Fishing down Canadian aquatic food webs

Pauly, Daniel; Palomares, M.L.D.; Froese, Rainer; Sa-a, Pascualita; Vakily, Michael; Preikshot, David; Wallace, Scott A.

doi:10.1139/cjfas-58-1-51

Cited by 40 publications

(27 citation statements)

References 2 publications

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“…The Kwando and Kavango rivers are less exploited than the heavily fished Upper Zambezi River floodplains, where declining artisanal fishery catch rates are documented for large bodied species which include both, herbivorous-detritivorous cichlids and large predators (Tweddle, 2010;Tweddle et al, 2015). The consequence of this fishing pressure aimed at both the apex and the base of the food web, could be construed as fishing up and down the food web and may have resulted in a reduction in food chain length (Jennings et al, 2002;Pauly et al, 2001). The reduction in food chain length and the removal of predatory fishes might explain the higher trophic positioning of various invertivorous groups (benthic cichlids, topminnows, alestids and synodontids) in the Upper Zambezi River compared to in the Kavango and Kwando rivers.…”

Section: Food-web Analysismentioning

confidence: 99%

Comparing the fish assemblages and food‐web structures of large floodplain rivers

et al. 2017

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The Upper Zambezi, Kavango and Kwando are large floodplain rivers with substantial biodiversity, providing water and ecosystem services to a large tract of southern Africa. These rivers differ in hydrological regime. The Upper Zambezi and Kavango rivers are in flood for 4 months (March, April, May, June) while, in the Kwando River, floods are later and last for 1–2 months in July and August. The Upper Zambezi River has the largest annual flood pulse, followed by the Kavango River, while the Kwando River experiences small and unreliable floods. During years of exceptional flooding of the Upper Zambezi and Kavango rivers, the rivers are interconnected at peak flows and therefore share a common ichthyofauna. This provided a natural experiment to investigate the responses of fish communities comprised of the same species to differing flood regimes by comparing the fish assemblages and food‐web structures between rivers. Fish assemblage structure was characterised by analysing biomass catch per unit effort data collected using gillnets in all water‐level seasons for all three rivers. Whole ecosystem‐stable isotope data collected once from each river were used to examine differences in food‐web structure and fish feeding ecology between rivers. Due to temporal differences in hydrology, the Upper Zambezi and Kavango river food webs were characterised during the low and falling water seasons, while the Kwando River food web was sampled during the rising water season. In the Upper Zambezi and Kavango rivers, fish assemblages varied with hydrological season due to the homogenising influence of the flood pulse, while in the Kwando River fish assemblages did not change seasonally. The Upper Zambezi River food web had a restricted nitrogen range (NR = 0.90), with a reduced food chain length and predators did not occupy elevated trophic positions compared to those in the Kavango and Kwando river food webs (NR = 1.05 and 0.97 respectively). The Kwando and Kavango rivers are less exploited than the heavily fished Upper Zambezi River, where fishing has reduced the abundance of primary and tertiary consumers, potentially resulting in the observed reduction in food chain length. The Upper Zambezi and Kavango river food webs were based on differing basal resources compared to the Kwando River food web. The Upper Zambezi and Kavango river food webs were likely supported by 13C‐enriched resources such as C4 riparian vegetation from the floodplain, while the Kwando River food web was likely based on 13C‐depleted resources such as filamentous algae and aquatic macrophytes. The influence of the varying flood pulses on the fish communities of these three rivers supports the flood pulse concept. There is also evidence that food‐web structures differ between rivers but, due to differing hydrological regimes in the rivers, further study is required to understand causal factors. These ecosystems are increasingly impacted by human population growth and development, as well as climate change, and improved predictions in fish communit...

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Section: Food-web Analysismentioning

confidence: 99%

Comparing the fish assemblages and food‐web structures of large floodplain rivers

et al. 2017

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“…As a consequence, maintaining sustainable fishing in Pelabuhanratu Bay can be achieved by reducing the number of lift nets and fixed gillnets proportionally. In addition, as the number of hand lines has increased annually, their expansion should be controlled because they target higher mean trophic level fishes, and this might lead to fishing down the food web (Pauly, Palomares, Froese, Sa-a, Vakily, Preikshot & Wallace 2001). This was indicated by the change in catch composition in Pelabuhanratu Bay in recent years; the proportion of Trichiurus spp.…”

Section: Fishing Gear Managementmentioning

confidence: 99%

Dynamics of fishing gear allocation by fishers in small‐scale coastal fisheries of Pelabuhanratu Bay, Indonesia

Wiyono

Yamada

Tanaka

et al. 2006

Fisheries Management Eco

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Fishing gear usage in small-scale coastal fisheries of Pelabuhanratu Bay, Indonesia was explained by two approaches: temporal fishing gear allocation analysis and adaptive responses of fishers to external factors, especially climate and abundance of target species. Gear usage, with the exception of hand lines and seine nets, was more intensive during the dry season than the rainy season. The decision to use seine nets was governed by seasonal variability in the abundance of Auxis thazard, Lacepe`de, and Trichiurus spp. to the catch. Sustainable management of fishing activities in Pelabuhanratu Bay requires proportional reductions in the use of lift nets and fixed gillnets across the seasons rather than gear specific effort reductions.fishing gear allocation, Indonesia, seasonal dynamics, small-scale coastal fisheries.

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“…We might expect that in sites where fishing is restricted the increase in numbers and sizes of carnivorous fishes (predators) will determine topdown processes with a decrease in both numbers and sizes of smaller fish species and a consequent increase in the invertebrates on which these fishes feed. Accordingly, we would also expect a decrease in the trophic level of fish communities in fished sites compared to no-take areas (Pauly et al 2001;Pinnegar et al 2002).…”

Section: Introductionmentioning

confidence: 98%

Stable isotopes and trophic positions of littoral fishes from a Mediterranean marine protected area

Vizzini

Mazzola

2008

Environ Biol Fish

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Stable isotope analyses were employed to explore feeding and foraging habitats and trophic levels of littoral fishes in a western Mediterranean Marine Protected Area (Egadi Islands, Sicily, Italy). Carbon and nitrogen stable isotope ratios were measured in primary producers, invertebrates and fishes collected in December 2001 and January 2002. Fishes of the littoral region of the Egadi Islands had isotopic signatures that fell into a wider range for δ 13 C (about 6‰) than for δ 15 N (about 3‰). Carbon isotope ratios were consistent with a food web based on mixed sources and two trophic pathways leading to different fish species. Differences in the isotopic composition between islands were higher for benthivorous than for planktivorous fishes. The overall picture gained from this study is of a isotopic distinction between planktivorous and benthivorous fishes, resource partitioning facilitating the coexistence of similar species within the same ecosystem, and spatial variability in the isotopic signatures and trophic level of fishes. Asymmetrical analysis of variance showed that estimated trophic levels were lower in the area with the highest level of protection (Zone A) for only two out of the nine fishes analysed. As a consequence, overall spatial differences do not seem to be a consequence of protection, since in most cases trophic levels did not change significantly between zone A and zones C where professional fishing (trawling apart) is permitted, but of natural sources of variation (e.g. variability in food availability and sitespecific food preferences of fishes). However, the results of this study suggest a different response at the species compared to the community level.

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Fishing down Canadian aquatic food webs

Cited by 40 publications

References 2 publications

Comparing the fish assemblages and food‐web structures of large floodplain rivers

Comparing the fish assemblages and food‐web structures of large floodplain rivers

Dynamics of fishing gear allocation by fishers in small‐scale coastal fisheries of Pelabuhanratu Bay, Indonesia

Stable isotopes and trophic positions of littoral fishes from a Mediterranean marine protected area

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