Research Document - 2006/054

A review of the analysis to evaluate the recovery of bowhead whales, Balaena mysticetus, in the eastern Canadian Arctic

By Alvarez-Flores, C.M.

Abstract

The present investigation calculates possible times to recovery of the bowhead whale population of the eastern Canadian Arctic Ocean, based on the limited knowledge currently available. Recovery was defined as the population growing up to 70% of the assumed pre-exploitation abundance. The simulation used a stochastic generalized logistic model and considered alternative assumptions about parameter values; current status and possible future catch levels. One single stock was assumed to constitute the bowhead whale population in the eastern Canadian Arctic, including Prince Regent Inlet, Baffin Bay, Davis Strait, Hudson Bay and Foxe Basin. The uncertainty associated with the current level of knowledge about the population dynamics and status of the bowhead whale population in the eastern Canadian Arctic leads to a wide range in the possible times to recovery. Results indicate that improvements in the estimate of the current population size would considerably narrow the range in times to recovery. Of all harvest levels explored, a removal of 50 animals caused the greatest delay in the time to recovery. Removing 15 animals per year can cause a considerable delay under some parameter assumptions, but if the catch is below 10 animals, there is virtually no delay in the time to recovery. This result will hold under the assumptions that this population is appropriately described by a logistic model with parameter values within the range used in the present analysis; that current environmental conditions won’t change beyond the limits imposed by the model (including the occurrence of catastrophic events); and that there are no other significant sources of mortality. Finally, the behaviour of the component of process error in the population model indicated that values of σ_process 0.015 and higher lead to annual growth values that may be unrealistic for the population of bowhead whales in the eastern Canadian Arctic. On the other hand, all tested values of σ_process allow negative growth when the population is approaching carrying capacity, but only if set to 0.2 or higher, can the population present negative growth at lower population levels. Although this can be considered a caveat of this component of the model, it was considered to be acceptable to represent natural variability. Fluctuations in the annual growth due to process error are expected to be smaller than the observed fluctuations in the eastern stock of gray whales and a choice of σ_process of 0.01 and σ of 0.8 was made for the analysis.

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