Quarterly Report of Investigations of Suspected Exotic Marine

MARINE AND FRESHWATER Quarterly report of investigations of suspected exotic marine and freshwater pests and diseases: July to September 2020 New to New Zealand nudibranch, Tauranga Exotic disease investigations are managed and reported by the MPI Diagnostic & Surveillance Directorate, Wallaceville. The following is a A new to New Zealand nudibranch, summary of investigations of suspected exotic marine and freshwater Goniodoris meracula, was identified from photos collected by the University diseases and pests during the period from July to September 2020. of Waikato. The specimen was found on a settlement plate in Tauranga Harbour in 2017, but not identified until July 2020 when the photos were available for testing. An MPI pathologist though one member of the public noted sent to an international nudibranch examined the photos but could not draw seeing a live one there in March 2020. expert who identified it as G. meracula. any conclusions without a sample for The dead rays were in an advanced state The photographed specimen was one testing. The lesion was consistent with of decomposition and had been dead for of several observed on the plates. those caused by A. salmonicida, but also some time. No samples were able to be Goniodoris meracula is native to Australia those caused by other pathogens such as taken for testing. and typically lives in a burrow inside a Flavobacterium psychrophyilum. As the colonial ascidian. Nudibranchs pose a The stingrays were likely stranded when Hinemaiaia Stream is within the Taupo low biosecurity risk as they are typically the water was released on 4 August 2020 freshwater region a local Department of rare in time and space. They do not and the carcasses remained trapped. Conservation ranger was informed. The typically reach densities that would have Some of the dead animals had become ranger stated that wounds of this nature a significant effect on local species. buoyant, which is highly unusual as were commonly seen on trout in the sharks and rays do not have swim area at this time of year, as the fish were Dead octopuses, Otago bladders. This supports the theory that in a weakened post-spawning state. The the stingrays had been dead for some Harbour causative agent was typically a parasitic time and had become buoyant owing A member of the public reported seeing nematode worm, Eustrongylides sp., to decomposition gases. Auckland six to eight dead octopuses washed up known locally as shagworm because it Council was notified, to investigate the in Sawyers Bay, Otago Harbour. The is vectored by shags (and other birds). possibility of water-quality issues, but the notifier described the water in the area as The nematodes cause large cysts to water parameters they measured were discoloured and foamy. No obvious signs develop, typically near the gut cavity, normal. Auckland Council stated that of trauma were visible on the octopuses, which eventually erupt and leave an open the earliest notification of a dead stingray suggesting the incident was unlikely to be wound. The investigation was closed. was received the day after the floodgates fishing-related. Information from Otago were last closed and they employed Regional Council suggested it was not Dead stingrays in Orakei contractors to remove the dead stingrays uncommon for octopuses to wash up Basin, Auckland (13 in total). While the cause of death is dead over winter. Octopuses die naturally Several members of the public contacted inconclusive it seems most likely that it after spawning but it is considered MPI to report a number of dead stingrays was related to the fault in the floodgates unusual to see more than one or two in Orakei Basin, Auckland. The Orakei and the retention of the water. dead animals at a time. It is unclear what Basin is a small (~730 m across) lagoon species of octopus they were. enclosed by floodgates that isolate it “Odd-looking” crab, Suspect Aeromonas from the sea. The floodgates are opened Mt. Maunganui roughly fortnightly for two tidal cycles to A crab described as “odd-looking” salmonicida in trout, Taupo flush and replenish the water, but owing was spotted in the marina at Mount A local fisherman in the Hinemaiaia to a fault with the gates the water was Maunganui. The notifier took several Stream, Lake Taupo, contacted MPI after retained within the basin from May to photos for identification but then released catching a rainbow trout (Oncorhynchus early August. the crab into the water. The photos were mykiss) with a large, open lesion on In total nine dead stingrays were reported sent to the Marine Invasives Taxonomic its side. Lesions of this nature can be from around the edge of the basin. They Service (MITS) at the National Institute caused by the pathogen Aeromonas were a mixture of long-tailed stingrays of Water & Atmospheric Research salmonicida, a notifiable organism that is (Bathytoshia lata) and short-tailed (NIWA) for identification. MITS not present in New Zealand. Aeromonas stingrays (B. brevicaudata), ranging in identified the crab from the photos as a salmonicida causes a disease known as size from about 50 cm to more than 1 native species, Metadromia wilsoni, using furunculosis. The fish was released back m wide. The presence of stingrays in the the morphological characteristics that the into the waterway after photos were Orakei Basin appears to be a rare event, submitter managed to get in the photos. taken of the lesion, so no samples were Surveillance 47 (4) 2020 33 Shellfish mortality event, Ninety Mile Beach A Waikato University marine ecologist reported a mass mortality of toheroa (Paphies ventricosa) at Ahipara, Ninety Mile Beach, disclosed by a local contact. Mass mortalities of shellfish on Ninety Mile Beach have been recorded on numerous occasions; the cause appears to be multi-factorial and may be related to the presence of certain Endozoicomonas- like organisms in the shellfish. In this case the shells washing up on the beach were empty so no samples were able to be collected for testing. A record was made for further reference. Nicholas Ward Incursion Investigator Biosecurity Surveillance & Incursion Investigation (Aquatic & Environment Health) Biosecurity New Zealand Ministry for Primary Industries [email protected] 34 Surveillance 47 (4) 2020.

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