Lumpsucker under the microscope

DTU Aqua to investigate the biology of an endangered species, funded by Seabreak

The lumpsucker has been overlooked, but knowledge is crucial if we are to protect and preserve it. With financing from the newly founded charity Seabreak, DTU Aqua is starting a pioneering project to map the biology of the lumpsucker and investigate how environmental changes affect its living conditions.

Lump sucker baby. Photo: © Henrik Carl, Danish Museum of Natural History — Lumpsucker baby. Photo: © Henrik Carl, Danish Museum of Natural History. NOTE: the photo may only be reproduced after agreement with the photographer by emailing hcarl@snm.ku.dk

Monday 06 October 2025

Anne Trap-Lind

For decades, the lumpsucker has been a regular feature in Danish waters, in Danish fishery and on Danish plates, where lumpsucker roe has been a harbinger of spring.

But in recent years, the population of lumpsucker has declined dramatically. To a degree that a total ban on fishing for lumpsucker was introduced from 1 January 2025, based on advice from DTU Aqua – an unprecedented decision that received considerable media attention.

This serious situation has also stressed how little we actually know about the biology and habitats of the lumpsucker, and the factors that threaten the species.

For that reason, a new research project at DTU Aqua has received a grant from the newly founded charity Seabreak to put the biology of the lumpsucker under the microscope for the first time.

An interaction between fishing and other factors
"With the new grant, we can start to fill in the gaps in our knowledge about the biology and living conditions of the lumpsucker, and how it copes with living in a sea with rising temperatures and more frequent and severe oxygen depletion, and this is crucial for understanding how best to protect and conserve the lumpsucker," says senior researcher Jane Behrens, who leads the project at DTU Aqua.

It will be exciting and likely also challenging to get live lumpsuckers into our experimental facility.

Jane Behrens, Senior researcher, DTU Aqua, and project leader of the lump sucker project, supported by Seabeak

The lumpsucker has been exploited in the fishery for decades, but researcher Ole Henriksen, who has been responsible for advising on lumpsucker in Denmark, does not believe that we can say with certainty that fishing alone has caused the significant decline in the population:

"We suspect that it is more likely an interaction between fishing and other factors that has led to the collapse we have seen in recent years."

How environmental changes shape the lumpsucker

The researchers' thesis is that in addition to fishing, climate change with rising sea temperatures and periods of prolonged oxygen depletion have also contributed to bringing the lumpsucker to its knees.

The lumpsucker's strange biology, with its dependence on both the free water masses in the North Atlantic and the coastal Danish waters during the spawning period, provides several clues as to how the environment can pressure the lumpsucker.

However, it is not yet known how environmental changes shape the lumpsucker's growth and survival potential, so this is something that the researchers now want to investigate:

"It will be exciting and likely also challenging to get live lumpsuckers into our experimental facility, and I am very much looking forward to delving into experiments that can clarify which environmental factors that contribute to the lumpsucker's influence," says Jane Behrens.

Jane Behrens adds that further knowledge gaps are that we do not know whether lumpsucker returns to coastal waters one or several times during its life to spawn, if it eats during the spawning season and if so, what, and what role it plays in the food web and ecosystem.
All these matters are central pieces to understand the decline of the species and how robust – or not – it is to external pressures.

With this opportunity for DTU Aqua to take the first, major steps towards understanding the biology of the lumpsucker with the grant from Seabreak, the results will also contribute to the understanding of the coastal marine environment.

Experience stories and research results and the lumpsucker itself at Denmark's four major aquariums

Project manager Jane Behrens and Seabreak agree that knowledge about the lumpsucker should reach the public. That is why they have entered a collaboration with the largest national exhibition aquariums, the Kattegat Centre, the North Sea Oceanarium, The Blue Planet and the Øresund Aquarium:

'"The aquariums can create the perfect framework for our talks and dissemination about the species and the results from the project. They have years of experience with this and can also show live lumpsuckers up close to the audience,'' says Jane Behrens.

The grant from Seabreak includes funding for a PhD student and a postdoc. In this way, the project also contributes to the research training of future fish nerds and ocean guardians.

The new project on the biology of the lumpsucker will start in January 2026 and run over a 4-year period.

Seabreak will give the sea a break

The newly founded charitable organization Seabreak, together with sister initiatives Change ventures and Earthbreak, was established by Camilla Zacho and Jacob Jelsing, both of whom are educated marine biologists.

They help and assist enthusiasts, companies and organizations working for a better future. Seabreak primarily supports nature restoration, dissemination and research in the marine environment in Denmark. The goal is better conditions, more biodiversity and greater knowledge about the sea and its organisms.

“For decades, we have overexploited marine resources, used destructive bottom trawling and polluted Denmark’s seas and initiated drastic climate change. The result is a sea in crisis, and we want to do something about that,” says Camilla Zacho and explaines:

“With seabreak, we wish to support, among other things, research projects that can contribute knowledge about marine organisms and the marine environment, as well as support more gentle management. The lumpsucker is an obvious place to start because it has both cultural and historical significance, and it is at the same time a likely indicator of how coastal habitats function.”

Lumpsucker baby. Photo: © Henrik Carl, Danish Museum of Natural History. NOTE: the photo may only be reproduced after agreement with the photographer by emailing hcarl@snm.ku.dk

FACTS about the lumpsucker project

Period: January 2026 – December 2029
Purpose: To fill in significant knowledge gaps about the lumpsucker's biology, habitats and vulnerability to environmental change.
Content: Telemetry to map the lumpsucker's migration routes and habitat selection. Biogeochemical analyses of otoliths to investigate life history traits such as growth, spawning and migrations. Isotopic analyses of muscle tissue to determine the lumpsucker's diet and where it is placed it in the food web. Experiments to determine environmental tolerances and effects of climate change. Modelling of population dynamics to assess the effects of fishing and climate change, both historically and in the future.
Communication about lumpsucker at Denmark's four major exhibition aquariums, the Kattegat Centre, the North Sea Oceanarium, the Blue Planet and the Øresund Aquarium
New applications for further work with lumpsucker from a Nordic perspective
Project management: Project management: Senior researcher Jane W. Behrens, DTU Aqua, in collaboration with Aarhus University and the University of Copenhagen
Funding: Grant from the newly founded charitable organization Seabreak, which supports nature restoration and increased biodiversity in the ocean

FACTS about the lumpsucker

Adult lumpsucker live in the open waters of the North Atlantic and migrate over great distances to spawn near the coast in Danish waters. Already in the cold winter months, male lumpsucker arrive in the shallow coastal areas, where they establish territories and build nests on stones, rocks and seaweed belts.
The females arrive later as a mythical harbinger of spring and lay eggs, which are guarded and cared for by the male until they hatch.
Small green miniature versions of the adults emerge from the eggs. They grow up in the shallow coastal areas with eelgrass, seaweed and stones, before swimming out to sea and then returning to spawn after many years in deep water. Sometimes thousands of kilometers from where they were hatched.
In the shallow coastal areas, the fry are exposed to high water temperatures and the risk of longer periods of oxygen depletion. These are conditions that can be crucial in determining how well they grow and how many survive and make the journey out to sea in the North Atlantic.
The Latin name for lumpsucker is Cyclopterus lumpus L.

Contact

Jane Behrens Senior Researcher National Institute of Aquatic Resources Mobile: +45 23296863 jabeh@aqua.dtu.dk