Fisheries Research 55 (2002) 1–9 Viewpoint Overfishing, tropicalization of fish stocks, uncertainty and ecosystem management: resharpening Ockham’s razor Konstantinos I. Stergiou* Laboratory of Ichthyology, Department of Zoology, School of Biology, Aristotle University of Thessaloniki, P.O. Box 134, 54006 Thessaloniki, Greece Received 4 December 2000; accepted 4 December 2000 Abstract Fishing at the early stage of fisheries development most probably approximated natural predation. Nowadays, fishing approximates ‘‘extermination’’ with dramatic effects on aquatic ecosystems. Conventional fisheries models and management practices are inadequate to handle the present situation because, among many other factors, fishing: (a) drives fish stocks to exhibit smaller body sizes and age/length at maturity (i.e., ‘‘tropicalization’’) and (b) increases catch variability, thus increasing uncertainty. The realization of (a) and (b) renders conventional practices even more inadequate, thus producing a never-ending positive feedback loop. Although the application of the precautionary approach to fisheries management together with the development of indicators and reference point values that trigger management actions seem to be an important step forward, their adoption within the framework of the same conventional models used to assess fish stocks could introduce another degree of complexity into existing models. With Ockham’s razor as a primary guiding principle, the advantage of using ever more complex models is suspect. Ecosystem management seems the only alternative. Within this framework, alternative simpler ‘‘models and strategies’’ such as large-scale marine protected areas, in which no fishing takes place, are available and promising, and their adoption as a primary management tool satisfies simultaneously all objectives that have been set for ecosystem management. Keywords: Overfishing; Life-history; Tropicalization of fish stocks; Uncertainty; Catch variability; Stock assessment; Precautionary approach; Ecosystem management ‘‘Fifty years ago, a single cod was large enough to feed a family of four or five. Today, it is barely enough for one’’, says Lord Perry of Walton, a member of the UK House of Lords (Anonymous, 1997b). There is a worldwide increasing concern for the future of fisheries resources and their management mainly because of recent failures in fisheries management and crisis at various levels. Such a concern has * Tel.: þ30-31-998268; fax: þ30-31-998279. E-mail address: kstergio@bio.auth.gr (K.I. Stergiou). 0165-7836/02/$ – see front matter PII: S 0 1 6 5 - 7 8 3 6 ( 0 1 ) 0 0 2 7 9 - X been the subject of many recent publications (e.g., Mooney, 1998; Pitcher et al., 1998; Flaaten et al., 1998; Payne, 1999; Briand, 1999; Hollingworth, 2000). In this essay, I tackle issues, albeit not new, from a different perspective. Thus, I briefly discuss how fishing activity has changed from natural predation, in early times, to ‘‘extermination’’ today, the latter being accompanied by important effects on marine ecosystems. Consequently, I consider in more depth some fishing-induced effects (i.e., ‘‘tropicalization’’ of fish stocks, increase in objective uncertainty), which, together with many other facts, contribute, 2 K.I. Stergiou / Fisheries Research 55 (2002) 1–9 through a never-ending loop, to the failure of conventional fisheries models and management practices to fulfill the very cause of their existence. I further attempt to show why the implementation of the precautionary approach and the development of ‘‘stockoriented’’ indicators and reference points are not consistent with the principle of Ockham’s razor and will not be successful. Finally, I argue that placing fisheries management into an ecosystem perspective is the only alternative. Within this framework, the adoption of large-scale, marine protected areas—where fishing is not allowed—as the primary management tool satisfies all objectives for ecosystem management, being also consistent with Ockham’s razor. 1. Fishing: from predation to extermination Fishing was developed gradually when humans moved from random collection of things found in nature to the first cultivation and systematic exploitation of food resources using learned practices and simple tools (Sahrhage and Lundbeck, 1992). Thus, although about 100,000 years BP Neanderthal man practiced fishing by hand, by about 50,000 years BP, Homo sapiens started to use various gears, made of wood, bone, ivory and horn (Sahrhage and Lundbeck, 1992). By Homer’s time (800–900 B.C.), fishing tools were already technologically improved (i.e., fine and pointed curved hooks, made of metal, bronze and iron; harpoons; nets of mesh sizes of 5–45 mm made of hemp and flax) (Sahrhage and Lundbeck, 1992). During the past several centuries, however, the mechanization of fishing and other developments (e.g., technological innovations in vessel design, development of trading organizations and of transport facilities), allowed fishing activities to expand spatially (Sahrhage and Lundbeck, 1992). Later technological innovations in vessel construction, in fishing gear material and manufacture, and in electronics (e.g., radar, echo sounders), the use of highly sizeunselective and efficient gears (e.g., trawls) and the subsidy-driven overcapitalization of the fishing industry (Beddington, 1995; Anonymous, 1997a; Garcia and Newton, 1997) all in a synergetic fashion allowed fishing effort and fishing efficiency to reach unsustainable levels. This has been particularly evident during the last 10–20 years, with the cost of fishing already exceeding the value of the world’s catch in the beginning of the 1990s (Cochrane, 2000). Indeed, very few areas of the world oceans are not being drastically affected today by fishing activities. Thus, fisheries landings, together with by-catch, require about 24–35% of the global marine primary production in the continental shelf and major upwelling areas of the world ocean, a figure much higher than previously thought (Pauly and Christensen, 1995). Moreover, 60% of the world fisheries stocks are fully exploited to overexploited and 6% are depleted (Anonymous, 1997a), with the case of the Canadian cod (Gadus morhua) being considered as one of the biggest disasters of recent years (Spurgeon, 1997a; Longhurst, 1998), and with so far very little evidence for rapid recovery of stocks from prolonged declines (Hutchings, 2000). In addition, the mean trophic level in fisheries landings—i.e., mean trophic level of all species making up the landings weighted by their catch—in the last 45 years has decreased steadily both at the global scale and at the regional, ocean-specific scale (i.e., the fishing-down the food web concept: Pauly et al., 1998a,b, 2000a). Finally, fishing-induced species’ extinctions, or near extinctions, seem to be more frequent than previously thought (see review by Roberts and Hawkins, 1999), even though fisheries models do predict them (Pitcher, 1998). Thus, humans, at the early stage of fisheries development, used fishing gears (e.g., nets, hooks, harpoons) that we now know are highly size-selective. Since their effect on aquatic ecosystems was spatially very localized, one may conclude that fishing during this early period most probably approximated natural predation. In contrast, there is no doubt that nowadays fishing approximates ‘‘extermination’’, with dramatic effects on aquatic ecosystems and important implications for fisheries management both of which are discussed below. 2. Tropicalization of fish stocks and objective uncertainty: the epitaph of conventional fisheries models and management schemes The ecosystem effects of fishing, some of which have been described above, can be generally classified into two categories (Fig. 1). The first includes effects K.I. Stergiou / Fisheries Research 55 (2002) 1–9 3 Fig. 1. A schematic, simplified representation of the major effects of fishing on marine ecosystems (modified from Stergiou, 1999). Key or example references per major effect portrayed on this graph are given below. Effects at the community level: (a) destruction of structure and heterogeneity of benthic habitats (see review by Jennings and Kaiser, 1998); (b) changes in relative species composition (e.g., Pauly, 1994a; Caddy and Rodhouse, 1998; Fogarty and Murawski, 1998; Stevens et al., 2000); (c) decrease in species diversity (e.g., Rijnsdorp et al., 1996; Stergiou et al., 1997a; Bianchi et al., 2000; but see Greenstreet and Hall, 1996); (d) species’ extinction (see review by Roberts and Hawkins, 1999); (e) changes in predation and competition rates, trophic cascades (e.g., Roberts and Polunin, 1991; Ramsay and Kaiser, 1998; Sala et al., 1998); (f) changes in trophic structures and energy flow (Pauly and Christensen, 1995, 1998a,b, 2000a); (g) decrease in stock abundances (e.g., Haedrich and Barnes, 1997; Anonymous, 1997a; Hutchings, 2000; Clark et al., 2000); (h) increase in variability with time (Stergiou, 1998). Effects of fishing at the life-history level of the individual species: (a) decrease in body size/weight (e.g., McAllister et al., 1992; Haedrich and Barnes, 1997; Ratz et al., 1999; Bianchi et al., 2000; Zwanenburg, 2000); (b) size and age at maturity: (Beacham, 1983; Jennings and Kaiser, 1998; Morgan and Colbourne, 1999; Law, 2000); (c) truncating age structures (e.g., Longhurst, 1998); (d) change in sex ratios (e.g., Buxton, 1993); and (e) decrease in population reproductive potential (e.g., Jennings and Kaiser, 1998; Jennings et al., 1998). at the community level and the second those at the lifehistory level of the individual species. There is no doubt that the effects at the two levels, which can be either direct or indirect (e.g., Gislason et al., 2000), strongly interact with each other in a complex and often unpredictable manner. From the various effects of fishing, I hereafter pay particular attention to those concerning the length structure and the length/age at maturity of the exploited stocks. The examples presented in Table 1 suffice to make the point that such effects, which may have a genetic basis (e.g., Policansky and Magnuson, 1998; Law, 2000), can be very dramatic indeed. They also clearly show that heavy fishing in non-tropical waters ‘‘tropicalizes’’ fish stocks, in the sense that it drives them to exhibit the characteristics of their tropical counterparts (i.e., smaller body sizes, earlier maturation: Pauly, 1998a). Such a ‘‘tropicalization’’ renders the application of the presently used conventional stock assessment models inadequate (e.g., Die 4 K.I. Stergiou / Fisheries Research 55 (2002) 1–9 Table 1 Examples of the effects of fishing on body size and length/age at maturity in fishes Species Effect of fishing Reference Various species Based on data from FishBase 1998, the mean maximum length of the fishes making up the catches of the NE and NW Atlantic has decreased from about 90 cm in 1950 to 60 cm in 1996 The mean weight of commercially targeted demersal fishes declined by 51 and 41% on the eastern and western Scotian shelf, respectively, between 1970–1974 and 1994–1998; in both areas the decline was faster during mid-1980s to mid-1990s The mean weight of adults has been reduced by up to 34% for several British Columbia stocks between 1950 and 1990 The length-at-age 4 and 5 years declined from about 61 and 67 cm in 1959 to 43 and 53 cm in the mid-1980s, respectively The mean weight of the northern Grand Banks (NAFO Div. 2J3KL) cod declined from >2 kg to about 0.5 kg after the collapse of the early 1990s, with the biomass of the 10–20-year-old individuals being reduced from 48% in 1962 to 8% in 1990 and to zero after 1990 The median length and age at maturity of the majority of the stocks on the Scotian shelf, which were heavily exploited in the 1960s and 1970s, declined by about 50% between 1959 and 1979 (from about 6 to 3 years and from 55 cm to about less than 45 cm The median age at maturity of the Northeast cod declined drastically from 11 years in the late 1940s to less than 8 years in the late 1980s The age and length at 50% maturity of the three major stocks, the Labrador-NE Newfoundland, Grand Bank and St Pierre Bank stocks, have both declined drastically between early 1960s and late 1980s (by 2–5 years and 3–10 cm depending on stock and sex) Froese and Pauly (1998) Various species Oncorhynchus gorbuscha Gadus morhua Gadus morhua Gadus morhua Gadus morhua Hippoglossoides platessoides and Caddy, 1997) and calls for the use of their ‘‘tropicalized’’ versions (see Pauly, 1998a). Body length is the most important demographic characteristic of a species that largely determines many processes: ecological (e.g., predation, competition, trophic level, mortality, longevity: Pauly, 1998a,b; variability: Stergiou, 1998); fisheries (e.g., gear size selectivity: Pauly, 1998a); and managerial (e.g., risk undertaken by fishery managers: Stergiou, 1998). Based on FAO catch data from 103 fish stocks throughout the world oceans, Stergiou (1998; unpublished data) showed that catch variability decreases with an increase in body size. Because however, there is a strong, significant relationship between body length and trophic level (Froese and Pauly, 1998), one may assume that fishing-down marine food webs, by decreasing body sizes (Pauly et al., 1998b) and truncating age structures, should increase catch variability. Indeed, Stergiou (1998) has also shown that the variability of fish catches during the last years increases with the length of time over which it is Zwanenburg (2000) McAllister et al. (1992) Ratz et al. (1999) Longhurst (1998) Beacham (1983) Jorgensen (1990) Morgan and Colbourne (1999) calculated (Fig. 2; sensu Pimm and Redfearn, 1988). This indicates that catches exhibit long-term trends and hence that there is not any equilibrium yield, the latter being the basis of the conventional single- and multi-species models presently used for fisheries management (e.g., Caddy and Sharp, 1986; Hilborn and Walters, 1992; Hollowed et al., 2000). Temporal variability in catches, and other parameters such as recruitment, introduce what is usually referred to as ‘‘objective uncertainty’’ (Ferson and Ginzburg, 1996). Objective uncertainty refers to uncertainties resulting from the underlying variability in stochastic processes, such as growth, mortality and recruitment, as opposed to ‘subjective uncertainty’ (Ferson and Ginzburg, 1996), which is mainly attributed to lack of knowledge (e.g., the case for many Eastern Mediterranean stocks: Stergiou et al., 1997b). Although it is widely recognized that objective uncertainty is one of the key-factors in predicting and managing fisheries resources (e.g., Walters and Maguire, 1996; Flaaten et al., 1998; Stokes et al., K.I. Stergiou / Fisheries Research 55 (2002) 1–9 Fig. 2. Variability of catches (standard deviation of logged catches, SDL) versus the number of years over which SDL was calculated for Mallotus villosus in Norwegian waters for the period 1918– 1991 (data from Stergiou (1984)). SDL is plotted against 2, 4, 8, 16, 32, 64 and 72 years. The slope of the regression line is significantly ðP < 0:05Þ different from zero (from Stergiou, 1998). 1999; Cochrane, 2000), and managers are aware of such uncertainty, it is still largely neglected in stock assessment or management procedures (Lauck et al., 1998). In fact, it is to this aspect of fisheries ecology that recent paradigms of fish stocks collapses are generally attributed to (e.g., Anonymous, 1995; Spurgeon, 1997b). Both, the fishing-induced tropicalization of fish stocks and the increase in uncertainty are involved in a never-ending positive loop (i.e., they will further contribute to the inadequacy of models and management strategies, which, in turn, will intensify tropicalization and uncertainty). Another point to be considered here is the effect of climate on fisheries, which further complicates things for fisheries scientists and managers. This is because most of the effects of fishing on ecosystems and individual species (Fig. 1) can also be brought about by, or related to, long-term climatic changes, as indicated by several earlier (e.g., Jensen, 1939; Dunbar, 1954; Cushing and Dickson, 1976) and recent examples of the effect of climate on marine communities and stocks (see Stergiou, 1999). In fact some of the effects shown in Table 1 have been partially related to climate (e.g., Ratz et al., 1999). The same may also be true of various anthropogenic impacts such as pollution and habitat modification (e.g., Caddy, 1993; Gislason et al., 2000). The case of ‘‘regime shifts’’ is also relevant here. Regime shifts are synchronized 5 changes in several commercial stocks at long, interdecadal, scales and these changes, being produced or enhanced by climatic changes either natural or anthropogenic ones, can be linked to changes in other components of marine ecosystems such as the abundance of planktonic invertebrates and temperature (Bakun, 1998; Steele, 1998). Steele (1998) maintains that because of the ‘‘regime shifts’’, the ‘‘sustainability’’ concept is not directly applicable to marine ecosystems and especially to fisheries. It must also be kept in mind that the effect of the climate and of the environment cannot be distinguished from that of fishing inasmuch as fisheries managers will always respond to catch declines by assuming that fishing is the main factor and, hence, both effects will be reflected in catch records (Hilborn and Walters, 1992). Thus, conventional fisheries models are inadequate for dealing with the present situation because of the: (a) fishing-induced tropicalization of fish stocks; (b) fishing-induced increase in objective uncertainty; (c) increase in catch variability with the time over which it is estimated (i.e., non-equilibrium yield); and (d) the confounding effects of climate and environment on fisheries stocks, which are not generally accounted for in the models. The above mentioned issues together with the facts that: (a) actual fishing mortality rates usually exceed target rates (e.g., because of unreported catches, discarding, ghost fishing: Lauck et al., 1998), (b) enforcement of traditional measures, such as limits by numbers, minimum landings sizes, is very difficult (Anonymous, 1997b; Stergiou et al., 1997a), (c) managerial decisions are, and will be, highly influenced by politics (Masood, 1997; Spurgeon, 1997b,c), and (d) objectives are poorly articulated in fisheries managements schemes (Stokes et al., 1999; Cochrane, 2000), have all, in a synergetic fashion, contributed to the recent failure of conventional fisheries management to fulfill the very cause of its existence (for more on the failure of management practices see: Smith, 1998; Cochrane, 2000). Thus, conventional fisheries models and management strategies should be reconsidered in order to account for the above issues. Recently, the ‘‘precautionary approach’’ has been applied to fisheries management, while the idea of ‘‘ecosystem management’’ has also been put on the table. These issues are discussed below. 6 K.I. Stergiou / Fisheries Research 55 (2002) 1–9 3. The precautionary approach, ecosystem management and Ockham’s razor A version of the precautionary approach derived from Principle 15 of the Rio Declaration reads: ‘‘Where there are threats of serious or irreparable damage, lack of full scientific certainty shall not be used as a reason for postponing cost-effective measures to prevent environmental degradation’’. The application of this principle to fisheries management and the development of sustainability indicators (e.g., stock biomass, fishing mortality) in relation to reference point values that trigger management actions for the target species (e.g., Garcia, 1994; Darcy and Matlock, 1999; Oliver, 2000), seems to be an important step forward. However, the adoption of ‘‘stock-oriented’’ indicators and reference points will be unsuccessful because they are implemented within the framework of the same conventional models used to assess fish stocks. In addition, the use of single-species reference points is questionable when species interactions are important (Gislason, 1999), as is usually the case for most fisheries. The adoption of ‘‘stock-oriented’’ indicators and reference points could also introduce another degree of complexity into the existing models (see for instance Gislason, 1999), with doubtful outcomes. It is noteworthy that the incorporation of longterm trends and cycles in commercial catches (e.g., Taylor and Prochaska, 1984), of uncertainties (e.g., Punt and Hilborn, 1997), or environmental factors (e.g., Basson, 1999) into various single-species stock assessment models, also adds complexity with doubtful outcomes. Indeed, attempts to address uncertainties generally lead to increased complexity in management systems without any sign of having the desired results, even for the commercial single-species fisheries for which they were developed (Cochrane, 1999). Thus, the adoption of ‘‘stock-oriented’’ reference points will delay the identification of the detrimental effects of fishing on any given stock, a fact that by itself may further contribute to the failure of management practices (Lauck et al., 1998). Placing fisheries management into an ecosystem perspective seems to be the only alternative (e.g., Jennings and Polunin, 1996; Mooney, 1998; Gislason et al., 2000; Cochrane, 2000; Pitcher, 2000), and the adoption of a variety of ‘‘ecosystem’’ indicators and reference points that trigger management actions (e.g., Table 1 in Gislason et al., 2000) becomes a necessity. These can be defined directly, through the use of modeling tools such as the ECOPATH/ECOSIM/ECOSPACE (Christensen and Pauly, 1993a; Walters et al., 1997; Pauly et al., 2000b), which are invaluable for studying the effects of fisheries, and have been successfully applied in various areas (e.g., Christensen and Pauly, 1993b; Shannon et al., 2000). Ecosystem objectives may also be satisfied indirectly, by establishing, what is considered to be the extreme case of the precautionary approach (Lauck et al., 1998), marine protected areas (MPAs; also known as no-take zones). MPAs, in which fishing is totally prohibited, provide a refuge in space rather than a refuge in numbers, the latter being the aim of most traditional fisheries management measures. Among many other benefits, MPAs protect the biomass of species, maintain biodiversity including genetic diversity, decrease the trend for heavy evolutionary fishing selection for earlier maturity and reproduction and smaller adult fish size, and hedge against inevitable uncertainties, errors in estimations, and biases (e.g., Roberts and Polunin, 1991; Agardy, 1994; Lauck et al., 1998; Guenette et al., 1998; Hall, 1998; Sumaila et al., 2000; Polunin, 2001). Thus MPAs satisfy simultaneously the objectives for ecosystem management proposed by Gislason et al. (2000) (maintenance of: ecosystem diversity, species diversity, within-species genetic variability, directly impacted species, ecologically dependent species and trophic level balance) or others (see Fowler, 1999). However, in the large-scale ecological context, the ability of MPAs to meet such objectives depends critically, apart from the degree of enforcement, on their size and the biology and mobility of the target species concerned (see thorough review by: Polunin, 2001). Such dependence might be true for the vast majority of the existing MPAs, which are of very small sizes (i.e., their median size being 1600 ha). In fact, such sizes do not always have fisheries or ecosystem benefits (Polunin, 2001). Yet, there is overwhelming evidence that MPA sizes encompassing large parts, e.g., 40% or more, of the fishable management areas (e.g., Sladek Nowlis and Roberts, 1999; Polunin, 2001) could have substantial benefits in rebuilding highly overfished stocks and thus the ecosystems in which they are embedded. I now turn to consider Ockham’s razor (e.g., Pauly, 1994b). With this principle as a primary guide, I K.I. Stergiou / Fisheries Research 55 (2002) 1–9 wonder what is the advantage of using ever more complex models, and management strategies based upon them (i.e., single- or multi-species fisheries models further complicated by reference points), which are likely to fail when alternative simpler ‘‘models and strategies’’ such as large-scale MPAs (see Agardy, 2000) are available and promising? The establishment of effectively large-sized MPAs must proceed quickly (Ludwig et al., 1993; Fogarty, 1999) and everybody that was previously dependent on these large areas must be provided with alternative sources of income. Discussions on issues such as the identification of optimum MPA size and location, socio-economic and political repercussions, and many others, albeit very important at some later stage, serve at present only as excuses for not adopting MPAs as a primary management tool. Is there anybody thinking that the establishment of an MPA will be ecologically harmful within the boundaries of the ecosystem where this was established? (It may, over the short term, be economically harmful, which is all that politicians and fishermen care about). Should large scale MPAs not be adopted as a primary management tool, we will ‘‘watch’’ more stocks collapse and maybe then use what will be left of natural fisheries to support an aquaculture production of fish and shellfish. Acknowledgements I would like to extend my gratitude to Drs. H. Browman, K. Erzini and A.D. McIntyre for their constructive criticisms and comments. References Agardy, T., 1994. Advances in marine conservation: the role of marine protected areas. Trends Ecol. Evol. 9, 267–270. Agardy, T., 2000. Effects of fisheries on marine ecosystems: a conservationist’s perspective. ICES J. Mar. Sci. 57, 761– 765. Anonymous, 1995. The cod that disappeared. New Scientist, September, 1995, 24–29. Anonymous, 1997a. Review of the state of world fishery resources: marine fisheries. FAO Fish. Circ. 920, 173. Anonymous, 1997b. Fishing by numbers reveals its limits. Nature 386, 110. Bakun, A., 1998. Ocean triads and radical interdecadal variation: bane and boon to scientific fisheries management. In: Pitcher, 7 T., Hart, P.J., Pauly, D. (Eds.), Reinventing Fisheries Management. Chapman & Hall, London, pp. 332–358. Basson, M., 1999. The importance of environmental factors in the design of management procedures. ICES J. Mar. Sci. 56, 933– 942. Beacham, T.D., 1983. Variability in median size and age at sexual maturity of Atlantic cod, Gadus morhua, on the Scotian shelf in the Northwest Atlantic Ocean. Fish. Bull. US 81, 303–321. Beddington, J., 1995. The primary requirements. Nature 374, 213– 214. Bianchi, G., Gislason, H., Graham, K., Hill, L., Jin, X., Koranteng, K., Manickchand-Heilman, S., Paya, I., Sainsbury, K., Sanchez, F., Zwanenburg, K., 2000. Impact of fishing on size composition and diversity of demersal fish communities. ICES J. Mar. Sci. 57, 558–571. Briand, F. (Ed.), 1999. Precautionary Approach to Local Fisheries in the Mediterranean Sea. CIESM Workshop Series 7, 89 pp. Buxton, C.D., 1993. Life-history changes in exploited reef fishes on the east coast of South Africa. Environ. Biol. Fish. 36, 47–63. Caddy, J.F., 1993. Toward a comparative evaluation of human impacts on fishery ecosystems of enclosed and semi-enclosed seas. Rev. Fish. Sci. 1, 57–95. Caddy, J.F., Rodhouse, P.G., 1998. Cephalopod and groundfish landings: evidence for ecological change in global fisheries? Rev. Fish Biol. Fish. 8, 431–444. Caddy, J.F., Sharp, G.D., 1986. An ecological framework for marine fishery investigations. FAO Fish. Tech. Pap. 283, 152. Christensen, V., Pauly, D., 1993a. ECOPATH II, a software for balancing steady-state ecosystem models and calculating network characteristics. Ecol. Model. 61, 169–185. Christensen, V., Pauly, D. (Eds.), 1993b. Trophic Models of Aquatic Ecosystems. Proceedings of the ICLARM Conference, Vol. 26, 390 pp. Clark, M.R., Owen, F.A., Francis, R.I.C., Tracey, D.M., 2000. The effects of commercial exploitation on orange roughy (Hoplostethus atlanticus) from the continental slope of the Chatham Rise, New Zealand, from 1979 to 1997. Fish. Res. 45, 217–238. Cochrane, K.L., 1999. Complexity in fisheries and limitations in the increasing complexity of fisheries management. ICES J. Mar. Sci. 56, 917–926. Cochrane, K.L., 2000. Reconciling sustainability, economic efficiency and equity in fisheries: the one that got away? Fish Fish. 1, 3–21. Cushing, D.H., Dickson, R.R., 1976. The biological responses in the sea to climatic changes. Adv. Mar. Biol. 14, 1–122. Darcy, G.H., Matlock, G.C., 1999. Application of the precautionary approach in the national standard guidelines for conservation and management of fisheries in the United States. ICES J. Mar. Sci. 56, 853–859. Die, D.J., Caddy, J.F., 1997. Sustainable indicators from biomass: are there appropriate reference points for use in tropical fisheries? Fish. Res. 32, 69–79. Dunbar, M.J., 1954. A note on climatic change in the sea. Arctic 7, 27–30. Ferson, S., Ginzburg, L.R., 1996. Different methods are needed to propagate ignorance and variability. Reliab. Engr. Syst. Saf. 54, 133–144. 8 K.I. Stergiou / Fisheries Research 55 (2002) 1–9 Flaaten, O., Salvanes, A.G.V., Scweder, T., Ultang, O. (Eds.), 1998. Objectives and Uncertainties in Fisheries Management with Emphasis on Three North Atlantic Ecosystems: A Selection of Papers Presented at an International Symposium, Bergen, Norway, June 3–5, 1997. Fish. Res. 37, 1–310. Fogarty, M.J., 1999. Essential habitat, marine reserves and fishery management. Trends Ecol. Evol. 14, 133–134. Fogarty, M.J., Murawski, S.A., 1998. Large-scale disturbance and the structure of marine systems: fishery impacts on Georges Bank. Ecol. Appl. 8 (Suppl.), 6–22. Fowler, C.W., 1999. Management of multi-species fisheries: from overfishing to sustainability. ICES J. Mar. Sci. 56, 927–932. Froese, R., Pauly, D. (Eds.), 1998. Fishbase 98: Concepts, Design and Data Sources. ICLARM, Manila. Garcia, S.M., 1994. The precautionary principle: its implications in capture fisheries management. Ocean Coast. Mgmt. 22, 99–125. Garcia, S.M., Newton, C., 1997. Current situation trend and prospects in world capture fisheries. In: Pikitch, E., Huppert, D.D., Sissenwine, M. (Eds.), Global Trends: Fisheries Management. American Fisheries Society Symposium, Vol. 20, Bethesda, USA, pp. 3–27. Gislason, H., 1999. Single and multispecies reference points for Baltic fish stocks. ICES J. Mar. Sci. 56, 571–583. Gislason, H., Sinclair, M., Sainsbury, K., O’Boyle, R., 2000. Symposium overview: incorporating ecosystem objectives within fisheries management. ICES J. Mar. Sci. 57, 468–475. Greenstreet, S.P.R., Hall, S.J., 1996. Fishing and the ground-fish assemblage structure in the North-western North Sea: an analysis of long-term and spatial trends. J. Anim. Ecol. 65, 577–598. Guenette, S., Lauck, T., Clark, C., 1998. Marine reserves: from Beverton and Holt to the present. Rev. Fish Biol. Fish. 8, 251– 272. Haedrich, R.L., Barnes, S.M., 1997. Changes over time of the size structure in an exploited shelf fish community. Fish. Res. 31, 229–239. Hall, S.J., 1998. Closed areas for fisheries management—the case consolidates. Trends Ecol. Evol. 13, 297–298. Hilborn, R., Walters, C.J., 1992. Quantitative Fisheries Stock Assessment: Choice, Dynamics and Uncertainty. Chapman & Hall, New York, 570 pp. Hollingworth, C.E. (Ed.), 2000. Ecosystem Effects of Fishing. Proceedings of the ICES/SCOR Symposium. ICES J. Mar. Sci. 57, 465–791. Hollowed, A.B., Bax, N., Beamish, R., Collie, J., Fogarty, M., Livingston, P., Pope, J., Rice, J.C., 2000. Are multispecies models an improvement on single-species models for measuring fishing impacts on marine ecosystems? ICES J. Mar. Sci. 57, 707–719. Hutchings, J.A., 2000. Collapse and recovery of marine fishes. Nature 406, 882–885. Jennings, S., Kaiser, M.J., 1998. The effects of fishing on marine ecosystems. Adv. Mar. Biol. 34, 201–352. Jennings, S., Polunin, V.C., 1996. Impacts of fishing on tropical reef ecosystems. Ambio 25, 44–49. Jennings, S., Reynolds, J.D., Mills, S.C., 1998. Life history correlates of responses to fisheries exploitation. Proc. R. Soc. London B 265, 333–339. Jensen, A.S., 1939. Concerning a change of climate during recent decades in the Arctic and sub-Arctic regions, from Greenland in the west to Eurasia in the east, and countemporary biological and geophysical changes. Biol. Mediterr. 14, 1–83. Jorgensen, T., 1990. Long-term changes in age at sexual maturity of Northeast Arctic cod (Gadus morhua L.). J. Cons. Int. Explor. Mer. 46, 235–248. Lauck, T., Clark, C., Mangel, M., Munro, G.R., 1998. Implementing the precautionary principle in fisheries management through marine reserves. Ecol. Appl. 8, 72–78. Law, R., 2000. Fishing, selection, and phenotypic evolution. ICES J. Mar. Sci. 57, 659–668. Longhurst, A., 1998. Cod: perhaps if we all stood back a bit? Fish. Res. 38, 101–108. Ludwig, D., Hilborn, R., Walters, C., 1993. Uncertainty, resource exploitation, and conservation: lessons from history. Science 260, 36. Masood, E., 1997. Fisheries science: all at sea when it comes to politics? Nature 386, 105–106. McAllister, M.K., Peterman, R.M., Gillis, D.M., 1992. Statistical evaluation of a large scale fishing experiment designed to test for a genetic effect of size-selective fishing on British Columbia pink salmon (Oncorhynchus gorbuscha). Can. J. Fish. Aquat. Sci. 49, 1294–1304. Mooney, H.A. (Ed.), 1998. Ecosystem Management for Sustainable Marine Fisheries. Ecol. Appl. 8 ( Suppl. 1), 1–174. Morgan, M.J., Colbourne, E.B., 1999. Variation in maturity-at-age and size in three populations of American plaice. ICES J. Mar. Sci. 56, 673–688. Oliver, P., 2000. The knowledge on the state of Mediterranean resources in relation to their sustainable management within the precautionary approach to fisheries: recent initiatives and proposals to fill the gaps. CIESM Workshop Series 12, 53–56. Pauly, D., 1994a. On the Sex of Fish and the Gender of Scientists: A Collection of Essays in Fisheries Science. Fish and Fisheries Series 14. Chapman & Hall, London. Pauly, D., 1994b. Resharpening Ockham’s razor. Naga 17 (2), 7–8. Pauly, D., 1998a. Beyond our original horizons: the tropicalization of Beverton and Holt. Rev. Fish Biol. Fish. 8, 307–334. Pauly, D., 1998b. Tropical fishes: patterns and propensities. J. Fish. Biol. 53 (Suppl.), 1–17. Pauly, D., Christensen, V., 1995. Primary production required to sustain global fisheries. Nature 374, 255–257. Pauly, D., Christensen, V., Dalsgaard, J., Froese, R., Torres Jr., F., 1998a. Fishing down marine food webs. Science 279, 860– 863. Pauly, D., Froese, R., Christensen, V., 1998b. Response to Caddy et al. How pervasive is fishing down marine food webs? Science 282, 1384–1386. Pauly, D., Christensen, V., Froese, R., Palomares, M.L., 2000a. Fishing down aquatic food webs. Am. Sci. 88, 46–51. Pauly, D., Christensen, V., Walters, C., 2000b. Ecopath, ecosim, and ecospace as tools for evaluating ecosystem impacts on marine ecosystems. ICES J. Mar. Sci. 57, 697–706. Payne, A.I.L. (Ed.), 1999. Confronting Uncertainty in the Evaluation and Implementation of Fisheries-management Systems. ICES J. Mar. Sci. 56. K.I. Stergiou / Fisheries Research 55 (2002) 1–9 Pimm, S.L., Redfearn, A., 1988. The variability of population densities. Nature 334, 613–614. Pitcher, T.J., 1998. A cover story: fisheries may drive stocks to extinction. Rev. Fish Biol. Fish. 8, 367–370. Pitcher, T.J., 2000. Ecosystem goals can reinvigorate fisheries management, help dispute resolution and encourage public support. Fish Fish. 1, 99–103. Pitcher, T.J., Hart, P.J.B., Pauly, D. (Eds.), 1998. Reinventing Fisheries Management. Chapman & Hall, London. Policansky, D., Magnuson, J.J., 1998. Genetics, metapopulations, and ecosystem management of fisheries. Ecol. Appl. 8 (Suppl.), 119–123. Polunin, N.V.C., 2001. Marine protected areas, fish and fisheries. In: Hart, P.J.B., Reynolds, J.C. (Eds.), Handbook of Fish and Fisheries, Vol. II. Blackwell, Oxford. Punt, A.E., Hilborn, R., 1997. Fisheries stock assessment and decision analysis: the Bayesian approach. Rev. Fish Biol. Fish. 7, 35–63. Ramsay, K., Kaiser, M.J., 1998. Demersal fishing disturbance increases predation risk for whelks (Buccinum undatum L.). J. Sea Res. 39, 299–304. Ratz, H.-J., Stein, M., Lloret, J., 1999. Variation in growth and recruitment of Atlantic cod (Gadus morhua) off Greenland during the second half of the 20th century. J. Nortw. Atl. Fish. Sci. 25, 161–170. Rijnsdorp, A.D., van Leeuwen, P.I., Daan, N., Heesen, H.J.L., 1996. Changes in abundance of demersal fish species in the North Sea between 1906–1909 and 1990–1995. ICES J. Mar. Sci. 53, 1054–1062. Roberts, C.M., Hawkins, R., 1999. Species extinctions in marine ecosystems. Trends Ecol. Evol. 14, 241–246. Roberts, C.M., Polunin, N.V.C., 1991. Are marine reserves effective in management of reef fisheries? Rev. Fish Biol. Fish. 1, 65–91. Sahrhage, D., Lundbeck, J., 1992. A History of Fishing. Springer, Berlin. Sala, E., Boudouresque, C.F., Harmelin-Vivien, M., 1998. Fishing, trophic cascades, and the structure of algal assemblages: evaluation of an old but untested paradigm. Oikos 83, 425–439. Shannon, L.J., Cury, P.M., Jarre, A., 2000. Modelling effects of fishing in the southern Benguela ecosystem. ICES J. Mar. Sci. 57, 720–722. Sladek Nowlis, J.S., Roberts, C.M., 1999. Fisheries benefits and optimal design of marine reserves. Fish. Bull. US 97, 604–616. Smith, T.D., 1998. Simultaneous and complementary advances: mid-century expectations of the interaction of fisheries science and management. Rev. Fish Biol. Fish. 8, 335–348. Spurgeon, D., 1997a. Canada’s cod leaves science in hot water. Nature 386, 107. 9 Spurgeon, D., 1997b. Scientists dispute wisdom of Canada reopening fishery. Nature 386, 748. Spurgeon, D., 1997c. Political interference skewed scientific advice on fish stocks. Nature 388, 106. Steele, J.H., 1998. Regime shifts in marine ecosystems. Ecol. Appl. 8, 33–36. Stergiou, K.I., 1984. Capelin and climatic change in the Barents Sea. M.Sc. Thesis. McGill University, Montreal, Canada, 225 pp. Stergiou, K.I., 1998. Variability of fish catches in different ecosystems. In: Durand, M.E., Cury, P., Mendelssohn, R., Roy, C., Bakun, A., Pauly, D. (Eds.), Global Versus Local Changes in Upwelling Systems. ORSTOM Editions, Paris, pp. 359–370. Stergiou, K.I., 1999. Precaution in fisheries within the context of ecological and environmental changes. CIESM Workshop Ser. 7, 33–36. Stergiou, K.I., Politou, Ch.-Y., Christou, E.D., Petrakis, G., 1997a. Selectivity experiments in the NE Mediterranean: the effect of trawl codend mesh size on species diversity and discards. ICES J. Mar. Sci. 54, 774–786. Stergiou, K.I., Christou, E., Georgopoulos, D., Zenetos, A., Souvermezoglou, C., 1997b. The Hellenic Seas: physics, chemistry, biology and fisheries. Oceanogr. Mar. Biol. Ann. Rev. 35, 415–538. Stevens, J.D., Bonfil, R., Dulvy, N.K., Walker, P.A., 2000. The effects of fishing on sharks, rays, and chimaeras (chondrichthyans), and the implications for marine ecosystems. ICES J. Mar. Sci. 57, 476–494. Stokes, T.K., Butterworth, D.S., Stephenson, R.L., Payne, A.I.L., 1999. Confronting uncertainty in the evaluation and implementation of fisheries-management systems. Introduction. ICES J. Mar. Sci. 56, 795–796. Sumaila, U.R., Guenette, S., Alder, J., Chuenpagdee, R., 2000. Addressing ecosystem effects of fishing using marine protected areas. ICES J. Mar. Sci. 57, 752–760. Taylor, G.T., Prochaska, F.J., 1984. Incorporating unobserved cyclical stock movements in fishery catch equations: an application to the Florida blue crab fishery. N. Am. J. Fish. Mgmt. 4, 67–74. Walters, C., Maguire, J.J., 1996. Lessons for stock assessment from the northern cod collapse. Rev. Fish Biol. Fish. 6, 125–137. Walters, C., Christensen, V., Pauly, D., 1997. Structuring dynamic models of exploited ecosystems from trophic mass-balance assessments. Rev. Fish Biol. Fish. 7, 139–172. Zwanenburg, K.C.T., 2000. The effects of fishing on demersal fish communities of the Scotian shelf. ICES J. Mar. Sci. 57, 503– 509.