Preferred gap structure within stone piles of fishing gear by Japanese eel Anguilla japonica at each life history stage: the search for an effective method to restore estuarine habitats

Published source details Oto Y., Sakanoue R., Hibino Y., Matsushige K., Utida K. & Mochioka N. (2022) ニホンウナギの各生活史段階における石倉カゴの浮石間隙構造への選好性 汽水域のハビタットの効果的な復元に向けて. Nippon Suisan Gakkaishi (Japanese edition), 88, 152-161.
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This study is summarised as evidence for the following.

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A replicated study in 2020–2021 in a river in Fukuoka Prefecture, Japan (Oto et al. 2022) found that baskets filled with stones were used by Japanese eels Anguilla japonica, and that more yellow eels were found in baskets with small stones compared to medium or large stones but there was no difference for silver eels. Over nine months, five glass eels (average length: 6 cm), 164 yellow eels (average length: 24 cm) and 10 silver eels (average length: 53 cm) were observed using baskets filled with stones. On average, more yellow eels were found in baskets with small stones (3.4 eels) compared to medium (1.2 eels) or large stones (0.8 eels). There was no difference in the average number of silver eels found in baskets with different stone sizes (small: 0 eels, medium: 0.7 eels, large: 0.3 eels). Overall, the length of yellow eels did not differ significantly between stone sizes (small: 10–51 cm, medium: 11–56 cm, large: 11–41 cm), nor did yellow eel weight (small: 2–175 g, medium: 3–295 g, large: 2–91 g). Six baskets, two of each filled with small (10 cm), medium (20 cm) and large stones (30 cm), were installed 550 m upstream of the river mouth. Baskets were placed on rubber mats on the riverbed at 1-m intervals and 1-m from the bank. Baskets were surveyed 15 times from August–December 2020 and April–July 2021. Eels were counted, anaesthetised and measured.

(Summarised by: Vanessa Cutts)