Population dynamics of the New Zealand southern right whale (Eubalaena australis)

• Main Author: Davidson, Anthony
• Other Authors: Slooten, Liz, Rayment, William
• Format: Thesis
• Language: English
• Published: University of Otago 2016
• Subjects: Eubalaena australis; southern right whale; Population dynamics; Population modelling; Matrix population model; Conservation; New Zealand; Auckland Islands; Southern Right Whale
• Online Access: http://hdl.handle.net/10523/6212

The southern right whale (SRW; Eubalaena australis), was nearly extirpated from New Zealand (NZ) waters by commercial whaling in the nineteenth century. The NZ population is thought to be recovering, but precision of the estimated population growth rate is low and population dynamics affecting the estimates are unknown. Population models act as powerful tools for estimating the population dynamics of endangered and vulnerable species, and help determine the viability of possible conservation actions. This thesis uses matrix population modelling to develop an understanding of the population dynamics, and specifically population growth, for the NZ SRW. Reproductive estimates are critical for population models. This thesis produces the first estimate of reproductive output for the NZ SRW. The calving interval is estimated to be 3.11 years (95% CI 2.79-3.43). The matrix population model constructed in this thesis incorporates new estimates of life history parameters estimated from photo-identification data collected in Port Ross, Auckland Islands (2006-2012) and additional estimates from similar conspecific populations. A three-stage, female-only, life cycle was used to estimate population growth using matrix population modelling techniques. The deterministic population growth rate was estimated to be 5.6%. Parameter uncertainty in demographic parameters was accounted for by incorporating estimates of variability from NZ SRW and conspecific estimates. The population growth rate decreases from 5.6% to 4.8% after parameter uncertainty was accounted for (95% CI 2.5% and 6.4%). Population projections included a range of year to year variability (SD=0.1, 0.5 and 1). These estimates were used to assess trends in abundance over 30 years and future population growth. As this variability increased, the mean population growth decreased from 4.8% to 3.3%. Abundance after thirty years decreased from 4333 to 2992 individual females. Estimates also became less precise as year to year variability increased. To understand which matrix entries and lower-level demographic parameters would have the greatest effect on population growth, I conducted a perturbation analysis. This included sensitivity and elasticity of the projection matrix. The resulting estimates of this analysis indicate that adult survival will have the highest absolute (sensitivity) and proportional effect (elasticity) on the population growth rate. The population models demonstrated in this thesis, coupled with recent re-colonization of former habitats around the NZ mainland and evidence from congeneric populations, suggest that NZ SRWs may become exposed to impacts such as fishing and shipping in the future. Conservation management aimed at reducing anthropogenic impacts that affect survival (e.g. MPAs, shipping restrictions) will be vital during the re-colonisation of southern right whales to the New Zealand mainland.