Use of Risk Analysis to Assess Fishery Management Strategies: A Case Study using Orange Roughy (Hoplostethus atlanticus) on the Chatham Rise, New Zealand

Abstract

Risk analysis can enhance the value of scientific advice to fishery managers by expressing the uncertainty inherent in stock assessments in terms of biological risk. I present a case study involving an overexploited population of orange roughy (Hoplostethus atlanticus) on the Chatham Rise, New Zealand. This analysis quantifies the risk to the fishery and shows how this decreases as the rate of reduction in total allowble catch increases. The technique helps fishery managers balance biological risk against economic risk. Ways of generalizing the technique are discussed.

Fisheries stock assessment and decision analysis: the Bayesian approach

“…Bootstrap or Monte Carlo methods (Francis, 1992;Restrepo et al, 1992) use resampling to calculate frequency distributions for the values of the parameters of a pre-specified model. These distributions are then used as if they represented the probabilities of alternative hypotheses.…”

“…Natural mortality is assumed to be independent of age and time, and age-specific selectivity is assumed to be time invariant. Models of this form have been used in the assessments of Cape hake (Punt, 1994), albacore tuna (Thunnus alalunga, Scombridae) (Punt et al, 1995a) and orange roughy (Francis, 1992). It is straightforward to generalize the model to incorporate more realistic assumptions, for instance that natural mortality is age and time dependent.…”

“…The value of R 0 is calculated from the value for the average pre-exploitation equilibrium exploitable biomass at the start of the year, B 0 , using the equation: where w a is the weight of a fish of age a at the start of the year. The stock-recruit relationship is often re-parameterized in terms of B 0 and the 'steepness' of the stock-recruit relationship ('steepness' is defined as the fraction of the virgin number of births expected when the spawner stock size is reduced to 20% of its virgin size (Francis, 1992) where C y is the catch (in weight) during year y.…”

An evaluation of management strategies for Atlantic tuna stocks

“…The model is then fitted to explain the trends in indices of abundance, given the observed yields and biological characteristics of the stock. The stock recruitment relationship was parameterised in terms of steepness and virgin biomass steepness (Francis, 1992), where steepness was assumed to be less for temperate than for tropical tunas: i.e. 0.6 for albacore and 0.9 for bigeye and skipjack.…”

General principles for risk assessment of living modified organisms: Lessons from chemical risk assessment

“…Formal risk assessment methodologies exist in a range of disciplines, including business and management (Vatter et al, 1978), insurance (see the Journal of Risk and Insurance), fisheries management (Francis, 1992) and conservation biology (Maguire, 1991). In the context of assessing potential risks associated with LMOs, however, there is one field of study which is particularly likely to provide insights regarding approaches to risk assessment.…”