The effect of different numbers of tickler chains on beam-trawl catches

An attempt is undertaken to analyse the ground-rope effect on the efficiency of beam trawls in assessing population densities of epibenthic animals, such as demersal fishes, shrimps, crabs, asteroids, ophiuroids, and gastropods, which burrow to a greater or lesser degree. Experimental beam-trawl hauls were carried out with different numbers of tickler chains. The results obtained in sandy as well as in muddy areas are discussed. In general, no significant effect of the number of tickler chains was found at muddy stations. At sandy stations, on the other hand, the number of tickler chains showed a positive effect on the catches of species that burrow occasionally and species that cling tightly to the bottom. In some species the catches reached an asymptotic level with increasing number of chains, whereas in other cases the increase in the catches was still significant even when reaching the maximum of 6 chains.