Improving fishing techniques

Do we know how fish are caught? Which methods and tools are used? Or, how various methods of fishing can impact the environment?

Which are the three most common fishing techniques in Europe?

The European Commission has grouped the different gears according to three major fishing techniques depending on how they are used. In the EU, fishing techniques are classified under three gear groups:_[1]

• Towed gear: It literally drags a net “bag” across the bottom of the ocean floor for capturing bottom-dwelling sea life (e.g. flatfish, mussels, and some cod species). Essentially, fishermen are “towing” their catch.
• Mobile gear: Seines, longlines and trolling lines (which are either nets or lines with hooks) are usually being used in the open water column. Techniques like these are effective for schooling fish species like sardines, herring or mackerel.
• Passive gear: Traps, nets or lines with hooks are anchored or left to drift in the water. Essentially, this widely used technique passively catches fish, rather than actively drawing them in.

What’s the environmental impact of these fishing techniques?

Towed gear

All towed gear can be quite fuel intensive since fishing boats actively drive to pull their net-bags. And since this technique involves contact with the ocean floor, they can impact habitats.

The gear with the least habitat impact is the midwater trawl, since this net-bag is dragged mid-water without touching the ocean floor.

_{Midwater trawl}

Generally, towed gear is not species selective, since a variety of species live on/in the bottom sediment. Catching unwanted fish means that fishermen have to throw them back into the ocean, but most fish do not return alive and are just wasted. When fishing for a specific size, it becomes tricky with trawls because mesh net sizes must be small enough to catch small organisms (like shrimp).

_{Beam trawl}

The towed gear that can catch specific-sized fish is the demersal seine. And, the demersal seine has a low bottom impact since it has no heavy parts scraping the sediment. However, unfortunately demersal seines may not reduce by-catch, since they are limited in catching specific species.

_{Towed dredge}

Mobile gear

The benefit of mobile gear is that you can catch specific fish species, which helps reduce by-catch. The most selective gear is the purse seine, which is used for tuna. Purse seine is a huge net that closes around a school of tuna from underneath. Before the 1980s, purse seining had caught thousands of dolphins as bycatch each year, but with management actions and economic pressures entailed a massive decline. Today, the annual by-catch of dolphins is less than 0.1%._[2]

_{Purse seine}

This type of gear is selective and has almost no impact on the bottom habitats, since it occurs in the pelagic water zone. But purse seines have small mesh sizes and cannot catch fish based on size.

_{Trolling line}

The most unselective gear (with the most by-catch) is the trolling line. Trolling lines can be unselective since these are lines with hooks and bait, which can attract sharks, turtles, and birds as well.

In terms of fuel consumption, mobile gear varies due to the different travel times to find schools of fish.

Passive gear

Passive gear includes nets, lines or traps. These types of gears have little to no impact on habitats, because most of them are not in contact with the bottom. However, passive gear can also accidentally catch other kinds of fish.

For example, gillnets are anchored or left to drift in the water column. Fish are captured when they swim through the net, which catches their gills (hence the name gillnets). But, larger animals such as cetaceans (whales, dolphins, and porpoises) are at times unable to detect the nets and become entangled.

_{Midwater gillnet}

Traps and lines, on the other hand, are able to catch fish by species and size. For traps, fishermen can manage size well, as small fish can swim straight through and fish that are too big simply cannot enter. Lines are size-selective due to hook sizes, so small fish cannot bite on bigger hooks

_{Bottom longline}

Habitat damage is low with traps—though, they have small impact when deployed since traps come in contact with the bottom. Lines have basically no impact since these are lines simply hanging in the open water.

_{Bamboo pot trap}

An added bonus with passive gear is that most bycatch is returned to the ocean alive. All the passive gears are relatively fuel-efficient since fuel is only used for deploying and retrieving the gear.

_{Funnel trap}

Which fishing gears have the highest environmental impact?

Unfortunately, to this day there are no fishing techniques or gear that have zero environmental impact, from physical destruction of sea bottoms (affecting habitats), catching unwanted species and wrong-sized fish, to the carbon footprint of fishing boats.

The gears with highest habitat impact are dredges and demersal trawls. They have more by-catch, especially trawls since they are the least species, and size-selective gears. The more sustainable gears to look for are traps and lines.

It is also important to understand that as long as we want to eat certain species of fish or seafood, some fishing techniques are unavoidable. You cannot, for example, catch flatfish with passive or mobile gear, at least not yet.

So when buying fish, the most sustainable fish-choice is to go for open-water living species, because the gears used to catch them seem to only be impacting vulnerable species caught as by-catch and not habitat on top.

If you want to know more about fishing techniques, you can take a look at Seafood Watch and EUMOFA, as both have detailed descriptions of various fish species to see how they are fished, where and if the fish stock is healthy or declining.

Author: Jessica Tengvall

Let’s discuss:

• Are you optimistic that we will find sustainable fishing methods?

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