Inside Stories

Consider the Wrasse

SOSF D’Arros Research Centre

Clare Keating Daly

Cover image

Photo by Ryan Daly

The facial expression of the humphead wrasse can fairly be described as one of concern. First there is its furrowed brow, made by the fish’s namesake forehead hump; then its mouth, downturned and slightly agape. But look more closely at those chameleon-like eyes and you’ll find an essence of curiosity and astuteness that pushes this reef fish’s charisma arguably past that of Nemo.

Listed by the IUCN as an Endangered and conservation-dependent species, the humphead wrasse has reason to be concerned. The species is naturally uncommon and faces a significant and increasing threat from the food trade in live reef fish, where it is one of the species with the highest market value. At the SOSF-D’Arros Research Centre in the Seychelles we were also concerned. And curious.

During annual coral reef and fish surveys, we had observed humphead wrasse but had very little understanding of the species’ population size and structure. Was it common or were we just seeing the same five individuals? A 2014 study near Farquhar Atoll, in the southernmost island group of the Seychelles, found a remarkable abundance of humphead wrasse. The numbers suggested that Seychelles waters may host the highest known densities of the species in the world. Were these healthy populations limited to the country’s most remote reaches or would we find a similar number around our little island as well? And if we did, which marine habitats provide refuge for them? Making the most of the acoustic receiver network around D’Arros Island and St Joseph Atoll, we set out to answer these questions by embarking on a study to acoustically tag humphead wrasse.
A meaningful study would need a decent sample size to answer our questions accurately, so we set the tagging target at 20 wrasse. Even then I worried that this was too ambitious a goal; the humphead wrasse we’d seen were shy and we still didn’t know how many there were. The team at the SOSF-DRC has worked on tagging sharks, rays and other fish for years, but humphead wrasse would be a different kettle. Expert help was the only way forward.

We first reached out to researcher and friend Andrew Gray from the National Oceanic and Atmospheric Administration (NOAA), who had been involved in a study of humphead wrasse at Palmyra Atoll in the Pacific. He was encouraging, but warned us about the challenges. ‘First off, don’t try to catch any until you are fully prepared,’ he wrote. ‘They are smart and wary and you only have one chance per wrasse. If you try and fail, you’re never going to get that wrasse again – it will just swim off when it sees you.’

One chance per wrasse. For a viable study, we needed to tag a minimum of 10 wrasse. If there really were only five of them, the project was doomed. If we discovered large numbers but bungled attempts to catch more than six, we’d fail.

With little room for mistakes, we knew we needed more help. The study would have to be led by the best. We’d have to find the person with the most experience of tagging humphead wrasse in the world, preferably in an environment similar to that of D’Arros Island and St Joseph Atoll. Someone with a passion for these fish, the kind of person who would go so far as to shave his hair into an outline of a humphead wrasse. That could only be Dr Kevin Weng, lead researcher for a landmark study of the species at Palmyra Atoll. Lucky for the D’Arros Research Centre, he accepted the position of project leader and fine-tuned the research proposal into an SOSF-funded project. When asked to assemble his team, he called on Andrew Gray as chief wrasse wrangler.

Our expert Kevin and wrangler Andrew joined us in the Seychelles in October 2017. With the help of SOSF-DRC research assistant Luke Gordon, we’d done our best to prepare for these wary fishes. But challenges arose from the start: schedule changes crunched our window for field work from one month to just under three weeks and Andrew’s luggage had been lost somewhere along his four connecting flights. The pressure was on: 20 tags in 20 days. Actually, less than 20 days – before deploying any tags we had to complete surveys to establish the population and develop a reliable catch method.

Cover image

Photo by Ryan Daly

Clare Keating Daly Lab Manager

Photo by Ryan Daly

Early surveys went well. It turned out we hadn’t been seeing the same five fishes on every dive. On one survey we saw a group of 11 individuals, upending the premise that humphead wrasse never congregate in groups of more than seven. Data from MantaCam, a remote underwater time-lapse system installed on a local manta cleaning station, revealed five humphead wrasse in one frame. The fishes were there, but could we catch them?

Humphead wrasse are often caught on hook and line in catch-and-release fisheries. But after half a day of watching clever wrasse sceptically eye our hook and line while tiny reef fishes devoured our bait, we switched gears. To catch these fish, Kevin and Andrew trained us in what can best be described as a ‘diver-capture’ method. Making the most of each day, we started at dawn, searching caves and crevices for the wrasse. Given dive depths of less than 10 metres (33 feet) and the considerable time necessary to track down an individual, dives often lasted more than two hours; chief wrangler Andrew’s dive watch frequently ticked past the 240-minute mark. But eventually a day’s effort would yield a humphead wrasse to tag and soon we knew we’d get our minimum of 10 tags out.

As relief took over from my worry, other emotions soon emerged. My job and field-work experience include working up sharks from the size of my forearm to nearly the length of the boat, rays with whiptails and spines, and seabirds with beaks adapted to skewer fish. Which is to say, field work usually involves high levels of stress and vigilance to ensure the welfare of the animal and the safety of the people involved. But the humphead wrasse was different. Of course, there was the heightened pressure of maintaining the well-being of an Endangered species, and the strength of a humphead wrasse is formidable, but the feeling was different when we worked with these charismatic fishes. Without anthropomorphising too much, I felt a level of intimacy and closeness with each brilliant wrasse we tagged. Maybe this feeling of tenderness was due to their lack of sharp teeth, sandpapery skin, barbed tail or stabbing beak. But I couldn’t help thinking that there was something beyond these emotions. As Andrew had said, humphead wrasse are smart, observant and curious.

And they’re hip. Humphead wrasse have facial tattoos, the technical term for the fingerprint-like markings on the cheeks of each fish. Each work-up included photographing these tattoos to provide a record of the individual and thus the chance to identify it later. When the tagging, measuring and photographing were done, we slid the fish back to waiting divers, who in turn released each wrasse into the cave or crevice where it had been found.

In the end, we released 20 healthy adult humphead wrasse equipped with acoustic tags. With these fish, our study is the largest telemetry survey of this Endangered species in the world. Moreover, the largest wrasse – ‘Gerald’ measuring 133 centimetres (four feet four inches) total length – broke the record for the world’s largest tagged humphead wrasse. The smallest, but not least, was ‘Wrassesaurus’, which came in at less than half the size of Gerald – a mere 52 centimetres (20 inches).

In any tagging study, a scientist effectively asks an animal to confide its secrets, to unveil its mysteries. In this one, we’ve perhaps uncovered a refuge for the humphead wrasse and we’ve asked this enigmatic fish to show us what we need to protect it and to help us understand its place. By the time you read this article, we will have begun the process of piecing together the first dataset from the study. Humphead wrasse will still look concerned, but these data may give us a chance to minimise the threats facing them. Perhaps they, like me, are curious about what scientists, conservationists and policy makers are capable of when armed with an animal’s inside story.

Photo by Ryan Daly