ICES Journal of Marine Science: Journal du Conseil Advance Access originally published online on June 3, 2008
ICES Journal of Marine Science: Journal du Conseil 2008 65(6):817-821; doi:10.1093/icesjms/fsn092
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Habitat–fisheries interactions: a missing link?
Department of Economics, Norwegian College of Fishery Science, University of Tromsø, N-9037 Tromsø, Norway
Correspondence to C. W. Armstrong: tel: +47 7 7645574; fax: +47 7 7646020; e-mail: claire.armstrong{at}nfh.uit.no
Armstrong, C. W., and Falk-Petersen, J. 2008. Habitat–fisheries interactions: a missing link? – ICES Journal of Marine Science, 65: 817–821.
Received 19 June 2007; accepted 25 April 2008; advance access publication 3 June 2008.
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Introduction |
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 Top Introduction The impact of fishing...The indirect effects of...The importance of habitats...Modelling habitat-fisheries...References |
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Many marine habitats are very sensitive to fishing activities, and such habitats are increasingly being tied to parts of the life cycle of commercially important species. Hence, fishing activity may indirectly be damaging the fishers themselves. Despite focused research, the extent to which habitat loss affects fisheries is not well known. Here, we show that there is still a large gap between the biological knowledge of how benthic communities are affected by fishing and how the fishing impacts upon commercial fish stocks, and hence upon the stakeholders in the fishery. The integration of quantitative habitat effects of fishing in population assessment needs development. The filling of this knowledge gap is crucial in ensuring that ocean resource stakeholders and managers take into account how ocean habitats are affected by fishing, in the stakeholders' interest, and in the interest of ocean ecosystem conservation.
In the past decade, the number of studies on the effects of fishing upon ocean habitats has increased drastically, and it has been shown that some habitats are indeed very sensitive to fishing activities (e.g. Auster et al., 1996; Jennings and Lock, 1996; Cesar et al., 1997; Russel, 1997; Jennings and Kaiser, 1998; Watling and Norse, 1998; Collie et al., 2000; Duarte, 2002; Roberts and Sargant, 2002; Mangi and Roberts, 2006). Moreover, the importance of habitat for fisheries production is increasingly being focused upon in the discussion of protecting essential habitat (Fluharty, 2000). Despite this, the ways that habitat loss affects the agents in the fisheries is known only tenuously (Auster et al., 1996; Turner et al., 1999). There is a substantial literature on the connections between fish species and habitats (Lough et al., 1989; Gibson, 1994; Rijnsdorp, 1994; Minello et al., 2003), and the importance of habitat is increasingly being included in marine management policy and plans (for instance in the amendment of Magnuson–Stevens Fishery Conservation and Management Act in the USA, and in the reform of the EU's Common Fisheries Policy in 2003). However, incorporating the knowledge of habitat in population dynamics is a challenge. Hence, habitat considerations are not included in stock assessment of major commercial species. As stock assessment is the central tool in fisheries management, the exclusion of habitat considerations from the assessment gives these issues less weight in fisheries management. We show that there seems to be a missing link to which both the natural and social science communities have to contribute before a clear connection between human behaviour and the ocean ecosystems can be made.
Working in resource economics, we have been involved in several large natural science projects studying marine environments. One of our tasks has been to tie together the modelling of human behaviour from an economic perspective with biological or ecological models, focusing on the interaction between habitat and fisheries. In this fashion, the use values from fisheries may be directly tied to the ecosystem goods and services that habitats may offer. Some fishing activities have negative effects on habitats, thereby impacting upon fish stocks. In other words, the fishers apply a so-called negative externality upon their own and other compatriots’ activities, as described in Figure 1. Despite this, stock assessment has most often focused on pure harvest effects on stocks, point 1 in Figure 1. Qualitative damage assessment of gear impacts on habitat has been carried out, as in point 2 in Figure 1, but the effect of habitat loss upon stocks, point 3 in Figure 1, is seldom included in stock assessment. Therefore, focus has been on direct connections between fishing activity and fish stocks, and fishing activity and habitat, but has bypassed the indirect effects of habitats upon fish stocks, and the resulting effect upon fisheries (point 4 in Figure 1).
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Fishers have a clear understanding of how the externality which their fishing activity, the effect of their harvesting on the stock, affects themselves and other fishers. The fact that some of them may also apply a secondary effect through gear–habitat interactions seems less clear. When asked for the reason behind the changes in fishing grounds of target species, 56% of Irish Sea fishers interviewed believed it was attributable to overfishing, and 28% thought that changes in fishing gear had caused the change (Bergmann et al., 2004). Only 8% considered habitat loss to be behind the change, this despite more than half the fishers believing that fishing altered grounds (Bergmann et al., 2004). It is not uncommon that fishers perceive that other entities than themselves affect habitat. For instance, gillnetters and trollers in New England believed habitat modifications associated with economic and urban development to be the main driver of the salmon collapse (Smith and Gilden, 2000). Disputes concerning the use of mobile fishing gear are often considered to be gear conflicts, so precluding the need to look at more basic questions of whether some gear types reduce the economic value of fisheries overall as a result of reduced habitat complexity (Watling and Norse, 1998).
The fact that gear impacts habitats directly is admitted, but the fact that this impact may also rebound upon fishers via negative effects upon the resource they harvest is less well understood (Turner et al., 1999). The lack of understanding of this indirect effect is perhaps no wonder considering the limited amount of research carried out to demonstrate this connection (Auster et al., 1996). Here, therefore, we introduce central research themes on the topic, organized according to Figure 1. We start by presenting some of the work that has been done on fisheries’ impact upon habitats, then show how fishing activity directly or indirectly affects commercially harvested species via their habitats. Finally, we discuss the effects that fishing, via habitats, has upon itself, i.e. the bioeconomic modelling of fishery–habitat interactions.
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The impact of fishing activity upon habitat |
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TopIntroductionThe impact of fishing...The indirect effects of...The importance of habitats...Modelling habitat-fisheries...References |
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The use of destructive fishing gear is a major cause of habitat deterioration, and in recent years, there has been a large and growing research emphasis on the physical effects of different gear types on different habitats (e.g. Auster et al., 1996; Auster, 1998; Jennings and Kaiser, 1998; Watling and Norse, 1998; Hall, 1999; Mangi and Roberts, 2006). Some studies have suggested that changes in habitat attributable to bottom gear have resulted in altered composition of harvested species (Sainsbury et al., 1997; Gutting, 1999). Most studies have been performed on relatively flat sandy and muddy sediments (Schwinghamer et al., 1998; Ball et al., 2000; Bradshaw et al., 2000; Fonteyne, 2000; Humborstad et al., 2003), but there is also research showing effects upon more charismatic habitats, such as deep-water coral reefs (Fosså et al., 2002; Etnoyer and Morgan, 2003). For many important habitats, however, there is still a lack of documentation of the effect of trawling (Watling and Norse, 1998).
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The indirect effects of fishing activity, via habitat, upon faunal species |
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TopIntroductionThe impact of fishing...The indirect effects of...The importance of habitats...Modelling habitat-fisheries...References |
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Fisheries can have indirect as well as direct effects on faunal communities through disturbance, exposure, and subsequent predation (Bergman and von Santbrink, 2000), sediment redistribution, changed nutrient cycling, altered oxygen, altered habitat structure, trophic cascades, and modified predator–prey relationships (Jennings and Kaiser, 1998; Pilskaln et al., 1998; Watling and Norse, 1998; Hall-Spencer and Moore, 2000). Furthermore, resuspension of sediments makes water turbid, creating problems for animals that hunt by sight, photosynthesizing organisms, and filter-feeders (Russel, 1997). Mobile fishing gear can remove biogenic and sedimentary structures, as well as the organisms creating the structure. Reduced habitat complexity may increase predation on juveniles of harvested species and ultimately impact recruitment to harvestable stocks (Auster et al., 1996; Jennings and Kaiser, 1998; Dayton et al., 2000; Stoner and Titgen, 2003). Also, when target fish species are under pressure, the removal of epifauna and microhabitats can push species beyond their population threshold (Auster et al., 1996; Sainsbury et al., 1997).
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The importance of habitats for fisheries |
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TopIntroductionThe impact of fishing...The indirect effects of...The importance of habitats...Modelling habitat-fisheries...References |
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How real and important are habitat–fisheries interactions, i.e. in what way does habitat feed into fisheries output? Although this is a well-developed field of research in fish ecology (Gibson, 1994; Rijnsdorp, 1994; Minello et al., 2003), the quantification of habitat effects is limited. For the most part, stock assessment implicitly incorporates destructive fishing practices through virtual population analysis, which does not include the explicit presentation of fish–habitat connections. Clearly, the incorporation of habitat effects of fisheries in stock assessment is challenging, because stock assessment is already complex. Nonetheless, in the search to find answers to ever-dwindling fish stocks, habitat loss has been cited as one of several possible reasons (Botsford et al., 1997). It is, however, a reason that seldom receives the same attention as, for instance, overfishing or discarding (Pascoe, 2000; Jackson et al., 2001; Myers and Worm, 2003). One reason for this is that overfishing and discarding are to some degree taken into account in stock assessment, whereas habitat effects and changes are less straightforward to determine and to quantify.
There is a substantial amount of knowledge of the physical environment and fish population dynamics (Botsford et al., 1997). Much work has been directed towards understanding the role of egg and larval mortality as a factor determining year-class strength, where the availability of suitable habitat, providing protection from predators, is believed to be an important factor (Auster and Malatesta, 1995). Moreover, fish species connections to specific habitat types are well known (Auster and Malatesta, 1995; Roberts, 1996).
A connection between habitat complexity and the production of exploited stocks was suggested first by Herrington (1947). Although a number of studies have suggested a link between the physical structure of habitat and fish diversity, it has proven more difficult to quantify the relationship between structural complexity and the abundance of fish (Jennings and Kaiser, 1998).
One important reason why the effects of fishing disturbance are difficult to manifest is that they are masked by a background of natural disturbances. To quantify the habitat–fisheries links, seabed disturbance by mobile fishing gear must be scaled against the magnitude and frequency of natural disturbance (Auster, 1998; Jennings and Kaiser, 1998; Kaiser, 1998; DeAlteris et al., 1999). Other obstacles to demonstrating population level effects of habitat degradation include a lack of unharvested control sites, data on the rates, distribution, and intensity of fishing disturbance, and large-scale studies (Auster et al., 1996; Engel and Kvitek, 1998; Jennings and Kaiser, 1998; Hall, 1999; Dayton et al., 2000).
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Modelling habitat–fisheries connections |
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TopIntroductionThe impact of fishing...The indirect effects of...The importance of habitats...Modelling habitat-fisheries...References |
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Because of the limited quantitative research on fisheries–habitat interactions, it is no wonder that the modelling of these issues is limited. There are few models that connect habitat and populations (though see MacCall, 1990; MacCall and Tatsukawa, 1994). Even in an area where one would expect habitat to play an important role, e.g. the study of marine protected areas (MPAs), habitat issues are given limited attention, although much of the information that does exist regarding habitat–fisheries effects is gleaned from studies of MPAs. The literature on MPAs refers to protection of habitat as one of the advantages of marine reserves (Garcia-Charton and Perez-Ruzafa, 1999; Roberts and Sargant, 2002), and where reserves have shown limited success, this has often been attributed to the failure to protect important habitat (Crowder et al., 2000). Yet, when modelling the effect of reserves on fish populations, authors have tended to consider the effects of decreased levels of fishing mortality (Horwood, 2000; Gell and Roberts, 2003; Rodwell et al., 2003; Flaaten and Mjølhus, 2005; Upton and Sutinen, 2005), only rarely taking into account possible benefits from improvement of habitat (Roberts and Sargant, 2002; Armstrong, 2007).
The effect of habitat upon population dynamics is of interest from a bioeconomic point of view. It has been studied from a terrestrial perspective (Skonhoft, 1999), as well as with regard to wetlands and coral reefs (Barbier, 2000; Mumby et al., 2004). These are, however, indirect interactions, where more land-based activities such as aquaculture, deforestation, pollution, logging, and damming impinge upon coastal systems, which further reduce the availability of nurseries and other habitats of importance for commercial fish species. In these cases, one economic activity affects another via damage to the habitat. In the fisheries case, the interaction feeds directly back upon the agent who carries out the activity, as illustrated in Figure 1 (although one vessel group's activity may feed back into another vessel group's revenues). The fisheries case may seem an easier problem to solve, given the implied self-harm involved. However, these interactions are not simple, and the economic effects enter in many different ways. In addition to reduced fish production, a charismatic habitat such as deep-water coral may give non-use or existence values, purely through the public valuation of the existence of these fascinating structures, although the general public may never actually observe the resources directly. Moreover, aggregation of some fish species has been demonstrated near deep-water coral (Husebø et al., 2002; Ross and Quattrini, 2007), resulting in lower costs of harvesting, and hence direct use values. Therefore, destructive harvesting by bottom trawls could then potentially reduce both non-use and use values, the former via loss of existence values, the latter by bottom trawling potentially reducing future harvests through destruction of essential or preferred habitat for commercial species or their prey, as well as through the reduction in the fish stocks. These habitat effects upon commercially interesting species could be included in bioeconomic models via the carrying capacity or the growth of the fish stock in question (Upton and Sutinen, 2005; Armstrong, 2007). Another way could be to model these effects by making habitat one of two species in multispecies models of commensal or symbiotic species. Clearly, in some cases, habitat should be modelled as non-renewable, in others as renewable. Adding some non-harvest value connected to the stock of habitat would allow the inclusion of existence values of habitats.
If habitat–fisheries connections are present, but not explicitly included in stock assessment, the inherent economic pressures in the system tend to increase the destruction of the habitat, so leading to a detrimental circle of events. This is where both natural and social sciences have clear jobs to do and roles to fill. Historically biological fisheries modellers have spent time interacting with fisheries managers with regard to how they should manage stocks. Increasing stakeholder involvement has led to more direct contact with the economic interests in the fisheries, which again makes it imperative that scientific knowledge regarding these agents' effects upon their own potential benefits be made clear. With such interactions, and knowledge of habitat effects both biologically and socially, the impetus to modify behaviour or gear will be more easily forthcoming, or enforced by policy. Also, between the natural science knowledge of these interactions and the stakeholder, economic evaluations of the actual cost of disregarding these effects enter naturally. Hence, both natural and social science inputs in more completely understanding such interactions are necessary to ensure sustainable use of our ocean resources.
Over the past 50 years, social scientists have presented the detrimental consequences of the "tragedy of the commons" in the oceans. This knowledge has been imparted and incorporated in fisheries management, and most agents in the fisheries have over time come to accept this knowledge. Access and output limitations to alleviate the tragedy are increasingly seen as legitimate in the fishing communities. Habitat destruction is another case of the "tragedy of the commons". How the knowledge regarding habitat destruction is applied in management is critical to understanding and accepting the principle of habitat protection in fisheries. To legitimize habitat protection, endeavours towards bridging the knowledge and communication gap present today regarding the importance of habitat for fisheries are crucial.
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Acknowledgements |
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We thank the editor and the anonymous referees for valuable input. The study was carried out with support of the Commission of the European Communities, specifically SSP8-2004-513670, PROTECT, GOCE-CT-2005-511234 HERMES, and EU INCO no. 003739: INCOFISH, but it does not necessarily reflect the Commission's views or anticipate future policy in this area.
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