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Is fishing with electricity less destructive than digging up the seabed with beam trawlers?

The pulse trawl: electrodes in the two direction of the gear cause an electric field above the seabed, which stimulate the flatfish so that come up and end up in the net

From The Conversation by Michel Kaiser

While many people may be interested in the sustainability and welfare of the fish they eat, or the health of the environment, fewer probably worry about the effect that trawl fishing – which accounts for 20% of landings – has on the ocean.

For a long time researchers and the industry have been trying to improve trawl fishing practices.
Things have moved on from practices such as beam trawling – where a large net is dragged across the ocean floor – to potentially less invasive and newer methods like electric pulse trawling.
This sees electrical pulses being sent into the seawater to flush out bottom-dwelling fish like plaice and sole, causing them to swim into the path of trawl nets.

Beam trawls have been the focus of environmental concern for decades, as it causes a substantial reduction in the abundance of animals living on the seabed.
These effects can be long lasting if the fishing occurs in areas which are inhabited by long-lived seabed dwelling species such as oysters and sponges.
Beam trawls are also associated with high amounts of bycatch – unwanted fish and other organisms – although the industry and researchers are working on ways to reduce this.

However, the relatively newer electric pulse fishing is not necessarily a perfect solution either.
Though it does not dig into the seabed to the same extent as traditional beam trawling, research has found it can fatally injure other species which may not be the target catch.

So why use this method if it still has its faults?
High fuel costs and EU legislation which has reduced the discarding fish at sea, have renewed interest in the use of electricity in fishing.
Across the world, millions are fed by the fish caught by trawlers so it is unrealistic for trawling to just be stopped altogether, but the variety of negative impacts on the marine ecosystem remain a cause for concern.

 courtesy of WUR / illustration Justin Tiand

For and against

The UK government recently announced an review into the use of electric pulses by foreign trawlers in British waters due to concerns about its potential effects on the environment and bycatch.
Campaign groups have also called on the EU to reinstate a ban on the electrical pulse method, calling it “destructive”.

The current pulse trawls are fine-tuned to catch larger fish (the spine of the fish acts as a conductor), so that bigger fish respond more strongly to the electric stimulus and are more likely to be caught in the nets.
This reduces catch of unwanted species that are less likely to respond to the electric pulse, and also reduces contact with the seabed.

Traditional beam trawls, on the other hand, are fitted with heavy “tickler chains” – horizontal chains strung across the mouth of the trawl – designed to “dig” fish like Dover sole out of the seabed.
Soles curl into a “c” shape in response to the electric stimulation used by pulse trawls, so they can be caught without the use of these “tickler chains”.

 courtesy of Pulse Fishing

Dispensing with the chains means that the gear is lighter, creates less disruption of the seabed, and substantially reduces the amount of other seabed organisms caught – by 75-80% per unit area of the seabed fished.
By not catching the unwanted species, this improves the quality of landed catch too, because skin abrasion is reduced in the net.
Together, improved catch quality and the reduced fuel consumption means greater profitability for the fishermen.

Electric pulse seems like a good idea from this perspective, but studies of its effects on other species of fish – that are not the intended catch – show that larger cod in particular are prone to spinal fractures when in contact with the electric pulses.
Small cod appear to be unaffected.
Cod typically have a low survival rate if they are unintentionally caught in most trawls, so this issue of spinal fracture may be irrelevant if they are caught using either method.

Additionally, though fewer seabed organisms end up in the trawl net when using electricity compared to traditional beam trawling, it is too early to tell whether the creatures remaining on the seabed are affected negatively by contact with the electric stimuli.
Aquarium experiments, have shown that worms and shrimps, for example, recover within seconds following the application of an electric shock.
However, these controlled laboratory experiments take place without natural predators – that may take advantage of a shocked creature – present.

The issues here are not solely environmental.
The pulse trawl fleet has encroached on grounds that historically were fished by fishermen using low impact netting methods, leading to some resentment and conflict with others in the fishing community.

Societal acceptance of any food production method is vital, and at present – for pulse trawling – this is a greater challenge than answering the ecological questions.
This issue could be resolved by more formal zoning of the sea so that pulse trawling is restricted to areas that do not impinge upon traditional low impact fisheries – initiatives which are currently in negotiation.

Taking both society and environment into account, electric pulse trawling may not be an infallible solution, but it might a better way of trawling than the use of traditional forms of beam trawling.

Links :

• UCN : NGOs, fishing groups claim EU has allowed pulse fishing on false grounds
• The Guardian : European parliament to decide future of pulse fishing
• Bloom : Electric Pulse fishing /  
• Pulse Fishing
• Wageningen Univ : Pulse fishing

Antiques road trip at UKHO

In this clip, antiques expert James Braxton visits the United Kingdom Hydrographic Office (UKHO) in Taunton, Somerset

A nice trip down memory lane ending with the most modern methods of hydrographic survey

Links :

• GeoGarage blog : UKHO ensures safe arrival of aircraft carrier into ...

Northwest Passage : a family adventure

This video is about KAMANA NWP Eastbound in 2017

'Plum' sailing boat, Solaris 72 21,55 m (skipper Enrico Tettamanti)

from Kamana Sailing Expedition

crew 12 persons (5 children)

Giant 'Blue Hole' found in Great Barrier Reef by marine biologist

According to new satellite imagery of the area, a giant blue hole was recently discovered within Australia's Great Barrier Reef.

Marine biologist Johnny Gaskell who has since explored the spot, said,

"What we found inside was hard to believe considering 5 months ago a Category 4 cyclone went straight over the top of it."

According to Gaskell, pristine colonies of giant birdsnest corals and extremely long Staghorn corals found in the "blue hole," were completely unaffected by Cyclone Debbie, which slammed into the region as a Category 4 storm back in late March.

From Johnny Gaskell

Blue Hole mission in the Great Barrier Reef.
This Blue Hole has previously been explored and documented by geologists who suggested it could be even older than the famous Great Blue Hole, in Belize.
It's location is in one of the least explored parts Great Barrier Reef, over 200km from our home @daydreamislandresort.

Gaskell began searching for blue holes in March last year after Cyclone Debbie hit, in hope of finding coral that was spared from the storm.
The high walls that line the sinkholes tend to preserve what lies below from damaging weather. Large hurricanes can be particularly dangerous for corals, as they are smashed by swells.
The blue hole that Gaskell spotted on Google Maps was in a remote location, nearly 190 kilometres away from the nearest island.
While the specific blue hole had been previously identified, its remoteness made it difficult to access and little was known about it.
Gaskell was able to finally confirm that it was a blue hole during the diving expedition in September.

The majority of blue holes are formed from sinkholes or caves that develop slowly over time, as rock begins to erode and collapse.
Many of the world’s blue holes formed during the last Ice Age, after sea levels rose and filled existing sinkholes with water.
The term blue hole simply comes from the dark, navy waters that characterise the formations, often creating a striking contrast with the turquoise that surrounds them.

 “This Blue Hole has previously been explored and documented by geologists who suggested it could be even older than the famous Great Blue Hole, in Belize."
pictures : Johnny Gaskell 

To get there we had to travel overnight for 10 hours and time the tides perfectly...
Was well worth it! Inside the walls was similar to the site we explored a few weeks back, but this hole was deeper and almost perfectly circular.
We dived down to just over 20m yesterday, before hitting bare sediment, that slowly sloped towards the centre.
Again it was great to see big healthy coral colonies.

“Due to the sediment build-up over thousands of years, blue holes can be like time capsules for the ocean,” Gaskell said. 

We call it 'The Crack'....
Up there with the most ultimate snorkels I've ever done...

“At around 15 to 20 meters deep, there were huge Birdsnest Corals (Seriatopora) and super elongated Staghorn Corals (Acropora), both of which were among the biggest and most delicate colonies I’ve ever seen,” Mr Gaskell said.

 

After diving the Blue Hole over the weekend, we decided to move sites and check out what looked like a huge crack in the reef
 Open to the ocean at one end, and closed in by Reef at the other.
The total length was over a 1Km long, about 50m wide and the depth is still unknown.

The Crack

The strong current along the walls meant we had to drift the whole way.
This video doesn't do the site justice as most of the bigger inhabitants were not keen to come close. Only filmed fish and corals at the top on the edges.
Freediving into the depths we saw Grey Reef Sharks, Whitetip Reef sharks, Maori Wrasse, a Tawny Nurse and a 3m Lemon shark.
Seeing a huge school of Humpnose Unicornfish was definitely my highlight.
Counted over 100 in one photo.

Want to know exactly where it is? Sorry, it's still a secret.

The blue hole sits in the heart of the Great Barrier Reef off the Whitsunday Coast.
“Its location is in one of the least explored parts Great Barrier Reef, over 200 km from Daydream Island. "
Gaskell however, hasn't revealed the exact location of his discovery, so it remains a new and local secret...
"Hopefully it will be left alone.
An influx of divers would severely damage the coral colonies, as they are more delicate than usual."

Picture : nautical charts (Australia AHS) overlaid upon Google Maps imagery in the GeoGarage platform webmapping.

It's a long way offshore this spot, but hopefully we'll get back there one day.
The Crack...

 Example of another Blue Hole in the GBR found in the GeoGarage platform ?
There are a couple of known blue holes in Australia but they are quite unexplored and due to the sheer size of the Great Barrier Reef, its certain that more are out there.
Wonky Hole is 80 metres (262 feet) deep and an amazing dive teaming with sea life and covered in whip coral and gorgonians.
The Barrier Star is another hole dropping to 90 metres (295 feet) with an overhang at the sandy bottom and an abundance of reef life and coral.

Gaskell plans to continue looking for and surveying blue holes in the Great Barrier Reef.
“Some of these sites have had scientists explore them in the past, but due to the remote offshore location, there are still parts of the Great Barrier Reef that remain a mystery,” he said.

Links :

• National GeoGraphic : Peer Inside a Mysterious Blue Hole in the Great Barrier Reef
• MNN : Biologist stumbles upon massive 'blue hole' in Great Barrier Reef
• Lostateminor : See inside the Great Barrier Reef’s incredible blue hole for the first time
• National Geographic : Peer Inside a Mysterious Blue Hole in the Great Barrier Reef
• AODN : Drowned dolines - the blue holes of the Pompey Reefs, Great Barrier Reef (pdf) 
• GeoGarage blog : Image of the week : Great Blue Hole in the Belize ... / Researchers just discovered the world's deepest ...