Distribution change of Orcinus Orca in the North-East Atlantic caused by overfishing and sea-surface temperature change

Sammanfattning

This study investigates the effects of overfishing and sea-surface temperature changes on the distribution of [i]Orcinus Orca[/i] in the North-east Atlantic and aims to evaluate which factors contribute the most to these shifts in orca presence. As apex predators, killer whales can have a great impact on ecosystems and food webs, and a migration to polar ecosystems could have big impacts on arctic systems and food availability for local species and indigenous peoples. Orca occurrence data from OBIS Sea map was used to analyze orca distribution from 1980 to 2024. Additionally, fish stock data for Atlantic herring and Atlantic mackerel and SST data and chlorophyll-a concentration was compared to the estimated “Orca population”. A big emphasis was put on assessing and eliminating observer bias. Findings of this study include a distribution shift of killer whales in the region primarily in connection to Atlantic herring and mackerel stock migration. The observed trends of the factors “Orca population”, Atlantic herring and mackerel stocks and of chlorophyll-a distribution are consistent with SST and a changing climate. In conclusion, these changes force a shift in orca distribution and could cause a new distribution in overall areas of high marine productivity.