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December 2009
Overfishing continues despite repeated warnings about the decline in the ocean’s population of Atlantic, or Northern, bluefin tuna ((Thunnus thynnus). Source: Osaka Aquarium, Japan; OpenCage.info.
Marine fisheries supply a major source of protein to the world’s population, and they support an industry worth over $85 billion annually.1 People have fished since the dawn of human history, and overfishing impacts were apparent even in some primitive societies at relatively low population density.2 It was during the 20th century that fishing expanded rapidly to the global scale as a result of motorized vessels, inexpensive oil, refrigeration, increasingly global commodity markets, and heavy government subsidies to increase fleets.3 Marine fisheries now use 24-35% of primary production on continental shelves and in major upwelling areas, including bycatch (marine animals caught in the nets inadvertently)—a figure similar to the roughly one-fourth of the land’s potential net primary production appropriated by humans.4 Fishing has transformed the world’s oceans. 5,6 Humans are now a dominant force of nature in the seas as we are on land, and we often affect marine fish resources negatively with such practices as:
Overfishing—this takes place when fish supplies fall below standard levels due to excessive fishing; it can be categorized into three main types: growth overfishing, recruit overfishing, and ecosystem overfishing.7
Destructive fishing practices—utilizing destructive fishing practices such as bottom trawling, where the fishermen suspend large nets from boats to drag the bottom of the oceans and end up with other marine animals and organisms such as corals in their nets, as well as threaten biodiversity by killing animals unnecessarily and damaging the ocean environment.8
Polluting the ecosystem—e.g., directly with litter, boat exhaust, and oil spills, and indirectly with phosphates and nitrates from agricultural runoff.
Status of global marine fisheries
Currently, fishing pressure appears to be near—if not beyond—the ocean’s capacity to provide. Estimates based on fisheries catch data, which were corrected for over-reporting by China, suggest that global fish catch peaked in the late 1980s, and this number has remained flat or begun to decline since.1,9 The Food and Agricultural Organization of the United Nations (FAO) conducts the most comprehensive analysis of global fish stocks every four years, and recently reported that “the maximum wild capture fisheries potential from the world’s oceans has probably been reached.”1 The situation is reminiscent of society’s reaching the point of peak oil—although fishery production is at least partially a renewable resource.
What about individual fish stocks? In 2008, the FAO estimated that roughly half of the world’s 523 assessed fishery stocks are “fully exploited,” meaning that they are harvested at rates near their maximum sustainable limits, while another 28% are “overexploited or depleted,” meaning that they are being harvested at rates not sustainable in the long term.1 Even these numbers are uncertain and possibly conservative since they do not include many small-scale commercial and artisanal tropical fisheries; furthermore, these numbers do not include stocks that have already collapsed and been abandoned.
Fishing impacts have fallen especially hard on slow-growing predators. Typically, deep-sea fisheries, such as those targeting Chilean sea bass (Dissostichus eleginoides) and orange roughy (Hoplostethus atlanticus), have undergone an initial boom followed by collapse. In addition, many sharks, which are slow growing and have very low reproductive rates, have been reduced by more than 75% in recent decades.10-13 Impacts are not restricted to such species, nonetheless. At the community level, a wide range of data sources conclude that average abundance, size, and habitat quality have declined substantially in many regions of the world ocean in recent decades.6
Marine biodiversity and fishery production
Long-simmering controversy about the state of world fisheries came to a head in 2006, when the scientist Boris Worm and colleagues reported the first comprehensive quantitative analysis of links between marine biological diversity and ecosystem services to human society.12 They concluded that disparate sources of data—from theory, controlled experiments, observed historical trends, and fishery catches—show a consistent pattern: marine ecosystems with fewer species, whether naturally or because of human impacts, have lower average productivity and stability. The greater fish productivity in more diverse ecosystems probably results in part from climate or resources that affect both diversity and productivity; however, such effects are less likely to explain the lower frequency of and faster recovery from collapse in diverse ecosystems.12 Although mechanisms remain speculative, the correlations of diversity with productivity and resilience probably result in part from a more efficient use of resources by diverse communities with broader functional capacity, and to the “portfolio effect,” whereby a diverse group of stocks (whether fish or financial instruments) is more stable in the face of environmental fluctuations than any single stock.
The primary message of Worm and his colleagues that links biodiversity to ecosystem services was overshadowed, however, by another point made in the press release associated with the paper’s publication, which was that if current trends continue, all currently fished marine species will have collapsed (fallen below 10% of their maximum historical harvest) by the middle of the 21st century. This claim generated worldwide attention and proved highly controversial. Much of the controversy centered on the use of catch data as a proxy for fish abundance. Critics pointed out, correctly, that catches may fail to track fish abundances because of changing markets, social factors, and management regimes.
While such factors can obscure population trends for individual stocks, however, no compelling evidence has been suggested that globally averaged catch data significantly misrepresent trends in global fish abundances. Indeed, one analysis concluded, “declining catches are an indication of declining stocks. Assuming otherwise would imply that all fishers or regulatory agencies in large marine ecosystems like the Mediterranean drastically reduce fishing of a species without the stock being in decline. Except for the World Wars, we are not aware of any such case.”14 This same analysis showed that the number of new stocks entering global fisheries declined steadily over recent decades and that if current trends continue, the world’s reservoir of unexploited fishable stocks will be exhausted by 2020. This general trend is consistent with the FAO’s conclusion noted above. It seems reasonable, therefore, to conclude that we are at the threshold, or even beyond, the world ocean’s capacity to provide fish and that significant changes are necessary to maintain this service over the long term.15
What do we want from the oceans?
Trawler hauling fishing nets near Galveston, Texas. Photo: Robert K. Brigham, NOAA.
Different parties can legitimately see statistics on the sizes of fish populations as showing a glass half full versus half empty. Beyond the disagreement about the data, debate involves fundamental values16: What do we, as a global society, want from the oceans? Are we content to treat them as essentially a planetary factory farm for inexpensive fish fillets (and mines and highways)? Or, do we want something more—a multifunctional, resilient ecosystem that provides a range of ecosystem services, and a stable reservoir of biodiversity, as well as commodities?
The consequences of different values can be seen most clearly by considering how we decide what the optimal abundance of fish in the ocean is.16 Fisheries professionals tend to see the ocean in economic terms as a producer of commodities, proteins, and jobs. They emphasize that fishery management explicitly aims to maximize long-term fish productivity (the amount of fish produced per year), which in theory occurs when a population is reduced to roughly half of its equilibrium biomass. This goal is called the Maximum Sustainable Yield (MSY), and it is the basis of much fishery management legislation. By this view, fishery management has historically aimed to reduce fish populations to somewhat less than half of what they would be without fishing; although more recently, a precautionary approach has begun to advocate less extreme harvest.15
Critics of this exclusively economic approach, in contrast, tend toward a more holistic view of the oceans, and they emphasize the intrinsic value of biological diversity and its important, albeit poorly quantified, role in producing non-market ecosystem services such as waste processing, climate regulation, and carbon cycling.17 This idea has recently begun to penetrate fishery management in the goal of “ecosystem-based management,” which aims for integrated, place-based approaches to manage the suite of human activities and interrelated ecosystem processes in a given area simultaneously.18,19 By this view, a long-term reduction by half, of multiple fish populations, is likely to have far-reaching consequences for the rest of the ocean ecosystem; although, these consequences are only now becoming well understood.20-23
The future of marine fisheries
While evaluating the future of fisheries depends in part on what we as a society want from the oceans, several issues complicate the more optimistic predictions:
Continued harvest stability is questionable. The theoretical target of MSY is exceeded in fisheries routinely— sometimes severely so3; yet, it is still poorly understood how such sustained high harvest levels affect stock stability in the face of natural and anthropogenic (i.e., human-derived) disturbances. Increasing evidence shows that both individual fish populations, and the more complex ecosystems in which they are included, can respond in a non-linear fashion to exploitation and other pressures; but these may cross a tipping point into a new stable state that is resistant to attempts to restore it to the original state.24,25
Demand will continue to increase. Global human population is increasing rapidly; it is likely to roughly double before stabilizing at an estimated nine billion. The average per capita resource use is increasing even faster, which means that the human population’s already large demand for fish and other resources will undoubtedly increase a great deal in the coming decades.6,26
Current fishery projections are not all-inclusive. The more optimistic projections of the future of world fisheries are typically based on extrapolating a handful of examples of well-managed fish stocks within the territorial waters of rich, stable, and well-governed western democracies.27 This is a non-representative sample of the world’s fisheries, nonetheless, and there will surely be formidable hurdles to spreading good management models through the rest of the world—particularly in the face of growing human population, per capita resource use, environmental change, and probable political instability resulting from global climate change interacting with these factors.
Indeed, the future of marine fisheries can be seen as a microcosm of the future of human society generally. Some basic questions include:
How important is abundant and inexpensive food, and the jobs associated with providing this food in the short term—relative to the many other tangible and intangible benefits that we receive from healthy ecosystems over the longer term? It is increasingly clear that many of these benefits cannot be achieved simultaneously.
How important is the availability of abundant fish now relative to long-term maintenance of a functioning ecosystem that can provide fish (and other ecosystem services) to our grandchildren and beyond?
What sacrifices, if any, are we willing to make now to ensure the long-term stability of that resource?
A recent consideration of how values influence the conflicting attitudes toward fishery management divided the major stakeholders in ocean ecosystems into consumptive users (i.e., fishers), government, and non-governmental organizations (NGOs)16; however, they could as reasonably be characterized into present users and future users. When we consider the interests of “users” of the ocean two, three, or four generations down the line, the interests of fishers and governments and others become much more closely aligned. Policies that maximize fish production now—but endanger the production of fish and other important ecosystem services in the next generation—would not benefit tomorrow’s fishers or any of the other citizens represented by governments and NGOs.
Potential solutions
As is true of environmental challenges generally, there is unlikely to be a single solution to making world fisheries sustainable. Effective marine conservation and management will involve several parallel approaches, among which three central proposed solutions should be mentioned.
1. Ecosystem-based management (EBM) recognizes and seeks to incorporate the complex interactions of fish stocks with one another and with the broader ecosystems that support them into fishery management.28 A related, more specific concept is the ecosystem approach to fisheries (EAF)—a form of fisheries governance that draws its conceptual basis and operational approaches from both conventional fisheries management and ecosystem management.29 The basic elements of both approaches involve maintaining single-species exploitation rates lower than would produce MSY and avoiding by-catch of non-target species. Thus, both EBM and EAF depart from traditional fisheries management, which focuses on maximizing productivity of individual stocks in isolation. Because complex indirect interactions are the rule in ecosystem dynamics, and are often unpredictable, EBM ascribes particular importance to precautionary measures that aim to avoid depleting stocks. Ecosystem-based management has been mandated by the Great Barrier Reef Marine Park Act of 1981, in Australia, the Magnuson-Stevens Fishery Conservation and Management Act (1996, reauthorized 2006) in the USA, and the International Convention on the Conservation of Antarctic Marine Living Resources.
2. Marine spatial planning is related to the concept of ecosystem-based management, and focuses specifically on better integrating management of the sundry, and often conflicting, human activities in the sea.30,31 Many of the challenges facing the oceans derive in part from uncoordinated governance. For example, fishing, mining, oil and gas extraction, marine mammal conservation, shipping, and other activities in U.S. territorial waters are regulated by more than 20 separate agencies in isolation from one another. Fixing this situation was a key recommendation of both the U.S. Commission on Ocean Policy and the similar Pew Commission reports in 2004. Zoning has been used routinely on land for many years. Marine spatial planning can strategically site compatible activities together and separate incompatible ones, and it seeks to accommodate the plethora of potentially conflicting human uses such as recreation, fishing, and energy generation in an optimal way. Ultimately, marine spatial management must also coordinate with activities on land to develop adjacent coastal watersheds responsibly; to reduce inputs of toxic contaminants and nutrients; and to mitigate and adapt to human-induced climate change.
3. Improved incentive systems for sustainable fishing include, most recently, an exploration of dedicated access such as catch-share programs, as well as more effective governance at national and local levels.32 Fundamentally, managing fisheries involves managing the people that fish, which can involve both sticks (such as the restrictions historically used in management) and carrots (such as financial incentives to switch to less damaging gear). The latter involves appropriate incentive systems for making fishing sustainable.33 One such promising approach that is gaining momentum involves Limited Access Privilege Programs (LAPP’s), also known as “catch shares,” in which a secure share of fish is allocated to an individual fisher, community, or association. The rationale is that because the shares are allocated before the season begins, fishers know how much fish they are allowed to harvest that year, and so there is incentive to do it efficiently, rather than in the counterproductive and expensive race to get the most fish possible that results under the often complicated, historic regulations. On the other hand, LAPPs limit access by definition, and therefore, these entail many difficult decisions about how shares are allocated, as well as the potential impacts of consolidating effort on both the environment and fishing communities.
Finally, no account of the future of fish would be complete without considering the rapidly growing global aquaculture industry, which accounted for more than a third of total global fishery production in 2006.1 Although aquaculture has been suggested frequently as a solution to the environmental impacts of ocean fishing, and it will surely be part of such a solution, the answer is not simple. Many farmed fish proposed for large-scale ocean ranching—notably salmon and tuna—are carnivorous. These operations can cause even greater harm than wild capture fisheries because such apex predators require large quantities of food, which comes from forage fish harvested from the ocean, and also because of their prodigious waste output, and the risk of disease and parasitism they pose to wild relatives.34,35 Moreover, farmed tuna are taken as juveniles from wild populations but are not recorded as catch in capture fishery statistics.
Thus, if aquaculture is to be part of a sustainable long-term solution, rather than part of the problem, it will need to focus on species low on the food chain such as catfish and tilapia, avoid transmitting diseases and genetic defects to wild fish, and produce minimal waste and habitat destruction. As in wild capture fisheries, achieving these goals requires effective management and policies that can adapt to a rapidly changing world.
© 2009, American Institute of Biological Sciences. Educators have permission to reprint articles for classroom use; other users, please contact editor@actionbioscience.org for reprint permission. See reprint policy.
