Summary To investigate the difference in growth rates of eels in the studied water bodies (Võrtsjärv, Ülemiste, Saadjärv, Vagula, Kaiavere and Kuremaa lakes, all in Estonia), 828 individual eel otoliths from the years 1999–2004 and 2008–2012 were examined for age determination. Anguilla anguilla captured in Lake Võrtsjärv mostly by professional fyke nets (mesh size >36 mm in the cod end) showed the best growth rate (gR = 6.9 cm/year) and had a high Fulton condition factor (K = 0.19), indicating suitable growth conditions in the lake. However samples caught using the same type of gear from the smaller lakes situated near Võrtsjärv, showed much slower gR (3 cm/year) and lower K (0.17) growth rates. The slowest gR (2.6 cm/year) was observed for specimens caught in Lake Kuremaa. Stocking densities are much higher in the small lakes of the region and have a direct effect on the growth rates.

To stop the decline of the European eel population, one of the measures taken is translocating eels for restocking, despite its conservational value being largely unknown. We aimed to contribute to this knowledge gap by (i) investigating the origin of eels caught in coastal waters of Estonia and Finland using otolith microchemistry and (ii) directly estimating restocked eel escapement from Narva River Basin District (NRBD), which is part of the primary Eel Management Unit in Estonia. In Estonia, 74% of the sampled eels (n = 140) were natural recruits and 26% were restocked. In Finland, 27% of the sampled eels (n = 235) were natural recruits and 73% were restocked. Only 1% of all the coastally collected eels were originally restocked to NRBD. These new data together with the reported commercial landings from the escapement route conflict with the current silver eel escapement estimation for NRBD and question the accuracy and value of such indirect calculations compiled for most Eel Management Units throughout the European Union. It is concluded that restocking eels to freshwaters may be futile as a conservation measure in some situations, and better escapement is likely achieved in restocking eels to coastal waters or undammed freshwater systems with a direct connection to the sea.

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Composting is a sustainable method for recovering nutrients from various organic wastes, including food waste. Every input waste has different nutrient contents, in turn, suggesting that every compost has different fertilizer and/or soil improvement values. The phosphorus (P) concentration and relative distribution of P forms is related to the original organic material. The relative distribution of P forms determines how readily plants can absorb P from the compost-amended soil. The aim of this study was to investigate the content and relative share of P forms in composts made from fish waste, sewage sludge, green waste, and horse manure. Six forms of P (labile; bound to reducible metals; bound to non-reducible metals; bound to easily degradable organic material; and bound to calcium) were determined using sequential extraction method. The results indicated that fish waste compost had relatively high proportion of labile P, suggesting good biological availability. In comparison, sewage sludge compost contained the highest overall P concentration per dry weight unit, while labile P constituted only 6% of summary of P forms. The results indicate that the evaluation of composts as alternative P sources in agriculture should rely on the relative distribution of P forms in the compost in addition to the typically recognized value of the total P.

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