Fishing down the food web#FAO critical rejoinder

File:Bluefin-big.jpg of the world fisheries catch has steadily declined because many high trophic level fish, such as this tuna, have been overfished.]]

File:Anchovy closeup.jpg and other forage fish.]]

File:Jelly cc11.jpg, if the trend continues, consumers may be eating jellyfish sandwiches.{{cite news |url=https://www.seattlepi.com/local/article/Jellyfish-for-lunch-It-s-no-joke-says-scientist-1143862.php |title=Jellyfish for lunch? It's no joke, says scientist |newspaper=Seattle Post-Intelligencer |date=May 4, 2004 |archive-url=https://web.archive.org/web/20130601112814/https://www.seattlepi.com/local/article/Jellyfish-for-lunch-It-s-no-joke-says-scientist-1143862.php |archive-date=2013-06-01 }}]]

Over the last 50 years, the abundance of large predator fish, such as cod, swordfish and tuna, has dropped 90 percent.{{cite journal |authorlink=Ransom A. Myers |last1=Myers |first1=Ransom A. |author-link2=Boris Worm |last2=Worm |first2=Boris |title=Rapid worldwide depletion of predatory fish communities |journal=Nature |year=2003 |volume=423 |issue=6937 |pages=280–283 |url=https://www.nature.com/articles/nature01610 |doi=10.1038/nature01610 |pmid=12748640 |bibcode=2003Natur.423..280M |s2cid=2392394 |url-access=subscription }} Fishing vessels now increasingly pursue the smaller forage fish, such as herrings, sardines, menhaden and anchovies, that are lower on the food chain. "We are eating bait and moving on to jellyfish and plankton", says Pauly.{{cite web |url=https://news.ubc.ca/2006/10/05/archive-ubcreports-2006-06oct05-06oct05innews/ |publisher=University of British Columbia |work=UBC Reports |title=In The News: Eating Jellyfish? |date=5 October 2006 |access-date=2 January 2023 }} Beyond this, the overall global volume of fish captured has been declining since the late 1980s.{{cite journal |url=http://www.seaaroundus.org/researcher/dpauly/PDF/2001/JournalArticles/SystematicDistortionsWorldFisheriesCatchTrends.pdf |doi=10.1038/35107050 |title=Systematic distortions in world fisheries catch trends |year=2001 |last1=Watson |first1=Reg |last2=Pauly |first2=Daniel |journal=Nature |volume=414 |issue=6863 |pages=534–536 |pmid=11734851 |bibcode=2001Natur.414..534W |s2cid=205023890 |archive-url=https://web.archive.org/web/20110928034146/http://www.seaaroundus.org/researcher/dpauly/PDF/2001/JournalArticles/SystematicDistortionsWorldFisheriesCatchTrends.pdf |archive-date=2011-09-28 }}

The mean trophic level is calculated by assigning each fish or invertebrate species a number based on its trophic level. The trophic level is a measure of the position of an organism in a food web, starting at level 1 with primary producers, such as phytoplankton and seaweed, then moving through the primary consumers at level 2 that eat the primary producers to the secondary consumers at level 3 that eat the primary consumers, and so on. In marine environments, trophic levels range from two to five for the apex predators.{{cite web |url=http://www.europarl.europa.eu/comparl/envi/pdf/externalexpertise/easac/biodiversity_indicators.pdf |title=A users' guide to biodiversity indicators |page=38 |publisher=European Academy of Science, Advisory Council |date=2004 }} The mean trophic level can then be calculated for fishery catches by averaging trophic levels for the overall catch using the datasets for commercial fish landings.{{cite web |publisher=Yale Center for Environmental Law and Policy |work=Environmental Performance Index |url=http://epi.yale.edu/MarineTrophicIndex |title=Marine Trophic Index |archive-url=https://archive.today/20080209171259/http://epi.yale.edu/MarineTrophicIndex |archive-date=2008-02-09 |year=2008 }}

Pauly's team used the catch data from the FAO{{cite web |url=http://www.fishbase.org/manual/fishbasefao_statistics00002679.htm |title=FAO Statistics |work=FishBase |access-date=22 March 2010 }} which it fed into an Ecopath model. Ecopath is a computerised ecosystem modelling system.{{cite journal |last1=Pauly |first1=Daniel |authorlink2=Villy Christensen |last2=Christensen |first2=V. |author-link3=Carl Walters |last3=Walters |first3=C |title=Ecopath, Ecosim, and Ecospace as tools for evaluating ecosystem impact of fisheries |url=http://www.icesjms.oxfordjournals.org/cgi/reprint/57/3/697.pdf |journal=ICES Journal of Marine Science |doi=10.1006/jmsc.2000.0726 |year=2000 |volume=57 |issue=3 |pages=697–706 |bibcode=2000ICJMS..57..697P }}

The functioning of an ecosystem can be described using path analysis to track the direction and influence of the many factors controlling the ecosystem. The original Ecopath model was applied to a coral reef food web. Scientists tracked tiger sharks at the top of the food web and collected data on their feeding behaviour, what they ate and how much. Likewise, they collected feeding data on the other organisms in the food chains down to the primary producers, such as algae. This data was fed into an Ecopath model, which then described the energy flow, in terms of food, as it moved from the primary producers up the food web to the apex predator. Such models allow scientists to compute the complex effects that occur, both direct and indirect, from the interactions of the many ecosystem components.{{cite web |url=https://celebrating200years.noaa.gov/breakthroughs/ecopath/welcome.html |title=ECOPATH Modeling: Precursor to an Ecosystem Approach to Fisheries Management |work=NOAA }}

The model showed that over the last 50 years the mean trophic level of fish catches has declined by somewhere between 0.5 and 1.0 trophic levels. This decline applied both globally, on a worldwide scale, and more locally on a scale specific to oceans, that is, for the separate FAO subareas: the Atlantic, Indian and Pacific Oceans, and the Mediterranean-Black Seas.{{cite book |last=Stergiou |first=KI |year=2005 |url=http://ichthyology.bio.auth.gr/files/stergiou/D/D06.pdf |chapter=Fisheries impact on trophic levels: long-term trends in Hellenic waters |archive-url=https://web.archive.org/web/20110721075532/http://ichthyology.bio.auth.gr/files/stergiou/D/D06.pdf |archive-date=2011-07-21 |page=326-329 |editor-last=Papathanassiou |editor-first=E |editor-last2=Zenetos |editor-first2=A |title=State of the Hellenic marine environment |publisher=Hellenic Centre for Marine Research |location=Athens, Greece }}

Pauly's team argued in their 1998 paper that the larger, more valuable predatory fish, such as tuna, cod and grouper, had been systematically overfished, with the result that fishing effort was shifting to less desirable species further down the food chain. This "fishing down the food web", said Pauly, would in time reduce people to a diet of "jellyfish and plankton soup". The colourful language and innovative statistical modelling by Pauly's team triggered critical reactions. Later in the same year, Caddy and his team from the FAO argued a counter position in a paper also published in Science. They argued that Pauly's team had oversimplified the situation and may have "misinterpreted the FAO statistics".{{cite journal |last1=Caddy |first1=JF |last2=Csirke |first2=J |last3=Garcia |first3=SM |last4=Grainger |first4=JRJ |year=1998 |doi=10.1126/science.282.5393.1383a |title=How Pervasive Is "Fishing Down Marine Food Webs"? |journal=Science |volume=282 |issue=5393 |pages=1383}} The response of Pauly's team was published in the same paper, claiming that the corrections suggested by the FAO, such as accounting for aquaculture, actually made the trend worse.{{cite journal |first=David |last=Malakoff |year=2002 |url=http://www.seaaroundus.org/OtherWebsites/2002/ScienceApril02.pdf |title=Daniel Pauly profile: Going to the Edge to Protect the Sea |journal=Science |volume=296 |number=5567 |pages=458–461 |doi=10.1126/science.296.5567.458 |pmid=11964458 |s2cid=8501655 }}

The concerns raised by the FAO were further countered by Pauly and others in 2005.{{cite journal |doi=10.1098/rstb.2004.1597 |url=http://www.seaaroundus.org/researcher/dpauly/PDF/2005/JournalArticles/BackgroundInterpretationMarineTrophicIndex.pdf |title=Background and interpretation of the 'Marine Trophic Index' as a measure of biodiversity |publisher=Philosophical Transactions of the Royal Society |journal=Biological Sciences |year=2005 |volume=360 |archive-url=https://web.archive.org/web/20120223234241/http://www.seaaroundus.org/researcher/dpauly/PDF/2005/JournalArticles/BackgroundInterpretationMarineTrophicIndex.pdf |archive-date=23 February 2012 |last1=Pauly |first1=Daniel |last2=Watson |first2=Reg |issue=1454 |pages=415–423 |pmid=15814354 |pmc=1569461 }}{{cite journal |last1=Pauly |first1=D. |first2=M.L. |last2=Palomares |year=2005 |url=http://www.fishingdown.org/pdf/FishingDownMarineFoodWebItisFarMorePervasivethanWeThought.pdf |title=Fishing down marine food webs: it is far more pervasive than we thought |journal=Bulletin of Marine Science |issn=0007-4977 |volume=76 |number=2 |page=197-211 }} Other researchers have established that "fishing down" also applies to smaller, regional areas, such as the Mediterranean,{{cite web |title=Fishing Down the Mediterranean Food Webs? Executive Summary. |year=2000 |last1=Briand |first1=F. |first2=K.I. |last2=Stergiou |url=https://www.researchgate.net/publication/239940107 }} the North Sea, Celtic Sea, and in Canadian, Cuban and Icelandic waters.

A 2006 study suggested that in a number of examined ecosystems, catches of species at high trophic level did not decline, but rather that low trophic level fisheries were added in parallel over time, resulting in confounding landing data through a related but different mechanism.{{cite journal |last1=Essington |first1=T. E. |first2=A. H. |last2=Beaudreau |first3=J. |last3=Wiedenmann |year=2006 |title=Fishing through marine food webs |journal=Proceedings of the National Academy of Sciences |volume=103 |issue=9 |pages=3171–3175 |doi=10.1073/pnas.0510964103 |pmid=16481614 |pmc=1413903 |bibcode=2006PNAS..103.3171E |doi-access=free}}{{cite web |url=https://www.sciencedaily.com/releases/2006/02/060215225431.htm |title=Shopping list gets longer -- not less choosy -- in some of world's largest fisheries |work=University of Washington |via=sciencedaily.com |date=February 22, 2006 }} A study on Alaskan marine fisheries concluded that in the examined area, the decline of mean catch trophic level was connected to climate-driven fluctuations in biomass of low trophic level species rather than predator collapses, and suggested that similar dynamics might be in play in other instances of reported food web degradation.{{cite journal|last1=Litzow|first1=M. A.|last2=Urban|first2=D.|year=2009|title=Fishing through (and up) Alaskan food webs|journal=Canadian Journal of Fisheries and Aquatic Sciences|volume=66|issue=2|pages=201–211|doi=10.1139/F08-207|bibcode=2009CJFAS..66..201L }}

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|image1=[http://www.greenfacts.org/en/global-biodiversity-outlook/figtableboxes/figure-2-11.htm Change in the Marine Trophic Index (early 1950s to the present)]

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In 2000, the Convention on Biological Diversity, an international treaty aimed at sustaining biodiversity which has been adopted by 193 member countries, selected the mean trophic level of fisheries catch as one of eight indicators for immediate testing. They renamed it the "Marine Trophic Index" (MTI), and have mandated that member countries report over time on changes in ocean trophic levels as a primary indicator of marine biodiversity and health.{{cite web |last=Jacquet |first=JL |year=2008 |url=https://scienceblogs.com/shiftingbaselines/2008/02/06/fishing-down-the-food-web-turn |url-status=live |title=Fishing Down the Food Web Turns 10! |archive-url=https://web.archive.org/web/20110314232217/http://scienceblogs.com/shiftingbaselines/2008/02/fishing_down_the_food_web_turn.php |archive-date=2011-03-14 |work=Shifting Baselines }}{{cite web |last=Pauly |first=D. |year=2005 |url=http://www.conbio.org/Publications/Newsletter/Archives/2005-9a-November/v12n4004.cfm#A14 |title=The ecology of fishing down marine food webs |archive-url=https://web.archive.org/web/20101103051009/http://conbio.org/Publications/Newsletter/Archives/2005-9a-November/v12n4004.cfm#A14 |archive-date=2010-11-03 |work=Society for Conservation Biology Newsletter |volume=12 |number=4 }}

The Marine Trophic Index is a measure of the overall health and stability of a marine ecosystem or area. The index is also a proxy measure for overfishing and an indication of how abundant and rich the large, high trophic level fish are.{{cite web |url=http://sso.conferenceboard.ca/HCP/Details/Environment/marine-trophic-index.aspx |title=Marine Trophic Index |work=Conference Board of Canada |access-date=22 March 2010 |archive-date=6 August 2020 |archive-url=https://web.archive.org/web/20200806120118/https://sso.conferenceboard.ca/HCP/Details/Environment/marine-trophic-index.aspx |url-status=dead }}

Changes in the Marine Trophic Index over time can function as an indicator of the sustainability of a country’s fish resources. It can indicate the extent that the fishing effort within a country's fishing grounds is modifying its fish stocks. A negative change generally indicates that larger predator fish are becoming depleted, and an increasing number of smaller forage fish are being caught. A zero or positive change in the Marine Trophic Index indicates the fishery is stable or improving.

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| quote = {{center|Development of fishing down
Fishing down is a succession which reverses the usual evolutionary sequence.

"It consists of a gradual loss of large organisms, species diversity, and structural diversity, and a gradual replacement of recently evolved, derived groups (marine mammals, bony fishes) by more primitive groups (invertebrates, notably jellyfishes, and bacteria)." – Daniel Pauly}}

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Ecologically, the decline in the mean trophic level is explained by the relationship between the size of the fish captured and their trophic level. The trophic level of fishes usually increases with their size, and fishing tends to selectively capture the larger fishes. This applies both between species as well as within species. When the fishing is intense, the relative abundance of the larger fish positioned high in the food chain is reduced. Consequently, over time, small fishes start to dominate the fisheries catches, and the mean trophic level of the catches declines. Recently the market value of small forage fishes and invertebrates, which have low trophic levels, has sharply increased to the point where they can be considered to be subsidizing fishing down.

Daniel Pauly has suggested a framework for the ecological impacts fishing down can have on marine ecosystems. The framework distinguishes three phases:

• Pristine – the first phase. Pristine environments are the states ocean ecosystem were in before fishing made strong impacts. Some outlier areas of the South Pacific may still be pristine. For most of the world what these pristine states may have been can only be inferred from archaeological data, historical accounts and anecdotes. In pristine ocean environments, the biomass of the large predator fish are 10 to 100 times greater than their present biomass. This implies a large supporting biomass of small prey fishes and invertebrates. On the seafloor, the benthos is dominated by deposit feeders which prevent resuspension of sediments, and filter feeders which keep the phytoplankton down. Thus the water column tends to be oligotrophic, free of both suspended particles and of the nutrients that leach from them.
• Exploited – the second phase. Exploited is the phase we are currently in. It is characterized by declines in the biomass of large predator fish, declines in the diversity, size and trophic level of captured fish, and declines in the benthos. Bottom trawlers progressively destroy the biogenic structures built over many years on the seafloor by the filter and detritus feeders. As these structures and animals that were filtering the phytoplankton and consuming the detritus (marine snow) disappear, they are replaced with the polyp stages of jellyfish and other small errant benthic animals. Storms resuspend the marine snow, and the water column gradually eutrophies. In the early part of this phase, ecological cascade effects compensate these declines with the emergence of new fisheries for opportunistic feeders, such as squid, shrimp and other invertebrates. But eventually this decline also.
• Fully degraded – the third phase. The dead zone is the biological endpoint of a fully degraded marine ecosystem. The dead zone is a zone with excessive nutrients in the water column, resulting in the depletion of oxygen and the elimination of multicellular organisms. The abundant detritus and marine snow are processed by bacteria rather than by the benthic animals. These dead zones are currently growing throughout the world in places such as the Bohai Sea in China, the northern Adriatic Sea, and the northern Gulf of Mexico. Some estuaries, such as the Chesapeake Bay estuary, also display features associated with a fully degraded marine ecosystem. In the Chesapeake Bay, overfishing eliminated the benthic filter feeders such as oysters, and most predators larger than a striped bass, the current apex predator. One hundred and fifty years ago, the oysters formed giant reefs and filtered the waters of Chesapeake Bay every three days. Because the oysters are gone, pollution entering the estuary from rivers now produces harmful algal blooms.

While the mean trophic level in wild fisheries has been decreasing, the mean trophic level amongst farmed fish has been increasing.{{cite journal |last1=Pauly |first1=D |last2=Tyedmers |first2=P |last3=Froese |first3=R |last4=Liu |first4=Y |year=2001 |title=Fishing down and farming up the food web |s2cid=127706851 |journal=Conservation Biology in Practice |volume=2 |number=4 |page=25 }}

As an example, the table above shows trends in the trophic levels of fish farmed in the Mediterranean. However, the farming of bluefin tuna is restricted to a fattening process. Juvenile tuna are captured from the wild and put in pens for fattening. Wild stocks of bluefin are now threatened, and the fisheries scientist Konstantinos Stergiou and colleagues argue that the "fact that the capacity of tuna farms greatly exceeds the total allowable catch indicates lack of conservation planning in development of the tuna-fattening industry, which, ideally, should have been linked to fisheries management policies, and may lead to illegal fishing".

Also, fish farming in the Mediterranean is a net fish consumer. Large amounts of animal feed are needed to feed a high trophic fish like the bluefin tuna. This feed consists of fishmeal processed from forage fishes like sardines and anchovies that humans would otherwise consume directly. In addition to ecological issues, this raises ethical issues. Much of the fish suitable for direct human consumption is being used to grow higher trophic level fish to indulge a relatively small group of affluent consumers.

• 2010 Biodiversity Indicators Partnership
• Biodiversity
• List of harvested aquatic animals by weight
• Shifting baselines
• Ecological release
• Population dynamics of fisheries

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• {{cite book |author=National Research Council |year=2006 |url=https://nap.nationalacademies.org/read/11608/chapter/1 |title=Dynamic Changes in Marine Ecosystems: Fishing, Food Webs, and Future Options |publisher=National Academies Press |isbn=9780309100502 }}

• {{cite web |url=http://www.fishingdown.org/ |title=Fishing Down Marine Food Webs |work=Sea Around Us Project |publisher=University of British Columbia }}
• {{cite web |url=https://www.scientificamerican.com/article/fishing-down-food-chain-fails-/ |title=Fishing down food chain' fails global test |work=Scientific American |date=10 November 2010 |access-date=3 January 2023 |first=Daniel |last=Cressey }}

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Category:Fisheries science

Category:Environmental impact of fishing