Eliminating implausible fisheries assessment models using fishers’ knowledge

• Published in: Canadian journal of fisheries and aquatic sciences Vol. 75; no. 8; pp. 1280 - 1290
• Main Author: Duplisea, Daniel E
• Format: Journal Article
• Language: English
• Published: Ottawa NRC Research Press 01.08.2018; Canadian Science Publishing NRC Research Press
• Subjects: Biomass; Bocaccio; Catch statistics; Fish; Fisheries; Fishers; Fishers (Persons); Fishery management; Fishery surveys; Marine; Methods; Modelling; Mortality; Observations; Redfish; Sebastes mentella; Stock assessment; Stock assessment (Wildlife management); Surveys; ANW, North Atlantic
• ISSN: 0706-652X; 1205-7533
• DOI: 10.1139/cjfas-2017-0178

Peer review of competing deepwater redfish (Sebastes mentella) assessment models revealed data inconsistencies where stock biomass decline shown by the survey in the 1990s was too rapid to be explained solely by reported catch. The models invoked different techniques to achieve fits, one by changing mortality at age and the other by survey weighting. The former fitted reported catch well, while the latter accepted a mismatch between reported and estimated catch. The assessments produced different estimates of historical stock size and future productivity. Interviews conducted with fishers of the stock suggested that catch was at least twice as high as the official record. In light of the fishers’ evidence, the model that invoked a large change in mortality with age to follow reported catch closely now appears less credible. This serves as a warning against introducing new biological mechanisms without credible justification. This is an example of how indicators derived from fisher’s knowledge, even if only from a small number of interviews, can be used to eliminate less plausible models.