Large contribution of pulsed subsidies to a predatory fish inhabiting large stream channels

Itakura, Hikaru; Miyake, Yoichi; Kitagawa, Takashi; Sato, Tadanobu; Kimura, Shingo

doi:10.1139/cjfas-2020-0004

Cited by 13 publications

(5 citation statements)

References 48 publications

(7 reference statements)

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“…A similar effect of concrete revetment on the density of large Japanese eel (≥25.5 cm TL) has also been detected in the tidal zone of rivers in Kyushu, southern Japan (Matsushige, Yasutake & Mochioka, 2020). Bank revetment would lead to a reduced carrying capacity for Japanese eel through losses of their prey, such as small fishes, aquatic invertebrates, and terrestrial earthworms (Kawaguchi et al, 2006; Itakura et al, 2015; Itakura et al, 2021), as well as of eel habitat per se.…”

Section: Discussionmentioning

confidence: 99%

Riverine distribution and abundance of Japanese eel in Shikoku, south‐western Japan: Varying importance of regional and local factors

Yamamoto

Uemura

Mimachi

et al. 2023

Aquatic Conservation

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Regional and local habitat factors affecting the distribution and abundance of Japanese eel (Anguilla japonica) were systematically analysed in 123 reaches of 21 stream systems in south‐western Japan, with particular attention paid to human habitat modification, such as artificial barriers and concrete revetment. The density of Japanese eel decreased upstream, and they were absent from the upper reaches of each stream system. The upper limits of their distribution were explained by the distance from the sea and the channel gradient, rather than barriers. However, the number of barriers had the highest explanatory capacity for the upstream decline in abundance of small eels (<40 cm in total length). Analyses of the relative importance of regional and local habitat factors showed that the number of barriers (regional factor) was more important than local habitat factors in determining small eel abundance, whereas regional and local habitat factors (e.g. concrete revetment or cover habitat) were similarly important for large eel abundance. These results suggest that: (i) barriers are not a major factor limiting the distribution (presence/absence) of the Japanese eel in the streams studied; (ii) barriers can substantially decrease the abundance of young eels; and (iii) as eels grow older and larger, local habitat factors, such as bank conditions and cover, become more important in determining their abundance. The results for the relative importance of regional and local habitat factors suggest that in habitat restoration for the Japanese eel, priority should be given to mitigating barrier effects. The improvement of longitudinal connectivity to facilitate colonization by young eels is primarily needed for a more efficient use of the existing carrying capacity of streams. The improvement of local habitat conditions to increase the carrying capacity should be conducted in stream reaches free from barrier effects.

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Section: Discussionmentioning

confidence: 99%

Riverine distribution and abundance of Japanese eel in Shikoku, south‐western Japan: Varying importance of regional and local factors

Yamamoto

Uemura

Mimachi

et al. 2023

Aquatic Conservation

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“…Any effects of pulsed prey supply on predators in our study were time-limited. In general, prey supplied pulse-wise are not regular food items for predators [3,31], and predators may be unable to accommodate these prey due to mismatches in, for example, foraging behaviour. Finally, our study highlights the importance of ‘ecosystem-based’ fisheries management strategies in which the effects of predator–prey interactions and intra- and interspecific competition on ecosystem structuring are taken into account [32].…”

Section: Discussionmentioning

confidence: 99%

Pulsed supplies of small fish facilitate time-limited intraguild predation in salmon-stocked streams

Hasegawa

Fukui

2022

R. Soc. open sci.

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Pulsed supplies of prey generally increase predator food intake. However, it is unclear whether this holds true when predators and pulsed prey are in the same guild (i.e. intraguild (IG) predators and prey). IG prey may increase IG-predator food intake through predation, but they may decrease food intake through competition. To test these hypotheses, we compared the food intake of white-spotted charr ( Salvelinus leucomaenis ) (IG predator) in streams that were stocked or unstocked with masu salmon ( Oncorhynchus masou ) fry (IG prey) in streams in Hokkaido, Japan. One day after stocking, mean stomach content weight of charr was six times higher than in unstocked streams due to fry consumption. In particular, large charr showed intense piscivory. However, predation on fry was rare after about three weeks. Some factors that could explain this time-limited IG predation include the growth and decreasing abundance of fry over time and the acquisition of predator-avoidance behaviour. In days other than the first-day post-stocking, food intake by charr did not differ between stocked and unstocked streams. No effects of interspecific competition on charr food intake were observed.

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“…In contrast to previous reports, any effects of pulsed prey supply on predators was short lived. In general, prey supplied pulse-wise are not regular food items for predators (e.g., Stephens et al 2019;Itakura et al 2021), and predators may be unable to accommodate these prey due to mismatches in foraging behavior or digestive ability. S2.…”

Section: Discussionmentioning

confidence: 99%

Pulsed supplies of small fish facilitate short-term intraguild predation in salmon stocked streams

Hasegawa

Fukui

2021

Preprint

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Pulsed supplies of prey organisms generally increase predator food intake. However, whether this holds true when predators and pulsed prey are in same guild (i.e., intraguild [IG] predators and prey) is unclear. IG prey may increase IG-predator food intake by providing a food source, but they may decrease food intake through competition. To test these hypotheses, we compared the food intake of white-spotted charr (Salvelinus leucomaenis) (IG predator) in streams that were stocked or unstocked with hatchery-reared masu salmon (Oncorhynchus masou) fry (IG prey) in streams in Hokkaido, Japan. One day after stocking, masu salmon fry occupied nearly 60% of the stomach contents by wet weight of white-spotted charr in stocked streams, and mean stomach content weight was six-times higher than in unstocked streams. However, predation of white-spotted charr on stocked fry was rare on other days. Acquisition of predator-avoidance behavior by stocked fry and/or a lack of accommodation by white-spotted charr to the sudden emergence of a new prey source (e.g., the charr in study sites were basically insectivorous, and their foraging behavior might have been ineffective for piscivory) may explain this time-limited intraguild predation. In days other than the first day post-stocking, food intake by white-spotted charr did not differ between stocked and unstocked streams. No effects of interspecific competition on white-spotted charr food intake were observed; this may be due to the body-size advantage of white-spotted charr and/or the low density of stocked masu-salmon fry.

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Large contribution of pulsed subsidies to a predatory fish inhabiting large stream channels

Cited by 13 publications

References 48 publications

Riverine distribution and abundance of Japanese eel in Shikoku, south‐western Japan: Varying importance of regional and local factors

Riverine distribution and abundance of Japanese eel in Shikoku, south‐western Japan: Varying importance of regional and local factors

Pulsed supplies of small fish facilitate time-limited intraguild predation in salmon-stocked streams

Pulsed supplies of small fish facilitate short-term intraguild predation in salmon stocked streams

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