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Vicerrectoria de Investigacion y Desarrollo of the Universidad de Concepcion 219.153.026-P

The relative occurrence of the 16 most common cetacean species in the Southern California Bight (SCB) was compared from the 1950s through 2012 by examining at-sea sighting and stranding data. While systematic survey and population abundance/density data have been available since the 1970s, prior data were collected opportunistically. Comparisons were made through a literature review and using recent results from 15 aerial surveys conducted in the SCB from 2008 through 2012. We attempted to address inconsistency in type of effort across studies by ranking the relative sighting frequency of the most common species based on the most representative study for each period. This comparison revealed changes in the relative occurrence of some species across the approximately 60-y reviewed period. Since the 1950s, common dolphins have remained the most common “species” of cetacean in the SCB. Risso’s dolphin and fin, blue, humpback, and Bryde’s whales appear to have increased in relative occurrence. The relative occurrence of the common bottlenose and northern right whale dolphins; Dall’s porpoise; and gray, killer, minke, Cuvier’s beaked, and sperm whales do not appear to have changed notably since the 1950s. There is possible indication of recent decreased relative occurrence of the Pacific white-sided dolphin. The short-finned pilot whale has decreased since the 1950s and has not been recorded in the SCB since the 1990s, concurrent with the observed relative increase in Risso’s dolphins. Overall, recent aerial surveys indicate that the 16 most commonly seen species in the SCB, in descending order of frequency, were common dolphins (two species), Risso’s dolphin, fin whale, common bottlenose dolphin, gray whale, blue whale, Pacific white-sided dolphin, humpback whale, northern right whale dolphin, common minke whale, Dall’s porpoise, killer whale, Bryde’s whale, Cuvier’s beaked whale (the latter three tied in ranking), and sperm whale. Given that the reviewed historical data from the 1950s and 1960s are virtually the only sources of information available to examine trends over the last 50 to 60 y in this area, we believe this comparative ranking approach provides useful information not available from other sources.

In Hawaiian waters, a single stock of Blainville s beaked whale (Mesoplodon densirostris) is recognized, extending throughout the U.S. Exclusive Economic Zone (EEZ) surrounding the archipelago and into adjacent international waters (Carretta et al., 2011). Abundance within the entire EEZ around Hawai i was estimated at 2,872 individuals based on a large vessel sighting survey (Barlow, 2006), with a single on-effort sighting near the western boundary of the EEZ (Hamilton et al., 2009). There is, however, considerable uncertainty associated with this estimate (CV = 1.17; Barlow, 2006), and there is recent evidence that individuals documented around the main Hawaiian Islands may not be part of an open-ocean population (McSweeney et al., 2007; Schorr et al., 2009). Individual Blainville s beaked whales instrumented with satellite tags off the island of Hawai i have remained strongly associated with the island, primarily using slope habitats for the entire duration of satellite tag transmissions (up to 71 d; Schorr et al., 2009). Schorr et al. (2009) noted a mean distance from shore of 16.9 km (range 4.4 to 27.7 km) and a mean depth of 1,156 m (range 880 to 1,455 m) for six satellite tagged individuals, over periods ranging from 15 to 71 d (median = 43 d), with from 26 to 405 locations per individual (median = 195 locations/ individual). Although these individuals moved a cumulative distance of at least 8,000 km over the duration of their tag attachments, median distances of locations from the tagging location for the different individuals ranged from 19.9 to 91.8 km, and the maximum distance any individual moved from where it was tagged was only 139 km (Schorr et al., 2009). Combined with long-term resightings of distinctive individuals off the island (McSweeney et al., 2007), such results suggest the existence of an island-resident population.

There have been several incidents in which U.S. Navy sonar operations at sea coincided in time and location with a mass stranding of marine mammals, particularly beaked whales. Although a conclusive cause-and-effect relationship has not been established, there is strong evidence and scientific concern that use of military sonar has resulted in beaked whale mass strandings. Most previous attempts to determine whether military sonar use and whale strandings are correlated have looked at mass stranding records of beaked whales and have singled out those instances in which military operations appear to coincide in time and location with a mass stranding event. In this study, historical data on beaked whale mass strandings and military exercises that were likely to include active sonar use were compiled, and statistical analyses were performed to determine the level of correlation between these events for four geographic regions. Strandings were significantly correlated with naval activity in the Mediterranean and Caribbean Seas, but not off the coasts of Japan and southern California.

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.

Seventeen new sightings, and a total of 32 records, of the little-known Longman’s beaked whale, (Indopacetus pacificus) (also called tropical bottlenose whale or Indo-pacific beaked whale) are reported from the western Indian Ocean. Field identification features are reviewed, and the possibilities of confusion with other beaked whales are noted. Mean group size for the western Indian Ocean sightings was 7.2 individuals (n = 22, SD = 10.9, range = 1 to 40). This is smaller than previously published estimates from the Pacific, reflecting a relatively large number of new sightings of individuals and small groups, which, in turn, reflect the recent description of the external appearance of this species. Recorded dive times were either short (mean = 14 min, range = 11 to 18 min, n = 5) or long (mean = 26 min, range = 20 to 33 min, n = 19). Longman’s beaked whales appear to be widely distributed in the warmer (> 27o C) waters of the western Indian Ocean, but most sightings were over or adjacent to deep slopes (depths 250 to 2,000+ m). Mean sighting rates were much higher in the western Indian Ocean (1 sighting per 31 sea days for visual surveys) and particularly around the Maldives (1 sighting per 21 sea days) than have been reported from the Pacific (1 sighting per 200 sea days). Longman’s beaked whales may therefore be more common in the western Indian Ocean than in the Pacific, although survey methodologies used in the two oceans were not identical. Widespread gillnet fisheries may pose a potential threat to this species in the Indian Ocean.

On 10 August 2001, a beaked whale was found dead on a rocky shore at Sa o Vicente (23 58 S; 46 24 W), Sa o Paulo state, Brazil. The damaged specimen was approximately 390 cm in length and in an advanced state of decomposition. It was identie ed as a Mesoplodon europaeus based on the following characteristics: (1) the presence of a e attened pair of teeth placed near the posterior half of the short mandible symphysis; (2) when viewed laterally in an upright position with the long axis of the rostrum horizontal, the premaxillary foramina straddle a horizontal plane, transecting the centres of the maxillary formamina; and (3) both the protuberance of the maxillary, which interrupts the antorbital notch, and the ridge that extends back from this protuberance are conspicuous. Cranial measurements are presented. This is the southernmost record of this species in the southern hemisphere, the e rst one to the southwest Atlantic and the e rst one along the Brazilian coast. Recent beaked whale records along the Brazilian coast, due to the increasing of cetological research, raises the possibility of ordinary distribution, rather than extra limital observations. Further investigations are needed to draw reliable conclusions on Gervais’ beaked whales in the southern hemisphere.