Divers continue boat hull checks for marine pests

20 Dec 2019, 10:44 AM

Divers will check around 2000 boat hulls from now until May next year for a range of unwanted marine pests threatening Northland’s precious marine environment.

Kathryn Lister, the Northland Regional Council’s Biosecurity Manager – Marine, says Northland-based dive contractors recently began the 2019-20 inspection programme in the Bay of Islands and Whangaroa and are now working in Whangārei.

“We’ve been carrying out these hull inspections for several years now and are especially keen to ensure vessels are free of marine pests before their owners start travelling to new areas with the onset of warmer summer weather,” she says.

Ms Lister says contractors checked the hulls of more than 2000 vessels during last year’s inspection season, covering everything from recreational boats to superyachts and fishing vessels to barges.

With pests like Mediterranean fanworm now established in Whangārei Harbour and recently discovered in Ōpua, the owners of vessels travelling from these areas to other spots are being urged to be extra vigilant.

Divers are also on the lookout for the new-to-New Zealand ‘little bottles’ sea squirt (Clavelina oblonga), a newly-detected pest so far limited to Great Barrier Island. (This sea squirt can form dense colonies, attach to vessel hulls and marine structures, compete with kaimoana and taonga species for food, and overgrow mussel and oyster farms.

Ms Lister says in addition to rules covering transportation of marine pests, the council has rules limiting the amount of ‘biofouling’ (build-up of microorganisms, algae, plants and pests) vessels can be carrying when they enter new spots.

“Vessel hulls are the most common way for marine pests to hitch a ride from one place to the next and our Marine Pathway Management Plan aims to manage this issue.”.

Under the plan, any vessel entering Northland waters or moving from one harbour to another must have no more than ‘light fouling’, defined as a slime layer and/or barnacles and a few patches of macrofouling.

“Marine pests can hitchhike and hide within boat fouling, so preventing the movement of affected vessels is the best way to stop the spread of marine invaders,” Ms Lister says.

“We notify the owners of vessels found with more than light fouling so they can ensure the vessel is clean before moving to a new area.”

“If a pest species is detected, owners will be asked to haul the vessels out and clean or treat them in a timeframe appropriate to the level of risk. A $500 fine may also apply.”

Ms Lister says while no-one can afford to drop their guard when it comes to marine pests, the council is very appreciative of the steps many boaties are already taking to keep their boat hulls clean.

“We’re impressed by a noticeable change in their attitude to maintaining clean vessel hulls in recent years. During the last few seasons of hull inspections there’s been a huge behaviour change in visiting vessels ensuring they are clean when entering Northland.”

She says it’s always worth bearing in mind that marine pests found on vessels have often been concealed in ‘niche’ areas, which require special attention when applying antifouling or during a ‘lift and wash’ period.

“We strongly recommend double-checking these niche areas, like the base of the keel, and behind anodes and bow thrusters, before your vessel goes back in the water.”

Ms Lister says the council has also had great support from Northland’s marina operators.

“Marina operators have been requiring a receipt proving a vessel conforms to what’s been dubbed the ‘six or one’ initiative; being either antifouled within the preceding six months or having undergone a ‘lift and wash’ within the preceding month.”

She says more information on the council’s rules and requirements can be found at www.nrc.govt.nz/marinebiosecurity