For marine mammal mitigation, the mitigation, or exclusion, zone, is a circle with a specified radius around an acoustic source (e.g. a seismic airgun array), not the vessel. On large vessels, or when the acoustic source is deployed far behind the vessel, animals sighted on the bow, may be outside the mitigation zone.
The mitigation zone principle is simple; marine mammals must be clear of the zone prior to source activation or in some circumstances, other operations. If a marine mammal is seen within a mitigation zone, the sound source may have to be delayed or shutdown.
MITIGATION ZONES IN THE NEW ZEALAND CODE OF CONDUCT BASED ON SPECIES
Unlike any other guidelines worldwide, New Zealand’s ‘2013 code of conduct for minimising acoustic disturbance to marine mammals from seismic survey operations’ has varying mitigation zones and procedures for different classifications of marine mammals. The categories are: species of concern with calf/calves, species of concern, other marine mammals, and New Zealand fur seals. A full list of the species of concern can be found at: www.speciesofconcern.co.nz. For both level 1 (www.nzlevel1seismicsurveys.co.nz) and level 2 (www.nzlevel2seismicsurveys.co.nz), seismic surveys species of concern with calf/calves are given the largest mitigation zone, compared to the other categories of marine mammals.
There is no shutdown procedure required for ‘other marine mammals’, and the mitigation zone needs only to be clear of New Zealand fur seals for 10 minutes, instead of the 30 minutes for other species, prior to source activation.
MITIGATION ZONES IN THE NEW ZEALAND CODE OF CONDUCT BASED ON SURVEY LEVEL
For each survey level the size of the mitigation zone for the different categories of marine mammal also varies. The mitigation zone sizes for species of concern are larger for level 1 surveys compared to level 2 surveys.
MITIGATION ZONE SIZE VARIATIONS
The mitigation zone sizes discussed here are standard in the Code; however, when working in an Area of Ecological Importance (AEI; www.areasofecologicalimportance.co.nz), the required sound transmission loss modelling (www.soundtransmissionlossmodelling.co.nz) may lead to larger mitigation zones. Changes to mitigation zone sizes will be outlined in the Marine Mammal Impact Assessment (MMIA; www.marinemammalimpactassessment.co.nz).