Abstract:
Increasing levels of sound in the ocean from human activity is a growing concern as it has the potential to mask biologically significant acoustics. Marine species such as crustaceans, fish and mammals use sound for communication, prey detection, predator avoidance, and orientation. Marine reserves are implemented for the protection of marine fauna against human activities and, currently, have no parameters for protection against anthrophony. Determining the vulnerability of marine reserve soundscapes to anthrophony is crucial. Long-term passive acoustic monitoring allows for identification of sounds and patterns in different habitats and has become more prevalent in studies determining biophony and anthrophony interactions. Anthrophony from recreational vessels was focused on because it is known that vessels for recreational activities, tourism, and scientific research are dominant in marine reserves. Here, two sites within the Cape Rodney-Okakari Point Marine Reserve and two outside the reserve were recorded for six months from March to September 2018. Vocalisations produced by twospot demoiselle (Chromis dispilus) were found to occur throughout the study duration and were used to represent how anthrophony can impact species reliant on marine reserve habitats. A notable increase in boat noise was observed the further the habitat was from the reserve centre, with a difference of 15% detection between the most central and the outer most listening station. Ambient levels were found to increase under 1,000 Hz when boat noise was present, raising median sound pressure levels at low and mid-frequency ranges at three sites. Vocalisations of two spot demoiselle occurred at the frequency range 600 – 2,500 Hz, with patterns indicating their biological function, may be for social cohesion. Recreational vessels are present in all areas of the marine reserve, dominating the lower-frequency bandwidths. This implies masking of biophony and therefore disruption of biologically important signals in all areas of the marine reserve. Species within marine reserves can be highly mobile, meaning they can encounter anthrophony levels in habitats both inside and outside the reserve boundaries. It is vital scientists quantify noise budgets for individual reserves in order for policymakers to make informed decisions on the protection of marine fauna in ecologically important areas.