Research Document - 2012/098
Recovery Potential Assessment of Eulachon (Thaleichthys pacificus) in Canada
By J. Schweigert, C. Wood, D. Hay, M. McAllister, J. Boldt, B. McCarter, T.W. Therriault, and H. Brekke
Abstract
In May 2011, COSEWIC assessed three designatable units (DU) of eulachon (Thaleichthys pacificus) in Canada: Fraser (endangered), Central Pacific (endangered), and Nass/Skeena (threatened; although this DU is being re-assessed by COSEWIC). In light of these designations, DFO undertook this recovery potential assessment to provide scientific advice in support of considering management scenarios and conducting socioeconomic analyses to inform SARA listing decisions and recovery planning. A lack of consistent long term indices of population abundance made it extremely difficult to determine the recovery potential for these DUs. Indices of in-river abundance were summarized for each DU and examined in relation to time series of putative threats in freshwater and marine environments, at both coastwide and localized scales. No single threat could be identified as most probable for the observed decline in abundances among DUs or in limiting recovery. However, mortality associated with coastwide changes in climate, fishing (direct and bycatch) and marine predation were considered to be greater threats at the DU level, than changes in habitat or predation within spawning rivers.
A Bayesian stock reduction model was developed for the Fraser DU. The analysis suggested that the decline in population abundance could be explained most parsimoniously by the sequential historical impacts of directed in-river catch (prior to 1970), bycatch in the shrimp trawl fishery (1990 to 2000), and several consecutive years of anomalously low productivity (2002-2007 brood years). The model indicates that, under conditions of average historical productivity and current levels of bycatch mortality from shrimp trawling effort but no directed exploitation, the Fraser River population should rebuild to 33-49 percent (range for the three cohorts) of the unfished abundance over a period of 16-18 years. A directed catch of 30 tonnes would reduce rebuilding to 1-30 percent of the unfished population. The analysis suggests that the species is relatively unproductive and can sustain a maximum sustainable fishing mortality rate of only 0.10. Data in the other DUs are sparse but not prohibitive for the development of similar models. One would expect these populations to share similar population dynamics and productivity, and also require a conservative approach to management and rebuilding. Continued monitoring of the Fraser DU is needed to determine whether productivity has returned to average levels and, therefore, permitting of any allowable harm should be considered with caution. A lack of adequate monitoring makes identification of recovery targets for the Fraser and Central Coast DUs difficult, but we recommend an initial goal of surpassing the COSEWIC criteria for special concern listing at a minimum is recommended, with a longer term goal of continued population increases towards historical levels.
Accessibility Notice
This document is available in PDF format. If the document is not accessible to you, please contact the Secretariat to obtain another appropriate format, such as regular print, large print, Braille or audio version.
- Date modified: