The novel use of harvest policies and rapid visual assessment to manage spatially complex abalone resources (Genus Haliotis)
Introduction
Decision rules and harvest policies provide a means for integrating and codifying systems of monitoring, assessing and managing fisheries. Much of the current work and discussion about harvest policies, decision rules, and their evaluation focuses on the use of indices that are quantitatively estimated using stock assessment models to assess the status of relatively large-scale and geographically extensive fisheries (e.g., Sainsbury et al., 2000, Punt et al., 2001).
There is, however, a growing realisation that many marine resources are not extensive uniform resources amenable to a ‘big-science’ approach through the application of quantitative assessment and management strategies (Hilborn et al., 2005). Instead, many resources, such as abalone (Haliotis spp.), occur as dispersed meta-populations (Shepherd and Brown, 1993). These mosaics of relatively independent populations effectively comprise multiple micro-fisheries within the larger resource that may be managed under a regional framework of assessment and management (Prince, 2005). In spatially complex fisheries managed at regional scales, fishing pressure is applied differentially across the component populations. Fishing pressure focuses on the most attractive populations according to a sliding scale of preferences. The most attractive component populations are particularly vulnerable to sequential overfishing, which may result in localized recruitment collapses and even localized extinctions, eroding the productivity of the resource.
Gulland (1969) stressed that at the basis of all fishery assessment models was the assumption that the unit of stock being fished had a level of homogeneity and mixing such that it responded uniformly to fishing. The challenge in small-scale and spatially complex fisheries is to reduce the scale at which management and assessment is performed down to the scale of the component populations. For some species, the difficulty is that the biological scale is far smaller than the scale at which government agencies can feasibly collect data, perform quantitative assessments, or enforce management regulations. The situation is further complicated by the cost of assessing and managing a large number of populations within a fishery. Larkin (1997) proposed that, as a rule of thumb, a fishery can only sustain management and assessment costs up to around 10% of its production value. In spatially complex fisheries comprised of multiple small-scale populations, the challenge is not only down-scaling the processes of assessment and management as a whole but also down-sizing the cost of the scientific and management processes for each component population or micro-fishery.
This paper describes the genesis of an approach to assess and manage spatially complex fisheries using principles of rapid visual assessment (RVA), decision rules and harvest policies. The approach is novel because of its use of qualitative morphometric markers (shell shape and appearance) to gauge fishing pressure at the scale of abalone reefs. It is also novel because the local industry associations assess component populations and decide and implement prescribed reef-scale harvest policies. Harvest policies are being implemented with reef-scale voluntary minimum length limits (VMLs) and voluntary capping of catches from reef-scale areas so as to distribute the total allowable commercial catch (TACC) set by government regulation for broad regions of the fishery. In a reversal of the normal ‘top-down’ approach to management, this process of reef assessment by industry is increasingly being used to inform the fisheries agency of the state government during the process of setting regional TACCs. To illustrate the advantages and some limitations of the novel RVA approach described in this paper, we provide a case study describing the initial development and implementation of the approach by the industry association in the Victorian Western Zone.
Section snippets
Abalone fisheries
Abalone are large herbivorous molluscs, highly prized by the eastern Asian markets, they inhabit shallow coastal reefs and are the basis for valuable dive fisheries in many countries around the world. Despite large investments in assessment, management, and sea ranching, global annual production from the wild has declined from around 29,000 t in 1969 to below 10,000 t in 2003 (Prince, 2004). Australia has the largest remaining commercial abalone fisheries, landing >5000 t per annum. While
Abalone ecology, assessment and management
The ecology of abalone has important implications for their assessment and management, and these implications have been discussed by Prince, 2003, Prince, 2004, Prince, 2005. Only a brief summary is found here to provide context for this study.
Rapid visual assessment
Central to the RVA technique described here is the proposition that the relative maturity of abalone can be visually gauged by the shape and appearance of their shell. Commercial divers first proposed that shell shape and appearance indicated the maturity of abalone in the early 1990s. Australian researchers, managers, and industry are generally accepting the proposition largely because it is consistent with a broad body of research and seems to be working. Recent research into the proposition
Extension and evaluation of the approach
In May 2004, the industry association for the Central Zone, the Victorian Abalone Diver’s Association (VADA), held its inaugural reef assessment workshop and used the decision tree developed for WADA to begin assessing their reefs. Since that time, VADA has basically followed the model of the adjoining Western Zone by holding two reef assessment workshops annually and has observed support for their process grow and take root. Notably VADA’s EO has facilitated all but the first two assessment
Acknowledgements
We acknowledge the WADA, and in particular the chairman Mr. Len McCall, for funding this work since 2001 and for contributing so much to its development. Acknowledgement and thanks again to Mr. Terry Adams of Western Australia who first drew our attention to the importance of the appearance and shape of abalone shells. My warm thanks for Skipper Ross Newton and the boys of the ‘F.V. Paragon’ who for 15 years shared their paua patches and opened their personal logbooks convincing us Mr. Adams
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