University of Auckland scientists have carried out the first large-scale investigation into the effects of ship noise in the waters of New Zealand's Hauraki Gulf.
The research shows a significant reduction in 'communication space' for at least two key marine species.
PhD candidate Rosalyn Putland and Associate Professor Craig Radford from the Institute of Marine Science combined sound recordings from four hydrophone listening stations, used to track underwater noise, over a nine-month period with automatic ship tracking data to understand the impacts of shipping.
Putland has found that her latest study provides further evidence that compliance with the 10-knot speed restriction within the Hauraki Gulf Marine Park area could benefit marine species as vessels travelling at lower speeds produce quieter levels of noise.
Suspended 1 metre to 2 metres above the seafloor, the hydrophones recorded two minutes of data every 20 minutes.
Rosalyn Putland and colleague installing a hydrophone in the Hauraki Gulf
The study focused on two species which use sound to communicate, Bryde’s whales (Balaenoptera edeni) and the common reef fish, ‘bigeye’ (Pempheris adspersa).
It found that the noise from cargo, container and tanker vessels overlapped their vocalizations to 20% of the time.
Every time a vessel passed within 10 kilometres of a listening station, it reduced communication space for bigeyes by up to 61.5% and by up to 87.4% for Bryde’s whales.
Research has shown bigeyes can communicate over distances of up to 31 metres, so a passing ship will reduce this to less than 12 metres.
Study co-author Associate Professor Craig Radford likened the concept of communication space to the hubbub of a cocktail party where the ability to hear what is going on is reduced the louder the party becomes.
Read the 'Vancouver Fraser Port Authority: Asking Vessels to Slow Down for Whales' technical paper: As part of its objective to better understand and manage the impact of shipping activities on at-risk whales throughout the southern coast of British Columbia, the Vancouver Fraser Port Authority’s initiative, the Enhancing Cetacean Habitat and Observation (ECHO) Program launched a trial in which ship operators voluntarily reduced vessel speed
Radford said: “Communication space is the range at which two species can hear each other and this study has found the range at which bigeyes and Bryde’s whales can communicate is significantly reduced when a ship comes past.”
The reduction of communication space for marine species is becoming an increasing concern for scientists worldwide as more is learned about how sound is used among groups of species to ensure survival including finding a mate, defending territory and warning of predators.
The biggest impact from ship noise was at Jellicoe Channel, the most regularly used shipping lane into Ports of Auckland where vessel passages were recorded 18.9% of the time.
Putland’s study focused on large commercial vessels, but more than 130,000 recreational boats regularly use the Gulf.
This number is expected to rise 40% in the next 20 years.
Putland stated: “The voluntary speed limit of 10 knots is fairly recent but we believe is having a significant effect on helping reduce noise in the Gulf to allow species to hear each other.
“Even so, when a ship is directly above marine animals, it reduces communication for those animals almost completely, or by 99%.”