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Fish Abundance (fish + abundance)
Selected AbstractsFish abundance and community composition in native and non-native plants following hydrilla colonisation at Lake Izabal, GuatemalaFISHERIES MANAGEMENT & ECOLOGY, Issue 2 2008C. A. BARRIENTOS Abstract, Fish community composition was assessed among six macrophyte habitats, including hydrilla, Hydrilla verticillata (L.F.) Royle, common native species (bulrush, Scirpus spp., muskgrass, Chara spp., eelgrass, Vallisneria americana Michx. and Illinois pondweed, Potamogeton illinoensis Morong) and no-plants, to assess potential impacts of recent hydrilla colonisation on the littoral fish community at Lake Izabal, Guatemala. Fish biomass was significantly different among habitats, with hydrilla supporting the highest fish biomass. Fish density did not differ significantly among habitats. Total fish species richness was similar (12-15 species) among habitats, but community composition changed with macrophyte presence. Biomass of mojarra, Cichlasoma maculicauda Regan, which supported the most important subsistence fishery at the lake, was significantly different among habitats and had the greatest biomass in the hydrilla habitat. Although hydrilla may adversely affect native plants, lake access and other uses, it provided useful fish habitat and likely was not detrimental to the Lake Izabal fish community composition. [source] Ecological responses to altered flow regimes: a literature review to inform the science and management of environmental flowsFRESHWATER BIOLOGY, Issue 1 2010N. LEROY POFF Summary 1.,In an effort to develop quantitative relationships between various kinds of flow alteration and ecological responses, we reviewed 165 papers published over the last four decades, with a focus on more recent papers. Our aim was to determine if general relationships could be drawn from disparate case studies in the literature that might inform environmental flows science and management. 2.,For all 165 papers we characterised flow alteration in terms of magnitude, frequency, duration, timing and rate of change as reported by the individual studies. Ecological responses were characterised according to taxonomic identity (macroinvertebrates, fish, riparian vegetation) and type of response (abundance, diversity, demographic parameters). A ,qualitative' or narrative summary of the reported results strongly corroborated previous, less comprehensive, reviews by documenting strong and variable ecological responses to all types of flow alteration. Of the 165 papers, 152 (92%) reported decreased values for recorded ecological metrics in response to a variety of types of flow alteration, whereas 21 papers (13%) reported increased values. 3.,Fifty-five papers had information suitable for quantitative analysis of ecological response to flow alteration. Seventy per cent of these papers reported on alteration in flow magnitude, yielding a total of 65 data points suitable for analysis. The quantitative analysis provided some insight into the relative sensitivities of different ecological groups to alteration in flow magnitudes, but robust statistical relationships were not supported. Macroinvertebrates showed mixed responses to changes in flow magnitude, with abundance and diversity both increasing and decreasing in response to elevated flows and to reduced flows. Fish abundance, diversity and demographic rates consistently declined in response to both elevated and reduced flow magnitude. Riparian vegetation metrics both increased and decreased in response to reduced peak flows, with increases reflecting mostly enhanced non-woody vegetative cover or encroachment into the stream channel. 4.,Our analyses do not support the use of the existing global literature to develop general, transferable quantitative relationships between flow alteration and ecological response; however, they do support the inference that flow alteration is associated with ecological change and that the risk of ecological change increases with increasing magnitude of flow alteration. 5.,New sampling programs and analyses that target sites across well-defined gradients of flow alteration are needed to quantify ecological response and develop robust and general flow alteration,ecological response relationships. Similarly, the collection of pre- and post-alteration data for new water development programs would significantly add to our basic understanding of ecological responses to flow alteration. [source] Lake depth rather than fish planktivory determines cladoceran community structure in Faroese lakes , evidence from contemporary data and sedimentsFRESHWATER BIOLOGY, Issue 11 2006SUSANNE LILDAL AMSINCK Summary 1. This study describes the environmental conditions and cladoceran community structure of 29 Faroese lakes with special focus on elucidating the impact of fish planktivory. In addition, long-term changes in biological structure of the Faroese Lake Heygsvatn are investigated. 2. Present-day species richness and community structure of cladocerans were identified from pelagial snapshot samples and from samples of surface sediment (0,1 cm). Multivariate statistical methods were applied to explore cladoceran species distribution relative to measured environmental variables. For Lake Heygsvatn, lake development was inferred by cladoceran-based paleolimnological investigations of a 14C-dated sediment core covering the last ca 5700 years. 3. The 29 study lakes were overall shallow, small-sized, oligotrophic and dominated by brown trout (Salmo trutta). Cladoceran species richness was overall higher in the surface sediment samples than in the snapshot samples. 4. Fish abundance was found to be of only minor importance in shaping cladoceran community and body size structure, presumably because of predominance of the less efficient zooplanktivore brown trout. 5. Canonical correspondence analysis showed maximum lake depth (Zmax) to be the only significant variable in explaining the sedimentary cladoceran species (18 cladoceran taxa, two pelagic, 16 benthic) distribution. Multivariate regression trees revealed benthic taxa to dominate in lakes with Zmax < 4.8 m and pelagic taxa to dominate when Zmax was > 4.8 m. 6. Predictive models to infer Zmax were developed using variance weighted-averaging procedures. These were subsequently applied to subfossil cladoceran assemblages identified from a 14C-dated sediment core from Lake Heygsvatn and showed inferred Zmax to correspond well to the present-day lake depth. A recent increase in inferred Zmax may, however, be an artefact induced by, for instance, eutrophication. [source] Detecting the impact of oceano-climatic changes on marine ecosystems using a multivariate index: The case of the Bay of Biscay (North Atlantic-European Ocean)GLOBAL CHANGE BIOLOGY, Issue 1 2008GEORGES HEMERY Abstract Large-scale univariate climate indices (such as NAO) are thought to outperform local weather variables in the explanation of trends in animal numbers but are not always suitable to describe regional scale patterns. We advocate the use of a Multivariate Oceanic and Climatic index (MOCI), derived from ,synthetic' and independent variables from a linear combination of the total initial variables objectively obtained from Principal Component Analysis. We test the efficacy of the index using long-term data from marine animal populations. The study area is the southern half of the Bay of Biscay (43°,47°N; western Europe). Between 1974 and 2000 we monitored cetaceans and seabirds along 131000 standardized line transects from ships. Fish abundance was derived from commercial fishery landings. We used 44 initial variables describing the oceanic and atmospheric conditions and characterizing the four annual seasons in the Bay of Biscay. The first principal component of our MOCI is called the South Biscay Climate (SBC) index. The winter NAO index was correlated to this SBC index. Inter-annual fluctuations for most seabird, cetacean and fish populations were significant. Boreal species (e.g. gadiformes fish species, European storm petrel and Razorbill ,) with affinities to cold temperate waters declined significantly over time while two (Puffin and Killer Whale) totally disappeared from the area during the study period. Meridional species with affinities to hotter waters increased in population size. Those medium-term demographic trends may reveal a regime shift for this part of the Atlantic Ocean. Most of the specific observed trends were highly correlated to the SBC index and not to the NAO. Between 40% and 60% of temporal variations in species abundance were explained by the multivariate SBC index suggesting that the whole marine ecosystem is strongly affected by a limited number of physical parameters revealed by the multivariate SBC index. Aside the statistical error of the field measurements, the remaining variation unexplained by the physical characteristics of the environment correspond to the impact of anthropogenic activities such overfishing and oil-spills. [source] Effect of river fragmentation and flow regulation on occurrence of landlocked brown trout in a fish ladderJOURNAL OF APPLIED ICHTHYOLOGY, Issue 1 2009O. Slavík Summary The movement pattern of brown trout Salmo trutta (L.) in a fish ladder on the heavily fragmented Oh,e River, Czech Republic was observed for 16 months. Some individually-tagged fish repeatedly occurred in the ladder. A total of 1640 fish represented captures of 595 S. trutta in the fish ladder; 247 fish were caught once and 348 individuals were caught repeatedly. Repeatedly-caught (348) individuals represented 1393 (84.9%) of the 1640 captures. The likelihood of repetitive occurrence decreased with the increase in fish body length. The number of individuals in the ladder was inversely related to temperature, and positively correlated with increasing water flow in the main channel. Fish abundance in the ladder was density-dependent, as the number of individuals was inversely related to fish size and time of residency in the ladder. Spawning migrations were not the best predictor of maximum fish occurrence in the ladder, suggesting that repetitive capture of individuals in the ladder was significantly affected by other factors influencing fish behaviour. Repetitive fish occurrence in ladders can be expected, particularly in rivers with numerous lateral obstructions. [source] Spatial and temporal variation of abundance, biomass and diversity within marine reserves in the PhilippinesDIVERSITY AND DISTRIBUTIONS, Issue 4 2010Jonathan A. Anticamara Abstract Aim, The objective of this study was to investigate the influence of protection duration (years of fishing closure) and location (distance from shore) on reef fish diversity. Location, Danajon Double Barrier Reef, Bohol, Philippines. Methods, Reef fish abundance and size structure, by species, were obtained monthly using replicated underwater visual belt transects (n = 8; 70 × 5-m belt transects) over 3 years (2002,2005) at eight sites that included six marine reserves and two unprotected reef areas. We analysed species accumulation curves, diversity indices and abundance,biomass comparison (ABC) curves within and across the study sites to assess the influence of protection duration and location. Results, Analyses showed that longer protection duration impacted reef fish diversity at both inshore and offshore sites by shifting ABC curves from higher abundance than biomass curves at fished sites to higher biomass than abundance curves at most of the protected sites. Protection duration did not significantly influence either the rate of species accumulation within sites or the 12 diversity indices measured across the study sites. The offshore sites consistently showed higher rates of species accumulation and diversity indices values than inshore sites with similar protection duration. One protected offshore young marine reserve site that has been assessed as the least well-managed showed patterns more consistent with the fished sites. Main conclusions, Analyses showed that protection duration mainly impacted diversity by increasing the dominance of large-bodied species and enhancing total biomass. Besides protection duration, reserve location influenced species accumulation curves and diversity indices. [source] Long term effects of cormorant predation on fish communities and fishery in a freshwater lakeECOGRAPHY, Issue 2 2001Henri Engström Cormorant impact upon natural fish populations has long been debated but little studied because of the requirements of sound data that are often hard to fill. In this study I have monitored fish community composition/abundance before and after a cormorant colony was established in a high productive lake, Ymsen, of south-central Sweden. Data on fish abundance before cormorant establishment enabled me to control for changes in fish densities prior to cormorant colonisation. To control for possible changes in fish populations caused by factors other than cormorant predation (i.e. large-scale regional changes due to climate) data were compared with a control lake, Garnsviken, with no cormorants. Since Lake Ymsen also harbour an important commercial fishery, cormorant impact upon fishery yields was evaluated. The most important fish species in the diet of the cormorants were ruffe (75% by number), roach (11%) and perch (10%). Except for perch, commercially important fish made up a very small fraction of the cormorant diet. Eel, the most important fish for the fishery, was absent in the cormorant diet, pikeperch constituted 0.2% and pike 1.5%. Estimated fish outtake by the cormorants was 12.8 kg ha,1 yr,1 compared to 8.6 kg ha,1 yr,1 for the fishery. Despite considerable fish withdrawal by the cormorants, fish populations did not seem to change in numbers or biomass. The present study indicates that cormorant impact upon fish populations in Lake Ymsen was small and probably in no case has led to declines of neither commercial nor of non-commercial fish species. Still, the number of breeding cormorants in Lake Ymsen, in relation to foraging area, is among the highest known for Swedish lakes. [source] Seasonal and spatial variation in a prairie stream-fish assemblageECOLOGY OF FRESHWATER FISH, Issue 3 2002K. G. Ostrand Abstract,,,Stream-fish assemblage and environmental data for 13 sites in the upper Brazos River, Texas, USA during 1997 and 1998 were used to assess the relationship between environmental conditions, and seasonal and spatial variation in fish species abundance and distribution patterns. There was considerable spatial variation in environmental conditions among sites. Spatial variation in species diversity and species composition was related to variation in conductance (salinity), depth and current velocity among sites and streams. Species diversity increased downstream and species composition shifted from primarily cyprinodontids upstream to cyprinids downstream. Among all dominant species, spatial components of variation in fish abundance were greater than seasonal components, suggesting that assemblage structure is determined more by average or persistent differences in environmental conditions among sites than by seasonal variation in environmental conditions. [source] The effects of epibenthic communities on reef fishes in the northern Gulf of MexicoFISHERIES MANAGEMENT & ECOLOGY, Issue 5 2009R. A. REDMAN Abstract, Reef fishes were compared between artificial reefs with (n = 20) and without (n = 20) epibenthic communities in the northern Gulf of Mexico. Artificial reefs were built in June 2003; half were coated with copper-based paint to prevent epibenthic community development. Reefs were surveyed by SCUBA divers to estimate fish abundance in the autumn and winter 2003 and spring 2004. Total fish abundance and abundance of red snapper, Lutjanus campechanus (Poey), and gray triggerfish, Balistes capriscus Gmelin, were significantly (P , 0.05) higher on reefs with epibenthic communities. In the spring 2004, the abundance of belted sandfish, Serranus subligarius (Cope), the size of red snapper and community measures of diversity and evenness were significantly (P , 0.05) greater on unpainted reefs. These significant differences provide evidence that reef fishes were positively affected by the presence of epibenthic organisms that probably provided increased food resources. [source] Can fishermen allocate their fishing effort in space and time on the basis of their catch rates?FISHERIES MANAGEMENT & ECOLOGY, Issue 1 2001An example from Spermonde Archipelago, Indonesia, SW Sulawesi Spatial and temporal patterns in catch rates and in allocation of fishing effort were analysed for the coastal fishery in Spermonde Archipelago, Indonesia, to assess whether fishermen can optimise their strategy from catch information, or whether they fish under great uncertainty and merely minimise risks. On average 517 fishing units operated in the 2800 km2 area, catching 21 t fish day,1. Major gear categories were hook and line (59% of total effort and 5% of total catch), and lift nets (16% of total effort and 70% of total catch). The size of individual resource spaces varied with gear type and was smaller in unfavourable weather conditions. Although spatial patterns in catch rates at the scale of the whole archipelago were evident, fishermen could not differentiate between locations, as catch variance within their individual resource spaces was high relative to the contrasts in spatial patterns. The aggregated distribution of fishing effort in Spermonde must be explained by factors such as the small scale of operations, rather than fish abundance. [source] Mechanistic links between climate and fisheries along the east coast of the United States: explaining population outbursts of Atlantic croaker (Micropogonias undulatus)FISHERIES OCEANOGRAPHY, Issue 1 2007JONATHAN A. HARE Abstract Climate has been linked to variation in marine fish abundance and distribution, but often the mechanistic processes are unknown. Atlantic croaker (Micropogonias undulatus) is a common species in estuarine and coastal areas of the mid-Atlantic and southeast coasts of the U.S. Previous studies have identified a correlation between Atlantic croaker abundance and winter temperatures in Chesapeake Bay, and have determined thermal tolerances of juveniles. Here we re-examine the hypothesis that winter temperature variability controls Atlantic croaker population dynamics. Abundance indices were analyzed at four life history stages from three regions along the east coast of the U.S. Correlations suggest that year-class strength is decoupled from larval supply and is determined by temperature-linked, overwinter survival of juveniles. Using a relation between air and water temperatures, estuarine water temperature was estimated from 1930 to 2002. Periods of high adult catch corresponded with warm winter water temperatures. Prior studies indicate that winter temperature along the east coast is related to the North Atlantic Oscillation (NAO); variability in catch is also correlated with the NAO, thereby demonstrating a link between Atlantic croaker dynamics, thermal limited overwinter survival, and the larger climate system of the North Atlantic. We hypothesize that the environment drives the large-scale variability in Atlantic croaker abundance and distribution, but fishing and habitat loss decrease the resiliency of the population to periods of poor environmental conditions and subsequent weak year classes. [source] Mesoscale physical processes and the distribution and composition of ichthyoplankton on the southern Brazilian shelf breakFISHERIES OCEANOGRAPHY, Issue 1 2006BÁRBARA CRISTIE FRANCO Abstract The southern Brazilian shelf supports the largest fish stocks in the country, and studies on physical,biological processes in the ecology of ichthyoplankton have been recommended to provide a better understanding of the variability of the recruitment of fishing resources. This study is the first to examine the influence of mesoscale physical processes on the distribution of early life stages of fish in this shelf-break region. Collections of fish eggs and larvae and measurements of temperature and salinity were made at 13 stations along cross-shelf transects in December 1997. Myctophidae, Bregmacerotidae, Clupeidae, Synodontidae and Engraulidae were the most abundant larvae in the northern region, while Engraulidae and Bregmacerotidae prevailed further south. In situ hydrographic data, NOAA/AVHRR images and merged TOPEX/POSEIDON + ERS-1/2 satellite altimetry taken during the cruise revealed an anticyclonic eddy dominating the shelf around 31°S. Larval fish abundance was lower at the centre of this feature, suggesting that the eddy advected poorer offshore waters of tropical origin towards the inner shelf-concentrating the larvae around the eddy. [source] Relationships among vertically structured in situ measures of turbulence, larval fish abundance and feeding success and copepods on Western Bank, Scotian ShelfFISHERIES OCEANOGRAPHY, Issue 3 2002ChristianS. Using vertically stratified data of the abundance of silver hake (Merluccius bilinearis) larvae and concentrations of copepods collected in the field, we examine relationships among the vertical distribution of larval fish, their potential prey, feeding success and water column turbulence. Water column turbulence and associated stratification parameters were estimated from: (i) in situ measures of turbulent kinetic energy dissipation (,) provided by an EPSONDE profiler; (ii) in situ wind speed; (iii) the Richardson number (Ri); and (iv) the buoyancy frequency (N2). Small (< 5 mm total length) silver hake were more abundant in the least turbulent waters (i.e. at a minimum in the rate of dissipation of turbulent kinetic energy, , < 10,7 W kg,1; Ri > 0.25; N2 > 0.001 (rad s,1)2). Partial correlations amongst ,, N2 and small hake larvae were significant only for N2. The abundance of larger (> 5 mm total length) hake larvae was positively correlated with depth and was not associated with either , or N2. Vertical distributions of three potential prey (classified by stage) were variable. Early stage copepodids were positively correlated with N2 and negatively correlated with ,. We found no evidence of diel distribution patterns for small (< 5 mm total length) hake larvae or for any of the developmental stages of the copepods examined. Neither estimate of water column turbulence inferred from wind speed nor from Ri was meaningfully related to in situ estimates of , or to larval fish abundance. Feeding success, measured either as prey items (gut),1, average prey length, or total prey volume (gut),1, was not related to predicted encounter rates between days. However, the average prey length (gut),1 was significantly (P < 0.01) related to water column turbulence. These conflicting results suggest that the relationship between larval feeding and the environment is more complicated than assumed. We conclude that without substantial high resolution in situ examination of the relationship between the vertical distributions of turbulence, larvae and their prey, the growing acceptance in the secondary literature that turbulence has a positive and biologically meaningful effect on trophic interactions between fish and their zooplankton prey (a generalization based largely on modelling and laboratory experiments) is premature. [source] Ecological and socio-economic impacts of invasive water hyacinth (Eichhornia crassipes): a reviewFRESHWATER BIOLOGY, Issue 2 2010A. M. VILLAMAGNA Summary 1.,Water hyacinth (Eichhornia crassipes) is one of the world's most invasive aquatic plants and is known to cause significant ecological and socio-economic effects. 2.,Water hyacinth can alter water clarity and decrease phytoplankton production, dissolved oxygen, nitrogen, phosphorous, heavy metals and concentrations of other contaminants. 3.,The effects of water hyacinth on ecological communities appear to be largely nonlinear. Abundance and diversity of aquatic invertebrates generally increase in response to increased habitat heterogeneity and structural complexity provided by water hyacinth but decrease due to decreased phytoplankton (food) availability. 4.,Effects of water hyacinth on fish are largely dependent on original community composition and food-web structure. A more diverse and abundant epiphytic invertebrate community may increase fish abundance and diversity, but a decrease in phytoplankton may decrease dissolved oxygen concentrations and planktivorous fish abundance, subsequently affecting higher trophic levels. 5.,Little is known about the effects of water hyacinth on waterbird communities; however, increases in macroinvertebrate and fish abundance and diversity suggest a potentially positive interaction with waterbirds when water hyacinth is at moderate density. 6.,The socio-economic effects of water hyacinth are dependent on the extent of the invasion, the uses of the impacted waterbody, control methods and the response to control efforts. Ecosystem-level research programmes that simultaneously monitor the effects of water hyacinth on multiple trophic-levels are needed to further our understanding of invasive species. [source] Benthic metabolism in two turbid dryland riversFRESHWATER BIOLOGY, Issue 2 2009CHRISTINE S. FELLOWS Summary 1.,Australian dryland rivers have among the most variable discharge of any rivers worldwide and are characterized by extended periods of no flow during which aquatic habitat contracts into isolated waterholes. Despite naturally high turbidity, benthic primary production is known to be the main source of carbon to waterhole food webs. The objective of this study was to quantify rates of benthic metabolism and identify factors influencing these rates in two Australian dryland rivers, the Cooper Creek and the Warrego River. 2.,Both rivers have similar variable hydrology and high levels of turbidity (photic depths < 0.4 m), but fish abundance in Cooper Creek is 10 times than that of the Warrego River. Therefore, an additional aim of the study was to determine if fish abundances reflected underlying differences in benthic primary production. 3.,Benthic gross primary production (GPP), benthic respiration, nutrient concentrations and light penetration were measured immediately after flow had ceased (,post-flow') and after at least 2 months of zero flow (,no-flow') in 15 waterholes from each river. A subset of four waterholes from each river was sampled on two additional occasions to determine if patterns were consistent over time. 4. Cooper Creek generally had higher rates of GPP and a more autotrophic benthic zone than the Warrego River. As a result, the expected positive relationship between fish abundance and GPP was generally observed at a broad catchment scale. 4.,Light was the major control in benthic GPP in both rivers, as nutrient concentrations were high on all sampling occasions. However, for similar values of photic depth, GPP was greater in Cooper Creek than in the Warrego River. This suggests that more frequent disturbance of the littoral zone may inhibit biofilm development in waterholes of the Warrego River. 5.,Although flow variability in dryland rivers is extreme compared with other rivers worldwide, cycles of expansion and contraction of aquatic habitat in these two rivers were associated with a shift in the dominance of regional scale (subcatchments contributing to river flow) versus local scale (waterhole morphology) influences on ecosystem functioning, similar to floodplain rivers in tropical and temperate regions. [source] Recruitment variability of resident brown trout in peripheral populations from southern EuropeFRESHWATER BIOLOGY, Issue 12 2008GRACIELA G. NICOLA Summary 1. Population regulation was studied for seven consecutive years (1992,98) in five rivers at the periphery of the distribution of Salmo trutta, where the fish were living under environmental constraints quite different from those of the main distribution area. 2. Recruitment is naturally highly variable and the populations had been earlier classified as overexploited. Thus we expected that densities of young trout in most populations would be too low for density-dependent mortality to operate. We tested this by fitting the abundance of recruits to egg densities over seven consecutive years (stock,recruitment relationship), and used the results to judge whether exploitation should be restricted in the interests of conserving the populations. 3. The density of 0+ trout in early September, as well as the initial density of eggs and parents, varied greatly among localities and years. The data for all populations fitted the Ricker stock,recruitment model. The proportion of variance explained by the population curves varied between 32% and 51%. However, in most cases the observations were in the density-independent part of the stock,recruitment curve, where densities of the recruits increased proportionally with egg densities. 4. Our findings suggest that recruitment densities in most rivers and years were below the carrying capacity of the habitats. Although density-dependent mechanisms seemed to regulate fish abundance in some cases, environmental factors and harvesting appeared generally to preclude populations from reaching densities high enough for negative feedbacks to operate. The findings thus lend support to Haldane's (1956) second hypothesis that changes in population density are primarily due to density-independent factors in unfavourable areas and areas with low density due to exploitation. Exploitation should be reduced to allow natural selection to operate more effectively. [source] Does high nitrogen loading prevent clear-water conditions in shallow lakes at moderately high phosphorus concentrations?FRESHWATER BIOLOGY, Issue 1 2005María A. González Sagrario Summary 1. The effect of total nitrogen (TN) and phosphorus (TP) loading on trophic structure and water clarity was studied during summer in 24 field enclosures fixed in, and kept open to, the sediment in a shallow lake. The experiment involved a control treatment and five treatments to which nutrients were added: (i) high phosphorus, (ii) moderate nitrogen, (iii) high nitrogen, (iv) high phosphorus and moderate nitrogen and (v) high phosphorus and high nitrogen. To reduce zooplankton grazers, 1+ fish (Perca fluviatilis L.) were stocked in all enclosures at a density of 3.7 individuals m,2. 2. With the addition of phosphorus, chlorophyll a and the total biovolume of phytoplankton rose significantly at moderate and high nitrogen. Cyanobacteria or chlorophytes dominated in all enclosures to which we added phosphorus as well as in the high nitrogen treatment, while cryptophytes dominated in the moderate nitrogen enclosures and the controls. 3. At the end of the experiment, the biomass of the submerged macrophytes Elodea canadensis and Potamogeton sp. was significantly lower in the dual treatments (TN, TP) than in single nutrient treatments and controls and the water clarity declined. The shift to a turbid state with low plant coverage occurred at TN >2 mg N L,1 and TP >0.13,0.2 mg P L,1. These results concur with a survey of Danish shallow lakes, showing that high macrophyte coverage occurred only when summer mean TN was below 2 mg N L,1, irrespective of the concentration of TP, which ranged between 0.03 and 1.2 mg P L,1. 4. Zooplankton biomass and the zooplankton : phytoplankton biomass ratio, and probably also the grazing pressure on phytoplankton, remained overall low in all treatments, reflecting the high fish abundance chosen for the experiment. We saw no response to nutrition addition in total zooplankton biomass, indicating that the loss of plants and a shift to the turbid state did not result from changes in zooplankton grazing. Shading by phytoplankton and periphyton was probably the key factor. 5. Nitrogen may play a far more important role than previously appreciated in the loss of submerged macrophytes at increased nutrient loading and for the delay in the re-establishment of the nutrient loading reduction. We cannot yet specify, however, a threshold value for N that would cause a shift to a turbid state as it may vary with fish density and climatic conditions. However, the focus should be widened to use control of both N and P in the restoration of eutrophic shallow lakes. [source] Effects of longitudinal variations in stream habitat structure on fish abundance: an analysis based on subunit-scale habitat classificationFRESHWATER BIOLOGY, Issue 9 2002Mikio Inoue SUMMARY 1.,Stream reaches contain assortments of various habitat types that can be defined at different spatial scales, such as channel unit (e.g. pools, riffles) and subunit (patches within channel units). We described longitudinal (upstream,downstream) patterns of stream habitat structure by considering subunits as structural elements, and examined their effects on the abundance of masu salmon (Oncorhynchus masou) and rosyface dace (Leuciscus ezoe) in a third-order tributary of the Teshio River in northern Hokkaido, Japan. 2.,Nine subunit types were determined on the basis of water depth, current velocity and substrate, using 0.5 × 0.5 m grids. Although both masu salmon and rosyface dace used pools as a major habitat, the former preferred a subunit type occurring at pool heads (PH subunit) while the latter preferred a slow-current edge type (SE-2 subunit). 3.,Along the course of the stream, slow-edge subunits (SE-1, 2 and 3) increased in frequency downstream while fast-edge subunits (FE-1 and 2) decreased, suggesting a downstream development of slow-current edges. Regression analyses indicated that longitudinal variation in masu salmon abundance was explained by the area of PH, rather than pools. Masu salmon density increased with the area of PH. Rosyface dace abundance was explained by a combination of water depth and the area of SE-2, both effects being positive. 4.,Longitudinal variations in the abundance of both species were related to the abundance of their preferred habitat at the subunit scale, rather than channel-unit scale. The results emphasise the importance of fine-scale patchiness when examining stream fish habitats. [source] Factors influencing the spatial distribution of zooplankton and fish in Loch Ness, UKFRESHWATER BIOLOGY, Issue 4 2000D. G. George Summary 1The vertical and horizontal distribution of phytoplankton, zooplankton and fish in Loch Ness, Scotland, were monitored during one day-time and one night-time survey in July 1992. The vertical samples were collected at a site located at the northern end of the loch and the horizontal samples along a longitudinal transect. 2The vertical distribution surveys demonstrated that the phytoplankton, the zooplankton and the fish were concentrated in the top 30 m of water above the seasonal thermocline. Within this layer, Cyclops stayed much closer to the surface than Eudiaptomus but both species moved towards the surface at night. 3The most important factor influencing the horizontal distribution of the phytoplankton was the north- south gradient in productivity. The sub-catchments surrounding the north basin contain a greater proportion of arable land than those to the south and the concentrations of nitrate-nitrogen and phytoplankton chlorophyll increased systematically from south to north. 4Zooplankton distribution patterns were influenced by wind-induced water movements and the dispersion of allochthonous material from the main inflows. The highest concentrations of Cyclops were recorded in the north, where there was more phytoplankton, and the highest concentrations of Eudiaptomus in the south, where there were higher concentrations of non-algal particulates. 5There was no spatial correlation between total zooplankton and total fish abundance but the highest concentrations of small (1,5 cm) fish were recorded in the south where there was a large patch of Eudiaptomus. The number of Eudiaptomus at specific locations within this patch were, however, negatively correlated with the numbers of small fish. These results suggest that the fish were actively foraging within the patch and were depleting their zooplankton prey in the areas where they were most abundant. [source] Exploitation and habitat degradation as agents of change within coral reef fish communitiesGLOBAL CHANGE BIOLOGY, Issue 12 2008S. K. WILSON Abstract Over-exploitation and habitat degradation are the two major drivers of global environmental change and are responsible for local extinctions and declining ecosystem services. Here we compare the top-down effect of exploitation by fishing with the bottom-up influence of habitat loss on fish communities in the most diverse of ecological systems, coral reefs. Using a combination of multivariate techniques and path analyses, we illustrate that the relative importance of coral cover and fishing in controlling fish abundance on remote Fijian reefs varies between species and functional groups. A decline in branching Acropora coral is strongly associated with a decline in abundance of coral-feeding species, and a decrease in coral-associated habitat complexity, which has indirectly contributed to reduced abundance of small-bodied damselfish. In contrast, reduced fishing pressure, brought about by declining human populations and a shift to alternate livelihoods, is associated with increased abundance of some piscivores and fisheries target species. However, availability of prey is controlled by coral-associated habitat complexity and appears to be a more important driver of total piscivore abundance compared with fishing pressure. Effects of both fishing and coral loss are stronger on individual species than functional groups, as variation in the relative importance of fishing or coral loss among species within the same functional group attenuated the impact of either of these potential drivers at the functional level. Overall, fishing continues to have an influence on Fijian fish communities; however, habitat loss is currently the overriding agent of change. The importance of coral loss mediated by climate change is expected to have an increasing contribution to fish community dynamics, particularly in remote locations or where the influence of fishing is waning. [source] Top-Down Control of Reed Detritus Processing in a Lake Littoral Zone: Experimental Evidence of a Seasonal Compensation between Fish and Invertebrate PredationINTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 2 2007Giorgio Mancinelli Abstract We investigated whether predatory fish exert a top-down control on reed leaf packs processing in a lake littoral zone through a trophic cascade. Exclosure experiments were repeated in summer and winter, under high and low natural fish abundance, respectively. Fish exclusion effects on detritus processing and fungal conditioning were consistent with trophic cascade predictions only in summer. In winter, however, results indicated that a trophic cascade was induced by predatory invertebrates. In both seasons, variations in detritivores abundance generally supported a cascade scenario, whereas several taxon-specific departures occurred during the experimental periods. We conclude suggesting that predators may continuously regulate leaf detritus processing in lake littoral zones, through a seasonal shift in the relative contribution of fish and invertebrate predation. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Nocturnal fish utilization of a subtropical mangrove-seagrass ecotoneMARINE ECOLOGY, Issue 2 2010Neil Hammerschlag Abstract Whereas diel fish migration between mangrove and seagrass habitats has been recognized for decades, quantitative studies have focused mainly on diurnal patterns of fish distribution and abundance. In general, previous studies have shown that fish abundances decline with increasing distance from mangroves; however, evidence for such a pattern at night, when many fishes are actively feeding, is scarce. The present study is the first to report nocturnal fish abundances along a continuous distance gradient from mangroves across adjacent seagrass habitat (0,120 m). Here, we used nocturnal seine sampling to test the null hypothesis (based on diurnal studies and limited nocturnal work) that fish abundance would decrease with increasing distance from shoreline. We focused on species and life-stage-specific abundance patterns of Lutjanus griseus, Sphyraena barracuda, Archosargus rhomboidalis, and Haemulon sciurus. Results indicated that assemblage composition and structure differed significantly by season, likely influenced by temperature. However, within each season, the fish habitat use pattern at both the assemblage and species-specific level generally failed to support our working null hypothesis. Species-specific analyses revealed that, for most species and life-stages examined, nocturnal abundance either did not change with distance or increased with distance from the mangrove-seagrass ecotone. Our results suggest that analyses where taxa are grouped to report overall patterns may have the potential to overlook significant species- and stage-specific variation. For fishes known to make nocturnal migrations, we recommend nocturnal sampling to determine habitat utilization patterns, especially when inferring nursery value of multiple habitats or when estimating fish production. [source] Fish Assemblages in Shallow Marine Caves of the Salento Peninsula (Southern Apulia, SE Italy)MARINE ECOLOGY, Issue 2002Simona Bussotti Abstract. Fish assemblages of three shallow marine caves from the Salento Peninsula (Apulia, SE Italy) were investigated in July 2000. Data were collected in situ by using visual census. A total of nineteen fish species were recorded inside the caves. The species richness generally displayed a similar pattern in all three caves, decreasing from the entrance towards the innermost sections, whereas the patterns of total fish abundance differed among caves. Apogon imberbis (mainly represented by juveniles) was the most important species in terms of number of individuals (accounting for more than 85% of the censused fish) and showed a fairly even distribution inside the investigated caves. Without the numerical contribution of A. imberbis, fish abundance decreased from the entrance to the inner sections and this pattern was common to all three caves. Juvenile fishes of economic interest (e. g., Diplodus vulgaris and Epinephelus marginatus) were also recorded inside. The present study suggests that: (1) environmental constraints could affect distribution patterns in fish species richness and in the abundance of several fish along the axis of "blind caves" (with a single entrance), as already observed for sessile benthos and plankton assemblages; (2) shallow marine caves of the Salento Peninsula could exert the role of refuge and/or nursery for some littoral fish species during the adult and/or juvenile stages of their life histories. [source] Assessing ecological changes in and around marine reserves using community perceptions and biological surveysAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 4 2010M. Yasué Abstract 1. Well-enforced partial or total no-fishing zones (collectively known as marine protected areas, or MPAs) can help restore degraded coral reefs and enhance fish populations. 2. A comparison was made of community perceptions of ecological changes in an MPA with concurrent scientific data on these changes in the same MPA. Such analyses are particularly important in community-based MPAs where local support is a key determinant of ecological success. 3. The no-take MPA in question was initially launched in partnership with the community in 1995 and formalized in 1998. The perceptions data come from interviews with community members in 1999 and 2004, the biological data come from underwater visual censuses of the MPA from 1998 to 2004. 4. Community members perceived more fish within the MPA and slight increases in catch outside the MPA. In contrast, fish censuses showed a high degree of stochastic variation and only minor increases in fish abundance, size and diversity in and around the MPA between 1998 and 2004. 5. Possible explanations for these discrepancies include different temporal, spatial or species frames of reference and/or limitations to the biological survey technique. Other options include wishful thinking, external influences, a desire to please, or confounding with other benefits. 6. This study demonstrates some of the strengths and weaknesses of community perceptions and biological data. In order to improve our understanding about the changes that occur over time in an MPA and engender community support for the long-term viability of MPAs, it is important to develop diverse and efficient monitoring schemes. Copyright © 2010 John Wiley & Sons, Ltd. [source] Quantifying the condition of Hawaiian coral reefsAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 1 2010Ku'ulei S. Rodgers Abstract (1)This investigation developed and tested descriptive models designed to evaluate coral reef ecological condition based on data developed using the basic techniques most often used in coral reef surveys. (2)Forty-three variables at 184 stations were analysed in order to identify specific factors that are useful metrics for describing reef condition. (3)The common practice of using ,reference sites' for paired site comparisons was evaluated by developing a reference site model (RSM). This use of reference sites proved to be subjective and unreliable, especially when multiple factors and multiple sites are involved. However, in some cases the RSM is appropriate in demonstrating severe degradation based on factors such as sediment, coral cover and fish abundance. (4)An objective ecological gradient model (EGM) was developed based on a wide range of metrics at numerous sites. A computer program was developed that allows a quantitative ranking of reef condition along a continuum and can be used to compare reefs across a wide range of conditions. Further, this approach permits the operator to alter and define criteria appropriate to a specific question. (5)Results of this investigation provide ecological insights into the importance of natural and anthropogenic ecological factors in determining coral reef condition. Copyright © 2009 John Wiley & Sons, Ltd. [source] Decadal changes (1996,2006) in coastal ecosystems of the Chagos archipelago determined from rapid assessmentAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 6 2009Andrew R.G. Price Abstract 1.The atolls and islands comprising Chagos are a biodiversity hotspot of global conservation significance in a remote part of the central Indian Ocean. 2.This study examines the condition of the archipelago's coastal ecosystems by rapid environmental assessment at 21 sites/islands, which were also investigated a decade earlier using the same methodology. Major changes in ecosystem structure and environmental disturbance were determined. 3.Coral fish abundance was significantly lower in 2006 than 1996. Decrease in the physical structural complexity of the reefs, as a result of coral bleaching and mortality induced by the 1998 warming event, may have been a contributing factor. 4.Evidence of collecting/fishing was significantly greater in 2006 than 1996. This is attributed mainly to an illegal fishery for holothurians (sea cucumbers), which has expanded over recent years and now exerts substantial pressure on the resource. The significant decline observed in beach wood, a readily accessible fuel for fishing camps, is consistent with this. 5.Solid waste on islands was high (median 2 to 20 items m,1 beach) in both 1996 and 2006. Potentially harmful biological impacts, determined from other studies, include entanglement, toxic effects and provision of transport for invasives or other ,hitchhiker' species. 6.Significantly higher bird abundances were recorded in protected areas than ,unprotected' areas, attributed mainly to absence of predation by rats. 7.Rapid assessment augments more comprehensive ecosystem investigations. It provides a valuable snapshot of environmental conditions based upon a broad suite of features (ecosystems and disturbances) determined, concurrently, within the same site inspection quadrats and using the same scale of assessment. Copyright © 2009 John Wiley & Sons, Ltd. [source] Marine protected areas in spatial property-rights fisheries,AUSTRALIAN JOURNAL OF AGRICULTURAL & RESOURCE ECONOMICS, Issue 3 2010Christopher Costello Marine protected areas (MPAs) and spatial property rights (TURFs) are two seemingly contradictory approaches advocated as solutions to common property failures in fisheries. MPAs limit harvest to certain areas, but may enhance profits outside via spillover. TURFs incentivize local stewardship but may be plagued by spatial externalities when the TURF size is insufficient to capture all dispersal. Within a numerical model parameterized to a California marine species, we explore the economic and ecological effects of imposing MPAs on a TURF-regulated fishery. Whether MPAs can enhance or diminish profits (or fish abundance) hinges critically on the level of coordination already occurring between TURF owners. If coordination is complete, private MPAs may already emerge in some TURFs; implementing additional MPAs reduces profits. However, to the extent that coordination is incomplete, strategically sited MPAs may be an effective complement to spatial property rights-based fisheries, increasing both fishery profits and abundance. [source] Benthic metabolism in two turbid dryland riversFRESHWATER BIOLOGY, Issue 2 2009CHRISTINE S. FELLOWS Summary 1.,Australian dryland rivers have among the most variable discharge of any rivers worldwide and are characterized by extended periods of no flow during which aquatic habitat contracts into isolated waterholes. Despite naturally high turbidity, benthic primary production is known to be the main source of carbon to waterhole food webs. The objective of this study was to quantify rates of benthic metabolism and identify factors influencing these rates in two Australian dryland rivers, the Cooper Creek and the Warrego River. 2.,Both rivers have similar variable hydrology and high levels of turbidity (photic depths < 0.4 m), but fish abundance in Cooper Creek is 10 times than that of the Warrego River. Therefore, an additional aim of the study was to determine if fish abundances reflected underlying differences in benthic primary production. 3.,Benthic gross primary production (GPP), benthic respiration, nutrient concentrations and light penetration were measured immediately after flow had ceased (,post-flow') and after at least 2 months of zero flow (,no-flow') in 15 waterholes from each river. A subset of four waterholes from each river was sampled on two additional occasions to determine if patterns were consistent over time. 4. Cooper Creek generally had higher rates of GPP and a more autotrophic benthic zone than the Warrego River. As a result, the expected positive relationship between fish abundance and GPP was generally observed at a broad catchment scale. 4.,Light was the major control in benthic GPP in both rivers, as nutrient concentrations were high on all sampling occasions. However, for similar values of photic depth, GPP was greater in Cooper Creek than in the Warrego River. This suggests that more frequent disturbance of the littoral zone may inhibit biofilm development in waterholes of the Warrego River. 5.,Although flow variability in dryland rivers is extreme compared with other rivers worldwide, cycles of expansion and contraction of aquatic habitat in these two rivers were associated with a shift in the dominance of regional scale (subcatchments contributing to river flow) versus local scale (waterhole morphology) influences on ecosystem functioning, similar to floodplain rivers in tropical and temperate regions. [source] Nocturnal fish utilization of a subtropical mangrove-seagrass ecotoneMARINE ECOLOGY, Issue 2 2010Neil Hammerschlag Abstract Whereas diel fish migration between mangrove and seagrass habitats has been recognized for decades, quantitative studies have focused mainly on diurnal patterns of fish distribution and abundance. In general, previous studies have shown that fish abundances decline with increasing distance from mangroves; however, evidence for such a pattern at night, when many fishes are actively feeding, is scarce. The present study is the first to report nocturnal fish abundances along a continuous distance gradient from mangroves across adjacent seagrass habitat (0,120 m). Here, we used nocturnal seine sampling to test the null hypothesis (based on diurnal studies and limited nocturnal work) that fish abundance would decrease with increasing distance from shoreline. We focused on species and life-stage-specific abundance patterns of Lutjanus griseus, Sphyraena barracuda, Archosargus rhomboidalis, and Haemulon sciurus. Results indicated that assemblage composition and structure differed significantly by season, likely influenced by temperature. However, within each season, the fish habitat use pattern at both the assemblage and species-specific level generally failed to support our working null hypothesis. Species-specific analyses revealed that, for most species and life-stages examined, nocturnal abundance either did not change with distance or increased with distance from the mangrove-seagrass ecotone. Our results suggest that analyses where taxa are grouped to report overall patterns may have the potential to overlook significant species- and stage-specific variation. For fishes known to make nocturnal migrations, we recommend nocturnal sampling to determine habitat utilization patterns, especially when inferring nursery value of multiple habitats or when estimating fish production. [source] Changes in northern Tanzania coral reefs during a period of increased fisheries management and climatic disturbanceAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 7 2009Tim R. McClanahan Abstract 1.Surveys of coral reefs in northern Tanzania were conducted in 2004/5 with the aim of comparing them over an,8-year period during a time of increased efforts at fisheries management and the 1998 El Niño Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) coral mortality event that caused 45% mortality in northern Tanzania and much of the Indian Ocean. 2.Changes associated with both management, its absence, and the ENSO were found but changes were generally small and ecological measures indicated stability or improvements over this period, particularly when compared with reports from much of the northern Indian Ocean. 3.Fisheries management in two areas increased the biomass of fish and benthic communities. A small fisheries closure (0.3,km2) displayed little change in the coral community but ecological conditions declined as measured by sea urchins and fish abundances. This change may be associated with its small size because similar changes were not measured in the large closure (28,km2). 4.The few sites without any increased management were still degraded and one site had experienced a population explosion of a pest sea urchin, Echinometra mathaei. 5.The lack of significant changes across this disturbance indicates that these reefs are moderately resilient to climate change and, therefore, a high priority for future conservation actions. Copyright © 2009 John Wiley & Sons, Ltd. [source] | |||||||||||||||||||||||||