Assessing the quality of groundfish population indices derived from the small-mesh multi-species bottom trawl survey / by Jillian C. Dunic and Sean C. Anderson.: Fs97-6/3667E-PDF

"Since 1973, Fisheries and Oceans Canada has conducted the Small-mesh Multi-species Bottom Trawl Survey (SMMS), the longest continuous fisheries-independent monitoring time series for groundfish off the west coast of Vancouver Island (WCVI). Initially designed to assess Pink shrimp (Pandalus jordani) populations, the survey also samples groundfish. The SMMS provides a valuable historical baseline for groundfish species, as current groundfish trawl surveys began in 2003 and are biennial across regions. However, changes to the SMMS, including changes to the sampling area, fishing gear, and catch recording procedures, may affect the quality of groundfish population indices. Here, we summarise these changes and examine their impact on relative biomass indices for groundfish. We compare spatiotemporal model-based population indices from the SMMS with other regional indices and examine the distribution of lengths and ages in comparison to the synoptic West Coast Vancouver Island trawl survey (SYN WCVI). Our analysis suggests that the modelled SMMS index is likely an appropriate index of relative biomass for many groundfish species. However, changes to the survey, such as the switch to comprehensive species sorting and identification, introduce uncertainties in the pre-2003 data. Additionally, the SMMS detected signs of rockfish recruitment earlier than the SYN WCVI for some species"--Abstract, page iv.

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