Aim: This study is the first in Indonesia to assess historical sperm whale (Physeter macrocephalus) seasonal distributions by combining historical whaling data with environmental factors associated with sperm whale habitat preferences. Since current records of whale occurrence covering the whole of Indonesian waters are incomplete, we used historical whaling data summarized by Charles Haskins Townsend in 1935 to model its potential distribution for each season.

Location: Indonesian waters (92-143E, 9N-14S)

Taxa: Sperm whale (Physeter macrocephalus)

Methods: We used a presence-only habitat model -Maximum Entropy (Maxent)-, and a presence-pseudo-absence method -Generalized Additive Model (GAM)- with nine submerged topographic variables to predict historical seasonal distributions.

Results: Both Maxent and GAM predict similar potential distribution which align closely with the whaling data. The results indicate that in four areas in the eastern part of Indonesia, no seasonal differences occurred in sperm whale distribution, while noticeable seasonal differences were indicated in other areas. The key parameters that characterise sperm whale habitat in both models were distance to coast, distance to -1000m and -5000m isobaths, and submarine key features such as trough and trench.

Main conclusions: The historical catch data of this species can be used to describe the historical species distribution and provide a baseline to assess present distribution, prioritize current research and monitoring, and recommend future data collection. Our models also predict distributions that are significantly larger than the ones occupied by sperm whales nowadays, another example of a shifting baseline. Our study demonstrates the benefits of incorporating historical whaling data into habitat models for ecological investigation and to inform conservation efforts for cetaceans.

The original data are available from Townsend (1935) through the permission from New Bedford Whaling Museum. We proceeded the original data by converting the data into a raster format using ArcGIS 10.6.1.