The Navy's Proposed Action is the same as the Proposed Action in the 2011 GOA Final EIS/OEIS and Record of Decision, which is to continue conducting periodic military training activities in the Gulf of Alaska, specifically the Temporary Maritime Activities Area, to ensure the Navy accomplishes its mission to maintain, train, and equip combat-ready military forces capable of winning wars, deterring aggression, and maintaining freedom of the seas.

The purpose of this document is to supplement the environmental impact analyses contained in the 2011 Final EIS/OEIS. This Supplemental EIS/OEIS compares the environmental impacts predicted in the 2011 EIS/OEIS to current circumstances and information. The 2011 Final EIS/OEIS used an acoustic modeling methodology and marine mammal density information that was the best available at that time. Following the completion of the 2011 Final EIS/OEIS, a new modeling system, Navy Acoustic Effects Model (known as NAEMO), was developed. By using this more technologically advanced modeling software and revised acoustic criteria, the predicted impacts on marine mammals are expected to change from those in the 2011 Final EIS/OEIS. The Supplemental EIS/OEIS will analyze the environmental consequences resulting from those changes. Continuing to conduct joint exercises in the Gulf of Alaska is needed to support the training of combat-capable naval forces. To ensure critical training requirements are met, the Navy will:

• Present the results of the evaluation of relevant new information, with that information incorporated into revised analysis where appropriate. Each resource area discussed within the 2011 Final EIS/OEIS will be evaluated to determine the need for discussion within this Supplemental EIS/OEIS. The Navy will provide a description of how and why exposure estimates and subsequent conclusions may differ from the 2011 Final EIS/OEIS due to the use of the NAEMO.
• Update the marine mammal take estimates and conclusions.
• Update resource mitigation measures with any new and updated mitigation that may apply since the 2011 Final EIS/OEIS.

In the 2011 GOA Final EIS/OEIS, the Navy analyzed the potential environmental impacts of three alternatives. No new alternatives or new activities are proposed, discussed, or analyzed in the GOA Supplemental EIS/OEIS.

No Action Alternative

Consists of training activities of the types and levels conducted prior to 2011, but does not include activities using active sonar.

Alternative 1

Includes the No Action Alternative, plus adjustments to the types and levels of training activities to support current and planned requirements. This alternative includes:

• Conducting one large-scale carrier strike group exercise for up to 21 consecutive days during summer months (April through October)
• Activities using active sonar
• Activities and requirements associated with the development and introduction of new weapons systems, instrumentation, technology, ships, submarines, and aircraft into the fleet
• Development and use of a portable undersea tracking range

Alternative 2 (Preferred Alternative) (Selected in 2011 Record of Decision)

Includes all activities under Alternative 1, plus additional adjustments to levels of training activities. This alternative includes:

• Conducting one additional carrier strike group exercise during summer months (April through October)
• Conducting one sinking exercise per carrier strike group exercise for a total of two per year*

*See U.S. DEPARTMENT OF THE NAVY, CHIEF, NAVAL OPERATIONS INSTR. 1541.5, GENERAL POLICY FOR SINKING EXERCISE APPROVAL (29 Jul. 2001) (hereinafter OPNAVINST 1541.5). “The Chief of Naval Operations shall approve or disapprove all valid SINKEX requests contingent upon availability of funding to complete environmental preparations.“ OPNAVINST 1541.5 para. 4a. “Further, SINKEX events are limited to those required to satisfy requirements for ship survivability or weapons lethality evaluation, major joint or multi-national exercises, or the evaluation of significant new multi-unit tactics or tactics and weapons combinations.” OPNAVINST 1541.5 para. 2. The Navy recognizes that the likelihood of there being two SINKEX events in any one year in the TMAA is presently unlikely. In order to ensure flexibility to meet potential Fleet training requirements, however, this Supplemental EIS/OEIS conservatively analyzes the potential impacts of conducting up to two SINKEX events per year in the TMAA.