Seasonal movements of short-beaked common dolphins (Delphinus delphis) in the north-western Bay of Plenty, New Zealand: influence of sea surface temperature and El Nino/La Nina

Movement patterns of small cetaceans are influenced by a great number of va riables including prey availability, sea floor profile, thermocline, oxygen minimum layer. and sea surface temperature (SST). Presented here are data on short-beaked common dolphins (Delphinus delphis L.) in New, Zealand, sho wing a seasonal offshore-shift in their distribution, which appears to be c orrelated with SST. D. delphis moved from a mean distance of 9.2 km (SD = 4 .42) from shore in spring and summer to a mean distance of 20.2 kin (SD = 3 .86) from shore in autumn. During warmer La Nina conditions their mean dist ance from shore was further reduced to only 6.2 km (SD = 2.56), and offshor e movement was delayed by a month. Worldwide, D. delphis can be found throu ghout a wide range of sea temperatures, and it is therefore unlikely that S ST is the primary factor influencing their distribution. It is hypothesised , that SST influences the distribution of D. delphis prey, which in turn af fects their seasonal movements.