Abstract
Studies on the behavioural function of sounds are very rare within heterospecific interactions. John Dory (Zeus faber) is a solitary, predatory fish that produces sound when captured, but has not been documented to vocalize under natural conditions (i.e. in the wild). The present study provides the first in-situ recordings of John Dory vocalisations and correlates them to behavioural response of snapper (Pagrus auratus) a common species found through New Zealand. Vocalisations or ‘barks’, ranged between 200–600 Hz, with a peak frequency of 312 ± 10 Hz and averaged 139 ± 4 milliseconds in length. Baited underwater video (BUV) equipped with hydrophones determined that under natural conditions a John Dory vocalization induced an escape response in snapper present, causing them to exit the area opposite to the position of the John Dory. We speculate that the John Dory vocalisation may be used for territorial display towards both conspecifics and heterospecifics, asserting dominance in the area or heightening predatory status.
Highlights
John Dory vocalisations consisted of short repeated low frequency pulses (Fig 1A), which were termed by Onuki & Somiya [20], who recorded the sound in air, as “barks”
To confirm sounds were produced by John Dory the spectral content (Fig 2A–2D) and cross correlation (Fig 2E) of the field recordings were compared to the tank recordings
John Dory is a solitary predator known to produce vocalisations using a pair of intrinsic sonic muscles, but to date these vocalisations have only been recorded in air [20]
Summary
This study was conducted in the Cape Rodney to Okakari Point (Leigh) Marine Reserve (549 ha, established in 1976) near Leigh, New Zealand and outside the reserve approximately 4 km due south, near Mathesons Bay. Sampling sites ranged in depth, from 5 to 20 m. Field recordings were taken between January-March 2015, with a hydrophone (ST202, Ocean Instruments Ltd), attached to a baited underwater video (BUV) allowing concurrent behavioural observation. A SoundTrap 202 recorder (sensitivity 171.8 dB re 1V/μPa; frequency response 20 Hz– 60 kHz) was attached to the pole approximately 0.5 meters from the base and recorded continuously at a sampling frequency of 144 kHz. A 2 l screw top clear plastic bait bottle was affixed with cable ties to the midpoint of the longest side of the base. From here on we call these recordings “tank recordings” and the recordings captured with the BUV “field recordings”
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