Analysing mortality patterns in salmon farming using daily cage registrations

Abstract

This study describes the patterns of mortality and investigates the sources of variation in mortality during the marine phase of commercial salmon farming. The study included daily mortality records from stocking to harvest of 21 million salmon from ten hatcheries in 136 fish‐groups (fish in the same cage from the same hatchery). The fish was stocked in 2017–2018 at 21 marine farms within two Norwegian companies. The sources of variation in mortality were investigated using multilevel linear regression models with ‘fish‐group’ nested within ‘farm’ as a random effect, cross‐classified with ‘hatchery’. In the final model, ‘fish‐group’ was the source of most variation (70%). Furthermore, the mortality categories ‘smolt‐related mortality’, ‘infectious diseases’ and ‘handling and treatment’ were responsible for 10%, 17% and 29% of the total number of dead fish respectively. Overall, the study shows that smolt‐related mortality is one of the major causes of death in the first part of the production, while handling and treatment was the dominating cause of mortality in total. Mortality varied by fish‐group to a large extent. This means that targeted preventive strategies to decrease mortality for individual fish‐groups might be more effective than overall measures at farm or hatchery level.

Exploring Options for Syndromic Surveillance in Aquaculture: Outbreak Detection of Salmon Pancreas Disease Using Production Data from Norwegian Farms

“…If the goal is to identify potential health problems in the early stage after sea transfer of salmon (i.e., the first 2-3 months), our approach is inadequate due to the frequency of the time series. This applies to diseases that typically occur in recently transferred fish, for example, tenacibaculosis, infectious pancreatic necrosis and mortality due to incomplete smoltification [20,21,56]. It is important to note that these diseases affecting recently transferred fish are likely to have been carried from the freshwater phase, as a certain exposure time is necessary for horizontal transmission from surrounding farms in the sea.…”

“…We excluded production months with salmon weighing less than 400 g as they are rarely affected by PD. Although fish in this weight class have a high overall mortality, it is most likely due to seawater adaptation of post-smolts [21,22,24]. We also excluded data from months with salmon weighing more than 6 kg or farms with salmon stocked for more than 24 continuous months.…”

“…The main single cause of mortality in captive salmon is injury due to increased handling during treatments. Together with infectious diseases, this accounts for almost half of the deaths [21]. The treatments generally target salmon lice (Lepeophtheirus salmonis) infestations, and they involve temporarily placing the salmon in heated water (thermal delousing) or mechanically removing the lice through brushing and flushing procedures.…”

Differential Expression of miRNAs and Their Predicted Target Genes Indicates That Gene Expression in Atlantic Salmon Gill Is Post-Transcriptionally Regulated by miRNAs in the Parr-Smolt Transformation and Adaptation to Sea Water

“…Suboptimal smoltification has been reported as a contributory factor to death shortly after SWT [ 10 , 13 ]. Disease during the SW phase was identified as another important contributor to losses prior to harvest [ 14 ].…”

Towards Generating Large Synthetic Phytoplankton Datasets for Efficient Monitoring of Harmful Algal Blooms

“…For example, in 2016, a HAB outbreak in Chile killed over 27 million farmed trout and salmon (Montes et al 2018). Furthermore, from 2015-2019, farmed salmon deaths due to fatal diseases caused by HABs increased by 27.8% from 41.3 to 52.8 million (Persson et al 2022). When millions of fish die due to HABs and other diseases, they are disposed of by being dumped back into the ocean, causing ocean pollution, or being brought to landfills, causing increased greenhouse gas (GHG) emissions (Armijo et al 2020;Bustos, Ramírez, and Rudolf 2021).…”