Empty nets in the Greek seas have no single cause. Fishing pressure, habitat loss, pollution and rapid warming weaken marine ecosystems, while species arriving from the Indo-Pacific reshape food webs and the daily work of coastal fishers.
A mixed picture. The 2025 report of the FAO’s General Fisheries Commission for the Mediterranean shows real progress: across 120 assessed stocks, fishing pressure has halved in a decade and the biomass of assessed commercial species grew by 25% between 2013 and 2023 [1]. Yet 52% of assessed stocks are still overfished – down from 87% in 2013 – and sardine still shows depleted biomass [1]. Recovery depends on enforced fishing rules, protected spawning and nursery grounds, healthy seagrass meadows, cleaner water and climate action; invasive species intensify these pressures but are not their only cause.
New arrivals through Suez. Close to 1,000 non-indigenous species have been validated in the Mediterranean, 751 of them established, and establishment is accelerating [2]; by 2020, 242 marine alien species had been recorded in Greek waters [3]. Many are Lessepsian migrants from the Red Sea, favoured by a warming eastern Mediterranean. The silver-cheeked toadfish (Lagocephalus sceleratus), first recorded in Greece in 2005 [4], eats commercial fish and cephalopods and bites through nets and lines [5]; its tetrodotoxin can reach levels lethal to adults, and pufferfish of its family may not be sold in the EU [6]. Lionfish (Pterois miles), recorded in Greece since 2015, is a voracious predator with venomous spines [3]. Rabbitfish (Siganus spp.) overgraze rocky reefs: where they abound along the coasts of Türkiye and Greece, canopy algae were 65% less abundant and species richness 40% lower [7].
The cost to fishing families. Small boats are the backbone of Greek fishing: 96.5% of the country’s 13,950 vessels in 2020 fished near the coast with static gear [8]. An HCMR study of 141 small-scale vessels (2020–2022) put the toadfish’s annual cost at about €6,315 per vessel in Crete, against €258 in the Ionian Sea; Cretan fishers responded by fishing deeper, shortening fishing time and changing their gear [9]. By 2026 HCMR researchers estimated average losses at around €8,500 a year per vessel [4]. When catches fall while fuel and nets grow dearer, a family boat – and the local knowledge it carries – is at risk.
Responses. In June 2026 the Ministry of Rural Development and Food launched a €1.5 million pilot for Crete and the South Aegean, co-financed by the EU fisheries fund: professional fishers will be paid up to €5.33 net per kilo of toadfish removed, with scientific monitoring and controlled collection and disposal; the two Regions must submit their joint implementation plan by 30 September 2026 [10]. Regular monitoring and targeted removals can keep lionfish in check in Mediterranean marine protected areas [11], and safe edible invaders such as lionfish and rabbitfish could gain regulated markets – but the toxic toadfish must never be promoted as food.
Learning with BLUE OCEAN. Schools can join real science: the citizen-science project “Is it Alien to you? Share it!!!” gathered 691 records from Greece and Cyprus in two years and added three new species to Greece’s official assessments [12]. Students can map sightings, interview local fishers, compare past and present catches, study food webs and design public information on safe and unsafe species, exploring careers in fisheries science, marine ecology, environmental economics and data analysis [13].
Above all, they learn that fishers are partners, not only victims: their observations are essential to any workable solution, and protecting biodiversity and protecting fishing income must become one strategy for healthier Greek seas.
Sources (web pages accessed 22 September 2026)
[1] FAO–GFCM (2025). The State of Mediterranean and Black Sea Fisheries 2025 – highlights; FAO news release, 28 Nov 2025.
[2] Zenetos, A. et al. (2022). Established non-indigenous species increased by 40% in 11 years in the Mediterranean Sea. Mediterranean Marine Science, 23(1), 196–212.
[3] HCMR – ELNAIS, Ellenic Network on Aquatic Invasive Species: national census and species profile of Pterois miles. elnais.hcmr.gr
[4] Euronews (2026). ‘I’ll have to buy new nets’: Killer pufferfish are devastating Crete’s fishing industry, 16 June 2026.
[5] Gomes, R. et al. (2025). The diet and feeding habits of Lagocephalus sceleratus in the eastern Mediterranean off Crete. Mediterranean Marine Science, 26(1), 97–114.
[6] Katikou, P. et al. (2009). First report on toxicity assessment of the Lessepsian migrant pufferfish L. sceleratus from European waters (Aegean Sea). Toxicon, 54, 50–55.
[7] Vergés, A. et al. (2014). Tropical rabbitfish and the deforestation of a warming temperate sea. Journal of Ecology, 102(6), 1518–1527.
[8] Ministry of Rural Development and Food (2021). Annual Fleet Report 2020 – Greece, submitted to the European Commission.
[9] Christidis, G. et al. (2024). Another one bites the net: assessing the economic impacts of L. sceleratus on small-scale fisheries in Greece. Fishes, 9(3), 104.
[10] Ministry of Rural Development and Food (2026). Pilot programme for the management of the silver-cheeked toadfish, press release, 29 June 2026.
[11] Kleitou, P. et al. (2021). Regular monitoring and targeted removals can control lionfish in Mediterranean marine protected areas. Aquatic Conservation, 31, 2870–2882.
[12] Giovos, I. et al. (2019). Citizen-science for monitoring marine invasions and stimulating public engagement. Biological Invasions, 21, 3707–3721.[13] BLUE OCEAN Erasmus+ project, 2024-MT01-KA220-SCH-00254518. blueoceaner