Horse mackerel DNA concentrations were higher near floating wind turbines off Japan

Researchers at Nagasaki University conducted water sampling across multiple depth layers—surface, middle, and bottom—near floating wind turbines fixed off Japan’s Goto Islands and at control stations.

It was established through the use of environmental DNA that there were large quantities of DNA shed by Japanese horse mackerel swimming near the floating steel turbines.

The maximum eDNA concentration recorded at a floating wind turbine station reached 2,280 copies/liter, compared to a maximum of 783 copies/liter measured at control stations.

Measuring aquatic life without catching a single fish

Water sampling across water layers provides marine biologists with a means of determining the presence of microscopic skin cells, mucus, and metabolic waste produced by fish passing through the area.

Environmental DNA sampling enables scientists to determine which species are present without having to use any form of invasive fishing nets or underwater cameras within the murky coastal waters.

The use of net collection systems near offshore infrastructure is dangerous because of the mooring cables and electricity lines that run underwater.

Nets can get tangled up in the underwater anchors made from steel, which can end up causing damage to the scientific equipment as well as the underwater electrical equipment.

Sampling the water bottles converted industrial turbine legs into biological habitat stations.

Transforming floating turbines into artificial reefs

The massive floating wind platforms project many feet into the ocean and are anchored at the bottom of the sea with heavy steel mooring cables.

The significantly higher eDNA concentrations suggest a potential aggregation or artificial-reef effect surrounding the floating structures.

While floating offshore wind infrastructure may attract fish schools, the specific driver behind this pattern remains unresolved.

Aggregation around the turbines is hypothesized to explain the elevated genetic material, but further investigation—combining eDNA sampling with visual (ROV) and acoustic tracking—is required to determine the exact mechanisms involved.

Distinguishing fish aggregation from true population growth

Fisheries biologists caution that elevated eDNA levels reflect species attraction and aggregation rather than true population growth, as drawing Japanese horse mackerel to floating structures does not translate to an increase in total biomass.

A potential artificial-reef effect may gather moving fish around the platform vessels, though whether this represents true population growth or temporary aggregation remains an open question.

The shadows created in the water underneath the giant pontoon hulls also create a quiet environment for fish.

A high concentration of fish near an energy facility may lead to the threat of concentrated fishing operations on the edge of such an area.

It is necessary to create a buffer zone for such fish in order to prevent commercial fishing in the vicinity.

Concentrating Japanese horse mackerel around floating platforms does not indicate an overall increase in fish population size.

Expanding environmental monitoring across offshore wind farms

The Japanese government intends to install many floating wind turbines within the deep coastal waters in order to achieve its clean energy objectives.

The regulatory framework stipulates that all energy projects developed offshore must undertake constant biological impact monitoring for the whole life of the projects.

Using standardized water sampling helps reduce costs associated with monitoring surveys and offers repeatable genetic data over large offshore leases.

Multi-species DNA sequencing helps scientists monitor many commercially important fish species in one go from water samples.

By using multi-depth eDNA monitoring together with water samplers, the operators are able to monitor biological impacts during annual fish migrations.

Genetic monitoring provides wind farm operators with an efficient approach for monitoring the marine environment, as reported by the University of Nagasaki.

Identifying the limits of genetic water sampling

High concentrations of eDNA indicate a strong spatial association between Japanese horse mackerel presence and the floating turbines.

The floating DNA indicates the biological waste being shed, not the actual number of living fish.

Very strong tides may carry the shed genetic material several miles away from the place where the fish group swims.

Temperature variations affect cell shedding and hasten the degradation of the floating DNA.

eDNA samples collected across depth layers indicate genetic presence, but cannot determine whether the DNA comes from healthy adult fish, young fish, or decaying biological material.

While higher eDNA levels suggest floating turbines attract Japanese horse mackerel, these genetic concentrations indicate localized aggregation rather than population growth, which must be evaluated by combining eDNA data with acoustic and visual tracking.

All the study details can be read here: Tsuchida, S., Kato, R., Nishitsuji, S., Anzai, S., Azmi, S. S., Tanaka, S., … & Yagi, M. (2025). Floating Offshore Wind Farms Attract Japanese Horse Mackerel. Aquatic Conservation: Marine and Freshwater Ecosystems, 35(7), e70189.