Density‐dependent growth, survival, and biomass production of stocked glass eels (Anguilla anguilla) in seminatural ponds

We sought to demonstrate how eel mortality, growth, and biomass production were related to initial stocking density of glass eels, 18 months after stocking. Glass eels with a mean body mass of 0.29 g were caught in three coastal streams of Denmark, and subsequently stocked at four densities (0.5, 1, 1.5, and 2 individuals m⁻²) in eight shallow, 200 m², open ponds. Recapture after 18 months ranged from 13% to 84% and was negatively correlated with stocking density. Likewise, growth (length and body mass) and body condition were negatively correlated with stocking density. The theoretical maximum biomass per stocked glass eel was 7.3 g at a density of 0.005 eels per m⁻² (one glass eel per pond), and the minimum was at a density of 3 glass eel m⁻² (600 glass eels per pond). The optimum eel biomass was 3.9 g m⁻² at a stocking density of ≈1 glass eel m⁻², which probably represented the present production capacity (food) of these ponds.