The purpose of this project was to study the selectivity of juvenile fish and Nephrops caught by Nephrops gear on two vessels with different horsepower. Is anecdotal evidence correct to suggest that gears towed by low-powered vessels are more selective than those towed by high-powered vessels? The assumption is that higher powered vessels can fish at faster towing speeds giving juvenile fish less opportunity to make escape attempts. There is also a perception that, in poorer sea states, greater power enables a vessel to maintain tension on the gear, making the codend less selective. Mallaig and North West Fishermen’s Association proposed a study to compare the selectivity of low- and high-powered vessels as a project under the Scottish Industry Science Partnership.
A 12 day research charter was commissioned to acquire data on the selectivity of juvenile fish and Nephrops when fishing on Nephrops grounds off Mallaig. At the request of the fishermen, the trip was split into two six day periods, separated by one week, to avoid strong tides that might affect fishing operations. Two local vessels, the Margaret Ann (low power) and Ocean Trust (higher power), carried out parallel, simultaneous fishing tows using Nephrops gear with 80 or 100 mm codends and 200 mm mesh square mesh panels (SMPs) fitted in the extension, 15-18 m from the codline, and extending 8 meshes into the taper of the net.
Fishing Grounds
Fishing was on commercial grounds to the west of Mallaig (ICES Area VIa). Severalgrounds (Table 1 and Figure 1) were targeted to provide a mix of roundfish and Nephrops.
Vessels
The vessels used for the charter were the Margaret Ann, a single-rig 177 kW trawler (L.O.A 17.2 m), and the Ocean Trust, a twin-rig 375 kW trawler (L.O.A 18.04 m) (Figures 2 and 3). The Ocean Trust was 198 kW more powerful than the Margaret Ann.
