Group behavior of common dolphins (Delphinus delphis) during prey capture

Abstract

FROM 1983 TO 1987, 54 FEEDING ASSOCIATIONGS BETWEEN COMMON DOLPHIN (DELPHINUS DELPHIS) AND SEABIRDS WERE OBSERVED WHILE FEEDING ON SHOALS OF FISH IN THE GULF OF CALIFORNIA. CAREFUL OBSERVATIONS WERE CONDUCTED ABOVE AND BELOW WATER OBSERVING THE NUMBER OF BIRDS AND DOLPHINS THAT FORMED THESE ASSOCIATIONS. COLLECTION AND IDENTIFICATION OF SAMPLES OF PREY SPECIES AND ENVIRONMENTAL DATA WERE ALSO TAKEN. EVIDENCE SIGGESTS THAT FISH SCHOOLS ARE ACTIVELY HERDED BY DOLPHINS, AS WELL AS SEA LIONS AND SEABIRDS. SARDINE, ANCHOVY AND MACKEREL WERE THE MAIN PREY IN THIS APPORTUNISTIC RELATIONSHIP AS EVIDENCED BY REGURGITIATION OF INGESTA COLLECTED FROM BOOBIES (SULA SPP) AND BY SAMPLES TAKEN IN THE MIDDLE OF THE FEEDING SWARMS. THESE ASSOCIATIONS OCURRED DURING SUMMER AND FALL, CLOSELY RELATED TO THE CHANGES IN UPWELLING ZONES AND ASSOCIATED SURFACES WATER TEMPERATURE THAT TAKES PLACE IN THE GULF OF CALIFORNIA.