trawl

Assessing Human-Caused Wildlife Mortality | Earth Wise

May 31, 2022 By EarthWise Leave a Comment

Bycatch is the fishing industry term used to describe the deaths of non-target fish and ocean wildlife during the fishing process. Some bycatch species are thrown away because regulations prohibit them from being kept. Others are thrown out because they won’t fetch high enough prices. According to some estimates, global bycatch amounts to about 10% of the world’s total catch.

Approximately half of global bycatch is a result of trawling. Trawling is a method of commercial fishing that involves pulling or dragging a fishing net – called a trawl – through the water or across the seabed in hopes of catching fish. Commercial fishing companies favor towing trawl nets because large quantities of fish can be caught. But the method is destructive to the seafloor and leads to the indiscriminate catch of all sorts of species, including whales, dolphins, porpoises, sharks, seals, rays, turtles, and seabirds.

Researchers have developed a new method to assess the sustainable levels of human-caused wildlife mortality. When this method is applied to a trawl fishery in Australia, it shows that the dolphin capture is not sustainable. The study, led by scientists at the University of Bristol in the U.K. and United Arab Emirates University, modeled different levels of dolphin capture, including those reported in logbooks and those reported by independent observers. According to the findings, which were recently published in the journal Conservation Biology, even the lowest recorded dolphin capture rates are not sustainable.

The new approach is extremely adept at assessing human-caused mortality to wildlife, and can be applied to fisheries bycatch, hunting, lethal control measures, or even wind turbine collisions.

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Wasted Catch

Dolphin bycatch from fishing practices unsustainable, study finds

Photo, posted May 18, 2011, courtesy of Pete Markham via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Biodiversity And Trawling Bans | Earth Wise

June 7, 2021 By EarthWise Leave a Comment

Trawling is a method of commercial fishing that involves pulling or dragging a fishing net – called a trawl – through the water or across the seabed in hopes of catching fish. Commercial fishing companies favor towing trawl nets because large quantities of fish can be caught in one go.

However, the trouble with trawling is that it’s destructive to the seafloor and indiscriminate in what it catches. When towing these large trawl nets, the largest of which is reportedly big enough to catch thirteen 747 jets, everything that happens to be in the way gets caught. As a result, trawling results in lots of bycatch, a fishing industry term used to describe the deaths of non target species during the process.

In 2012, the Hong Kong government implemented a territory-wide trawling ban in its waters in hopes of rehabilitating the marine benthic habitat. The benthic zone refers to the ecological region at the bottom of the ocean.

Researchers from City University of Hong Kong collected sediment samples from 28 locations six months before the trawl ban and two and a half years after the trawl ban to see whether such interventions can facilitate ecosystem recovery.

According to the study, which was recently published in the journal Communications Biology, the ban on trawling significantly improved marine biodiversity. The researchers observed substantial increases in the richness of species and the abundance of benthic marine organisms following the trawling ban. And since small benthic organisms are the main source of food for large species like fish and crabs, the trawling ban actually helps support fisheries.

More governments should consider a trawl ban to promote sustainable fisheries and marine biodiversity conservation.

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Research confirms trawl ban substantially increases the abundance of marine organisms

Photo, posted December 4, 2018, courtesy of John via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Much More Microplastics In The Ocean | Earth Wise

January 28, 2020 By EarthWise Leave a Comment

We’ve been hearing more and more about plastic contamination (microplastics) in the ocean. It is pulled from the nostrils of sea turtles, found in Antarctic waters, and tracked in increasing quantities in sedimentary layers dating back to the 1940s. A new study by researchers from the Scripps Institution of Oceanography suggests that there could be a million times more pieces of plastic in the ocean than previously estimated.

Oceanographers found that some of the tiniest countable microplastic particles in seawater occur at much higher concentrations than previously measured. Apparently, the traditional way of counting marine microplastics most likely misses the smallest particles, and therefore underestimates the number of particles by a factor of anywhere from 10,000 to a million.

The new measurements estimate that the oceans may be contaminated by 8 million pieces of so-called mini-microplastics per cubic meter of water. Earlier studies that only looked at larger pieces of plastic found only 10 pieces per cubic meter.

Microplastic studies typically trawl or pull a fine net behind a ship to collect samples. But the meshes previously used could only capture plastics as small as 333 microns. The new study found plastic particles as small as 10 microns, which is less than the width of a human hair.

Plastics keep breaking down into smaller and smaller particles, but they are so chemically strong that their chemical bonds don’t break down. They remain bits of plastic. Scientists are concerned that these particles can get small enough to enter the human bloodstream. The potential effects on human health are not well known and not extensively studied.

The problem of plastics just keeps getting bigger.

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Microplastics a million times more abundant in the ocean than previously thought

Photo courtesy of UC San Diego.

Earth Wise is a production of WAMC Northeast Public Radio.