There is a multitude of different fishing gears that are used to catch fish. These gears generally vary in the scale of fishing undertaken, and are dominated by a few categories of gear. These different gear types and categories range in their impact on the ecosystem’s habitat. In addition to my work on reduction fisheries, I have started a project on global fisheries gear use to assign all fisheries catches to a general gear type based on the fishery, country, species, and time period. This will give a great insight into the evolution of gear use over time and global trends associated with gear use; but, it has also made me think more about the effects of different gears.
The two main gears most important to dedicated reduction fisheries are pelagic trawls and purse seines. A pelagic trawl, or mid-water trawl, is a net towed behind a boat that is
targeting species not on the ocean floor. This is in contrast to a bottom trawl that generally targets species that live on or near the ocean floor. In contrast to the bottom trawl, a pelagic trawl has a minimal impact on the ocean floor, as it is not meant to touch it. Gears like bottom trawl fisheries have a large impact on the surrounding ecosystem by catching non-target fish and changing the physical structure of the ocean floor ecosystem. As pelagic trawls don’t drag along the ocean floor, it also catches less of species that are not targeted, both fish and otherwise, a common complaint against bottom trawl fisheries.
Purse seines on the other hand operate by releasing a net off a fishing boat and then making a sharp turn in a circle to meet up with the net. In this way, the net
surrounds a targeted school of fish and then the ‘purse wire’ is drawn tight at the bottom
of the net like an old-styled purse with a drawstring. The fish can then be brought aboard from the contained net. Purse seines are frequently used to target fish for fishmeal like Peruvian anchoveta, Atlantic herring, and Chilean jack mackerel, but are also a major gear for tuna fisheries worldwide.
While these gears make up the majority of dedicated reduction fisheries, by-catch from bottom trawls (including shrimp trawls) are increasingly retained and turned into fishmeal. I have touched on this earlier in my post on sources of fishmeal and this gear
is important as both a source of by-catch and for ‘biomass fishing’. As bottom trawls are highly nonselective in the species they catch, this is problematic in monitoring the health of the individual fish populations. Furthermore, this method of fishing can have destructive impacts on the physical structure that is often built by slow growing organisms such as corals. This physical structure is important for the ecosystem as it creates a sheltered environment for small and juvenile fish, and other organisms.
Both pelagic trawls and purse seines are considered relatively ‘clean’ gears with little or no by-catch when compared to other gears. The other major difference in these gears is that they have relatively low fuel use per tonne of fish landed when compared to other gears like bottom trawls. This makes them ‘cleaner’ from a carbon footprint standpoint, as fuel use is a major contributor to the carbon footprint of fisheries, and to fishmeal and oil production. These dedicated reduction fisheries generally operate as a very low-impact fishing method when compared to other fishing gears. However, as more and more fish for fishmeal is coming from by-catch of bottom trawl fisheries and a shift toward biomass fishing, the general trend seems to be a shift from these cleaner methods to a more problematic method of fishing for fishmeal. As a whole this would signal a shift from lower impact fishmeals to higher impact fishmeals mainly based on the gear being used for catching the fish. This highlights the importance of gear when evaluating different forms of fishing for feed.