Insights into North Pacific right whale Eubalaena japonica habitat from historic whaling records

摘要

Whaling records from the mid-1800s provide the largest set of observations with which to conduct a basin-scale analysis of potential North Pacific right whale Eubalaena japonica habitat. Since these data lack the concurrent oceanographic data necessary to investigate the species’habitat characteristics I used ocean climate from a 20th century circulation model to create a suitable set of habitat predictors. My goals were to (1) identify regions of suitable habitat and (2)investigate the processes underlying the species–habitat relationship by (3) examining model performance at different spatial and temporal scales. The results show 2 non-overlapping habitat regions in the subarctic North Pacific, supporting the notion of 2 distinct subpopulations. The analysis also implicates surface temperature and temperature variability as strong indicators of potential right whale habitat. Tests of model performance at different scales strongly suggest that at the basin-scale, right whales use regions of cold water with low inter-annual variability and high within-season variability (i.e. areas where high frontal activity occurs predictably from year to year). The significance of these indicators decreased at the egional scale emphasising the coupling of scale and process, and thus the need for different predictors at different scales. Comparisons of models built using different subsets of the dependent data showed how hypotheses can be tested and potential biases in observational data can be explored. Analyses of rare species’ habitat such as this can provide guidance for more directed survey efforts and help identify areas and processes of potential biological importance.