Researchers from Shandong University Reveal How Ocean Mesoscale Eddies Modulate Global Human Fishing Activities

JINAN,China,March 28,2023 --Fishing is one of the oldest forms of human use of the ocean,playing an important role in supporting food security and in national revenues and employment. Recently,researches from the Institute of Marine Science and Technology,Shandong University,have published a research paper entitled "Mesoscale eddies modulate the dynamics of human fishing activities in the global midlatitude ocean" in Fish and Fisheries. For the first time,this study quantified the global pattern of how mesoscale eddies affect fishing activities and found that fishing activities (mainly targeting tuna) in mid-latitude oceans exhibit opposite responses to cyclonic eddies and anticyclonic eddies. The study also proposed a novel "ecological conduits (barriers)" hypothesis related to mesoscale eddies to explain this phenomenon.

Mesoscale eddies are high-energy rotating water masses that are widely present in the upper ocean,with spatial scales ranging from 10s-100s km and typically lasting for weeks even years. The complex physical processes caused by mesoscale eddies,such as trapping,stirring,pumping,and mixing,dominate local biogeochemical processes. Generally,cyclonic eddies are considered to be regions of high primary productivity and conversely,anticyclonic eddies are thought to be impoverished "ocean deserts". Due to the changes in local environmental and foraging conditions caused by eddies,the distribution of high trophic organisms,such as fish species,are expected to be significantly affected,which in turn affects human fishing activities.

Clarifying the effects of mesoscale eddies on these high trophic organisms is key to the comprehensive understanding of the biophysical interactions in the ocean as well as the fishermen decision-making behaviors.

It has been challenging to comprehensively understand the influence of mesoscale dynamics on fish distribution. The impact of cyclonic and anticyclonic eddies on the distribution of high trophic level organisms has been a subject of controversy due to the strong migratory behavior of these high trophic level organisms and the limited observational data. Here,for the first time,researchers used large-scale fishing activity data derived from deep learning algorithms as an indicator of fish distribution and combined it with satellite observations of mesoscale eddies to statistically quantify global patterns of mesoscale eddy influence on human fishing activities.

Interestingly,the research showed that fishing activities mainly targeting tuna in mid-latitude oceans were more frequently concentrated in the core of anticyclonic eddies and farther away from the core of cyclonic eddies. By combining satellite observations of sea surface and deep ocean data from ARGO/BGC-ARGO,this study found that the global pattern of eddy-induced fishing activities was significantly related to the temperature and dissolved oxygen distribution of deeper water masses within mesoscale eddies. Scientifically,the warm and oxygen-rich deeper water masses formed an "ecological conduit" within anticyclonic eddies,facilitating deep diving foraging of tuna. In contrast,cold and hypoxic cyclonic eddies acted as "ecological barriers," making it difficult for tuna to dive deep and search for food for prolonged periods of time.

In comparison,the intensity of mesoscale eddies in low-latitude waters is much weaker,making this pattern mainly restricted to mid-latitude waters. These findings provide important support for elucidating the physical-biological coupling mechanisms of mesoscale dynamics and offer new insights for improving the prediction of fishery resources and potential fishing grounds.

Clarifying the spatiotemporal variations in fishing activities has important practical implications for improving the prediction of fishery resources and potential fishing grounds,and promoting the sustainable development and management of fishery resources.

In recent years,Institute of Marine Science and Technology,Shandong University has been dedicated to establishing high-quality and internationally influential research on the frontiers of marine climate,marine science and technology. The institute conducts several national key programs and has close collaborations with many countries,including building SDU-DAL joint lab (LORE) with Dalhousie University. The path of its development shows the whole chain of "process-key technologies-validation-designing equipment model",which is a great advantage of Ocean Carbon Sink and mCDR technology. Lately,the institute made advanced progress in the areas of ocean negative carbon emissions,the marine microbial diversity,eukaryotic genome evolution,Raman spectroscopy and its application.

The article can be accessed at https://doi.org/10.1111/faf.12742.