, with 71% of New Zealand’s birds being unique to the islands. This is largely because they have been separated from other continents for over 40 million years, which has allowed species to evolve. Here we present the Top 25 Birds of Australasia. Thank you for everyone who submitted photographs for this week’s theme, your pictures have brought the uniqueness of Australasia’s birds to life.

Greater Crested Terns are known to follow fishing boats, feeding on any discards that they throw over. This one was photographed on Penguin Island, off the coast of Australia (Ashvij Putta)An Australian Pelican with a fish in his bucket-like bill. These pelicans often forage in groups, sometimes numbering up to 1900 birds! (Shashi Sood)This beautiful bird is called a Galah, it is related to the cockatoos (Radhakrishnan Sadasivam)The Straw-necked Ibis is the most abundant and widespread ibis in Australia (Boopathy Murugavel)The Zebra Dove occurs in the Indonesian islands and has been widely introduced, leaving some doubt as to what their natural range is (Owen Deutsch)White-eyes are a diverse group of birds, multiple species are found in Asia and Africa. In Australia there are also relatives of the white- eyes, called Silvereyes, like this one photographed in Tasmania, Australia (Radhakrishnan Sadasivam)The Black-fronted Dotterel is the most widespread wader in Australia. They colonised New Zealand fairly recently, in the last 70 years (Jamie Rattus Dolphin)Little Wattlebirds are common in the urban gardens of south-east Australia and Tasmania (Radhakrishnan Sadasivam)A Black-shouldered Kite photographed in Perth, Australia by Ashvij PuttaBush Stone-curlews are found only in the open woodlands of Australia and New Guinea (Jamie Rattus Dolphin)Researchers have found interesting differences between the diets of female and male Pied Oystercatchers. Males tend to take more hard prey while females take more worms (Radhakrishnan Sadasivam)The endangered Kea is endemic to the mountains of New Zealand’s south island. they were once believed to kill sheep and were widely extirpated by farmers. we now know that Keas actually eat mainly fruit and vegetation, only scavenging on carcasses opportunistically (Michal Richter)A Double-banded Plover ruffles its feathers in Perth, Australia (Jamie Rattus Dolphin)Rainbow Lorikeets reside in the woodlands of eastern Australia, feeding on nectar, pollen and fruits (Radhakrishnan Sadasivam)Red-winged Parrots prefer eating eucalyptus and acacia seeds (Judi Fenson)Noisy Miners are highly aggressive, they will attack, and occasionally kill, birds that cross in their territories (Shashi Sood)Pied Oystercatchers can be found in salt marshes and sandy beaches in Australia (Ashvij Putta)Here you can see how the Rainbow Lorikeet got its name! (Jamie Rattus Dolphin)The Red-vented Bulbul of southern Asia has been introduced to the Polynesian Islands, it is listed as one of the worst 100 invasive species in the world (Owen Deutsch)like many of New Zealand’s birds, the New Zealand Rockwren is endangered. Their main threat is introduced mammalian predators like stoats and mice (Fran Bell)Western Yellow Robins of western Australia are sedentary, ringing records show most recaptures are less than 10 km from the original ringing site (Jamie Rattus Dolphin)A White Tern photographed on Ducie Island by Owen DeutschThis is the sub-species leuconotus of the White-winged Fairy-wren. These are blue, while the other sub-species is black (Jamie Rattus Dolphin)Two Yellow-billed Spoonbills photographed on the Alcoa-Wellard Wetlands in Western Australia (Ashvij Putta)A White-fronted chat photographed in Tasmania, Australia by (Radhakrishnan Sadasivam)

Our mission is to build a global community around the freedom and beauty of birds in the wild as ambassadors for the natural ecosystems that they depend upon. They are the music, decoration, and character of every terrestrial habitat on the planet and have been around since the dinosaurs. They are the witnesses and ambassadors of the awesome power of nature. The wide availability of good, cheap optics has opened their world to us for the last few decades. Amazing, affordable DSLR cameras with long lenses are delivering brilliant digital bird imagery to online communities.

We are in a day-and-age during which more bird species are threatened with extinction than ever before. The Wild Birds! Revolution aims to publish the “Top 25 Wild Bird Photographs of the Week” to 1 million people every week by the end of the year. That is a revolution that will change the world! Join thousands of other weekend naturalists, photographers, birders, experts, hikers, nature-lovers, guides, scientists, conservationists and artists that share the thousands of wild bird photographs submitted to the Wild Bird Trust website and Facebook page. Thousands of wild bird enthusiasts are going out every day to photograph our planet’s beautiful birdlife. Pick up your camera, fill your bird feeder, open your heart, and join the Wild Birds! Revolution!!

Edited by Christie Craig, Campaign Manager

Top 25 Birds of Africa

Originally posted 2018-06-23 14:56:38.


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