A Breakthrough for Data-Poor Fisheries Starts in Palau

Find out how a new technique piloted in Palau by The Nature Conservancy could help solve one of the world's greatest challenges in fisheries management -- a simple, low-cost method for assessing fish stocks.

On a dock in the small fishing village of Ollei, at the northern tip of Palau’s largest island, Babeldaob, Harper Skang is about to cut open a fish — to save a fishery.

First, Skang calls out the length of the fat, pink keremlal (a type of snapper) — 300 millimeters as measured on a board. Then he saws open its belly and pulls out a stringy clump: the gonads, or reproductive organs. He inspects the gonads closely and, after some debate, concludes, “Mature male.”

Sound odd? The inspection is actually key to an inexpensive new approach The Nature Conservancy is piloting to assess fish stocks in Palau, where resources — as they are in much of the developing world — are too scarce to carry out costly traditional stock assessments.

The findings have been convincing enough to motivate some Palauan communities to adopt more sustainable fishery management practices. And the Conservancy is now working to bring the approach to “data-poor, resource-poor” developing world fisheries across the globe — from Indonesia to Belize to California and even freshwater fisheries like Kenya’s Lake Tanganyika.

“There are quite a few methodologies for data-poor stock assessment, but this technique is the simplest and requires less data collection than others,” says Carmen Revenga, the Conservancy’s fisheries strategy lead. “And it’s one that engages fishers, which is vital to achieving a successful outcome.”

Palau’s Fisheries ‘Skidding to the Edge of Collapse’ — Could Others Be As Well?

The approach involves data collection by fisherman like Skang, a Palauan community leader who has been fishing for more than 50 years.

Like many fishers in this small Pacific island nation, he has seen the reef fish populations decline in recent years — but he didn’t know how severe the problem was until becoming involved with the Conservancy’s stock assessment project.

Even though Palau has a deeply rooted conservation ethic and a large network of marine protected areas (MPAs), tourism and modern catch techniques have put pressure on fish stocks there. Data that Skang and other Palauan fishers helped collect revealed that 60% of Palau’s fish catch is juvenile — meaning the majority of fish being caught haven’t had a chance to spawn or reach full size.

Mature gonads of an emperor fish caught for the Palau Stock Assessment Project. Credit: Andrew Smith.
Mature gonads of an emperor fish caught for the Palau Stock Assessment Project. Credit: Andrew Smith.

With so few fish reproducing, Palau’s fisheries are skidding to the edge of collapse.

“It’s like sitting down in your house and finding out it’s about to burn down,” says Skang.

Having accurate information about their fish stocks is a problem that many of the world’s fisheries face. To manage a fishery sustainably, you need to know how many fish it has, which species, how quickly they grow and reproduce, and how many can be harvested without putting the fishery in danger of collapse.

But traditional stock assessments are so expensive and resource intensive — requiring years of data collected by trained experts at a cost of hundreds of thousands of dollars per stock or more — that they are prohibitive for most fisheries, especially those in developing countries.

In fact, only 350 of the world’s 10,000 fisheries have full stock assessments, says Chuck Cook, who started the Conservancy’s program in Palau in 1992. The remaining 90% are what scientists call “data-poor.”

And without the stock data to inform management decisions, these data-poor fisheries — like Palau’s — can easily become overfished, threatening to upend the livelihoods and food security of the people who depend on them.

A Simple, Low-Cost Assessment Method for ‘Data-Poor’ Fisheries

The new technique piloted by the Conservancy aims to solve this problem by providing a simple, low-cost method for assessing fish stocks. Using a minimum amount of data collected by fishers themselves, the technique can be implemented at a fraction of the cost and time of traditional stock assessments.

“With our data-poor stock assessment technique, we don’t need to count how many fish are in the water,” explains Steven Victor, the Conservancy’s deputy director of conservation in Palau and a native Palauan. “Rather, we are looking at how much breeding population there is for a given fish species.”

The technique relies on simple size ratios to assess how much spawning is happening and how much is enough. At its most basic, the technique uses two pieces of local data — size of fish and maturity of fish — combined with existing biological information to produce a ratio of spawning potential.

Measuring fish length as part of the Palau Stock Assessment Project. Credit: Andrew Smith
Measuring fish length as part of the Palau Stock Assessment Project. Credit: Andrew Smith

“Spawning potential is sort of like the replacement rate for people,” explains Australian fisheries scientist Dr. Jeremy Prince, who helped the Conservancy develop and implement the project.

“If every couple has 2.1 children, population levels will flat-line — no growth and no decline.”

For fisheries, that magic number is 20% — if fish can achieve at least 20% of their natural lifetime spawning, a fishery can sustain itself. Less than that, and the fishery will decline. And 20% is just a minimum number — scientists hope to see fisheries achieving 30-50% of natural spawning.

There are huge benefits to meeting these spawning numbers. By waiting for fish to reach the maturity needed for 20% spawning, they will be bigger. For example, a coral trout that has lived long enough to achieve 20% of its spawning will weigh 4 times more than a juvenile caught at 0% of its spawning.

“So you stand to gain more food by waiting a little longer to catch fish,” says Prince.

But the findings were startling for the spawning potential of some commonly caught species in Palau. “The fish are achieving just 3-5% of their lifetime spawning, far below minimum numbers for sustainability,” says Prince. “Basically, most of these fish stocks are in decline.”

The consequences of this are clear: If most fish aren’t reproducing, in a short time there will be no more fish.

To the Fish Market: Turning the Findings into Awareness and Action

From August 2012 to June 2013, Skang and other trained fishers helped scientists collect data on species, size and maturity for about 2,800 fish caught in Palau’s waters. They measured their own catch as well as fish for sale at the country’s only fish market, Happy Fish Market.

Palauans like to buy their fish whole, so gutting market fish to assess gonads was not initially a welcome idea with the fish sellers at the Happy Fish Market. But a $300 “rental” fee negotiated with the local women sellers gave them access to 600 pounds of fish for data collection — a fantastic resource that also provided an opportunity to discuss Palau’s overfishing problem with a broad community of fish sellers and buyers.

This cooperative effort between scientists and fishers has been key to the success of the project. Palauan fishers’ extensive knowledge and experience — “they’re practically marine biologists” says Prince — helped inform the scientific process and increase community awareness of the problem.

“When you bring in the fishers to be part of the data collection effort, it changes how they look at their fishery — they see that their livelihoods are at risk,” says Revenga.

Palau’s Rock Islands seen from the air. The Rock Islands are a top tourist destination for Palau, but the reefs here have been overfished. Credit: Ian Shive.
Palau’s Rock Islands seen from the air. The Rock Islands are a top tourist destination for Palau, but the reefs here have been overfished. Credit: Ian Shive.

Prince and Victor have been presenting the findings of the pilot project at community meetings across Palau. With the new knowledge provided by the data, Palau’s northern fishing communities have moved quickly toward developing management strategies that could restore fish populations.

In a traditional meeting house in Palau’s northern Ngarchelong state one June evening, Prince and Victor present the findings to a dozen fishers. Dressed in shorts, t-shirts and flip-flops or bare feet, the fishers chew betel nut while listening.

Most are men, a few women. Mosquitos spin around the room. This is one of many community meetings to inform fishers about the overfishing problem and begin discussing solutions.

“The reefs are empty right now, we all know it,” says Prince. “It’s an empty garden that’s not replenishing itself, a wasted resource. The fish are being caught before they can reproduce.”

At the end of the presentation, there are a few questions about the science and the data. But most of the discussion focuses on what to do about the problem.

“Everyone knows that what we are catching now is not the same as 10 years ago, but we didn’t know why,” says Skang. “Now we know why, and we can figure out what to do about it.”

Solving the overfishing problem is never easy — there are trade-offs and sacrifices. Management options range from imposing size limits to closing areas for a certain length of time until fish populations can rebound.

But these choices — which tend to be contentious and complicated to work out — are much easier to adopt and apply when fishers are part of assessing the problem and are engaged in discussing the solutions.

“In Palau, it’s the fishers who have been the first to advocate for management measures that will bring fish stocks back to plentiful levels, because they understand the data and what it means and see the risk of continuing business as usual,” explains Revenga.

Everyone involved in the project, from scientists to fishers, are optimistic that Palau’s reefs will soon be on the road to recovery.

“I think things will turn around here very quickly,” says Prince. “Community-based responsibility with simple scientific rules of thumb is what will work.”

“The whole way of life in Palau has always depended on fish,” adds Victor. “We exchange fish between families as part of our customary obligations, we give fish to our sisters as an investment in their families. Without fish, we really can’t call ourselves Palauans anymore.”

Published on

Join the Discussion

Join the Discussion

Please note that all comments are moderated and may take some time to appear.


  1. Jane Brandenburg says:

    Thank you for this Jeremy. It is something that I will be sharing with my students.

  2. This is cutting edge eco-science. Data-poor solution are to the mind of fuel effective effective economies are to the environment: a sustainable and empowering way forward that everyone can understand and apply.
    Ecology is the native tongue of nature and unless it it translated into dialect we all can understand it will remain ineffective.
    Congratulation to Jeremy Prince for stetting an example of how science can serve the environment with common sense and simple low cost solutions.