A trawl touches the seabed and is towed for a little over half an hour at about three and a half knots. It works in daylight, the same way at every haul. That is how scientific surveys have counted fish on the European continental shelf since 1983. Forty years of those nets say that fish are going down more than they are going north.
The study was published on 15 July 2026 in Nature Communications. It has sixteen authors. The first is Arnaud Auber of Ifremer, the French marine research institute, in Boulogne-sur-Mer. The last is Camille Albouy of the Swiss federal research institute WSL and ETH Zurich. The team pooled 92,961 hauls from 21 bottom trawl programmes covering some 4.8 million square kilometres of seabed. Atlantic data come from the DATRAS database. Mediterranean data come from MEDITS, the international Mediterranean bottom trawl survey. The hauls contained 607 identified species.
The authors worked with populations, meaning one species followed within one survey series. For each they tracked, year by year, the centre of its distribution in latitude and in depth, weighted by the number of fish caught. Then they measured how far that centre moved.

Six populations in ten went deeper. On average the centre dropped 18 metres per decade, with a standard deviation of 27 metres. A spread larger than the mean means the stories differ widely, and some populations moved up. Among species with a statistically significant shift, 76 per cent went down, at 24 metres per decade.
In latitude the account balances. Forty-nine per cent of populations moved poleward, at 63 kilometres per decade on average. Fifty-one per cent moved towards the equator, at 70 kilometres. In the Northeast Atlantic no direction dominates. In the Mediterranean, southward shifts prevail.
The authors give two reasons for the Mediterranean, and temperature is not one of them. In the northern part of the basin the seabed deepens towards the south, so a fish seeking deeper water also moves south. The Strait of Gibraltar and the coastline block the way north. A Mediterranean species has no more northerly sea to move into.

The common expectation is that warming pushes marine species towards the poles. In Europe the data do not bear this out. Bottom temperature rose for 70 per cent of populations, yet it is not among the strongest drivers of deepening in the models. Species traits weigh more, along with what the authors call environmental safety margins. These measure how close a population's conditions sit to the limits the species tolerates, taken from occurrence records worldwide. Temperature, oxygen and depth all enter the calculation. A population near its limit has less room to stay put.
Deepening was more likely in predators high in the food chain, in slow-growing and long-lived species, and in species that prefer cold, shallow water. It was also more likely in species with narrow niches, those tolerating only a small range of depth, oxygen or temperature.

The least expected figure concerns abundance. Sixty-one per cent of populations expanded their range and 73 per cent increased in number, whichever way they moved. Among exploited species, 76 per cent of commercial populations and 75 per cent of minor commercial ones increased, against 61 per cent of the most valuable. The authors link the rise to the recent fall in fishing pressure and present it as suggestive, not proven. In their models fishing effort has only a marginal effect on the direction of shifts.
The limitations are stated. A bottom trawl catches demersal fish well and midwater fish poorly, so estimates for pelagic species are uncertain. The surveys cover only part of the seabed, and a move outside the sampled area goes unseen. The data cannot tell an adult that moves from larvae that settle elsewhere, or from a population growing in one place and shrinking in another. Depth increases with distance from shore, and part of the deepening could be a move offshore. That was not tested directly.
The work comes from the MAESTRO group at CESAB, the synthesis centre of the French Foundation for Research on Biodiversity. MAESTRO is supported by France Filière Pêche, a French fishing-sector body. The authors declare no competing interests. Data and code for the figures are publicly deposited.
For forty years the nets counted in the same way, at the same speed, in daylight. Over that time Europe's fish looked for the bottom more often than for the north.

References
Auber Arnaud, Marzloff Martin P., Mouillot David, Ellingsen Kari E., MacKenzie Kirsteen M., Leprieur Fabien, Belloeil Patrica, McLean Matthew J., Boyce Daniel G., González Ortiz Adrián A., Vasconcelos Rita, Keith David M., Maire Eva, Receveur Aurore, Mourguiart Bastien, Albouy Camille, "Marine fish ranges are expanding and shifting deeper across the European continental shelf", Nature Communications, 17, 1, 8702, 15 July 2026 (received 25 June 2025, accepted 4 June 2026), open access, CC BY 4.0 licence. doi: 10.1038/s41467-026-74371-8
Data and R code for the figures: figshare, doi: 10.6084/m9.figshare.28081469