Weekly round-up: March 21

Implementing no-fishing zones could increase global catch by eight million metric tonnes

Safeguarding 30 per cent of the world’s seas and oceans would protect almost 80 per cent of marine species and increase catch by eight million metric tonnes – while also preventing the release of one billion tons of carbon dioxide annually due to bottom trawling, reports an international team of scientists and economists.

Their study, published in the journal Nature, quantifies the benefits of preserving key marine habitats – at present, just seven per cent of the ocean is under any form of protection, with 2.7 per cent ‘highly protected’.

The team proposes the deployment of carefully-placed Marine Protected Areas with outright fishing bans, resulting in increasing biodiversity and larger catches in neighbouring areas. The majority of priority locations for protection lie within the 200-mile Exclusive Economic Zones of coastal nations.

In addition to boosting biodiversity and protecting species, the banning of bottom trawling would prevent the release of stored carbon – trawling gear disturbs the sea floor, releasing carbon which contributes to ocean acidification and atmospheric CO2. The study found CO2 emissions from bottom trawling are higher than those of most countries – and global aviation.

Co-author Trisha Atwood of Utah State University said: “The ocean floor is the world’s largest carbon storehouse. If we’re to succeed in stopping global warming, we must leave the carbon-rich seabed undisturbed. Yet every day, we are trawling the seafloor, depleting its biodiversity and mobilising millennia-old carbon – thus exacerbating climate change. Our findings about the climate impacts of bottom trawling will make the activities on the ocean’s seabed hard to ignore in climate plans going forward.”
Publication Nature

Cows are significant producers of methane, which is a more potent greenhouse gas than carbon dioxide (Breanna Roque/UC Davis)

Adding seaweed to cows’ diets can reduce their methane emissions by up to 82 per cent, helping reduce a significant source of greenhouse gases.

Over five months, researchers at UC Davis fed 80g doses of seaweed to beef cattle and found no difference in weight gain, but a significant and long-term reduction in emissions – which the team hopes can lead to the sustainable production of livestock across the world. 

Professor and co-author Ermias Kebreab said: “Only a tiny fraction of the earth is fit for crop production. Much more land is suitable only for grazing, so livestock plays a vital role in feeding the ten billion people who will soon inhabit the planet. Since much of livestock’s methane emissions come from the animal itself, nutrition plays a big role in finding solutions.”

Beef and dairy cattle contribute about 5 gigatonnes of CO2-eq annually, about half of which is methane. The team found seaweed inhibits an enzyme in the cow’s digestive system that produces the potent greenhouse gas.
Publication PLoS One

Sperm whales are thought to have learnt evasive tactics to escape hunters (Gabriel Barathieu)

Sperm whales learned how to avoid harpoon attacks from 19th century hunters – and taught others to do the same, a new study suggests.

Using digitised logbooks from American hunters in the North Pacific, the research team found a 58 per cent drop-off in success rate within the first few years of industrial whaling, which could not be explained by better competence in earlier whalers or the killing of vulnerable individuals in the first years.

Instead, they concluded that whales quickly learnt defensive behaviour, which was passed between social units – including changing their defence against orcas, previously the whales’ biggest threat. Gathering in slow-moving groups at the surface, the whales would fend off killer whales with their jaws or flukes – but the strategy left them extremely vulnerable to whalers. 

A reduction in strike-rate – the number sighted versus the number successfully harpooned  – suggests the whales weren’t simply better at avoiding detection, but actively escaping.

“Encounters with whalers typically lasted hours and sperm whales through their echolocation and communication systems can probably sense and coordinate behaviour over ranges of several kilometres,” said the team, composed of cetacean scientists Hal Whitehead and Luke Rendell and data scientist Tim D Smith.

“We suggest that naive social units learned defensive measures from grouped experienced social units and adopted them.”
Publication Biology Letters

Green sea turtles were the first species to be observed showing mysterious circling behaviour

Turtles, whales, sharks, seals and penguins have all been observed exhibiting an unusual circling behaviour – and scientists have no idea why.

The display was first noted by a team from the University of Tokyo during a displacement project observing green sea turtles.

Lead author of the study, Tomoko Narazaki, said: “To be honest, I doubted my eyes when I first saw the data because the turtle circles so constantly, just like a machine! When I got back in my lab, I reported this interesting discovery to my colleagues who use the same 3D data loggers to study a wide range of marine megafauna taxa.

“We’ve found that a wide variety of marine megafauna showed similar circling behavior, in which animals circled consecutively at a relatively constant speed more than twice.”

It may be that the circling serves more than one purpose, having been observed in foraging areas, during courtship, and at important navigation locations – possibly for geomagnetic detection.

The team hopes to continue their research to understand why animals exhibit the behaviour.
Publication iScience

Efforts to eradicate an invasive species could backfire in spectacular fashion – as discovered by a team at UC Davis whose attempts to remove European green crabs from a California estuary resulted in a near three-fold increase in population.

The crab is among the world’s top 100 invasive species, and costs the US shellfish industry around $20 million annually. In a bid to lessen these effects on a local level, in 2009 researchers worked to eradicate the crab from Seadrift Lagoon on Stinson Beach. By 2013 the population dropped from 125,000 individuals to just 10,000. However, a year later numbers soared to around 300,000 – thought to be caused in part by the fact adult crabs cannibalise younger individuals, and with the older crabs removed, the population grew unchecked.

Lead author Edwin Grosholz, a professor and ecologist at UC Davis, said: “A failure in science often leads to unexpected directions. We slapped our foreheads at the time, but with thought and understanding, it’s told us a lot about what we shouldn’t be doing and provided a way forward for us. The world should get less focused on total eradication and work toward functional eradication.”

No similar population gains were seen in neighbouring bays, adding further support that the increase was not a result of atmospheric or oceanic changes, but the eradication efforts.

Co-author and Smithsonian Environmental Research Center marine biologist Greg Ruiz said: “Instead of a one-size-fits-all approach, this study highlights the need to evaluate possible unintended consequences in selecting management strategies and tailoring these to the particular context and expected outcome.”

Grosholz concludes: “Don’t try to get them all, or it could come back to bite you.”
Publication Frontiers in Ecology and the Environment

Two species of reptile already extinct in the wild are now at risk of dying out in captivity due to a deadly bacterium.

Lister’s gecko and the blue-tailed shinning-skink, both native to Christmas Island, an Australia territory south of Java, suffered catastrophic population declines due to predation – with the invasive wolf snake thought to be the biggest culprit – and habitat destruction. In August 2009, as many individuals of both species as possible were collected for use in captive breeding programmes. The last Lister’s gecko observed in the wild was in October 2012, while a blue-tailed shinning-skink has not been seen since August 2010.

There are now only around 1,000 of each species left in captivity, but individuals of both populations have been mysteriously dying – until scientists identified the presence of Enterococcus lacertideformus, first discovered in 2014 after reptiles presented with facial deformities and lethargy, sometimes leading to death. The bacterium, which grows in an individual’s head before infecting its internal organs, is spread by direct contact.

Jessica Agius, co-lead author and PhD candidate at the Sydney School of Veterinary Science, said: “This means that healthy captive animals need to be kept apart from infected ones and should also be kept away from areas where infected animals have been.

“We also found that the bacterium can surround itself with a biofilm – a ‘community of bacteria’ that can help it survive. Understanding how E. lacertideformus produces and maintains the biofilm may provide insights on how to treat other species of biofilm-forming bacteria.”

The team also sequenced the bacterium’s genome, which suggested it may be susceptible to most antibiotics – the search is now on for the right one.

“It’s critical we act now to ensure these native reptiles survive,’ said Agius.
Publication Frontiers in Microbiology

Read How the critically endangered regent honeyeater is forgetting its song

Watch See how bottom trawlers operate in this explainer from Monterey Bay Aquarium

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