Box 1 The IWC, NMP, RMP, CLA and RMS
How few whales were there after whaling? Inference from contemporary mtDNA diversity
Article first published online: 24 SEP 2007
© 2007 The Authors. Journal compilation © 2007 Blackwell Publishing Ltd
Volume 17, Issue 1, pages 236–251, January 2008
How to Cite
JACKSON, J. A., PATENAUDE, N. J., CARROLL, E. L. and BAKER, C. S. (2008), How few whales were there after whaling? Inference from contemporary mtDNA diversity. Molecular Ecology, 17: 236–251. doi: 10.1111/j.1365-294X.2007.03497.x
For assessing the status of whale stocks, the Scientific Committee of the International Whaling Commission (IWC) has generally adopted an age- and sex-structured, density-dependent, deterministic logistic population model, referred to as BALEEN II (de la Mare 1986; Punt 1999). The model is currently implemented in two programs, ‘hitter’ and ‘fitter’. The former shoots a population trajectory through a population estimate for a specified year, while the latter uses several years of whaling catches and catch effort data together with abundance estimates to estimate past changes in population size and resilience (i.e. the ability of the stock to recover from depletion). BALEEN II has been used with differing degrees of complexity depending on available data and has incorporated both maximum likelihood and Bayesian estimators (e.g. Raftery et al. 1995; Wade 2002; Whitehead 2002).
A simple age- and sex-aggregated logistic population model describes the relationship between the following variables
where Ny represents the population abundance in year y, K the population initial carrying capacity (Ny in year 0), z the density dependent exponent and Cy the total catch in year y; r represents the intrinsic growth rate of the population.
In belated recognition of overexploitation of most whale stocks, the IWC agreed in 1982 to a moratorium on commercial hunting to take effect in 1986. The agreement called for the Comprehensive Assessment of depleted whale populations (including an historical reconstruction of population trends and abundance) and the development of a revised procedure to calculate catch limits for any future commercial whaling. Prior to the moratorium, the so-called New Management Procedure (NMP) was designed to provide maximum catches by maintaining populations at the level of maximum sustainable yield level (MSYL) but failed to account for uncertainty in many population parameters. The NMP is nominally still in force but has been in abeyance during the moratorium. The Revised Management Procedure (RMP), developed since the moratorium to replace the NMP, was designed to provide for reasonable levels of exploitation while minimizing the risk of population depletion or extinction. At the core of the RMP is the Catch Limit Algorithm (CLA) which requires relatively straightforward information on population size (with an associated coefficient of variation), past and present catches and population structure (Donovan 2002). In brief, the CLA works by fitting the basic logistic model to a time series of abundance data and incorporates feedback from new data (e.g. abundance estimates or new catches) to refine estimates of the required parameters (Cooke 1999). Uncertainty is accounted for using a quasi-Bayesian approach to generate a posterior probability distribution of parameter values. The recommended catch limit is a chosen percentile (less than the median) of the posterior distribution of a specified function of the estimated stock level and the model parameters. The nominal population level below which catches are prohibited is set to 54% of K for consistency with the IWC's previous management procedure. The actual fraction of K at which exploitation can resume is expected to be in the range 50–90% of K, depending on the history of exploitation and the values of the unknown parameters, particularly rmax. Unlike its predecessor, the RMP does not attempt to hold a stock to a particular target level, but is designed such that depletion of a stock to less than 50% of K would be very unlikely. Before hunting can be initiated, extensive computer-based simulations, referred to as Implementation Simulation Trials, are designed to evaluate the performance of the RMP for a particular stock under a range of plausible scenarios including uncertainty (usually in terms of fixed values) in current abundance, pre-exploitation abundance, catch history, stock structure, MSYL and MSYR (IWC 1999). Although the RMP has been tested extensively in silico and found to be robust to a wide range of uncertainty in most assumptions (Cooke 1999), it will not be implemented until the IWC agrees to a Revised Management Scheme (RMS). This Scheme is intended to include the many conditions required for robust and transparent observation and inspection [such as a DNA register to verify all catches records (Baker et al. 2000)]. A new procedure for management of aboriginal subsistence whaling (the AWNP) is under development by the Scientific Committee. Whaling programmes conducted under provisions for scientific research are not subject to the conditions of the RMP or the CLA (Clapham et al. 2003).
- Issue published online: 24 SEP 2007
- Article first published online: 24 SEP 2007
- Received 19 March 2007; revision accepted 10 July 2007
Vol. 18, Issue 19, 4134–4135, Article first published online: 15 SEP 2009
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