Implications of uncertainty for Canada’s commercial hunt of harp seals (Pagophilus groenlandicus)

Russell Leaper,Justin Matthews

doi:10.1038/npre.2008.1798.1

Russell Leaper, Justin Matthews

Open Access

https://doi.org/10.1038/npre.2008.1798.1

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Abstract

AbstractThe Canadian government's current management procedure for harp seals is described by Fisheries and Oceans Canada as using the Precautionary Approach. Employing a similar underlying population model, we simulated the effects of uncertainty involving bias in estimates of human induced mortality, natural mortality, and pup production estimates as a set of robustness trials. Our results indicated that for the range of annual total allowable catches (TAC) considered and set for Canada’s commercial harp seal hunt (250,000 – 350,000), there were plausible circumstances under which the government's management procedures failed to meet their own conservation objectives. By contrast, a precautionary management regime should be robust to such levels of uncertainty. For some scenarios the current management strategy, although not fully specified, is likely to maintain a high TAC despite a declining population. In particular, once a high TAC has been set, the assessments are unlikely to provide the necessary evidence that the TAC should be reduced until the population is at a low level. Hence there is a substantial risk that the population may be depleted below the ‘minimum’ (N50) and ‘critical’ (N30) population reference points. There is a need for a management procedure based on risk analysis to be fully specified and tested. In the interim, reducing TACs to within limits calculated from a well-established precautionary procedure, such as Potential Biological Removal, would be a step towards more precautionary management.

Highlights

The commercial exploitation of harp seals (Pagophilus groenlandicus) by Canada is the largest marine mammal hunt in the world with an average annual reported catch of 324,000 between 2003 and 2005 (Hammill and Stenson, 2007)
Simulations were conducted using the same population modelling approach underlying the assessments by Department of Fisheries and Oceans (DFO, 2005). These were intended as a set of robustness trials to provide a basis for evaluating whether the total allowable catch (TAC) set for harp seals by Canada can be considered as following a precautionary approach
DFO (2005) lists key aspects of the Objective Based Fisheries Management (OBFM) framework adopted in the last Canadian management plan for harp seals

Summary

Introduction

The commercial exploitation of harp seals (Pagophilus groenlandicus) by Canada is the largest marine mammal hunt in the world with an average annual reported catch of 324,000 between 2003 and 2005 (Hammill and Stenson, 2007). Simulations were conducted using the same population modelling approach underlying the assessments by Department of Fisheries and Oceans (DFO, 2005). These were intended as a set of robustness trials to provide a basis for evaluating whether the TACs set for harp seals by Canada can be considered as following a precautionary approach. More stringent management measures would be implemented in the event that the population falls below 50% of its highest estimated abundance ( N 50 ) including closure of much, if not all, of the commercial seal hunt. If the population drops below the level of 30% of its highest estimated abundance ( N 30 ) all removals would be stopped

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