European Eel (Anguilla anguilla) 

Along the coastlines of Scotland and the rest of the UK several eel species can be found, including sand eels, conger eels, and European eels. Most sightings are of European eels in various developmental stages, such as glass eels, elvers, and yellow eels. The European eel has long been a staple in European cuisine, featured in traditional dishes like smoked eels in Germany and the Netherlands, eel-based soups and risottos in Italy, and jellied eels in London (Käller, 2024). However, over the past 20 years, the species has experienced a sharp decline in numbers, raising significant concerns about its future. Once widespread across European waters, including the Baltic Sea, European eels are now primarily found in the rivers of Atlantic EU countries and parts of the Mediterranean (European Commission, n.d.).

Population & Distribution
The European eel is a highly adaptable species that thrives in a range of habitats, including rivers, lakes, estuaries, lagoons, and coastal waters (ICES, 2015). Eels are known to travel across vast stretches of open ocean during their migrations, though encounters in these areas are uncommon. While they are typically found in aquatic systems linked to the sea, they have also been introduced to new regions. Most of their lives are spent in freshwater, brackish, or coastal environments, with their journey to the open ocean occurring primarily for breeding purposes (Tsukamoto et al., 1998; Tzeng et al., 2000). Although their behaviour in rivers and lakes is well-documented, little is known about what occurs during their time in the ocean. 

The species has a wide distribution across Europe, extending from northern Norway to the Mediterranean and North African coasts (Fig. 2). They are rare in the Arctic seas but can occasionally be found as far east as the Pechora River in Russia. Small populations exist in the Black Sea region, with some individuals reaching the Volga River via canals. The species thrives in various habitats, including freshwater rivers and lakes, brackish estuaries and lagoons, and coastal waters, migrating to the open ocean to breed (Pike, Crook & Gollock, 2020).

Lifecycle
The European eel has a fascinating and complex life cycle, marked by one of the most extraordinary migrations of any eel species. For years, their sudden appearance in European waters puzzled scientists, until a Danish biologist in 1904 traced their larvae to the Sargasso Sea. This discovery shed light on their remarkable journey (ZSL, 2016).

Eels begin life as eggs in the depths of the Sargasso Sea, rising towards the sunlit surface as they develop. Once hatched, the transparent larvae are carried across the Atlantic Ocean by currents on a journey of around 6,000 km, which can take up to two years. This is the longest migration route known for any eel species, with survival rates estimated at just 1 in 500 larvae. Upon reaching European coastlines, the larvae transform into small, transparent glass eels about 6 cm long. At this stage, they begin searching for a suitable habitat, darkening into their next form, known as elvers, which provides camouflage from predators (ZSL, 2016).

As Elvers, they migrate upstream, overcoming numerous obstacles and avoiding predators such as fish, birds, and small mammals. Once settled in a habitat with enough food and shelter, they develop into yellow eels. Males may remain in this stage for up to 12 years, while larger females can stay for as long as 20 years. The final stage of their life cycle sees them transform into silver eels, preparing for their return journey to the Sargasso Sea. During this transition, they undergo physical changes to adapt to saltwater conditions, enabling them to survive the long and perilous migration. It is suggested that there, they lay their eggs and perish, however this has never been confirmed (ZSL, 2016). 

Threats
Sadly, the migratory nature of this species makes it particularly vulnerable to a range of threats. Overfishing at different life stages, barriers to migration like dams and other infrastructure, habitat loss, pollution, climate change, rising water temperatures and the spread of parasites and diseases have all played a significant role in its decline (OSPAR, 2022)

Conservation Status:
The European eel (Anguilla anguilla) was last assessed for The IUCN Red List of Threatened Species in 2018, where it was classified as Critically Endangered (Pike, Crook & Gollock, 2020). The species has suffered a 95% decline since the 1980s, attributed in part to factors occurring during the marine phases of its life-cycle.

Future of European Eel in Scotland
The future of European eels in Scotland remains uncertain, as their populations continue to decline across Europe. In response, the European Commission introduced the Eel Recovery Plan (Council Regulation No. 1100/2007) to help restore eel stocks to sustainable levels, requiring each member state to develop its own management plan (European Commission, n.d.). Scotland implemented its own eel management plan in 2008, focusing on conservation efforts to support both adult and juvenile eel populations. The European eel is also listed as a priority species under the UK Biodiversity Action Plan, highlighting its importance for biodiversity and the need for ongoing protection (NatureScot, 2023). Despite these efforts, challenges such as man made barriers, habitat loss and climate change remain significant obstacles to the species' recovery. WIth the future of the species largely unknown