Sections 291 & 293, Boundary Bay Herring Spawn Records
Click an area on the habitat map to see spawn records within each pool (S=surface D=dive).
Herring spawners (red dash line) were estimated by apportioning spawner biomass (SB - see recent CSAP document) to each assessed herring section using an area-specific, spawn habitat index (SHI). Spawners in non-assessed, herring sections were estimated using a SHI versus SB linear regression equation of post-1950 spawn records (insufficient spawn deposition records and/or catch bio-sampling in several peripheral sections). Some inter-annual fluctuations shown on the graph may indicate migratory movements to adjacent herring sections (see-saw effect). Other inter-annual fluctuations may suggest changes in overall, coastal abundance. Most section boundaries in BC do not delineate discretely defined, spawning stocks (Hay et al. CSAS 2007/086).
Only herring catches accomplished close to the spawning season (Jan 1 - Apr 30) were plotted on the graph (blue line). Most of these herring aggregations, had they not been intercepted, would likely have spawned within the geographical section of capture or at spawning sites in adjacent herring sections. Catches accomplished during other seasons of the year (May 1 - Dec 31) were not plotted on the graph. Summer, fall and winter catches often represented significant proportions of total annual herring landings prior to 1982 but such catches were negligible after 1982. See catch tables or mixed-stock graph. Most herring schools captured between the months of May and December would have potentially spawned in other geographical sections, apart from the section of capture and for that reason were not plotted on section plots. These herring were often intercepted while feeding on, or migrating from, offshore banks (summer distribution) or while en route (inshore stop-over or over-wintering "holding areas") to spring spawning areas. Investigate the rationale and basis for regional stock assessments or view catch and spawner plots aggregated at the scale of a region or statistical area.