Documentation for the Pacific herring spawn index in BC

The spawn index time series is one component of Pacific herring (Clupea pallasii) stock assessments in British Columbia (BC), Canada. This report documents how we calculate the spawn index from spawn survey observations (e.g., spawn extent, number of egg layers, substrate type). There are three types of spawn survey observations: surface observations, underwater observations of spawn on Macrocystis (Macrocystis spp.), and underwater observations of spawn on understory. We calculate the spawn index in several steps. First, we quantify Pacific herring fecundity, which is critical to calculating the spawn index. Second, we describe the calculations for each of the three spawn survey types: surface, Macrocystis, and understory. Finally, we combine the three spawn indices, and aggregate by stock assessment region and year to match the spatial and temporal scale of science advice and fishery management for Pacific herring in BC. In addition, we identify uncertainties in the spawn index calculations, and we detail how users can download the script to calculate the spawn index on an example database. Note that the 'spawn index' is not scaled by the spawn survey scaling parameter, q; therefore it is an index, not a direct estimate, of spawning stock biomass.