Research Document - 2014/113

Review of harvest control rules for the Pacific sardine (Sardinops sagax) population, and harvest advice for 2013 and 2014

By L. Flostrand, J. Schweigert, J. L. Boldt, S. McFarlane, and J. Mah

Abstract

Prior to and during summer months, large aggregations of the California Current sardine population migrate from key spawning habitat off California to more northern waters, but migratory patterns can be affected by population size and oceanographic conditions. DFO has been applying a Fishery Management Framework using a harvest control rule (HCR) that calculates annual total allowable catch (TAC) options of sardine in British Columbia (BC) waters as the product of three parameters:

1. an annually updated biomass estimate of age 1 and older (1+) fish in the population,
2. an estimated average seasonal migration rate of sardine into BC waters, and
3. a regional harvest rate of 15%. 

Migration rate values have been based on estimates associated with an annual summer trawl survey off the west coast of Vancouver Island, BC.  There are several concerns associated with annually updating the estimate of migration rate, one of which is that the trawl survey may not occur during a time representative of when sardine migration into BC waters has occurred. A second concern is the operational cost of annually conducting a survey and reporting on results.

This report presents results on the trends and status of sardine biomass and exploitation in the California Current population and in BC waters, including various determinations of migration rates, and describes three alternative types of HCRs that do not explicitly include a migration rate and which do not rely on information from an annual summer trawl survey. Collectively, regional and population biomass estimates indicate that the California Current sardine population biomass and migration to BC have decreased relative to 2011 and earlier years, whereas exploitation rates have increased, especially from 2011 to 2012 and in the Pacific Northwest. Of the three types of alternative HCRs that do not rely on annual observations from a summer trawl survey, two apply harvest rates on a population scale (rather than a regional scale), one of which includes an escapement buffer (cutoff) of 150,000t. The other type is one with a constant annual TAC, which is not sensitive to variations in population biomass and is believed to be the least precautionary and is therefore not supported.  None of the four HCRs described in this report are fully compliant with DFO’s Fishery Decision-making Framework but the one including the cutoff adheres to some principles of that policy. This report does not advise on actual harvest rates or harvest options because no objective and quantitative evaluations could be conducted and related to conservation measures, since conservation measures have not been defined. However, it does discuss uncertainty associated with scientific observations, HCR parameters and harvest options. One important conclusion is that at the higher harvest rates, not only will TACs and realized exploitation rates increase and be more variable, but uncertainty and possible risks to stock productivity and ecosystem dynamics will also increase. In the future, it would be valuable to thoroughly evaluate HCRs and related parameters, with the inclusion of defined uncertainty, conservation and fishery performance measures.

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