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 variables 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, showing a seasonal offshore-shift in their distribution, which appears to be correlated 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 distance from shore was further reduced to only 6.2 km (SD = 2.56), and offshore movement was delayed by a month. Worldwide, D. delphis can be found throughout a wide range of sea temperatures, and it is therefore unlikely that SST is the primary factor influencing their distribution. It is hypothesised, that SST influences the distribution of D. delphis prey, which in turn affects their seasonal movements.