General approach

During the survey we target key anchorages and club moorings where boaters tend to congregate when out and about. Divers check the boats and moorings, as well as marine structures (not marine farms) like high-use jetties, and some areas of adjacent seabed. On boats, divers pay particular attention to ‘niche’ areas where fouling tends to accumulate. Depending on vessel type, these areas can include the keel, rudder, trim tabs (power boats), propeller shaft, pipe outlets, bow-thruster tunnels, and hard-stand support strips.

Level of fouling assessment

Divers score boat fouling on a ‘Level of Fouling’ (LOF) scale developed by NIWA, show in the Table below. These videos give you an idea of what different fouling levels look like in the water.

LOF examples

LOF categories

From Floerl et al. 2005.

Rank Description Visual estimate of fouling cover
0 No visible fouling. Hull entirely clean, no biofilma on visible submerged parts of the hull. Nil
1 Slime fouling only. Submerged hull areas partially or entirely covered in biofilm, but absence of any macrofouling. Nil
2 Light fouling. Hull covered in biofilm and 1-2 very small patches of macrofouling (onle one taxon). 1-5% of visible submerged surfaces
3 Considerable fouling. Presence of biofilm, and macrofouling still patchy but clearly visible and comprised of either one or more different taxa. 6-15% of visible submerged surfaces
4 Extensive fouling. Presence of biofilm and abundant fouling assemblages consisting of more than one taxon. 16-40% of visible submerged surfaces.
5 Very heavy fouling. Diverse assemblages covering most of visible hull surfaces. 41-100% of visible submerged surfaces

aBiofilm: thin layer of bacteria, microalgae, detritus and other particulates that are required for settlement of the larvae of many species of marine invertebrates.

Target pests

Divers check for target marine pests on boats, structures and seabed, some of which are already in the TOS and some not. The sea squirt Didemnum vexillum is of regional interest, and the others are biofouling organisms listed by the Ministry for Primary Industries in the ‘New Zealand Marine Pest ID Guide’.

Recorded within TOS

Recorded outside TOS

Boater surveys

A topside person records all survey information and if boaters are present we get information on things like home port, number of months since the boat was antifouled, and number of months since the boat was last cleaned (if at all) subsequent to antifouling. We also have a general chat about marine biosecurity.

Definition of active versus inactive vessels

Boats in active use are more likely to have been recently maintained, or have accumulated less biofouling, than boats that have been idle for extended periods (e.g. boats unused on swing moorings).

To distinguish these situations, boats are categorised as ‘active’ when they are known to be in active use (i.e. from talking to the skipper), or the boat is unattended but at anchor or temporary berth (e.g. on a boat club/resort mooring). Often the vessel skippers we work with (i.e. Harbourmaster or DOC skippers) are able to distinguish visiting boats from those that are resident and haven’t moved for some time.

Boats that do not meet the active criteria are assumed to be inactive. Hence, the classifications may underestimate the number of active boats. For example, we sometimes encounter instances of relatively clean boats on private moorings adjacent to baches; these are classed as inactive but may in fact have been in active use at the time of the survey.