What question did this study set out to answer?

The research aims to estimate population parameters of European eel subpopulations in different habitats in Croatia.

February 25, 2026Open Access

Habitat-Driven Population Parameters Insights for European Eel Anguilla anguilla (Linnaeus, 1758) in Croatian Waters

Key Points

The research aims to estimate population parameters of European eel subpopulations in different habitats in Croatia.
Sampling conducted at 23 locations along the Croatian coast
Data collected included age, length, weight, and habitat type
Statistical analysis included length-weight relationships and mortality rates
Population dominated by undifferentiated eels in freshwater and females in brackish habitats
Higher b-coefficient and better condition in freshwater eels
Natural mortality estimated at 0.191 year−1 in freshwater and 0.174 year−1 in brackish areas
More than 50% of three-year-old eels are over-exploited
Recommendations to increase minimum landing size for better population resilience.

Abstract

Key parameters were estimated separately for the European eel, Anguilla anguilla (Linnaeus, 1758) subpopulations across freshwater and brackish environments within the Eastern Adriatic Eel Management Unit (EMU: EA). Between 2023 and 2024, European eel sampling was carried out at 23 locations along the Croatian coast (N = 678). Ages ranged from 1 to 13 years in freshwater and 1 to 8 years in brackish waters. The population structure was dominated by undifferentiated (42.8%) in freshwater and females (46.3%) in brackish habitats. Eels in freshwater exhibited a significantly higher b-coefficient in their length–weight relationship and better condition. Based on the otolith annuli patterns, age classes 3 to 5 predominated in both groups. A slightly longer asymptotic length and lower growth rate were found for the freshwater group compared to a shorter length and higher growth rate in the brackish habitat. Natural mortality was estimated at 0.174 ± 0.09 year−1 and 0.191 ± 0.133 year−1 for brackish and freshwater habitats, respectively. Total mortality was higher in freshwater (0.86 year−1) in comparison with the brackish (0.83 year−1) habitat. According to obtained results, more than 50% of eels aged three years are under exploitation. The maximum Yield per Recruit (Y/R) was 0.082 g/recruit in brackish at Lc = 44.88 cm, and a current Lc is 19.4 cm in the samples. In freshwater, Y/R peaked at 0.042 g/recruit at Lc = 55.49 and a current Lc 11.1 cm. It is recommended, following a precautionary approach to management, that the current fishing practices change in order to increase the minimum landing size (MLS), at least to 45 cm (above the current official MLS of 35 cm), to increase the fishing yield, and directly enhance population resilience. Findings emphasise the need for sustainable eel management policies considering different subpopulation parameters along the freshwater/brackish gradient at a small spatial scale when proposing and implementing stock management measures.

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