Underwater hearing (of vertebrates)

Human ear

The inner ear

Fish ears

Odontocete receiving system CT scan from Darlene Ketten “Acoustic fat” found ONLY here & melon

How do we test hearing? Behavioral methods –Animal trained –Responds Go/no-go 2 alternative choice Auditory brainstem response –No training required –Record firing of auditory cortex Usually test pure tones Occasionally test pulses –Thresholds much lower for pulsed sounds than pure tones

Up-down staircase procedure 50% ‘catch trials’ (no signal present)

Envelope following response Supin et al.

Envelope following response ABR

ABR threshold calculation

ABR Magnitude

Behavioral vs. ABR Yuen et al. 2005

Behavioral vs. ABR Behavioral –Requires months to train, months to test –Usually only 1 subject ABR –Requires no training, rapid testing Can be used to test for transient effects –Can be done on more species e.g. stranded animals, catch and release animals Both require placement of a threshold that varies with conditions

Fish hearing Carp (goldfish) Cod Salmon Damselfish Tuna Popper et al.

3 types of fish ears General fish –No hearing specialization –100-1,000 Hz –Best hearing Hz Specialized hearing –Goldfish, catfish, etc. –100-3,000 Hz –Best hearing 300-1,000 Hz High frequency adaptations –Clupeids (herring, shad, menhaden, sardine, anchovy) –Swimbladder morphology facilitates broad frequency hearing range –1-200,000+ Hz

Cetacean hearing Human From: Au, 1993

Pinniped external ears Elephant seal Harbor seal Sea lion Kastak et al. 1999

Pinniped in-air hearing Kastak et al. 1999

Pinniped underwater hearing Kastak et al. 1999

In air vs. underwater – pressure or intensity? Phocids (true seals) generally hear equally well in air and underwater – amphibious Elephant seal – a deep diver hears better underwater (bone conduction in air) Fur seals hear better in air – primarily terrestrial socialization and mating Fur seal Pressure – assumes hearing mechanism Intensity – corrects for acoustic properties of media. Energy flow measure Does not require knowledge of stimulus mechanism Elephant seal Harbor seal

Hearing curves combined Bottlenose dolphin Cod Sea lion Catfish Harbor porpoise

Project “Deep EAR” Human hearing attenuates with increasing pressure (chamber experiments) Beluga whales (a dolphin species) experience large pressure increases with diving Effects on whistling and hearing in free- swimming animals Ridgway, S. H. et al. J Exp Biol 2001;204:

Up to 40 tones were presented to the whale during a dive

Depth effects – Beluga whales

“Deep EAR” results Increasing pressure (up to 300 m dives) Did not affect hearing Changed whistle spectra and intensity One whale only clicked at 300 m depth

Diving and elephant seal hearing Kastak et al. 2001

Temporary threshold shifts Aural fatigue Hearing threshold increased Recovery follows with varying time course (minutes – weeks) Experiments in chinchillas and humans have shown the relationship between TTS and PTS (permanent threshold shifts) Good predictor of auditory damage

TTS Finneran et al 2005

Temporary threshold shifts Longer exposures to quieter sounds have the same effect as shorter exposures to louder sounds Exposure intensity usually relative to hearing threshold except for impulsive sounds The total exposure energy of the sound to which an animal is exposed important

Signal effects on hearing Received intensity (source level + range + environmental conditions) Frequency Duration Timing (spacing between sounds)