Mass strandings of beaked whales (family Ziphiidae) have been reported in the scientific literature since 1874. Several recent mass strandings of beaked whales have been reported to coincide with naval active sonar exercises. To obtain the broadest assessment of surface ship naval active sonar operations coinciding with beaked whale mass strandings, a list of global naval training and antisubmarine warfare exercises was compiled from openly available sources and compared by location and time with historic stranding records. This list includes activities of navies of other nations but emphasizes recent U.S. activities because of what is available in publicly accessible sources. Of 136 beaked whale mass stranding events reported from 1874 to 2004, 126 occurred between 1950 and 2004, after the introduction and implementation of modern, high-power mid-frequency active sonar (MFAS). Of these 126 reports, only two reported details on the use, timing, and location of sonar in relation to mass strandings. Ten other mass strandings coincided in space and time with naval exercises that may have included MFAS. An additional 27 mass stranding events occurred near a naval base or ship but with no direct evidence of sonar use. The remaining 87 mass strandings have no evidence for a link with any naval activity. Six of these 87 cases have evidence for a cause unrelated to active sonar. The large number of global naval activities annually with potential MFAS usage in comparison to the relative rarity of mass stranding events suggests that most MFAS operations take place with no reported stranding events and that for an MFAS operation to cause a mass stranding of beaked whales, a confluence of several risk factors is probably required. Identification of these risk factors will help in the development of measures to reduce the risk of sonar-related strandings.

We examined inter-island movements and offshore migrations of six humpback whales (Megaptera novaeangliae) tagged during March and April 1995 with satellite-monitored radio tags off Kaua´i, Hawai´i. The tags transmitted 0.5-17 days ( x bar = 8.5 ± 2.7 days) and produced 1-66 locations that met our screening criteria. Total travel distances per individual ranged from 30 to 1860 km. After screening criteria were applied, satellite-acquired locations ranged from 1.8 to 3.9/day for individuals (group average 2.7/day). One adult traveled 250 km to O´ahu in 4 days. Another visited Penguin Bank and five islands (820 km) in 10 days, suggesting faster inter-island movement than had been previously thought. Three whales traveled independent, parallel courses toward the upper Gulf of Alaska on north-northeast headings. A female with a calf was the fastest: 670 km in 4.5 days (150 km/day). Two whales traveled for 14.7 and 17 days, an average speed of 110 km/day (4.5 km/h). A 4200-km migration to the upper Gulf of Alaska at that speed would take 39 days. If the fastest whale's speed was maintained on a straight course, the entire migration could be accomplished in as little time as 28 days. Based on the two longest tracks, the first third of the migration route is within 1° of magnetic north. These data represent the first route and travel speeds for humpbacks migrating from Hawai´i toward Alaska.

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Certain anthropogenic sounds are widely believed to cause strandings of beaked whales, but their impacts on beaked whale populations are not known and methods for mitigating their effects are largely untested. The sound sources that have been coincident with beaked whale strandings are military, mid-frequency sonar (2-10kHz) and airgun arrays, both of which are used widely throughout the world for defence and geophysical exploration, respectively and for which alternative technologies are not readily available. Avoidance of beaked whale habitats is superficially a straightforward means of reducing the potential effects, but beaked whales are widely distributed and can be found in virtually all deep-water marine habitats that are free of ice. Some areas of high beaked whale abundance have been identified, but the geographic distribution is poorly known for most species. Beaked whales are both visually and acoustically difficult to detect. Commonly used mitigation measures (e.g. ‘ramp-up’ and ‘detection-modification-avoidance’) have not been assessed for their effectiveness. Surveys to detect population-level impacts would likely require many years of regular monitoring and for most areas where beaked whale strandings have occurred, there are no pre-exposure estimates of population sizes. Risk assessment models can be used to estimate the sound levels to which beaked whales might be exposed under a variety of scenarios, however, the lack of information on the causal mechanism for soundrelated beaked whale strandings makes it difficult to identify exposure levels that would warrant mitigative actions. Controlled exposure experiments, which measure the behavioural responses of animals to fully characterised sound sources, may hold the greatest potential for understanding the behavioural responses of beaked whales to sound and for designing mitigation methods to avoid future impacts.