Assessment of Scotian Shelf Snow Crab in 2023

Abstract

In the Scotian Shelf Ecosystem, Snow Crab (Chionoecetes opilio) have been a dominant macro-invertebrate since the decline of the groundfish fishery in the 1990s. They are generally observed in deep, soft-bottom substrates ranging from 60-300 m and at temperatures usually less than 6 degrees Celsius. The Scotian Shelf Snow Crab are in the southern-most extreme of their spatial distribution in the Northwest Atlantic Ocean and vulnerable to climate variability. The fishery is made up of 3 fishing areas: north-eastern Nova Scotia (N-ENS), south-eastern Nova Scotia (S-ENS) and 4X. The Snow Crab assessment is based on a fishery independent survey, the Maritimes Region Snow Crab Trawl Survey, and focuses on indicators of abundance, reproductive potential, recruitment, and exploitation rates. Spatiotemporal models incorporate habitat viability based on ecosystem variables such as depth, species composition and bottom temperatures. At-sea observer coverage aims to quantify bycatch, and carapace conditions for the crabs in the fishery but has been unreliable since 2020 with minimal observations per year. Fishery data provides catch rates, landings, effort, and monitors historic trends. Total allowable catches (TACs) are generally caught every year (except 4X as the fishery is always ongoing at the time of assessment). Survey indices indicate recruitment in N-ENS will be minimal with a potential gap for the next 1 to -3 years. In S-ENS, recruitment is likely to continue at a moderate rate in the upcoming season. 4X is expected to see low to moderate levels of recruitment for two years. Fishing mortality was higher than desirable in N-ENS. Bottom temperatures have been continually rising since the early 2000s until a decrease observed during the 2023 survey. This is positive news for the Snow Crab fishery and will be monitored with future surveys in hopes this decreasing trend continues. The model suggests that N-ENS and S-ENS are in the healthy zone and 4X is in the critical zone.