The Groundbreaking Discovery of Silver Eels in Cyprus
Researchers from Bournemouth University have made a landmark discovery by confirming the presence of silver European eels, Anguilla anguilla, in the inland waters of Cyprus for the first time. This finding, detailed in a peer-reviewed study published in the Journal of Fish Biology, marks the easternmost record of this critically endangered species in its mature migratory phase. Led by Sotiris Meletiou, the team captured migrating silver eels at two key sites: Oroklini Lake and the Polis River, challenging long-held assumptions about the species' distribution in the Eastern Mediterranean.
The significance cannot be overstated. Until now, only juvenile yellow eels were known in Cyprus, leading to the island's exemption from mandatory European Union Eel Management Plans (EMPs). This breakthrough provides concrete evidence that eels complete their full life cycle here, from glass eel recruitment to silver eel emigration.
Deciphering the Enigmatic Life Cycle of the European Eel
The European eel, Anguilla anguilla, exhibits one of nature's most extraordinary life histories—a catadromous strategy spanning continents and oceans. Adults spawn once in the Sargasso Sea, a remote region in the North Atlantic, releasing eggs that hatch into leptocephalus larvae. These leaf-like, transparent larvae drift on ocean currents for up to three years, traveling thousands of kilometers to reach European and Mediterranean coasts as glass eels (pigmented juveniles).
Upon entering estuaries and rivers, glass eels metamorphose into elvers and then yellow eels, residing in freshwater for 6-19 years (females longer than males). During this growth phase, they feed voraciously, accumulating energy for the return journey. The pivotal silvering process then occurs: yellow eels undergo profound physiological changes. Eyes enlarge dramatically (up to 3-4 times) for deep-sea vision, skin turns silvery for camouflage, pectoral fins expand, the digestive tract degenerates, and gonads mature. Classified into stages (I-V) by Durif et al. (2005), silver eels (stages IV-V) cease feeding and embark on a 4,000-6,000 km migration back to the Sargasso Sea, navigating via olfactory cues, Earth's magnetic field, and possibly infrasound.
- Leptocephalus: Oceanic larval drift (0.6-10 cm).
- Glass eel: Coastal entry (5-7 cm).
- Yellow eel: Freshwater growth (up to 1.5 m).
- Silver eel: Migration readiness (eyes index >0.11, pectoral index >0.4).
In Cyprus, this cycle was incomplete in records until now, with silver eels confirming local maturation.
Methodology: Targeted Surveys Yield Historic Captures
The BU-led study employed rigorous, permit-approved methods to target silvering hotspots. At Oroklini Lake (a Natura 2000 site, coords 34.970731, 33.654347), two fyke nets (1.0 × 2.3 m) were deployed overnight from December 2-4, 2024, post-heavy rainfall. This yielded 473 silver eels during overflow events. In the Polis River (35.031902, 32.424179), electric fishing with SmithRoot LR24 gear from February 24 to March 1, 2025, captured 5 silver eels over 10 km inland.
Each eel underwent biometric assessment: total length (TL), mass, head length, eye diameters (horizontal/vertical), pectoral fin length. Silvering was verified via Durif indices (eye index = eye diameter/head length; pectoral index = fin length/head length). Water quality (pH, DO, conductivity, temp) was monitored. Oroklini eels were conditioned (rested, salinity-acclimated) and trucked to sea due to artificial barriers; Polis eels released onsite.
Historical eDNA, electrofishing, and glass eel trap data corroborated recruitment, showing low-elevation distribution negatively correlated with coastal distance and barriers.Read the full study.
Biometrics and Silvering Confirmation
Oroklini Lake eels averaged 456 ± 60 mm TL (range 382-680 mm) and 173 ± 83 g mass (120-555 g), all stage IV/V silver. Polis River specimens ranged 35-56 cm TL, 90-355 g. Morphometrics included eye indices 0.071-0.182 and pectoral indices 0.399-0.689, aligning with migratory readiness. These data affirm advanced maturation despite harsh conditions.
| Site | n | TL Mean (mm) | Mass Mean (g) | Durif Stage |
|---|---|---|---|---|
| Oroklini Lake | 473 | 456 ± 60 | 173 ± 83 | IV/V |
| Polis River | 5 | ~350-560 | 90-355 | IV/V |
Such sizes indicate 8-12+ years residency, highlighting resilience.
Hurdles Posed by Habitat Fragmentation in Cyprus
Cyprus's Mediterranean climate exacerbates eel challenges: 108 dams fragment rivers, summer droughts dry channels, and barriers like sluices block passage. At Oroklini, road construction severed sea links; Polis River drying stalled upstream juvenile access and downstream silver eel escape. This reduces Sargasso spawning biomass, perpetuating decline.
- River drying: Limits refugia, delays migration.
- Barriers: Prevent 90%+ escapement in fragmented systems.
- Climate extremes: Amplify pollution/parasite impacts (e.g., Anguillicola crassus).
Yet, eels persist, showcasing adaptability.Bournemouth University announcement.
Conservation Shake-Up: Cyprus Joins EU Eel Efforts
With silver eels confirmed, Cyprus loses exemption under EU Regulation (EC) No 1100/2007, mandating EMPs targeting 40% silver escapement (pre-anthropogenic biomass). Measures include fishing bans (marine closure since 2018), restocking 60% juveniles, habitat restoration. Populations crashed 90-95% since 1980s (IUCN Critically Endangered), from overfishing, barriers, pollutants.
Cyprus can pioneer Mediterranean recovery via reconnection (e.g., Oroklini sluice mods), telemetry tracking, restocking—boosting regional stocks. Dr. Malen I. Vasquez urges urgent EMP implementation.
Bournemouth University's Pivotal Role in Eel Research
Bournemouth University's Faculty of Science & Technology excels in fish ecology, with experts like Prof. J. Robert Britton and Dr. Demetra Andreou driving conservation science. Collaborations with Cyprus University of Technology and UK Environment Agency amplify impact. This study exemplifies BU's FishE group's evidence-based approach to threatened species.
For aspiring marine biologists, BU offers specialized Environmental Sciences programs. Explore research jobs in Europe or European higher ed opportunities.
Mediterranean and European Eel Crisis: Stats and Trends
EU-wide, recruitment hit record lows; Mediterranean stocks show no recovery. Threats: dams (habitat loss), climate (droughts), invasives. Yet, unexploited Cyprus populations offer hope. ICES advises zero commercial catches in 2026.
Stakeholders: Fisheries, NGOs, governments push restocking (millions glass eels/year EU-wide), barrier removals. Success stories: Restored rivers in UK/France boosted escapement 20-50%.
Photo by Kamsin Kaneko on Unsplash
Future Outlook: Research Frontiers and Actionable Steps
Next: Telemetry for migration routes, hormone assays for silvering cues, eDNA scaling. Cyprus EMP could model barrier-free designs, AI-monitored traps. Higher ed implications: Boom in fieldwork roles; pursue academic CV tips.
Optimism prevails: "Survival in extreme conditions furthers our understanding of resilience," says Dr. Ros Wright. Interested in rating profs or finding faculty positions? Visit Rate My Professor, higher ed faculty jobs, and career advice.
