Estimating historical eastern North Pacific blue whale catches using spatial calling patterns.

Area of Science:

• Marine Biology
• Conservation Science
• Bioacoustics

Background:

• Blue whales (Balaenoptera musculus) are endangered globally, with unclear population structures in the North Pacific.
• Estimating pre-exploitation abundance and recovery for the eastern North Pacific (ENP) population is hindered by difficulties in separating historical catches from other North Pacific populations.

Purpose of the Study:

• To create the most current estimates of North Pacific blue whale catches by collating previously unreported Soviet catches with known catches.
• To differentiate historical catches between the ENP and western North Pacific (WNP) blue whale populations using acoustic call data.

Main Methods:

• Combined previously unreported Soviet catches with known catches to estimate total North Pacific blue whale catches.
• Utilized generalized additive models fitted to acoustic call patterns to estimate the spatiotemporal occurrence of blue whales.
• Differentiated ENP and WNP blue whale catches based on the proportion of distinct acoustic calls recorded by latitude, longitude, and month.

Main Results:

• Total North Pacific blue whale catches were estimated at 9,773 from 1905-1971.
• Eastern North Pacific blue whale catches were estimated at 3,411 (35% of total), while western North Pacific blue whale catches were estimated at 6,362 (65% of total).
• Acoustic data uncertainty influenced results more than catch location/date uncertainty, with findings being relatively insensitive to ecological assumptions.

Conclusions:

• This study provides crucial data for future research on blue whale population recovery and the impact of anthropogenic mortality.
• Accurate historical catch data is essential for understanding population dynamics and informing conservation strategies for endangered whale species.