SELECTIVITY OF SQUARE MESH CODENDS ON PELAGIC TRAWLS FOR ATLANTIC MACKEREL (SCOMBER-SCOMBRUS L)

To assess possible management strategies for conserving small, immature Atlantic mackerel (Scomber scombrus L.), selectivity trials were undertaken in the western English Channel aboard F.V. Marbella (H99) during the period 24 January to 6 February 1990. An experimental codend of 60 mm polypropylene knotless square netting was attached to a 3700 Ijmuiden stores midwater trawl (Type No. P. 101.B) used with superkrub doors. This experimental gear was fished against a similar trawl fitted with a codend constructed from 40 mm knotted nylon mesh rigged in the conventional diamond configuration. A total of 14 successful tows were made, nine using the trawl fitted with the experimental codend and five using the standard trawl. An estimated total catch of some 470 tonnes of mackerel was taken using both gears, and mackerel were caught on all tows except one. The size composition of the mackerel caught ranged from 18 to 37 cm, well within the expected selection range for the gear under test. A comparison of the length-frequency distributions indicated that there was no difference in the size composition, and hence selection, of fish taken by the two gears.