Reduced dry season fish biomass and depleted carnivorous fish assemblages in unprotected tropical oxbow lakes

Strong relationships between seasonal flooding, instream habitat structure and fish assemblages have been well documented in large tropical rivers (e.g. the flood pulse concept). However, the mechanics of these relationships are likely to differ substantially in smaller coastal rivers, such as those in Costa Rica, south-east Brazil and Australia’s Wet Tropics. These systems typically feature steep upland streams with short, deeply incised lowland channels and poorly connected floodplains. This hypothesis was investigated by documenting spatial and temporal variation in fish-habitat relationships in the Mulgrave River, north-east Queensland. Sampling was conducted at four lowland sites under a range of flow conditions, from dry-season baseflows to a one-in-ten-year flood. Longitudinal environmental gradients and fine-scale habitat patches were important in regulating fish assemblage structure during the dry season. However, high wet-season flows, constrained by the deep channel, acted as disturbances rather than gentle flood-pulses. In particular, the mobilisation of bed sediments led to scouring of aquatic vegetation and a dramatic reduction in habitat heterogeneity. Seasonal movements of fish led to significant changes in assemblage structure – from a community dominated by Neosilurus ater, Hypseleotris compressa, Awaous acritosus and Redigobius bikolanus during the dry season, to one dominated by Nematalosa erebi, Ambassis agrammus and Glossamia aprion during the wet season. Based on these observations, together with information from the literature, a conceptual model of fish-habitat dynamics is presented that is better suited to small tropical rivers than those developed in larger systems with expansive floodplains.

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What are the main local drivers determining richness and fishery yields in tropical coastal fish assemblages?

Zoologia (Curitiba) ◽

10.3897/zoologia.35.12898 ◽

2018 ◽

Vol 35 ◽

pp. 1-12

Author(s):

Cynthia Diniz Souza ◽

Vandick S. Batista ◽

Nidia Noemi Fabré

Keyword(s):

Wind Speed ◽

Rainy Season ◽

Fish Assemblages ◽

Principal Component ◽

Dry Season ◽

Community Diversity ◽

Tropical Species ◽

Coastal Fish ◽

Wide Range ◽

Diversity Profiles

Seasonal ecological effects caused by temperature and photoperiod are typically considered minimal in the tropics. Nevertheless, annual climate cycles may still influence the distribution and abundance of tropical species. Here, we investigate whether seasonal patterns of precipitation and wind speed influence the structure of coastal fish assemblages and fishing yields in northeast Brazil. Research trips were conducted during the rainy and dry seasons using commercial boats and gear to sample the fish community. Diversity was analyzed using abundance Whittaker curves, diversity profiles and the Shannon index. Principal Component Analysis (PCA) was used to analyze associations between the abundance of species and various environmental variables related to seasonality. A total of 2,373 fish were collected, representing 73 species from 34 families – 20 of which were classified as both frequent and abundant. Species richness was greater and more equitable during the rainy season than the dry season – driven by changes in the precipitation rather than to wind speed. Species diversity profiles were slightly greater during the rainy season than the dry season, but this difference was not statistically significant. Using PCA was identified three groups of species: the first associated with wind speed, the second with precipitation, and the third with a wide range of sampling environments. This latter group was the largest and most ecologically heterogeneous. We conclude that tropical coastal fish assemblages are largely influenced by local variables, and seasonally mediated by annual changes related to precipitation intensity and wind speed, which in turn influences fishery yields.

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Subsistence harvesting by a small community does not substantially compromise coral reef fish assemblages

ICES Journal of Marine Science ◽

10.1093/icesjms/fsx043 ◽

2017 ◽

Vol 74 (8) ◽

pp. 2191-2200 ◽

Cited By ~ 6

Author(s):

Tyson S. H. Martin ◽

Rod M. Connolly ◽

Andrew D. Olds ◽

Daniela M. Ceccarelli ◽

Douglas E. Fenner ◽

...

Keyword(s):

Reef Fish ◽

Fish Assemblages ◽

Fish Communities ◽

Marshall Islands ◽

Fish Biomass ◽

Small Community ◽

Fish Community Structure ◽

Small Communities ◽

Top Predators ◽

Subsistence Fishing

Abstract Fisheries usually first remove large predators before switching to smaller species, causing lasting changes to fish community structure. Reef fish provide essential protein and income for many people, and the impacts of commercial and high-intensity subsistence fishing on reef fish are well documented. However, how fish communities respond to low levels of subsistence fishing using traditional techniques (fishing for food, few fishers) is less well understood. We use three atolls in the Marshall Islands as a model system to quantify effects of commercial and subsistence fishing on reef fish communities, compared to a near-pristine baseline. Unexpectedly, fish biomass was highest on the commercially-fished atoll where the assemblage was dominated by herbivores (50% higher than other atolls) and contained few top predators (70% lower than other atolls). By contrast, fish biomass and trophic composition did not differ between pristine and subsistence-fished atolls – top predators were abundant on both. We show that in some cases, reefs can support fishing by small communities to provide food but still retain intact fish assemblages. Low-intensity subsistence fishing may not always harm marine food webs, and we suggest that its effects depend on the style and intensity of fishing practised and the type of organisms targeted.

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Assessing the importance of fishing impacts on Hawaiian coral reef fish assemblages along regional-scale human population gradients

Environmental Conservation ◽

10.1017/s0376892908004876 ◽

2008 ◽

Vol 35 (3) ◽

pp. 261-272 ◽

Cited By ~ 63

Author(s):

I. D. WILLIAMS ◽

W. J. WALSH ◽

R. E. SCHROEDER ◽

A. M. FRIEDLANDER ◽

B. L. RICHARDS ◽

...

Keyword(s):

Coral Reef ◽

Population Density ◽

Human Population ◽

Fish Assemblages ◽

Regional Scale ◽

Reef Fishes ◽

Human Populations ◽

Fish Biomass ◽

Human Population Density ◽

General Decline

SUMMARYHumans can impact coral reef fishes directly by fishing, or indirectly through anthropogenic degradation of habitat. Uncertainty about the relative importance of those can make it difficult to develop and build consensus for appropriate remedial management. Relationships between fish assemblages and human population density were assessed using data from 18 locations widely spread throughout the Main Hawaiian Islands (MHI) to evaluate the significance of fishing as a factor potentially driving fish trends on a regional scale. Fish biomass in several groups was negatively correlated with local human population density and a number of lines of evidence indicate that fishing was the prime driver of those trends. First, declines were consistently evident among fish groups targeted by fishers, but not among lightly fished or non-target groupings, which indicates that declines in target groups were not simply indicative of a general decline in habitat quality along human population gradients. Second, proximity to high human populations was not associated with low fish biomass where shoreline structure prevented ready access by fishers. Relatively remote and inaccessible locations within the MHI had 2.1–4.2 times the biomass of target fishes compared to accessible and populous locations, and may therefore function as partial refugia. However, stocks in those areas were clearly far from pristine, as biomass of large predators was more than an order of magnitude lower than at more intact ecosystems elsewhere in the Pacific.

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Patterns of Fish Assemblage, Growth, and Diet Composition in a Tropical River between Two Cascading Hydropower Dams

International Journal of Ecology ◽

10.1155/2021/6652782 ◽

2021 ◽

Vol 2021 ◽

pp. 1-10

Author(s):

Lee Nyanti ◽

Chen-Lin Soo ◽

Afina-Yian Chundi ◽

Elsa-Cordelia-Durie Lambat ◽

Alvinna Tram ◽

...

Keyword(s):

Fish Species ◽

Diet Composition ◽

Fish Assemblages ◽

Condition Factor ◽

Dry Season ◽

Growth Patterns ◽

Native Fish ◽

Wet Season ◽

Fish Samples ◽

The Impact

Construction of cascade dams has been shown to have impacts on fish assemblages and biodiversity. Yet, there is no literature on fish assemblages in the Murum River that connects the cascading Bakun and Murum dams in Sarawak, Malaysia. Hence, study on this modified ecosystem is necessitated to better understand the effects of the cascade dam construction on fish fauna. For this, fish samples were caught at five stations located along the river during both dry and wet seasons. Environmental parameters were taken concurrently with fish sampling. Length-weight relationship, condition factors, and diet composition of selected fish species in the river were also determined. The present study demonstrated that there are indications of the impact of cascading dams on the formation of a complex ecosystem in the Murum River, that is, changing from the shallow downstream of the Murum Dam to the deep transitional and inundated zone of the Bakun reservoir. The transitional zone in the Murum River exhibited the lowest fish species diversity, richness, and evenness during the dry season due to low pH and DO coupled with high turbidity. The biological indices improved when the water quality improved during the wet season. On the contrary, the diversity and evenness indices at the inundated tributary station decreased remarkably during the wet season, likely due to the migration of fish during the onset of the rainy season. This study showed that Barbonymus schwanenfeldii has a wider feeding habit which contributes to its higher distribution and abundance in the Murum River. The growth patterns of B. schwanenfeldii, Cyclocheilichthys apogon, Hampala macrolepidota, Lobocheilos ovalis, and Osteochilus enneaporos were better during wet than dry season. Overall, the condition factor of all native fish species in the Murum River was in poor to fair condition, whereas the exotic species, Oreochromis mossambicus, exhibited excellent condition (K value > 2) for both seasons. The increase in the number of O. mossambicus coupled with its high condition factor indicates biological intrusion and a potential threat to the native fish species in the Murum River. Continuous monitoring is essential to detect in-time risk issues associated with environmental degradation and biological invasion in this regulated and inundated river ecosystem.

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Fish Assemblages in a Small Mangrove System on Príncipe Island, Gulf of Guinea

Frontiers in Marine Science ◽

10.3389/fmars.2021.721692 ◽

2021 ◽

Vol 8 ◽

Author(s):

Mariana Cravo ◽

Armando J. Almeida ◽

Hamilton Lima ◽

João Azevedo e Silva ◽

Salomão Bandeira ◽

...

Keyword(s):

Fish Species ◽

Fish Assemblages ◽

Developmental Stages ◽

Environmental Parameters ◽

Mangrove Ecosystem ◽

Dry Season ◽

Fish Distribution ◽

Food Sources ◽

Revealed Preferences ◽

Sao Tome And Principe

Mangroves are highly productive ecosystems with complex adaptations to the transition between freshwater and sea. Mangroves function as nursery habitats for many organisms, providing protection and food sources for early developmental stages of crustaceans and fish, helping to maintain adjacent marine stocks. Mangroves in São Tomé and Príncipe remain poorly studied. This study addresses the importance of a small mangrove stand to ichthyofauna. The main goal of the study was to describe the fish assemblages of the Praia Salgada mangrove stand on Príncipe Island, and assess if variations in the season, tide, and mangrove zone affected fish distribution. Fish assemblages were sampled with mosquito nets during the rainy and dry seasons, and neap and spring tides, while environmental parameters such as water depth, temperature, pH, and salinity measurements were taken. The characteristics of the water column were affected by a sandbank that developed between sampling seasons, impacting on the dynamics of the water and biological exchanges between the mangrove stand and the adjacent marine environment. The study identified 14 fish species occurring in the Praia Salgada mangrove stand from a total of 772 specimens caught. Five species were recorded for the first time as occurring in the country’s mangrove areas, namely Caranx latus, Ethmalosa fimbriata, Mugil curema, Gobioides cf. africanus, and Citharus cf. linguatula. Most of the reported species are of commercial interest, and were predominantly juveniles, suggesting that the mangrove ecosystem provides a nursery function for several species. Some species revealed preferences for either the upper or lower part of the mangrove forest. The size of fish sampled tended to be bigger during the dry season, especially for the Mugilidae, Aplocheilichthys spilauchen and Gobiidae groups. E. fimbriata and Eucinostomus melanopterus displayed similar sizes between seasons. The average quantity of fish caught per day in the rainy season was three times higher than in the dry season. The fish species distribution in the mangrove stand varied significantly according to the season and mangrove zone. The overall results suggest that the Praia Salgada mangrove stand provides a nursery function for several of the studied fish species.

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Wetland dynamics at the transition between humid and semiarid environments of inland Brazil: São Francisco river morphodynamics and implications for the Pandeiros wetland.

10.5194/egusphere-egu21-9075 ◽

2021 ◽

Author(s):

Diego Alves de Oliveira ◽

Cristina Helena Ribeiro Rocha Augustin ◽

Trevor Hoey ◽

Cristina Persano

Keyword(s):

Hydrological Regime ◽

Dry Season ◽

Oxbow Lakes ◽

Wet Season ◽

Buffer Zones ◽

Mato Grosso ◽

Base Level ◽

Level Data ◽

Annual Range ◽

Flood Pulses

The presence of wetlands as a result of local fluvial and hydrological conditions constitutes a frequently observed feature of such rivers. Therefore, they are important elements of the basin, because besides functioning as buffer zones for CO2 and sediments they also house important ecosystems, playing an important role in the control of water circulation.&#160;Brazilian wetlands have different typologies and sizes, varying from huge swamplands such as the Pantanal do Mato Grosso, to flooded savannas called &#8220;veredas&#8221; or oxbow lakes. Their distribution in inland areas depends on the variety of flood pulses mainly linked to seasonality with the presence of distinct dry and wet seasons (Junk et al., 1989).&#160;This strong seasonality affects the S&#227;o Francisco River (SFR), the 4th largest river in Brazil, which has frequent marginal lakes and swamps as it passes through five Brazilian states. This research aims to analyze the effect of the variation of the SFR level from 1925 to 2018, on the flow of the Pandeiros River which is one of many tributaries on the left side of SFR and on its wetland (&#8220;Pantanal Mineiro&#8221;). This wetland is hydrogeomorphologically linked to the SFR and receives water inputs during SFR flood periods.&#160;Measurements of the SFR water level performed once daily in the morning were obtained from gauging station no 44200000 belonging to the Companhia de Pesquisa de Recursos Minerais (CPRM) [altitude 445 m; 15&#176;56'57.84"S; 44&#176;52'4.68"W. The hydrological year starts at the end of the dry season on October 1st. Time series analyses (level duration curve, Seasonal Trend Decomposition (STL) of the daily level data, monthly level, mean, maximum, minimum level for each day of the year) were conducted to describe the hydrological regime and to assess temporal changes of the SFR levels and how these affect the magnitude, frequency and duration of flooding of the Pandeiros&#8217;s River wetland.&#160;Field observations (March 14, 2018) show that when SFR, which is Pandeiro&#8217;s base level, reaches a level of 5.0 m this leads to flooding conditions of the Pandeiros River wetland.&#160;Over the full period of record (1925-2018) the average level of the SFR was 3.86 m, with a minimum annual average of 2.43 m during the dry season (winter) and maximum of 5.98 m during the wet season (summer), with an average annual range of 3.55 m between both seasons. The SFR was above the 5.0 m threshold flooding level for 20% of the time 1925-2018, which corresponds to an average of 77.8 days of flooding per year in the wetland. The longest period of inundation was 178 days in 1926, when the SFR reached its maximum recorded level, and the shortest was 1 day in 2015, when it reached its minimum. The number of days per year of inundation have decreased over the full record, but that this is mainly due to a significant decrease since 1985. Prior to this, cyclic differences between wetter (1925 and 1985) and drier periods (1925 to 1945, 1945 to 1965) are observed.

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Trophic ecology of the ichthyofauna of a stretch of the Urucu River (Coari, Amazonas, Brazil)

Acta Limnologica Brasiliensia ◽

10.1590/s2179-975x2013000100007 ◽

2013 ◽

Vol 25 (1) ◽

pp. 54-67 ◽

Cited By ~ 2

Author(s):

Igor David da Costa ◽

Carlos Edwar de Carvalho Freitas

Keyword(s):

Trophic Structure ◽

Trophic Ecology ◽

Fish Assemblages ◽

Hydrological Cycle ◽

Taxonomic Diversity ◽

Dry Season ◽

Water Levels ◽

Seasonal Fluctuations ◽

Flood Season ◽

Wide Range

INTRODUCTION: The floodplains of the large Amazonian rivers are very productive as a result of seasonal fluctuations of water levels. This favors the fishes as they are provided with a wide range of habitats and food resources; AIM: In this study, we identified the trophic structure of fish assemblages in the upper river Urucu area (State of Amazonas - Brazil), observing seasonal changes determined by the hydrological cycle; Methods: Samples were collected with the aid of gillnets, during the flood season (April/2008) and the dry season (August/2008) in areas upstream and downstream of ports of the Urucu river within the municipality of Coari, Amazonas, Brazil; RESULTS: 902 individuals of seven orders, 23 families and 82 species were collected. Fishes were more abundant in the dry season than in the flood season, and the piscivores and carnivores (Serrasalumus rhombeus and Osteoglossum bicirrhosum) were the most significant trophic categories in the dry season whereas piscivores and insectivores (Serrasalumus rhombeus, Bryconops alburnoides and Dianema urostriatum) were more abundant in the flood season. The trophic diversity, dominance and evenness were very similar in all sampling periods and show lower values than taxonomic index patterns, except for the trophic dominance in the dry season. Taxonomic diversity and dominance were higher in the flood season if compared to the dry season, but figures were quite uniform and there were no great discrepancies between seasons. CONCLUSION: We found through our studies that the dry and flood seasons work as regulatory factors of abundance of fishes of certain trophic categories in the Urucu river, what can be possibly explained by the availability of resources and the food spectrum of each category.

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Biodiversity–ecosystem functioning relationships in fish communities: biomass is related to evenness and the environment, not to species richness

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2019.1189 ◽

2019 ◽

Vol 286 (1906) ◽

pp. 20191189 ◽

Cited By ~ 5

Author(s):

Aurore Maureaud ◽

Dorothee Hodapp ◽

P. Daniël van Denderen ◽

Helmut Hillebrand ◽

Henrik Gislason ◽

...

Keyword(s):

Species Richness ◽

Ecosystem Functioning ◽

Structural Equation ◽

Fish Assemblages ◽

Current Knowledge ◽

Marine Ecosystem ◽

Experimental Studies ◽

Fish Communities ◽

Trophic Levels ◽

Fish Biomass

The relationship between biodiversity and ecosystem functioning (BEF) is a topic of considerable interest to scientists and managers because a better understanding of its underlying mechanisms may help us mitigate the consequences of biodiversity loss on ecosystems. Our current knowledge of BEF relies heavily on theoretical and experimental studies, typically conducted on a narrow range of spatio-temporal scales, environmental conditions, and trophic levels. Hence, whether a relationship holds in the natural environment is poorly understood, especially in exploited marine ecosystems. Using large-scale observations of marine fish communities, we applied a structural equation modelling framework to investigate the existence and significance of BEF relationships across northwestern European seas. We find that ecosystem functioning, here represented by spatial patterns in total fish biomass, is unrelated to species richness—the most commonly used diversity metric in BEF studies. Instead, community evenness, differences in species composition, and abiotic variables are significant drivers. In particular, we find that high fish biomass is associated with fish assemblages dominated by a few generalist species of a high trophic level, who are able to exploit both the benthic and pelagic energy pathway. Our study provides a better understanding of the mechanisms behind marine ecosystem functioning and allows for the integration of biodiversity into management considerations.

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