To Pinpoint the Origin of a Fish, Check Out Its Physique

A new cost-effective tool may help small-scale fisheries simply and accurately determine the origins of a day’s catch.

A fisher from a small-scale fishery in Honduras hooks a yellowtail snapper—a species of fish that may vary its shape depending on where it's sourced. (Claudio Contreras-Koob, International League of Conservation Photographers)
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Illegal, unreported and unregulated fishing cost the global economy $36.4 billion every year—a figure that exceeds the annual gross domestic product of over half the world’s countries. Overfishing and regional trespassing threaten not only the security of small local fisheries, but also vulnerable species in dire need of conservation. Now more than ever, there is an urgent need for new cost-effective tools that can facilitate both improved fishery management and the protection of marine biodiversity.

This week, Smithsonian scientists report a new way to track where fish are sourced—information key to detecting and preventing unsustainable fishing practices. Their technique is neither technologically cumbersome nor prohibitively expensive: To locate a fish’s origin, analyze its shape. In fact, even when held up against more cutting-edge methods, the process of measuring the body of a fish isn't just simpler—it's also more precise.

Such findings are especially important for small-scale fisheries, which tend to be concentrated in under-resourced countries and fly under the radar of standardized management practices. Traditionally, regulatory bodies have turned a blind eye to the mom-and-pop shops of fishing, dismissing them as inconsequential compared to industrial fleets.

But millions of these smaller fishing companies exist around the world, and cumulatively, their catches can exceed or equal those of their larger counterparts. What’s more, small-scale fisheries are key sources of income and cultural capital for local communities around the world, necessitating their preservation on several fronts. Currently available tools, however, are unevenly distributed due to expense and lack of oversight, ultimately falling short in the fight against illegal fishing. Businesses across the world continue to suffer the repercussions of overfishing and trespassing across designated fishing boundaries. Complicating matters is the fact that the sources of individual fish are tough to track once they've been caught and aggregated.

With this in mind, lead author Steven Canty, a program coordinator for the Marine Conservation Program at the Smithsonian's National Museum of Natural History and researcher with Manchester Metropolitan University, set out to test the efficacy of three methods for identifying the geographic origins of fish. Their efforts focused on 149 yellowtail snapper gathered from three different fishing grounds off the coast of Honduras. The locales were separated from each other by several miles, reliably isolating the reef-dwelling fish. Additionally, each fishing ground was characterized by drastically different surroundings, including the depth of the waters, proximity to beachy shores and mixing with the surrounding ocean waters.

Sourced from local fishermen, most of the snapper were already dead at the time of sampling. Upon receiving the fish, Canty and his colleagues performed three different tests. The first, a genetic analysis, compared signatures in each individual fish’s DNA that might reveal its home habitat. Although all the fish were within the same species, Canty reasoned that small differences may have accumulated over time based on the local environment. The second test analyzed the chemical composition of a small structure in the fish’s inner ear that is known to absorb unique elements from surrounding waters. In the third, the researchers took measure of each fish’s form, pinpointing different bodily landmarks and calculating the ratios between them. This method capitalizes on the idea that fish living in different conditions will subtly adapt their physique to their surroundings.

In Honduras, small scale fisheries can catch over twice the amount captured by industrial fleets, highlighting their prominent role in the global fish market. (Luciano Candisani, International League of Conservation Photographers)
Analyzing the bodies of fish is a simple task that involves pinpointing anatomical landmarks and measuring the distance between them. (Steve Canty, Smithsonian Institution)
Two small-scale fishers from Honduras boating on a shallow reef. (Luciano Candisani, International League of Conservation Photographers)
A simple and cost-effective analysis of fish body shape may be useful for both small-scale fisheries and conservationists, who both benefit from tracking fish and their habitats. (Luciano Candisani, International League of Conservation Photographers)
A fisher from a small-scale fishery in Honduras hooks a yellowtail snapper—a species of fish that may vary its shape depending on where it's sourced. (Claudio Contreras-Koob, International League of Conservation Photographers)

The first two methods, though well-established in the field of fish ecology, bear logistical hindrances: both are financially costly, technically laborious and incredibly time-consuming, requiring up to two months to analyze samples at $20 to $35 per fish. Body shape analysis, on the other hand, requires only a set of calipers and a couple hours of training. And once this minimal equipment is purchased and an individual has learned the ropes, there is no additional cost.

Canty was amazed to find that simply scrutinizing fishy forms—the most straightforward and cost-effective method—was also the most accurate, honing in on fish home turf with almost 80 percent accuracy. The anatomical differences between locales were subtle—not necessarily incongruities one would see with the naked eye—but consistent.

“We were surprised how well the [shape analysis] actually worked—it’s such a simple tool compared to the others,” says Canty.

The researchers believe that the different environments that house the fish—which are otherwise very genetically similar—are responsible for these changes. It turns out that factors as unassuming as diet, water temperature and the speed of passing currents can mold fish in unexpected ways. This means that, even within a species, anatomy can be incredibly diverse.

As a whole, this work appears to shed light on how bodies converse with their environments over time. “You adapt to the place you live,” Canty explains.

Both the genetic and chemical analyses performed modestly in comparison, each clocking in at around 50 percent accuracy. Canty had expected both to yield better results, but theorizes that the yellowtail snapper populations he sampled may not be as physically separate as once thought. Snapper eggs can drift, for instance, and these three communities of fish may occasionally mate, blending their genes past the point of distinction.

Though they fell short in this particular case, the more technically advanced tools are still crucial to research efforts in marine fisheries around the world. However, Canty’s findings add what could be a game-changing technique to the small fishery toolkit—one that doesn’t need to compromise precision for price.

“I think that these findings are fascinating and surprising,” says Susan Lowerre-Barbieri, a professor of fisheries ecology at the University of Florida and researcher at the Florida Fish and Wildlife Research Institute. “I wouldn’t have expected this to show up on such a small spatial scale.”

Body shape analysis, however, has its limitations. For one, it can only be performed on adults: Juvenile fish still in the throes of growing pains exhibit body ratios distinct from those of adults. Additionally, findings like Canty’s may not be recapitulated in other locations, especially where environments exhibit less diversity, for instance, or where the boundaries between fishing grounds are blurry, says Lowerre-Barbieri. Unfortunately, these same conditions may contribute to the very problem of unauthorized fishing that Canty and his colleagues hope to address. Furthermore, the researchers only assessed the body ratios of one species—the yellowtail snapper. Other fish may be less sensitive to their surroundings, or show less loyalty to a restricted locale. But only time will tell: In future work, the team will test the transferability of their technique on a more global scale.

In the meantime, Canty is hopeful that there may be applications of body shape analysis above and beyond fisheries management. This tool could equip conservationists tracking endangered fish in protected habitats, for example. Importantly, the team’s method is fairly non-invasive and amenable to a catch-and-release procedure: Fish need not sacrifice lives for this brand of science.

There is hope yet for the future of sustainable fishing. It's a mission that may just harken back to basics.

About Katherine J. Wu
Katherine J. Wu

Katherine J. Wu is a PhD student in Microbiology and Immunobiology at Harvard University and Co-Director Emeritus of Science in the News, a graduate student organization that trains young scientists to communicate science to the general public. She is also a 2018 AAAS Mass Media Fellow at Smithsonian magazine. Website: katherinejwu.com

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