LED Lights on Fishing Nets Help Reduce Bycatch

A simple technique to illuminate the exits in trawling nets could cut accidental bycatch by half a recent study has shown. The study, published in the Journal of the Marine Biological Association of the United Kingdom, found that attaching LED lights to the larger holes in a net allows non-target species to escape, reducing the number that are killed. The research was conducted by a team from Bangor University, led by marine ecologist, Dr Lucy Southworth.

Bycatch, the capture of non-target species, can significantly damage the populations of these species, many of which are vulnerable or endangered, and drastically reduce their numbers. Similarly, seabirds and marine mammals can become victims of accidental bycatch through entanglement in fishing nets, which often kills them in the process.

But it's not just the environment that is negatively affected by bycatch. There is also a significant cost to the fishermen. Under EU law, fishermen are required to bring almost everything they catch to shore, including that which is not a part of their quota. If too many non-target fish are caught, the entire fishery may be closed to allow stocks to recover. As a result, even fishermen doing their best to comply with the rules can cause unintended damage and end up risking their livelihoods.

Trawler at sea

The new study, conducted between June and August 2017, is a clever inversion of an old fishing technique: shining a light on the water to attract fish into the net. The team set out to test the effect of lights in reducing the number of haddock and flatfish that were accidentally caught in a queen scallop fishery off the Isle of Man.

They found that, while the devices that are currently used to reduce bycatch were effective in shallower waters of around 29 to 40 m, they had little to no effect in deeper waters of around 45 to 95 m. This is likely due to the lack of light and, therefore, visibility. Once LED lights were attached to the net exits in these deeper waters, haddock bycatch was reduced by 47% and flatfish bycatch by 25%.

The team even found of evidence of sharks escaping the lit nets, which could be a topic for future research. LED lights could also potentially reduce the number of whales, dolphins, and porpoises entangled in nets each year as they alert the animals to the presence of these nets and give them the chance to avoid the hazard.

Dr Southworth and her colleagues believe that this could be a popular solution to the current issues with bycatch. Not only are LED lights fairly cheap, they are easy to apply to the nets and can be easily adjusted for different environments. Though there is still a long way to go before the issue of bycatch is solved, it's certainly refreshing when simple answers can be found for complicated problems.

Aquatic News: October 2019

October has been another eventful month in our watery world. If you're an aquarium keeper, it turns out you could be the key to saving several species of freshwater fish. Florida has been hit with its second red tide of this year. We have the good news that dolphins are living in the Potomac River, and the bad news that whales are living in the Great Pacific Garbage Patch.

A new initiative to save fish from extinction

Freshwater fish are a highly diverse group, but they are also the most threatened of the vertebrates. Many species go extinct before conservation efforts can even begin.

A recently published study by Dr Jose Valdez, of Aarhus University, and Kapil Mandrekar, of SUNY College of Environmental Science and Forestry, has shown that aquarium hobbyists can play an important role in freshwater fish conservation.

In some cases, dedicated hobbyists are actually more knowledgeable on certain species than the scientific community due to their hands on experience with the fish. In fact, some species that have not yet been scientifically described are already well-known to hobbyists. When these hobbyists are able to share their knowledge, they can make a real difference and have already helped discover new species and save others from extinction. Some have even provided individuals from their own aquariums to conservation efforts.

The largest organisation coordinating such conservation programmes is the CARES (Conservation, Awareness, Recognition, Encouragement, and Support) preservation programme. It encourages hobbyists to keep the most endangered (or even extinct in the wild) freshwater fish species to ensure their survival. In many cases, these species would have been otherwise overlooked by conservation efforts.

Valdez and Mandrekar found that CARES listed almost 600 freshwater fish species, over 80 of which are unknown by the scientific community. There are also more than 30 species included that are already extinct in the wild.

As it turns out, many of these species are only still here because of hobbyists breeding them in their aquariums. With that in mind, collaboration between scientists and aquarium hobbyists could prove to be a real turning point for the effective conservation of freshwater fish.

Further reading

Deadly red tide returns to Florida

Example of a red tide, this one in La Jolla, California

A new red tide began in Florida in early October. Samples of water taken off the shore of Collier County showed high concentrations of Karenia brevis, the toxic algae responsible for this nasty phenomenon. It also kills marine life and can cause respiratory problems in humans, both of which have been recorded in the affected area.

The locations currently affected include Barefoot Beach, Naples Bay, and around the Gordon River. The species most affected by the toxicity so far has been mullet (of the family Mugilidae).

The last red tide in this area cleared up just eight months ago and, at 15 months in duration, it was the longest lasting red tide in decades. It began in November 2017 and ended in February of this year. Thousands of fish, turtles, and marine mammals were killed and all three of Florida's coasts were affected.

This current red tide is, so far, only affecting the southwestern coast. It is not known how long it will last or how far it will spread as these things are difficult to accurately predict. Hopefully, it won't be as long, or as destructive, as the previous red tide.

Further reading

Dolphins have returned to the Potomac

Dolphins were once common in the Potomac River in the 1800s but, by the 1960s, it was so badly polluted that they could no longer survive there. So they moved on.

This kickstarted 50 years of cleanup efforts that have finally paid off as there are now around 1,000 bottlenose dolphins (of the genus Tursiops) living in the river. Even better, one dolphin was seen giving birth there back in August. The fact that dolphins are now choosing to reproduce and raise their young in the Potomac is a really good sign for the improving health of the river. Long may it continue.

Further reading

Whales are living in the Great Pacific Garbage Patch

The Great Pacific Garbage Patch is the largest accumulation of ocean plastic in the world. It is located between Hawaii and California, where ocean currents to form the North Pacific subtropical gyre. There is a shocking 80,000 tonnes (or 88,000 US tons) of plastic in this patch.

A survey of the area has found that there are, in fact, whales and dolphins living there, some with calves. This could prove to be very dangerous for them.

As you are probably aware, ocean plastic is a significant issue for marine life. There are more and more reports in the news of whales washing up dead after accidentally swallowing plastic waste. For example, in Indonesia, a sperm whale (Physeter macrocephalus) recently washed ashore with a whopping 115 drinking cups, 25 plastic bags, plastic bottles, two flip-flops, and thousands of pieces of string in its stomach. It's an issue of great concern.

The most common debris found in the Great Pacific Garbage Patch is ghost nets, which is fishing gear that has been discarded or lost. They can drift for years, trapping marine life. Whales and dolphins can easily become ensnared in these nets and their calves are especially vulnerable.

The findings of this survey should be a real wake-up call to clean up the area. It needs to be made safer for the whales and dolphins living there and efforts must be made to protect marine life as a whole. If we don't act soon, we will simply continue to see reports of dead whales on the news for the foreseeable future.

Further reading

The Weird and Wonderful: Endothermic Fishes

There are certain things about the animal kingdom that we are taught are absolutes. Birds fly. Reptiles have scales. Fish are cold-blooded. But, if you're anything like me, it's the exceptions to these rules that you'll find the most fascinating. Which is why I'd like to take some time to talk about endothermy, where heat is generated and maintained from within, in fishes.

The vast majority of fish species are ectothermic, which means their body temperature is largely controlled by the environment around them. As a result, their internal temperature can vary greatly and they don't have much physiological control over this. But, despite how it sounds, it's actually an advantage.

Water acts as a heat sink and tends to drain heat from anything it is in contact with, including living organisms. Due to a fish's gills, its blood is constantly in near direct contact with this heat-draining environment. With that in mind, it makes sense that a fish would not have the means to use its metabolism to warm up internally. It would be a massive waste of the fish's energy. It is far more efficient to rely on external factors instead.

But that's not the case for all fishes. Some have physiological mechanisms that enable them to be at least partially endothermic.

Tunas, swordfishes, and certain species of shark, such as the salmon shark (Lamna ditropis), are able to maintain body temperatures warmer than the surrounding water. They generate heat with their powerful swimming muscles, which they can then use to stay warm. For example, bluefin tuna (Thunnus thynnus) is able to maintain muscle temperatures of between 27 and 32°C (82 to 91°F) in waters of around 7 to 25°C (45 to 80°F).

Atlantic sailfish (Istiophorus albicans) mid-leap

Large, predatory billfishes, such as marlins, swordfishes, sailfishes, and spearfishes, are able to use the heat that they generate from swimming to warm their brain and eyes. This serves them well when they are hunting as it allows them to function efficiently and effectively in the deeper waters where they catch their prey.

Many sharks, including the great white (Carcharodon carcharias) and shortfin mako (Isurus oxyrinchus), also have a large vein that helps to warm the central nervous system (CNS). It does so by transporting blood from the swimming muscles to the spinal chord, keeping the nervous system in good working order at a functional temperature. This, again, serves them well when hunting in deeper waters where the temperature is lower.

Great white shark (Carcharodon carcharias)

The only truly endothermic fish that we currently know of, as in one that is fully warm-blooded, is the opah (of the family Lampridae), of which there are two living species. It can maintain its body temperature above the surrounding water temperature. They are found in tropical to temperate waters and swim at depths between 50 and 500 m. They are able to generate heat by constantly flapping their pectoral fins and retain this heat within their layers of fat, which acts as insulation.

An opah, of the species Lampris guttatus, in a rather unfortunate position

However, in 2015, it was discovered that opah also possess a rete mirabile, a specialised system of arteries and veins, within their gill tissue. This rete mirabile is found in several warm-blooded vertebrates and it allows for countercurrent heat exchange, where warm blood is carried from the heart and, in the case of the opah, warms the veins in the gills, which are carrying colder blood. In the reverse, the gills are also able to be cooled by contact with the surrounding water.

So, as you can see, what we think of as fact doesn't always line up with what is actually true. Not all fish are cold-blooded, and those that defy the norm each have their own way of warming the blood. Each method has been developed over time to suit the individual species, their lifestyle, and the habitat they live in. And, though each method is different, they are all effective in their own right.

The diversity of fishes is truly remarkable, as is the diversity of the animal kingdom as a whole. Life is so much stranger than we could ever possibly imagine. I will be covering more Weird and Wonderful creatures on the blog in the future, focusing on nature's oddballs and all the animals that dare to be different!