This article was featured in Eurofish Magazine 6 2025.
The arrival of the Atlantic blue crab in the Ebro (Ebre) delta has transformed one of Spain’s most important coastal wetlands into a testbed for invasive-species governance.
The Atlantic blue crab has moved from curiosity to constant presence along much of the Spanish Mediterranean. It is established in the Albufera of Valencia, the Mar Menor, the Balearic Islands, Santa Pola, El Hondo, and in the Ebro Delta, where it was first detected in 2012. Since then it has spread rapidly across the Ebro delta including the river mouth, two shallow bays (Fangar and Alfacs), lagoons, and the adjacent shelf—areas that also underpin Catalonia’s artisanal fisheries and shellfish aquaculture. Among the blue crab’s prey are razor clams, cockles, and clams. Faced with ecological pressure and mounting conflicts with traditional fisheries, Catalonia’s government and other stakeholders including several research institutions invested in managing the invader. The aim was not eradication, but an attempt to convert a threat into a resource based on science and markets.
Choosing a management pathway
At the outset, the administration weighed two starkly different scenarios. If blue crab were listed as an invasive alien species, commercialisation, possession, transport, and traffic would be banned, forcing reliance on costly, long-running eradication campaigns of doubtful effectiveness. If it remained unlisted locally, a targeted commercial fishery could be authorised, creating income for professionals, generating auction-based data on removals, and—critically—exerting sustained pressure on the population. Catalonia chose the latter path, authorising only professional, not recreational, fishing for blue crab. This decision gave fishers another source of income, while giving managers a picture of the state of the stock from catches passing through the fish auctions. According to Margarita Fernández Tejedor from IRTA and colleagues, captures in the Ebro delta peaked in 2020 at close to 500 tonnes falling to under 200 tonnes in 2023. The crabs feed on molluscs, crustaceans, fish, and algae and have a high fertilisation rate, bearing 700,000 to two million eggs. Moreover, egg-earing females appear through much of the year.
Margarita Fernández Tejedor, IRTA, is among the researchers working with blue crabs.
A dedicated co-management committee for the blue crab convened fishers and their federations, the Catalan public administration, NGOs (e.g., Ecologistes en Acció), the scientific community (ICATMAR and ICM), and aquaculture representatives. Decision-making is on an equal footing and allows rules to tighten or relax as conditions change. The committee’s primary mandate was to create a legally robust management plan.
Monitoring programme in line with international recommendations
ICATMAR designed a three-pillar monitoring programme to (1) evaluate the status of the crab, (2) control its population, and (3) underpin a regional fishing programme aligned with General Fisheries Commission for the Mediterranean (GFCM) Recommendation 42/2018/7 on blue crab research. The Ebro delta accounts for almost all of Catalonia’s blue crab landings, so studying daily first-sale records from fishers’ associations to track volumes, value, and price trends would give a good picture of the state of the resource and the market. Before auctions, teams conducted monthly measurements of sex, carapace size, presence of epibionts, and ovigerous status, and recorded per-boat weights with locations provided by fishers. These data reveal habitat use across deep and shallow bay zones, channels, and adjacent open sea, enabling managers to spot demographic shifts and spawning periods. Complementary, standardised trap surveys run bimonthly at 13 fixed stations spanning river (four stations), bays (four), lagoons (two), open sea (two), and a protected zone (one). In the lab, individuals are sexed and measured; maturity stage and gonad weight are recorded to track changes. Findings include a pronounced autumn migration, with about 95% of females inseminated, and habitat-linked maturation patterns. Importantly, independent and dependent data converge on the same distribution picture, boosting confidence in management measures.
Managing the stock is also about managing prices
Turning a pest into a managed resource depends on viable prices. Since the first sale in La Ràpita in 2016, blue crab catches in Catalonia have exceeded 1,865 tonnes, with first-sale income above €4.54 million and an average auction price of €3.9/kg across the early years. By 2025, cumulative landings reported for the fishery had reached around 2,688 tonnes—roughly ten million crabs—with average first-sale prices approaching €4.8/kg. These figures reveal both the rapid expansion of the fishery and the success of efforts to develop demand. Price management can sustain the removal effort. When first-sale prices collapse, incentives to target crab vanish, undermining control. The committee therefore monitors catching effort to prevent market saturation. At the same time, promoting the crab in gastronomy and new value chains has been encouraged, with the explicit objective of maintaining prices so that fishers have an incentive to keep fishing.
The management plan approved in 2022 formalised the rules: only professional fishers may target blue crab; specific gears and fishing areas are authorised; authorisations are listed openly; and a monitoring programme is mandatory. This approach was designed to mitigate an invasive population. Other statutes specify the fine print (areas, gears, numbers of gears, and the list of authorised fishers) and can be updated quickly to respond to environmental or market changes. Internationally, GFCM Recommendation 42/2018/7 helped align Catalonia’s monitoring with a Mediterranean-wide research framework, ensuring that methods and indicators in the Ebro delta contribute to, and benefit from, regional evidence.
Sustained pressure on the stock and an extra income for fishers
Six to seven years after the initial management choices, officials close to the process characterise the decision to authorise a professional fishery—embedded in co-management and backed by monitoring—as the right one. They point to interest and investments from the fishers as indicators that the system is working. However, the autumn migration of inseminated females, the role of the river’s saline wedge in structuring abundance, and the crab’s capacity to exploit multiple deltaic habitats mean that pressure must be continuous. The Ebro model’s strength is precisely this continuity: traps in the river and lagoons, targeted fishing in the bays and adjacent sea, and auctions that convert removals into traceable data and income.
Socio-economically, the managed fishery has offered an alternative income stream that is particularly useful when traditional shellfisheries face pressure from predators and climate change. Yet the committee has had to balance catch effort with market absorption, so that at times when prices dip, communication and product development have been used to maintain catches., and. The committee has also worked to build trust. By publishing the list of authorised fishers, gears, and areas, and requiring monitoring as a condition of access, it has prevented opportunistic, poorly controlled removals. Justifying those controls with a scientific programme has helped their acceptance by fishers.
The Ebro delta’s blue crab initiative is an experiment in adaptive co-management involving professional fishers, market signals, and continuous monitoring to convert an ecological threat into an income-generating fishery. As the Mediterranean continues to grapple with blue crab, the Ebro’s lessons can surely be adapted to other countries in the region for the benefit of both fishers and the environment.
