Quantification of P-flux through shallow, agricultural and natural waters as found in wetlands of the Camargue (S-France)

The flux of phosphate in the aquatic ecosystems of the Camargue was modelled. The model developed for the hydrological unit, the water basin of the Aube de Bouic, is based on the hydrology of the system, the reaction equations of the adsorption of phosphate onto Fe(OOH) and the solubility product of apatite. The water basin consists of an inlet canal, the Aube de Bouic, ricefields and natural marshes, plus a drainage canal through which the excess water is pumped into the Etang de Vaccarès. Phosphate is introduced into ricefields either with the irrigation water, taken from the Rhône, or as fertiliser. Most of the phosphate will be fixed on the ricefield soils either as iron-bound or as calcium-bound phosphate, depending on the pH. The o-phosphate concentration will slowly increase to an extent depending on the pH. From the ricefields water will flow towards the Etang de Vaccarès; the amount of phosphate reaching the Etang de Vaccarès depends on the pH of the system and the depth of the water outlet of the ricefields. In six different scenarios the amount of phosphate reaching the Etang de Vaccarès is calculated depending on the quantity of fertiliser, the depth of the water outlet and the pH. For the Etang de Vaccarès the model predicts the present concentration of o-P relatively well and shows that the loading is considerable. This should cause concern; the danger of serious eutrophication is real. Part of the irrigation water is used to refill or keep under water the natural marshes in this hydrological unit, which without irrigation would dry out during summer. Again high P-concentrations are found in the marshes, but mostly in the form of Fe(OOH)P or CaCO₃P, the ratio of which depends again on the pH of the sediments. The o-P concentration has remained low up to now.     

Environmental factors influencing the gobiid assemblage of a Mediterranean Lagoon: Empirical evidence from a long-term study

A severe freshwater inflow during our long-term ichthyological study of the brackish Vaccarès lagoon (1993–1998) helped us to assess the impact of sudden environmental changes on the specific biomass composition of the gobiid population and the catches per unit effort of the black goby Gobius niger, the common goby Pomatoschistus microps and the sand goby P. minutus. In 1993, the composition of the Gobiid fish assemblage of the Vaccarès lagoon was dominated by the black goby (63%) and finally evolved to an assemblage dominated by the common goby (80%). The black goby disappeared from the Vaccarès lagoon 2 years after the inflow, whereas catches of the common goby increased significantly after the environmental changes and reached maximum values in 1998. Catches of sand goby did not seem to be affected by environmental changes and depended on the communication between sea and lagoon. This study showed that evolution of an ecosystem after environmental changes is linked to the reaction that species developed to face perturbations.     

Use of seasonally flooded marshes by fish in a Mediterranean wetland: timing and demographic consequences

In the Camargue (southern France), movements of fish between a canal and two seasonally flooded marshes were monitored continuously by fish traps for 3 years for one marsh and for 2 years for the other. The timing of the entry and exit of the main species was determined together with species annual demographic balance, defined as the difference between the number of fish leaving and the number of fish entering. Only some of the species inhabiting the canal colonized the marshes. Except those species that reproduced in salt or brackish waters, all the species colonizing the marshes reproduced in it. The most abundant of these species were small sized (mosquitofish, sand smelt and three-spined stickleback). The unpredictability of water levels in summer was particularly unfavourable for recruitment and survival of species that breed late in the year, e.g. pumpkinseed sunfish, or which prolonged their stay in the marsh and only attempted to leave just before the connection was broken, e.g. carp. Only the three-spined stickleback always had a positive demographic balance as a result of colonizing the marshes. Adults of this species entered in winter and young-of-the-year left in April. By limiting its stay in the seasonally flooded marshes, the stickleback minimized the risks related to environmental unpredictability. These results suggest that hydrology (temporal variations of water depth) may influence the fish community structure through interspecific differences in survival and recruitment, as a result of temporal variations in the use of seasonally flooded marshes.     

The biology of the common carp, Cyprinus carpio L. in the Camargue, southern France

Carp were sampled monthly during one and a half years in the Etang du Vaccarès, Camargue, southern France using fyke nets. Densities of carp in temporary marshes and canals were determined using rotenone. Carp is the dominant species in biomass in the fresh and brackish waters (14%0) with densities from 11–58 kg/ha in temporary marshes and up to ten times greater in the canals. Scales were used to determine age and growth of 201 carp. The relative condition factor of female and male mature and unsexed fish are not statistically different throughout the year and follow the variations of gonadal development in spring. The best predictive equation of fecundity, Log F = 7.03504 + 0.83829 log ovary weight, was found using a stepwise multiple regression. The sex-ratio in the temporary marshes (♂ : ♀; 1.66–1.76) is greater than the general sex-ratio of the monthly samples (0.67). The diet of carp is characterized by the presence of large numbers of seeds and the absence of large benthic invertebrates. Predation by fish-eating birds and carnivorous fish is minimal, and the annual drying of many marshes is considered the main mortality factor., Accepted 22 July 1980     

Migration flexibility between freshwater and marine habitats of the pond smelt Hypomesus nipponensis

The life histories of the pond smelt Hypomesus nipponensis collected from Japanese fresh waters and brackish (sea) waters were studied by examining the strontium (Sr) and calcium (Ca) concentrations in their otoliths. The Sr:Ca ratios in the otoliths changed with the salinity of the habitat. The pond smelt living in a freshwater environment showed consistently low Sr:Ca ratios throughout the otolith, averaging 1·2–1·3 × 10⁻³. These samples were identified as a standard freshwater type. In contrast, fish collected from the intertidal zone showed higher otolith Sr:Ca ratios than those in the standard freshwater type, and the ratios fluctuated along the growth phase. In addition to the two representative life‐history types of H. nipponensis , i. e . freshwater and anadromous life‐history types, other pond smelts were found to have an estuarine resident life history‐type with no freshwater phase, indicating that the pond smelt has a flexible migration strategy with a high degree of behavioural plasticity and an ability to utilize the full range of salinity in its life history.     

New record and range extension of the big‐scale sand smelt Atherina boyeri Risso, 1810 (Atherinidae) in the Devegecidi Dam Lake,Tigris River basin,Turkey

The big‐scale sand smelt, Atherina boyeri, is recorded from the Devegecidi Dam Lake in 2016, the first record of this invasive species in the Tigris River basin, with potential to extend to all countries in the Middle East. The smelts were caught with a trawl net mesh size of 6 mm. The captured specimens are described and compared. Records of A. boyeri from Turkish inland waters are summarised from the literature.     

Clonorchis sinensis metacercarial infection in the pond smelt Hypomesus olidus and the minnow Zacco platypus collected from the Soyang and Daechung Lakes

The pond smelt Hypomesus olidus and minnow Zacco platypus were collected from the Soyang and Daechung Lakes in January 2003, and their metacercarial infections was examined by the muscle compression and artificial digestion techniques. In the Soyang Lake, 161 metacercariae of Clonorchis sinensis (0.35 per fish) were harvested from 459 pond smelts examined. Also, 13 metacercariae of C. sinensis (0.43 per fish), 1 of Metagonimus sp., 4 of Echinostoma sp., 148 of Centrocestus armatus and 44 unidentified species were collected from 30 minnows. In the Daechung Lake, 369 metacercariae of C. sinensis (3.69 per fish) and 51 unidentified species were recovered from 100 pond smelts. The metacercariae of C. sinensis were fed to experimental rats, in which the adult flukes were identified. The pond smelts and minnows collected from the Soyang and Daechung Lakes were verified to be the second intermediate hosts and the sources of human C. sinensis infection.     

A metalimnetic oxygen minimum indirectly contributing to the low biomass of cladocerans in Lake Hiidenvesi – a diurnal study on the refuge effect

The diurnal vertical migrations of smelt (Osmerus eperlanus), larvae of phantom midge (Chaoborus flavicans) and cladoceran zooplankton in eutrophic Lake Hiidenvesi were studied in order to clarify the factors behind the low zooplankton biomass. In the study area, an oxygen minimum occurred in the metalimnion in the 10–15 m depth. No diurnal fluctuations in the position of the minimum were observed. Cladocerans inhabited the epilimnion throughout the study period and their vertical movements were restricted to above the thermocline and above the oxygen minimum. C. flavicansconducted a diurnal migration. During the day, the majority of the population inhabited the 12 – 15 m depth just in the oxygen minimum, while during darkness they were found in the uppermost 8 m. Smelts started ascending towards the water surface before sunset and reached the uppermost 3 m around 23:00. During daytime, the majority of smelts inhabited the depth of 7–9 m, where the water temperature was unfavourably high for them (18 °C). Smelts thus probably avoided the steep oxygen gradient in the metalimnion, whereas Chaoborusused the oxygen minimum as a refuge against predation. Those smelts that were found in the same water layers as Chaoborusused the larvae as their main prey. The metalimnetic oxygen minimum thus seemed to favour the coexistence of vertebrate and invertebrate predators, leading to a depression of cladoceran zooplankton.     

Relation between climatic factors,diet and reproductive parameters of Little Terns over a decade

We used 10 years of data on clutch size, egg size and diet, and 8 years of data on timing of laying on Little Terns (Sternula albifrons) breeding in Ria Formosa lagoon system, Algarve, Portugal to assess whether diet acts as an important intermediary between climatic conditions and breeding parameters. We used Generalized Linear Models to relate (1) the relative occurrence and size of the main prey species, sand smelts (Atherina spp.), with environmental variables, a large-scale climate variable, the North Atlantic Oscillation (NAO) index, and a local scale variable, the sea-surface temperature (SST), and (2) the respective effects of sand smelts relative occurrence, NAO index and SST on Little Tern breeding parameters. The diet of Little Terns was dominated by sand smelts, with a frequency occurrence of over 60% in all years. The winter SST (February) was negatively associated with the relative occurrence of sand smelts in the diet of Little Terns during the breeding season which, in turn, was positively associated with Little Tern clutch size. Our results suggest that negative NAO conditions in the Atlantic Ocean, often associated with rougher sea conditions (greater vertical mixing, stronger winds and lower SST) were related with earlier breeding, and lower SST in the surroundings of the colony during winter–spring favour the abundance of prey fish for Little Terns as well as their reproductive parameters. Climate patterns at both large and local scales are likely to change in the future, which may have important implications for estuarine seabirds in Southern Europe.     

Diplostomiasis in sand smelt, Atherina presbyter Cuvier, from the Fleet, Dorset and its use as a population indicator

The population of sand smelt, Atherina presbyter , breeding in the Fleet, Dorset, shows a high infection of diplostomiasis. The population was studied in 1983 to clarify aspects for this parasitic condition previously analysed for the sand smelt population at Fawley, Southampton Water. All age classes showed a higher percentage infection and mean number of metacercaria per fish than at Fawley. Analysis of postlarvae and juveniles showed that infection can occur at 1 week old, and verified the hypothesis that the scales of older fish inhibit cercarial settlement. Circumstantial evidence suggests that Potamopyrgus jenkinsi may be the first vector host for this parasite, and the densities of this species and of nesting little tern colonies would account for the differential infection between these two sand smelt populations. The increase in infection of 2 fish at Fawley cannot be attributed to mixing with the Fleet population, and the different infection levels demonstrate population isolation. High levels of infection are limited to this part of the English Channel: sand smelt samples from around the coasts of the British Isles show minimal infection rates elsewhere and suggest a southerly distribution of the parasite, away from Atlantic oceanic waters.     

Mitochondrial DNA in Atherina (Teleostei,Atheriniformes): differential distribution of an intergenic spacer in lagoon and marine forms of Atherina boyeri

The big‐scale sand smelt Atherina boyeri lives in fresh water, brackish water and sea water of the western Atlantic Ocean and Mediterranean Sea. Previous studies concerning distribution, biometric characters and genetic molecular markers have suggested the possible existence of two or even three different groups or species of sand smelt, one ‘lagoon’ type and one (or two – punctuated and non‐punctuated on the flanks) ‘marine’ type. In this study, the presence and the localization of an insertion was described, c. 200 bp in length, in the mtDNA of the lagoon and marine punctuated specimens of A. boyeri and its absence in the marine non‐punctuated specimens, as well as in other two congeneric species, Atherina hepsetus and Atherina presbyter, and in the atheriniform Menidia menidia. The intergenic spacer is located between the tRNA^Glu and cytochrome b (cyt b) genes and shares a c. 50% sequence similarity with cyt b. The distribution and the features of the intergenic spacer suggest that it might have originated from an event of gene duplication, which involved the cyt b gene (or, more likely, a part of it) and which took place in the common ancestor of the lagoon and the marine punctuated specimens. The data obtained therefore support the hypothesis of the existence of three cryptic and, or sibling species within the A. boyeri taxon and provide a genetic molecular marker to distinguish them.     

Influence of the annual flood-pulse on catch per unit effort,condition and reproduction of Clarias gariepinus from the upper Okavango Delta,Botswana

Catch per unit effort (CPUE), length, weight and maturity data for Clarias gariepinus were collected during monthly gillnet surveys in the upper Okavango Delta between 2001 and 2009 to investigate their relationship with the annual flood-pulse. CPUE, condition factor (K) and the proportion of ripe-running fish (P_RR) in the population followed a unimodal annual cycle that could be modelled using water temperature and flood-pulse hydrology. Increased CPUE during declining water levels was most likely a result of feeding migrations and aggregation behaviour. The observed increase in K during low floods in October and November preceded the increase in P_RR, which increased mainly with increasing temperature but appeared less dependent on flow. This study provided quantitative evidence that the biology of fish in the Okavango Delta is mainly dependent on the annual flood regime and, therefore, that conservation efforts should be focused on maintaining natural flow patterns in the face of climate change and potential water extraction schemes upstream.     

Size-selective overwintering mortality in the sand smelt, Atherina boyeri Risso, and its role in population regulation

The fat laid down as a winter reserve by O-group sand smelt, Atherina boyeri , was found to be size-dependent. The larger, earlier-spawned fish lay down more fat prior to the onset of winter. During the winter the fish do not feed for some 100 days and rely on this fat for energy; laterspawned O-group fish (<59 mm s.l. in November) have insufficient fat reserves and starve to death in a normal winter. This loss of the smallest 46% of the O-group is shown as an increase in the mean size of the O-group over the winter period. Older sand smelt age classes have more than sufficient fat reserves for overwintering. There is thus a clear advantage in spawning early in the season, and any restriction on spawning ground availability at that time will result in overall population regulation. This conclusion supports the hypothesis that the density-dependent control on population size in the sand smelt is a limitation on the number of fish which can spawn at the optimum time.     

The spectral sensitivity of the retinal photoreceptors of the Asiatic smelt <Emphasis Type="Italic">Osmerus dentex</Emphasis> (Steindachner et Kner, 1870)

The spectral sensitivity and complement of the retinal photoreceptors of the Asiatic smelt from the Sea of Japan were studied by microspectrophotometry and light microscopy. Apart from rods, one type of single cones and one type of unequal double cones were found in major parts of the retina. The dominant type of the cone pattern (mosaic) is a row pattern consisting of various linear arrangements of separate single and double cones. The absorbance maxima of rods and a majority of singe cones and double cones equaled 516, 425 and 514/565 nm, respectively. It has been established that all of the pigments are based on retinal. The findings are compared with data on the osmerid retina from the literature and discussed with respect to the adaptations to light conditions, peculiarities of behavior, and seasonal migrations of smelts.     

Density-dependent and inter-specific interactions affecting European eel settlement in freshwater habitats

Identifying the factors influencing the settlement of European eel (Anguilla anguilla) juveniles in continental habitats is crucial to designing effective management and conservation measures for this endangered species. A long-term data series (1993–2008) of European eel and European catfish (Silurus glanis) abundance in a freshwater canal of the Camargue water system (southern France), along with parallel data on water salinity and glass eel abundance in the adjacent Vaccarès lagoon, was analysed to identify the possible causes of decline in eel abundance observed in the canal during the last two decades. A model including glass eel recruitment and catfish abundance as covariates explained 78% of the observed variation in eel settlement success. Results suggest that (1) salinity does not play a significant role in determining the fraction of eels moving from the brackish lagoon to the canal; (2) density dependence affects settlement success, possibly through a reduction of juvenile survival in the adjacent lagoon; and (3) catfish abundance is negatively correlated with eel settlement. We discuss this latter point in terms of possible predation of catfish upon eels and/or inter-specific competition between the two species.     

Occurrence of the parasite Glugea hertwigi in young‐of‐the‐year smelt in Lake Tuusulanjärvi

Young‐of‐the‐year smelt Osmerus eperlanus in Lake Tuusulanjärvi were examined for Glugea hertwigi cysts. Cysts were visible on smelt in the beginning of August and showed a peak at the end of August. Glugea hertwigi may cause mortality among the most heavily infected young‐of‐the‐year smelts.     

The New Zealand common smelt: biology and ecology

The common smelt is one of the most widespread indigenous freshwater fishes in New Zealand. One other member of the family Retropinnidae, Stokellia anisodon (Stokell), is present but is confined to a small region of the South Island. There are many diadromous as well as river and lake resident populations, the latter, sometimes a result of introductions to serve as forage fish for trout. Diadromous smelt spawn during austral autumn–winter on sand bars of lower riverine reaches. Larval stages inhabit coastal marine waters, and the postlarvae to immature stages re‐enter rivers and some lowland lakes. Diadromous smelt are distinguished from lowland lake resident forms by high vertebral but low gill raker numbers and larger size and from those present in some isolated waters, by high vertebral numbers alone. Lake or reservoir resident smelt usually spawn in austral spring–summer on sandy shallows at stream mouths or along shorelines. Verified smelt ages (otolith analyses) indicate that in some populations most smelt mature and spawn after c. 1 year. Adult smelt feed on a spectrum of primarily invertebrate animals ranging from small zooplankters to insects and occasionally small fishes. Smelt are a major prey for both brown trout and rainbow trout. Adult smelt are a minor food for the Maori people. As postlarvae they are a component of a few 'whitebait' fisheries. Most smelt populations are increasingly affected by environmental changes induced by human activities. Although many studies have examined problems affecting smelt, further effort is required, along with more basic research.     

Euryhaline adaptations in the fat sleeper, Dormitator maculatus

Salinity tolerances and plasma osmotic concentrations were determined in the fat sleeper, Dormitator maculatus , a common species in estuarine and coastal fresh waters along the Atlantic and Caribbean coasts of North, Central and South America. Analyses followed sequential laboratory acclimations to a series of ambient salinities at a constant temperature of 20 ± 1° C and photoperiod of 12L: 12D. These fish tolerated a range of ambient salinities from fresh water through a salinity of 75‰. Plasma osmotic concentrations were regulated at an essentially constant level in the salinity range from fresh water through a salinity of 50‰, beyond which plasma concentrations trended upward with increased ambient salinity. We conclude that D. maculatus , while truly euryhaline, docs not show the extreme euryhalme capabilities of several teleost fishes that are 'full-time' estuarine inhabitants.     

Distribution and abundance of young fish in the St. Clair River and associated waters,Ontario

Fish larvae were sampled in 1986 in the St. Clair River, and adjacent waters. Species richness (9 taxa as larvae; 4 others as juveniles) and abundance was lowest in the river, where many larvae (e.g., burbot, rainbow smelt, and yellow perch) were in transit from Lake Huron. The most abundant, and localized, species was gizzard shad, which reached a peak mean density of 4600 larvae 100 m^-3 in an agricultural canal. Adjacent waters contribute greatly to the fish communities of the river and adjoining Lakes Huron and Erie, especially in terms of the number and quantity of forage species.