Results of the Mackerel (Scomber scombrus L.) egg surveys conducted in the Southern Gulf of St Lawrence from 1979 to 2022

Abstract

Atlantic mackerel Total Egg Production (TEP) in the southern Gulf of St. Lawrence is a key indicator of the stock’s state, as egg production is related to spawning stock biomass through stock composition and fecundity. We revisited the TEP calculations to increase reproducibility, incorporate methodological improvements, assess the statistical robustness of the results to various assumptions and parameter uncertainties, and to develop quantitative indicators of bias. The revised index was highly similar to the index presented during the 2021 assessment, but performed better in a year with fewer samples. Sensitivity analyses suggested that the TEP time series is robust against a variety of assumptions and uncertainties. Values for sampling years 1991 and 1999 were identified as potentially biased based on the indicators of bias presented herein, and were therefore excluded from the assessment. There was no evidence of bias for years 2006, 2017 and 2019, when eggs were sampled outside of the peak spawning period (when 70% of spawning had occurred in that year). The 2022 fishery closure and associated lack of adult samples from early in the spawning period resulted in relatively higher uncertainty around this year’s index value, but again without any indication of bias. The revised index presented here has been used in the 2023 stock assessment as it outperformed the previously used method.