Research Document - 2016/067

Abundance indices and selectivity curves from experimental multi-panel gillnets for the southern Gulf of St. Lawrence fall herring fishery

By T.J. Surette, C.H. LeBlanc, and A. Mallet

Abstract

In partnership with Fisheries and Oceans Canada (DFO), fish harvesters participating in the Atlantic herring (Clupea harengus) fall fishery in NAFO 4T surveyed five spawning grounds in the southern Gulf of St. Lawrence using multi-panel experimental gillnets over the course of their regular fishing activities from 2002 to 2013. The results of these surveys are analyzed to identify whether they can be used as indices of local abundance for assessment of fall 4T herring. Catches were analyzed with a selectivity model, which produced mesh-specific selectivity curves, length-based population indices, and age disaggregated indices for the North, Middle, and South regions of the southern Gulf of St. Lawrence. The selectivity model has little ability to estimate how fishing power varies with mesh size, so population indices might be length-biased. Uncertainties also underlie the scale of catches due to methodological and biological differences between years and regions. Nevertheless, cohort tracks in the catch-at-age were fairly consistent between regions and indicate that some dynamics of the underlying population are captured. Consequently, the selectivity and catch-at-age indices were approved for use in future population dynamics models of Altantic herring for the southern Gulf of St. Lawrence.

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