Code and Data supporting manuscript: 'Multi-decadal trends in abundance reveal a dramatic decline in wild Norwegian Atlantic salmon'

This repository contains code and data used to reproduce analyses presented in main text of manuscript “Multi-decadal trends in abundance reveal a dramatic decline in wild Norwegian Atlantic salmon”. The analysis estimates national and regional abundance of wild Atlantic salmon (Salmo salar L.) in Norwegian rivers using reported catch statistics from nearly 450 populations. Abundance is reconstructed over multiple decades (national: 1983–2023; regional: 1989–2023) using a Monte Carlo simulation framework. Reported catch data, parameter values, and auxiliary datasets are used as inputs to generate 1000 simulated time series of salmon abundance, with estimates stratified by size group and sea-age group. The workflow is implemented in three R Markdown scripts. The first script performs Monte Carlo simulations to estimate abundance. The second script analyses temporal trends in abundance at the level of individual simulations. The third script aggregates simulation-level results to produce summary statistics (medians and 95% confidence intervals) and figures presented in the manuscript. All required input data are included in the repository (CSV and RDS formats), and intermediate and final outputs are generated within the workflow.