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5 Easy Pieces: The Impact of Fisheries on Marine Ecosystems

5 Easy Pieces: The Impact of Fisheries on Marine Ecosystems

by Daniel Pauly
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5 Easy Pieces features five contributions, originally published in Nature and Science, demonstrating the massive impacts of modern industrial fisheries on marine ecosystems. Initially published over an eight-year period, from 1995 to 2003, these articles illustrate a transition in scientific thought—from the initially-contested realization that the crisis of fisheries and their underlying ocean ecosystems was, in fact, global to its broad acceptance by mainstream scientific and public opinion.
Daniel Pauly, a well-known fisheries expert who was a co-author of all five articles, presents each original article here and surrounds it with a rich array of contemporary comments, many of which led Pauly and his colleagues to further study. In addition, Pauly documents how popular media reported on the articles and their findings. By doing so, he demonstrates how science evolves. In one chapter, for example, the popular media pick up a contribution and use Pauly’s conclusions to contextualize current political disputes; in another, what might be seen as nitpicking by fellow scientists leads Pauly and his colleagues to strengthen their case that commercial fishing is endangering the global marine ecosystem. This structure also allows readers to see how scientists’ interactions with the popular media can shape the reception of their own, sometimes controversial, scientific studies.
In an epilog, Pauly reflects on the ways that scientific consensus emerges from discussions both within and outside the scientific community.

Product Details

ISBN-13: 9781597267199
Publisher: Island Press
Publication date: 07/14/2010
Series: The State of the World's Oceans Series
Edition description: 1
Pages: 208
Product dimensions: 6.80(w) x 9.90(h) x 0.50(d)

About the Author

Daniel Pauly is a professor in the Fisheries Centre and Zoology Department at the University of British Columbia. Until 2008, he was Director of the University of British Columbia Fisheries Centre.

Read an Excerpt

5 Easy Pieces

How Fishing Impacts Marine Ecosystems

By Daniel Pauly


Copyright © 2010 Daniel Pauly
All rights reserved.
ISBN: 978-1-59726-968-1


Primary Production Required

A Summer in Manila

Some people complain about spending too much time commuting. In 1994, during the "International Year of the Family," I started on a transpacific commute that, for five uneasy years, allowed me both to continue living with my family and furthering my research in Manila, Philippines, and to work in my new position as a faculty member of the University of British Columbia, in Vancouver, Canada. In Manila, my employer was the International Center for Living Aquatic Resources Management (ICLARM), which I had joined, fresh from university, in 1979.

As a scientist, I had always straddled two worlds. Although I was born and raised in Europe and was trained at a German university, I had always intended to work in the tropics. This was in no small part because so few of my colleagues had really looked at the tropical fisheries on which so many of the world's poor subsisted. And when they did, they used models and techniques developed for temperate fisheries and fish populations, which had very different characteristics from those of the tropics. But in addition to the geographical worlds I inhabited, I also found myself torn between two scientific worlds: that of theory and that of the application of science to problems in the real world. These tensions proved to be creative ones, and they lie behind the contributions in this book.

ICLARM, in which much of my approach was developed, was, when I joined it, a young organization (it was founded in 1977). It was one of the few research centers devoted to problems of developing-country fisheries, and its scope extended throughout the intertropical belt. ICLARM was a delightful place to work, and the productivity and creativity of its international and national staff were widely recognized (Dizon and Sadorra 1995). Consequently, we were reorganized. By the early 1990s, the bureaucracy had become intolerable, eventually triggering my departure and that of many other colleagues. But not before it had forced upon us at least one positive, if unintended, consequence.

One of the purest manifestations of the bureaucratic mummification then taking place at ICLARM was the development of a "strategic plan." In 1990/1991, the entire scientific staff of ICLARM (plus the inevitable consultants) was engaged in developing the plan, which was then supposed to provide guidelines for a midterm plan, which then should provide a framework for annual plans, etc. As a result, we had long discussions on how to evaluate the potential of fish farming (aquaculture) and capture fisheries. Strangely and ironically enough, these discussions inspired the first contribution to this book.

At the time, there was a lot of optimism about the potential of aquaculture, a situation that has not changed, over two decades later. However, the information then available at the eco-regional and global levels did not allow extending this optimism to capture fisheries, notwithstanding their more important contribution to the food security and livelihood of people, notably in developing countries. This did not trouble most fisheries scientists at the time, because for the most part, they didn't look at such data.

This was very much in contrast with agriculture. We noted that the agronomists at the International Rice Research Institute (IRRI) in Los Baños, near Manila, did not write only about their own research plots, or rice culture in the Philippines, their host country, or even that of Southeast Asia, but rather they knew and wrote about global rice production. My colleague Villy Christensen and I found, in comparison, the parochial view of fisheries science odd, since fish were a globally traded commodity and the market saw to it that demand at one place was met with supply from others. We decided to begin to rectify this shortcoming by reviewing the state of, and potential for, catches of fisheries in the entire world. Global fisheries data had been available since 1950, when the Food and Agriculture Organization of the United Nations (FAO) began issuing its admirable global statistical compendia (Figure 1.1).

But only two groups had attempted to produce a global synthesis of the data available at the time: (a) staff of and consultants to FAO, who produced a comprehensive, but already then dated, review composed of chapters by the leading marine biologists and fisheries scientists of the time (Gulland 1970, 1971), and (b) a group led by Moiseev (1969), in the Soviet Union (remember?), whose main conclusions were very different from those then current in the West.

We never formally published our own effort, which was buried as an appendix by Christensen et al. (1991) to ICLARM's very forgettable Strategic Plan for International Fisheries Research. It was better so: this review later turned out to have been overly optimistic with regard to the future prospects of fisheries. However, the exercise itself was useful. In particular, it helped us to understand that by examining fisheries at a systemic level, in such a way that we could describe the dynamics of the ecosystem, rather than simply the behavior of any of its component species, we could gain critical new insights.

The standard practice among fisheries scientists of the time was to study one species and/or one fishery at a time, in isolation from other factors. This was in part a product of the reductionist tendencies of science in general—to isolate the subject of study from confounding variables in an effort to gain an uncompromised understanding of its properties and behavior. This of course should not be viewed as a condemnation of reductionism; indeed, it is what makes science so powerful (Pauly 1990). But often, reductionism causes big problems e.g., when one of the variables that was neglected turns around and bites us. Fisheries research in particular had to be reductionist at first— there were too many factors (notably environmental variability and trophic interactions) to sort out when the discipline began over a century ago. But the tendency of fisheries science to focus on single species was also due to its role in supporting the fishing industry, which was supposed to respond (e.g., by adjusting its effort) to assessments of their target stocks. Thus, fisheries scientists could tell you the status of, say, cod off Newfoundland, but they had nothing to say about the status of the ecosystem on which this cod depended—and this was the same for other fisheries around the world. We believed that by looking at the health of ecosystems, we could better understand how to manage them at a time when catches had begun to decline and the future of many fisheries was in doubt.

At the time, I was working with Villy Christensen on developing ways to summarize ecosystem properties based on the Ecopath approach and software (Christensen and Pauly 1992a), about which there will be more to say later. In trying to model the interactions among the components of ecosystems, we became interested in what H.T. Odum (1988) called "emergy"—not a misspelling, but rather a neologism standing for "embodied energy," or the amount of energy, in the form of food eaten, it takes to produce a particular animal, in our case typically a fish. Emergy could be calculated based on knowledge of food webs in ecosystems, but it was too abstract and theoretical to be of practical use (also, people got tired of telling their word processors that the spelling was OK).

Coincidentally, however, just a few years earlier, Peter Vitousek and his Stanford colleagues had been trying to estimate the proportion of the planet's primary productivity—the capture of the sun's energy by plants—appropriated by humans (for food, fiber, or fuel, or paved over to build shopping malls). I liked the way Vitousek et al. (1986) had derived their estimates for terrestrial systems as the sum of estimates by sector and industry. They relied on a counterintuitive, but robust, statistical truth known as the "central limit theorem": that multiple independent estimates of the same unknown quantity have a normal distribution, and they yield an accurate mean when averaged. Thus, when Vitousek and his colleagues used numerous, independent estimates of the primary production requirements of various subsectors of the global economy, the errors in those estimates largely canceled out upon being added up. The result, which has held up to scrutiny over time, was that humans in the late 1980s were appropriating, that is, requiring and/or consuming, 35–40% of terrestrial primary production. By contrast, they found that humans appropriated only 2.2% of marine primary production.

Box 1.1

Definitions of Fish, Landings and Trophic Level

Fish: In fisheries science, this term refers to the aquatic animals taken by fishing gears and includes bony fishes (herring, cod, tuna, etc.), cartilaginous fishes (sharks, rays), animals that look like fish but are not (hagfish), and invertebrates (shrimps, crabs, lobsters, oysters, clams, squids, octopi, sea urchins, sea cucumbers, jellyfish, etc.). The term usually excludes marine mammals, reptiles, corals, sponges, and algae, though these are included in some statistics, such as the global fisheries statistics assembled by FAO from annual submissions by its member countries and which provided the starting point for most analyses in this book (Figure 1.1).

Landings: Fishing gears are meant to capture fish by disabling or killing them (von Brandt 1984). Technically, the term yield is used for the weight of all fish that are killed (I do not consider, in this book, the fisheries servicing the aquarium trade or other nonfood fisheries), while catch, strictly speaking, refers to their number (Holt et al. 1959). In this book, we shall ignore the difference between weight and numbers in catch. Not all fish that are caught are landed and marketed, however. Some are thrown back overboard, and these are called "discards." Thus, one can define Catch = Landings + Discards. Making the distinction between catch and landings is not being pedantic: in the early 1990s, the amount of fish that was discarded annually was estimated at 20–30 million tonnes (t) per year, that is, nearly a third of officially reported landings (Alverson et al. 1994), while more recent estimates put this figure at 7.3 million t (Kelleher 2004; Zeller and Pauly 2005).

Trophic level (TL): This, as I shall elaborate later in this book, is the number of steps in a food web that separates an organism from the primary producers (TL = 1) at the base of that food web.

This was an intriguing finding for us. First, primary productivity required (PPR) was just the flip side of Odum's embodied energy concept, and I realized that the "primary production required" by fisheries would itself be a useful, and easily understandable, measure of the impact of humans on marine systems (Christensen and Pauly 1993a; Ulanowicz 1995; Dulvy et al. 2009).

Second, it seemed to me as a fisheries ecologist that Vitousek et al. had not dealt adequately with primary productivity in the oceans. Their estimate of the marine primary production required by fisheries was based on one single multiplication, involving a then-current estimate of marine fish landings (FAO 1984) times the primary production required to support an "average fish," that is, a fish that would have to be at the exact center of marine food webs (this was defined as having a trophic level of 3.0; see Box 1.1 for definitions of fish, landings, and trophic level).

Box 1.2

Why We Can't Use Mean Trophic Levels to Calculate Primary Production Required

Due to the nonlinearity of the relationships between trophic levels and trophic fluxes, use of mean trophic level (as in Iverson 1990 or Vitousek et al. 1986; see text) for estimating fluxes in multispecies fisheries leads to a strong bias, which can be illustrated using the data in Table 1.1. Inspired by a similar table for the use of terrestrial primary production in Vitousek et al. (1986), it contains estimates of the primary production required (PPR) to sustain the global catches (Yi) of 39 different groups of fish (i), each calculated using the equation [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] with a mean value for the transfer efficiency (TE) equal to 0.10 (see Figure 1.3), and trophic levels (TLi) derived from 48 trophic models such as the one in Figure 1.4.

The sum of these estimates is 2.84 × 109 t·year-1. The mean trophic level of these 39 groups, weighted by their catch, is 3.10. This, applied to the sum of the catches, leads, via the above equation, to a PPR estimate of 1.33 × 109 t year-1, or only 47% of the previous estimate that is obtained with disaggregated data. Thus, using mean trophic levels, as in most publications previously reviewed above, completely distorts, through a phenomenon known as "aliasing," the relationships between primary production and catches (or potential yields).

In reality, this was more complicated. Given the definitions in Box 1.1, one can infer the primary production required to generate a given catch of, say, pollock, if one knows its trophic level and the transfer efficiency of biomass between trophic levels. However, such efficiencies, in marine ecosystems, are rather low (2–20%, with a mean of about 10%; see below). This means that small errors in trophic level assignment will induce large errors in the estimation of primary production required. Thus, the assumption of an "average fish" of trophic level 3.0 in Vitousek's work was misleading because there is no such thing as an "average fish," and even less, one with a mean trophic level representing all fishes (see Box 1.2). Moreover, the trophic levels of most fish were unknown at the time. As it turned out, the solution to this quandary was to be found in Ecopath, a software and modeling approach developed, then abandoned, by Polovina (1984a, 1984b, 1993). It allowed for the first rigorous estimation of trophic levels in aquatic ecosystems, and it had just been rescued from oblivion (Christensen and Pauly 1993a).

Villy Christensen and I used it to reassess the findings of Vitousek et al., and I presented our work at the 1994 meeting of the British Ecological Society in Manchester, where it was viewed by Lawton (1994) as "the most important and disturbing piece of information from the whole conference." I was encouraged to submit a manuscript to Nature by Sir (now Lord) Robert May, then already one of the world's leading theoretical ecologists. Actually, at that time, that submission had already occurred, and Nature, after providing three easyto-accommodate referees' reports, not only published our contribution (and listed it on its cover of March 16, 1995), but asked John Beddington, now science advisor to the UK government, to introduce it to its readers (Beddington 1995). This piece is reproduced below, modified only as to its reference style:

The Primary Requirements

J.R. Beddington | Vol. 374 No. 6519

Concern that fish are being harvested unsustainably has usually centered on the dramatic collapses of individual stocks or on the conflicts associated with the over-capacity of the fishing industry. At a global level, marked declines in the rate of increase of the total world catch, and indeed falls in that total, have recently prompted the question of whether catches are close to or exceeding the maximum that is sustainable.

Pauly and Christensen (1995) address the issue by calculating the level of primary production necessary to sustain world fish catches. They estimate that some 8% of global aquatic primary productivity is required, a figure that is much higher than previous estimates (Vitousek et al. 1986) but, on the face of it, not particularly large. However, when the contribution of different ecosystems is examined, major differences emerge. For the open ocean, the primary productivity requirement is only around 2%, but open-ocean fisheries contribute only a small proportion of the world fish catch. For the areas of greatest importance to fish production, for instance the continental shelves, the requirements range from 24 to 35%. Such figures imply that current levels of fishing—and certainly any increases—are likely to result in substantial changes in the ecosystems involved.

Pauly and Christensen's calculations start from data collected by the UN Food and Agriculture Organization (FAO) and involve classifying catches of different species into different groups and calculating a fractional trophic level for each group: this statistic is essentially a weighted average of the levels at which species feed. For example, Antarctic krill are given a fractional trophic level of 2.2 on the assumption that they feed 80% at the phytoplankton level and 20% at the herbivorous zooplankton level.


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Table of Contents

List of Exhibits
Chapter 1. Primary Production Required
Chapter 2. Fishing Down the Food Web
Chapter 3. China and the World's Fisheries
Chapter 4. Sustainability
Chapter 5. Future of Fisheries
Appendix 1: The origins of the 100 million tonnes myth
Appendix 2: Rejoinder: Response to Caddy et al.
Appendix 3: Post-1998 Studies of 'Fishing Down'

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