Biosonar/Echolocation Odontocetes –Toothed whales Dolphins, porpoises, sperm whales Bats Cave swiftlets Used for navigation, hunting, predator detection, …. primary sense in these animals
Signals from Different Species Odontocetes that whistle (Type II – near & offshore, social, low object density) –Bottlenose dolphin –Beluga –False killer whale Odontocetes that DO NOT whistle (Type I – near shore and riverine, dense complex environment) –Family Phocoenidae (Harbor porpoise, Finless porpoise, Dall’s porpoise) –Genus Cephalorhynchus (Commerson’s dolphin, Hector’s dolphin)
non-whistling odontocete Phocoena phocoena SL pp ~ 150 - 170 dB 0 200 s Typical echolocation signals Smaller animals have amplitude limitations, so emit longer sounds?
Echolocation clicks Capable of whistling Non-whistling
Discrimination capabilities Cylindrical targets with 0.2 mm wall thickness difference Au, 1993
Summary of echolocation clicks Short, loud, broadband signals –High resolution –Outstanding Discrimination capabilities Highly directional Emitted in trains –Spacing 2 way transit time + processing Variable by species –Porpoises longer and narrower bandwidth –Delphinids shorter and wide bandwidth –Sperm whales much lower frequency Variable in individual –By task/target –With range Deformations of melon
The other side – fish hearing Clupeoid fish –Herring, shad, menhaden, sardine, anchovy –Swimbladder morphology facilitates broad frequency hearing range 2 ‘fingers’ of swimbladder surround auditory bullae Can they hear (and respond to) the acoustic signals of a primary predator?
Herring feeding rate Control Click train Regular clicks
Fish polarization Control Click train Regular clicks
Conclusions Respond to echolocation clicks –Stop feeding –School –Swim down –Swim faster Do not respond to other signals in same frequency range Can hear and appropriately respond to predator cue
Prey stunning by sonar signals Hypothesis –Odontocetes use acoustic signals to capture prey Stun, disorient, debilitate prey Existing support –Sperm whales – rapid swimming prey in stomachs intact –Fish school depolarization while under attack in captivity –Fish lethargy while under attack in wild –Some acoustic signals can injure/kill fish Benoit-Bird et al 2006
Some acoustic signals can affect fish Observed effects –Loss of buoyancy control –Abdominal hemorrhage –Death Sound characteristics –Fast rise times –High pressures Examples –Explosives Dynamite, TNT229-234 dB Black powder234-244 dB –Spark discharges 230-242 dB Dolphin click levels 225 dB
Problem –Odontocete signals of intensities observed to affect fish not observed in nature Question –Can odontocete click trains or bursts debilitate fish?
Video camera Transducers Monofilament enclosure Calibration hydrophone
Fish responses 15 minutes pre-exposure observation 15 minutes post-exposure observation Fish behavior observed –Changes in activity level –Changes in pitch/roll –Post-experiment survival
Signals 050100150200 -60 -50 -40 -30 -20 -10 0 0 250 s 050100150200 -60 -50 -40 -30 -20 -10 0 0 250 s 050100150200 FREQUENCY (KHZ) -60 -50 -40 -30 -20 -10 0 500 s 0 SL = 203 dB EL = 212 dB SL = 200 dB EL = 208 dB SL = 187 dB EL = 193 dB Bottlenose dolphin Killer whale Sperm whale
Pulse rates Static pulse rate –100, 200, 300, 400, 500, 600, & 700 pulses/second –Exposure times of 7 seconds – 1 minute –6 individuals of 2 species (sea bass, cod) –Groups of 4 individuals of each species Modulated pulse “sweeps” –From 100 to 700 pulses/second in 1.1, 2.2, 3.2 seconds –Similar to a “terminal buzz” –6 individuals of 2 species (cod, herring) –Groups of 4 individuals of each species
Subject selection Proposed “stunning” mechanism: Acoustic interaction with air-filled cavities –Swim bladder Physostomous –“Open” - Air comes from gulping at surface Physoclistous –“Closed” - Air is produced biochemically “Stunning” proposed from field observations –Salmon Physostomous –Anchovy Physostomous with extensions to lateral line & labyrinth –Mahi mahi No swim bladder 3 species commonly preyed upon by Odontocetes –Variety of swimbladder types
Herring (Clupea harengus) Physostome with air bladder extensions to labyrinth & lateral line - Increased sensitivity to sound - Respond to echolocation signals Modified primitive form
No measurable change in behavior –Swimming activity –Balance/buoyancy control –Orientation No mortality Variables explored –Frequency of signal –Pulse rate “Terminal buzz” simulation –Long exposure times –Multiple individuals, different sizes, different species
Conclusions No response to stimuli –Signals near maximums recorded for odontocete clicks Stimulation with odontocete-like clicks alone is not enough to induce fish stunning –Additional stress? –Other sensory inputs? –Odontocete behavior?