855 words • 4~6 min read

PolitiFact calls claims of menhaden declines “Mostly False”, is completely wrong

davesquare

A menhaden, image courtesy Pew Environment Group

A menhaden, image courtesy Pew Environment Group

Despite their small size and plain appearance, menhaden have been called “the most important fish in the sea” because numerous coastal fish species rely on them for food. Although they aren’t typically eaten by humans, there is still a huge fishery for them for bait, aquaculture food, and oil. That fishery has been essentially unregulated, allowing fishermen to take as many as they want. Recently, there’s been a campaign among certain environmental groups to fix this problem and put catch limits in place for menhaden.

I was surprised to see PolitiFact, a non-partisan political fact-checking website, address this issue. I’ve checked PolitiFact pretty regularly for years, and I’ve never seen them cover a topic like this before. They focused on a claim by the Pew Environment Group that “In recent years, menhaden numbers along our coast have plummeted by 90 percent.” While I admit I am not familiar with specific details of menhaden population trends,  anyone who has paid any attention at all to the ocean knows that we’re overfishing at alarming rates. According to the UN Food and Agriculture Organization, approximately 1/3 of all global fisheries are depleted or overexploited, many by more than the 90% referenced for menhaden. Shockingly, PolitiFact called the claim by Pew “mostly false”. Their reasoning for this ruling is even more ridiculous than the ruling itself:

“Whether the population declined by 90 percent, as Pew asserts, depends on where you want to start calculating and when you want to stop.The Pew ad says the 90-percent decline was “in recent years.” It gives no time frame. If you think of “recent” as the last 10 years, the drop from 1999 to 2008 has been 43 percent, far from 90 percent, according to the chart Pew referenced.Over the last 20 years, it’s been 76 percent.To show a drop close to 90 percent, you have to start at 1982, when the estimated number of menhaden was 20.2 billion.”

This is a classic case of “shifting baselines”- how severe the decline is obviously depends on when you start counting. If you “think as recent as the last ten years”, as PolitiFact suggests, the decline from 1999 to 2008 is less severe than the decline from 1982 to present. What PolitiFact leaves out, however, is that the % decline from 1999 to 2008 is less severe than the 1982-present decline because so many of the fish were already gone by 1999!  Of course the percentage of decline between an extremely depleted and a severely depleted population is less severe than the percentage of decline between a (relatively) healthy population and a severely depleted population!

For a simplistic example, consider having a population with biomass of 100 tons. Over 20 years, the population is reduced to 10 tons.  Over the next ten years, the population is reduced to 6 tons. The % decline from 10 tons to 6 is only 40%. However, the percentage from when we started to where we are now is over 90%, and that’s what really matters in terms of assessing the health of a fish population!

From a menhaden stock assessment by the Atlantic States Marine Fisheries Commission

From a menhaden stock assessment by the Atlantic States Marine Fisheries Commission

The definition PolitiFact uses for “Mostly False” is “The statement contains some element of truth but ignores critical facts that would give a different impression.” That’s nonsense. Regardless of whether you consider “30 years” to be “recent” (and in terms of evolutionary or long-term fisheries management time, it certainly is), the central point that Pew made is that menhaden are overexploited, menhaden populations are seriously declining, and better management is needed, which is all unambiguously true. If anything, this falls much closer to the category of “Mostly True”, defined by PolitiFact as “The statement is accurate but needs clarification or additional information.” It also falls under the category of “I need to take an introductory marine biology class”, which PolitiFact strangely has not used to date.

Fortunately, the Atlantic States Marine Fisheries Commission voted Friday to improve the management regulations for menhaden. In the meantime, I’ve written to PolitiFact asking them to change the rating.