Abundance and diversity of fish on mussel farms in New Zealand

Fish are often attracted to floating structures, particularly as juveniles, and in many parts of the world longline mussel farms provide complex, three-dimensional floating structures in coastal waters. There have been few quantitative studies of the assemblages of fish living on and around mussel farms. We sampled fish on mussel farms at three sites in the north of the South Island of New Zealand over a year to characterise the assemblages present and their variability. Predictions of the species likely to be present were made on the basis of their occurrence in the general area, habitat preferences, and occurrence around floating structures in previous studies. The farms differed in their degree of exposure, distance from shore and degree of riverine and oceanic influence. Fish were sampled by underwater visual census, and a remote-operated vehicle, and destructively sampled using an anaesthetic. Abundances of fish on the mussel lines were small (median values up to 1.25 fish m(-1) of line) and were dominated by small, demersal species characteristic of rocky reefs in the area, notably triplefins (Forsterygion lapillum and Grahamina gymnota, Family Tripterygiidae) and the wrasse Notolabrus celidotus. The abundances and species of fish present differed among sites and among sampling methods (but the small and inconsistent numbers of fish recorded precluded formal statistical testing of differences). Few large, commercially or recreationally important species (demersal or pelagic) were recorded. Triplefins may recruit to the lines at settlement from planktonic larvae and spend their entire lives there. N. celidotus, in contrast, may recruit to stands of macroalgae on nearby rocky reefs and move to farms later. Direct recruitment of N. celidotus may be limited by the low abundances of macroalgae on the mussel lines. (c) 2005 Elsevier B.V. All rights reserved.