Classics: Fishing down the web

17 09 2008

A Classic

Daniel Pauly and colleagues’ classic paper in Science, Fishing down marine food webs, is one that merits citation in Classics section. The trend identified by Pauly and colleagues is fairly simple – data from the Food and Agriculture Organisation (FAO) of the United Nations revealed that the average trophic level (i.e., the position in the food web relative to autotrophs – primary producers such as phytoplankton) has declined by an overall average of 0.2 units. In this case, a trophic unit varied from 1 (phytoplankton) to 4.6 (e.g., snappers, family Lutjanidae). The trends varied by region and whether or not one takes certain overrepresented species into account, but the average decline was more or less consistent across the dataset.

What does all this reveal? Put simply, it means that fishing on a massive and global commercial scale has essentially removed many of the larger species to the point where it has become no longer economically viable to sustain a targeted fishery. This does not necessarily mean that these species have disappeared, but it does indicate a large drop in relative abundance (and thus, ease of capture) necessary to support an industry, with the corollary that highly reduced populations are now much more extinction-prone if they fall below their minimum viable population size. The corollary is that marine species we wouldn’t consider palatable for a dog 50 years ago are now considered top-quality market delicacies.

The paper did not go without critique – Caddy and colleagues argued that Pauly and colleagues oversimplified the case for marine fishes and misinterpreted some data; however, a subsequent paper by Pauly’s team published in 2005, Fishing down marine food web: it is far more pervasive than we thought, argued that the original paper didn’t go far enough, and that fisheries over-exploitation worldwide is much worse than originally reported. Indeed, there are certainly some high-profile examples to support the case (e.g., the Atlantic cod and Peruvian anchoveta fisheries collapses, to name a few).

What did this do for biodiversity conservation? I think it can be argued that this is one of the first big papers to identify that the over-fishing problem was global in extent and massive in magnitude, and that high-seas over-exploitation was stripping our seas of its bigger (generally slower-growing and more extinction-prone) species. I believe things have changed for the better, but we’re still a long way off. Fishing in international waters still operates without an international body to enforce regulation and document catch precisely, and the classic tragedy of the commons applies so well to fisheries that it should be one of the principal examples used to illustrate the concept. People tend to jump up and down about elephants, pandas and whales, but the reduction in fish worldwide is a biodiversity crisis in progress that has not attracted nearly enough attention. We need more papers like Pauly’s on this issue, as well as demonstrations of the loss of marine ecosystem function and services with the loss of species brought about by excessive fishing harvests. Only then can we expect the careless greed driving quick-profit high-seas fisheries to ease up enough to prevent extinctions on a massive scale.

CJA Bradshaw

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4 responses

29 07 2013
Fast-lane mesopredators |

[…] Our dive surveys1 and earlier studies, in combination, have pieced together a story of ecosystem change. In the Howe Sound of today, lingcod rarely exceed body lengths of 80 cm. But up to 30 years ago, when overfishing had yet to inflict the full extent of its current damage, lingcod with lengths of 90 to 100 cm had been common in the area. There is nothing unique about this; most fisheries target the biggest individuals, ultimately reducing maximum body size within each spe…. […]

5 05 2012
Sharks: the world’s custodians of fisheries «

[...] body-sized) piscivorous to planctivorous fish and invertebrates, indicating that fishery fleets are exploiting a trophic level down to collapse, then harvesting the next lower trophic level [...]

2 11 2011
Oceans need their giants «

[...] but on the species that reach the largest sizes, i.e., apex predator species, we are actually ‘fishing down marine food webs’ 24 – one of the main anthropogenic impacts on global [...]

29 09 2008
Geoff Russell

Nutritionist Suzie Ferrie and I criticised the CSIRO Total Wellbeing diet
recently in Nutrition and Dietetics (2008, 65, 139-143) for its high fish
component. This diet recommended people eat double the current level
of fish consumption. CSIRO has actually calculated what it would
take to double national fish consumption — a rise in imports of
other people’s fish from 280,000 tonnes annually to about
900,000 tonnes (assuming that people “own” fish). In their reply (65, 232-233)
Noakes and Clifton acknowledge that “other methods are needed to
supply enough long-chain omega-3s …”. ie., even current levels
of fish consumption in Australia are unsustainable.

What is the evidence that people need fish omega-3s? There
is heaps, but its junk. There is a cohort of about 65,000 people in the
European Prospective Investigation into Cancer who kind-of stick out
from the other cohorts. About half are vegan or vegetarian, the other half
average about 20g meat per day, 80% eat no fish at all. How is
their health? They have about half the standardised mortality rate of all
major diseases, they have the lowest obesity rate and the lowest protein
intake! The Cochrane Collaboration did a meta-analyses of the omega-3
data a couple of years back — “Omega 3 fatty acids for prevention and treatment of cardiovascular disease (Review)”. Here is the conclusion:
“It is not clear that dietary or supplemental omega 3 fats alter total mortality, combined cardiovascular events or cancers in people with,
or at high risk of, cardiovascular disease or in the general population.” For
people who don’t know the Cochrane Collaboration, these are people who
actually understand the statistical tests they use. Which is why they threw out
about half the possible randomised controlled trials — because of
poor methodology … like I said, just junk science. That’s a bit harsh, this
sort of research is really hard to do properly.

Now of course Manny Noakes and Peter Clifton are launching a new
diet which looks (according to the press news) like it is recommending
even more fish than the Total Wellbeing Diet.

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