Sustainable fisheries and habitat-fishery interactions

The sustainable management of fishery resources is a highly complex undertaking, requiring a balance between the socio-economic needs of fishery users and the biological constraints of the fishery resource. The impacts of fishing activity on marine habitats can make this already complex problem even more difficult. This fishing-induced habitat damage may undermine the sustainability of fishery resources by causing irreversible habitat loss, or by slowing the fish stock regeneration process. Given the essential role of fishery resources in providing economic and social benefits for many nations, as well as their vital role in the global food supply, the question of how to sustainably manage these resources where habitat degradation is of concern, is therefore of high importance and interest. This thesis seeks to improve understanding of how the impacts of fishing activity on marine habitats influence the sustainable management of fishery resources. The objective of this thesis is to explore how information concerning the marine habitat may be incorporated into the decision-making processes of fishery management where fishing-induced habitat degradation is of concern, and the circumstances in which management tools usually used to achieve habitat improvements may generate fishery benefits. This thesis consists of three essays which explore the interplay between fish stocks and the habitats that support these resources, and how this relationship impacts the effectiveness of management mechanisms implemented to optimise across biological and economic outcomes. The first two essays examine how information concerning the habitat may be incorporated into decision-making to improve fishery management outcomes. The first essay examines alternative ways of exercising precaution in stock recovery plans in achieving stock rebuilding when fishing-induced habitat damage occurs, while taking into consideration the economic and socio-economic objectives of fisheries management. The second essay explores the connection between fishing-induced habitat damage and the optimal allocation of harvest across multiple user groups and explores the consequences of omitting information concerning the marine environment for fishery performance and catch share allocations. The extent of habitat degradation in the first essay is controlled by management through the total protection from fishing mortality, and in the second essay, through the allocation of harvest between user groups which use fishing gears that have different levels of habitat impacts. The third essay undertakes an empirical analysis of the effect of a marine protected area (MPA) network, established for habitat conservation, on adjacent fisheries, using Australia's south-east network of MPAs as a case study. This essay examines the effect of this network on catch and the gross value of production for adjacent fisheries, while considering the potentially confounding influence of fishery management changes occurring in the same time period. The results in this thesis highlight the importance of having adequate knowledge of the marine habitats in which fishing activity takes place, and of the circumstances in which this knowledge ought to be included when making decisions concerning the management of fishery resources. Results show that the trade-offs between socio-economic outcomes for fishery users and the biological objectives of fishery management may be heightened in the presence of fishing-induced habitat damage. However, the combined use of fishery management tools to control fishing mortality may allow these trade-offs to be avoided, particularly in cases where a comparatively relaxed stock recovery plan is implemented, or where the ecosystem is relatively resilient to habitat damage. Additionally, a failure to incorporate habitat-fishery connections into decisions concerning catch share allocations may have devastating consequences in sensitive environments, due to inadvertent overfishing and the inability of these environments to recover from destructive fishing activity. Finally, results show that, while the implementation of an MPA network for the purposes of habitat management may lead to declines in catch for adjacent fisheries, favourable market conditions may have a compensatory effect, such that overall revenue for adjacent fisheries is not affected. However, the impacts of an MPA network on adjacent fisheries will be highly contextual, and dependent on key factors such as the age of the MPA network, the region-specific effects of climate change, and the ability of fishers to adapt their behaviour in terms of fishing location and target species.