The soundscape of Arctic Charr spawning grounds in lotic and lentic environments: can passive acoustic monitoring be used to detect spawning activities?

The aims of this study were to (i) assess the efficacy of passive acoustic
monitoring (PAM) for detecting Arctic Charr at their spawning grounds
and (ii) characterize the overall acoustic soundscape of these sites.
PAM was carried out over three Arctic Charr spawning grounds in
the UK, one lotic and two lentic. 24-h cycles of recordings were
collected prior to and during the Arctic Charr spawning season,
which was determined from data returns by simultaneous net
monitoring. Acoustic analysis consisted of manual quantification
of sound sources, Acoustic Complexity Index (ACI) calculation and
spectral analysis in 1/3 octave band (SPL; dB re 1 μPa). In the lotic
spawning ground, prior to the beginning of Arctic Charr spawning,
SPL and ACI showed a restricted range of variation throughout the
24-h, while during spawning the night values of SPL and ACI were
found to significantly increase, concurrently with the rate of gravel
noise induced by fish spawning activities and fish air passage sounds.
Both prior to and during the Arctic Charr run, the lentic soundscape
was characterized by diel variation due to the daytime presence of
anthropogenic noise and the night-time presence of insect calls, while
only a few occurrences of fish air passage sounds and gravel noise
were recorded. These findings suggest that PAM over Arctic Charr
spawning grounds could provide meaningful information to be used
in developing management plans for this threatened species, such as
determining the location and time of arrival, diel pattern and length
of spawning activities.