Offshore windfarms - monitoring impacts on the commercial fishing industry: good practice guidance

Appendix E Overview of Common Scottish Fishing Practices

E.1 Demersal trawling

Demersal trawling is a form of fishing which drags a funnel-shaped net along or very close to the seabed to target demersal fish, such as cod, haddock or monkfish, and shellfish species, such as Nephrops. The most valuable demersal species recorded in 2022 was monkfish, accounting for six percent of total value from Scottish vessel landings. The size of the vessels can vary greatly, and the distance from the trawl doors to the end of the net (cod end) can be between 50 to 200 m (Figure 7-1) (Scottish Government, 2022).

Demersal trawls have the option to operate with one vessel and one net (otter) (Figure 7‑2a), one vessel with two nets (twin rig trawl) (Figure 7‑2b), or two vessels with one net (pair trawling) (Figure 7‑2c). The net function operates similarly with all three demersal trawling methods, the exception being pair trawling as otter doors are not needed there.

The net is held open laterally by trawl doors on either side (otter boards) and vertically by floats attached to the headline of the net. Where the net is in contact with the seabed (groundline/ground rope), the materials used often depend on the ground conditions and target species (Figure 7-2).

As the net is being dragged across the seabed, consideration for environmental impacts is required, such as through gear protection or through targeting specific species. Bobbins (rubber discs) may be attached to the groundline during trawls through uneven or rocky grounds. Demersal trawlers working soft sandy and muddy substrate (e.g. to target Nephrops) may use lighter materials in the groundline, due to the need to disturb seabed dwelling species in these habitats. Lighter gear may also be used in sensitive areas, to reduce the impacts on the seabed (Seafish, 2023a).

Demersal trawling from Scottish vessels is the second most utilised fishing method (Seafish, 2023a). Between 2018 – 2022, demersal trawling accounted for 25.2% (525,969 tonnes) of all live weight caught. The commercial value of the demersal trawling effort was the greatest of all the methods accounting for 37.7% (£1,074,153,294) of revenue between 2018 – 2022 (Scottish Government, 2022).

E.2 Pelagic trawling

Pelagic trawling is similar in design to demersal trawling; however, the targeted species dwell within the mid-water as opposed to the seabed. The most valuable pelagic species recorded in 2022 was mackerel, accounting for 35% of total value from Scottish vessels’ landings (Scottish Government, 2022). Similarly to demersal trawling, the size of the vessels and the distance from the trawl doors to the cod end can vary greatly, the latter varying between 50 to 200 m (Scottish Government, 2022).

Pelagic trawls have the option to operate with one vessel with one net (pelagic trawl), or one net between two vessels (pelagic pair trawling) (Figure 7‑3). The net is held open laterally by trawl doors on either side (otter boards), and vertically by floats attached to the headline of the net. The net has weights attached to the bottom of the net and the positioning of the net is dependent on the vessel speed and trawl warp (Figure 7‑4) (Bilec, and Obreja, 2020; Seafish, 2023b).

Pelagic trawling collects large volumes of pelagic fish, due to the size of the nets, and therefore, accounts for a high amount of live weight. Between 2018 – 2022 pelagic trawling accounted for 60.5% (1,262,553 tonnes) of all live weight caught. The commercial value of the pelagic trawling fishing effort accounting for the second highest revenue of 36.1% (£1,029,682,912) between 2018 – 2022 (Scottish Government, 2022s).

E.3 Scallop dredging

Scallop dredging vessels use a rigid metal frame onto which a chain mail bag is attached (Figure 7‑5). At the mouth, a series of spring-loaded teeth are present, which penetrate the seabed, dredging the mostly sedentary and seabed dependent scallops (Seafish, 2023c).

Scotland has restrictions on the number of scallop dredges which can be used under ‘The Regulation of Scallop Fishing (Scotland) Order 2017’, where dredges are limited to:

• Scottish inshore waters (0 – 6 NM)
• No more than 8 scallop dredges from each of the port and starboard sides of the fishing boat; or
• No more than 16 scallop dredges in total;
• Any other part of the territorial sea of the United Kingdom adjacent to Scotland (6 – 12 NM)
• No more than 10 scallop dredges from each of the port and starboard sides of the fishing boat; or
• No more than 20 scallop dredges in total; and
• Any other part of the Scottish zone (12 – 200 nm)
• More than 14 scallop dredges from each of the port and starboard sides of the fishing boat; or
• More than 28 scallop dredges in total.

Scallop dredging from Scottish vessels is the third most utilised fishing method. Between 2018 – 2022 demersal trawling accounted for 4.2% (87,648 tonnes) of all live weight caught (Scottish Government, 2022). The commercial value of the scallop dredging additionally accounted for the fourth highest revenue of 6.0% (£170,186,467) between 2018 – 2022 (Scottish Government, 2022).

E.4 Creeling (pots and traps)

Creel fishing, also referred to as fishing with pots and traps, targets various shellfish species such as crab, lobster, Nephrops and whelks. Multiple traps are set along a length of seabed, marked by either dhans (marker flags), buoys or cans (Figure 7‑6a). The design of the creels may vary dependant on the targeted species; however, most designs include a bait holder, eye, and door as shown in Figure 7‑6b. The number of creels deployed will depend on the size of the vessel and number of crew, with larger vessels allowing for longer strings across a larger area. Inshore creel vessels are usually relatively small, under 10 m, and consist of one or two crew members. The engine size of the vessels and weather conditions dictate how far offshore the vessel can travel to fish (Scottish Creel Fishermen’s Federation, 2023). Larger creel vessels may include a vivier tank, where specimens can be kept fresh until landing. In 2021 there were 879 active creel vessels in Scotland (Scottish Government, 2022).

Creel fishing from Scottish vessels is the fourth most utilised fishing method. Between 2018 – 2022 creel fishing accounted for 3.5% (73,725 tonnes) of all live weight caught (Scottish Government, 2022). The commercial value of the creel fishing accounted for the third highest revenue, 11.6% (£330,973,238), between 2018 – 2022 (Scottish Government, 2022).

E.5 Other fishing types

Pelagic trawls, demersal trawls, scallop dredging, and creel fishing are the primary fishing methods used by Scottish vessels. A variety of other methods used by Scottish fishing vessels include:

• Pelagic seine (Figure 7‑7a);
• Demersal seine (Figure 7‑7b);
• Longlines;
• Drift and fix nets;
• Handlines;
• Beam trawl.

The most commonly used method of the other fishing methods is seine fishing. Pelagic seine fishing, also referred to as purse seine, uses a large net shot around a shoal of fish which are then slowly hauled onboard (Figure 7‑7). Demersal seine fishing deploys the net from the back of the vessel and gradually reels the net in (Figure 7‑7) (Seafish, 2023e; 2023f).

Between 2018 – 2022 these other fishing methods from Scottish vessels accounted for 6.6% (137,637 tonnes) of all live weight caught, with seine fishing responsible for 4.2% (87,463 tonnes) (Scottish Government, 2022). The commercial value of the other fishing methods from Scottish vessels accounted for revenue of 8.6% (£245,466,297) between 2018 – 2022 (Scottish Government, 2022).

E.6 References

Bilec, M. and Obreja, C.D., 2020, September. Ship resistance and powering prediction of a fishing vessel. In IOP Conference Series: Materials Science and Engineering (Vol. 916, No. 1, p. 012011). IOP Publishing.

Scottish Creel Fisherman’s Federation. 2023. Scottish Creel Fishing. Available at: SCFF website [Accessed January 2024]

Scottish Government (2022). Scottish Sea Fisheries Statistics 2022. Available at: Scottish Government website [Accessed January 2024]

Seafish (2023a). Demersal Trawl – General. Available at: Seafish website [Accessed January 2024]

Seafish (2023b). Pelagic Trawl– General. Available at: Seafish website [Accessed January 2024]

Seafish 2023c. DRB - Scallop Dredge. Available at: Seafish website [Accessed January 2024]

Seafish 2023d. Pots and Traps – General. Available at: Seafish website [Accessed January 2024]

Seafish 2023e. PS-Purse Seine Available at: Seafish website [Accessed January 2024]

Seafish 2023f. SSC-Scottish Seine. Available at: Seafish website [Accessed January 2024]