## Facts

- The U.S. Fish and Wildlife Service (FWS) issued a five-year rule under Marine Mammal Protection Act (MMPA) § 101(a)(5)(A) authorizing incidental, nonlethal take (including harassment) of polar bears and Pacific walruses from oil and gas exploration activities in the Chukchi Sea and adjacent Alaska coast.
- The rule conditioned authorization on mitigation and monitoring measures and did not permit intentional killing.
- FWS concluded the expected take would involve a relatively small number of animals compared to affected stocks and would have a negligible impact on the species or stocks.
- The rule defined “small numbers” in relative, population-based terms and defined “negligible impact” as an impact not reasonably likely to adversely affect annual rates of recruitment or survival.
- Conservation organizations sued under the MMPA, Endangered Species Act (ESA), and National Environmental Policy Act (NEPA); the district court granted summary judgment for the government, and plaintiffs appealed.

## Issues

1. Whether FWS permissibly interpreted the MMPA’s “small numbers” requirement using a relative, population-based standard rather than a fixed numerical cap.
2. Whether FWS unlawfully collapsed the MMPA’s distinct “small numbers” and “negligible impact” requirements, making “small numbers” superfluous.
3. Whether FWS’s ESA and NEPA analyses supporting the rule were arbitrary or capricious, including regarding climate change, sea ice loss, and cumulative impacts.

## Decision

- The Ninth Circuit affirmed summary judgment for FWS and upheld the incidental-take regulations.
- The court held the MMPA does not unambiguously require a fixed numeric cap for “small numbers,” and FWS’s population-based interpretation was reasonable and entitled to deference.
- The court held FWS did not render “small numbers” meaningless because it treated “small numbers” (quantity/ratio of take) and “negligible impact” (population-level biological effect) as analytically distinct findings.
- The court rejected the ESA and NEPA challenges, concluding the agency relied on the best available science, adequately explained its determinations, and took the required hard look at environmental effects.

## Legal Principles

- When an environmental statute leaves a key term undefined and ambiguous, a reasonable agency interpretation may receive Chevron deference.
- Under MMPA § 101(a)(5)(A), “small numbers” may be determined using a proportion-of-stock approach; the statute does not compel a universal, fixed numerical ceiling across species and contexts.
- The MMPA’s “small numbers” and “negligible impact” requirements may overlap but must retain separate analytic roles: a threshold constraint on amount of take versus an assessment of effects on recruitment and survival.
- ESA and NEPA challenges to supporting analyses are reviewed under the arbitrary-and-capricious standard; courts uphold agency decisions supported by record-based reasoning and appropriate consideration of impacts and uncertainty.

## Conclusion

The Ninth Circuit sustained FWS’s MMPA incidental-take rule for Chukchi Sea oil and gas exploration, holding that a population-based reading of “small numbers” was permissible, that “small numbers” and “negligible impact” remained distinct statutory findings, and that the agency’s ESA and NEPA analyses were not arbitrary or capricious.


Ctr. for Biological Diversity v. Salazar, 695 F.3d 893 (9th Cir. 2012)