Search

Prosjektleder Trine Dale Noen ganger forårsaker oppblomstringer av alger og maneter skadelig for akvakulturvirksomhet og forårsaker fiskedød og redusert fiskevelferd. Et ferskt eksempel er oppblomstringen av Chrysochromulia leadbeateri i 2019 som forårsaket massiv fiskedød og store tap for de oppdretterne som ble berørt. Det er en bekymring for at havbruksnæringen vil oppleve økte problemer med skadelige alger og maneter i fremtiden grunnet klimaendringer. Et steg på veien mot et system som kan bidra til å forebygge og håndtere episoder med skadelige alger og maneter er å sammenstille eksisterende kunnskap, både den som finnes i forsknings- og teknologimiljøene og den som næringen selv besitter. I dette prosjektet har vi samlet vitenskapelig og erfaringsbasert kunnskap om hvordan skader grunnet alger og maneter kan forebygges og håndteres, og laget en prototype på et brukervennlig verktøy som tilgjengeliggjør dette kunnskapsgrunnlaget. Vi har innhentet erfaringsbasert kunnskap gjennom dybdeintervjuer med oppdrettere og fiskehelsepersonell fra Norge, Chile, Canada og UK. Her rapporteres resultatene fra disse intervjuene herunder respondentenes beskrivelser av hvordan episoder med skadelige alge og manetoppblomstringer arter seg, deres erfaringer med ulike avbøtende tiltak og hvordan disse har virket, tanker omkring hvordan man kan bygge beredskap for fremtiden. FHF – Fiskeri- og havbruksnæringens forskningsfinansiering

The ecosystems with their relationships between fish species and stocks, have been established by evolution for millions of years, but during the last 50 years, the ecosystems in the North Sea and along the Norwegian coast have been changed fundamentally by fisheries. The North Sea mackerel stock has been depleted and its feeding grounds have been invaded by the Western mackerel which spawns west of Ireland. This stock is now very rich in numbers and occupies the North Sea, the Norwegian Sea and the western Barents Sea. If the trend continues, mackerel may outcompete many of the other fish stocks in the area. Traditionally and until the beginning of the 1970s, there was a large stock of sandeel spawning in the North Sea and on the Norwegian coast. Sandeel juveniles was an important food source for a wide range of species, including sea mammals and birds. The fact that this stock has also been overfished, may explain many changes observed in the ecosystem on the west coast of Norway, for example a large reduction in the populations of sea birds. There are several instances where ecosystems shift to sustain jellyfish blooms in response to depletion of forage fish stocks. This was registered in Namibia in the 1990’s, where the pilchard stock was decimated and the biomass of jellyfish soon became overwhelming. On the west-coast of Norway, there are now frequent blooms of jellyfish, yet another indication that a controlling factor is missing in the system, in this case sandeel, which is a key species in the transfer of nutrients from zooplankton to higher trophic levels in the area. In this paper, I give a description of the situation and some suggested measures that should be taken in fisheries management.

Disclaimer: This article was prepared by Johannes Hamre in his personal capacity. The opinions expressed in this article are the author's own and do not reflect the views of the Institute of Marine Research The ecosystems with their relationships between fish species and stocks, have been established by evolution for millions of years, but only during the last 50 years, the ecosystems in the North Sea and along the Norwegian coast have been changed fundamentally by fisheries. The North Sea mackerel stock has been depleted and its feeding grounds have been taken over by the Western mackerel which spawns west of Ireland. This stock is now very rich in numbers and distributes into the North sea, the Norwegian sea and the western Barents Sea. If the stock of Western mackerel is allowed to grow further it may outcompete many of the other fish stocks in the area. 50 years ago there was a large stock of sandeel, which spawned in the North Sea and on the Norwegian coast. Sandeel juveniles was an important food source for a wide range of species, including sea mammals and birds. The fact that this stock has also been overfished, may explain many of the changes seen in the ecosystem on the west coast of Norway, for example a large reduction in the populations of sea birds. There are indications that ecosystems shift to sustain jellyfish blooms in response to depletion of forage fish stocks. This was registered in Namibia in the 1990’s, where the pilchard stock was decimated and the biomass of jellyfish was overwhelming. On the west-coast of Norway, there are now frequent blooms of jellyfish, yet another indication that sandeel, a key species in the transfer of nutrients from zooplankton to higher trophic levels in the area, has been depleted. In this paper, I give a description of the situation and some suggested measures that should be taken in fisheries management.