'Fishing down the food web' debunked in new Scientific paper

 Fishing down the food web - the idea that fishermen target the largest species, then smaller, than the forage fish, until eventually the oceans have nothing but jellyfish, is a cornerstone belief of many environmentalists concerned about overfishing.  It was accepted without challenge at the recent Monterey Bay Aquarium Cooking for Solutions event.  It was popularized in papers by Daniel Pauly and Boris Worm, that gave the media the idea that all fish would disappear by 2048.  This idea is also the central premise behind the new movie 'End of the Line.'  A new study, published in a Canadian Journal, has debunked this theory, and shown that over 112 years in the N. Pacific, there is no evidence for fishing down the food web, and in fact the average tropic level of target species appears to have increased.   Here is the article on this which was in our news the other day, and which is being reprinted in New Zealand and elsewhere. 

Fishing down the food web debunked in new 112 year study of fish statistics

SEAFOOD.COM NEWS by John Sackton - June 16, 2009 - Several years ago, Dan Pauly's paper predicting extinction of commercial fisheries by 2048 was seized on by the media and many environmental groups as the raison d' tre for updending the existing practices of fisheries management, since they had led to a total depletion of the larger fish species in the oceans.

At the time, the paper was widely criticized for being a simple extrapolation of data across a wide variety of fisheries that did not take into account more recent changes in management practice.

The idea that the commercial seafood industry was going to cause the oceans to become devoid of all life but jellyfish was highly popularized under the term fishing down the food web.

The idea has become ingrained in many media stories. The basic argument is that fishermen first harvest the large fish, then the forage fish, and eventually no fish. Over time, more and more fishing is concentrated on the lower trophic levels, so eventually we are left with nothing but jellyfish.

Now, a peer-reviewed, scientific study that looked at 112 years of historical fishing records in the North Pacific, has thoroughly debunked the myth of "fishing down the food web."

Michael Litzow and Daniel Urban, from the Alaska Fisheries Science Center and the Alaska Dept. of Fish and game, respectively, writing in the Canadian Journal of Fisheries and Aquatic Science (66: 201-211 (2009)), have shown this is a false hypothesis.

They show that the fishing down the food web is localized to the history of fisheries in the North Atlantic, and that when applied to the history of fishing in the North Pacific, the effect disappears. 

Further, they say that the primary drivers of the trophic level of fisheries in major ocean basins is correlated with the size of the fishery on forage fish, which is in turn primarily driven by changes in climate and ocean conditions.

In the pacific for example, the abundance of anchovies is known to vary over time. The scientists who thought they were seeing evidence of fishing down the food chain actually were seeing anchovies come and go depending on ocean conditions - but they mistook the ratios to to deduce a false relationship between fishing at the higher trophic levels and the lower ones.

In Alaska, the authors say, over a 112 year fishery, there has been no net change in the trophic levels of the catch. The abundance of the higher trophic level fish like salmon, pollock, halibut, as remained constant over time compared to the abundance of the lower trophic fish, and in some cases increased.

Instead, the principal causes of fluctuation have been related to multi-decade scale temperature changes in the North Pacfiic.

They say "A broad consensus holds that global fisheries are poorly managed and unsustainable, and over exploitation of high trophic level stocks has been identified as a central part of this problem. However, a rigorous debate has recently played out over the exact nature of the global fisheries crisis."

"To our knowledge, our study and the study of Essington et al (2006) are the only published studies to explicitly test for declining catches of upper trophic level fish during the times when the mean trophic level of an entire fishery is declining. "

"Our results show that historical periods of declining mean trophic level in Alaskan commercial fisheries were due to increases in lower level trophic catches, rather than declines in upper trophic level catches. "

"We found that in recent decades the mean trophic level of the catch has been stable, or actually increased. " 

They go on to say that the results show that when sound fisheries management principles are applied that fisheries can exist for decades without impacting the trophic level of the harvest, completely contradicting the positions of those scientists who say trends in fishing are inexorably leading to commercial extinctions. 

This paper needs much more visibility, and it should be cited as an antidote to the claims of fishing down the food web, or that fishing will end in 2048, which serves to scare people, but is not scientifically accurate.

The fact is that the premise of the movie, End of the Line, is completely false. The issue is not that fisheries will become extinct if they continue. The issue is that poor management is a threat to the continuation of fisheries, and that poor management (such as is the case with bluefin tuna and Big eye tuna) should be targeted, and not the commercial industry.