Research Document 2018/033
Sentinel Surveys 1995-2016 – Catch rates and biological information on Atlantic Cod (Gadus morhua) in NAFO Subdivision 3Ps
By L.G.S. Mello, C.M. Miri, D. Maddock-Parsons, H. Rockwood, and Simpson, M.R.
Abstract
Catch rates and biological information for Atlantic Cod from the Sentinel Survey Program in the Northwest Atlantic Fisheries Organization (NAFO) Subdivision 3Ps are updated for 2016, and preliminary results presented for 2017. Temporal trends in gillnet (small 3¼ inch mesh, large 5½ inch mesh) and linetrawl unstandardized catch rates were similar for all gears, with the highest values at the beginning of each time-series, sharp declines after 1997, and oscillations around or below the series’ mean catch rate thereafter. Mean catch rate for small mesh gillnets was consistently higher than that of large mesh gillnets for the entire time-series: peaking at 142 fish per net in 1996, and then averaging 11-36 fish/net; except for its lowest value of 6 fish/net in 2011. Large mesh gillnets yielded the lowest mean catch rate of all gears: declining from 49 fish/net in 1997 to less than 9 fish/net since 2000. Mean catch rate for linetrawls peaked at 223 fish per 1,000 hooks in 1996, and fluctuated around 100 fish/1,000 hooks until 2010 (except in 2006); prior to reaching its lowest value of 62 fish/1,000 hooks in 2014-2015. Sentinel catch rates for large mesh gillnet and linetrawl “control” locations were standardized using Generalized Linear Models. Age-disaggregated standardized catch rates for recent year-classes were generally weaker than those in the past; although proportions-at-age of large mesh gillnet catch rates suggested that the 2008 year-class was relatively stronger. Age-aggregated catch rates were higher at the beginning of each time-series for both gears, declined over the mid-to-late 1990s, then remained at their lowest levels; decreasing below the series’ mean of 6.4 fish/net (large mesh gillnets) in 1999, and 86 fish/1,000 hooks in 2009 (linetrawls). Gillnet and linetrawl catch rates for 2016 were 1.5 fish/net and 57.5 fish/1,000 hooks, respectively.
Length frequencies of Atlantic Cod measured in Sentinel Surveys indicated that the small mesh gillnet was the least selective gear (retaining small and large fish from multiple year-classes), whereas large mesh gillnets and linetrawls captured larger fish in specific size ranges and few overlapping year-classes. Fish lengths from small mesh gillnets showed several modes between 35 cm and 62 cm throughout the time-series, while those of fish from large mesh gillnets and linetrawls ranged between 62-68 cm and 54-62 cm, respectively. Indices describing the physiological condition of Atlantic Cod varied at both seasonal and annual scales: the liver (hepatosomatic index) and gutted body condition (Fulton’s K condition factor) declined over winter and early spring (while the gonadosomatic index increased), then improved over summer after spawning. These trends varied annually over the time-series, but generally declined in 2004‑16. Both length and weight-at-age (6+ years) have decreased since the early part of each time-series.
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