C-DRONE GUIDE · 22 SEPTEMBER 2026
Marine cage fish farming: what a drone documents on an offshore sea bass and bream farm, price
An offshore fish farm looks like no other livestock operation: its stock lives below the waterline, in floating cages anchored on a plot of public maritime domain that the operator only holds under concession. The French sector stays modest — 34 companies, 688 jobs — but is heavily concentrated around two species, sea bass and sea bream, and a handful of coastlines where Corsica alone accounts for a third of national output. Here is what a marine-culture concession requires, what a drone flight concretely documents on the surface structures, and why most of what actually matters — underwater — stays entirely out of its reach.
Published on 22 September 2026, reviewed on 22 September 2026 — regulations in force as of September 2026.
A concession, not ownership: the AECM and ICPE heading 2130-2
Raising fish offshore first requires obtaining an authorisation to operate marine cultures (AECM) on a precisely delimited plot of the public maritime domain. This authorisation is issued by the prefect, after an opinion from the marine cultures commission of the departmental directorate for territories and the sea (DDTM) and a public inquiry, for a term of up to 35 years. The regime, originally set by the decree of 22 March 1983, is now codified in book IX of the rural and maritime fishing code devoted to marine aquaculture, following a recodification completed in late 2014. The operator therefore never owns the water plot: they temporarily occupy a public plot, under precise location and footprint conditions that the concession fixes to the metre.
These facilities also fall under the nomenclature of installations classified for environmental protection, under heading 2130-2 "sea-water fish farming": declaration between 5 and 20 tonnes of annual production, prefectural authorisation beyond that. The sector stays concentrated: France counted 34 marine fish-farming companies and 688 jobs in 2021, for two dominant species — sea bass (2,570 t) and sea bream (1,872 t) — nearly half of which is produced in Corsica, Provence-Alpes-Côte d'Azur and Nouvelle-Aquitaine. Corsica alone gathers 4 farms (sea bass, sea bream, meagre) for around 1,000 tonnes a year, half of French Mediterranean output and 16% of national production, for around a hundred direct jobs.
This activity should not be confused with the two other marine cultures already covered in our guides: shellfish farm monitoring covers fixed installations on racks or tables, mostly exposed at low tide and fully surveyable from the air, while freshwater pond fish farming is a land-based operation, with no public maritime domain concession or floating cage in open sea.
What the drone documents: the floating structures, never what they hold
The drone stays above the water, and that is exactly what defines what it can bring an operator. It produces a georeferenced orthophoto of the whole concession, useful for checking that the actual position of the cages matches the plan appended to the AECM — a gap of a few metres between the observed layout and the authorised plan is grounds for a remark when the concession comes up for renewal. It documents the visible condition of the surface structures: buoys, visible anchor blocks, mooring-line tension, the walkways and floating collars that carry the cages, and the anti-predator nets stretched above the waterline against cormorants and gulls — their presence, their tension, a visible tear at the surface.
A second, more occasional use: before/after storm assessment. A cage that has drifted, a displaced anchor block, a snapped mooring line can be documented in a few minutes of flight, with a dated orthophoto backing an insurance claim or a report to the DDTM. Schooling behaviour at the surface after feeding — fish briefly rising to feed — can also be filmed, but stays a qualitative sign of general vitality, never a measure of density or stock.
This scope stays strictly at the surface: the drone replaces neither the periodic diving inspection of the net nor the mooring check by a certified professional, which remain the only reliable sources on the condition of what is submerged.
The honesty clause: everything that matters happens below the waterline
The honesty clause. Most of what makes up a fish cage is submerged, and none of it is visible from a drone: the integrity of the net below the surface (holes, wear, chafe points on the frame), mortality at the bottom of the cage, water quality at depth (dissolved oxygen, temperature, current) that directly governs the stock's survival, and above all the actual biomass — the real number and weight of fish present. Checking the submerged net is the exclusive job of a professional diver or a certified remotely operated vehicle (ROV), never aerial imagery.
A team from Stanford's Regulation, Evaluation and Governance Lab published a computer vision model in 2024 that automatically detects 4,010 fish cages (average area 69 m²) from aerial and satellite imagery of the French Mediterranean between 2000 and 2021, aiming to estimate the sector's production from cage surface area alone. The notable point for an operator: the authors had to build an entire dedicated uncertainty-quantification framework around that estimate — proof, through the method itself, that a cage's size seen from above is only an indirect, approximate proxy for its real production, never a measurement. An operator who needs a reliable biomass figure still relies on the count at harvest, tracked feed distribution and submerged probes — not on an orthophoto.
Who commissions this service and 2026 prices
Demand comes from concession-holding operators preparing an AECM renewal file who must demonstrate that the layout matches the authorised plan, from property-damage insurers putting figures on a storm claim on floating structures that are otherwise hard to access, from DDTMs checking a concession remotely without mobilising a boat, and from buyers running due diligence before acquiring a fish farm. Ranges observed in France in 2026, excl. VAT:
| Service | Observed price (excl. VAT) |
| Concession orthophoto and cage-position survey | €500 to €900 |
| Before/after storm assessment (insurance or DDTM report) | €400 to €700 |
| Periodic concession monitoring (annual package, several passes) | €1,500 to €3,000 |
These amounts cover the flight from shore or a boat, processing and the report; they exclude the underwater net inspection by a certified diver or ROV, water-quality monitoring by probes, and the actual stock count, which remain the responsibility of the operator and their specialised contractors. Request a quote stating the concession's location, the flight's starting point (shore or boat), and whether a post-incident assessment is needed.