Did over-reliance on commercial catch rate data precipitate the collapse of northern cod?

• Published in: ICES journal of marine science Vol. 62; no. 6; pp. 1139 - 1149
• Main Author: Shelton, Peter A.
• Format: Journal Article
• Language: English
• Published: Oxford University Press 01.09.2005
• Subjects: catch rate; cod; collapse; Gadus morhua; Marine; model calibration; population estimation; stock assessment; ANW, Canada, Newfoundland and Labrador; ANW, Atlantic; model calibration; cod; population estimation; catch rate; collapse; stock assessment
• ISSN: 1054-3139; 1095-9289
• DOI: 10.1016/j.icesjms.2005.04.009

It has been suggested that a number of “lessons” can be learned from the collapse of the northern cod stock off Newfoundland and Labrador. However, not all purported lessons have been validated with available data. One lesson is thought to be that over-reliance on commercial catch rate data and an incorrect assumption regarding the functional relationship between catch rate and population size were major contributors to overestimating stock size, precipitating the collapse. The current study describes calibration approaches used in assessments, and evaluates alternative functional relationships between commercial catch rates and stock size. In addition, historical population size is re-estimated using only research vessel data and compared with estimates obtained based on both commercial catch rate and research vessel data. Calibration with commercial catch rate contributed to overestimating stock size in some years, but there is no evidence that the assumed functional relationship between commercial catch rate and population size was a significant factor in the collapse.