The National Marine Fisheries Service has finalized a rule and issued a letter of authorization letting the U.S. Navy incidentally take marine mammals during training and testing with Surveillance Towed Array Sensor System Low Frequency Active sonar, known as SURTASS LFA. The authorization runs seven years, from August 12, 2026, through August 11, 2033, and covers the western and central North Pacific Ocean and the eastern Indian Ocean.

SURTASS LFA is a Navy sonar system. The new rule gives the Navy a legal basis to run that system in these two ocean regions through August 11, 2033.

The legal mechanism

NMFS issued the authorization under the Marine Mammal Protection Act, which bars the take of marine mammals except in specific cases. The MMPA defines "take" as to harass, hunt, capture, or kill a marine mammal, or to attempt any of those. Section 101(a)(5)(A) lets NMFS allow the incidental take of small numbers of marine mammals when it finds the activity will have a negligible impact on the species or stock, and no unmitigable adverse impact on the availability of the species or stock for subsistence use. Before issuing a letter of authorization, NMFS must also prescribe the permissible methods of take and set mitigation, monitoring, and reporting requirements aimed at the least practicable adverse impact on the animals and their habitat.

The Navy's SURTASS LFA training and testing qualifies as a military readiness activity under the MMPA, as amended by the National Defense Authorization Act for fiscal year 2004 and the fiscal 2019 NDAA.

What the 2004 defense law changed

The 2004 NDAA, Public Law 108-136, rewrote how the MMPA applies to military readiness activities. It removed the old requirement that an incidental-take authorization cover only "small numbers" of animals within a "specified geographical region." It also split the law's definition of harassment into two levels for these activities. Level A covers any act that injures a marine mammal or has significant potential to injure one. Level B covers any act that disturbs, or is likely to disturb, natural behavior such as migration, surfacing, nursing, breeding, feeding, or sheltering, to the point that the behavior is abandoned or significantly altered.

The same law also set what NMFS must weigh when it decides on the "least practicable adverse impact" for a military readiness activity:

  • personnel safety
  • how practical a mitigation measure is to carry out
  • the activity's military effectiveness

Filing and comment status

NMFS filed the rule as FR Doc. 2026-15206. It was published in the Federal Register as 91 FR 47664, after appearing on public inspection on July 27, 2026. The public comment period on the rule has closed.

What to watch

The authorization holds through August 11, 2033. Questions on the rule go to Alyssa Clevenstine in the NMFS Office of Protected Resources.