DOI: 10.5061/dryad.m0cfxpphh
title: Effects of salmon lice on numbers and size distributions of Atlantic salmon populations returning to spawn in Norwegian rivers

description: Negative effects of salmon lice from salmon farms on wild salmonids have
 been a controversial issue for decades, and concerns are expressed from
 virtually all areas where salmon farming coexists with important fisheries
 for wild salmonids. A key question is to what extent lice infestation from
 farms reduces the number of wild mature salmon returning to spawn in the
 rivers. Here we study counts and recreational catches of small (&lt; 3
 kg), medium-sized (3 – 7 kg), and large mature salmon (&gt; 7 kg)
 returning to spawn in Norwegian rivers, in association with lice burdens
 on out-migrating post-smolt recruits. The expected number of returning
 mature salmon was modelled as a function of theoretical smolt production
 in the rivers, river catches one generation back in time, size classes of
 returning salmon, year as a factor, a non-linear spatial effect, and
 parasite-induced mortality (PIM) of out-migrating post-smolts of salmon.
 PIM was attributed to small, medium-sized, and large salmon, assuming they
 spend one (1 SW), two (2 SW), or three winters at sea (3 SW),
 respectively. There was a significant negative effect of PIM on returns of
 1 SW salmon and a negative but non-significant effect on returns of 2 SW
 salmon. For 3 SW salmon, the effect of PIM was significantly positive, but
 for comparably low numbers, implying an overall negative effect of PIM on
 returning salmon. The size-specific effects of PIM were manifested by
 decreasing proportions of 1 SW salmon in returning populations with
 increasing PIM, from ~0.6 for rivers exposed to low levels of PIM, to
 predictions of &lt; 0.2 for rivers exposed to high levels of PIM. This
 study presents a quantitative relationship between infestations of
 post-smolt recruits and size-structured returns of mature salmon to
 Norwegian rivers, suggesting that louse infestation from farms may reduce
 returns of spawners and restructure the size distribution of mature river
 populations of Atlantic salmon. The presented relationship opens up for a
 more targeted approach to obtaining sustainable salmon farming. To
 accommodate the Norwegian Government’s goal for sustainable aquaculture,
 reductions in lice abundances in farms are necessary.
description: # Effects of salmon lice on numbers and size distributions of Atlantic
 salmon populations returning to spawn in Norwegian rivers Dataset DOI:
 [10.5061/dryad.m0cfxpphh](https://doi.org/10.5061/dryad.m0cfxpphh) ##
 Description of the data and file structure The data was collected to
 explore the effects of salmon lice from salmon farms on the numbers and
 size distribution of wild Atlantic salmon returning to spawn in Norwegian
 rivers. ### Files and variables #### File: Data.csv **Description:** 
 Empty cells are **not available data** ##### Variables * river.id: River
 identifier. Variable Geo = numeric of first three digits * year: Year for
 salmon population * size: Small salmon (1SW), medium sized (2SW), large
 (3SW) * percent.surv: Percentage of river surveyed for mature salmon *
 method: Survey method * in.data: Data in the main analyses indicated by 1,
 others 0 * pop: Adjusted count of salmon + catch * count: Adjusted count
 of salmon * count.nadj: Non-adjusted count of salmon * catch: Catches of
 salmon with missing imputed by 0 * catch.noimp: Non-imputed catches *
  PIM: Parasite-induced mortality with random area and year effects (only
 used in Supplementary Information) * PIMUJ: Parasite-induced mortality
 used in the main paper * HIPIM: PIM by the IMR (only used in Supplementary
 Information) * ant: Louse infestation index (only used in Supplementary
 Information) * antUJ: Louse infestation index with random area and year
 effects (only used in Suppl. Info.) * TS: Theoretical smolt production *
 CWG: Catches in prior generation, weighted ## Code/software R or Excel ##
 Access information Data was derived from the following sources: *
 [https://bestand.nina.no/#/](https://bestand.nina.no/#/)