TY - JOUR
AU - Brandão, A.
AU - Butterworth, D.S.
PY - 2020/10/22
Y2 - 2021/04/21
TI - Concerning demographic limitations on the population growth rate of West Australian (Breeding Stock D) humpback whales
JF - J. Cetacean Res. Manage.
JA - JCRM
VL -
IS - 3
SE -
DO - 10.47536/jcrm.vi3.328
UR - https://journal.iwc.int/index.php/jcrm/article/view/328
SP - 201-208
AB - <p>The upper bound of 0.126 on the maximum demographically possible annual growth rate for humpback whales that has standardly been imposed<br>on recent applications of age-aggregated assessment models for this species in the IWC Scientific Committee, is based on an analysis that assumes<br>steady age structure. It is conceivable that transient age-structure effects could admit greater population growth rates for short periods than suggested<br>by such a bound. This possibility is addressed by developing an age-structured population model in which possible density dependent changes in<br>pregnancy rate, age at first parturition and natural mortality are modelled explicitly, and allowance is made for the possibility of natural mortality<br>increasing at older ages. The model is applied to the case of the west Australian humpback whale population (Breeding Stock D), for which breeding<br>ground surveys over the 1982–1994 period provide a point estimate of 0.10 for the annual population growth rate. Results based upon the breeding<br>population survey estimate of abundance of 10,032 in 1999 suggest that 0.12 is the maximum demographically feasible annual rate of increase for<br>this stock over 1982–1994 if it is a closed population. This result is based on essentially the same parameter choices as led to the earlier r = 0.126<br>bound, i.e. that in the limit of low population size the age at first parturition approaches five years from above, the annual pregnancy rate 0.5 from<br>below, and the annual natural mortality rate 0.01 from above. Transient effects do not appear able to reconcile the observed rate of increase with<br>less extreme values of demographic parameters than led to the previously imposed upper bound of 0.126 on the maximum possible annual growth<br>rate. Although use of extreme values reported for demographic parameters for Northern Hemisphere humpback whale populations, rather than those<br>considered here, would reduce this suggested maximum rate of 0.12, the conclusion that transient effects have a very limited impact on observed<br>population growth rates would be unlikely to change.</p>
ER -