American Lobster (Homarus americanus) stock assessment in the Magdalen Islands (LFA 22), Quebec, in 2022

Abstract

Landings reached an all-time high of 6,715 t in 2022, which is 124.3% above the average of the past 25 years (2,994 t, 1997–2021), along with an increase in fishing effort since 2020. The increase in landings between 2018 and 2022 was greater in the north (69.8%) than in the south (26.5%). In 2022, for the Islands as a whole, the catch per unit effort (CPUE) by weight of the commercial sample (1.26 kg/trap) was 29.2% higher than in 2018 and 139.4% (south: 120.1%, north: 197.1%) higher than the 1985–2021 average. The density of commercial lobsters in the trawl survey increased significantly from 2014 to 2019 (19.6 lobsters/1,000 m2). Since then, the density has decreased to 14.4 lobsters/1,000 m2 in 2022, which remains 37.1% higher than in 2018 and 80% higher than the 1995–2021 average (8.0 lobsters/1,000 m2). With respect to demographic indicators, the average size of commercial lobsters sampled was 92.3 mm in 2022 and has been stable since 2017. In the trawl survey, the value for 2022 is higher than that for 2018, and close to the peak observed in 2013. Fishing pressure indicators show a slight decrease in exploitation rates since 2005. The rates for 2021 (south: 59%, north: 60.3%) were comparable to those in 2017 and 2018. In 2021, the exploitation rate in the north was equal to the 1985–2021 average, while the rate in the south was 6.4% below the average for the same period. Productivity indicators remained high. For the Islands as a whole, theoretical egg production in 2022 was 1.7 times higher than in 2018 and 6.8 times higher than in 1994–1996. However, a decrease in individual mating success has been observed since 2004. Pre-recruitment indices in 2022 (Pr1=12.4 lobsters/1,000 m2) were 14.1% higher than in 2018 and 132.8% higher than the 1995–2021 average. The benthic recruitment index has been stable at high levels since 2018. The number of degree-days for the 2018 and 2019 fishing seasons is below the average for the past 25 years, while that for 2020 is above the average. Small rock crab is a key prey source for lobster. The size structures of the trawl survey in subareas A and B suggest very low abundance of crabs under the legal size. In addition, rock crab CPUE in the commercial fishery has been declining since 2020, and is below the 1998–2021 average in 2022. With abundance and productivity remaining high and growing, it can be concluded that the Magdalen Islands lobster stock is in good condition relative to current exploitation rates. However, since 2021, a discrepancy has been observed between fishing yield trends in the north and south of this area, skewed towards the north. According to the precautionary approach, the Islands’ lobster stock is currently in the healthy zone. Indicators of the health status of the rock crab population in the Magdalen Islands were examined using an ecosystem approach. The population status of this key prey source of lobster is of great concern. In an effort to ensure the sustainability of the lobster stock and that of its preferred prey, while maintaining their trophic link, all exceptional measures should be considered to minimize rock crab mortality.