“A study by a food engineering student…”

That’s how a recent item from Seafood Source begins, describing alleged evidence of the presence of bycatch in samples of canned tuna purchased in Mexico.

Specifically, the study purported to show that of fifteen cans of tuna purchased in Mexico, “three were found to contain traces of dolphin DNA, confirming the presence of dolphin meat.”

That’s an explosive claim… and ultimately an inaccurate one. No bycatch, no dolphin – it’s just that simple.

From the start, it was unclear how reliable the specific methods employed to isolate and identify the purported DNA were. We knew that attempts to determine DNA sources in canned product were exceedingly difficult. Why? Because the product is cooked in the process, degrading the proteins in the tuna inside the can. And even if the methods could reliably pick up these traces, we knew there were any number of other human errors and environmental factors that could have led to its presence. As the world has learned all too well these last months, false positives in protein tests are real, and not as rare as any of us would like. 

As it turns out the skepticism surrounding this report was justified, and then some. Or, as Atuna put it: “Expert Shreds Dolphin Meat in Canned Tuna Study”. Here’s the crux of it:

“Enrique de la Vega, a molecular biologist with over 15 years of experience with PCR testing, told Atuna that a series of essential steps were skipped by the student and her supervisors in charge of the research, which could explain the reported findings.

“Without these steps, it’s impossible to reach the conclusion that the dolphin DNA was present in the cans tested without a shadow of a doubt,” said the scientist.”

Among the missed steps and irregularities de la Vega identified:

• The study did not control for the presence of human DNA from the very people handling the product, which could lead to false positives.
• It used different DNA extraction methods for the tuna sample than the other products tested, meaning there was no apples-to-apples comparison between the “positive” tuna result and other results using the same method.
• It conducted the test at a lower temperature than recommended, resulting in non-specific results, which the student then misinterpreted.
• The student conducted more match tests, or “cycles of amplification”, than normal. The more cycles conducted, the higher the chance of false positives.
• Perhaps most glaringly, the student never took the samples that turned back “positive” and further analyzed them to confirm the DNA found was actually dolphin.

The overall conclusion? “Essential scientific steps were not included in the methodology used for the research, making it impossible to even claim that dolphin DNA was found in tuna cans, much less dolphin meat.”

The interesting thing is, even in the absence of de la Vega’s specific and expert critique, the chances that this project found actual bycatch DNA in tuna—especially if that tuna was subject to dolphin-safe labeling—was always going to be vanishingly small. In fact, the whole enterprise seemed to rest on a false understanding of what bycatch is and how it affects—or rather does not affect—what goes into the finished product.

The student author refused to identify the brand of tuna she used in her project. But in North America, bycatch is simply not canned with tuna, and for companies operating in the United States, the Food and Drug Administration imposes rigorous identity standards on everything canned, processed, and sold. Bycatch simply never makes it into the processing supply chain.

Luckily, the discredited research never made it into wide circulation. But it could have – and that would have been a huge disservice to consumers, and an undeserved smear against tuna companies who are acting ethically and responsibly.