Fish assemblages and their ecological traits along an elevational gradient in the Río Pacuare, Costa Rica

Co-management is increasingly recognized as an effective model for managing fisheries, but little information exists on whether co-management can produce effects in species other than the target species. Fishery co-management in the tropics, where fish diversity is high and fish catches tend to be multispecies, is prone to produce assemblage-wide effects via alterations in the food web and changes in the overall capture of non-target species. Here, we assessed the effects of co-management for the species Arapaima sp. in relation to the structure and composition of the overall fish assemblage in floodplain lakes of the central Amazon Basin. These floodplain lakes are managed under a system of zoning of fishing activities. We used data from surveys of six floodplain lakes, including two lakes of each of three categories (lakes where fishing is prohibited, limited-access lakes, and open fishing lakes). The surveys were carried out before and after implementation of co-management, through gillnet fishing. The study area was the lower Solimões River, in the Amazon Basin, Brazil. Statistical models showed significant changes in the composition and structure of the fish assemblages after the implementation of the co-management, regardless of the zoning category. Through regulation of gear use and fishing practices, co-management allowed the colonization of species that had not been present before, which lead to higher richness and consequently increased fish sizes, abundance and biomass. Species of sedentary habits, migrants of short and medium distances, with commercial importance benefited the most from co-management. In the results presented in temporal scale, it was possible to observe a potential spillover effect being provided by the lakes where fishing is prohibited (no-take zones) and those of limited access that benefited those open to fishing. Thus, co-management had positive effects in the structure and composition of fish assemblages in all lakes, regardless of zoning category.

Fish assemblages inhabiting the mountain streams of the Guiana shield have scarcely been studied. Here we investigated fish assemblages in eight headwater mountain streams of the Mount Itoupe (French Guiana), and tested how local freshwater fish assemblages are shaped by environmental characteristics. We show that Mount Itoupe streams host uneven species assemblages, characterized by low species richness (less than ten species per site) and a high proportion of small Siluriform species. Differences in fish assemblage composition between the sites were mainly due to basin identity, but regional climate and position of the site in the river gradient also had a significant effect, although of lower magnitude. In contrast, local habitat hardly affected fish richness, abundances or assemblage composition. Species richness increased along the upstream–downstream gradient, whereas fish abundance depended mainly on the slope orientation of Mount Itoupe. Although these results need confirmation on a larger amount of sampling sites, located on other Guianese mountains, this preliminary study shows that the mountain streams of the Guiana Shield, although rarely investigated, host not only uneven species assemblages, but also present an original combination of environmental determinants shaping fish assemblage structure. Those rare and original ecosystems hence deserve more attention and should be preserved from human disturbances.

Regional patterns of fish diversity, abundance, distribution, and assemblage composition are driven by a combination of biotic and abiotic conditions in the marine environment, but these conditions can be altered through anthropogenic activities, such as those associated with oil and gas extraction. The present study utilises data on fish relative abundance and diversity obtained from 1546 baited remote underwater video deployments conducted between 2004 – 2019 in depths of 9 – 170 m across 2000 km of coastline in north-west Australia on natural habitats and subsea pipelines to understand the influence of oil and gas infrastructure on fish assemblages. A total of 450 fish taxa from 56 families was observed, with populations dominated by generalist and invertebrate carnivore taxa. At the regional scale, subsea pipelines had lower diversity (lower taxonomic richness) than natural environments, but possessed a higher abundance of piscivorous and herbivorous fish taxa. Clear patterns in fish assemblage composition were observed in multivariate analyses, reflecting the proximity of oceanic shoals and banks, depth, and to a lesser extent, oil and gas infrastructure. Shallow-water and close to shoals assemblages were characterised by a diversity of site-attached (e.g., wrasses, tuskfish), reef-associated taxa (e.g., emperors). Mesophotic fish assemblages were characterised by commercially important (e.g., goldband snapper), wide-ranging (e.g., sharks) and sand-affiliated (e.g., toadfish, threadfin bream) taxa. Proximity to pipelines and platforms ranked low as predictors in the multivariate analyses suggesting a negligible regional influence of these structures on fish communities in comparison to depth and shoal habitats. Local-scale influences of subsea infrastructure, however, may be important for some fish species (infrastructure vs. immediate surrounds). Our study highlights the influence of abiotic factors on regional-scale patterns in fish assemblage structure across north-west Australia.

Summary Surface water connectivity can influence the richness and composition of fish assemblages, particularly in harsh environments where colonisation factors and access to seasonal refugia are required for species persistence. Studies regarding influence of connectivity on Arctic fish distributions are limited and are rarely applied to whole assemblage patterns. To increase our understanding of how surface water connectivity and related hydrologic variables influence assemblage patterns, we investigated species richness and composition of Arctic lake fishes over a large region, 8500 km2, of the central Arctic Coastal Plain, Alaska. We collected fish presence/non‐detection data from 102 lakes and used a hierarchical multispecies occupancy framework to derive species richness and inform species composition patterns. Our mean estimate of regional richness was 12.3 (SD 0.5) species. Presence of a permanent channel connection was an overriding factor affecting species richness (mean 3.6, 95% CI 3.1–4.9), presumably driving lake colonisation potential. In lakes without a permanent channel connection, data suggest richness (mean 2.0, 95% CI 1.7–3.3) increased with the availability of in‐lake winter refugia and with the potential of ephemeral connections during spring floods. Fish species functional traits and environmental faunal filters contributed to patterns of richness and assemblage composition. Composition corresponded with richness in a coherent manner, where each successive level of richness contained several discrete assemblages that showed similar responses to the environment. Lakes with permanent channel connections contained both widespread and restricted species, while the species‐poor lakes that lacked a connection contained mainly widespread species. This work provides useful baseline information on the processes that drive the relations between patch connectivity and fish species richness and assemblage composition. The environmental processes that organise fish assemblages in Arctic lakes are likely to change in a warming climate.

Summary1. The species composition of stream fish assemblages changes across the longitudinal fluvial gradient of large river basins. These changes may reflect both zonation in species distributions and environmental filtering of fish traits as stream environments change from the uplands to the lowlands of large catchments. Previous research has shown that taxonomic diversity generally increases in larger, lowland streams, and the River Continuum Concept, the River Habitat Template and other frameworks have provided expectations for what functional groups of fishes should predominate in certain stream types. However, studies addressing the functional trait composition of fish assemblages across large regions are lacking, particularly in tropical river basins.2. We examined functional trait–environment relationships and functional diversity of stream fish assemblages in the Río Grijalva Basin in southern Mexico. Traits linked to feeding, locomotion and life history strategy were measured in fishes from streams throughout the catchment, from highland headwaters to broad, lowland streams. Relationships between functional traits and environmental variables at local and landscape scales were examined using multivariate ordination, and the convex hull volume of trait space occupied by fish assemblages was calculated as a measure of functional diversity.3. Although there were a few exceptions, functional diversity of assemblages increased with species richness along the gradient from uplands to lowlands within the Grijalva Basin. Traits related to swimming, habitat preference and food resource use were associated with both local (e.g. substratum type, pool availability) and landscape‐scale (e.g. forest cover) environmental variables.4. Along with taxonomic structure and diversity, the functional composition of fish assemblages changed across the longitudinal fluvial gradient of the basin. Trait–environment relationships documented in this study partially confirmed theoretical expectations and revealed patterns that may help in developing a better understanding of general functional responses of fish assemblages to environmental change.

Organisms living in tide pools in the intertidal zone are exposed to daily and abrupt changes in temperature, dissolved oxygen, pH and salinity, during tidal cycles. Fish assemblages in tide pools are usually very different from those in surrounding areas; resident species exhibit morphological and ecological adaptations to deal with such a variable environment. In this study, we described the environmental conditions and the fish diversity and composition from four tide pools at the continental margin of the São Sebastião Channel, São Sebastião (23º41'-23º54'S; 45º19'-45º30'W), in southeastern Brazil. Monthly, from January to December 2011, we sampled four tide pools (12 samples per pool), applying a standard protocol to record environmental variables, and visual censuses to record abundance, richness and composition of fish assemblages. Environmental and fish data were compared among tide pools and periods throughout the year (warm and cold) using both univariate and multivariate analyses of variance. Tide pools showed significant environmental differences, mainly in area, volume and complexity of substrata. We observed 13 species of fishes (10 families), which belong to five trophic guilds (roving herbivores, territorial herbivores, mobile invertebrate feeders, omnivores and carnivores). Density and richness of fish were almost constant during the studied period, except for a reduction in fish density in São Francisco's Beach during a cold period. However, assemblages from the sampled tide pools differed from each other in composition and relative abundance of species, resulting in four distinct assemblage structures. Bathygobius soporator was the dominant species in most of the tide pools, corresponding to 66% of all recorded fish. The tide pool from Baleeiro's Point was intermediate in size, but was covered by a complex algae community and supported the most diverse fish assemblage, suggesting that habitat complexity may contribute to the diversity of fish.

Environmental drivers of earthworm communities along an elevational gradient in the French Alps

Variations in fish community structure during winter in the southern Yellow Sea over the period 1985–2002

The composition and structure of fish assemblages in the inner continental shelf of the Paraná State are affected by cold fronts and the rainfall regime. Data from fishing activities in this region, as well as the analysis of environmental characteristics, are the main tools available for understanding fish dynamics, under influence of increasing human activities. In order to better understand patterns and temporal variations in fish assemblages in the inner continental shelf of the Paraná State, a total of 24 double trawls were performed with an otter trawl between August 2000 and July 2001, in two sampling areas, the North area in front of the northern mouth of the Paranaguá Estuary Complex, and the South area, in front of the Leste beach. A total of 45,277 fish specimens belonging to 35 families and 97 species were caught. Sciaenidae was the most abundant family, with 37.1% of the total number of individuals caught, and with the highest richness (18 species). Statistical analyses evidenced significant differences in environmental characteristics and in fish fauna, and that both areas disturbances were observed in the fish assemblages during the dry and wet season, being more intense in the Southern area, disturbances that would be related to the shrimp fishing present in the two areas sampled in this study.

Studies on fish assemblages in streams point out, that understanding the relationship between species and their environment is crucial for conservation. The present study aimed at evaluating the effects of changes in abiotic variables on the composition and structure of fish assemblages in Neotropical urban streams from southern Brazil with different levels of urbanization. The composition and structure of fish assemblages showed significant differences along the urbanization gradient observed in the streams. Tolerant and non-native species were found in more urbanized sites. A matrix correlation revealed a relationship between abiotic variables and the spatial pattern of structure and composition of fish assemblages. Abiotic variables, such as total phosphorus, dissolved oxygen, and conductivity, determined the distribution of fish assemblages. Streams without urban influence exhibited intrinsically low species richness, suggesting that they are highly susceptible to species loss and diversity reduction. Thus, changes in water quality or hydrological conditions induced by urbanization may intensify these impacts.

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.

The baited remote underwater video technique (BRUVS) was used to compare fish assemblages at three sites with different habitat characteristics: sandy bank (SB), rock reef (RR) and degraded coral reef (DCR) in Port Essington, Garig Gunak Barlu National Park, Northern Territory, Australia. The Carangidae family dominated, representing 35% of all recorded fish. The highest species number was recorded at RR followed by DCR and SB. The highest total fish number was recorded at DCR followed by SB and RR. Fish assemblages from all three sites are clearly different at high confidence level, but still overlapping and higher overlapping was found between SB and RR. Fish assemblages at all three studied sites contained some coral-associated species, fish fauna was less rich compared to coral reefs in the mouth of the bay and fish assemblages were noticeably different from typical coral fish communities. None of the fish assemblages at studied sites were presented by the ‘pure’, single habitat-associated association of species—at all three sites fish communities were a mixture of fish with various habitat preferences. Reef-associated species have a larger proportion at DCR and at RR their habitat complexity was higher; still soft-bottom habitat fish make substantial fractions in fish assemblages at both DCR and RR. Similarly, fish usually identified as ‘reef associated’ were found in notable proportions on SB. Fish with wide distribution and low selectivity in habitat preferences comprised a significant part in fish assemblages at all studied sites. In this study the BRUVS technique worked well in the area where diving visual surveys were impossible to implement because of high water turbidity. Another advantage of this method is the non-impact nature of visual survey; they can be used in long-term monitoring of fish assemblages at reference sites.

Chouinard, P-M., and Dutil, J-D. 2011. The structure of demersal fish assemblages in a cold, highly stratified environment. – ICES Journal of Marine Science, 68: 1896–1908. Fish are a major component of marine ecosystems, with many species co-occuring in the same habitats. Potential interactions among species and with the environment can be studied through the identification of species assemblages. Data from bottom trawl surveys (2004–2008) conducted in the estuary and northern Gulf of St Lawrence were analysed using multivariate methods (cluster, multidimensional scaling, and detrended canonical correspondence analysis) to describe the structure and composition of demersal fish assemblages, including rare and smaller non-commercial species. The spatial variability in environmental conditions that characterizes the study area has a significant impact on the composition of fish assemblages in the region. In all, 35 taxa were classified as key, and 6 main fish assemblages were described, based on catch in numbers. These assemblages had a coherent spatial distribution in the study area, associated with either depth, salinity and temperature, or dissolved oxygen. The analyses showed overall strong correlations between species abundance and prevalent environmental conditions and explained 18.4% of the variance in species abundance data and 79.2% of the variance in the species–environment relationship.

Tropical short, steep coastal streams are typically dominated by diadromous species, especially amphidromous fishes, crustaceans, and molluscs. We undertook a study to determine the distribution of fishes along the stream continuum and determine if substantial natural instream barriers influenced assemblage composition. We surveyed fish assemblages in three short, steep coastal streams in the Australian Wet Tropics by snorkelling and performing single pass counts in each 100‐m section along the entire main channel from the high‐tide mark to the source (or near source: until fish were no longer recorded). A primary focus was mapping the distribution and relative abundance of sicydiine gobies, and we also estimated freshwater crustacean numbers (Caridea: Palaemonidae and Atyidae). In total, 2,837 individual fish of 25 species were recorded upstream of the high‐tide mark across the three streams and the first records of an additional sicydiine goby (Smilosicyopus leprurus) were obtained from continental Australia. Consistent with findings from tropical Pacific island streams, we observed a shift in fish assemblage composition along the elevation gradient and in relation to major instream barriers (e.g. waterfalls >5 m, and high flow chutes across smooth bedrock surfaces). Species richness of diurnal predatory fishes was greatest in the lower course of streams and absent upstream of major instream barriers. Diurnal predatory fishes were, in some instances, found upstream of barriers. Specifically, large adult (>200 mm total length) Kuhlia rupestris (diurnal predators) accessed reaches above challenging sequences of cascades combined with small waterfalls. In contrast, all sizes of that species, adult Kuhlia marginata (>150 mm total length) and a diversity of other diurnal predatory fishes occupied the lower course of streams including upstream of gentle cascade sequences or isolated small waterfalls. Where abundances of diurnal predatory fishes were high, freshwater carideans were rarely observed. Peak densities of carideans were observed upstream of major barriers, with moderate densities in the upper mid‐course in the presence of few Kuhlia spp. The current study demonstrates the value of complete single‐pass surveys of fish assemblages in tropical short, steep coastal streams by revealing the highly localised occupation of particular reaches by rare fishes. It also points towards the importance of stream‐specific characteristics, namely the position of waterfalls in dictating diadromous predator distribution with consequences for community structure, thereby aligning with the Riverine Discontinuum Concept.

Eutrophication-induced shifts in fish assemblages from a Mediterranean coastal lagoon.