The ways in which fish use estuaries: a refinement and expansion of the guild approach

This study refines, clarifies and, where necessary, expands details of the guild approach developed by Elliott et al. (2007, Fish and Fisheries 8 : 241–268) for the ways in which fish use estuaries. The estuarine usage functional group is now considered to comprise four categories, that is, marine, estuarine, diadromous and freshwater, with each containing multiple guilds. Emphasis has been placed on ensuring that the terminology and definitions of the guilds follow a consistent pattern, on highlighting the characteristics that identify the different guilds belonging to the estuarine category and in clarifying issues related to amphidromy. As the widely employed term ‘estuarine dependent’ has frequently been imprecisely used, the proposal that the species found in estuaries can be regarded as either obligate or facultative users of these systems is supported and considered in the guild context. Thus, for example, species in the five guilds comprising the diadromous category and those in the guilds containing species or populations confined to estuaries are obligate users, whereas those in the marine and freshwater estuarine‐opportunistic guilds are facultative users.     

Assessing the health of European rivers using functional ecological guilds of fish communities: standardising species classification and approaches to metric selection

Abstract  The functional ecological guild approach is the cornerstone for the development of Indices of Biotic Integrity and multi-metric indices to assess the ecological status of aquatic systems. These indices combine metrics (unit-specific measures of a functional component of the fish community known to respond to degradation) into a single measure of ecological assessment. The guild approach provides an operational unit linking individual species characteristics with the community as a whole. Species are grouped into guilds based on some degree of overlap in their ecological niches, regardless of taxonomic relationships. Despite European fish species having been classified into ecological guilds, classification has not been standardised Europe-wide or within the context of classifying species into guilds from which metrics can be developed for ecological assessment purposes. This paper examines the approach used by the EU project FAME to classify European fish species into consistent ecological guilds and to identify suitable metrics as basic tools for the development of a standardised ecological assessment method for European rivers to meet the requirements of the Water Framework Directive.     

海州湾及邻近海域鱼类群落的营养功能群及其动态变化

根据2011年及2013―2016年春季和秋季在海州湾及邻近海域进行的渔业资源底拖网调查,对该海域鱼类群落营养功能群的组成及其季节和年间变化进行了研究。结果表明,海州湾及邻近海域鱼类群落可以划分为5个营养功能群,即虾食性、底栖动物食性、虾/鱼食性、浮游动物食性和鱼食性。整体来说,春季海州湾鱼类群落以底栖动物食性营养功能群为主,其中方氏云鳚(Enedriasfangi)在各年所占比例均较高;而秋季以虾食性营养功能群为主,小眼绿鳍鱼(Chelidonichthys kumu)为主要优势鱼种。从生物量组成角度分析,海州湾鱼类群落各营养功能群所占比例有明显差异,以虾食性和底栖动物食性的功能群为主,其次为虾/鱼食性,而浮游动物食性和鱼食性所占比例较小。方氏云鳚、小眼绿鳍鱼、长蛇鲻(Saurida elongata)、小黄鱼(Larimichthys polyactis)、狮子鱼(Liparis sp.)、玉筋鱼(Ammodytespersonatus)等6种鱼类为各营养功能群的主要优势种类。海州湾及邻近海域鱼类群落的营养功能群和优势种呈现出明显的季节和年间变化,海洋环境变化和鱼类的季节性洄游移动等是主要的影响因素。     

Rhithronic and potamonic fishes coexist in wadeable streams under distinct metacommunity processes

Recent metacommunity ecology research has demonstrated that local communities can be divided into different guilds. We hypothesised that wadeable streams are occupied by fishes that follow distinct metacommunity processes. The mainstem is a river corridor for the potamonic fish guild (PFG) but represents a nonhabitat matrix for the rhithronic fish guild (RFG). Accordingly, the PFG should be filtered out from the headwaters by dispersal limitations or environmental filtering along the longitudinal gradient, and the guild should have a nested pattern of beta diversity. The RFG should be structured by the local species sorting, and the species turnover component should prevail. We sampled fishes in 42 streams distributed in four subbasins that were separated by at least one mainstem channel. We modelled the influences of spatial and environmental predictors using a partial redundancy analysis and variance partitioning and by quantifying the components of beta diversity that were associated with species turnover and nestedness. Both environment and space affected the structure of the RFG, owing to the influence of substrate type, riparian cover and presence of downstream barriers. The PFG was structured by only the influence of downstream barriers. Species turnover predominated within the RFG, and species nestedness dominated within the PFG. Our results support the hypothesis that potamonic and rhithronic guilds coexist in wadeable streams and follow distinct metacommunity assembly mechanisms. Potamonic guilds are structured by regional dispersal from the mainstem channels, whereas rhithronic guilds are sorted by local filtering along the longitudinal gradient in a spatially structured environment.     

Isotopic trophic guild structure of a diverse subtropical South American fish community

Characterization of food web structure may provide key insights into ecological function, community or population dynamics and evolutionary forces in aquatic ecosystems. We measured stable isotope ratios of 23 fish species from the Rio Cuareim, a fifth‐order tributary of the Rio Uruguay basin, a major drainage of subtropical South America. Our goals were to (i) describe the food web structure, (ii) compare trophic segregation at trophic guild and taxonomic scales and (iii) estimate the relative importance of basal resources supporting fish biomass. Although community‐level isotopic overlap was high, trophic guilds and taxonomic groups can be clearly differentiated using stable isotope ratios. Omnivore and herbivore guilds display a broader δ¹³C range than insectivore or piscivore guilds. The food chain consists of approximately three trophic levels, and most fishes are supported by algal carbon. Understanding food web structure may be important for future conservation programs in subtropical river systems by identifying top predators, taxa that may occupy unique trophic roles and taxa that directly engage basal resources.     

Beyond the reef: The widespread use of non‐reef habitats by coral reef fishes

Marine ecology seeks to understand the factors that shape biological communities. Progress towards this goal has been hampered by habitat‐centric approaches that ignore the influence of the wider seascape. Coral reef fishes may use non‐reef habitats (e.g. mangrove and seagrass) extensively, yet most studies have focused on within‐reef attributes or connectivity between reefs to explain trends in their distribution and abundance. We systematically review the evidence for multihabitat use by coral reef fishes across life stages, feeding guilds and conservation status. At least 670 species of “coral reef fish” have been observed in non‐reef habitats, with almost half (293 species) being recorded in two or more non‐reef habitats. Of the 170 fish species for which both adult and juvenile data were available, almost 76% were recorded in non‐reef habitats in both life stages. Importantly, over half of the coral reef fish species recorded in non‐reef habitats (397 spp.) were potential fisheries targets. The use of non‐reef habitats by “coral reef” fishes appears to be widespread, suggesting in turn that attempts to manage anthropogenic impacts on fisheries and coral reefs may need to consider broader scales and different forms of connectivity than traditional approaches recommend. Faced with the deteriorating condition of many coastal habitats, there is a pressing need to better understand how the wider seascape can influence reef fish populations, community dynamics, food‐webs and other key ecological processes on reefs.     

Fish conservation in South African estuaries

1. Habitat degradation, mainly through land use changes and excessive freshwater abstraction, has a major negative effect on southern African estuarine systems. Less important at present, but showing increasing signs towards becoming a major problem is environmental pollution, especially organic and inorganic wastes from industrial, agricultural and domestic sources. Although the major threats to estuarine-associated fishes are usually linked to environmental degradation, there is also evidence to suggest that certain fish species are declining in abundance primarily as a result of overfishing. 2. The viability of estuaries as nurseries and feeding grounds for fishes is directly related to the accessibility and productivity of these systems. Examples of the mismanagement of South African estuaries through excessive siltation, freshwater deprivation, poorly planned dredging activities, and artificial manipulation of estuary mouths, are discussed. 3. The need for conservation legislation based on a sound knowledge of the biology and ecology of threatened fish species, their communities and their habits is highlighted. Examples of possible ‘indicator’, ‘keystone’, ‘umbrella’ and ‘flagship’ species for South African estuaries are given. 4. Although estuaries on the subcontinent have long been recognized as nursery areas for a number of recreationally important marine fish species, these systems have not formed an integral component in the selection of marine reserves. The dependence of many marine teleosts on estuarine habitats necessitates the inclusion of these ecosystems in any aquatic reserve planning exercise. 5. The plight of endemic fish species is discussed, with the effects of both environmental degradation and overexploitation being highlighted. 6. It is concluded that the future health of South Africa's estuaries and their fishes depends on imaginative resource management and on the improved implementation of conservation measures in partnership with decision-makers, managers, scientists and estuarine users. © 1997 John Wiley & Sons, Ltd.     

Fish species redundancy in estuaries: A major conservation concern in temperate estuaries under global change pressures

1. Fish assemblages in estuaries have a much lower species richness (number of taxa) when compared with the combined numbers of freshwater and marine species from adjacent aquatic ecosystems. This is primarily because of the relatively harsh and fluctuating physico-chemical conditions in estuaries compared with the more stable freshwater and marine environments.
2. A comprehensive fish survey of estuaries in South Africa is used as a basis to determine fish species richness in subtropical, warm temperate, and cool temperate systems along the coast, and to assess the degree of redundancy in the different biogeographic regions.
3. In general, only one or two species belonging to each of the detritivorous, piscivorous, zoobenthivorous, and zooplanktivorous fish guilds are numerically well represented in the larger cool temperate estuaries, but between four and 10 species in each of these guilds are usually recorded in the larger subtropical estuaries.
4. Although the overall low redundancy of fish species groups in estuaries has already been formally recognized in the literature, this short note highlights the sensitivity of certain trophic guilds in temperate South African estuaries to any form of redundancy, a characteristic that may be equally applicable, based on declining species richness with increasing latitude, to temperate estuaries in other parts of the world.

     

Modes of ingress by larvae and juveniles of marine fishes into estuaries: From microtidal to macrotidal systems

We review published research on the ingress of larvae and early juveniles of marine fishes into estuaries subjected to different tidal regimes and provide perspectives on the abilities and responses of these early-life stages to the physico-chemical, hydrodynamic and biological drivers that facilitate such ingress. We focus on documenting ingress and the mechanisms employed by early-stage fishes from coastal waters to enter different types of microtidal and macrotidal estuaries but also include information on ingress into mesotidal systems. Spawning localities for estuary-associated marine fishes are assessed with respect to ontogeny of larvae and their ability to ingress estuaries during the preflexion and postflexion stages. The processes and physico-chemical cues employed by larvae and early juveniles to locate estuaries are reviewed, with olfactory cues being recognised as especially important. Particular emphasis is directed to vertical migratory behaviours and selective tidal stream transport (STST) employed by many larvae ingressing macrotidal estuaries, contrasting with mainly passive flood-tide entry and active swimming modes typically used by larvae and early juveniles that enter microtidal estuaries and estuarine lakes and lagoon systems.     

Ancient and modern mitochondrial haplotypes of common bream (Abramis brama L.) in Poland

Abstract –  Genetic data on archaeological specimens provide complementary information for addressing questions on distribution and migration of fishes over long time scales. In this study DNA was extracted from common bream bones ( N  = 4), dated c. 6000–1000  bp , and a 172 bp fragment of mitochondrial cytochrome b gene has been sequenced. The obtained sequences differed from homologous sequences of breams living contemporarily ( N  = 4), inhabiting the same geographical areas as 'ancient' fish. None of ancient mitochondrial haplotype was found in fish living at present. Our results suggest that fish vicariance could be affected also by other than glacial retreat historical events, and the mechanisms that influenced present distribution of freshwater fishes are still unclear.     

Patterns of diel activity and species richness in young and small fishes of European streams: a review of 20 years of point abundance sampling by electrofishing

Originally developed to assess the relative abundance of ≥1+ fishes in large rivers, point abundance sampling by electrofishing (PASE) was adapted for 0+ fishes in the mid‐1980s. Being both economical and widely applicable, PASE for 0+ fish has become a commonly used sampling approach in Europe, but its use for estimating 0+ fish density and species richness has attracted particular concern because of size and species selectivity. As such, this review is both timely and necessary. It summarizes the development of PASE and evaluates its various applications: studies of 0+ fish community composition, relative abundance and density, species richness (S), population size structure, larval and juvenile growth dynamics, microhabitat use, diel dynamics of species–species and species–microhabitat interactions, and the analysis of data emanating from PASE databases. The use and potential misuse of replicate sampling in estimates of S are examined, with PASE data from various European rivers re‐analysed to assess geographical patterns in 0+ fish S. Comparisons of PASE and other approaches for estimating 0+ fish density and species richness have all demonstrated PASE to be cost‐effective and relatively reliable, but sampling accuracy and precision do decrease as fishes enter the juvenile period of development.     

Diet and dietary overlap in fishes of temporary waters of southwestern Australia

The diets of six species of fish occurring in seasonally inundated waters of the southern acid peat flats of southwestern Australia were studied over a 23 month period. Fishes could be allocated to a benthos/lower water column guild or a midwater column/water surface guild. Segregation on the basis of prey size was noted for one species only, and this species had a larger mouth than the remaining species. Seasonal variation in within- and between-guild overlap was observed. Highest overlap occurred in the mid-wet season when inundation was greatest and all species foraged in extensive areas of very shallow water. Little segregation based on feeding position within the water column was possible, and some prey species (e. g. simuliid larvae) were particularly abundant at this time. Dietary overlap decreased as the dry season progressed and fish became concentrated in smaller areas of habitat. As fish demonstrated lower levels of food acquisition, this change in overlap was suggested to be in response to increased competition for limited food resources.     

Fishes and the environmental status of South African estuaries

Abstract More than 100 fish species are associated with southern African estuaries, many of which are caught by recreational anglers and/or commercial fishermen. Mismanagement of either a catchment or an estuary invariably leads to an impoverished system which is of little value to fishes or people. By taking this cause-and-effect scenario to its logical conclusion, it should be possible to assess the ‘state’ of an estuary by monitoring the biological ‘health’ of the aquatic community. Fishes are a dominant and highly visible component of the estuarine fauna and, by virtue of their key positions in the aquatic food web, can reflect either natural or anthropogenic alterations to the environment. In addition, their mobility enables them to respond rapidly to both deteriorating and improving estuarine conditions. Such attributes may assist scientists and managers in being better able both to assess the magnitude of detrimental impacts, and to monitor the ecosystem response to ameliorative actions. This paper attempts to show that an understanding of the biology and ecology of fishes associated with estuaries can lead to the identification of threats to the environment and result in improved management of these systems. The use of fish communities as an indicator of estuarine health is also examined, and ways of incorporating biological and ecological data into decision-support systems are discussed. The adoption of a set of environmental quality objectives for South African estuaries, together with a system of appropriate environmental quality standards, is recommended.     

Fish and flows: Abiotic drivers influence the recruitment response of a freshwater fish community throughout a regulated lotic system of the Murray-Darling Basin,Australia

1. Fish assemblages in dryland rivers have life-history strategies that have evolved in response to environmental conditions and triggers, particularly water temperatures and flow regimes. The regulation of rivers through the construction of dams, weirs and other water diversion structures has altered natural flow regimes and the associated ecological processes of river systems worldwide.
2. Over a 3-year period, using standardized fish sampling and daily otolith ageing, the recruitment of eight freshwater fish species was monitored in response to various abiotic drivers, including hydrology and water temperatures, throughout the Macquarie River, a large regulated river system of the Australian Murray-Darling Basin.
3. A data-driven statistical classification system is provided that groups species into reproductive guilds, based on their recruitment response to hydrology and water temperature, specifically designed for use in environmental flow management.
4. The eight species were grouped into three distinct reproductive guilds that showed similar recruitment responses to the abiotic drivers. Murray-Darling rainbowfish, Murray cod, and eel-tailed catfish were considered as a single guild, characterized by seasonal recruitment during a relatively narrow thermal window under low to moderate stable discharges. The second group included common carp, bony herring, and golden perch, which recruited primarily in association with larger flow events. Un-specked hardyhead and Australian smelt formed a more differentiated guild, recruiting over a broad range of temperatures and discharges. Limitations associated with using a reproductive guild approach to simplify water management are discussed.
5. This study highlighted important relationships among hydrology, water temperatures, and successful recruitment that can, in turn, be used to inform development of adaptive flow management plans and effective use of environmental water for the conservation management of native fish communities. Important considerations in the design of studies that aim to examine relationships between recruitment and abiotic drivers are also discussed.

     

Can bycatch in a flatfish gillnet fishery be reduced with rectangular mesh?

Gillnets fished in North Carolina, USA, estuaries have high rates of bycatch relative to the target catch of southern flounder, Paralichthys lethostigma Jordan & Gilbert. This study tested whether rectangular‐mesh gillnets would maintain catch rates of southern flounder and reduce fish bycatch relative to conventional diamond‐mesh gillnets in two North Carolina estuaries. In the Neuse River estuary, catch rates of legal southern flounder were not different between the two mesh shapes, but the bycatch of red drum, Sciaenops ocellatus (Linnaeus) and other fish species was reduced with rectangular‐mesh net. In the Newport River estuary, southern flounder and red drum catches were reduced in rectangular‐mesh net, but the decrease was greater for red drum. Catches of sublegal southern flounder were reduced in the rectangular‐mesh net in both estuaries. Reduced catch rates of sublegal southern flounder and bycatch species suggest rectangular mesh may help manage stocks of estuarine fish species in areas where gillnets are used to target flatfishes.     

Assemblages of vertical migratory mesopelagic fish in the transitional region of the western North Pacific

Assemblages of vertical migratory mesopelagic fish are described for the nighttime upper 20 m layer of the transitional and adjacent waters in the western North Pacific. Twenty-three mesopelagic fish species belonging to six families and 16 genera were collected during June 1996. Family Myctophidae was most speciose, represented by 17 species, followed by Sternoptychidae (two spp.) and Bathylagidae (one spp.). Six assemblages are recognized based on their species composition: Subarctic, Northern Transition, Southern Transition, Subtropical, Slope Water and Seamount Assemblages. These assemblages are also characterized by size composition and biomass of the catches. The distributions of the Subarctic, Northern Transition, Southern Transition and Subtropical Assemblages are approximately defined by the Kuroshio and Oyashio fronts and the Subarctic Boundary. Slope Water and Seamount Assemblages are closely related to the slope water around the shelf edge off Japan and waters around the Shatsky Rise and the Emperor Seamount chain, respectively. The importance of the Southern Transition Assemblage area between the Kuroshio front and Subarctic Boundary as spawning and nursery grounds of many subarctic, transitional and subtropical fishes is elucidated, based on the geographical distribution patterns of their larvae and juveniles.     

Biogeographical region and environmental conditions drive functional traits of estuarine fish assemblages worldwide

Assessing trait–environment relationships is crucial for predicting effects of natural and human‐induced environmental change on biota. We compiled a global database of fish assemblages in estuaries, functional traits of fishes and ecosystem features of estuaries. And we quantified the relative importance of ecosystem features as drivers of patterns of fish functional traits among estuaries worldwide (i.e. drivers of the proportions of fish traits). In addition to biogeographical context, two main environmental gradients regulate traits patterns: firstly temperature, and secondly estuary size and hydrological connectivity of the estuary with the marine ecosystem. Overall, estuaries in colder regions, with larger areas and with higher hydrological connectivity with the marine ecosystem, have higher proportions of marine fish (versus freshwater), macrocarnivores and planktivores (versus omnivores, herbivores and detritivores) and larger fish, with greater maximum depth of distribution and longer lifespan. The observed trait patterns and trait–environment relationships are likely generated by multiple causal processes linked to physiological constraints due to temperature and salinity, size‐dependent biotic interactions, as well as habitat availability and connectivity. Biogeographical context and environmental conditions drive species richness and composition, and present results show that they also drive assemblage traits. The observed trait patterns and trait–environment relationships suggest that assemblage composition is determined by the functional role of species within ecosystems. Conservation strategies should be coordinated globally and ensure protection of an array of estuaries that differ in ecosystem features, even if some of those estuaries do not support high species richness.     

Big floods,big knowledge gap: Food web dynamics in a variable river system

While flow regime is widely recognised as an over‐arching feature structuring aquatic ecosystems, the influence of flood events on feeding habits in fish assemblages inhabiting variable environments remains largely unknown. In this study, we investigated how diets of a fish assemblage changed in response to fluctuations in hydrology in a highly variable, wet‐dry tropical Australian river. We compared dietary habits, trophic guilds and intra‐ and interspecific dietary overlap and diet breadth across different seasons. Wet‐season floods acted as major geomorphic and ecological perturbations that exerted substantial effects on the trophic dynamics of the terapontid assemblage, particularly through the removal of in‐stream plant production and detritus. Forced by major shifts in food source availability due to seasonal flooding, fishes responded to these perturbations by marked changes in diet, with significant guild switching following wet‐season floods. Rather than the predictable, gradual, changes in consumer–resource interactions associated with the gentler seasonal flood pulse evident in other tropical river systems, study results instead emphasised rapid and profound changes to species' diets and trophic interactions following abrupt flood pulses. These sudden shifts in food sources may also explain some of the lack of clarity in discrimination of specific carbon sources or species' trophic levels evident in isotopic food web studies from the region. Results indicate that the effects of flood pulses on assemblage trophic interactions may differ among ecosystem types and across the broad potential scale of hydrological disturbance mediated by flood events.     

Diel variation in the seagrass ichthyofaunas of three intermittently open estuaries in south-eastern Australia: implications for improving fish diversity assessments

Diel variation in the ichthyofaunas associated with Zostera capricorni Ascherson was investigated in three intermittently open estuaries in the Illawarra region, New South Wales. Each estuary showed differing diel shifts in fish assemblages, which appeared to be related to estuary size. In the largest estuary (Lake Illawarra) significantly more species were caught during the night than the day for all months. In contrast, there was little diel variation in the fish assemblages at Werri Lagoon and Shellharbour Lagoon, although many species were only caught during the night at both estuaries. The distinct diel changes at Lake Illawarra was thought to be attributable to the relatively deep channels adjacent to the seagrass beds which are better habitats for larger fishes compared with the shallow sand bars without deep channels throughout the two smaller estuaries. The composition of fish species within the three estuaries were significantly different, although each assemblage was characterised by large numbers of small-sized fish (<100 mm FL) indicating the importance of intermittently open estuaries as fish habitats. It was concluded that night sampling provided a more complete picture of the ichthyofaunas associated with Z. capricorni . As a result, inclusion of night sampling in fish diversity assessments would increase the chance of catching diurnally rare species and therefore attain a better representation of the true community structure.     

苏北浅滩中部典型沙脊潮沟海域不同空间鱼类群落的分析

利用2011年5月(春季)和2010年11月(秋季)在苏北浅滩大丰沿岸海域(32°44?~33°23?N、120°54?~121°38?E)开展渔业资源调查获取的资料,运用聚类分析方法划分群落结构,从鱼类的种类组成、多样性以及优势种等不同方面,探讨苏北浅滩沙脊潮沟地形对鱼类群落的影响。研究表明:春秋季苏北浅滩沙脊潮沟沿岸海域鱼类可划分为西部近岸群落、中部沙脊群落以及东部潮沟群落3个群落,其鱼类群落结构差异表现为,春季鱼类总种类数表现为潮沟(15种)沙脊(11种)近岸(3种);多样性指数(H')类似,即潮沟(1.57,1.89)沙脊(1.19,1.57)近岸(0.51,0.69);秋季鱼类种类数表现为潮沟(18种)近岸(12种)沙脊(11种),鱼类多样性指数表现为潮沟(1.54,1.54)近岸(1.02,0.96)沙脊(0.92,0.83)。潮沟海域与外海相连,外海鱼群顺着潮沟向近海移动,在潮沟末端遇到沙脊地形的阻挡,底栖性鱼群停留在沟底,造成种类数累积,多样性增加。优势种分布上,潮沟群落多为方氏锦鳚(Pholos fangi)、鮸(Miichthys miiuy)、小带鱼(Eupleurogrammus muticus)等产卵性鱼类;沙脊群落鱼类主要由赤鼻棱鳀(Thryssa kammalensis)和大银鱼(Protosalanx chinensis)等滤食性鱼类组成。苏北浅滩沙脊潮沟海域鱼类群落空间差异显著,而地形变化以及由此导致的环境变化是苏北浅滩沙脊潮沟海域鱼类群落结构差异的主要原因。以沙脊潮沟地形因素为突破口,不仅丰富了鱼类群落结构变化的环境影响因素,也为苏北浅滩渔业的管理和保护提供可靠依据。