65205 Appendix Eight The Northland Regional Council Report on Wider Surveillance for exotic Caulerpa in Northland.pdf

Wider Surveillance for exotic

Caulerpa in Northland
C0036060

Introduction

Background

On 5th July 2021 Biosecurity New Zealand (BNZ) was notified about, and subsequently identified, the
invasive  alga  Caulerpa  brachypus  at  Aotea/Great  Barrier  Island.  Delimiting  surveys  confirmed
populations in three locations on the southwestern side of the island (Blind Bay, Tryphena Harbour,
and  Whangaparapara  Harbour).  On  15th  March  2022  four  populations  of  Caulerpa  brachypus  and
Caulerpa parvifolia (hereon referred to as ‘exotic Caulerpa’) were discovered at two locations on the
western side of Ahuahu/Great Mercury Island, and the response was extended to include this island.
In May 2023 BNZ were notified about, and subsequently identified, exotic Caulerpa in several locations
surrounding Te Rāwhiti inlet, Omākiwi Cove, and into Albert Channel, Bay of Islands (Te Rāwhiti and
Northland response).

As exotic Caulerpa is most likely spread via entanglement in or attachment to anchors, it is possible
that populations of exotic Caulerpa are present in other locations which have not yet been surveyed.
The Northland Regional Council (NRC) and BNZ consequently recognized the need to conduct wider
surveillance for exotic Caulerpa across well-known anchorages throughout the Northland region.

Prior  to  the  discovery  of  exotic  Caulerpa  in  Northland,  but  after  discovery  of  infestations  at
Aotea/Great  Barrier  Island  and  Ahuahu/Great  Mercury  Island,  NRC  and  the  Cawthron  Institute
obtained a medium Envirolink grant (reference 2343-NLRC238). This grant supported a project that
mapped  a  connectivity  network  between  known  infestation  sites  in  Northland,  and  identified
potential  anchoring  hotspots  that  were  accessible  within  10  days  of  a  vessel  visiting  a  known
infestation site (10 days is the assumed survival period of exotic Caulerpa fragments; Fig. 1). This data
informed the locations of interest to be surveyed as part of this contract.

Contract objectives

-
Provide an Operational Specification and Health & Safety Management Plan and  a Ministry
for Primary Industries (MPI) Health & Safety Questionnaire.
-
Complete dive surveillance for exotic Caulerpa at high-risk sites in Northland.
-
Provide access to ArcGIS platform for live data for BNZ contract manager.
-
Provide a written report of findings from dive surveillance, including:
o  Achievement of each contract objective.
o  Effectiveness of the surveillance programme logistics, costs, cultural considerations,
etc.
o  Any other conclusions or results relevant to the project goal or objectives.

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C0036060 Wider Surveillance in Northland

Figure 1. Potential anchoring events along the Northland coast of vessels that had departed locations with known
populations of exotic Caulerpa (blue circles) within the 10 previous days. Nodes where potential anchoring events occurred
(red circles) are sized according to their relative risk, i.e. the proportion of the total number of Northland anchorage events
that occurred at each location. Left panel is for the Automatic Identification System (AIS) data network and the right panel for
the Survey data network. Source: Floerl O, Hilliam K, Faubel C, Stevenson S, Treml E. 2023. Prioritising surveillance sites for
exotic Caulerpa in Northland. Nelson: Cawthron Institute. Cawthron Report 3952. Prepared for Northland Regional Council.

Methods

Location selection

Survey  areas  were  identified  as  popular  anchorages  throughout  the  Northland  region  using  the
following knowledge sources (in no particular order):

-
Floerl, O., Hilliam, K., Faubel, C., Stevenson, S. and Treml, E. (2023) Prioritising surveillance
sites for exotic Caulerpa in Northland. Cawthron Institute Report 3952, prepared for Northland
Regional Council.
-
Local knowledge from skippers.
-
BNZ Marine High Risk Site Surveillance maps.

Areas were surveyed from the Hen and Chicken Islands near Whangārei harbour, up to the Cavalli
Islands and Whangaroa Harbour  (Figs  2 and 3). The Hen and Chicken Islands were included in this
surveillance  work  following  the  discovery  of  exotic  Caulerpa  at  Rākino  Island  and  the  Mokohinau
Islands in Auckland.

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C0036060 Wider Surveillance in Northland

Figure 2. Exotic Caulerpa diver-based transect surveillance from Whangaroa Harbour to the Bay of Islands harbour, including
various islands completed between 15th April to 28th April and 13th May to 16th May. Transects with exotic Caulerpa detected
are in orange, transects without exotic Caulerpa detected are in blue.

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C0036060 Wider Surveillance in Northland

Figure 3. Exotic Caulerpa diver-based transect surveillance from Tutukākā Harbour, Whangārei Harbour and the Hen and
Chicken Islands conducted between 1st May and the 12th of May 2024. No exotic Caulerpa was detected in these areas.

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C0036060 Wider Surveillance in Northland

Surveillance methodology

Surveillance was conducted between 15th April 2024 to 16th May 2024. All diving was completed by
Commercial Dive Specialists (CDS) Ltd who have experience conducting exotic Caulerpa surveillance
alongside  NRC  staff  and  have  been  involved  in  benthic  matting  operations  at  Waiheke  Island,
Auckland.

Divers followed a predetermined bearing for 15 minutes and systematically scanned the seafloor for
exotic Caulerpa. The area searched was calculated using the length of the transect swum, and assumed
divers could effectively search to a width of 2m (1m either side). If exotic Caulerpa was found, the
diver informed the surface attendant either by surfacing or by using a surface float to signal presence.
The  surface  attendant  recorded  the  GPS  position  on  NRC’s  ArcGIS  FieldMaps  platform,  which  is
accessible to BNZ staff. The relatively shallow depth of anchorages (<10m) allowed for multiple sites
to be searched daily without depth related restrictions or issues arising from bounce diving.

Dive  operations were conducted in a manner that ensured minimum contamination between dive
sites  to  prevent  the  spread  of  exotic  Caulerpa.  Diving  was  not  undertaken  in  areas  where  exotic
Caulerpa was not known to be present directly after diving in infested areas. After each dive day that
exotic  Caulerpa  was  detected,  NIWA’s  decontamination  protocols  were  followed  for  all  dive  and
survey gear (soaked in a detergent and freshwater solution).

Results

Divers  spent  27  days  conducting  surveillance  around  25  harbours  and  bays  and  19  islands/island
groups within the Northland region, swimming 93.3 km and searching approximately 186,600 m2(Figs
2 and 3; Tables 1 and 2).

Exotic  Caulerpa  was  identified  at  one  of  these  locations;  Poroporo  Island,  Te  Rāwhiti  Inlet,  Bay  of
Islands (Fig. 2; Table 2). This island is within the boundary of the Controlled Area Notice (CAN) zone.
Benthic mats with chlorine tablets were placed over six infestations at this site (Fig. 4; Table 3).

Table 1. Number and length of delimitation survey transects conducted per month between May and April 2024, and the
presence of exotic Caulerpa found during these surveys.

Transects with
Transects with
Approximate area
Month
Transect count
Total length (km)
exotic Caulerpa (#)
exotic Caulerpa (%)
searched (m2)
April 2024
226
55.2
4
1.76
110,400
May 2024
156
38.1
0
0
76,200
TOTAL
382
93.3
4
1.04
186,600

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C0036060 Wider Surveillance in Northland

Table 2. Number of transects completed each day at each location between 15th April and 16th May 2024 (n = 382).

Date
Location
Specific location
Number of transects
Substrate
Notes
15/04/2024
Bay of Islands
Manawaora Bay
19
Mud, sand

16/04/2024
Cavalli Islands
Papatara Bay
2
Sand, gravel

16/04/2024
Cavalli Islands
Motukawanui Island
5
Reef, sand, shell, gravel

16/04/2024
Cavalli Islands
Kahangaro Island
6
Sand, shell, gravel

16/04/2024
Matauri Bay
Putataua Bay
8
Reef, sand

17/04/2024
Cavalli Islands
Motukawanui Island
17
Sand, shell, gravel, reef

17/04/2024
Whangamumu Harbour
Whangamumu Harbour
1
Sand

18/04/2024
Whangamumu Harbour
Whangamumu Harbour
14
Sand, reef

18/04/2024
Te Toroa Bay
Te Toroa Bay
2
Sand, reef

18/04/2024
Outu Bay
Outu Bay
1
Sand

18/04/2024
Bay of Islands
Manawaora Bay
1
Sand, mud, shelly gravel

19/04/2024
Bay of Islands
Manawaora Bay
15
Sand, mud, shell, gravel

19/04/2024
Bay of Islands
Motuarohia Island
2
Sand

20/04/2024
Bay of Islands
Motuarohia Island
18
Sand

21/04/2024
Bay of Islands
Moturua Island
19
Sand, shell, gravel

22/04/2024
Bay of Islands
Moturua Island
7
Sand, gravel, reef

22/04/2024
Bay of Islands
Motukiekie Island
4
Sand, gravel

22/04/2024
Bay of Islands
Okahu Passage
3
Sand, gravel

22/04/2024
Bay of Islands
Waewaetorea Island
3
Sand, shell, gravel, reef

22/04/2024
Bay of Islands
Urupukapuka Island
1
Sand

23/04/2024
Bay of Islands
Waewaetorea Island
3
Sand, shell, gravel, reef

23/04/2024
Bay of Islands
Urupukapuka Island
14
Sand

24/04/2024
Bay of Islands
Urupukapuka Island
2
sand

24/04/2024
Bay of Islands
Poroporo Island
12
Sand, shell, gravel
Exotic Caulerpa found.
25/04/2024
Bay of Islands
Poroporo Island
5
Sand, shell, gravel
Exotic Caulerpa patches marked, and 6 benthic mats
placed (Fig. 4).
25/04/2024
Bay of Islands
Urupukapuka Island
5
Sand

26/04/2024
Kerikeri Inlet
Te Puna Inlet
14
Mud, shell, gravel

27/04/2024
Whangaruru Harbour
Whangaruru Harbour
15
Sand, mud

27/04/2024
Whangaruru Harbour
Tuparehuia Bay
7
Sand, mud

28/04/2024
Whangaruru Harbour
Whangaruru Harbour
3
Sand, mud

28/04/2024
Whangaruru Harbour
Tuparehuia Bay
5
Sand, mud

28/04/2024
Whangaruru
Bland Bay
5
Sand

28/04/2024
Whangaruru South
Ōakura Bay
3
Sand

01/05/2024
Tutukākā Harbour
Tutukākā Beach
2
Shell, gravel, sand, reef

02/05/2024
Tutukākā Harbour
Tutukākā Harbour
15
Shell, gravel, sand, reef

03/05/2024
Whangārei Harbour
Parua Bay
9
Mud

Date
Location
Specific location
Number of transects
Substrate
Notes
03/04/2024
Whangārei Harbour
Whangārei Heads
7
Sand, mud, shell, gravel

04/05/2024
Hen and Chicken Islands
Whatupuke Island
5
Reef

04/05/2024
Hen and Chicken Islands
Coppermine Island
3
Reef

04/05/2024
Hen and Chicken Islands
Taranga Island
10
Sand, reef

05/05/2024
Hen and Chicken Islands
Mauitaha Island
1
Reef

05/05/2024
Hen and Chicken Islands
Lady Alice Island
15
Reef, sand

05/05/2024
Hen and Chicken Islands
Whatupuke Island
2
Reef

05/05/2024
Hen and Chicken Islands
Coppermine Island
2
Reef

05/05/2024
Hen and Chicken Islands
Wareware and Muriwhenua Islands
2
Reef

06/05/2024
Whangārei Harbour
Whangārei Heads
18
Reef, sand
Potential sighting of exotic Caulerpa, NRC identified this
to be Ulva sp.  (Fig. 5).
07/05/2024
Whangārei Harbour
Whangārei Heads
17
Sand, shell, gravel

12/05/2024
Whangārei Harbour
Parua Bay
11
Sand, mud

13/05/2024
Whangaroa area
Mahinepua Bay
3
Sand, reef
NRC additional funding
13/05/2024
Whangaroa area
East Bay
2
Sand
NRC additional funding
13/05/2024
Whangaroa area
Whangaihe Bay
3
Sand, reef
NRC additional funding
13/05/2024
Whangaroa area
Taiaue Bay
4
Sand, reef
NRC additional funding
14/05/2024
Mahinepua Island
Mahinepua Island
4
Sand, reef
NRC additional funding
14/05/2024
Whangaroa Harbour
Pekapeka Bay
4
Sand, mud
NRC additional funding
14/05/2024
Whangaroa area
Tauranga Bay
3
Sand
NRC additional funding
14/05/2024
Whangaroa area
Waimahana Bay
2
Sand
NRC additional funding
14/05/2024
Whangaroa Harbour
Whangaroa Harbour
1
Sand, mud
NRC additional funding
16/05/2024
Whangaroa Harbour
Okura Bay
1
Sand, mud
NRC additional funding
16/05/2024
Whangaroa Harbour
Wairaupō Island
5
Sand. mud
NRC additional funding
16/05/2024
Whangaroa Harbour
Waitapu Bay
4
Sand, mud
NRC additional funding
16/05/2024
Whangaroa Harbour
Whangaroa Harbour
1
Sand, mud
NRC additional funding
TOTAL

382

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C0036060 Wider Surveillance in Northland

(A)
Poroporo Island
1
2  3 4


  5   6

(B)
(C)

  (D)
(E)

Figure 4. (A) Map of the locations where benthic mats were placed on exotic Caulerpa infestations around Poroporo Island, Bay of Islands.
Dates correspond to when the benthic mats were placed. Red dots indicate where patches of exotic Caulerpa were found, and numbers
indicate benthic mats were placed (Table 3) (n = 6). (B - E) Exotic Caulerpa patches found at Poroporo Island.

Table 3. Summary of benthic treatments undertaken on April 25th 2024 for exotic Caulerpa infestations near Poroporo Island,
Te Rāwhiti, Bay of Islands (n = 6). Site labels correspond to Figure 4.

Mat
Mat Size (m)
Treatment
Mat depth (m)
Number
1
Benthic matting and chlorine
1 x 1
6.2
2
Benthic matting and chlorine
2 x 2
4.3
3
Benthic matting and chlorine
1 x 1
5.2
4
Benthic matting and chlorine
1 x 1
4.7
5
Benthic matting and chlorine
2 x 2
5.3
6
Benthic matting and chlorine
1 x 1
5.3

Figure 5. Images from Commercial Dive Specialists (CDS) of Ulva sp. from Whangārei Heads area on 6th May 2024. Photo on
the left shows the algae in situ and photo on the right shows the algae out of the water.

Discussion

No exotic Caulerpa was detected outside the Controlled Area Notice (CAN) in Te Rāwhiti, Bay of Islands
(Figs 2 and 3). However, there was a range extension within the boundaries of the CAN; divers found
small patches of exotic Caulerpa at a depth of 5 – 8 m along the western bay of Poroporo Island (Figs
2 and 4). This area had been searched 12 months earlier and no exotic Caulerpa was detected at that
time. Upon finding exotic Caulerpa in April 2024, divers placed six benthic mats with chlorine pucks
underneath the mats (within the guidelines of NRC’s resource consent  AUT.036500.01.03 for using
chlorine to respond to marine pest incursions in Northland). Not all patches around Poroporo Island
were treated due to lack of weights used to secure the mats to the substrate.

Divers  completed  93.3  kilometres  of  surveillance  transects  over  27  diving  days,  equating  to
approximately $1,822 per kilometre swum, or $6,296 per day (using a combined budget of $170,000
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C0036060 Wider Surveillance in Northland

all costs exclude GST). This contract provided an effective way to cover a lot of ground to search for
exotic Caulerpa – more so than what could be achieved by NRC divers or other government agencies.
It  is  highly  recommended  that  this  work  is  continued  to  ensure  exotic  Caulerpa  does  not  spread
outside of the CAN. Further to survey effort, consistent presence of divers on the water also assisted
with  compliance;  divers  were  able  to  get  in  touch  with  hapū  members  to  inform  them  of  vessels
anchoring in the CAN.

A lot of diving effort was put into the surrounding Bay of Islands area and although this is still a popular
area for vessel movements and anchoring, and therefore a high-risk area, some of this effort should
have  been  distributed  to  conduct  surveillance  in  Whangaroa  harbour  which  is  another  popular
destination  and  anchoring  area.  Therefore,  NRC  provided  additional  budget  to  this  surveillance
contract to ensure the Whangaroa area and surrounding bays were surveyed.

Contract objectives revisited

The completion of the contractual objectives are noted below in bold.
•  Provide an Operational Specification and Health & Safety Management Plan and MPI H&S
Questionnaire. COMPLETED PRIOR TO COMMENCING SURVEILLANCE.
•  Complete dive surveillance of Northland high-risk sites for exotic Caulerpa. COMPLETED
PRIOR TO THE WRITING OF THIS REPORT.
•  Provide access to ArcGIS platform for live data for BNZ contract manager. COMPLETED
PRIOR TO THIS CONTRACT AS PART OF NRC/BNZ PARTNERSHIP.
•  Provide written report of findings from dive surveillance. COMPLETE.

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C0036060 Wider Surveillance in Northland

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