Magne Aldrin

Cleaner fish are commonly used as a biological control measure against salmon lice infestations in salmonid farming. However, there have been few attempts at quantifying the effect of cleaner fish on the louse abundance at commercial farms. Our study estimates a delousing effect for wrasses (Labridae) and lumpfish (Cyclopterus lumpus) by fitting a partially stage-structured lice development model to historical production data on all salmonid farms in Norway. We investigate different models, and evaluate them according to a statistical model selection criterion (BIC). The final model includes temperature dependence for the delousing effect of cleaner fish, as a quadratic function. The estimated optimal temperature for lice grazing was found to be 6.7 °C for lumpfish and 15.3 °C for wrasses. The final model also included separate delousing effects for adult female and other motile salmon lice. In general, the estimated delousing effect was larger for wrasses than for lumpfish. However, for temperatures below 8.3 °C, the estimated delousing effect of other motile lice was larger when using lumpfish compared to wrasses. The estimated delousing effect was larger for lower abundances of salmon lice. This implies that cleaner fish should be used at low louse abundances, and not as a delousing method during outbreaks. Our study is an important contribution to quantifying the temperature-dependent delousing effect of cleaner fish, which can be used to guide the farmers in their decision-making when planning cleaner fish strategies.

Lumpfish (Cyclopterus lumpus) are frequently used as “cleaner fish” to control parasitic sea lice in salmonid fish farms, but it has been questioned whether the benefits in terms of sea louse control outweigh the economic and lumpfish-welfare costs involved. Here we estimated the efficacy of lumpfish in controlling salmon lice (Lepeophtheirus salmonis) in salmonid farms by combining analyses of occurrence of salmon lice in stomach contents of lumpfish and experimental results on digestion time. We then conducted scenario simulations of salmon louse dynamics in salmonid fish farms, by combining the lumpfish feeding model with a lumpfish growth model and a salmon louse population model. Results showed that at a mean lumpfish weight of 50 g and typical conditions for other factors (9 °C, 2 kg salmonids, and 0.8 pre-adult and adult salmon lice per salmonid), the estimated feeding rate was 0.17 salmon lice per lumpfish per day (95 % confidence interval: 0.12–0.22). This rate increased with salmon louse concentration, temperature and salmonid weight and decreased with lumpfish weight. Scenario simulations of salmon louse dynamics under conditions representative for salmonid farms in Norway suggested that stocking lumpfish from the start of the production cycle with a 1:10 lumpfish per salmon ratio on average postponed the first salmon louse treatment by 43 days. The longest postponement was at intermediate external infestation pressure. Scenario simulations for a network of farms suggested that coordinated and strategic use of lumpfish after a spring treatment may succeed in supressing salmon louse outbreaks through spring and summer.

Advice on fishing opportunities is based on stock assessment models. Modern stock assessment frameworks are designed to account for uncertainty in model parameters. However, some parameters are often fixed at specific values and assumed to be known precisely. Paradoxically, these fixed values often relate to parameters we understand the least—such as the natural mortality rate. For example, in the assessment of Norwegian Spring-Spawning Herring, the natural mortality rate is assumed to be exactly 0.9 for age 2 fish and 0.15 for older fish. In this study, we investigate how sensitive the assessment results—and, more specifically, the resulting fishing quotas (total allowable catch, TAC)—are to assumptions regarding natural mortality and maturity-at-age for both Norwegian Spring-Spawning Herring and North-East Arctic Cod. The assessment models for both stocks are formulated within the SAM framework. Furthermore, we explore a simple approach for adjusting harvest control rules that seeks to preserve the TACs when fundamental fixed assumptions are altered. Our intention is that this serves as an exploratory tool to investigate sensitivity to new assumptions, and is not intended to replace a more formal process for defining new biological reference points and harvest control rules. The results indicate that, under the current harvest control rules, the TACs for both herring and cod may be sensitive to assumptions regarding natural mortality rates and maturity-at-age. For herring, sensitivity to natural mortality is significantly greater than is reflected by the estimation uncertainty in model parameters. However, when basic assumptions are changed, it is also natural to consider corresponding adjustments to the harvest control rules. Our proposed simple adjustments to the control rules reduce sensitivity to these assumptions in many cases, though not in all.

Stock assessments are often based on age-structured data obtained by interpreting calcified structures. Due to readability and human error, the observed age may be wrong. We propose a parametric model for age-reading error matrices, which is more realistic and robust than the commonly used empirical matrices. The parameters have meaningful interpretations, allowing for direct comparison of age-reading properties. We compare different species (Atlantic mackerel ( Scomber scombrus) and herring ( Clupea harengus)), stocks (North Sea autumn-spawning vs. Norwegian spring-spawning herring), and calcified structures (otoliths vs. scales). Three out of four data sets had an asymmetry tendency towards reading higher ages than the true age. The estimated probability of reading the wrong age was lower for scales than for otoliths. The true age is often unknown and assumed to be the modal age. We assess the systematic bias due to this assumption. Finally, when including age-reading error in stock assessment, the dominating age classes were estimated to be larger and spawning stock biomass lower. Our study contributes with methods and insight for including age-reading error in stock assessment.

Current debate on the sustainability of using cleaner fish to control parasitic lice in salmon farming suffers from extremely variable scientific evidence on the efficacy of this practice. This paper presents novel experimental results on evacuation rates of salmon lice through the digestive tract of ballan wrasse. These results are combined with quantitative field data on contents of salmon lice in ballan wrasse, to derive a method to study the efficacy of ballan wrasse in cleaning salmon of salmon lice. From a fitted binomial regression model on the probability of finding lice in the digestive tract after ingestion, we found a median evacuation time of 11.0 h. The mean evacuation time was 12.2 h. Furthermore, by integration, we found that if a wrasse on average consumes one louse per day, then the expected number of observable lice in the digestive tract is 0.472. This gave an estimated daily consumption of salmon lice per wrasse expressed as the number of salmon lice in the digestive tract divided by 0.472. As an example, analyses of lice contents in the digestive tract of 6406 ballan wrasse used as cleaner fish in salmon farming revealed that salmon lice were found in 2.9% of the wrasses, with a mean number of 0.15 lice per fish. This translates to an estimate of 0.32 lice consumed per day per ballan wrasse. The present way of estimating the efficacy of wrasse as cleaner fish may contribute to a more robust evaluation of louse control effects of ballan wrasse.

En ny studie viser at mye lus på utvandrende laksesmolt har en klar sammenheng med at færre gytefisk vender tilbake etter ett år. Forskere ved AquaLife R&D, Norsk Regnesentral og Veterinærinstituttet har utviklet en statistisk modell for å undersøke sammenhengen. Vi tallfestet i vår modell i hvilken grad lusebelastningen fisken opplevde på sin smoltvandring har påvirket antall og alder på gytefisk i norske elver. Det vi fant var at mye lus på utvandrende laksesmolt har en klar sammenheng med at færre gytefisk vender tilbake etter ett år i sjø. På fisk som hadde vært to år i sjø var den samme effekten ikke til stede. På fiskene som hadde vært tre år i sjø fant vi motsatt effekt; det var en klar sammenheng mellom høy lusebelastning på utvandrende smolt og økt antall fisk som returnerte som gytefisk, men denne økninga var langt mindre enn den tilhørende nedgangen i antall fisk som hadde vært ett år i sjø. Dette vises i figuren under. Én mulig årsak til denne forskjellen i effekt mellom årsklassene er at lusepåkjenning kan forsinke vekst og kjønnsmodning.

Abstract 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 reduce numbers of wild mature salmon returning to spawn in the rivers. Here, we study counts and recreational catches of small (<3 kg), medium‐sized (3–7 kg) and large mature salmon (>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, two or three winters at sea (SW), respectively. There was a significant negative effect of PIM on returns of one SW salmon and a negative but non‐significant effect on returns of two SW salmon. For three 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 one SW salmon in returning populations with increasing PIM, from ~0.6 for rivers exposed to low levels of PIM, to predictions of <0.2 for rivers exposed to high levels of PIM. Synthesis and applications . 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 re‐structure the size distribution of mature river populations of Atlantic salmon. The presented relationship opens 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.

Environmental risk analyses of sewage systems shall be an integrated part of municipalities’ master plan for wastewater and storm water, as well as applications for permission of outlet to the State Governor. Such analyses are often performed in a manual and ad hoc, yet time-consuming way. Such simplified analyses typically include relatively few pipes, and the probability for different risk categories are often provided as crude estimates only. This approach does not at all harvest the full potential of connections and explanatory power that is contained in all the data available from the pipe system and the environment in combination. In this project, we develop a statistical framework that calculates environmental risk for 6200 sewage pipes based on data available for the municipality. The data set comprises three major sources: 1) Data from the professional VA wiring network system Gemini VA. This data set holds information on the geographical position of pipes, their age, material, diameter and slope, along with a history of maintenance and failures. 2) Data obtained from simulations of the sewage system in the hydraulic-hydrological software tool MIKE+. We perform model simulations for different precipitation events and prolonged dry weather periods. From these simulations we obtain for each pipe values of importance to pollution risk, for example: Overload, pressure, maximum and minimum water flow. 3) Data from environmental monitoring of the storm water system and urban streams in dry as well as wet weather. We measure six parameters: E.coli, total phosphorus, ortophosphate or total reactive phosphorus, total nitrogen, nitrate and ammonia in 400 manholes and stream monitoring locations. These data, called “weather pollution”, are assigned to the closest upstream sewage pipe, which also incorporates system information representative of the total upstream exposure. The analysis produces three main results: 1) Model simulation of a base risk value for each sewage pipe in dry weather or prolonged dry weather periods. The main risk is accumulation of sewage. 2) Calculation of a risk value for each pipe during overflow. The calculations are performed for different weather exposures represented via local precipitation intensity, duration and frequency (IDF) values for selected return periods. 3) Prediction of a “dry weather pollution” base risk value for pipes that have no monitored values, based on feeding their properties to the statistical framework. Most municipalities monitor their streams and lakes through the water areas, and many perform source tracking in the storm water system. If, in addition, a calibrated hydraulic-hydrological model of the sewage system is available, the suggested methodology can provide a more comprehensive analysis which is also more efficient.

We investigate various approaches to reduce the problem of salmon louse for the salmon farming industry. Salmon lice are parasites that can be spread through water from one fish farm to wild fish and to neighbouring fish farms. Various measures have been used to control salmon lice in fish farms, but frequent use of the same type of treatment may cause resistance, especially for medicinal treatments and possibly for non-medicinal treatments (e.g. freshwater). Our work focuses on resistance development caused by genetic selection. This means that some genotypes of lice have a higher probability of surviving a given treatment than other lice, and consequently the proportion of lice of resistant genotypes tends to increase by using that kind of treatment. We consider treatment policies involving two types of treatments with similar efficacy properties, but with independent selection mechanisms. The investigation is done by simulating the population of lice in neighbouring fish farms using a population model for lice. When the density of lice on a small sample of fish exceeds a given threshold, a treatment, which type depends on the strategy, is applied. For each simulation we record the number of required treatments and the levels of resistance. Regarding delaying resistance our results suggest that applying the two treatment types in combination is more effective than any of the considered strategies with separate use of the two types. This is joint work with researchers at the Norwegian Veterinary Institute, Aqualife R&D, Pharmac and the Norwegian University of Life Sciences.

The present study is an extension of a study on the evacuation time of salmon lice (Lepeophtheirus salmonis) in ballan wrasse (Labrus Berggylta). In the already existing study, the evacuation time of salmon lice in ballan wrasse was studied through an experiment conducted at 10-11 °C. We here supplement their analysis with additional experiments conducted at 6.5 °C and 15 °C. Quantifying the evacuation time of salmon lice in cleaner fish is important in order to assess cleaning efficacy from gastric lice count data, which are routinely collected by salmon farmers. We fit a binomial logistic regression model for the probability of finding lice in the digestive tract over time after ingestion based on data from experiments at all three temperatures. The estimated median evacuation time was 12.0 hours (95% confidence interval (10.8, 13.1), and the estimated mean evacuation time was 12.6 hours. By integrating the estimated probability, we derive that dividing the average number of salmon lice per wrasse in their digestive tracts by 0.504 gives an estimate of the average number of salmon lice consumed per wrasse per day. Assuming 0.39 salmon lice per digestive tract of ballan wrasse, as was found in the previous study, we hence estimate 0.77 salmon lice consumed per ballan wrasse per day. Comparing with the previous study which is based only on the experimental data at 10-11 °C, our estimate is similar but lower, as they found 0.83 salmon lice consumed per ballan wrasse per day.

I dette notatet vurderer vi ulike tiltak mot lakselus i produksjonsområde 6 ved hjelp av scenariosimulering fra en lusemodell. Vi tilpasser lusemodellen til historiske data fra BarentsWatch. I modellen inngår smitte mellom lokaliteter, og her modelleres denne både som funksjon av sjøavstand og vannkontakt basert på en hydrodynamisk modell for havstrømmer. Vi definerer et basisscenario basert på historiske produksjonsdata for lokalitetsstruktur, tiltaksgrenser og utsettsmønster, og simulerer lus over tid. Vi simulerer deretter luseutvikling for ulike alternative scenarioer og sammenlikner med basisscenarioet. Vi undersøker effekten av innføring av stortsmoltsone, bruk av dypdrift, endret utsettsmønster, endret tiltaksgrense og endring av lokalitetsstruktur/lukking av anlegg på gitte lokaliteter eller i underområder i produksjonsområdet.

Cleaner fish are utilised as a preventive control measure against sea lice infestations in salmon farms. In recent years, lumpfish (Cyclopterus lumpus) has been the most commonly deployed cleaner fish species in Norway. However, there have been few studies aiming to quantify the cleaning effect of lumpfish. There are many studies which document the number of sea lice in lumpfish stomach contents. These numbers cannot be used to infer the cleaning efficacy of lumpfish without also knowing the evacuation time of sea lice in lumpfish. In this study, we aimed to replicate an experiment of the evacuation time for salmon lice (Lepeophtheirus salmonis) in lumpfish. We found a median evacuation time of 50 h, and a mean evacuation time of 65 h. Combining with the data from the previous experiment, we found a median evacuation time of 31 h, and a mean evacuation time of 49 h. Interestingly, we found significantly slower digestion for adult female salmon lice than for other motile salmon lice. This implies that if lumpfish consumed the same (absolute) number of lice in different stages of lice, then one would expect more adult female lice in the stomach contents, as these require a longer time to be fully evacuated. This study is an important contribution to further understand the digestion time of salmon lice in lumpfish, which ultimately can be combined with an estimated number of salmon lice in the stomach contents of lumpfish to estimate a cleaning effect.

The stock assessment model SAM contains multiple age-dependent parameters that must be manually grouped together to obtain robust inference. This can make the model selection process slow, non-extensive and highly subjective, while producing unrealistic parameter estimates with discrete jumps. We propose to model age-dependent SAM parameters using spline functions, which can produce smoother parameter estimates, while making the model selection process faster, more automatic and less subjective. We develop a SAM spline model and compare it, using simulation studies and cross- and forward-validation methods, with published SAM models for 17 different fish stocks. The results show that our automated spline models overall outcompete the final accepted SAM models from stockassessment.org. We also demonstrate how our proposed spline model can be employed as a diagnostics tool for improving and better understanding properties of other SAM models.

Arbeidet som beskrives her er utført av Norsk Regnesentral, i samarbeid med Aqualife R&D, og er en del av er del av prosjektet “Opplevd smittepress for lakse smolt og sjøaure i Nordfjord, Sogn, Bjørnafjorden og Hardanger 2012-2023” som finansieres av Vestaland fylkeskommune. Hovedmål i prosjektet har vært å modellere opplevd smittepress av lakselus fra oppdrett hos laksesmolt og sjøaure fra elver i Nordfjord, Sogn, Bjørnafjorden og Hardanger basert på observerte vand ringsforløp i fjordsystemene. Delmål i prosjektet har vært å: • Sammenstille datasett på vandringsruter til laks og sjøaure ervervet ved bruk av akustisk telemetri som metode i fjordsystem på Vestlandet • Beregne lusepåslag og videreutvikling til forekomst av skadelige bevegelige lus på laksesmolt og sjøaure med kjente vandringsruter • Genetiske analyser av sjøaure; for kartlegging av effektiv bestandsstørrelse og slektskap med sjøaure fra andre elver i fjordsystemet • Styrke samarbeidet mellom villfiskinteresser, forskningsmiljø, forvaltning og oppdrettsnæring ved å etablere en kunnskapsbasert dialog mellom aktørene I denne rapporten beskrives bruken av en avansert populasjonsmodell for lakse lus til utvikling av en smittemodell basert på sammenhengen mellom forekomster av hunnlus på oppdrettsfisk og 1. forekomster av lakselus på utvandrende post smolt av laks som er sporet til en oppvekstelv, og 2. luseforekomster på trålfanget laksesmolt. Videre beskrives hvordan smittemodellen anvendes til beregning av smittebyrde, både av kjønnsmodne hunnlus og andre mobile stadier av lakselus, på utvandrende laksesmolt fra i alt 9 elver og 35 elve-år i PO3 og 22 elver og 91 elve-år i PO4 i Vestland. Endelig beskrives en analyse av effekten av beregnet smittebyrde på antall gytelaks som returnerer til disse elvene i gitte år.

Acoustic surveys of mixed fish aggregations often rely on manual allocation of acoustic energy to target species, with auxiliary information such as trawl catches and target strength distributions aiding interpretation. However, different teams of experts may use the same auxiliary data differently. In this experiment, seven teams of experts interpreted the same acoustic data, and we compared their classification to target categories to quantify uncertainty in the manual classification process. The teams largely agreed on the total acoustic energy attributable to organisms, but there was significant variation in how the teams split this energy on different target categories. This was caused by differences in applied thresholds for separating plankton and fish, as well as disagreements in species classification. For all target categories, the variation due to teams was lower than the overall variability across acoustic segments, but when scaled up to the number of segments in a typical survey, the team effect either dominated or was of similar magnitude as the segment variability. These results imply a need for further standardisation and uncertainty estimation of expert evaluations in acoustic surveys involving manual interpretation of echo sounder data.

During the COVID-19 pandemic in Norway, the testing criteria and capacity changed numerous times. In this study, we aim to assess consequences of changes in testing criteria for infectious disease surveillance. We plotted the proportion of positive PCR tests and the total number of PCR tests for different periods of the pandemic in Norway. We fitted regression models for the total number of PCR tests and the probability of positive PCR tests, with time and weekday as explanatory variables. The regression analysis focuses on the time period until 2021, i.e. before Norway started vaccination. There were clear changes in testing criteria and capacity over time. In particular, there was a marked difference in the testing regime before and after the introduction of self-testing, with a drastic increase in the proportion of positive PCR tests after the introduction of self-tests. The probability of a PCR test being positive was higher for weekends and public holidays than for Mondays-Fridays. The probability for a positive PCR test was lowest on Mondays. This implies that there were different testing criteria and/or different test-seeking behaviour on different weekdays. Though the probability of testing positive clearly changed over time, we cannot in general conclude that this occurred as a direct consequence of changes in testing policies. It is natural for the testing criteria to change during a pandemic. Though smaller changes in testing criteria do not seem to have large, abrupt consequences for the disease surveillance, larger changes like the introduction and massive use of self-tests makes the test data less useful for surveillance.

Lumpfish (Cyclopterus lumpus) are used as cleaner fish in Atlantic salmon (Salmo salar) aquaculture as one of multiple control measures against salmon lice (Lepeophtheirus salmonis). Numerous studies have documented weight as an important factor for characterising the cleaning efficacy of individual lumpfish. Hence, the efficacy of lumpfish in fish farms depends on the size at stocking and the weight development over time. Here, we aimed to quantify how weight developed over time for lumpfish deployed in salmon farming sea cages in Norway through modelling the daily growth rate. We found that the coefficient of variation for lumpfish weight increased over time, implying that the standard deviation increased more than the expected weight. The data thus showed heterogeneous growth for lumpfish in salmon farming cages, where some individuals exhibited no apparent growth, and others significant proliferation. We found that the daily growth rate was best described as bell-shaped functions of weight and temperature, consistent with a sigmoid-shaped growth curve and an optimal temperature around 10 °C. These results allow for more realistic modelling of the efficacy of lumpfish in controlling salmon lice in fish farms, as one can combine estimates of weight-dependent cleaning efficacy with weight development over time.

Climate sensitivity and aerosol forcing are two of the most central, but uncertain, quantities in climate science that are crucial for assessing historical climate as well as future climate projections. Here, we use a Bayesian approach to estimate inferred climate sensitivity and aerosol forcing using observations of temperature and global ocean heat content as well as prior knowledge of effective radiative forcing (ERF) over the industrial period. Due to limited information on uncertainties related to the time evolution of aerosol forcing, we perform a range of sensitivity analyses with idealized aerosol time evolution. The estimates are sensitive to the aerosol forcing pathway, with the mean estimate of inferred effective climate sensitivity ranging from 2.0 to 2.4 K, present-day (2019 relative to 1750) aerosol ERF ranging from −0.7 to −1.1 W m−2, and anthropogenic ERF ranging from 2.6 to 3.1 W m−2. Using observations and forcing up to and including 2022, the inferred effective climate sensitivity is 2.2 K with a 1.6 to 3.0 K 90 % uncertainty range. Analysis with more freely evolving aerosol forcing between 1950 and 2014 shows that a strong negative aerosol forcing trend in the latter part of the 20th century is not consistent with observations. Although we test our estimation method with strongly idealized aerosol ERF pathways, our posteriori estimates of the climate sensitivity consistently end up in the weaker end of the range assessed in the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR6). As our method only includes climate feedbacks that have occurred over the historical period, it does not include the pattern effect, i.e., where climate feedbacks are dependent on the pattern of warming which will likely change into the future. Adding the best estimate of the pattern effect from IPCC AR6, our climate sensitivity estimate is almost identical to the IPCC AR6 best estimate and very likely range.

The effective control of ectoparasitic salmon lice, Lepeophtheirus salmonis, in fish farms is challenged by the salmon lice having developed resistance towards several antiparasitic drugs and by the effectiveness of non-medicinal treatments being limited by considerations of fish welfare. When new antiparasitics are introduced to the market, these should be used sparingly to slow resistance development. Using a population model for salmon lice parameterised for salmonid fish farms in Norway, we quantified how reduced treatment effectiveness influences treatment frequency and lice abundance. Furthermore, we investigated when in the production cycle a highly effective lice treatment leads to the largest reduction in the total number of treatments, mean lice abundance and lice larvae production. Results showed that reductions in treatment effectiveness to lower than 50% led to the steepest increases in treatment frequency and mean lice abundance, as well as to increased risk that lice abundance increased beyond control. The timing of the most effective treatment had only moderate effects on the total treatment need and the mean number of adult female lice through the production cycle, but large effect on the production of lice larvae in spring. These findings imply that farmers can optimise the timing of the most effective treatment to reduce the release of lice larvae in the period of year when wild salmonids are in coastal waters, without compromising total treatment need or mean lice levels.

Atlantic salmon aquaculture may benefit from improved tools for behavioural monitoring and data-derived models that predict behaviour in commercial scale production cages. In the present study, timeseries depth registrations from individual farmed Atlantic salmon in commercial cages have been compiled from various projects, with the aim to resolve general swimming depth behaviour during the marine production stage. By implementing acoustic depth sensor tags, swimming depth data from 126 individuals of Atlantic salmon from ten different cages and five different farm sites were analysed over study periods lasting from 195 to 316 days. The study covers all seasons and were conducted at a latitude where there is hardly daylight during winter solstice nor nighttime or dusk during summer solstice. Average hourly swimming depth registrations for individual salmon were analysed by applying generalized additive modelling (GAM), where the main effects, hour of the day, temperature and sunlight hours were modelled as smooth terms in a non-linear way. The main effects were further modelled conditioned on the presence or absence of submerged lights and/or skirts used to shield the fish from salmon lice infestations. The results reveal that Atlantic salmon generally resided higher in the water column during nighttime than in daytime in all seasons except in the summer. The general tendency for diurnal depth patterns was most pronounced in winter and spring in cages without submerged lights, where average swimming depths varied from about 10–12 m during daytime to about 5–6 m during nighttime. The use of submerged lights in the cages disrupted the diurnal depth patterns and lead the fish to swim deeper in the water column during night-time in months with few sunlight hours. There was no substantial effect of the use of skirts on swimming depths. In addition to these general diurnal and day of the year trends, there were large individual variations in swimming depth. The study emphasises the utility of behavioural traits, particularly in modelling expected depth patterns as a surveillance tool in conjunction with real-time biomonitoring during the ongrowing phase at sea for Atlantic salmon.

Lumpfish (Cyclopterus lumpus) are extensively used as part of the control measures against salmon lice in fish farms. In recent years, there has been an increased focus on lumpfish welfare, and how to increase survival of lumpfish during production. To survey lumpfish welfare and compare welfare between different fish farms, welfare indicators are necessary. Condition factor is an attractive welfare indicator since it depends only on the length and weight of the fish, which is easy to measure and does not require euthanisation. Fulton’s K is commonly used to assess body condition for fish. However, this condition factor assumes isometric growth, which has been found not to be a reasonable assumption for lumpfish. In this study, we suggest an alternative expression for lumpfish body condition, which is based on almost 30 000 lumpfish sampled from Norwegian fish farms during production. The resulting condition factor is given as 5.85 ⋅ W∕L2.5016, where W is the lumpfish weight measured in grams, and L is the standard length measured in centimetres. We demonstrate that our proposed condition factor is more suitable for comparing body condition of lumpfish than Fulton’s K, since Fulton’s K is negatively correlated to length such that small fish tend to have high Fulton’s K factors. We conclude that Fulton’s K is an inappropriate indicator of lumpfish welfare, and propose to rather use a condition factor tailored to lumpfish, like the presently proposed condition factor. We also illustrate why standard length (length up to the caudal fin) is more appropriate for measuring body condition than total length (i.e. length including the caudal fin). For condition based on standard length, we found that caudal fin erosion was less prevalent among the lumpfish with comparatively higher body condition. The same relationship was not found for body condition based on total length.

The benchmark was tasked with evaluating proposed developments to the assessment model used for two stocks of harp seals (East Ice [White Sea/Barents Sea, seh.27.1] and West Ice [Greenland, seh.27.125a14]) and one stock of hooded seals (West Ice [Greenland, sez.27.2514]) in the Northeast Atlantic. The benchmark concluded that there were sufficient data to produce an assessment model for the West Ice (Greenland Sea) stock of harp seals but that data were insufficient for the East Ice (Barents Sea / White Sea) harp seal stock and too weak a signal for the West Ice hooded seals for viable assessments for these stocks.

Vi beregner her i hvilken grad passering av brønnbåter eller nærhet til slakterier øker risikoen for at fisken på et oppdrettsanlegg (lokalitet) blir smittet med PD (pancreas disease). Beregningene gjøres på grunnlag av data fra produksjonsområdene fra 2 til 7 fra starten av 2013 til midten av 2022. Vi bruker så en smittemodell for PD til å etablere sammenheng mellom registrert PD-smitte og ulike smittekilder. Den klart viktigste smittekilden er smitte fra naboanlegg, og 85 % av smittetilfellene tilskrives dette. Videre anslår vi at 12 % av smittetilfellene er relatert til at det var PD på forrige utsett på samme anlegg. Smitte relatert til nærhet til slakteri tilskrives 0,3 % av smittetilfellene. Når det gjelder brønnbåter tilskrives 0,2 % av smittetilfellene passering av brønnbåter og 0,2 % besøk av brønnbåter. Til sammen kan slakterier og brønnbåter tilskrives 0,7 % av smittetilfellene. Øvrige smittekilder utgjør 2,6 %. Det er viktig å redusere risikoen fra alle smittekilder, men når det gjelder PD er det aller viktigst er å hindre smitte mellom oppdrettsanlegg.

Retrospective patterns are commonly investigated to validate fish stock assessment models. A widely applied measure for retrospective bias is Mohn’s ρ and corresponding retrospective plots. However, retrospective patterns can be interpreted differently by experts. To make decisions regarding significant retrospective patterns less subjective, we proposed a post-sample Mohn’s ρ significance test. As case studies, we applied the state space assessment model SAM with data on Northeast Arctic cod and Norwegian coastal cod north of 67°N. We showed that the acceptance regions of Mohn’s ρ depends on both the data available and the assessment model complexity. We also assessed the test power under a range of assumption violations and conclude that Mohn’s ρ is useful for detecting violations associated with bias, but not for violations associated with variances and correlations.

We here estimate the effectiveness of ten types of salmon lice treatments currently used in the salmonid industry by analysing daily and cage-wise data from 90 full production cycles from farms spread along the Norwegian coast. The calculations are based on a stage-structured population model for salmon lice and accounts for the structure of the data, including the uncertainties that arise from the weekly counting of lice on a subset of the fish. Results suggest that the most commonly used treatment methods in the data set, i.e. thermal, mechanical and freshwater treatments, kill 70–80% of the lice in average, but with high variability. Feed treatments with emamectin benzoate are also commonly used, but are only estimated to kill around 35% of the lice in average. Bath treatments with hydrogen peroxide are estimated to kill around 74% and pyrethroids 50% of the lice in average. The other medicinal treatments were infrequently used in the data set and the estimates are therefore more uncertain. Of note is that the recently licenced bath treatment with imidacloprid is estimated to kill more than 99% of sessile and 98% of pre-adult and adult lice in average. The estimated effects of hydrogen peroxide, pyrethroids and azamethiphos, here based on data from 2017–2020, are lower than estimates from a previous analysis of production data from 2011–2014, possibly because of resistance development. In contrast, there is no indication of reduced effects of thermal, mechanical or freshwater treatments compared to previous analyses of production data from 2013–2018. These results allow comparing the effectiveness of the different treatment methods in a consistent and comprehensive way, hence enabling fish farmers and authorities to better balance the expected benefits of the treatments in terms of lice control against the economic costs, fish welfare and risk of resistance development.

Atlantic salmon aquaculture employs lumpfish as a control method to combat ectoparasites, given their unique cleaning behaviour. There are multiple studies which estimate the average number of salmon lice in the stomach contents of dissected lumpfish. However, these numbers cannot be used to assess the cleaning efficacy of lumpfish (e.g., the average number of lice consumed daily per lumpfish) without knowing the digestion time of lice in lumpfish. The aim of the study was to provide quantitative estimates of the degradation of salmon lice, through a blinded clinical study over a duration of seven days. Individually tagged lumpfish (45.8 g, SD ± 10.28) were randomly arranged in triplicate tanks (n = 28 per tank) and acclimatised for three days. Subsequently, lumpfish were fed using oral gavage dosing with counts of lice (0–6), feed pellets (0–6) or a combination of both. Lice used were recently captured and stored at −80 °C to prevent parasite transmission at the study location and photographed before and after digestion to estimate degradation. Samplings ranged from 6 h intervals during the first two days, to 24 h and eventually 48 h for the last two days. Analysis of salmon lice revealed an expected digestion time of 29 h while the median digestion time was estimated to 15 h at 9 °C. Pellets dissolved quickly and had no impact on the lice digestion time. The findings of this study can be used to estimate cleaning efficacy of lumpfish from stomach contents of salmon lice.

Cleaner fish are commonly used as a control measure against salmon lice infestations in salmonid farms. Lumpfish (Cyclopterus lumpus) is the most common cleaner fish species used in Norwegian farms. However, little is known about how different operational, including environmental, conditions affect the salmon lice grazing efficacy by lumpfish. In this paper, we analyse salmon lice (Lepeophtheirus salmonis) in the stomach contents of a large sample of more than 20,000 lumpfish from 80 different Norwegian farms. We investigate the proportion of lumpfish with salmon lice and the mean number of salmon lice in the stomach contents of the lumpfish. We further explore how the salmon lice contents vary with different factors like lumpfish weight, weight of salmonids, salmon lice abundance in the cage, cloud cover, and sea temperature. We find that 3.1% of the 24,693 lumpfish contained salmon lice. Most of the lumpfish with salmon lice in their stomach contents contained few (one or two) lice, while there were a few lumpfish which contained many salmon lice. We find more salmon lice in the stomach contents with increasing abundance of salmon lice in the sea cage, lower weight of the salmonids, and in clear weather. Interestingly, for the relationship between lumpfish weight and salmon lice in the stomach contents, we find increased salmon lice grazing from ca. 5 g up to an optimal weight of ca. 40 g, and then a decrease from 40 g. Surprisingly, we find no relationship between sea temperature and salmon lice per lumpfish. We find more salmon lice in the stomach contents of the lumpfish with comparatively high condition. By studying the factors associated with most efficient salmon lice grazing, our paper contributes to understanding how different operational factors affect salmon lice grazing by lumpfish. For controllable factors, the results thus contribute to guiding the best practice for use of lumpfish as a salmon lice control measure.

Infeksiøs lakseanemi (ILA) er en alvorlig virussykdom som forårsaker økonomisk tap og redusert velferd hos atlantisk oppdrettslaks. Vi har undersøkt forskjellige kontrollstrategier, eller scenarier, for mulige tiltak for å bekjempe ILA. Strategiene inkluderer vaksinering, utslakting etter klinisk ILA-utbrudd, screening med påfølgende utslakting ved påvist ILA-virus og kombinasjoner av de ulike strategiene. Vi beregner hva hver strategi medfører av antall smittetilfeller og registrerte kliniske utbrudd av ILA. De samme beregningene gjøres for en strategi der vi ikke gjennomfører tiltak i det hele tatt. For å komme frem til resultatene simulerer utviklingen av smitte fremover i tid ved hjelp av en statistisk modell for spredning av ILA. Modellen beskriver hvordan smitte- og utbruddsdynamikken påvirkes av ulike faktorer som inkluderer smittestatus på de ulike oppdrettslokalitetene, anleggenes beliggenhet, størrelsen av anleggene og tid på året. For å estimere modellen benytter vi historiske produksjonsdata som dekker alle oppdrettsanlegg i Norge i perioden f.o.m. januar 2004 t.o.m. februar 2019. I denne perioden ble det påvist 142 kliniske ILA-utbrudd. Fra den estimerte modellen finner vi at omtrent halvparten av all smitte kommer fra smittet fisk på naboanlegg. En stor del av den resterende smitten skyldes trolig infeksjon med virusvarianten HPR0 som har utviklet seg til HPRdel-varianten. For hvert scenario vi undersøker, tar vi utgangspunkt i en gitt nåsituasjon og simulerer hvordan ILA utvikler seg ti år frem i tid. For at simuleringene skal bli mest mulig realistiske, antar vi at beliggenheten av anleggene og produksjonsperiodene er som i perioden f.o.m. mars 2009 t.o.m. februar 2019. Samtidig antar vi at gjennomsnittlig antall fisk per lokalitet er omtrent som i februar 2019 gjennom hele simuleringsperioden. Simuleringene viser at smitten stabiliserer seg på et nytt nivå etter et par år avhengig av hvilken kontrollstrategi som benyttes. Vi finner at 18,4% av alle utsett i Norge vil få påvist et klinisk utbrudd av ILA dersom vi ikke bruker kontrolltiltak. Dersom vi gir alle utsett en vaksine som reduserer sannsynligheten for å bli smittet med 50%, vil andelen med utbrudd bli rundt 3,8%. Dersom vi istedenfor vaksinering velger utslakting seks uker etter deteksjon av utbrudd, reduseres andelen med utbrudd til 3,4%. Andelen reduseres ytterligere til 0,36% ved screening av 20 fisk hver fjerde uke og utslakting seks uker etter deteksjon av virus. Vår studie viser hvordan scenariosimulering kan benyttes som verktøy for beslutningsstøtte.

Mortality in the production of farmed salmonids is a major constraint to the sustainability of this form of animal husbandry. We have developed a model for the daily mortality in salmon farming over a full production cycle from stocking to harvest, considering different environmental and production factors. These factors included sea temperature, salinity, day within year, fish weight at stocking, stocking day, four types of lice treatments and the possible occurrence of pancreas disease (PD). We considered a generalized additive model following full production cycles, allowing for non-linear descriptions of how relevant factors relate to the daily mortality. We saw a high overall mortality rate immediately after stocking, which decreased the first three months in the cycle and thereafter increased. We found that the total mortality could be reduced by 21% if avoiding all lice treatments, and similarly reduced by 20% if no PD infections occurred. If avoiding jointly PD and all lice treatments, the accumulated mortality could be reduced by 34%. A single thermal or hydrogen peroxide treatment was associated with a mortality of around 1.6% and 1.3%, respectively. This modeling approach gave a unique opportunity to model how different factors interact on the overall global mortality and can easily be extended by other factors, such as additional fish diseases.

Thermal protection in marine electrical propulsion motors is commonly implemented by installing temperature sensors on the windings of the motor. An alarm is issued once the temperature reaches the alarm limit, while the motor shuts down once the trip limit is reached. Field experience shows that this protection scheme in some cases is insufficient, as the motor may already be damaged before reaching the trip limit. In this paper, we develop a machine learning algorithm to predict overheating, based on past data collected from a class of identical vessels. All methods were implemented to comply with real-time requirements of the on-board protective systems with minimal need for memory and computational power. Our two-stage overheating detection algorithm first predicts the temperature in a normal state using linear regression fitted to regular operation motor performance measurements, with exponentially smoothed predictors accounting for time dynamics. Then it identifies and monitors temperature deviations between the observed and predicted temperatures using an adaptive cumulative sum (CUSUM) procedure. Using data from a real fault case, the monitor alerts between 60 to 90 min before failure occurs, and it is able to detect the emerging fault at temperatures below the current alarm limits.

Pancreas Disease (PD) is a viral disease caused by Salmonid Alphavirus (SAV). It affects farmed salmonids in the North Atlantic, and leads to reduced feed intake and increased mortality with reduced production and welfare as a consequence. In 2013, the estimated cost of an outbreak on an average salmon farm was about 6.6 mil €. In Norway, PD has been notifiable since 2008, and regulations to mitigate disease spread are in place. However, despite the regulations, 140–170 farms are affected by PD every year. The aquaculture industry is growing continuously, introducing farms in new geographical areas, and fish are moved between hydrographically separated zones for trade and slaughter. All such movements and relocations need to be approved by the competent authorities. Thus, there is a demand for support to farmers and competent authorities when making decisions on disease management and especially on the effect of moving infected fish. We have used a disease-transmission model for outbreak-simulation in real time for assessing the probability of disease transmission from a farm that gets infected with PD. We have also simulated the effects of three different control-regimes: no stamping-out, delayed stamping-out or immediate stamping-out, on the transmission of PD to surrounding farms. Simulations showed that the immediate stamping out of an infected farm led to effective containment of an outbreak. No stamping out led to up to 32.1% of farms within 100 km of the index farm to become effected. We have used real production data for the model building and the scenario simulations, and the results illustrate that a risk assessment of horizontal disease transmission must be undertaken on a case-by-case basis, because the time and place of the outbreak has a large influence on the risk of transmission.

We consider the challenge in estimating the natural mortality, M, in a standard statistical fish stock assessment model based on time series of catch- and abundance-at-age data. Though anecdotal evidence and empirical experience lend support to the fact that this parameter may be difficult to estimate, the current literature lacks a theoretical justification. We first discuss the estimatability of a time-invariant theoretically and present necessary conditions for a constant M to be identifiable. We then investigate the practical usefulness of this by estimating from simulated data based on models fitted to 19 fish stocks. Using the same data sets, we next explore several model formulations of time varying M, with a pre-specified mean value. Cross validation is used to assess the prediction performance of the candidate models. Our results show that a time-invariant M can be estimated with reasonable precision for a few stocks with long time series and typically high values of the true . For most stocks, however, the estimation uncertainty of M is very large. For time-varying M, we find that accounting for variability across age and time using a simple model significantly improves the performance compared to a time-invariant M. No significant improvement is obtained by using complex models, such as, those with time dependencies in variability around mean values of M.

I dette notatet vurderer vi ulike tiltak mot lakselus i produksjonsområde 3, et intensivt produksjonsområde som står i fare for å miste retten til produksjonsvekst, på grunn av høyt smittepress av lakselus. For å kunne vurdere effekter av ulike tiltak, tilpasser vi en eksisterende lusemodell til oppdaterte data. Deretter bruker vi den tilpassede lusemodellen til å simulere lus over tid. Vi undersøker effekten av ulike tiltaksgrenser for behandling, å slå sammen lokaliteter, mer bruk av storsmolt og økt bruk av forebyggende tiltak mot lus. Effekten av å slå sammen lokaliteter sammenliknes med tidligere resultater fra Havforskningsinstituttet og Veterinærinstituttet. Vi undersøker også hvordan lusemodellen kan ta i bruk strømkontakt mellom lokaliteter i stedet for smittekontakt basert på sjøavstander som er brukt fram til nå.

Norway produces more than one million tonnes of salmonids every year, almost exclusively in open-water net pens. In 2014, the Norwegian government announced plans to increase salmonid production. However, increasing the number of farmed salmonids can have negative effects on the marine environment that threaten the industry’s sustainability. In particular, production growth can lead to an increase in density-dependent diseases, including parasitic sea lice. The aim of this study was to simulate the effects of increased salmonid production on sea lice abundance using different scenarios for increasing the number of fish and for the management of sea lice. We used a previously developed, partly stage-structured model based on Norwegian production and environmental data to simulate the different scenarios. Our results show that increasing the marine farmed salmonid population at a national level by two or five times the current production leads to an increase in the sea lice abundance by 3.5% and 7.1%, respectively. We also found that by lowering the maximum allowable level of sea lice to an average of 0.049 adult females per fish, weekly treatments can be used to control sea lice population growth with a five times increase in production. However, this increases the number of farms treating per week by as much as 281.3%, which can lead to high costs and increased mortality among farmed salmonids. Overall, the results from our study shed light on the effects of increasing salmonid production in Norway with respect to the ongoing threat of sea lice infestations.

Infectious salmon anaemia (ISA) is an important viral disease causing economic losses and reduced welfare in farmed Atlantic salmon. Here, we present a spatio-temporal stochastic model for the spread of ISA between and within marine aquaculture farms. The model is estimated on historical production data for all marine salmonid farms in Norway from 2004 to February 2019. In this time 142 outbreaks of ISA occurred. We find that transmission from infected neighbouring farms accounts for around 50% of the infections, whereas transmission from “non-specified sources” accounts for around 40%. We hypothesise that the most important of the latter are viruses mutating from the non-virulent ISAV HPR0 to the virulent ISAV HPRdel. The model is used for scenario simulation, or what-if analysis, to investigate the effects of potential strategies to combat ISA, including screening, vaccination and culling. Changing from the current strategy of culling farms with detected ISA-outbreaks to mandatory screening and culling when virus is detected will reduce the fraction of cohorts with a clinical ISA outbreak from 3.8 to 0.36%. Introducing mandatory vaccination would have approximately the same effect as the current stamping-out strategy. The scenario simulation is a useful tool for deciding on appropriate mitigation measures.

The REDUS project (2016-2020) has been a strategic project at the Institute of Marine Research (IMR) aimed at quantifying and reducing the uncertainty in data-rich and age-structured stock assessments (e.g., cod, herring, haddock, capelin). Work was organized in four topical work-packages: Fisheries-dependent (catch) surveys and assessment modeling (WP1), Fishery-independent (scientific) surveys (WP2), Evaluating and testing of long-term management strategies (WP3), and Communication of uncertainty, dissemination of project results and capacity building (WP4). The Norwegian Computing Center (NR) was contracted in as a strategic partner in statistical modeling and analysis, contributing mainly to WP1 and WP2, but found the research of fundamental interest therefore also allocating internal (NR) funding to develop the statistical science base of several of the methods.

I dette notatet, ser vi på lusebeitingsadferd hos rognkjeks, og undersøker hvordan lusebeiting avhenger av vekt. Fra fangst-gjenfangst forsøket i CycLus, har vi informasjon om mageinnhold av lakselus på totalt n = 599 rognkjeks, fra lokalitetene Kråkholmen og Nausttaren.

This paper considers a general state-space stock assessment modeling framework that integrates a population model for a fish stock and a data model. This way observed data are linked to unobserved quantities in the population model. Using this framework, we suggest two modifications to improve accuracy in results obtained from the stock assessment model SAM and similar models. The first suggestion is to interpret the “process error” in these models as stochastic variation in natural mortality, and therefore include it in the data model. The second suggestion is to consider the observed catch as unbiased estimates of the true catch and modify the observation error accordingly. We demonstrate the efficacy of these modifications using empirical data from 14 fish stocks. Our results indicate that the modifications lead to improved fits to data and prediction performance, as well as reduced prediction bias.