Tag Archives: turtles

LED-equipped fishing nets help protect wildlife from unintentional captures

Green light-emitting diode (LED) lights can help protect wildlife from fishing nets, new research reports.

Image credits Paul Lee.

Affixing green LED lights to fishing nets can significantly reduce the catch of nontargeted animals such as sharks, squids, or turtles, according to a team led by researchers from the Arizona State University. The addition of these lights doesn’t impact the quantity or quality of desired catch species (i.e. commercially-available fish), which helps raise confidence that fisheries will adopt the measure. That being said, the installation of these lights comes with a significant upfront cost per net, which many fisheries may not be able to afford.

Beyond practical concerns, however, the findings showcase that it is possible to maintain our current fishing efficiency while insulating species that aren’t desired from capture.

Lights in the deep

Coastal fisheries routinely use gillnets, devices that resemble chain-link fences, to capture fish. These nets are deployed for up to several days at a time and capture virtually every kind of marine wildlife that cannot fit through their holes. Undesired captures (“bycatch”) are tossed overboard once the nets are recovered. These animals experience very high rates of death following this, adding up to significant pressure on marine species such as dolphins and sea turtles. It also impacts the fisheries’ bottom line, as personnel waste time removing these animals from the nets.

In other words, both business and nature lose out from the use of gillnets.

John Wang, a marine ecologist at the National Oceanic and Atmospheric Administration (NOAA), and his colleagues previously designed illuminated nets in order to protect turtles from becoming bycatch, back in 2016. Turtles seem to be particularly good at noticing green light, and these nets cut down on turtle bycatch by 64%. The current study builds on those findings, examining whether other marine animals could benefit from the same idea.

It turns out, they would. The authors worked with small-scale grouper and halibut fisheries in Baja California, Mexico, as the area is known for its large populations of turtles and other large marine species. They deployed 28 pairs of nets, one of each being equipped with groups of green LED lights every 10 meters. The team gauged their efficiency by identifying and weighing the animals each net captured overnight.

Nets outfitted with lights captured 63% less bycatch overall. Per species, they reduced bycatch by 51% for turtles, 81% for squid, and 95% for elasmobranchs (sharks and rays) — the last one being the most “gratifying” result for the authors, as shark bycatch in the Gulf of California is “a huge issue”.

Fish capture was not affected by the lights. However, the LEDs cut down on time wasted by fishermen on hauling and unloading bycatch, and on untangling the nets, by half. The only drawback so far, according to Senko, is the upfront installation costs of the lights: around $140 per net. Some fisheries, especially those in poorer areas such as Indonesia and the Caribbean, simply can’t afford this price per net, they add. The team is toying with using fewer lights and having them be solar-powered rather than battery-powered to reduce some of these costs. Meeting the needs of fisheries is essential for the success of this project, as they are the ones who will decide on using the LED nets or not.

Exactly why some animals seem to avoid lights, and why they do so more than others, is still up for debate. While it is possible that some species’ better eyesight helps them perceive the lights more clearly, it’s very unlikely that this is the cause — any species with sight can see these lights, after all.

The paper “Net illumination reduces fisheries bycatch, maintains catch value, and increases operational efficiency” has been published in the journal Current Biology.

Most baby turtles in the oceans have plastic in their guts. ‘It’s an evolutionary trap,’ scientists say

Green turtle (Chelonia Mydas). Credit: Wikimedia Commons.

Plastic pollution is so rampant in the oceans that it has created an “evolutionary trap” for juvenile sea turtles. This was the conclusion of a new study that found plastic in most juvenile turtles they caught along both the Pacific and Indian Ocean coasts of Australia.

The plastic trap

An evolutionary trap occurs when a previously adaptive behavior now has negative effects on the overall survival and reproduction of an organism. This usually happens when a species’ habitat is altered much faster than the organism can adapt. These traps are quite perverse since species are deceived into making poor habitat choices based upon formerly reliable environmental cues — even when higher quality habitat or resources are still available.

For instance, changing land use in an isolated Nevada meadow has driven the extinction — and subsequent recolonization — of a local population of checkerspot butterflies (Euphydryas editha).

In this particular case, newly hatched turtles have adapted to enter the oceanic zone where they travel on currents, feeding and growing to maturity. These habitats are ideal for their development, mainly because that’s where ample food is being funneled straight to their mouths. The problem is that the same currents also carry plastic debris.

“Juvenile turtles have evolved to develop in the open ocean, where predators are relatively scarce,” said Dr. Emily Duncan, of the Centre for Ecology and Conservation on Exeter’s Penryn Campus in Cornwall. “However, our results suggest that this evolved behavior now leads them into a ‘trap’ – bringing them into highly polluted areas such as the Great Pacific Garbage Patch.

“Juvenile sea turtles generally have no specialized diet – they eat anything, and our study suggests this includes plastic,” she added.

Researchers at the University of Exeter in the UK and Murdoch University in Australia looked at how much and what type of plastics are ingested by small juvenile turtles. The study included 121 sea turtles from five of the world’s seven species: green, loggerhead, hawksbill, olive ridley, and flatback.

The results showed that the vast majority of turtles from the Pacific coast had plastic inside them: 86% of loggerheads, 83% of greens, 80% of flatbacks, and 29% of olive ridleys. On the Indian Ocean coast, the proportion of turtles containing plastic was much smaller, but still concerning. There,  28% of flatbacks, 21% of loggerheads, and 9% of green turtles contained plastic.

No plastic was found in hawksbill turtles on either coast, but this is likely due to the very small sample size consisting of only seven hawksbill.

All the animals included in the study were stranded post-hatchlings and bycaught oceanic juveniles from the longline fisheries in the Coral Sea.

Plastics now represent 80% of all marine debris and can be found virtually everywhere, from surface waters to deep-sea sediments. This debris is generally classed as either macroplastics (with a diameter greater than 1mm) and microplastics (smaller than 1mm). But for the purpose of this study, the researchers classed the debris according to color and type (hard plastics, rope, or plastic bags).

The highest number of ingested plastic pieces occurred in green turtles: one animal in the Indian Ocean contained 343 pieces, and one animal in the Pacific Ocean contained 144. 

“Plastic in the Pacific turtles was mostly hard fragments, which could come from a vast range of products used by humans, while Indian Ocean plastics were mostly fibers – possibly from fishing ropes or nets,” says Duncan, who is the lead author of the study.

The most commonly ingested polymers in both oceans were polyethylene and polypropylene. However, these plastics are so widely used in products that it’s impossible to trace the source. As such, there is no viable solution other than stopping plastic pollution as much as possible at its land-based source before it reaches the ocean.

It’s still not clear how the turtle juveniles’ health is affected by ingesting plastic, though scientists suspect it can lead to malnutrition, chemical contamination, and even death from laceration, obstruction, and perforation of the gastrointestinal tract.

“Hatchlings generally contained fragments up to about 5mm to 10mm in length, and particle sizes went up along with the size of the turtles,” Duncan said.

“The next stage of our research is to find out if and how plastic ingestion affects the health and survival of these turtles. This will require close collaboration with researchers and veterinarians around the world,” she added.

The findings were reported in the journal Frontiers in Marine Science.

Credit: Pixabay.

Just a few pieces of plastic are enough to kill sea turtles

Credit: Pixabay.

Credit: Pixabay.

Scientists estimate that more than half of all sea turtles have eaten plastic debris in some proportion. The rubbish, which was once in the hand of a human before it made its way into the world’s oceans, comes in all shapes and sizes, from microscopic pebbles to jellyfish-like undulating plastic bags.

A recently published study cataloged the damage done to sea turtles by plastic pollution. The findings suggest that just 14 pieces of plastic are enough to significantly increase the animals’ risk of death. If an animal had ingested more than 200 pieces of plastic, death was inevitable. In some cases, a single piece of plastic was deadly.

The international team of researchers wanted to investigate the inflection point where the ingested plastic reaches a lethal level. To this aim, they examined the necropsies of 246 sea turtles, as well as 706 records from a national stranding database relating to sea turtles in Queensland, Australia.

The researchers found that the animals that died for reasons unrelated to eating plastic had less plastic in their gut than sea turtles that died of unknown causes or direct ingestion of plastic.

The most vulnerable group are juveniles — half of which are expected to die if they ingest 17 pieces of plastic of more. A sea turtle typically lives to be 80 years old but a juvenile, which is too young to reproduce, can range from 20 to 30 years of age. The authors estimate that 90% of juvenile green sea turtles off the coast of Brazil have ingested plastic.

“Young small turtles actually drift and float with the ocean currents as does much of the buoyant, small lightweight plastic,” Dr. Britta Denise Hardesty from Australia’s Commonwealth Scientific and Industrial Research Organisation (CSIRO), told BBC News.

“We think that small turtles are less selective in what they eat than large adults who eat sea grass and crustaceans, the young turtles are out in the oceanic area offshore and the older animals are feeding in closer to shore.”

It’s difficult to pin the cause of death of a turtle to plastic except for in cases where the damage is self-evident. However, the work quantifies the toll of plastic pollution on sea turtle health and provides a measurable yardstick for future research.

In one case, researchers found as many as 329 pieces of plastic in the gut of a sea turtle. On the opposite end, a deceased turtle was found with its digestive tract blocked by a single item — a soft piece of plastic. In another turtle, its intestines were perforated by a sharp plastic debris.

The authors of the study write that even though plastic might not kill all turtles, its presence will certainly weaken the animals by impending their normal digestion.

The next step in the research is to establish whether plastic pollution in the oceans is causing a population decline. In some places, the problem is worse than in others. For instance, the Mediterranean and the southern Atlantic Ocean are so riddled with debris that it’s almost impossible for turtles to avoid the debris.

More research will hopefully paint a clearer picture of the damage — done not just to sea turtles, but other animals as well. Previously, a study found plastic debris in the guts of 90% of seabirds.

The authors say that it’s possible to reduce plastic exposure by banning certain high-impact items, such as straws or coffee pods. 

The findings appeared in the journal Scientific Reports.