Abundance Of Fish Communities Research Articles

Replicated whole‐lake experiment reveals the ineffectiveness of stocking five example fish species in small lakes

AbstractFish stocking is common practice in fisheries management, but its effectiveness to support or increase stock size or catches is debated. In Lower Saxony, Germany, a controlled, replicated stocking experiment of five native fish species in eight gravel pit lakes <20 ha was conducted to examine the potential additive effects of fish releases on abundance, indexed by catch per unit effort (CPUE) in electrofishing and gillnet samples. Fish were stocked twice in four study lakes, while the remaining four control lakes were not subjected to any stocking over a 6‐year study period. Recapture rates of individually marked fishes were extremely low in all five species. Consequently, stocking did not increase species‐specific and total fish community abundance. In additional control experiments in separate ponds all stocked fish species, except bream (Abramis brama), showed high survival in at least one study year, indicating general survival of the stocking material. Fish marking with passive integrated transponders did not affect fish survival, except for roach (Rutilus rutilus), and can thus be ruled out as an explanation for the high post‐stocking mortality. We conclude that stocking failed to enhance stocks of five native fish species in small gravel pit lakes.

Environmental DNA biomonitoring reveals seasonal patterns in coral reef fish community structure

Coral reef fish populations are declining due to multiple factors including habitat destruction, overfishing, and climate change. While these can include seasonal impact, seasonal changes can also be a confounding factor, so that seasonal monitoring is essential for detecting true temporal changes in fish community abundance and composition. However, seasonal monitoring is rarely implemented. The aim of this study was to detect the seasonal patterns of coral reef fish community structure around Tidung Kecil Island, Indonesia, using eDNA metabarcoding (eDNA) and underwater visual census (UVC). The UVC identified 32 species belonging to 10 families in the rainy season and 29 species belonging to 7 families in the dry seasons. The eDNA metabarcoding identified 209 species belonging to 56 families and 27 species belonging to 17 families in the rainy and dry seasons, respectively. Based on eDNA metabarcoding data, coral reef fish abundance and community composition differed significantly between seasons (Mann Whitney, p < 0.01), while the UVC method did not detect these seasonal differences (Mann Whitney, p > 0.05). UVC and eDNA data both showed a predominance of omnivorous fishes in the rainy season and carnivorous fishes in the dry season. Ecological indices did not differ significantly between seasons for the two used methods, although the species making the highest contributions to the similarity (SIMPER) analysis differed between methods. Overall, this study confirms the premise that eDNA metabarcoding can be an effective tool for monitoring seasonal variation in coral reef fish communities.

Marine Biodiversity of Coral Reef Fishes in Pieh Marine Recreational Park After Bleaching and Acanthaster Outbreaks

Highlight ResearchAfter bleaching disturbance and Acanthaster planci outbreaks, herbivore fishes species were dominated in MRP PiehThis explains the marine recreational activities in utilization zone MRP Pieh have no impact on reducing fish biomassAfter disturbance in MRP Pieh shows the coral reef fishes still endurance on bleaching event, and Acanthaster planci outbreak after disturbance in MRP Pieh shows the coral reef fishes still endurance on bleaching event and Acanthaster planci outbreak. However, the composition of corallivorous has decreased but has been an increase in herbivorous and carnivorous fish populationsAbstractPieh MRP encountered non-anthropogenic phenomena, precisely massive coral bleaching in 2016, 2017, and massive predators from Acanthaster planci outbreaks in 2018. This study aimed to understand the pattern of coral reef diversity in the core zone and utilization in the MRP area and compare it to non-MRPS locations that accept the same non-anthropogenic pressure conditions. Coral fish sampling using a UVC is categorized into three zones: the core zone, the utilization zone, and outside the MRP area. 8 Families of coral reef fishes were counted based on categories of level function in ecologies and economy. Taxonomic distinctiveness estimates were calculated mathematically for each sample, including species richness and taxonomic diversity were compared among zonation area. Pearson’s Coefficient Correlation Matrix was used to measure the correlation relationship between zonation areas. There are 91 species of fish and 3002 individuals found. The richest family in the MRP Core Zone and MRP Utility Zone was Acanthuridae with 20 species and non-MRP has a lower species richness and abundance of fish communities. The dominant species in Pieh MRP was Ctenochaetus striatus with average abundant per site (21.3 ± 7.62, n = 3). Acanthuridae represents 55.98% of the total biomass in MRP-Core Zone, 63.13% in MRP-Utility Zone, and 41.55% in Non-MRP Area. This study showed the number of species and populations from corallivores fishes have decreased but has been an increase in herbivorous and carnivore diversity. The diversity indices (H’) and ENS also shows no differ significantly between zonation.

Hydrological connectivity, surface water quality and distribution of fish species within sub-locations of an urban oxbow lake, East India

Ecological processes and distribution of biodiversity within river floodplains are driven by the hydrological regime of the area. The relationship between fish abundance/diversity and surface water quality at four impact points of the Sashadanga oxbow lake was examined based on hydrological connectivity (distance of lake sections from parent channel; density of buffer vegetation and hydrological phases of seasons). Fish sample populations (n = 1440) belonging to 10 orders showed greater numerical abundance in the pre-and post-flooding phases. Oxbow sites proximal to the parent channel showed higher comprehensive pollution index (CPI), higher dominance and lower species evenness during the pre-monsoon (minor flooding) and vice versa during the monsoon and post-monsoon (greater flooding periods). Diversity descriptors using curve/asymptote based on Hill’s numbers indicate significant site-specific fish diversity within the oxbow lake at different seasons. Discriminant analysis revealed that change in temperature, turbidity and concentration of inorganic nitrogen were significant predictors in differentiating the quality of the different sites of the lake. Principal component analysis (PCA) revealed that the relative abundance of each species order across sites was significantly influenced by changes in seasons and physicochemical parameters, and showed a weak association with the density of buffer vegetation at sites. Depending on the distance of oxbow areas to the parent channel, the combination of periodic flooding, riparian buffer and lake morphology define the degree of hydrological connectivity which in turn affects the composition and abundance of fish communities at different points of the lake.

Coarser taxonomic resolutions are informative in revealing fish community abundance trends for the world’s warmest coral reefs

Coarser taxonomic resolutions are informative in revealing fish community abundance trends for the world’s warmest coral reefs

A standardised analytical framework for sampling fish communities: relevance to Turkish riverine ecosystems

Fish communities are important indicators of the health of riverine ecosystems. Fish monitoring for The Living Murray (TLM) initiative, one of Australia’s most ambitious restoration undertakings for the degraded river-floodplain biota of the River Murray system (south-eastern Australia), was carried out annually from 2005 to 2011 across six ‘Icon Sites’, including the habitats and reaches therein. These spatial and temporal components of variation in fish community abundance and composition must be taken explicitly into account for consistent assessment of riverine ecosystem health. To address this requirement, a standardised analytical framework, consisting of a sampling design and appropriate statistical methods, is outlined in this study. Based on an extensive dataset, multivariate patterns and univariate trends in fish community structure were analysed to show the flexibility, modularity and ability of the framework. The applicability of the framework to Turkish riverine ecosystems is then discussed with emphasis on the need for participatory discussion between researchers and environmental managers. The possibility to incorporate other measures of fish health such as biomass and condition, and to extend the proposed framework to the quantitative assessment of vegetation and bird communities also exists.

Wood Removals from Lakes May Not Necessarily Elicit Fish Population Responses

AbstractCoarse woody habitat (CWH) in aquatic ecosystems provides structural complexity and a surface for food production for fish. Depending on abundance and complexity of CWH, it is usually associated with influencing predator–prey dynamics, fostering greater localized fish abundance, increasing fish growth, and contributing to fish production, but some conflicting evidence exists about its importance as fish habitat. Our experiment was designed to test for direct linkages between whole‐lake CWH availability and fish community abundance, biomass, and production. We removed ~50% of CWH from three lakes while concurrently sampling them and two other unaffected lakes as controls in a before‐after–control‐impact (BACI) design. Due to the loss of quality foraging habitat, structure, and cover for small fish, we hypothesized that the CWH removal would cause a measurable decline in fish abundance, biomass, and/or production. Despite CWH being a preferred habitat type for fish, our hypothesis was not supported because observed changes in measured fish community metrics could not be attributed to the CWH removal. The inability to directly link the wood removal to changes in the fish metrics we examined may have been due to a number of factors including the composition of the fish community, the high availability of alternate habitat structure (rocks, macrophytes), large quantities of wood remaining in the lakes, the relative lack of littoral habitat use by piscivores, or low statistical power (small sample size, high variance). However, we still urge resource managers to be cautious when considering authorizing removal of CWH from lakes because it does provide temporally stable year‐round structure and high‐quality foraging habitat with unique microbial, fungal, and invertebrate communities. Coarse woody habitat was a preferred habitat for fish and may have a greater relative importance in lakes with minimal alternative cover for fishes or in lakes containing different fish assemblages.

Assessment of a terrestrial protected area for the conservation of freshwater biodiversity

AbstractFreshwater ecosystems are essential to human well‐being and most have high biodiversity. However, this biodiversity has been suffering severe declines owing to the expansion of human activities. Protected areas (PAs) are essential for biodiversity conservation and have proved to be successful in stopping species extirpation if managed properly. Unfortunately, they are usually focused on terrestrial biodiversity, leaving freshwater ecosystems aside.The main goal of this study was to determine the influence of a PA (Montesinho Natural Park (MNP), Portugal) on freshwater biodiversity. Aquatic macroinvertebrates and fishes were surveyed, and biodiversity (richness, abundance, Shannon‐Wiener diversity, and Pielou's evenness) and water quality (IASPT) indices were calculated inside, at the periphery and outside the MNP.Results showed that the PA does not affect positively either water quality or the two faunal groups monitored. Macroinvertebrate communities were not influenced by the PA; however, the abundance of pearl musselMargaritifera margaritiferawas significantly higher and size was significantly lower inside the MNP. The richness and abundance of fish communities were significantly higher outside the MNP, except for troutSalmo truttaabundance which was higher inside the MNP.Given these results, the MNP does not guarantee the safeguard of overall aquatic biodiversity and habitats and we propose an extension of MNP to downstream areas in order to increase the number of species (mostly cyprinids) under legal protection. This work demonstrates that terrestrial PA planning and management should also consider aquatic biodiversity to achieve successful conservation.

Herbivorous Crabs Reverse the Seaweed Dilemma on Coral Reefs

Coral reefs are on a steep trajectory of decline, with natural recovery in many areas unlikely.1-3 Eutrophication, overfishing, climate change, and disease have fueled the supremacy of seaweeds on reefs,4,5 particularly in the Caribbean, where many reefs have undergone an ecological phase shift so that seaweeds now dominate previously coral-rich reefs.6-8 Discovery of the powerful grazing capability of the Caribbean's largest herbivorous crab (Maguimithrax spinosissimus)9 led us to test the effectiveness of their grazing on seaweed removal and coral reef recovery in two experiments conducted sequentially at separate locations 15km apart in the Florida Keys (USA). In those experiments, we transplanted crabs onto several patch reefs, leaving others as controls (n= 24 reefs total; each 10-20 m2 in area) and then monitored benthic cover, coral recruitment, and fish community structure on each patch reef for a year. We also compared the effectiveness of crab herbivory to scrubbing reefs by hand to remove algae. Crabs reduced the cover of seaweeds by 50%-80%, resulting in a commensurate 3-5-fold increase in coral recruitment and reef fish community abundance and diversity. Although laborious hand scrubbing of reefs also reduced algal cover, that effect was transitory unless maintained by the addition of herbivorous crabs. With the persistence of Caribbean coral reefs in the balance, our findings demonstrate that large-scale restoration that includes enhancement of invertebrate herbivores can reverse the ecological phase shift on coral reefs away from seaweed dominance.

Implications of the depth profile on the functional structure of the fish community of the Perdido Fold Belt, Northwestern Gulf of Mexico

Studies have demonstrated that environmental conditions affect the richness, diversity, and abundance of fish communities. Depth is an important variable with many species showing preferences for specific depth ranges. Here, we present a functional analysis of the fish community in the Perdido Fold Belt (PFB), Gulf of Mexico. The sampling design was structured across a depth range of 40–3500 m, using 20 oceanographic stations. The aims of our study were: (1) to determine the functional arrangement of the fish community in the PFB; and (2) to describe the effect of the environmental variables on fish richness and functional diversity. A total of 232 species were identified; 195 were grouped into 42 functional groups (FGs). Thirty-seven species did not group with any others and are referred to as “functionally independent species” (FIS). According to our results, depth changes in physicochemical variables allow us to segregate three vertically stratified zones: shelf, slope, and deep. Temperature was the most important environmental variable constraining functional distribution of fishes. The highest FG diversity, species diversity, and biomass were found in the shelf/slope zone (SSo), while the highest diversity of FIS was found in the shelf zone. As the SSo displays its highest diversity, and since greater diversity has been linked with greater resilience and stability of fish communities, the SSo may be the most resilient zone of the PFB. Our study provides the first description of the diversity and resilience of the PFB fish community and helps our understanding of the factors constraining the distribution and functional diversity of fishes across depth gradients.

Annual and non‐annual fish assemblages respond differently to environmental and spatiotemporal variations of temporary wetlands from southern Brazil

Abstract The fish community of temporary wetlands is highly dynamic due to the marked seasonal changes in hydrological and limnological conditions. In this study, we evaluated spatiotemporal variation in the fish community and the influence of environmental factors on this variation in temporary wetlands in southern Brazil. Two different life cycles—annual and non‐annual fishes—were recorded among species. Variation in the fish community appeared to be associated with differences in the life history strategy of species. While species of annual fish were present throughout the hydroperiod, gradually decreasing in density over time, non‐annual fish species had an opposite pattern, with higher densities in the final phase of the hydrological cycle. Variations in the composition and abundance of fish community in temporary wetlands were related to habitat and landscape attributes (area, number of microhabitats and isolation between temporary wetlands) and climate indicators of water availability (air temperature, average rainfall, and water level of the São Gonçalo channel), but not to water conditions (dissolved oxygen, pH, conductivity and water temperature). We concluded that the ichthyofauna of temporary wetlands are composed both of rare species, highly specialised for life within these ephemeral environments, and widespread generalist species that reach the wetlands opportunistically for short periods. Habitat and landscape attributes and changes in climate and hydrological variables over the hydroperiod are the factors that had the greatest influence on spatiotemporal variation of the fish community. Maintaining physical characteristics and the hydrological cycle of temporary wetlands is critical for the conservation of fish species inhabiting these vulnerable environments in southern Brazil. Habitat and landscape attributes and climate and hydrology fluctuations affect the annual and non‐annual fishes inhabiting temporary wetlands differently.

Dispersal drives changes in fish community abundance in intermittent stream networks

AbstractIncreasing trends in fragmentation and dewatering of streams warrants research on how populations and communities respond to varying water levels and barriers to movement. Although these responses are complicated by many spatial and temporal processes, long‐term datasets might help reveal complex patterns and processes driving variability in species abundances. The objective of this study was to develop a predictive framework for fish community and population responses to varying levels of water availability across six sites in two intermittent stream networks sampled &gt;10 years. We predicted that fishes would emigrate into intermittent reaches during wet conditions; thus, overall abundances within perennial source locations will decline. Accordingly, when intermittent reaches dry, fishes will contract to wetted habitats resulting in high abundance. Observed fish community abundances were highly variable within and among study sites, but four of six sites matched our predictions. A tagging study confirmed these results and demonstrated a substantial proportion of individuals moved away from perennial reaches and into newly wetted intermittent reaches. However, site and species‐specific relationships were variable and likely depended on the habitat, metacommunity dynamics, and life history strategies. Findings suggest that species dispersal dynamics, in addition to recruitment and mortality, should be carefully considered when interpreting species responses to varying water levels, particularly in intermittent stream networks where access to habitat can change drastically with water availability.

Contrasting patterns in the abundance of fish communities targeted by fishers on two coral reefs in southern Mozambique

Coastal populations of maritime countries in eastern Africa rely on fish as a primary source of protein, but baseline information on the abundance of fish communities on these coastlines is often lacking. We used baited remote underwater video stations to compare the abundance and diversity of reef fishes targeted by fishing at two sites in southern Mozambique, one at Lighthouse Reef within the Bazaruto Archipelago National Park and the other to the south at San Sebastian Reef on the San Sebastian Peninsula. Fish that are known targets of fisheries (mostly small-scale and artisanal) had an abundance that was almost three-times greater at San Sebastian Reef (80.22 ind. h–1 [SE 18.00]) than at Lighthouse Reef (29.70 ind. h–1 [SE 8.91]). Similarly, there was greater mean species richness at San Sebastian Reef (38.74 species h–1 [SE 2.79]) than at Lighthouse Reef (25.37 species h–1 [SE 3.66]). The main drivers of targeted fish abundance were habitat and depth, with shallow (<15 m) and mixed reef areas having the greatest abundance and richness. More sampling was done over sand habitat at Lighthouse Reef, which likely led to the lower abundance and species richness observed at this site; however, that finding could also be attributable to the fact that protection is provided to only a section of available coral reef habitat in a small area. Nevertheless, fish community structure was comparable between the sites, with similar proportions of carnivores (78–81%), herbivores (12–14%) and omnivores (7–8%). Our findings highlight the variation in species abundance and assemblages of coral-reef fish targeted by fishing in Mozambique and emphasise the importance of localised environmental variables as a driver of these patterns. To ensure maximum protection of Lighthouse Reef fish communities, we recommend an extension of the no-take zone to include the entire reef complex.

The influence of natural flow and temperature and introduced brown trout on the temporal variation in native fish abundance in a “reference” stream

Understanding what drives variation in fish abundance at reference sites provides perspective for assessing the effects of human alterations to river flow and land use. We examined temporal variation in fish community abundance in a headwater tributary of a large river in the upper South Island (New Zealand) over 10 years. We were interested in the influence of natural flow variation and temperature on native fish abundance within the context of potential competition/predation pressure from juvenile introduced trout. Results from biannual sampling highlighted the dominating influence of floods on fish population dynamics, overriding biotic effects. We found no evidence for adverse effects of trout on native fish, and flow-related habitat performed more poorly in explaining variation in fish abundance than low- and median-flow statistics. Differences in temporal variation in abundance between species were largely consistent with life histories that provide resistance and (or) resilience to flood flows and relative insensitivity to low flows. Long-term data (≥10 years) are needed for detecting meaningful trends and quantifying the effects of human activities on fish community abundance.

Identifying management challenges and implementation shortcomings of a new fishing refuge: Akumal reef, Mexico

No-take marine reserves (fish refuges -FR-in Mexico) eliminate fishing pressure for long periods in delimited areas, promoting fish reproduction and recruitment, recovery of fish community abundance and biomass, augment resistance and resilience in coral reef-associated marine ecosystems, and support local fishing-based economies. A FR was implemented on Akumal reef in 2015 limiting fishing for six years with the specific aim of increasing the biomass of commercial and sport-recreational interest fish species. However, no previous reference data were considered to establish an ecological baseline to quantify progress towards this aim, or to implement any other policy necessary to ensure compliance with this objective. To fill this gap, Akumal FR's current level of potential success was assessed (relating reef fish community characteristics and habitat components characteristics). FR's potential success was quantified as low due to the absence of 50% of listed commercial-sport fish species, critical biomass values for recorded species on the list, and generally low reef fish abundance and biomass values. In addition, current habitat condition is critical because of coral-algal phase shift, changes in coral community structure, and loss of reef structure and the associated reef's refuge function for fish species. Considering the performance of existing no-take marine reserves, Akumal low FR's potential success implies that a much longer no-take period (than the established six years), will be necessary to allow reef fish populations to recover biomass and attain functional levels within the ecosystem that could support on-going fishing impact. Based on this, a number of recommendations were established in order to strengthen the management provisions to allow the reef to attain a better condition, including an extension of the no-take period, enforcement of non-extractive uses, and simultaneous implementation of coastal management strategies.

Possible unintended effects of management at an invasion front: Reduced prevalence corresponds with high condition of invasive bigheaded carps

Limiting the prevalence of invasive species is a global conservation priority. Invasive species can have varying ecosystem effects and responses to control throughout an invaded range, and removal near invasion fronts may inadvertently alter these characteristics. Bigheaded carp (bighead carp (Hypophthalmichthys nobilis Richardson) and silver carp (H. molitrix Valenciennes)) are invasive fishes from Asia invading North American freshwater ecosystems. We used mobile hydroacoustic surveys to examine bigheaded carp population characteristics from 2012 to 2015 across an invasion gradient in the Illinois River (USA), one of the most likely pathways to the Laurentian Great Lakes. These bigheaded carp species comprised 23–46% of fish community abundance and 45–78% of fish biomass across reaches, with lower contribution near the invasion front where intensive management by harvest occurs. Bigheaded carp prevalence in the community did not differ by habitat and comprised >50% of community abundance and biomass throughout the river for most size classes. We identified negative relationships between density and relative weight (an index of body condition) of bigheaded carp, suggesting evidence of potential density-dependent intraspecific competition. Efforts to reduce invasive species abundances near invasion fronts may reduce prevalence. However, this could inadvertently release individuals from density-dependent competition and could enhance reproductive potential, growth or movements. By employing a suite of control efforts, including continuous removal efforts (including novel approaches) and by limiting movements (e.g., utilizing roads, fences, dams), it may be possible to offset undesired consequences of increased condition.

The community diversity of two Caribbean MPAs invaded by lionfish does not support the biotic resistance hypothesis

Marine protected areas (MPAs) conserve diversity and abundance of fish communities. According to the biotic resistance hypothesis, communities with higher diversity and abundance should resist invasions better. To test this idea, the presence of lionfish in two Caribbean MPAs was studied: Parque Nacional Guanahacabibes (PNG) in Cuba and Parque Nacional Arrecifes de Xcalak (PNAX) in Mexico. Selection of these MPAs was based on both their different levels of success with enforcement and different abundances of native fish, with a more abundant native fish fauna at PNG. Underwater visual censuses were used to evaluate both the native fish structure and composition and at the same time distribution and abundance of lionfish. The abundance of potential predators on lionfish was also measured to determine possible effects of lionfish on both the abundance and the size of its prey and competitors. Lionfish showed higher abundance and larger size in PNG compared to PNAX, even though its probable competitors and predators were also more abundant and larger in PNG. Prey abundance and size decreased after the invasion. No correlation was detected between potential predators and lionfish, which might indicate natural predation is not substantial. In PNAX, lower abundance of prey, potential competitors and predators can also be attributed to historical overfishing, but this did not provide an advantage to lionfish. Lionfish were less abundant and reached smaller sizes in PNAX compared to PNG. This work confirms the effectiveness of lionfish culling at PNAX, but does not support the biotic resistence hypothesis that native fish might have controlled this invasive species.

Determining a More Environmental than Spatial Influence on Structuring Fish Communities and Ecological Boundaries of Fangcheng Coastal Waters, Northern South China Sea

ABSTRACT Wang, X.; Wang, L.; Chen, H.; Jia, X., and Jackson, D.A., 2017. Determining a more environmental than spatial influence on structuring fish communities and ecological boundaries of Fangcheng coastal waters, northern South China Sea. In: Zhi, Y. and Guido Aldana, P.A. (eds.), Sustainability of Water Resources and the Development of Coastal Environments: Select Proceedings from the 2016 International Conference on Water Resource and Environment (WRE2016). Journal of Coastal Research, Special Issue No. 80, pp. 55–68. Coconut Creek (Florida), ISSN 0749-0208. Fangcheng coastal waters in the northern South China Sea provide critical habitats for many commercially important fish species by offering essential spawning, feeding, and nursery areas for one or more stages of their life history. A total of 127 fish species and environmental data were collected by trawl surveys at 18 sites of Fangcheng coastal waters in Spring and Fall of 2014. The species richness and abundance of fish community were analyzed...

Environmental Factors Structuring Fish Communities in Floodplain Lakes of the Undisturbed System of the Biebrza River

We evaluated the influence of habitat connectivity and local environmental factors on the distribution and abundance of functional fish groups in 10 floodplain lakes in the Biebrza River, northeastern Poland. Fish were sampled by electrofishing, and 15 physico-chemical parameters were recorded at three sampling sites at each lake in the period of 2011–2013. A total of 18,399 specimens, belonging to 23 species and six families, were captured. The relationships between environmental factors and fish communities were explored with the use of canonical correspondence analysis (CCA). Sampling sites were grouped based on fish communities using a hierarchical cluster analysis (HCA). Along a lateral connectivity gradient from lotic to lentic habitats (parapotamic–plesiopotamic–paleopotamic), the proportions of rheophilic species were determined as 10:5:1, whereas the proportion of limnophilic species was determined as 1:2:5. The predominant species were the roach (Rutilus rutilus), and pike (Esox lucius) in parapotamic lakes, rudd (Scardinius erythropthalmus) and pike in plesiopotamic lakes, and sunbleak (Leucaspius delineates) and Prussian carp (Carassius auratus gibelio) in paleopotamic lakes. The findings indicated that the composition and abundance of fish communities are determined by lake isolation gradient, physico-chemical parameters and water stage. Although intact riverine ecosystems may promote fish biodiversity, our findings suggest that lateral connectivity between the main channel and floodplain lakes is of utmost importance. Thus, the conservation of fish biodiversity requires the preservation of this connectivity.

Fish use of intertidal mangrove creeks at Qeshm Island, Iran

Habitat use by fish in intertidal mangrove creeks is relatively unstudied in the Persian Gulf. We investigated the role of temporal variations and creek elevation in shaping fish community structure in intertidal mangrove creeks in the Strait of Hormuz, Qeshm Island, Iran (western Indian Ocean). Block net sampling was carried out to examine the influence of 3 types of temporal dynamics on patterns of fish diversity and biomass. Tides, diel day/night variations, and season all proved important for fish dynamics. The fish assemblage of 29 species was dominated by Mugilidae, which constituted 62% of biomass and 41% by abundance. Although the most abundant species occurred in all creeks and months, the number of species, community biomass and abundance of individuals were significantly influenced by tide and day/night cycles, with highest values during nighttime spring tides and lowest values during daytime neap tides. Gut content studies showed that fish accessing marsh surfaces on nighttime spring tides generally had 75-100% full guts, indicating trophic use of mangrove areas. The findings from this meso-tidal arid area generally agree with previous studies of mangrove creeks from wetter tropical sites, but there were some exceptions. Notably, fish community abundance and biomass in February winter conditions were highest during nighttime neap tide conditions, instead of during nighttime spring tide conditions. This neap tide maximum was associated with a relatively greater dominance of resident fish species during winter, but may also indicate some temperature-related differences in fish use of mangroves that are at the northernmost regional limit of their distributions at Qeshm Island.