Herring Stock Assessments
The rationale and basis for regional stock assessments are examined in DFO research documents. These documents are located on the Web sites of the Canadian Science Advisory Secretariat (CSAS) and the Canadian Journal of Fisheries and Aquatic Sciences (CJFAS). In cases where there may be small discrepancies in recorded catches or estimated spawners observed between graphs on this page and those in CSAS documents, the CSAS or CSA-Pacific (formerly PSARC) versions should prevail. Discrepancies may be attributable to the spatial and temporal partitioning of data (e.g. Jan 1 to Dec 31 statistical catch year versus a Jul 1 to Jun 30 herring life cycle year) and/or the inclusion or exclusion of herring spawners from "non-assessment areas". Other research and technical publications are available on the Herring Geographical Bulletin website.
The abundance of herring spawners (shown as a red dash line on graphs) has been estimated for specific stock assessment areas within each region of British Columbia (see Cleary, J.S. and J. F. Schweigert CSAS 2011/115 or a more recent CSAS document). Spawner abundance in "non-assessment areas" has been estimated using a spawn habitat index (SHI) versus spawner biomass (SB) linear regression equation of post-1950 spawn records. These peripheral spawning sites do not contribute substantially to regional spawning stock biomass but are included here as they are known and potential spawning habitat (Hay and McCarter, CSAS 1999/014). Such areas have insufficient spawn records and/or catch bio-sampling coverage to perform population assessments.
Inter-annual fluctuations of herring spawners may indicate migratory movements (to some degree) between adjacent regions. Tagging evidence reviewed by Hay et al. (2001) suggests that approximately 10 to 20 percent of the spawning biomass in any region may move to adjacent regions in subsequent years. Considerably greater inter-area movements occurs between smaller spatial units such as statistical areas, herring sections or locations. Migratory movements of tagged herring (1936 to 1992) are shown in detail, on tag origin and recovery maps.
Metapopulation theory examined in two papers by Ware, D.M. and Schweigert, J. (CSAS 2001/127) and (CSAS 2002/107) provides further analysis into population structure, possible mechanisms and climatic influences.
Herring captured during the advancing spawning seasons (Jan 1 to Apr 30) were also plotted (blue line) on time-series graphs. These herring, had they not been intercepted, would most likely have spawned in (or close to) the region of capture. Herring captured during other times of the year (May 1 to Dec 31) were plotted separately (green line). Summer, fall and winter catches often represented significant portions of total annual herring landings prior to 1982 but such catches were negligible after 1982 - See catch tables or mixed-stock graph. Some herring captured between the months of May and December would have potentially spawned in other regions, apart from the region of capture and for that reason were plotted separately (e.g. Swiftsure Bank herring migrants captured in statistical area 21 on the west coast of Vancouver Island while en route to Strait of Georgia spawning areas). Herring catches and estimated spawners were partitioned further and plotted by 29 statistical areas and 101 herring sections of British Columbia.
REGION 1 - Catch and Spawners (click graph)
REGION 2 - Catch and Spawners (click graph)
REGION 3 - Catch and Spawners (click graph)
REGION 4 - Catch and Spawners (click graph)
REGION 5 - Catch and Spawners (click graph)
REGION 6 - Catch and Spawners (click graph)
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