Sound production in mysticetes. Background. Cetacean vocal frequency ranges Dolphins

Transcription

1 Sound production in mysticetes Fish May Background Cetaceans produce sound in the widest range of frequencies for any Class of animal Subsonic to supersonic and everywhere in between Sound (production and reception) is probably the most important sense for these animals Baleen whales produce species-specific sounds Unknown if there are individual signature sounds Cetacean vocal frequency ranges Dolphins Blue Fin Gray Bryde's Mysticete whales Minke Humpback Right (2) Pygmy right Bowhead Sei Sperm whale Beaked whales (3) Monodonts (2) River dolphins (3) Cephaloryhnchinae (2) Delphininae (14) N. Rt. whale dolphin Steninae (3) Porpoises (3) Pilot whales (2) Killer whales (2) Frequency, Hz ??? 10 Dave Mellinger and Sara Heimlich Oregon State Univ. & NOAA/PMEL 1

2 Sound production Unlike toothed whales, how baleen whales produce and receive sound is unknown No melon No air sacs near the blowholes May use the laryngeal sac May not use external ears Ears are acoustically isolated from the skull by air spaces No audiograms available Figs. from Jefferson et al Marine Mammals of the World Figs. from Jefferson et al Marine Mammals of the World 2

3 Sound transmission in water Sound in air ~330 m/s, in water ~1500 m/s The speed of sound in water is due to temperature (! as temp!) pressure (! as pressure!) salinity (! as pressure!) Because of this, transmission is not uniform around the world Low frequency sounds can travel long distances in water with little attenuation Attenuation caused by reflection with surface/bottom spherical and cylindrical spreading heat and chemical absorption absorption by bottom Propagation very different in shallow v. deep water SOFAR channel Physical properties of the water column allow low-frequency sound to travel great distances with relatively little loss Sound is refracted towards the sound speed minimum (Snell s Law) Large whales may use this duct to communicate over relatively long distances 3

4 temperature sound speed (m/s) mixed layer SOFAR channel depth axis of channel Why do baleen whales make noise? Navigation Foraging Reproductive display Group cohesion Segregation? Navigation Bowhead whales 4

5 Foraging Reproduction 5

6 Group cohesion Segregation? 6

7 Summary As far as we know, all baleen whale species produce sound Complete repertoires still unknown for most spp, completely unknown for sei, pygmy right Different sounds used in different contexts May be gender differences in sound use/production Still lots to discover. Applying acoustic methods to marine mammal population problems Problem: Most large whales pelagic, highly migratory Data traditionally restricted to certain locations, time of year and weather Solution: Deploy instruments to monitor regions over long time periods Caveat: Need to know when animals make sound Seasonal patterns vs. year-round Can only generalize about calling animals Problem: Need to know numbers of animals in certain regions in order to assess populations Visual surveys used to estimate numbers Limited to daylight hours, good weather Solution: Use a towed array or deploy a moored array during the survey Can hear animals much further away than can see them Not limited to daylight hours or good weather Caveats: Difficult to relate # sounds to # animals Need to know what proportion of a population is vocalizing at any one time Need to know local propagation effects for each species 7

8 Specific example: migratory timing and destination of northeast Pacific blue whales Northeastern Pacific Blue Whales Time (s) 8

9 average occurrence NEP ETP Gulf of AK jan feb mar apr may jun jul aug sep oct nov dec month July-December July-January! February-June June- November March- June Year round Peak February-May Questions, comments, etc. Kate Stafford stafford@apl.washington.edu