Long-term variability of growth and recruitment of cod (Gadus morhua) off Greenland

• Published in: ICES Journal of Marine Science
• Main Authors: Rätz, Hans-Joachim, Lloret, Josep
• Format: Article in Journal/Newspaper
• Language: English
• Published: Oxford University Press (OUP) 2005
• Subjects: Ecology; Aquatic Science; Ecology, Evolution, Behavior and Systematics; Oceanography; atlantic cod; Gadus morhua; Greenland; Greenland cod; Iceland
• Online Access: http://dx.doi.org/10.1016/j.icesjms.2005.07.009; http://academic.oup.com/icesjms/article-pdf/62/7/1310/29125191/62-7-1310.pdf

Abstract Growth variation was estimated from mean lengths-at-ages 4 and 5 for Atlantic cod off Greenland based on 52 973 fish taken from commercial and scientific catches from 1955 to 2002. Mean length-at-age values were corrected for area and seasonal effects, and significant growth reductions occurred during the 1960s and from the mid-1970s until the mid-1980s. Annual growth rates of cod in Greenland waters during the most recent decade (1993–2002) were consistently among the highest recorded. Statistical growth models accounting for temperature, fishing mortality, and stock abundance effects were constructed. Multiple linear regressions revealed significant positive temperature effects on growth of both age groups and a significant negative stock density effect on length-at-age 4. Correlations between exploitation intensity and length-at-age were statistically insignificant. During the period 1955–2002, the number of recruits at age 3 was significantly correlated with the Greenland cod spawning-stock biomass, June water temperature on top of Fyllas Bank (West Greenland), and Iceland cod recruitment. All factors had a positive effect on the number of Greenland recruits and, combined, accounted for 60% of the observed variation. Spawning stock size was, by far, the most important factor contributing to recruitment variability, while June water temperature below 1°C and Iceland recruits below 150 million never coincided with high year-class strength in Greenland during the past 50 years. Thus, previous conclusions regarding a close relation between the Greenland and Icelandic cod stocks might need to be reconsidered in the light of a continued recruitment failure in Greenland waters over the two most recent decades, despite the improved environmental conditions and near-average recruitment of the Icelandic stock. The low precision of the recruitment model, however, prevents reliable predictions in the short or medium term, but a substantial short-term recovery of the Greenland cod stock remains unlikely.