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Keywords:

  • birth seasonality;
  • calf survival;
  • reproduction;
  • demographic stochasticity;
  • bottlenose dolphins;
  • Fiordland;
  • New Zealand

Abstract

Understanding the reproductive parameters of very small or declining populations is of clear importance to conservation. From 1995 to 2011 we recorded calf production (n = 71) and calf survival for 27 breeding females in the bottlenose dolphin (Tursiops truncatus) population in Doubtful Sound, New Zealand; a population with a recent history of declining abundance. Overall, 67% of calves survived their first year, and 40% survived to 3 yr (or are 2 yr old and still alive). Most calves that died in the first year died in their first month (87%). Multiparous mothers (n = 18) showed high variation in calf survival. The most successful six had all but one of their 20 calves (95%) survive to 1 yr. Fourteen of the 20 (70%) survived to 3 yr, and another four are still alive and are 1 or 2 yr old. In contrast, the least successful seven mothers produced a similar number of calves (21), eight of which (38%) survived to 1 yr, and none to 3 yr. Here we describe calving seasonality and calf survival, observed over 16 yr, and show that large variation in reproductive success of individual females is an example of extreme demographic stochasticity in this small, endangered population.