STRUCTURE AND SEASONAL FLUCTUATIONS OF ROCKY LITTORAL FISH ASSEMBLAGES IN SOUTH-WESTERN PORTUGAL - IMPLICATIONS FOR OTTER PREY AVAILABILITY

The fish assemblages of rocky intertidal and subtidal (<3 m depth) hab itats of the southwestern Portuguese coast were sampled between May 19 92 and November 1993, using traps, angling and hand-netting, to invest igate their structure and seasonal dynamics. The main purpose of the s tudy was to describe the patterns of prey availability for marine-feed ing otters (Lutra lutra L., Mammalia) in south-western Portugal, and t o compare these with other areas in Europe. A total of 475 fish of 14 species was captured over 150 d of trapping (788 trap-days), and 1575 fish of 15 species were captured over 24 d of angling (76.3 h). Hand-n etting was carried out occasionally, to supplement the observations fr om the other methods, and only 96 fish of seven species were captured. The three methods yielded different patterns of the fish assemblage: giant gobies (Gobius cobitis Pallas, 33.7%) and rock gobies (G. pagane llus L., 22.9%) were the most frequently trapped fish; corkwing wrasse (Symphodus melops (L.) 81.2%) were the usual species caught by anglin g; shannies (Lipophrys pholis (L.), 42.7%) and Montagu's blennies (Cor yphoblennius galerita (L.), 28.1%) were the most frequently netted spe cies. Conger eels (Conger conger (L.)) giant gobies and shannies showe d an uneven distribution along the coast, occurring most frequently in schist shelves, rather than in areas of large sandstone boulders. The re was a large seasonal variation, with the catches of most species pe aking in winter and early spring, including the majority of those most important in the diet of otters: conger eels, shore rocklings (Gaidro psarus mediterraneus L.) rock gobies and corkwing wrasse. This was als o the period when the individuals of several species were heaviest. Sh annies and Valenciennes' blennies (Lipophrys trigloides Valenciennes), which are also important in the diet of otters, showed a peak in capt ures in late spring and early summer. The numbers caught in late summe r and autumn were comparatively low, and this is suggested to be the ' lean season' to otters in south-western Portugal, whereas the winter i s the period of maximum prey abundance for the species. This pattern o f prey abundance is different from that found in other areas of Europe .