The low-frequency vocalizations of fin and blue whales are the most powerful and ubiquitous biological sounds in the ocean. Here we combine acoustic localization and molecular techniques to show that, in fin whales, only males produce these vocalizations. This finding indicates that they may function as male breeding displays, and will help to focus concern on the impact of human-generated low-frequency sounds on recovering whale populations.
ABSTRACT:Collisions with vessels are a well-documented conservation problem for some populations of large whales (LW) in the Northern Hemisphere. Less attention has been given to incidents in the Southern Hemisphere or to small cetaceans (SC) worldwide, therefore an experimental database was compiled (N=256; 119 LW, 137 SC) to allow a rapid assessment. Confirmed collision records were identified for 25 species (7 LW, 18 SC) and unconfirmed but probable records for 10 other species (2 LW, 8 SC). Among LW, ship-caused mortality and traumatic injuries seem to affect primarily southern right (56 reported cases), humpback (15) and Bryde's whales (13), but also sperm (8), blue (5), sei (4) and fin whales (2) are involved, and probably Antarctic minke and dwarf minke whales. Southern right whale populations off South Africa and off eastern South America (Brazil, Uruguay and Argentina) suffer significant mortality. Incidence and potential population impact vary widely among the 26 small cetacean species for which collision records exist. Vessel strikes in at least two populations each of the Indo-Pacific humpback dolphin (Xiamen and Hong Kong/Pearl River, possibly western Taiwan), Irrawaddy dolphin (Mahakam River, Chilika Lagoon, possibly Laos) and finless porpoise (Yangtze River, Hong Kong) may directly compromise long-term survival. Annual vessel-caused mortality (min. 2.9% of population) for Irrawaddy dolphins in the Mahakam River may not be sustainable. The quasi-extinction of the baiji warns for a potential similar fate for the Yangtze River finless porpoise and Ganges river dolphin. Two calves of the endangered Hector's dolphin are known killed by boats. All highly impacted species have a neritic, estuarine or fluviatile habitat, areas where vessel traffic is concentrated. Species that may receive a moderate impact from collisions but which may be sustainable at species level (because many strikes are nonlethal), include common bottlenose dolphins, killer whales, short-finned pilot whales and pygmy sperm whales. Almost 2% of common bottlenose dolphins in the Gulf of Guayaquil showed propeller-inflicted injuries and scars. Propeller guards should be made compulsory for all boat-based cetacean tourism, as habituation to boat traffic seems a contributing factor in accidents. Low impact occurs in 15 small cetacean species with only few reported vessel strikes. However, vast underreporting is thought to be the norm and there is a need for a global, standardised database. RESUMEN:Las colisiones con barcos constituyen un problema de conservación bien documentado en el caso de ballenas grandes (BG) en el hemisferio norte. Menos atención se le ha brindado a los incidentes en el hemisferio sur y a los cetáceos menores (CM) alrededor del mundo. A fin de realizar una evaluación rápida de este problema se ha compilado una base de datos preliminar (N=256; 119 BG, 137 CM), la cual incluye registros confirmados de colisión para 25 especies (7 BG, 18 CM) y registros no confirmados pero probables para otras 10 (2 BG, 8 CM). Entre B...
Understanding the seasonal movements and distribution patterns of migratory species over ocean basin scales is vital for appropriate conservation and management measures. However, assessing populations over remote regions is challenging, particularly if they are rare. Blue whales (Balaenoptera musculus spp) are an endangered species found in the Southern and Indian Oceans. Here two recognized subspecies of blue whales and, based on passive acoustic monitoring, four “acoustic populations” occur. Three of these are pygmy blue whale (B.m. brevicauda) populations while the fourth is the Antarctic blue whale (B.m. intermedia). Past whaling catches have dramatically reduced their numbers but recent acoustic recordings show that these oceans are still important habitat for blue whales. Presently little is known about the seasonal movements and degree of overlap of these four populations, particularly in the central Indian Ocean. We examined the geographic and seasonal occurrence of different blue whale acoustic populations using one year of passive acoustic recording from three sites located at different latitudes in the Indian Ocean. The vocalizations of the different blue whale subspecies and acoustic populations were recorded seasonally in different regions. For some call types and locations, there was spatial and temporal overlap, particularly between Antarctic and different pygmy blue whale acoustic populations. Except on the southernmost hydrophone, all three pygmy blue whale acoustic populations were found at different sites or during different seasons, which further suggests that these populations are generally geographically distinct. This unusual blue whale diversity in sub-Antarctic and sub-tropical waters indicates the importance of the area for blue whales in these former whaling grounds.
Time averaged narrow-band noise near 27 Hz produced by vocalizations of many distant Antarctic blue whales intensifies seasonally from early February to late October in the ocean off Australia's South West. Spectral characteristics of long term patterns in this noise band were analyzed using ambient noise data collected at the Comprehensive Nuclear-Test-Ban Treaty hydroacoustic station off Cape Leeuwin, Western Australia over 2002-2010. Within 7 day averaged noise spectra derived from 4096-point FFT (∼0.06 Hz frequency resolution), the -3-dB width of the spectral peak from the upper tone of Antarctic blue whale vocalization was about 0.5 Hz. The spectral frequency peak of this tonal call was regularly but not gradually decreasing over the 9 years of observation from ∼27.7 Hz in 2002 to ∼26.6 Hz in 2010. The average frequency peak steadily decreased at a greater rate within a season at 0.4-0.5 Hz/season but then in the next year recovered to approximately the mean value of the previous season. A regression analysis showed that the interannual decrease rate of the peak frequency of the upper tonal call was 0.135 ± 0.003 Hz/year over 2002-2010 (R(2) ≈ 0.99). Possible causes of such a decline in the whale vocalization frequency are considered.
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