Introduction & Objectives

Species distribution models (SDMs) have been established as valuable tools for estimating the density and distribution of cetaceans and assessing potential impacts from anthropogenic activities. Habitat-based SDMs estimate cetacean density as a continuous function of habitat variables (e.g., sea surface temperature, mixed layer depth, etc.) and the resulting density estimates are spatially defined, typically at the resolution of the environmental data used for model development and thus show variation in species density and distribution. Given these advantages over other methods (e.g., design-based methods), the U.S. Navy has identified habitat-based SDMs as the most preferred method of density estimation for assessing potential impacts on cetaceans as required by U.S. regulations such as the Marine Mammal Protection Act, Endangered Species Act, and National Environmental Policy Act. 

Currently, region-specific SDMs have been used to support environmental planning efforts for the Navy’s individual study areas, which are typically addressed sequentially over time. This has created a few issues, particularly when the geographic scope of the assessments has expanded outside a regional SDM modeling area and overlaps an area that is covered by a different SDM. This has resulted in either “edge effects”, i.e., when density estimates at the boundary of two regional SDMs have substantially different values or sometimes results in inconsistent density estimates used for two different projects that cover the same geographic scope. When combined, substantial edge effects are apparent, particularly at the EEZ boundary which mirrors dramatic differences in the amount of survey coverage. Recently, when a need arose to model acoustic impacts from SURTASS modelling site center-points, to maintain consistency with the density estimates used for MITT, uniform density estimates were used instead of the spatially-explicit Kanaji et al. (2017) SDM estimates. This resulted in substantial edge effects for the expanded buffer around one of the SURTASS modeling sites, as well as the use of a less-preferred density estimate.

The objective of this project is to develop North Pacific-wide SDMs to provide substantial improvements to the density estimates used for the Navy’s environmental planning efforts throughout the Pacific. This will improve the Navy’s acoustic analyses and allow for more accurate take estimates. 

Technical Approach

Create a North Pacific modeling dataset including systematic sighting data with comprehensive coverage of North Pacific waters by combining data sets.

Develop separate seasonal density layers for regions and species with demonstrated variability in seasonal distribution.  

Progress & Results

In progress