Advances in Trawling


August 1, 2017

Humans by our very nature fear what is new. For better and sometimes worse, a fear of “new” can slow critical progress, especially where sticking with “tried and tested” becomes a safely known position. Therefore, driving progress requires individuals willing to bravely explore their mysterious world. And we continue to rely on these pioneers to help us ensure that new becomes now. Indeed, the application of logic and reason over thousands of generations has enabled us to claim our place as custodians of our planet, even while our activities have proven how powerful we can be.

Humans possess the ability to dramatically alter the condition of the planet and have the intelligence and foresight to do something about it. The explosion of technology following the introduction of the scientific method in the 17th century highlights our potential to adapt to global problems and overcome. This is particularly evident in the advancements seen in our commercial trawling operations.

Boatswain's Locker

Fish is a profoundly important source of nutrition for much of the world; it provides essential micronutrients, vitamins and omega-3 fatty acids. Earth’s population consumes an average of more than 20 kilograms of fish each year. In total, fish contributes around 17 percent of the world’s animal protein consumption to about 3 billion people. There are many methods we use to harvest this fish. Each method, whether it uses a line, a pot, or a net has advantages and disadvantages and each technique has centuries of adaptation and improvement. And each of them, until very recently, has literally been based on mere hope and experience that what lies deep below the surface will prove worthy of the effort spent by fishermen and their support team (currently an estimated 1 in 15 humans support fishing directly or indirectly). Fishermen have had a very daunting task of feeding communities with product they had relatively little scientific observation of.

Our oceans, which account for 71 percent of Earth’s surface are still 95 percent unexplored. And even though our modern ancestors began fishing more than 40,000 years ago, it has only been in the past half century that we have been able to effectively study the deep in earnest.

Subsequently, as technology and data processing has developed, our ability to realize what happens underwater because of our fishing has improved immensely. We’ve uncovered some concerning yet manageable trends. Catching the wrong fish, too many fish, or even stocking the wrong fish in an ecosystem can cause problems, and our natural resistance to change can hinder our response.

After significantly reduced landings following World War 2, the United States Congress passed the Fishery Conservation and Management Act in 1976. This was one such catalyst that created pressure to determine what was going on beneath the waves. But identifying a symptom of a problem doesn’t offer any real understanding of what the problem is. We needed a concentrated effort, not only to increase our stocks, but also to identify which stocks are being depleted and why.

Success in this arena required a great deal of innovation and commitment to solving problems previously unknown to us.

Fishermen, who are often unjustly denigrated by the court of public opinion, have been instrumental in the achievements made so far and continue to work with scientists, technology companies, and each other to develop solutions and provide key research opportunities. After all, they as much as anyone else rely on steady and sustainable harvests to continue their operations. By nature, fishermen are competitive so they appreciate even small advantages in collecting intended fish efficiently. But answers to the problems in maintaining sustainable healthy populations of fish are complex. They require a steady concerted effort to understand, and small adjustments made to each year’s activities to avoid inserting unintended variables. So, while we can generally agree that there can be negative impacts resulting from our activities in harvesting fish, the solution isn’t as simple as ceasing fishing operations worldwide or only using aquaculture. If we look at the ocean as one big opportunity, we have vast potential in learning to work within the parameters that also benefit and protect the environment. We can do so while meeting the global demand for nutrition, much like we did when we learned to rotate crops on land.

Philips Publishing Group

The modern fishing trawler was developed in the 19th century. They carry large, sweeping nets and are capable of hauling many thousands of fish back to the vessel in a single tow. This efficiency provides relatively low-cost sustenance for much of the world’s population. Trawling is generally divided into two categories, bottom and midwater. Bottom trawling is conducted by dragging a net on the bottom of the ocean (benthic trawling) or just above the bottom (demersal trawling). Midwater (pelagic) trawling is conducted higher in the water column.

Like most techniques, trawling for fish requires a healthy blend of raw instinctive experience and increasingly advanced technology to stand out in a crowd. Bottom trawling is considered more harmful to the environment than pelagic trawling, but great strides are being made to reduce the impact of both. In partnership with technology companies, vessels are now using some very powerful tools during their tows.

Excluders are being designed, developed, and tested which allow the vessel to purposely avoid collecting incorrect or protected species. One very successful program has been the development of Turtle Excluder Devices (TEDs). Current TED designs are estimated to be 97 percent effective in excluding turtles from shrimp trawls. Work continues the development of other excluders and programs to prevent the collection of other species like halibut, salmon, and many more.

Advanced sonar technology is being developed to scout and search large areas, minimizing fuel consumption and increasing selectivity. In addition, forward looking sonars offer resolution capable of monitoring for and avoiding previously unseen snags.

Specialized fisheries sounders can determine hardness of the seabed, which provides important information for the type of gear to be used and expected species to be collected. They often use split beam technology to look through the water column in multiple dimensions; this provides information on biomass density, fish sizes, and with proper experience discriminate species.

Great strides have been made in studying resonant frequencies for individual species. As different fish respond differently to higher and lower frequencies, having a broadband sounder capable of generating a variable frequency can result in excellent identification of the species being looked at directly underneath the vessel.

The doors, which are supported by two wires, are large hydrofoils used to keep the net stretched open. They have sensors on them that can provide data like door spread distance, pitch, roll, depth, and temperature at hundreds of fathoms below the surface. This allows for the captain to ensure that the net is flying properly instead of digging in or folding up.

Trawl sonars monitor the catch as it enters the net opening. These “suitcases” can be wireless or powered via a cable known as the “3rd wire”. At more than two thousand meters long, this cable allows for transmission of high-bandwidth telemetry data and power over one cable.

Even more recent has been the addition of live video streaming being sent along with sounder data directly from the net. This allows for confirmation of identification, exclusion, and catch performance. Importantly, it also allows scientists and fishermen to see what they don’t haul in. What is happening to the ground? What is happening to the excluded fish? Are fish escaping? This feedback is essential in improving net layout and trawl practices.

Fishermen's News Celebrates 75 Years

On the horizon, further improvements are constantly being developed. Efficiency and performance is constantly being improved throughout modern day trawlers; from power generation on board to the winch drive control systems, to the shape and size of the nets used to gather fish. The partnership created by pioneers in the fishing community, manufacturers, scientists, and regulatory agencies continue to ensure that our ocean will provide jobs, food, and adventure for the next 40,000 years and beyond.

David J. Pratt has nearly two decades of experience in marine technology including eight years of service in the US Navy. He founded and now serves as Vice President of Fusion Marine Technology, which specializes in electrical and electronics integration for vessels in the Pacific Northwest.


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