Thursday, January 12, 2017
JUMPING THE GUN: FISHERIES RESEARCH AND THE NULL HYPOTHESIS
Science is not static. Instead, it is a continuing act of discovery, in which even long-established truths may be questioned, modified and sometimes abandoned altogether as new knowledge comes to light.
Yet, in order to assure that research is revealing new truths, and not providing false and misleading information, each purported new discovery must be met with an appropriate dose of skepticism, as experts in the field analyze the data, try to reproduce the reported results and otherwise test the validity of the researcher’s conclusions.
In the fisheries world, we see this most often in stock assessments which, once completed, are . Such panel decides whether each assessment meets its stated goals, called “terms of reference,” and whether the analysis of the relevant data was rigorous enough to render the assessment “adequate for management purposes.”
However, stock assessments aren’t the only sort of fisheries research being conducted. At any given time, a number of studies are underway. Some are purely academic in nature, intended only to expand the pool of knowledge. Others have industry sponsors, who hope to use the studies’ results to promote industry interests and guide government policy.
Any of those studies can result in flawed data. Yet it is not flawed data, but flawed conclusions drawn from good data, which may pose the greatest threat to the management process.
That’s where the “null hypothesis” comes in.
as “a general statement or default position that there is no relationship between two measured phenomena, or no association among groups.” A researcher must disprove the null hypothesis in order to successfully defend a study’s conclusions.
The null hypothesis is often ignored here on the coast, where fishermen readily accept any data that might support their calls for less restrictive regulations and bigger harvests. They seldom wait to see whether there is any connection between such data and the health of a fish population.
The current debate over summer flounder regulations provides an example.
, summer flounder are becoming less abundant. In response, , in order to protect the spawning stock from overfishing.
, claiming that they will cause economic harm to various coastal businesses. As part of their campaign against the harvest reductions, industry spokesmen have repeatedly cited calling itself the , which suggests that current regulations, and more particularly current size limits, result in a recreational harvest that is composed primarily of female flounder.
The implication is that such harvest of female flounder is having a direct, negative impact on the species’ spawning success. published in magazine asked, “could it be all the tinkering over the past 8 years, the increasing size limits and intensified harvest on broodstock fluke that actually impacted the overall biomass and recruitment numbers?”
A lot of readers, faced with that question, will intuitively answer “Yes.” But fisheries management decisions aren’t based on intuition or the theories of disgruntled magazine editors. They’re based on demonstrable facts.
Right now, there is no data that demonstrates a relationship between the number of female summer flounder landed by recreational anglers and the number of young-of-the-year summer flounder that are recruited into the population each year.
The null hypothesis has not been disproven, and until it is, the SSFFF study has no relevance to summer flounder management.
Another recent example of ignoring the null hypothesis occurred after a team of , an area that lies just off the edge of the continental shelf, east of the Mid-Atlantic coast.
which argued that the presence of 6-day old bluefin larvae, so far from known spawning grounds in the Gulf of Mexico and Mediterranean Sea, was evidence that a third spawning area, probably used by young adult bluefin, had been discovered.
As the scientists noted, “The implications…are most pronounced for western Atlantic bluefin tuna, which [if they also spawn in the Slope Sea] have a life history less vulnerable to overexploitation and extinction than is currently estimated.”
In other words, if bluefin spawn in the Slope Sea, fishermen would be able to harvest more of them without putting the stock at risk.
Fishermen were quick to validate the results of the study. “there are already suggestions being heard from various interests that bluefin populations may be more resilient than we had thought, that stocks may be in better shape, and that more generous fishing quotas may be called for.”
Barbara Block, a Stanford University biologist who has long been involved with bluefin research, called the study “interesting,” but not conclusive, and feels that more evidence is needed before the Slope Sea can be considered a bluefin spawning ground.
Even if the fact of bluefin spawning in the Slope Sea is accepted, biologists disagree as to what such finding would mean. While , if young bluefin are actually spawning in the Slope Sea, it “will increase estimates of spawning stock biomass and will likely lead to higher estimates of sustainable fishing mortality rates.”
. He argues that if bluefin are spawning in the Slope Sea, and the current spawning stock is larger than previously believed, then the historic spawning stock was also larger. And if bluefin were, historically, more abundant than biologists had thought, then the target biomass defining a rebuilt stock must also be modified upward, to reflect that historical abundance. He then goes on to say that achieving that higher target might even require a reduction in landings.
Turning again to the null hypothesis, in order to justify increasing bluefin landings, the biologists who claim that young bluefin tuna spawn in the Slope Sea must prove not only that such spawning occurs, but that it justifies an increased harvest.
Clearly, some noted bluefin tuna biologists aren’t willing to draw that conclusion just yet.
On the other hand, tuna fishermen are more than willing to do so, and have no patience for any scientist or conservationist who requires more proof. , a discussion board, expresses such fishermen’s view:
“I just returned from the [International Commission for the Conservation of Atlantic Tunas] meeting and after the discovery of such good news it is almost laughable how certain scientists, [non-governmental organizations] and green groups tried to poke holes in the discovery…They are very smart, well-funded, narrow minded and focused on ‘proving’ that this fishery/stock is in trouble and will go to any length to get people to believe it.”
It never occurred to the fisherman making the comment that he was being at least as “narrow minded and focused” on accepting the existence of a bluefin spawning ground in the Slope Sea, and supporting an increased harvest.
And that is the value of the null hypothesis in fishery management.
It requires management decisions to be based on established facts, and not merely on data selected to support a particular, perhaps politically palatable, position.
This post first appeared in From the Waterfront, the blog of the Marine Fish Conservation Network, which may be found at http://conservefish.org/blog/.