Shrimp Boat Operations: A Guide To Inner Workings

Shrimp boats, or trawlers, have been using the same basic technique to catch shrimp for over 100 years, with advancements mainly focused on improving efficiency and sustainability. The primary feature of a shrimp trawler is the trawl itself, which is a large specialised net. The trawl net is shaped like a flattened cone, with weights at the bottom and buoys at the top, allowing it to open its mouth to catch shrimp. In this paragraph, we will explore the inner workings of a shrimp boat and understand the process of shrimp trawling.

Shrimp trawlers use large specialised nets

In front of the bottom of the net is a metal chain, known as a tickler chain, which skims the ocean floor and jostles shrimp, making them easier to catch. The cone structure then funnels the shrimp downward until they reach a bag at the end of the net. The trawls are then hauled in by powerful wenches, and the catch is released onto the deck of the boat, where it is gathered, iced, and frozen for further sorting and processing.

Shrimp trawlers often incorporate up to four trawls, two on each side of the boat, which are lowered into the water by outriggers—long, metallic poles that stabilise the trawls and the boat, even in rough waters. The industry has also implemented turtle excluder devices (TEDs) and bycatch reduction devices (BRDs) to minimise the impact on the environment and other sea life. These devices help to ensure that turtles can escape and that bycatch—other fish that end up in the net—is reduced.

Turtle excluder devices (TEDs)

TEDs were developed in the 1970s by Wil Seidel, who worked for NOAA. The first TED was based on a device called the jellyball shooter, used to remove cannonball jellyfish from shrimp trawls. In 1987, the United States required all shrimp trawlers to equip their nets with TEDs. Two years later, the shrimp-turtle law was implemented, requiring all countries that export shrimp to the US to certify that the shrimp were harvested by boats equipped with TEDs.

Despite their effectiveness, there has been some resistance to the use of TEDs, with some fishermen believing that they cause a loss of shrimp and other targeted species. There are also a few drawbacks to TEDs. For example, larger sea turtles may be too large to fit through the escape hatches installed in most TEDs. Additionally, it is difficult to enforce TED compliance as they can reduce net efficiency, and it is easy to tamper with TEDs to increase fishing efficiency while eliminating their turtle-excluding properties.

To address some of these issues, the TTED (trash and turtle excluder device) was developed as a refinement of the TED. The TTED can free other forms of bycatch, in addition to turtles, and may also lead to a reduction in fuel consumption by boats.

Bycatch reduction devices (BRDs)

BRDs function by guiding larger fish towards an open hole in the trawl net, allowing them to escape before they reach the codend. This design ensures that only shrimp remain in the net, while larger fish, such as halibut, canary, and yelloweye rockfish, can swim away unharmed. The effectiveness of BRDs relies on proper water flow management, achieved through the use of a guiding panel, which directs the catch towards the BRD's escape exit.

The use of BRDs is strictly regulated, with current regulations mandating that each net must be equipped with at least one compliant BRD while fishing in certain areas, such as the Gulf of Mexico. For a device to be certified by the National Oceanographic and Atmospheric Administration (NOAA) as a BRD, it must demonstrate a minimum 30% reduction in bycatch weight through rigorous testing. This certification process ensures that shrimping operations adhere to environmental standards and minimise their ecological footprint.

The development and implementation of BRDs have been a collaborative effort between fishermen and biologists, and government agencies. For example, Oregon's shrimp industry worked closely with the Oregon Department of Fish and Wildlife, leading the mandatory adoption of BRDs in their fishery. This initiative resulted in a significant reduction in bycatch, enabling shrimp boats to operate in previously inaccessible areas due to high bycatch levels.

Trawl net shape and function

The primary feature of a shrimp trawler is the trawl net itself. The net is shaped like a flattened cone, with a wide front end that allows for a large range of capture. This flattened cone structure is designed to funnel caught shrimp downward. The "mouth" of the net is at the wide front end, and this is where the shrimp enter. The bottom of the mouth is fitted with weights, while the top is fitted with buoys that allow the top to lift up and open the mouth to catch the shrimp. In front of the bottom of the net is a metal chain known as a tickler chain. This tickler chain skims along just above the ocean floor, with the net itself lightly dragging along the bottom. The tickler chain jostles shrimp from the ocean floor, making them easier to catch. The shrimp are then funnelled downward through the cone-shaped net until they reach the "bag" at the narrow end of the cone, where they are kept until the net is hauled in.

The trawls are hauled in by the boat's powerful wenches, and the catch is then released on deck, where it is gathered, iced, or frozen for further sorting and processing. A shrimp boat may incorporate up to four trawls, with two on each side of the boat. These trawls are lowered into the water using outriggers—long, metallic poles that extend from the sides of the ship and help to stabilise the trawler in the water.

The shrimping industry has made significant advancements over the years to reduce the environmental impact of trawling. This includes the development of turtle excluder devices (TEDs) to allow turtles to escape and bycatch reduction devices (BRDs) to minimise the capture of other fish. These advancements not only help to protect the environment but also to sustain the shrimp fishery, which is crucial for the industry's long-term viability.

Environmental impact of shrimp trawling

Shrimp trawling has a significant negative impact on the environment. Trawling is the most popular and efficient way to harvest shrimp. It involves using a large specialised net, known as a trawl, that sinks towards the ocean floor and is pulled behind the trawler. While trawling is an effective method for catching shrimp, it has a number of environmental consequences.

Firstly, trawling can damage seabeds and corals. The nets used in trawling scrape the ocean floor, destroying the habitats of various marine organisms. This practice has been compared to ploughing a field, and while some newer trawling techniques cause less damage, they still inflict significant harm on the ocean floor.

Secondly, trawling often results in high levels of bycatch, which is the accidental capture of non-target species. According to the Food and Agriculture Organization of the United Nations (FAO), shrimp trawlers' nets can catch up to 25 times more non-target species than shrimp. This bycatch includes young fish, invertebrates, and even marine turtles, rays, and sharks. The bycatch is either sold or thrown back into the ocean, almost always dead, posing a threat to marine biodiversity and long-term food security.

Additionally, shrimp trawling can impact artisanal fishing communities. Traditional fishers often lose their catches to trawlers' large nets, as they scoop up a variety of marine life along with shrimp. This can create competition and conflict between industrial shrimp trawlers and small-scale fishers.

Furthermore, shrimp farming, which is closely linked to trawling, poses a significant threat to mangrove forests. Mangrove forests are often cleared to make way for shrimp farms, disrupting natural ecosystems and destroying crucial nurseries for marine species, including shrimp and fish. Mangrove forests also act as carbon sinks, binding up to four times as much CO2 as rainforests, so their destruction contributes to climate change.

While efforts are being made to mitigate the environmental impact of shrimp trawling, such as the development of new nets that reduce bycatch, it is clear that trawling continues to have a detrimental effect on marine ecosystems and biodiversity.

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