Causes and consequences of human induced impacts on a ubiquitous estuary-dependent marine fish species

Whitfield, Alan K.; Grant, Gareth N.; Bennett, RH; Cowley, Paul D.

doi:10.1007/s11160-017-9499-5

Cited by 20 publications

(4 citation statements)

References 86 publications

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“…This was seen anecdotally in the laboratory and also evidenced by a decrease in respiration rates at high salinities found in pilot studies (Kisten 2018). In an ecological context, these results show why R. holubi is able to tolerate and proliferate under high-salinity conditions (Whitfield et al 2006) and can be the most populous marine estuarine-dependant species in intermittently open estuaries during the closed mouth state (James et al 2007, Whitfield et al 2017.…”

Section: Discussionmentioning

confidence: 75%

The effects of hypersalinity on the growth and skeletal anomalies of juvenile Cape stumpnose, <em>Rhabdosargus holubi</em> (Sparidae)

2019

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Estuarine organisms are exposed to hypersaline conditions for prolonged periods during drought conditions and under severely restricted river flow resulting from freshwater abstraction and impoundments. Consequently, marine estuarine-dependent fish such as Rhabdosargus holubi may be subjected to extreme conditions, such as hypersalinity prevailing for long periods ( > 2 months). Hypersalinity may impact the energetic demands of fish due to osmoregulation leading to compromised growth. This study assessed the impact of high salinity on the growth and skeletal development of R. holubi juveniles. Skeletons of juveniles grown at different salinities in the wild and in aquaria were analysed for anomalies. The impact of hypersaline conditions on juvenile R. holubi growth was also determined in aquaria. Aquarium experiments indicated that hypersalinity of 50 did not significantly impact growth rates over two months. Overall, anomalies were rare and vertebral-related anomalies specifically did not differ significantly between salinities. However, fin rays were significantly impacted in fish growing at higher salinities in the wild. It was concluded that the strong osmoregulatory ability of R. holubi offers protection against hypersalinity affecting internal structures, but external structures may remain vulnerable. As such, from a locomotory standpoint, R. holubi may be vulnerable to long periods of exposure to hypersaline conditions.

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Section: Discussionmentioning

confidence: 75%

The effects of hypersalinity on the growth and skeletal anomalies of juvenile Cape stumpnose, <em>Rhabdosargus holubi</em> (Sparidae)

2019

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“…Habitat choice is, however, species-specific, and what is described in the literature cannot always be applied generally. The estuarine-dependent sparid Rhabdosargus holubi is one of the most abundant marine fish species in estuaries along the eastern and southern coasts of South Africa (Whitfield et al, 2018). Although R. holubi juveniles (<140 mm standard length [LS]) occur throughout shallow estuarine habitats (Becker et al, 2010(Becker et al, , 2012, it is primarily regarded as a vegetation-associated species (Hanekom & Baird, 1984;James et al, 2019;Sheppard et al, 2012).…”

Section: Introductionmentioning

confidence: 99%

“…However, the relationship between habitat complexity and habitat choice and whether habitat choice is mediated by predation risk and fish size has never been empirically tested for this species. Being estuarine dependent, this species is under pressure from numerous anthropogenic impacts, including habitat loss, and in particular reduced submerged macrophyte areas in estuaries (Whitfield et al, 2018). Thus, assessing habitat choice for this species has potential implications for general estuary ecosystem functioning.…”

Section: Introductionmentioning

confidence: 99%

Juvenile sparids (Rhabdosargus holubi) consistently select structurally dense vegetated habitat in nursery seascapes

Welch,

Childs,

Hempel

et al. 2023

Journal of Fish Biology

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Seagrass habitats provide structural complexity in coastal estuarine and marine environments, which offer fish optimal foraging grounds and refuge from predation. However, seagrasses are some of the most threatened ecosystems globally, with anthropogenic activities such as population growth and environmental degradation leading to the fragmentation, thinning, and loss of these habitats. Rhabdosargus holubi is one of only a few vegetation‐associated marine fish species in South African estuaries. Although field studies have shown a strong association with seagrass over other aquatic vegetation for the juveniles of this species, habitat choice has never been empirically tested. Here, we used artificial vegetation units to test habitat choice (different structural complexities) for this species. We also tested whether habitat choice is influenced by a predatory threat, with fish preferentially selecting dense habitat in the presence of a predator and whether this effect may be more apparent in smaller individuals. We found that R. holubi significantly prefer greater structural complexity over less complex habitats, in both the absence and presence of a predator and for both small and large juveniles, showing that R. holubi actively choose more complex structures and are attracted to the structure per se irrespective of the threat of predation. This study highlights the importance of dense seagrass as nursery areas for this species and demonstrates how the loss of these habitats could impact the nursery function of estuaries.

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“…Convenient fish habitat is a crucial factor for the robustness and sustainability of fish populations [11]. Nevertheless, destroying the habitats over time has resulted in habitat declination for many fish species by leaving their natural habitats and even the disappearance of breeding, feeding, and nursery areas [12]. In addition, IUCN Bangladesh categorized a total of 64 freshwater fish species as threatened, with 9 critically endangered, 30 endangered, and 25 vulnerable among them [13].…”

Section: Introductionmentioning

confidence: 99%

Community-Driven Insights into Fish Assemblage, Microhabitats, and Management Strategies in the Meghna River Basin of Bangladesh

et al. 2023

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The present study aimed to delve into the local ecological knowledge of fisheries in the Meghna River Basin (MRB) of Bangladesh by exploring the insights and perspectives of local communities. A survey was administered among six fishing communities from five districts along the MRB between August 2015 and January 2016 to accumulate data for this study. The study sites were selected meticulously based on three crucial criteria: upstream river, coastal area, and fish sanctuaries, which covered three major rivers, namely the Meghna, Andharmanik, and Payra. The study employed participatory rural appraisal (PRA) tools, including 120 individual interviews using purposive sampling, 25 focus group discussions, and 36 key informant interviews. The study identified the ten most frequently caught fish species along with their temporal and spatial variation as reported by the respondents. Nine of these species fell into the least concern category, which indicate their stable population status. Meanwhile, six out of ten species cited as highly caught in the previous one to two decades belong to the threatened or near-threatened category. Findings also reveal that fishers are able to recognize important microhabitats of the study area and their significance for fish species. In addition, fishers identified the negative drivers of ecosystem degradation as well as suggested several management measures to address these challenges. The results of this study underscore the critical role of engaging with local communities and integrating their ecological knowledge into initiatives for the sustainable exploitation and conservation of aquatic resources in the MRB.

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Causes and consequences of human induced impacts on a ubiquitous estuary-dependent marine fish species

Cited by 20 publications

References 86 publications

The effects of hypersalinity on the growth and skeletal anomalies of juvenile Cape stumpnose, <em>Rhabdosargus holubi</em> (Sparidae)

The effects of hypersalinity on the growth and skeletal anomalies of juvenile Cape stumpnose, <em>Rhabdosargus holubi</em> (Sparidae)

Juvenile sparids (Rhabdosargus holubi) consistently select structurally dense vegetated habitat in nursery seascapes

Community-Driven Insights into Fish Assemblage, Microhabitats, and Management Strategies in the Meghna River Basin of Bangladesh

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