Research Document 2022/041
The Status of Yellowtail Flounder (Limanda ferruginea) in NAFO Division 4T to 2020
By Rolland, N., Swain, D. and Ricard, D.
Abstract
Yellowtail Flounder (Limanda ferruginea) tends to be distributed in shallow, near shore areas of the southern Gulf of St. Lawrence (sGSL; NAFO Division 4T). Yellowtail Flounder have been fished primarily for bait since 1995 and this fishery is mainly located off the Magdalen Islands. A Total Allowable Catch (TAC) of 300 tonnes (t) was established in 2000 but was revised down to 225 t in 2016. This document provides an assessment of the status of Yellowtail Flounder in the sGSL. Trends in abundance and biomass have differed markedly between commercial (>=25 cm) and pre-commercial (<25 cm) lengths. The survey abundance index for fish <25 cm increased 10-fold from 1985 to 2013. In contrast, the index for fish >=25 cm declined by 94% from 1981 to 2011 and has since remained near this low level. Based on a population model, natural mortality of large, old Yellowtail Flounder (ages 6+) increased from 21% annually in the late 1980s to 86% annually in 2009-2020. For younger Yellowtail Flounder (ages 1-3) estimated natural mortality declined from 34% annually in 1985-1990 to 15% in 2003-2008, increasing to 34% in 2015-2020. In contrast to natural mortality, fishing mortality was estimated to be low for all ages over the entire time series. Thus changes in the abundance and biomass of the 4T Yellowtail Flounder stock appear to have been driven by changes in natural mortality since 1985. Natural mortality of the older, larger fish is currently unusually high. Predation by grey seals appears to be an important cause of this elevated mortality. Estimated spawning stock biomass (SSB) has declined by 50% from its peak biomass in the early 2000s, considerably less than the 95% decline in the abundance of large (>=25 cm) or old (6+ years) fish. This reflects a large change in the composition of the spawning stock. Size at 50% maturity has declined steadily in this stock. The spawning stock has changed from one dominated by fish aged 7 years and older to one now composed almost entirely of fish 4 years and younger. The Limit Reference Point (LRP) for this stock is estimated to be 5,710 t in the commercial length class (>=25 cm). The stock was estimated to be 39% of the LRP in 2020 and the probability that the stock was below the LRP was estimated to be 99% in 2016 to 2020. The population was projected forward 10 years assuming that current productivity conditions would persist over this period. Fishery catch was assumed to be 0, 100 or 300 t. Estimated SSB declined more than 50% over the 10-year projection with negligible impact of the catch level on the trajectory. The estimated biomass of the large length class was also projected over 10 years. The probability that the stock was below the LRP was 100% in all projection years. In conclusion, this stock is well below the LRP and is expected to continue to decline even with no fishing. The current status of this stock appears to be driven by high natural mortality rather than fishing mortality. However, this assessment is for the entire sGSL stock. Fishing is now confined to the Magdalen Islands region. Fishing may play a more important role in this region than over the sGSL as a whole.
Accessibility Notice
This document is available in PDF format. If the document is not accessible to you, please contact the Secretariat to obtain another appropriate format, such as regular print, large print, Braille or audio version.
- Date modified: