Islanders asked to report sightings of European eel in Guernsey

Guernsey’s Nature Commission and Guernsey Water are issuing an urgent appeal to islanders to report any sightings of the European eel (Anguilla anguilla) within the island’s freshwater systems and coastal waters. This critical initiative forms a vital part of ongoing efforts to understand and protect this globally endangered species, which faces significant threats to its survival. The European eel, a creature of remarkable endurance and an incredibly complex life cycle, holds a precarious place in both global and local ecosystems, making every piece of local data invaluable for its conservation.

The European eel is renowned for its extraordinary catadromous breeding cycle, a life strategy that sets it apart from most fish species. Unlike salmon, which are anadromous (growing in the sea and spawning in freshwater), eels perform the reverse journey. Their epic life begins in the mysterious depths of the Sargasso Sea, a vast, current-bound region in the western Atlantic Ocean, south-east of Bermuda. Here, in this unique marine environment, the adult eels, known as silver eels, undertake their final reproductive act, laying their eggs and subsequently perishing. From these eggs hatch minute, leaf-shaped larvae called leptocephali, which drift on the Gulf Stream currents across the Atlantic, a journey that can take up to two years. Upon reaching the continental shelves of Europe and North Africa, including the waters surrounding Guernsey, these translucent larvae metamorphose into "glass eels," transparent, miniature versions of the adult form, ready to enter estuaries and begin their freshwater lives.

Once in freshwater environments, such as Guernsey’s streams, ponds, and reservoirs, the glass eels develop into "elvers" – small, pigmented eels that continue to migrate upstream. They then transition into their "yellow eel" phase, where they spend the majority of their lives, potentially several decades, growing and feeding. During this extensive freshwater residence, they are highly adaptable, inhabiting various aquatic habitats, from the smallest ditches to larger water bodies. Eels are known for their robust physical attributes; they are strong swimmers, capable of navigating challenging currents and even short distances over damp land. They are primarily nocturnal hunters, emerging under the cover of darkness to prey on insects, crustaceans, small fish, and carrion, playing an important role as both predator and scavenger in their ecosystems. Their longevity is particularly striking, with some individuals documented to live for up to 80 years in captive or undisturbed environments, though typically their lifespan in the wild is shorter, ranging from 15 to 20 years before they undergo their final transformation.

This final transformation, from yellow eel to "silver eel," marks the onset of their perilous return migration. Their bodies undergo physiological changes: their sides turn silvery, their eyes enlarge, and their digestive system shuts down as they cease feeding, focusing all energy on the arduous journey back to the Sargasso Sea. It is during this phase that they are most vulnerable to both natural and anthropogenic threats. Understanding the presence and distribution of these eels at various life stages within Guernsey’s unique environment is crucial, especially given their critically endangered status globally. The island’s network of freshwater habitats, though small, could play a significant role as either a feeding ground for yellow eels or a migratory pathway for silver eels departing for their oceanic spawning grounds.

Globally, the European eel population has plummeted by an estimated 95% over the last few decades, leading the International Union for Conservation of Nature (IUCN) to classify the species as Critically Endangered. This alarming decline is attributed to a complex interplay of factors, including habitat loss and degradation, migration barriers, pollution, disease, climate change impacting ocean currents and the Sargasso Sea, and historical overfishing. For Guernsey, a proactive approach to understanding its local eel populations is not just a local environmental concern but a contribution to a broader international conservation effort. Every piece of information gathered on the island helps to build a clearer picture of the species’ remaining strongholds and the specific challenges it faces in different regions.

To address this knowledge gap, the Nature Commission and Guernsey Water have embarked on an innovative research project utilising environmental DNA (eDNA) sampling. This cutting-edge technique involves collecting water samples from various freshwater ponds and streams across the island. The eDNA method works by detecting minute traces of genetic material (DNA) that organisms shed into their environment through skin cells, mucus, faeces, or urine. By filtering these water samples and analysing the extracted DNA, scientists can determine the presence or absence of specific species, such as the European eel, without directly observing or capturing the animals. This non-invasive and highly sensitive approach offers a powerful tool for mapping the distribution of eels across Guernsey’s diverse freshwater network, providing crucial baseline data on where eels are currently present, even in elusive or hard-to-reach locations. The initial eDNA results will complement direct sightings and provide a robust foundation for future conservation strategies.

Despite its relatively pristine appearance, Guernsey’s freshwater habitats are under increasing pressure, mirroring global trends that directly impact eel populations. Freshwater environments on the island are declining due to various factors, including drainage for agricultural expansion, land clearance for development, and general habitat mismanagement. These activities reduce the total area of suitable habitat available for eels to feed and grow. Furthermore, pollution from agricultural runoff, containing pesticides and fertilisers, as well as domestic and industrial waste, can severely degrade water quality, making habitats unsuitable or toxic for eels and their prey.

A significant challenge highlighted by ecologists is the increasing fragmentation and isolation of waterbodies. As natural landscapes are altered, the continuous pathways that eels once used to move freely between different freshwater habitats become disrupted. This fragmentation prevents eels from accessing optimal feeding grounds or finding suitable refuge. Adding to this issue is the proliferation of infrastructure along the coast and further inland. Structures such as pipes, culverts, dams, weirs, and sluice gates create formidable physical barriers that impede the upstream migration of returning glass eels and elvers from the sea to their feeding grounds. Conversely, these structures can also pose a threat to mature silver eels attempting to migrate downstream back to the sea, potentially causing injury or mortality. These man-made obstacles disconnect vital parts of the eel’s life cycle, making it harder for populations to sustain themselves.

"These species are declining globally, so it would be great to understand more about populations on island," stated a representative from the Nature Commission. The comprehensive understanding gained from both eDNA sampling and citizen science reports will be instrumental in identifying critical habitats, pinpointing specific migration barriers, and developing targeted conservation interventions. This information can inform decisions on habitat restoration projects, the implementation of ‘eel passes’ at problematic structures, and improvements in water quality management across the island.

This is where the invaluable contribution of Guernsey’s islanders comes into play. The Nature Commission and Guernsey Water are making a direct appeal for the community’s help. Islanders are urged to report any sightings of European eels, regardless of their size or life stage. When reporting a sighting, please provide as much detail as possible: the exact location (GPS coordinates if possible, or a clear description of the landmark), the date and time of the sighting, an estimate of the eel’s size and colour, and any notable behaviour. High-quality photographs or videos are exceptionally useful for verification and identification. Sightings can be of small, transparent glass eels entering estuaries, larger brown or yellow-bellied eels (yellow eels) in streams or ponds, or the distinct silvery-bellied silver eels heading towards the coast.

To report a sighting, islanders should contact the Nature Commission directly via their official website or designated email address. Clear instructions on how to submit reports, including any online forms, will be provided through local media and the commission’s platforms. It is crucial for reports to be accurate and timely to ensure the data is reliable for scientific analysis. While eels are generally harmless, it is advisable not to handle them unless absolutely necessary for rescue (e.g., if trapped) and to do so with care and appropriate protective measures. The collective effort of citizen scientists is vital for filling crucial data gaps that traditional survey methods alone cannot cover, empowering conservationists to develop effective strategies to protect this remarkable and critically endangered species within Guernsey’s unique environment. By working together, the community can play a direct role in securing a future for the European eel on the island and contributing to its global survival.