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Solving the dog death mystery

During 2009, several dogs died on Narrow Neck and Cheltenham beaches in Auckland. While the general public were speculating over their deaths, scientists from Cawthron Institute, who had long been working with marine toxins, felt sure natural toxins were involved. The dogs had vomited and behaved in ways that indicated they had ingested toxins.

At that time, one of the scientists was in Auckland and visited the beaches. Her background – working with toxic algae – caused her to wonder if the dogs had eaten some. She rang her colleagues at Cawthron to discuss it, and the investigation began. Another Cawthron scientist made a special trip to the beaches, and together, they tried to imagine what they would eat if they were dogs. They gathered up anything they could find that a dog might possibly try to eat such as seaweed, sponges and bits of other sea creatures, anything smelly, seawater and rubbish.

A culprit is identified

Paul McNabb and Andy Selwood, chemists at Cawthron, started to investigate whether any of the samples contained toxins. Once back at Cawthron, samples were sent off to a toxicologist to be tested. All of the samples proved harmless except one that was found to be very toxic! This sample had come from a rotting blob the scientists had found on the beach. They didn’t even know what it was at first. After some investigation, they discovered it was a grey side-gilled sea slug Pleurobranchaea maculata. The scientists found there were large numbers of them in the harbour near the beaches where the dogs died. They collected some slugs from the area and keep them in an aquarium at Cawthron.

The hunt for a toxin

The sea slugs had been identified as the killers. However, the question now was what was the toxin in the slugs that killed the dogs and where had it come from? The scientists at Cawthron used liquid chromatography-mass spectrometry (LC-MS) to gather some information about the new toxin such as its molecular mass. Stored in the freezers at Cawthron are large numbers of different marine toxins. The scientists already have information for these identified toxins. The new information from the sea slug toxin was compared to over 40 known marine toxins. Unfortunately, none of the toxins held by Cawthron matched the toxin found in the sea slugs.

Tetrodotoxin (TTX) is identified

Paul knew about tetrodotoxin (TTX). It had been made famous by the Japanese pufferfish and the deaths of some people in Japan who ate pufferfish. Even though TTX had never been found in anything around New Zealand, he thought about TTX because it was water soluble like the sea slug toxin and they both had a similar mass.

After Paul had tested the sea slug toxin for its molecular mass using LC-MS, he then checked with published results for the mass of TTX. It was a match, but they needed to be sure. Paul contacted a scientist he knew had a sample of TTX and asked him to courier the sample to Cawthron. In the very first test using the LC-MS, the results were 90% positive for TTX. The scientists had found a match! TTX was identified as the toxin in the grey side-gilled sea slugs that had caused the death of the dogs.

It was the first identification of TTX in New Zealand. It also makes the grey side-gilled sea slug our most toxic creature. One average slug could kill up to four adults if they ingested it! It took just 1 week to identify the sea slugs as the culprit and the TTX as the toxin within them.

Funding for on-going research

They still had many questions. How did the slugs obtain the TTX? Are there other sea creatures with TTX? Is it in the food web? Might it affect kaimoana? Cawthron decided to fund research to try to find the answers. A year later, they received a substantial grant from the Marsden Fund of the Royal Society of New Zealand to help them continue their research. (The Marsden Fund was established by the government in 1994 to fund research.)

This project is now funded by the Marsden Fund and Ngā Pae o Te Māramatanga. Paul McNabb is supported by a New Zealand Ministry of Business, Innovation and Employment Te Tipu Pūtaiao PhD Fellowship.

Nature of science

There is no one way to conduct science investigations. Scientific investigations can be carried out in a myriad of ways. In this case, the scientists were like detectives, and the problem concerning what was killing the dogs was solved easily and in a short space of time, but not all investigations are this straightforward.

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