Nora Røhnebæk Aasen

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.

I denne rapporten estimerer vi mengden bundet og forbrukt plast i resirkuleringssystemet (dagens system) og et ombrukssystem for PET-flasker som drikkevareemballasje. Vi beregner og sammenligner forbrukt og bundet plast for PET-flaskene både isolert sett og når vi tar hensyn til lastbærere som plastkasser, -brett og -sekker som brukes til frakt og lagring av flaskene. Bundet plast er beregnet utfra antall flasker (med tilhørende lastbærere) som til enhver tid må innes for å holde det sirkulære systemet gående. Her finner vi at antall flasker som bindes opp er større i ombrukssystemet, hvilket skyldes en større følsomhet for sesongvariasjon og logistikkubalanse. Ettersom flaskene også veier mer i ombrukssystemet, blir effekten ytterligere forsterket når vi ser på mengden plast istedenfor antall flasker. Vi estimerer mer enn dobbelt så mye plast i ombrukssystemet som i resirkuleringssystemet. Hvis vi også tar hensyn til lastbærere i form av plastkasser, -brett og -sekker, blir forskjellen mellom systemene i bundet plast enda større. Forbruk av plast er her definert som mengden jomfruelig plast som må tilføres systemet for å dekke tapet av plast. Her finner vi at forbruket er større i ombrukssystemet enn i resirkuleringssystemet for små PET-flasker, og mindre for store PET-flasker. Dette skyldes blant annet at pantegraden er høyere for store PET-flasker enn for små PET-flasker. Totalt har ombrukssystemet størst plastforbruk når vi inkluderer forbruket fra plastkasser, -brett og -sekker. Plastforbruket fra PET-flasker i ombrukssystemet går ned ved høyere pantegrad. I resirkuleringssystemet får man en begrensende faktor i form av andel resirkulert plast som kan benyttes i nye flasker. Dette fører til at vi ved høy pantegrad ikke ser en nedgang i plastforbruket fra PET-flasker til tross for videre økning i pantegraden.

In this report, we estimate the amount of tied up plastic and plastic consumption in the single-use system (the current system in Norway) and a reuse system for PET bottles as beverage packaging. We calculate and compare the consumed and tied up plastic for PET bottles both isolated and when accounting for Transport Items such as plastic crates, trays, and bags that are used in shipping and storing of the bottles. Tied up plastic is calculated from the number of bottles (and corresponding Transport Items) that at all times must exist in order to keep the circular material system operational. Here we find that the number of bottles that are tied up is greater in the reuse system than in the single-use system, which is due to a higher sensitivity to seasonal variation and logistical imbalance. As the bottles weigh more in the reuse system, the effect is further reinforced when we consider the amount of plastic instead of the number of bottles. We estimate more than twice as much tied up plastic in the reuse system as in the single-use system. If we also take into account Transport Items in the form of plastic crates, trays, and bags, the difference between the systems becomes even greater. Plastic consumption is here defined to be the amount of virgin plastic that must be put in to the system to cover the loss of plastic. Here we find that consumption is greater in the reuse system than in the single-use system for small PET bottles, and smaller for large PET bottles. This is partly due to the fact that the DRS collection rate by unit is higher for large PET bottles than for small PET bottles. In total the reuse system has the highest plastic consumption when we take into account the consumption of plastic crates, trays, and bags. Plastic consumption from PET bottles in the reuse system decreases as the DRS collection rate by unit increases. In the single-use system there is a limiting factor in terms of the proportion of recycled plastic that can be utilized in new bottles. Hence, after a certain threshold of high DRS collection rate by unit we do not see a decrease in plastic consumption from PET bottles despite further increase in the DRS collection rate by unit.