Spatio‐temporal variations in mortality during the seawater production phase of Atlantic salmon (Salmo salar) in Norway

Abstract

In a sustainable production of animals, monitoring and minimizing mortality must be a top priority. Systematic measuring of mortality over time can be used to evaluate the impact of changes in management and production strategies in Norway. To aid understanding of the potential for reducing mortality, we have used data from 2014 to 2018 to investigate the spatio‐temporal patterns of mortality, by descriptive analyses and statistical modelling of possible determinants of mortality. The results show large differences in mortality across different production zones and between years. The areas with the highest density of farmed salmon are also the ones with highest mortality. The total cumulated mortality of farmed salmon increased from 32.3 million in 2014 to 35.2 million in 2018, corresponding to 14.3% and 15.8% of the standing stock. An initial higher mortality was observed during the first 3 months after stocking (mean: 1.5% [0.9%–8.6%] mortality/month). This was followed by a period of stability and lower mortality (mean: 0.8% [0.9%–3.1%] mortality/month), until month 10, when mortality started to increase again. The month of first stocking, the year of slaughter, production zone and number of months at sea were all found to be statistically significant determinants for mortality, with p‐values < 1e−15.

Towards cost‐effective biofouling management in salmon aquaculture: a strategic outlook

“…2020), with maximum mortalities at the beginning and at the end of the production cycle (Salama & Murray 2011; Bang Jensen et al . 2020). While there are no reliable data on the exact contribution of biofouling‐ or biofouling management‐related impacts to farm mortality, we consider, based on recent assessments (Bannister et al .…”

“…The average mortality of salmon during the grow-out phase at sea is 14-16% (Sommerset et al 2020), with maximum mortalities at the beginning and at the end of the production cycle (Salama & Murray 2011;Bang Jensen et al 2020). While there are no reliable data on the exact contribution of biofouling-or biofouling management-related impacts to farm mortality, we consider, based on recent assessments (Bannister et al 2019), that improved biofouling management has the potential to significantly improve fish health and welfare, and thereby survival.…”

Estimating cage‐level mortality distributions following different delousing treatments of Atlantic salmon (salmo salar) in Norway

“…There is a growing concern regarding increasing mortality of farmed Atlantic salmon (Salmo salar ) in Norway (Bang Jensen et al., 2020; Tørud et al., 2019). In the seawater phase of the production, the total cumulated mortality of salmonid fish increased from 2014 to 2018, from 14.3% to 16.8% of the standing stock (Bang Jensen, Qviller, et al., 2020). The increasing mortality constitutes a serious welfare problem as well as an economic challenge.…”

“…The increasing mortality constitutes a serious welfare problem as well as an economic challenge. Treatment against salmon lice by physical removal of the lice (so called non‐medicinal treatments) has been discussed as one of the reasons for the increased mortality in the seawater phase of the production (Bang Jensen, Qviller, et al., 2020; Hjeltnes et al., 2019; Oliveira et al., 2021; Overton, Dempster, et al., 2018).…”

“…Neither has the change over the past years been explored. There can be large variation in mortality between groups of fish within a site (Bang Jensen, Qviller, et al., 2020). Production data from aquaculture companies have a cage‐level resolution, which makes it possible to describe variation between groups of fish when looking at mortality after delousing.…”