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Expert warns: “Hypoxia hyperbole” could discredit science and obscure underlying threats to gulf fisheries


Editor’s Note: This post was contributed by Jim Cowan, a highly published fishery ecologist at LSU. Colleagues from various scientific disciplines have offered to submit articles of broad coastal interest but Jim is the first to deliver!   I recommend a careful read of this technical, provocative and very thoughtful paper.

Given the fisheries theme of this post I couldn’t resist the impulse to include two links to video clips, one on fish predation from and one on squid sex from



Aren’t the Ugly Truths Ugly Enough?

James H. Cowan, Jr. , Ph.D.
“Personally, I believe that detecting significant impacts on Louisiana fishery resources would be far more reassuring than failing to do so, given the combined effects of obvious stressors such as coastal land loss … eutrophication and hypoxia, hydrologic changes in coastal wetlands made for flood control and by the oil and gas industry, and climate change, which is affecting rates of sea level rise, and contributing to large scale replacement of Louisiana Spartina sp. salt marshes by black mangroves.”  Jim Cowan, Ph.D.



Science, if nothing else, should be objective, and scientists who receive funding from public sources are ethically and morally obligated to speak truth to managers and policy makers that work on the public’s behalf (1,2).  In recent years, however, there has been an increase in the number of papers, many of which have been published in high profile journals, that address real environmental or ecological problems with flawed and subjective arguments. Two such examples are being played out in the Gulf of Mexico, and I use both to illustrate the problem and express my concerns.  

De Mutsert and coauthors (3) showed that conclusions that marine fisheries ecosystems in the Gulf of Mexico (GOM) are severely degraded and overexploited, based on commercial landings data (4,5) were flawed, and overly pessimistic.  In their re-analyses, De Mutsert and co-authors (3) used both commercial landings and fishery-independent survey data to show that commercial targeting and high landings of target species, and an overly simple definition of a “collapse” that failed to account for the effects of targeting, variability in fishing effort, and market forces, led to erroneous conclusions.

The aforementioned authors (5) further concluded that all of the world’s capture fisheries would be depleted by the year 2048.  This outcome is highly unlikely, and would seem to imply that the fishery management communities have learned nothing from past mistakes. There now exist more than ten published rebuttals of this paper alone.

That said, 20% of GOM fisheries have collapsed, but several of these have recovered and others are recovering.  Clearly, the most controversial fishery in the GOM is the northern red snapper, which collapsed during the late 1980’s, when it was commercially extinct in ~50% of its former range.  Management of red snapper began in earnest in 1989, and the stock is slowly recovering.  More detail is available (3), but user conflict has made management of red snapper especially difficult because recreational and commercial fishers almost equally split the directed harvest, and until recently, more than 80% of the fishing mortality occurred as bycatch of juveniles in the shrimp fishery. 

The Gulf of Mexico Fisheries Management Council has been tugged in many directions and slow to make reductions in catches sufficient to rebuild the stock in a timely fashion.  Compliance with the 2007 reauthorization of the Sustainable Fisheries Act has resulted in the need for draconian cuts in the harvest of red snapper, and this ugly truth, which in my opinion could have been avoided, needs no hyperbole to increase public perception and discontent.

In another example, Bianchi and coauthors (6) raised questions about the causes and effects of seasonal hypoxia on the Louisiana inner continental shelf.  During most summers, nutrient enriched Mississippi and Atchafalaya River waters are discharged onto the shallow shelf where resultant organic matter production has led to extensive bottom-water hypoxia (through microbial respiration). 

During some years the hypoxic zone has covered more than 15,000 square kilometers since 1993 (7).   Some believe strongly that hypoxia in the northern GOM is controlled primarily by algal production, stimulated by excess nitrogen delivered from the Mississippi-Atchafalaya river basin, and by seasonal vertical stratification of incoming stream-flow and Gulf waters, restricting replenishment of oxygen from the atmosphere.

Bianchi and his coauthors (6) did not discount the need to reduce nutrient loads in the rivers because this, after all may be the only forcing factor that we can attempt to control.  However, they expressed legitimate concerns about the monetary costs of nutrient reductions in the Mississippi River drainage basin and they suggested considering less “nutrient-centric” causes, or alternative mechanisms for reducing the seasonality and extent of hypoxia.  These could include, e.g., the role of non-riverine organic matter inputs and physical processes that affect water column stability.  

These examples are linked explicitly by claims that the fishery ecosystem in the northwestern GOM has been negatively impacted by overexploitation and/or hypoxia on the Louisiana shelf (4, 5, 7, 8) and by fisheries landings and monitoring data that do not support these claims.  Indeed, the hypoxic zone in the GOM is frequently is referred to as the “Dead Zone,” both in the scientific and popular literature, implying that the zone is devoid of life.  

In contrast, data sets compiled by De Mutsert and coauthors (3), including 50 years of commercial landings data for 72 GOM fisheries, a 50-year time series of fishery resource monitoring data collected by the Louisiana Department of Wildlife and Fisheries and a >20-year time series of shrimp bycatch data collected by NOAA Fisheries, were used by Cowan and co-authors (9) to raise a red flag. Reductions in fisheries productivity and changes in community structure are not evident in these data – in the face of large natural and anthropogenic stressors in Louisiana’s coastal waters.  Others have reached similar conclusions (11.12) and studies attempting to explicitly document the impacts (as opposed to effects) of hypoxia on the Louisiana shelf have produced few definitive results (13, 14). 

Ironically, on the same day that the Washington Post published a story on the “Dead Zone,” which included a statement claiming that “there is an area on the Louisiana shelf the size of Massachusetts where you can’t catch any fish or shrimp,” a group of scientists, including a member of my research group, were on the shelf sampling in the hypoxic zone.  Samples were collected with high resolution imaging sonar and data were ground-truthed by biological samples collected in trawls. 

Several species of ground fishes and a penaeid shrimp (Atlantic croaker, cutlassfish, Atlantic bumpers, and pink shrimp) were abundant on the bottom in < 2 mg L-1, and the water column contained post-larval and juvenile anchovies (several species) and Atlantic bumpers.  In addition, there was a dense scattering layer just above the oxycline that included ctenophores and several species of juvenile fishes, including snappers.  Similar conditions were observed at several locations.

For what purpose?

In summary, if GOM food webs are not badly degraded, the worlds capture fisheries will not be depleted by 2048, and the Dead Zone is not really dead, why the hyperbole?  Why do some feel the need to exaggerate the effects of real environmental or ecological problems with flawed and subjective arguments?  Are there consequences for such actions?  Both gulf fisheries overexploitation and hypoxia are high profile issues and widely recognized as “ugly truths” and real risks to the sustainability of GOM natural resources (3,6,10).

I can only surmise that some of my colleagues must believe that the ugly truths are not sufficiently ugly to impress funding agencies, managers, and policy makers.  Personally, I believe that detecting significant impacts on Louisiana fishery resources would be far more reassuring than failing to do so, given the combined effects of obvious stressors such as coastal land loss (Louisiana alone accounts for 80% of US coastal wetland loss), eutrophication and hypoxia, hydrologic changes in coastal wetlands made for flood control and by the oil and gas industry, and climate change, which is affecting rates of sea level rise, and contributing to large scale replacement of Louisiana Spartina sp. salt marshes by black mangroves.

Some thoughts about why GOM fisheries may be buffered from the effects of hypoxia relative to other ecosystems have been discussed (6), and the difficulty of teasing environmental signals from ecosystems that contain many exploited species is well documented.  Nevertheless, the effects of the aforementioned stressors should, intuitively, be large and easily detectible.  

For example, more than 25% of Louisiana’s coastal wetlands have disappeared within the last few decades, and more that 75% of our fishery resources are species considered to be estuarine-dependent.  Yet a direct cause-and-effect relationship between wetland loss and fisheries productivity has remained elusive.

Our inability to detect a relationship between the degradation of coastal habitats, including large-scale seasonal hypoxia, and the animals that are believed to be dependent upon these habitats, may be the scariest, if not the most ugly, truth of all.  It suggests to me that we still have very little understanding of the factors that are responsible for the high secondary productivity that we Louisianans have long enjoyed, and which accounts for 75% of all fisheries landings in the US part of the GOM. 

More discussion is provided by Cowan and coauthors (10), who infer that it is likely that cumulative impacts will write the last chapter about a fishery ecosystem that reached a tipping point prior to a precipitous and perhaps irreversible decline (15).  These truths are ugly enough, in my opinion, to preclude the need for hyperbole.

When scientists politicize science

In the opening few sentences, I suggested that one purpose of this post was to express my concerns about the consequences of using flawed and exaggerated arguments to address real environmental and ecological issues.  Very early in my career, I read Gene Likens’ (1) description of the obligation he felt to inform managers and policy makers of his work at Hubbard Brook, in which he identified the threat of acid rain to aquatic and terrestrial ecosystems in the US and elsewhere.  He proceeded to use objective and defensible research results to convince managers and policy makers of the need to make changes.  In this case the ugly truth apparently was ugly enough.  Likens’ small book is mandatory reading for my students, and it has inspired me never to lose touch with the needs of managers and policy makers that are tasked to make informed, but very often difficult, decisions.

I have been directly engaged with fisheries governance for the last 15 years.  Many decisions must be made in the absence of conclusive study.  Nevertheless, Pielke in 2007 (2) offers the following admonition that expresses my basic concern: “If scientists evaluate the research findings of their peers on the basis of the implications for issue advocacy, then ‘scientific’ debate among academics risks morphing into political debates.  From the perspective of the public or policy-makers, scientific debate and political debate on many environmental issues already have become indistinguishable, and such cases of conflation limit the role of science in the development of creative and feasible policy options.  In many instances science has become little more than a mechanism for marketing competing political agendas, and scientists have become leading members of the advertising campaigns.  

Exactly, and this truth is very ugly indeed.  As a community of  “advertisers,” we should not be surprised when managers and policy makers who need objective, defensible, scientific answers no longer solicit our inputs.


1. G.E. Likens, The Ecosystem Approach: Its Use and Abuse (Ecology Institute, W-2124

Oldendorf/Luhe Germany 1992) pp. 103-124.

2. R.A. Pielke, Jr., The Honest Broker. Making Sense of Science in Policy and Politics

(Cambridge University Press 2007) pp. 116-134.

3. K. De Mutsert et al., Proc. Natl. Acad. Sci. USA 105, 2740 (2008).

4. D. Pauly, M-L Palomares, Bull Mar Sci. 76, 197 (2005).

5. B. Worm, E.B. Barbier, N. Beaumont, J.E. Duffy et al., Science 314, 787 (2006).

6. T. Bianchi et al., Eos Forum 89, 236 (2008).

7. N.N. Rabalais, R. E. Turner, W. J. Wiseman, Annu. Rev. Ecol. Syst., 33, 235 (2002).

8. R.R. Turner, N.N. Rabalais, BioScience 41, 130 (1991).

9. N.N. Rabalais et al., BioScience 52, 129 (2002).

10. J.H. Cowan, Jr., et al., Bull. Mar. Sci. 83, 1 (2008).

11. E.J. Chesney, D. M. Baltz, in Coastal hypoxia—consequences for living resources and ecosystems. N. N. Rabalais, R. E. Turner Eds. (Coastal and Estuarine Studies 58. American Geophysical Union, Washington, D.C. 2000), pp. 321-354.

12. E.J. Chesney, D. M. Baltz, R. G. Thomas, Ecol. Appl. 10, 350 (2001).

13. J.K. Craig, L. B. Crowder. Mar. Ecol. Prog. Ser., 294, 79 (2005).

14. T. O’Conner, D. Whitall. Mar. Poll. Bull., 54, 460 (2007)

15. J.B. Jackson et al., Science 293, 629 (2001).


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  4. Don-
    I was not alluding to you when I criticized those who for years have successfully lobbied to keep gulf hypoxia separate from ecosystem restoration. For exampe, despite repeated comments from Doug Daigle, me and a few others, the state master plan was in final draft before there was a begrudging agreement to insert a little paragraph on reducing nutrient conentrations in river water. Lip service is better than silence, I suppose.

  5. Don Boesch says:

    Mike, eutrophication is the process of increasing the loading of an aquatic ecosystem with organic matter. Frequently, this results from adding more nutrients (forms of nitrogen and phosphorus), which stimulates the growth of phytoplankton. Some of this increased growth sinks toward the bottom where bacteria degrade it and consume dissolved oxygen in the process. Where water column has strong density stratification (fresher and warmer water near the surface over saltier and colder water below) the oxygen supply can’t be replenished fast enough and concentrations fall too low to allow active animals like fish and shrimp to live there very long–that’s hypoxia.

    Len, as you know I have been preaching for years that the solutions for coastal restoration and hypoxia abatement must be integrated in an ecosystem-based management context because both problems are part and parcel of the disruption of the Mississippi River system. See In particular, it will be necessary to significantly reduce nutrient pollution of the river so that restoration of the Mississippi and Atchafalaya deltas can proceed while minimizing collateral impacts on water quality and ecosystem health. As Garret Graves, chairman of the Louisiana Coastal Protection and Restoration Authority, told the Gulf Hypoxia Task Force: “The Mississippi River built almost all of South Louisiana. We will rely upon it to help us rebuild what has washed away over the last century. The river must be healthy in order for us to succeed.”

  6. At the risk of further muddying the water, so to speak, let me provide some observations after representing Louisiana on the national hypoxia task force for about a decade, while being intimately involved in ecosystem restoration..
    1) hypoxia has become a serious problem in the northern gulf and in other deltas around the world, even though fisheries data remain inconclusive and no smoking gun has been demonstrated in terms of an imminent collapse;
    2) the extent of the summer hypoxic zone in the gulf has expanded in parallel with increases in agricultural nitrogen, related to corn production in the midwest;
    3) the Bush administration was derelict for eight years by never funding even modest action to reduce nutrient runoff within the Miss. R. watershed;
    4) many participants in the gulf hypoxia issue have ignored the breakup of the Louisiana delta and/or denied any connection between that issue and hypoxia;
    5) conversely, many participants in Louisiana’s coastal restoration program have dismissed the reduction of eutrophicatio and hypoxia as goals complementary to and compatible with ecosystem restoration;
    6) as a result of 4 and 5 integrated and comprehensive solutions to both challenges are rarely discussed, e.g., a brand new report on wetland loss in the eastern US by NOAA and FWS is a perfect example of treating problems in a vacuum, stovepiping technical issues and ignoring connections.

    Finally I think there are several basic and critical science questions that need resolution so as to assure the public that our science is credible and that we can reasonaby predict the outcome of the expenditure of billions of public dollars. These questions include: (1) what would be the outcome of releasing all the flow of the Mississippi-Atchafalaya river system within the shallow estuarine zone; (2) how rapidly is subsidence occurring and where and why; and (3) how much sediment would be needed to restore Louisiana’s inundated landscape to some sustainable level and are there sufficient sources available.

  7. Eutrophication vs. hypoxia ?

  8. Hypoxia Meiosis

    Jim Cowan seems to be accusing the numerous scientists who have published scores of papers on Gulf hypoxia or have been involved in several high level national assessments of: hyperbole; flawed, exaggerated, and subjective arguments; ignoring their ethical and moral obligations; discrediting science; obscuring the underlying treats to Gulf fisheries; and, if those weren’t bad enough, advertising. These are rather harsh words to be throwing around, even if one is a paragon of objectivity. It’s hard to see how such serious accusations are helpful.

    Jim says that he can find no evidence that hypoxia, wetland loss, fishing or anything else, for that matter, has affected Gulf fishery landings, but he “infers” that it is likely that “cumulative impacts will write the last chapter about a fishery ecosystem that reached a tipping prior to a precipitous and perhaps irreversible decline.” If that is true, why would one risk letting extensive and recurring oxygen depletion on the Louisiana shelf get worse, coastal wetlands further deteriorate, or wasteful by-catch discards to continue?

    Jim seems to react viscerally to reference to the Dead Zone, a term initiated by the press rather than scientists, but now used world-wide and with its own Wikipedia listing. He might regard this as hyperbole, but get used to it, the popular reference to the Dead Zone is here to stay. Scientists have always been clear that there are organisms living in the Dead Zone, although we await with interest the publication of the observations by Cowan’s group that ground fish and shrimp are abundant on the bottom under oxygen concentrations less that 2 mg/L. This is at odds with all other scientific observations and the actual practices of shrimpers, who know better than to lower the trawl where the Dead Zone is well formed. Jim also seems also to have fallen into the shifting baseline trap in claiming there is no evidence for hypoxia effects on fishery landings because the have not declined between 1985 and 2007 (Bianchi et al. 2008). Hypoxia was already severe and widespread by 1985–the appropriate comparison is with the period prior to the 1970s when recurrent hypoxia first began to develop. The atlas that Rez Darnell produced for MMS clearly showed that the highest summer biomass of bottom fish during the 1960s was found on parts of the shelf now occupied during the summer by hypoxia rather than bottom fish. There have also been dramatic changes in the dominant fish species caught in bottom trawls since the 1930s when Gordon Gunter first conducted scientific surveys on the inner Louisiana shelf (Chesney and Baltz, 2001).

    AS Doug Daigle points out, the national policy to abate hypoxia by reducing nutrient pollution has already been determined based on extensive scientific assessment and political compromise. Rather than “advertisers,” the scientists who participated in these assessments have functioned as what Roger Pielke, Jr. calls Honest Brokers of Policy Alternatives. The science behind this policy was reviewed in depth and confirmed by an independent expert panel convened by the EPA. The EPA panel considered the issues of non-riverine organic matter and physical processes affecting water column stability in reaffirming “the basic conclusion that contemporary changes in the hypoxic area in the northern Gulf of Mexico are primarily related to nutrient fluxes from the Mississippi-Atchafalaya River Basin.” Meanwhile, Cowan and his co-authors (Bianchi et al. 2008) express “concerns about the monetary costs of nutrient reductions in the Mississippi Basin” without a shred of evidence or analysis of what the benefits and costs are. This is not objectivity and rigor, but the opposite of hyperbole, meiosis, or purposeful understatement.

  9. Doug Daigle says:

    An additional risk here is that academic rivalries will negatively impact progress on public policy issues. Anyone who has been involved in or followed the hypoxia issue closely knows that the biggest problem there has been lack of action, not “hyperbole.” It may be unfortunate that the “Dead Zone” monicker has been used soextensively in the media. But the realities of the situation (and not hyperbole) have informed the open discusions in the national forum involving federal agencies and the states along the Mississippi River since the Gulf Hypoxia Task Force formed in 1998.

    The national policy effort on Gulf Hypoxia has been stymied by lack of resources to implement any comprehensive action for almost a decade. The national Action Plan that was developed in 2000 explicitly stated that, while questions remained about the impacts of hypoxia, the importance of the national resource at stake (the Gulf fishery) justified a national investment to protect it. Specifically, this involved a national investment in actions (programs, projects, etc.) to reduce nutrient loading in the Mississippi River Basin.

    This effort, and the voluntary framework adopted to implement it, were pragmatic policies, but they were not funded by the Bush administration or Congress. Some parties have propogated overestimates of the costs of reducing nutrient loadings, and for obvious reasons. But the failure to make even a modest investment in protecting a resource as important as the Gulf fishery continues to be striking.

    The Gulf Hypoxia Task Force and Action Plan were developed prior to the boom in biofuel production in the Mississippi River Basin, which has resulted in millions of acres being put back into production that were formerly in conservation programs (with concurrent increases in fertlizer application on those lands), just over the past two years. That development was not anticipated in 2001, and unfortunately the Task Force was prevented from effectively addressing it even after it became apparent.

    It’s a striking trend, yet Louisiana academics are arguing about “hypoxia hyperbole” rather than how to respond to a dramatic land use change that has serious implications for the state’s resources. Perhaps we can add that to the cumulative impacts that will be studied in years to come.

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