Harold DeLouche, trawl design expert with the Centre for Sustainable Aquatic Resources (CSAR), has seen significant changes during his 35 years in the trawling sector.
Current focus is now on sustainable fishing, capturing the target species only, having as little impact on the seabed as possible and on vessel fuel efficiency. As well, consumer insistence on sustainable certifications, such as The Marine Stewardship Council, has created an economic model for sustainable harvesting.
In the past, DeLouche says things were different.
“Trawl-makers effectively designed trawls to capture fish only. Little to no attention was paid to bycatch reduction, hydrodynamics and fuel efficiency or the types of footgear used.” In fact, he notes, that “harvesters had little to no idea what was involved in the making of fishing gear.”
DeLouche cites the Nordmore grids, first introduced in Canadian shrimp fisheries in 1993 and made mandatory in 1997, as one of the earliest and most successful examples of a bycatch reduction device, with the offshore fleet adapting the grates even prior to the regulation coming into effect.
DeLouche also stated that the issues challenging the harvesting sector today are more complex than in the past, with more focus placed on fuel efficiency and seabed impact. He did note, however, that there are technologies currently in existence or in development that can help support the industry.
In terms of applied research, DeLouche noted that sustainable gear technology research is most effective when behavioural strategies are combined with mechanical strategies. For example, he cites the east coast haddock fishery for which cod is a critical bycatch issue. When entering a trawl, research revealed that haddock swim up when encountering the trawl whereas cod swim downwards. Understanding this behavioural difference enabled trawl makers and regulators to include escapement panels in the bottom of the trawls as a condition of the fishery. There are many modifications that can be made to fishing gear to make it more efficient and sustainable, such as modifications to mesh size, inclusion of bycatch reduction devices, inclusion of escapement panels and reduced footgear contact points.
However, understanding the size, morphology and behaviour of the fish is always critical to the success of any proposed technology.
Whether it is an emerging or an existing fishery, the researchers at CSAR encourage harvesters to meet with specialists so that gear can be tailored specifically to the target species and the parameters of the fishing vessel.
DeLouche noted that new technologies, such as trawl simulation software DynamIT ™, enable gear specialists to design and simulate gear to the exact specifications of your vessel.
As the simulations allow for relatively simple design changes to the trawl, they permit a number of towing simulations in a relatively cost-effective manner. They also enable harvesters to determine how the trawls will perform under a number of conditions and technology changes.
Having constructed scaled model trawls for almost 30 years, DeLouche is a proponent of using the flume tank for testing models of the proposed system. The flume tank can be a significant learning tool, enabling the crew of a fishing vessel to see how a trawl will perform in different situations and it provides an opportunity to handle all aspects of the trawling system, including doors, warps, bridles and trawls.
Typically, once systems are perfected through numerical simulations and flume tank testing, trials on the full-scale systems are conducted at sea. It is during this phase that advances in technologies, such as sophisticated underwater camera systems, are facilitating a better understanding of behavioural responses to new technologies.
With cod stocks still in flux, the introduction of marine protected areas and no-bottom contact zones, and fisheries like redfish expecting to make a commercial recovery over the next few years, it is increasingly clear that new strategies for sustainable gear technology need to be considered as past practices are no longer permitted.
Researchers at CSAR are able to assist gear specialists and gear manufacturers identify the best options for their vessels to ensure a sustainable and economically viable fishery.
By Kelly Moret
Centre for Sustainable Aquatic Resources