Section 4(d) of the Endangered Species Act (ESA) directs NOAA Fisheries to issue regulations to conserve species listed as threatened. This applies particularly to “take," which can include any act that kills or injures fish, and may include habitat modification. The ESA prohibits ANY take of species listed as endangered, but some take of threatened species that does not interfere with salmon survival and recovery can be allowed.

Before 2000, NOAA Fisheries Service had simply adopted 4(d) rules that prohibited take of threatened species. In a salmon and steelhead 4(d) rule (PDF 468KB) signed in July of 2000, the agency pioneered a new approach. It applied take prohibitions to all actions except those within 13 “limits” to the rules (described in detail in the rules) where the specified categories of activities contribute to conserving listed salmon. A separate but closely related tribal 4(d) rule (PDF 138KB) created an additional limit for tribal resource management plans.