Methods for accounting for the impact of the COVID-19 pandemic on adult salmon stock estimates in Scotland : Scottish Marine and Freshwater Science Vol 12 No 8

• Main Author: Marine Scotland
• Format: Article in Journal/Newspaper
• Language: English
• Published: Marine Scotland Science 2021
• Subjects: Fish and shellfish catch statistics; Fish biomass in water bodies; Atlantic salmon; North Atlantic
• Online Access: https://dx.doi.org/10.7489/12376-1; https://data.marine.gov.scot/dataset/methods-accounting-impact-covid-19-pandemic-adult-salmon-stock-estimates-scotland

Estimation of Scotland’s Atlantic salmon stocks is a key component of national and international management and requires information on rod catches. During 2020 rod fisheries were adversely impacted by restrictions associated with the COVID-19 pandemic. Without accounting for reduced fishing effort, stock abundance may be underestimated due to lower-than-expected catch. This report describes methods used to account for the impact of the COVID-19 pandemic on adult salmon stock assessments in Scotland. : Two complimentary approaches to account for lower-than-expected catches on stock estimates were developed and presented to the Working Group on North Atlantic Salmon in March 2021. The first approach uses historic catches to estimate expected-catches for the affected months in 2020. This simple approach captures the within year pattern of catches and allows overall catches to vary between years. The second approach was based on estimating expected-catch by first modelling a “corrected effort” that would have been expected in the absence of restrictions and then converting this to expected-catch using a model of monthly catch per unit effort. The choice of which model to apply to each of the 173 assessment areas used for national management was made by comparing model fits for the 2019 season. There was a fairly even balance between the number of areas that were favoured by the two overall approaches. Applying a COVID-correction to catches increases the whole-of-Scotland stock estimate by approximately 22%, although the degree of correction differed between different assessment areas depending on area-specific catch and effort data. Although it is not possible to fully account for the complexity of the pandemic and it’s impact on rod fishing the methods described allow the impact of the COVID-19 pandemic to be accounted for in stock assessments