Taihoro Nukurangi

Field surveys to determine the extent of distribution and relative abundance of Charybdis japonica in the Whangarei region

Authors Graeme J. Inglis, Nick Gust, Graeme Mackay, Rob Tasker

Final Research Report for Ministry of Fisheries Research Project ZBS2001/01 Objective 3

National Institute of Water and Atmospheric Research

May 2004 " I

Final Research Report

Report Title: Field surveys to determine the extent of distribution and relative abundance of Charybdis japonica in the Whangarei region

Authors: Graeme 1. fuglis, Nick Gust, Graeme Mackay, Rob Tasker

1. Date: II-May-04

2. Contractor: National fustitute of Water and Atmospheric Research Ltd

3. Project Title: Surveillance for exotic marine organisms in

4. Project Code: ZBS2001/01 Objective 3

5. Project Leader: Graeme fuglis

6. Duration of Project: 48 days

Start date: 13/04/04 Completion date: 31105104

7. Background

The non-indigenous portunid crab, Charybdis japonica, was first reported in New Zealand from Waitemata Harbour in 2000 (Webber 2001, Smith et al. 2003). C. japonica is likely to have been introduced to New Zealand by ships arriving from its native range in coastal regions of China, Japan, Korea, Taiwan and Malaysia and the western Pacific. Delimitation surveys of the introduced popUlation were undertaken in April and October 2002 throughout Waitemata Harbour and the Hauraki Gulf. At that time C. japonica was widely distributed and abundant throughout Waitemata Harbour, but the population did not appear to have spread further than about 30 km from the harbour entrance (Gust et al. 2002). The northern-most specimens were trapped in Wieti Estuary, approximately 25 km north of Waitemata Harbour, whilst the southern-most record was from Tamaki estuary, ~ 10 km south of the harbour entrance.

fu September 2003, a single, mature female C. japonica was captured adjacent to Port Whangarei in Whangarei Harbour, approximately 140 km north of Waitemata Harbour (fuglis and Gust 2003). This record represented a significant range extension from the Auckland popUlation. The crab was captured during the Winter 1 targeted 1 surveillance survey of Whangarei Harbour. More than 180 baited traps were set during the survey, at 69 locations throughout Whangarei Harbour, but no further specimens were ,captured. Shortly after the survey, NIWA received two anecdotal reports of "unusual" crabs near Whangarei; one from the vicinity of Snake Bank, an important cockle harvesting area in Whangarei Harbour, and another from the Estuary, south of Whangarei Harbour. The report from Ruakaka described a large, blue or purple-coloured crab present in shallow water near the Ruakaka camp ground. In each case, the reports were made by members of the public, but no specimens were retained to confirm identification.

In March 2004, NIWA again trapped more than 50 locations in Whangarei Harbour as part of the Summer 2 targeted surveillance and did not capture any additional specimens of C. japonica (Gust et al. 2004). The Ministry of Fisheries contracted NIWA to extend the trapping surveys for C. japonica to four additional estuaries (, , Ruakaka and Mangawhai) north and south of Whangarei (Fig. 1) to determine the extent of distribution and relative abundance of Charybdis in the Whangarei region.

8. Objective: i' • To determine the extent of distribution and relative abundance of Charybdis in the Whangarei region by trapping for Charybdis in four other estuaries north and south of Whangarei.

9. Methods:

The four estuaries were sampled between 20th and 28th April 2004 (Table 1). Ten to ~ ~. ! 15 locations, distributed throughout the navigable area of each estuary (i.e. > 0.5 m ,,', ,," water depth), were trapped for Charybdis (Table 1, Fig.s 2-5). Sampling was done '.,;.

~'.., using collapsible box crab traps (62 cm x 42 cm x 20 cm) baited with 1-2 pilchards , ~/£. :"'1" each. At each location, three baited traps were clipped to a 30 m trap line at U ~,. approximately 5 m intervals. The lines were weighted with a single anchor and ':' marked by a floating buoy at the water surface. The GPS location of the trap line and .r,'~ ,., ',' the water depth were recorded at the time of each deployment. All traps were left overnight before being retrieved. Brachyuran crabs recovered from the traps were identified in the field and reference specimens kept for validation.

Table 1. Summary of trapping effort in each estuary. The numbers of locations sampled and total numbers of traps (brackets) deployed in each estuary are indicated.

Estuary Date surveyed No. of locations , ; trapped (No. of traps) Ngunguru 27-28 April 2004 15 (45) Pataua 26-27 April 2004 15 (45) Ruakaka 21-22 April 2004 10 (30) Mangawhai 20-21 April 2004 15 (45)

The field teams also undertook visual searches of the intertidal shoreline in each estuary to look for cast exuviae along the driftline. Contact was also made with commercial crab fishermen from the to determine if they had rec~rded C.japonica in any of their recent catches.

2 10. Results:

No specimens of C. japonica were captured during the survey of the four estuaries. The most abund~t brachyuran crabs recorded from the traps were the native portunid, Ovalipes catharus (White, 1843) and the hairy handed crab, Hemigrapsus crenulatus (H. Milne Edwards, 1837) Ovalipes catharus was most abundant in Mangiwhai estuary (Fig.s 6 and 13). H. crenulatus was particularly abundant in Ruakaka estuary, where it was caught at all trapped locations at an average of 12 (±4) crabs per trap line (Fig.s 6 and 12). In contrast, very few H. crenulatus were captured in the three other estuaries « 1 crab per trap line) (Fig.s 6,8,10 and 14).

Three commercial crab fishers in the Whangarei region were interviewed by NIW A to determine if Charybdis had appeared in their catch. Bill Richardson is based in and fishes within and Whangarei Harbour; Phil Tanner is based at Ruakaka and also fishes in the Whangarei district; and John Charles fishes out of Mangawhai Heads. None of the fishermen had seen C. japonica in that region, but all three agreed to notify MFish and NIWA of any unusual specimens that they trapped. , '.' Interestingly, John Charles fished Waitemata Harbour and surrounding areas of the inner Hauraki Gulf during the 1990's and claimed to be catching C. japonica for at least 6 years prior to the first official record in 2000, when specimens were lodged with Te Papa for formal identification.

11. Conclusions:

We found no evidence from field surveys carried out in Whangarei Harbour (Gust et al. 2004), Ngunguru, Pataua, Ruakaka and Mangawhai estuaries that the introduced portunid crab, C. japonica, has established a permanent population in the Whangarei region. This finding was reinforced by the observations of commercial crab fishermen t;, " , in the region, none of whom had recovered C. japonica from their catches. It appears . ,~~ that the capture of a single specimen in September 2003 may have been an isolated event, rather that an expansion of the current known range.

12. Literature Cited: Gust, N.; Inglis, G.J.; Smith, M. 2002. Delimitation survey for the invasive swimming crab Charybdis japonica in the Auckland region. Final Research Report for Ministry of Fisheries Research Projects ZBS2001l01 Objective 1 & ZBS2001/13A. NIW A Client Report, Wellington. 28 p. Gust, N.; Inglis, G.J.; Hayden, B.; Floer!, O. 2004. Surveillance for exotic marine organisms in New Zealand: Summer 2 (2003-2004) surveillance. Research Progress Report for Ministry of Fisheries Research Proj ect ZBS200 110 1, NIWA Client Report, Wellington. 12 p. (+maps). Inglis,GJ.; Gust, N. 2003. Surveillance for exotic marine organisms in New Zealand: Winter I (2003) surveillance. Research Progress Report for Ministry of Fisheries Research Project ZBS2001/01, NIWA Client Report, Wellington. 9 p. (+maps) Smith, PJ.; Webber, W.R.; McVeagh, S.M.; Inglis, GJ.; Gust, N. 2003. DNA and morphological identification of an invasive swimming crab, Charybdis japonica (A. Milne-Edwards, 1861), in New Zealand waters. N.z. J. Mar. Freshw. Res. 37: 753- 762. Webber, R. 2001: Space invaders: crabs that turn up in NZ unannounced. Seafood New Zealand. November 80-84 .

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