September 19, 2019
Introduction to a new blog series, A Question of Science, reflecting on how the health of Atlantic menhaden, one of the most important prey fish in the sea, is assessed.
Confirmation bias is a tendency to search for or interpret information in a way that confirms one’s preconceptions. – Science Daily
Up until about eight years ago, the science was considered sound enough to declare Atlantic menhaden “not overfished” and thereby reject repeated calls by anglers and environmentalists to regulate the catch of what many consider the most important prey fish in the sea.
That all changed in 2011, when the Atlantic States Marine Fisheries Commission (ASMFC) adopted more conservative reference points to assess the health of the menhaden population – that is, standards for measuring fishing mortality and abundance more in line with, although still less restrictive than, those in place for most other fisheries.
When these new standards were applied to the results of the 2010 stock assessment, menhaden were found to be “overfished” and the first-ever coast-wide catch limits were imposed on the fishery a year later.
But while this was going on, the ASMFC’s technical advisors began looking for and finding problems with the assessment, questioning whether it was even fit for managing the fishery, even though it had been approved for management by the Menhaden Management Board at the recommendation of these same advisors. Nevertheless, they gave the assessment – the model, the data and the assumptions that go into it – a complete and thorough overhaul in 2014.
Lo and behold, according to a revised stock assessment presented to the Menhaden Management Board at the beginning of 2015, the stock’s status had improved dramatically; so much so that it was once again no longer overfished and overfishing was not occurring. In fact, the stock was considered so robust that the Commission could safely and substantially increase catches again…and again.
Now, a cynic might be tempted to think this 180-degree turnaround is – as a former mayor of Philadelphia once memorably remarked – “too much of a coincidence to be a coincidence”. Indeed.
But before jumping to that conclusion, let’s back up a little. In the next blog in our A Question of Science series, we look at how in less than a year the menhaden assessment went from what the ASMFC’s technical team assured us was the most reliable assessment they’d ever worked on to one they deemed not suitable for maThe second in a series of blogs, A Question of Science, which looks at changes in the way we assess the health of one of our most important prey species.
I started following and attending Atlantic menhaden stock assessments on a regular basis in 1999. That same year, as a member of the National Ecosystem Principles Advisory Panel, I’d helped write the panel’s Report to Congress, Ecosystem-Based Fishery Management, in which we’d recommended that a first important step toward EBFM would be considering predator-prey relationships within fishery management plans. Also that year, I organized a workshop, Conservation in a Fish-Eat-Fish World, bringing together scientists and policy makers from up and down the east coast to explore ways to manage related predator and prey species. We used the well-known link between striped bass and menhaden as a case study.
What confounded me from the start was why scientists advising the Atlantic States Marine Fisheries Commission kept reporting that menhaden were abundant, when it seemed to me, and quite a few others, that the signs of decline were unmistakable. Widespread concerns about the lowest numbers of menhaden on record, as consistently reported in those same assessments, were amplified by signs of stress in dependent predators, most notably striped bass and osprey in the Chesapeake Bay area.
Time and time again over the next decade I was assured that the Commission’s menhaden assessment, including its reference points for determining whether or not the stock is overfished, was state-of-the-art, using decades of reliable data from the fishery and sophisticated modeling developed at the National Marine Fisheries Service’s Beaufort (NC) Laboratory. In fact, some members of the Menhaden Technical Committee testified that “the menhaden assessment is far more reliable than any other they have worked on because of the length of the time series and accuracy of the data.”
Still I prodded and probed. The assessment team listened with faux patience, as one does to a child you hope will someday understand. And then I did.
An independent panel of scientists reviewing the 2010 stock assessment pulled back the curtain. The problem was not the assessment per se, but the reference points the scientists were using to detect overfishing. The reviewers advised the ASMFC’s Menhaden Management Board that the reference points were set far too low, giving the Board a false sense of security. The peer review panel recommended that the Board raise the bar in order to provide the stock with better protection.
The following year, based on that advice and bolstered by overwhelming public support for leaving more menhaden in the water as prey for striped bass and other predators, the Board re-defined overfishing. New reference points were adopted – abundance targets and fishing mortality limits more conservative than the old ones, more in line with those used for other species of fish (although still not up to the then-emerging standards for important forage species like menhaden).
When the new reference points were applied to the 2010 assessment, the menhaden stock was declared “overfished.” The Menhaden Board responded in 2012 with regulations to stop overfishing and, notably, “increase menhaden abundance and availability as forage” (emphasis added), cutting the coast-wide catch by 20%. That was a savings of 50,000 tons or about 250 million fish a year. Implemented in the 2013 fishing season, the lower menhaden quotas were to stay in place through at least 2015, when another full stock assessment would be completed and catch levels revisited, if necessary.
But before we get to the results of the 2015 assessment, let’s first reflect on the effect of the 2012 management decision on the Commission’s confidence in the science, because even as these landmark changes to the way menhaden are managed were being drafted, the menhaden stock assessment was coming under increased scrutiny.
First, in a routine update in the summer of 2012 – basically a ‘turn of the crank’ assessment where the most recent years of data are plugged into the base model – the assessment team tried some alternative, best-case-scenario assumptions about how many fish might really be out there; basically, estimates of fish the fisheries and the surveys being used might be missing (as if they were actively looking to find more fish). With these scenarios in mind, in early 2013 – just as the new catch restrictions were set to take effect – the menhaden scientists backed away from their previous conclusion that menhaden are being overfished, instead telling the commissioners they really couldn’t be sure.
Then a year later, at the Menhaden Board’s February 2014 session, the chair of the menhaden stock assessment team gave a progress report on a series of meetings held to prepare for that year’s benchmark assessment workshop. She identified several key elements that were being re-examined, including the estimates of natural mortality and age-at-maturity, as well as new fishery-independent indices that could be used to estimate the number of adult fish. Asked by the Board what this might mean for the status of menhaden, she told the commissioners they’d have to wait and see, adding cryptically: “We have made so many changes to this assessment you won’t recognize it.”
And so the tide was going out. The ASMFC and its technical advisors had heretofore expressed full confidence in the menhaden science. After all, every previous benchmark assessment (including the now suspect 2010 report) passed independent peer review and was subsequently approved by the Board for management use. But as soon as the results are being used to actually regulate the fishery, all of a sudden the assessment is no longer management-worthy. In fact, according to the assessment team, it has so many flaws that they need to tear it apart and rebuild it into something we “won’t recognize.”
In the next part of our series, A Question of Science, we will begin looking at the changes in the assessment, the thinking behind them, and how decisions on the science are influenced by management considerations.aging the fishery.
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