Analysis Species diversity, fishing induced change in carrying capacity and sustainable fisheries management Wisdom Akpalu a, ⁎, Worku T. Bitew b a Department of History, Economics and Politics, SUNY-Farmingdale, Farmingdale, NY, United States b Department of Mathematics, SUNY-Farmingdale, Farmingdale, NY, United States abstract article info Article history: Received 5 May 2010 Received in revised form 3 December 2010 Accepted 16 February 2011 Available online 2 April 2011 Keywords: Fishing impact on carrying capacity Fishing policy Phenotypic diversity Stock collapse It is well established in the fisheries management literature that marine ecosystems are complex and marine species depend on one another. As a result, it is important to account for species diversity to ensure sustainable management. In addition, recent research published in the marine sciences literature has provided unequivocal evidence that fishing activities destroy habitats and inhibit production of planktons. This paper illustrates that if a conventional bioeconomic model is employed, an optimum effort policy as opposed to quota appears to result in sustainable management even if fishing impacts carrying capacity. However, the so-called optimum effort may collapse the stock if species diversity is not accounted for. Conversely, if species diversity and the impact of fishing on carrying capacity are considered, neither the equilibrium quota nor effort may guarantee sustainable yield. © 2011 Elsevier B.V. All rights reserved. 1. Introduction In two recent papers, the authors have shown that fisheries management authorities must incorporate species diversity in designing sustainable fisheries management policies (see Sterner, 2007; Akpalu, 2009). Specifically, although species diversity may generally increase the stability and resilience of an ecological system, phenotypic diversity could result in lower equilibrium or optimum yields if suboptimum populations are present (Akpalu, 2009). Sterner (2007) and Akpalu (2009) used examples of cod and tuna species, respectively, to illustrate that without accounting for diversity, catch potentials may be over-exaggerated and this could lead to stock collapse. Indeed, the collapse of a number of fisheries such as the North Sea cod, in spite of the plethora of management policies, and the near collapse of the Atlantic and Mediterranean bluefin tuna, may have resulted from such errors (Myers and Worm, 2003). Conse- quently, an ecosystem-based approach to fisheries management is essential and highly recommended (Jennings and Kaiser, 1998; Sanchirico et al., 2007). 1 In addition to the role of phenotypic diversity in sustainable fisheries management, recent studies have also examined the impact of fishing activities on fish habitats (see Auster et al., 1996; Auster, 1998; Watling and Norse, 1998; Hall, 1999; Mangi and Roberts, 2006; Armstrong and Falk-Petersen, 2008). Fishing activities may impact productivity of fisheries through their effect on species composition or destruction of habitats. For example, studies have shown that commercial fishing gears impact benthic (seafloor) habitats, resulting in changes or disturbances to the physical and biological structures as well as species composition of the ecosystems (Collie et al., 1997; Ratana et al., 2003; Armstrong and Falk-Petersen, 2008). If the ocean bottom is soft, fishing gears could plane off structures and upset the nutrient content and organisms in sediments. Further, the gears may damage corals, boulders, and other bottom-dwelling organisms, thereby reducing plankton production capacity of the ecosystem. By destroying the corals, several important functions they perform are lost. These functions may include provision of substrata for primary production, habitats for invertebrates and fishes, and protection of coasts from wave exposure and erosion in tropical environments. Scientific investigation carried out by Fisheries and Oceans Canada (DFO) in the Atlantic on a multi-year study of the impact of ground fish otter trawling showed that the technology disrupted benthic communities and reduced the biomass and diversity of benthic organisms (Fuller et al., 2008). In addition, fishing activities could have cumulative effects on many individual plants and invertebrates since habitats such as kelp forests, coral reefs, or living organisms form bryozoan beds. Moreover, fishing activities lead to changes in the structure of marine habitats and can determine the diversity, composition, biomass, and productivity of the associated biota. For example, there is increasing evidence that the indirect effects of fishing have caused some reef communities to shift from coral to algal or urchin-dominated phases (Jennings and Kaiser, 1998). As reported by Auster and Langton (1998), there is incontrovertible evidence showing that in heavily fished areas of the world there are negative ecosystem-level effects, and shifts in benthic community structure have occurred. Additionally, it has been found that creating marine Ecological Economics 70 (2011) 1336–1343 ⁎ Corresponding author. Tel.: +1 631 794 6102. E-mail addresses: akpaluw@farmingdale.edu (W. Akpalu), biteww@farmingdale.edu (W.T. Bitew). 1 An ecosystem refers to a biological community and its physical environment. 0921-8009/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.ecolecon.2011.02.008 Contents lists available at ScienceDirect Ecological Economics journal homepage: www.elsevier.com/locate/ecolecon