Pacific Sardines — A Flatland Case Study (Part I)

This is the first of two posts on the collapse of Pacific sardine populations. I will finish up tomorrow.

Back on  April 16, 2015, National Public Radio reported on the closure of the Pacific sardines fishery (species Sardinops sagax).

Life has suddenly gotten easier for the sardine. Federal regulators are not only closing the commercial sardine fishing season early in Oregon, Washington and California, but it will stay closed for more than a year.

The decision to shut down the sardine harvest is an effort to build up depleted stocks of the small, oily fish. The conservation group, Oceana, says that sardine populations have crashed more than 90 percent since 2007.

There are a number of theories about why the fish stocks have collapsed. Oceana says it comes from overfishing. But a report by the Pew Charitable Trusts says the wide swings in the sardine population are normal and usually related to "decades-long shifts in ocean conditions."

Now, before I get into the details of the collapse of Pacific sardines populations, I want you to note the following:

• NPR reports that "the conservation group Oceana says that sardine populations have crashed more than 90 percent since 2007..."

  In stating it this way, NPR implied that there is a (perhaps dubious) claim that sardine populations have crashed by more than 90%. In fact, here are the population numbers, as reported by SFgate.com on April 14, two days before the NPR story.

  

• NPR reports the sardines collapse as though it's Democrats versus Republicans. Here, your choice is between Oceana (a conservation group) and Pew Charitable Trusts, which said on March 6, 2015 that (emphasis added)

  "... it would not be fair to blame the current collapse on fishing.

  We know that sardine populations fluctuate widely with decades-long shifts in ocean conditions. Sardines grow scarce with shifts to cooler water. However, when the population reaches this extreme low level, it is a scientific no-brainer that fishing should be curtailed so sardines don’t continue to decline and perhaps reach the point of no return."

  These little fish are a big deal for a vibrant ocean. Fishery managers will be making the right decision by agreeing to strengthen protections for sardines at this critical time."

  Thus we learn that, as late as March of this year, fishermen were still taking sardines in Pacific coast waters. 

Pacific sardine populations do indeed fluctuate according to ocean conditions. Cooler waters depress breeding in these fish, and in the past several years, the waters off the California coast have been cooler than normal (up until recently).

That said, on April 6, 2015, 10 days before the NPR report, the news section of the journal Science ran a story on a recent study by Timothy Essington of the University of Washington, Seattle (and colleagues). The story was called —wait for it...ready?— Sardines hit hard by overfishing (emphasis added).

A new study looks at seven species over 25 years and finds that overfishing exacerbates natural boom-and-bust cycles of the fish, which are not only a food source for humans but for countless larger marine animals.

There’s no mystery about the status of tuna and other large predators; many of these stocks are clearly overfished. But it’s harder to know the impact of fishing on forage fish populations. That’s because populations of these small fish naturally alternate between abundant and scarce. Whether commercial fishing makes the collapses more frequent, prolonged, or severe has been hard to pin down. “There was this notion that … fishing doesn’t really matter,” says ecologist Timothy Essington of the University of Washington, Seattle.

Essington and his colleagues turned to stock assessments—regular surveys of fish populations that are collected by both commercial fisheries and research vessels. They analyzed 55 stocks from around the world of seven forage fish species, which had been tracked for at least 25 years.

Then they used the stock assessments to not only calculate the overall fish populations, but also local fishing rates—how much of a fish population was being caught at a given time. When fishing rates were high, the scientists found, populations collapsed to levels six times lower than they would have been otherwise [link to the PNAS study].

The collapses weren’t more frequent, however, the team reports online today in the Proceedings of the National Academy of Sciences.

Here's the money quote about "a problem" in fishery management.

This highlights a problem in fishery management: “We usually increase fishing at exactly the same time the population is struggling,” Essington says. Because the forage fish tend to congregate in large schools, it remains easy for fishermen to catch many fish at once; but as populations decline, one school can be a larger fraction of the total population. “But the problem is that once you get to these lower abundances, you end up in this really risky zone.”

And that's not all, regarding risk.

Using the new data set, Essington and his colleagues also developed a simulation to explore the risk. If fishing is halted when populations start to decline, forage fish remain plentiful, the models show. “If you just turn off all fishing and let the populations do what they would have done naturally, most of them will completely recover within a few years,” Essington says, suggesting a time frame that fishing bans might be enforced for.

Now, look again at the graph above. In 2012, 3 years ago, scientists studying Pacific sardine populations warned the powers that be that the time to stop fishing sardines had arrived. I'll quote from a recent Yale environment 360 article called A Little Fish with Big Impact In Trouble on U.S. West Coast (June 18, 2015, emphasis added).

In 2012, when nearly 100,000 tons of sardines were caught off the U.S. coast, this fishery was worth more than $21 million. But scientists are particularly concerned about what this means for the marine food web. Many fisheries experts, including some scientists working for the National Oceanic and Atmospheric Administration (NOAA), think the fishery closure has come too late...

In 2012, two federal fisheries biologists — David Demer, senior scientist at NOAA’s Southwest Fisheries Science Center and NOAA fisheries research biologist Juan Zwolinski — warned that fishing pressure on Pacific sardines was unsustainable given that cool ocean conditions were also depressing sardine numbers. They said it was “alarming” that the fishing industry was once again responding to a declining sardine population with “progressively higher exploitation rates targeting the oldest, largest, and most fecund fish.” The pair predicted an “imminent collapse” of sardine stocks.

And what happened after the warning?

Other NOAA fisheries scientists disagreed, and fisheries managers publicly criticized this assessment. Fishing industry representatives said management measures were responding adequately to the downturn. Officials dropped allowable catch numbers by 40 percent in 2013 and made further cuts in 2014.

But under the existing management plan, sardine populations had to drop to today’s low levels before a shutdown of the fishery was triggered. 

To be continued tomorrow.

Comments

[Brian]

It would be nice if these people would try to be at least a little intellectually honest in these articles. Between the every shifting baselines that seem to ignore everything that preceded some arbitrary (but convenient for their argument) date, and the cherry-picking of sample dates to maximize or minimize impact, most of these stories end up being essentially worthless. Drives me crazy.

It looks like NOAA is primarily using the Baumgartner paper (1992, PDF) as the basis for its long-term historical sardine stocks. Figure 7 in that paper appears in at least a couple places on the NOAA fisheries site. Whether the methodology is really robust, I don't know, but it certainly implies a very noisy boom-bust population pattern, which one would tend to expect in a prey species. This at least provides some longer term comparison for the more recent numbers and behavior. I'm sure you've seen that, Dave, but I thought it might be a useful longer-term comparative reference for others.

Of course, as you are clearly alluding to, we humans have an amazing ability to throw gas on the fire until the last possible moment (or maybe even later, since our cluelessness can sometimes impede our ability to make intelligent and timely decisions ;-).

Looking forward to part 2.