The diet of spotted-necked otters foraging in trout-stocked waters in Mpumalanga, South Africa

Jordaan, Rowan K.; Somers, Michael J.; Hall, Grant; McIntyre, Trevor

doi:10.1080/15627020.2020.1741447

Cited by 3 publications

(4 citation statements)

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“…Stable isotope analysis is an important method to study the relationships within consumer food web [24]. The δ 15 N value of consumer is 3.4±1.1‰ higher than that of their food [1][2][3][4][5][6][7]. According to this characteristic, we studied the food chain and its nutritional level characteristics in the aquatic ecosystem in the Pearl River.…”

Section: Consumer Food-web Structure and Trophic Levelmentioning

confidence: 99%

“…Analysis of δ 15 N values is the most common method to study the food network and TL in water ecosystems [61]. Previous studies have found that the δ 15 N value of a predator will be 2.4‰-4.4‰ higher than that of its prey, with an average value of 3.4‰ [1][2][3][4][5][6][7]. There was evidence showing that the TL of POM (phytoplankton) is set to one, the structure of the food web in the system is usually at four TL.…”

Section: Consumer Food-web Structure and Trophic Levelmentioning

confidence: 99%

“…Stable isotope technology has been used to study food-network structure and trophic levels in aquatic ecosystems. Studies have shown that the average carbon stable isotope δ 13 C value of consumers is 1‰ higher than that of their food, while the average nitrogen stable isotope δ 13 N value of consumers is 3.4 ±1‰ higher than that of their food [1][2][3][4][5][6][7]. Based on this principle, food sources and trophic levels in the ecosystem can be established.…”

Section: Introductionmentioning

confidence: 99%

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Nutrients Affecting the Characteristics of Food-Web Structure in Aquatic Ecosystem of Pearl River

Xiang¹,

Long²,

Dang³

2022

Pol. J. Environ. Stud.

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The water quality has degraded with economic development globally. However, the relationship between food-web structure and nitrogen and phosphorus is of rare concern. To study food chain in this ecosystem, we measured the concentrations of stable isotope value δ 13 C and δ 15 N in aquatic matter and organisms in Pearl River. The δ 13 C and δ 15 N concentrations ranged from −41.2‰ to −19.4‰ and from 0.81‰ to 25.4‰, respectively. The δ 13 C concentrations in consumers were significantly higher than the particulate organic matter (POM), periphyton, phytoplankton, and higher aquatic plants. The δ 13 C of POM was likely derived from phytoplankton and exogenous organic detritus entering from a tributary, rather than from endogenous phytoplankton in the main river channel. The δ 13 C of phytoplankton was derived from eutrophic water with high nitrogen and phosphorus concentrations. Total δ 13 C was significantly higher in fish than in POM, phytoplankton, higher aquatic plants, and zooplankton, indicating that those components were the main carbon sources for fish. The carbon sources tended to be the same for different fish species in the same season at the same site, but different for a given fish species among seasons and sampling sites. This finding suggested that the feeding habits of different fish species converge as an adaptation to change environment. The food chain was longer (trophic level = 4.4) in river subsections with more carnivorous fish, such as Erythroculter pseudobrevicauda and Coilia grayii, and shorter in areas with more omnivorous fish. The total nitrogen and total phosphorus concentrations in the water were negatively correlated with food-chain length (R 2 = 0.67, P<0.05; R 2 = 0.40, P<0.05). These results suggested that limiting nitrogen and phosphorus inputs into the water body would reduce the ecological risk in this area.

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Section: Consumer Food-web Structure and Trophic Levelmentioning

confidence: 99%

Section: Consumer Food-web Structure and Trophic Levelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Nutrients Affecting the Characteristics of Food-Web Structure in Aquatic Ecosystem of Pearl River

Xiang¹,

Long²,

Dang³

2022

Pol. J. Environ. Stud.

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“…Stocked trout face many challenges to their survival including competition with conspecifics, angling, as well as injury or mortality from piscivorous predators. Indeed, recent work demonstrated that trout form a substantial part of the diets of both African clawless‐ and spotted‐necked otters foraging on fly‐fishing properties (Jordaan et al, 2019, 2020). Furthermore, densities of African clawless otter are substantially higher on some of these properties, when compared to nearby natural areas (Majelantle et al, 2021).…”

Section: Introductionmentioning

confidence: 99%

Stakeholder perceptions of human–predator conflict in the South African fly‐fishing industry

Vos

McIntyre

2023

Afr J Ecol

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Human–wildlife conflict in African aquaculture and fisheries is poorly understood. We investigated this conflict through a questionnaire aimed at owners and managers of fly‐fishing properties in South Africa. While perceptions of losses varied, all respondents reported losses to predators. Resulting mitigation measures, including lethal control, were employed mostly against cormorants (Phalacrocorax spp.) and otters (Aonyx capensis and Hydrictis maculicollis). Given that fly‐fishing properties potentially provide valuable habitat for protected species such as otters, our results highlight a need for improved mitigation measures and exploring alternative options of potentially generating income from tourism associated with the presence of charismatic predators.

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The diving behavior of African clawless and spotted-necked otters in freshwater environments

Jordaan

Somers

McIntyre

2021

Journal of Mammalogy

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Understanding the diving behavior of semiaquatic mammals, particularly in relation to estimated aerobic dive limits and diet, is important to understand their adaptability and potential vulnerability to changes in prey type and distribution. The diving behavior of African clawless otters, Aonyx capensis, and spotted-necked otters, Hydrictis maculicollis, is poorly known, and no estimates of their dive performance in relation to targeted prey and calculated dive limits have been reported previously for freshwater environments. We investigated the diving behavior of both these otter species in freshwater environments within South Africa through video recordings of direct observations and subsequent video analyses where dive and recovery durations and dive function were recorded. African clawless otters were found to perform longer dives (mean ± SD = 26.9 ± 12.2 s), compared to spotted-necked otters (8.5 ± 7.6 s). African clawless otters showed substantial variation in dive durations, with the shortest dives sometimes lasting < 5 s, and the longest recorded dive being 70 s. The majority of spotted-necked otter dives lasted < 10 s, with the shortest recorded dive lasting 0.66 s and the longest recorded dive lasting 50.9 s. Spotted-necked otters performed different dive types that were evidently dependent on prey targeted, with dives targeting crabs (16.10 ± 1.91 s) being longer than dives targeting rainbow trout, Oncorhynchus mykiss (5.58 ± 0.17 s). The theoretical dive durations of African clawless otters were exceeded during play dives, while spotted-necked otters sometimes exceeded their theoretical dive durations when performing successful foraging dives. The results of this study suggest that spotted-necked otters can vary behavior in relation to prey and exceed theoretical dive duration during successful foraging dives to maximize the net rate of energy gain. Furthermore, when considering known individual-level dietary specialization and plasticity in these species, it may be predicted that dive behaviors are likely to vary substantially among individuals, and in relation to prey availability and localized habitat conditions.

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The diet of spotted-necked otters foraging in trout-stocked waters in Mpumalanga, South Africa

Cited by 3 publications

References 59 publications

Nutrients Affecting the Characteristics of Food-Web Structure in Aquatic Ecosystem of Pearl River

Nutrients Affecting the Characteristics of Food-Web Structure in Aquatic Ecosystem of Pearl River

Stakeholder perceptions of human–predator conflict in the South African fly‐fishing industry

The diving behavior of African clawless and spotted-necked otters in freshwater environments

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