Research Document 2021/073
Assessment of St. Mary’s Bay Longhorn Sculpin (Myoxocephalus octodecemspinosus), 1999–2019
By Stone, H.H.
Abstract
A directed fishery for Longhorn Sculpin in St. Mary’s Bay began in 1999 and has continued through to 2019, with the exception of 2007 and 2008 when the fishery was closed. Four license holders are permitted to direct for Longhorn Sculpin using otter trawls with 90–100 mm diamond mesh cod ends. The fishery occurs over a 6-week period during April and May, and the Sculpin catch is sold for Lobster bait. Longhorn Sculpin landings from St. Mary’s Bay peaked at 235 t and 229 t in 2011 and 2012, but declined to 29 t in 2019. At the same time, landings of Winter Flounder bycatch increased from 1% of total landings in 2011 (3 t) to 58% in 2019 (51 t) and currently exceed those of Longhorn Sculpin. The average size of Longhorn Sculpin and percentage > 23 cm (size at 50% maturity) in fishery catches has been below the long-term average since 2015. At-sea-observer coverage levels for the 2009–2019 directed Longhorn Sculpin fishery averaged 15% of landings and trips per year, which is lower than the earlier period of the fishery (1999–2006). Crustaceans represent 74% of all discarded bycatch (1999–2019 average) and include American Lobster (46%), Jonah Crab (16%), and Rock Crab (12%). Since 2015, there has been an increase in the percentage of Winter Flounder discards, which represent 40% of all discards in 2018 and 2019. The overall spatial distribution of Longhorn Sculpin from the DFO Summer Research Vessel (RV) Survey does not appear to have changed; however, there has been a notable decrease in survey catches on the Eastern Scotian Shelf and the outer Bay of Fundy since 2000. Biomass indices for DFO Summer RV Survey strata in 4X and stratum 490 (adjacent to St. Mary’s Bay) have been below the long-term mean (1970–2019) since 2010. The average size of Longhorn Sculpin and percentage > 23 cm in survey catches show a declining trend in 4X strata and stratum 490 from 1970–2019, but the decline is steeper for stratum 490, especially since 2000. The directed Longhorn Sculpin fishery Catch Per Unit Effort (CPUE) index shows a pattern of “fishing up” and “fishing down” the stock before and after the 2007–2008 closure. The median of the CPUE time series was used as a proxy for Biomass at Maximum Sustainable Yield (BMSY). A Limit Reference Point (LRP) was calculated as 40% of BMSY. The 3-year median CPUE was used for determining stock status. CPUE declined rapidly to levels approaching 40% of the time series median (LRP proxy) in 2006 and 2019, in close proximity to the Cautious/Critical Zone boundary. In-season exploitation was above 30% in 2006 and from 2009–2015 and potentially as high as 75–76% in 2011 and 2012, when landings were highest. At the same time, catch rates of Winter Flounder increased steadily since 2009, but it is unclear if this was due to an increase in Winter Flounder abundance or to targeting of this species by the directed Longhorn Sculpin fishery license holders. The current prognosis for the Sculpin fishery in St. Mary’s Bay appears to be poor and this species has clearly undergone periods of localized depletion at a time when the overall population biomass appears to be lower than average.
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