Research Document 2021/028
An Assessment of Newfoundland and Labrador Snow Crab (Chionoecetes opilio) in 2018
By Baker, K., Mullowney, D., Pedersen, E., Coffey, W., Cyr, F., and Belanger, D.
Abstract
The status of the Snow Crab (Chionoecetes opilio) resource surrounding Newfoundland and Labrador (NL) in Northwest Atlantic Fisheries Organization (NAFO) Divisions (Divs.) 2HJ3KLNOP4R is assessed using a variety of metrics. Data from multi-species bottom trawl surveys conducted during fall in Divs. 2HJ3KLNO and spring in Divs. 3LNO and Subdiv. 3Ps are examined to provide information on trends in biomass, recruitment, production, and mortality over the time series. Multi-species trawl survey indices are compared with other relevant indices toward inferring changes in resource status for 2019 and beyond. These other indices are derived utilizing data from harvester logbooks, at-sea observers, the dockside monitoring program (DMP), and inshore and offshore trap surveys, as well as oceanographic surveys. Snow Crab landings remained near 50,000 t from 2007 to 2015 but have since steadily declined to a two-decade low of 27,700 t in 2018. Overall effort remained at approximately 3.5 to 4.5 million trap hauls per year over that time. Overall catch per unit effort (CPUE) was at a time-series low in 2018. Despite modest increases in the past two years, the trawl survey exploitable biomass index has remained at its lowest level for the past four years. Meanwhile, the trap survey index has declined by nearly 60% in the last two years to a time-series low. Despite modest increases in some divisions in the past two years, overall recruitment into the exploitable biomass will remain low in most divisions in 2019. Total mortality in exploitable Snow Crab is estimated to be near time-series’ averages in most divisions. It has declined from very high levels in most divisions during the past two years, with the exception of Division (Div.) 3K, where it remains at a time-series high. Exploitation rate indices were at or near time-series highs in most divisions in 2017. In 2018, exploitation rates subsequently increased to a new high in Div. 3L Inshore, remained high in Divs. 2HJ3KLNO, and declined to be near or below long-term average levels in Divs. 3Ps and 4R3Pn. Elements of the Precautionary Approach Framework presented in this assessment are tentative. Limit Reference Points defining the critical zone have been established by a peer-reviewed Science process, but Upper Stock Reference lines defining the cautious and healthy zones remain under development. In 2019, most divisions are projected to fall within the cautious zone of the proposed Precautionary Approach Framework. Div. 3L Inshore would be in the critical zone. These projections assume status-quo landings. The thermal habitat index (defined as the areal extent of <2°C bottom water) has returned to near-average conditions in all divisions in recent years. Broad-scale climate indices appear favourable for improved recruitment to occur in most major areas of the stock range over the next few years. Ecosystem conditions in the NL Bioregion are indicative of an overall low productivity at the lower trophic levels (phytoplankton and zooplankton) in recent years with changes in zooplankton community structure potentially impacting the transfer of energy to higher trophic levels. A sharp decline in male size-at-maturity (i.e., terminal molt size) in most Assessment Divisions (ADs) in recent years will dampen short-term prospects for recruitment into the Snow Crab exploitable biomass.
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