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Webs and scales
Fisheries Research 23 (1995) 381-383
Book review
Webs and scales webs and Scales, Michael M. Mullen. University of Washington Press, Washington, DC, 1993, 148 pp., US$ 15, ISBN O-295-97245-9.
What are the interactions between fish stocks and their environment? This question, as a scientific issue, has been around since fisheries research began. But there is now another issue that can be framed by the same question, concerned with relatively new concepts such as sustainability and the precautionary principle. Even the term ‘environment’ is now so heavily laden with meanings that it adds unwanted resonance in arguments or, especially, in titles. What exactly is the role of an Advisory Committee on the Marine Environment? These questions arose because, after reading Mullin’s book, I came across a Forum on sustainability (Ecol. Appl., 1993,3:548-589) where much of the detail concerns fisheries management. This forum provided a context to Mullin’s text. This volume is one of a series on recruitment fishery oceanography. Mullin provides a perceptive assessment of plankton ecology as it relates to fish stock recruitment. He says “I have attempted to illustrate physical/chemical influences on the distribution of biomass and ... production of plankton at various scales, and to show how larval fish may be affected by them”. The “scales” are spatial, from encounters of individual copepods with their food, through fronts and eddies, to ocean basins. Most of the examples are from the Pacific but there are references to Georges Bank and the North Sea. “Webs” are dealt with more perfunctorily. Microbial loops are discussed but I was surprised that there was no mention of the theories of Cohen or Pimm and their relevance to planktonic webs. The title of the series and the author’s stated aim may seem to beg the question of whether or not recruitment is determined by the physical, chemical or planktonic environment. The minimalist approach might allow that random physical variability supplies the noise but the persistence of fish stocks, apart from excessive harvesting, is a density dependent process within fish populations. What is the evidence for direct involvement of the planktonic food web? This book provides a valuable review of the diverse ways in which the environment may affect the survival of fish larvae. The issue of scale arises from the fact
382
Book review /Fisheries Research 23 (1995) 381-383
that “the dynamics of populations depend on the summation of outcomes of smallscale, individualistic interactions”. In the ocean it is very difficult to perceive these individual behaviors, Yet, somehow there is interaction across these spatial scales. This is a consequence of the ‘non-linearities’ in food web dynamics. As Mullin points out it has proved difficult, if not impossible, to establish both the individual mechanisms and the outcome at the level of fish stocks. The reason usually given is that, although we can sample the larvae, the critical processes appear to be in the juvenile phase. For these reasons the stock recruit relation is derived empirically - or taken out of a black box. Mullin notes that “predation and cannibalism on juveniles may be at least as significant as larval food supply”. (Remember that mathematically, if not morally, cannibalism is the simplest and most effective means of achieving density dependence.) The one-species-at-a-time approach to fisheries management is being expanded to multi-species models where natural mortality is dependent on predation by larger fish. This avoids Mullin’s question - does the distribution and abundance of their food affect the size of fish populations? The predation assumption can be justified by the fact that fluctuation in stock biomass is dominated by variability in numbers rather than changes in growth rate. Can individual behavior of juveniles in searching for and capturing food be shown to affect the rates of predation? Or are the environmental aspects confined to physical transports that take larvae to suitable habitats? Finally, do these questions have any relevance to fisheries management? There are no definite conclusions in this book. Mullin says; “I have attempted to illustrate physical/chemical influences on the distribution of biomass and primary and secondary production of plankton at various scales, and to show how larval fish may be affected by them, possibly [but not necessarily] resulting in variations in recruitment”. Mullin’s knowledge and experience make this an authoritative statement of the present position. Where do we go from here? Do we need better time series or further knowledge of processes to improve management? Or, after so much effort, should we abandon this approach at least in the context of fisheries applications? This is the crux of the argument in the Forum. An article by Ludwig et al. (see also Science, 1993,260( 17):36) states “resource problems are not really environmental problems; they are human problems”. Further, “our lack of understanding and inability to predict, mandate a much more cautious approach to resource exploitation than is the norm”. They recommend “the well-developed theory of decision making under uncertainty”. It may not be their intention, but they appear to propose a choice of alternative scientific methods rather than between conflicting philosophies. Terms like ‘sustainability’ and ‘precautionary principle’ are inherently vague or ambiguous - qualities that may be useful in poetry or politics. The fact that these terms have achieved common use by scientists does not mean they are suitable for scientific discourse. Ludwig et al. inveigh against the claim that “the key to a sustainable biosphere is research on a long list of ... topics in ecology”. I agree, but only because I consider it inappropriate to mix ‘poetic’ and scientific lan-
Book review /Fisheries Research 23 (1995) 381-383
383
guage. Yet this mixture is becoming commonplace to justify, or deny, research objectives, as well as to link science and management. These options are absent from Mullin’s text yet. For him the scientific uncertainty provides a spur for further research. His own work has been a significant part of a long term effort to understand oceanic food webs. He states, “there is no question that our intellectual, technological and financial resources for environmental research are limited and therefore must be deployed efficiently”. I hope he is right in his underlying assumption about the future. J.H. STEELE Woods Hole Oceanographic Institution Woods Hole, MA 02543 USA
Book review
Webs and scales webs and Scales, Michael M. Mullen. University of Washington Press, Washington, DC, 1993, 148 pp., US$ 15, ISBN O-295-97245-9.
What are the interactions between fish stocks and their environment? This question, as a scientific issue, has been around since fisheries research began. But there is now another issue that can be framed by the same question, concerned with relatively new concepts such as sustainability and the precautionary principle. Even the term ‘environment’ is now so heavily laden with meanings that it adds unwanted resonance in arguments or, especially, in titles. What exactly is the role of an Advisory Committee on the Marine Environment? These questions arose because, after reading Mullin’s book, I came across a Forum on sustainability (Ecol. Appl., 1993,3:548-589) where much of the detail concerns fisheries management. This forum provided a context to Mullin’s text. This volume is one of a series on recruitment fishery oceanography. Mullin provides a perceptive assessment of plankton ecology as it relates to fish stock recruitment. He says “I have attempted to illustrate physical/chemical influences on the distribution of biomass and ... production of plankton at various scales, and to show how larval fish may be affected by them”. The “scales” are spatial, from encounters of individual copepods with their food, through fronts and eddies, to ocean basins. Most of the examples are from the Pacific but there are references to Georges Bank and the North Sea. “Webs” are dealt with more perfunctorily. Microbial loops are discussed but I was surprised that there was no mention of the theories of Cohen or Pimm and their relevance to planktonic webs. The title of the series and the author’s stated aim may seem to beg the question of whether or not recruitment is determined by the physical, chemical or planktonic environment. The minimalist approach might allow that random physical variability supplies the noise but the persistence of fish stocks, apart from excessive harvesting, is a density dependent process within fish populations. What is the evidence for direct involvement of the planktonic food web? This book provides a valuable review of the diverse ways in which the environment may affect the survival of fish larvae. The issue of scale arises from the fact
382
Book review /Fisheries Research 23 (1995) 381-383
that “the dynamics of populations depend on the summation of outcomes of smallscale, individualistic interactions”. In the ocean it is very difficult to perceive these individual behaviors, Yet, somehow there is interaction across these spatial scales. This is a consequence of the ‘non-linearities’ in food web dynamics. As Mullin points out it has proved difficult, if not impossible, to establish both the individual mechanisms and the outcome at the level of fish stocks. The reason usually given is that, although we can sample the larvae, the critical processes appear to be in the juvenile phase. For these reasons the stock recruit relation is derived empirically - or taken out of a black box. Mullin notes that “predation and cannibalism on juveniles may be at least as significant as larval food supply”. (Remember that mathematically, if not morally, cannibalism is the simplest and most effective means of achieving density dependence.) The one-species-at-a-time approach to fisheries management is being expanded to multi-species models where natural mortality is dependent on predation by larger fish. This avoids Mullin’s question - does the distribution and abundance of their food affect the size of fish populations? The predation assumption can be justified by the fact that fluctuation in stock biomass is dominated by variability in numbers rather than changes in growth rate. Can individual behavior of juveniles in searching for and capturing food be shown to affect the rates of predation? Or are the environmental aspects confined to physical transports that take larvae to suitable habitats? Finally, do these questions have any relevance to fisheries management? There are no definite conclusions in this book. Mullin says; “I have attempted to illustrate physical/chemical influences on the distribution of biomass and primary and secondary production of plankton at various scales, and to show how larval fish may be affected by them, possibly [but not necessarily] resulting in variations in recruitment”. Mullin’s knowledge and experience make this an authoritative statement of the present position. Where do we go from here? Do we need better time series or further knowledge of processes to improve management? Or, after so much effort, should we abandon this approach at least in the context of fisheries applications? This is the crux of the argument in the Forum. An article by Ludwig et al. (see also Science, 1993,260( 17):36) states “resource problems are not really environmental problems; they are human problems”. Further, “our lack of understanding and inability to predict, mandate a much more cautious approach to resource exploitation than is the norm”. They recommend “the well-developed theory of decision making under uncertainty”. It may not be their intention, but they appear to propose a choice of alternative scientific methods rather than between conflicting philosophies. Terms like ‘sustainability’ and ‘precautionary principle’ are inherently vague or ambiguous - qualities that may be useful in poetry or politics. The fact that these terms have achieved common use by scientists does not mean they are suitable for scientific discourse. Ludwig et al. inveigh against the claim that “the key to a sustainable biosphere is research on a long list of ... topics in ecology”. I agree, but only because I consider it inappropriate to mix ‘poetic’ and scientific lan-
Book review /Fisheries Research 23 (1995) 381-383
383
guage. Yet this mixture is becoming commonplace to justify, or deny, research objectives, as well as to link science and management. These options are absent from Mullin’s text yet. For him the scientific uncertainty provides a spur for further research. His own work has been a significant part of a long term effort to understand oceanic food webs. He states, “there is no question that our intellectual, technological and financial resources for environmental research are limited and therefore must be deployed efficiently”. I hope he is right in his underlying assumption about the future. J.H. STEELE Woods Hole Oceanographic Institution Woods Hole, MA 02543 USA