Declining Weight-at-age in Northern Cod and the Potential Importance of the Early Years and Size-selective Fishing Mortality

• Main Authors: Martha M. Krohn, Stephen R. Kerr
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Key words; Atlantic cod; growth; size-specific growth; atlantic cod; Gadus morhua
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.568.9911; http://archive.nafo.int/open/studies/s29/krohn.pdf

Weight-at-age of northern cod (Gadus morhua) declined between 1979 and 1993 for all age-classes, with the greatest reduction in size-specific growth evident at ages 3, 4 and 5. The extent to which the declines in weights at these young ages have been responsible for smaller weights in older age-classes was determined. On average 68 % of the decline in weight of 4- to 8-year-olds was attributable to a decline in weight-at-age in previous years. Differences in weight-at-age among cohorts suggested that cohorts that are small early in life tend to remain small, and that size in early years greatly influences future production. These findings suggest that the environment for growth may have worsened specifically for these young ages, highlighting the importance of studying what is affecting growth processes in the early years. These results also point to the possibility that size-selective fishing on the 3- to 5-year-olds may have played an important role in the decline in weight-at-age.