Colonisation tactics of three temperate catadromous species,eel Anguilla anguilla,mullet Liza ramada and flounder Plathychtys flesus,revealed by Bayesian multielemental otolith microchemistry approach

Daverat F, Martin J, Fablet R, Pécheyran C. Colonisation tactics of three temperate catadromous species, eel Anguilla anguilla, mullet Liza ramada and flounder Plathychtys flesus, revealed by Bayesian multielemental otolith microchemistry approach.
Ecology of Freshwater Fish 2011: 20: 42–51. © 2010 John Wiley & Sons A/S Abstract – The colonisation of Gironde (SW France) river catchment by juvenile, eel, Anguilla anguilla, flounder Platychtys flesus and thinlipp mullet Liza ramada was investigated comparatively using Sr:Ca and Ba:Ca composition of otolith. The relation between Sr, Ba and habitat was investigated based on Sr and Ba water composition sampled each month along the estuary‐river gradient. A total of 50 mullets, 30 eels and 47 flounders were collected in the Gironde river catchment. Analysis was performed with a Femtosecond LA‐ICPMS along a trajectory from the core to the edge. Sr and Ba water concentrations discriminated three habitats within the Gironde system, the lower estuary, the upper estuary and the freshwater sites. A signal processing method based on Gaussian hidden Markov models was applied to the multielemental life‐history data. The linear model used to allocate a Gironde habitat to coupled Sr, Ca values was parameterised with seasonal patterns and magnitude of Sr and Ba water values in the different habitats. The results showed that the three species used three different habitats and they had a large diversity of habitat use patterns with resident and nomadic tactics. Resident tactics were less frequent than nomadic tactics that suggested individual fish used two or more habitats. Mullet used a wider range of habitats in the lower part of the estuary than eel and flounder and switched habitats more frequently. Flounders tended to colonise initially freshwater, and then estuarine habitats later in life while mullets used the entire range of available catchment habitats throughout their life.     

Difference in factors explaining growth rate variability in European eel subpopulations: the possible role of habitat carrying capacity

As a key parameter in the management of fish populations, individual growth rate (GR) variations were examined in the European eel (Anguilla anguilla; > 150 mm) using extensive mark–recapture surveys in the lotic habitats of two small rivers of western France: the Frémur, supposed to be saturated, and at the same latitude, the Oir with densities fivefold lower than those of the Frémur. In both systems, generalised linear models were used to test whether spatiotemporal factors such as dominant habitat type or local density affect GR variability. In the presumed unsaturated system, the Oir, GR variability is mainly explained by a set of habitat suitability drivers (density, dominant habitat type). In the Frémur, GRs appear independent of differences in habitat density or productivity. Below saturation, an increase in density will decrease the GR through intraspecific competition. At saturation, intraspecific competition reaches such high levels that regardless of eel density and productivity, the resources available by individual are similar throughout the system. In these circumstances, the effect of density on growth was presumed undetectable. Despite these contrasted results, mean GRs observed in both catchments were closed (~20 mm·year^?1). This is an unexpected result as GR is expected to be higher in unsaturated systems. This similarity could be explained by the difference between the two systems in terms of: (i) sex ratio (the Frémur is dominated by male, whereas the female is dominant in the Oir), (ii) habitat type distribution or (iii) possible interspecific competition (important salmonid populations in the Oir).     

Rapid response of fish and aquatic habitat to removal of a tidal barrier

1. River barrier removal is used increasingly as a conservation tool to restore lotic habitat and river connectivity, but evidence of its efficacy is incomplete. This study used a before–after methodology to determine the effects of removing a tidal-limit barrier on the fishes, macroinvertebrates, and habitats of an English coastal stream.
2. Following barrier removal, habitat diversity increased immediately upstream and remained similar downstream. Mobilized silt altered the substrate composition immediately downstream, but this was temporary as silt was flushed out the following winter. Changes to macroinvertebrate communities occurred upstream and downstream of the former barrier but these were transient.
3. A dramatic and sustained increase in fish density occurred immediately upstream of the barrier after its removal, but effects downstream were minor. The fish community upstream changed, largely due to rapid recruitment and dispersal of endangered European eel (Anguilla anguilla). Eel density in the formerly impounded zone increased from 0.5 per 100 m² before barrier removal to 32.5 per 100 m² 5 months after removal. By 17 months after barrier removal there was no difference in eel density across the six sections sampled.
4. Although resident stream fishes such as bullhead (Cottus gobio species complex, protected under the European Habitats Directive) were abundant in middle and upper-stream sections, brown trout (Salmo trutta, a listed species for biodiversity conservation in England and Wales) density remained low during the study and recruitment was poor. This suggests that although colonization access for anadromous trout was available, habitat upstream may have been unsuitable for reproduction, indicating that wider catchment management is required to complement the restoration of connectivity.
5. These findings suggest that tidal barrier removal is an effective method of restoring lotic habitats and connectivity, and can be beneficial for resident and migratory fishes including those of conservation importance (e.g. European eel) in coastal streams.

     

Growth differences of Japanese eels Anguilla japonica between fresh and brackish water habitats in relation to annual food consumption in the Kojima Bay‐Asahi River system,Japan

To learn about the relationships between feeding and growth of temperate eels in freshwater and brackish water habitats, we analysed 533 yellow‐phase Japanese eels Anguilla japonica collected in both types of habitats in southeastern Japan. Because male eels were very rare in each habitat (FW, N = 1; BW, N = 20), characteristics of female eels were compared between the different habitats. Annual food consumption was evaluated with the consideration of instantaneous food consumption and annual activity period. Stomach fullness index (stomach content weight/body weight) was used as an indicator of instantaneous food consumption. The ratios of number of months with eel catch to those when eel sampling was conducted were used as an indicator of activity period. Female yellow eels tended to be older and slower growing in fresh water (N = 78; age, mean ± SD = 7.9 ± 2.4 years; growth rate, 59.8 ± 14.0 mm year^?1) than in brackish water (N = 229; age, 5.5 ± 1.8 years; growth rate, 90.1 ± 24.4 mm year^?1). Irrespective of sex, yellow eels in brackish water had a higher stomach fullness index and a greater ratio of months with eel catches, indicating greater annual food consumption by brackish water eels. These results indicate that greater annual food consumption contributes to the greater growth rates of Japanese eels in brackish water habitats.     

Evaluation of a spatially sex‐specific assessment method incorporating a habitat preference model for blue marlin (Makaira nigricans) in the Pacific Ocean

Blue marlin, widely distributed throughout the Pacific Ocean, are sexually dimorphic, have certain preferred habitats, and migrate seasonally. These characteristics have been ignored in previous stock assessment models. A population dynamics model that includes spatial structure, and sex and age structure was therefore constructed and fitted to fisheries data for blue marlin, along with information on the relative density of the population over space derived from a habitat preference model that uses the oceanographic and biological variables sea‐surface temperature, mixed layer depth, sea‐surface height anomaly, and chlorophyll‐a concentration. Monte Carlo simulation was then used to examine the estimation performance of the stock assessment method. Estimates of management‐related quantities including current spawning stock biomass are substantially biased when the assessment method ignores seasonal movement and sexual dimorphism. We also found that (i) uncertainty about the relationship between catch rate and abundance influences estimation performance to a larger extent than uncertainty in catches, (ii) the outcomes of the assessment are sensitive to the values assumed for natural mortality and stock‐recruitment steepness, and (iii) the ratio of current spawning stock biomass to that at pre‐exploitation equilibrium appears to be the most robust among the quantities considered. We conclude that assessment methods for blue marlin in the Pacific Ocean need to take account of seasonal migration and sex structure to improve stock assessments.     

Connectivity between lentic and lotic freshwater habitats identified as a conservation priority for coho salmon

1. Juvenile Pacific salmon exhibit diverse habitat use and migration strategies to navigate high environmental variability and predation risk during freshwater residency. Increasingly, urbanization and climate-driven hydrological alterations are affecting the availability and quality of aquatic habitats in salmon catchments. Thus, conservation of freshwater habitat integrity has emerged as an important challenge in supporting salmon life-history diversity as a buffer against continuing ecosystem changes.
2. To inform catchment management for salmon, information on the distribution and movement dynamics of juvenile fish throughout the annual seasonal cycle is needed. A number of studies have assessed the ecology of juvenile coho salmon (Oncorhynchus kisutch) during summer and autumn seasons; catchment use by this species throughout the annual cycle is less well characterized, particularly in high-latitude systems.
3. Here, n = 3,792 tagged juvenile coho salmon were tracked throughout two complete annual cycles to assess basin-wide distribution and movement behaviour of this species in a subarctic, ice-bearing catchment.
4. Juvenile coho salmon in the Big Lake basin, Alaska, exhibited multiple habitat use and movement strategies across seasons; however, summer rearing in lotic mainstem environments followed by migration to lentic overwinter habitats was identified as a prominent behaviour, with two-thirds of tracked fish migrating en masse to concentrate in a small subset of upper catchment lakes for the winter. In contrast, the most significant tributary overwintering site (8% of tracked fish) occurred below a culvert and dam, blocking juvenile fish passage to a headwater lake, indicating that these fish may have been restricted from reaching preferred lentic overwinter habitats.
5. These findings emphasize the importance of maintaining aquatic connectivity to lentic habitats as a conservation priority for coho salmon during freshwater residency.

     

Habitat differentiation between sei (Balaenoptera borealis) and Bryde's whales (B. brydei) in the western North Pacific

Two closely related baleen whale species, sei and Bryde's whales, in the western North Pacific were studied to identify differences in habitat use. Data were obtained from May to August 2004 and 2005. This study examined the relationship between oceanographic features derived from satellite data and the distribution of sei and Bryde's whales using basic statistics. We investigated oceanographic features including sea surface temperature (SST), sea surface chlorophyll a (Chl‐a), sea surface height anomalies (SSHAs), and depth of the habitat. These two whale species used habitats with different SST, Chl‐a, and SSHA ranges. The 0.25 mg m^?3 Chl‐a contour (similar to the definition of the Transition Zone Chlorophyll Front) was a good indicator that separated the habitats of sei and Bryde's whales. Then generalized linear models were used to model the probabilities that the whale species would be present in a habitat and to estimate their habitat distribution throughout the study area as a function of environmental variables. The potential habitats of the two species were clearly divided, and the boundary moved north with seasonal progression. The habitat partitioning results indicated that SST contributed to the patterns of habitat‐use and might reflect differences in prey species between the two whales. This study showed that the habitats of the sei and Bryde's whales were clearly divided and their potential habitat‐use changed seasonally.     

Ecology and conservation of the American eel in the Caribbean region

The majority of American eel, Anguilla rostrata LeSueur, knowledge is derived from temperate regions in the United States and Canada, with little known from its tropical Caribbean distribution. Findings of original research on American eel distribution, abundance, population biology, habitat ecology and threats from the Caribbean island of Puerto Rico were synthesised. American eel were captured from 48 of 116 sites (41.4%) in 26 of 49 river basins (53.1%) during 2005–2016, and it was extirpated upstream of dams and migration barriers >3.0 m high (38.9% of habitat). Mean density and biomass were 438.9 fish/ha and 23.44 kg/ha, respectively. Upstream habitats favoured larger individuals, and females were larger than males. The swim‐bladder parasite Anguillicoloides crassus Kuwahara, Niimi & Hagaki was not found in 120 eels examined. Realised threats include dams and other migratory barriers, habitat loss and alteration and pollution; exotic species and commercial fishing are impending threats; and the least understood is climate change.     

Long‐term records (1781–2013) of European eel (Anguilla anguilla L.) production in the Comacchio Lagoon (Italy): evaluation of local and global factors as causes of the population collapse

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Multiple survey methods reveal greater abundance of endangered pupfish in restored habitats

1. Freshwater organisms inhabiting arid ecosystems are imperilled by human alterations to water-limited landscapes. This is especially true among desert-dwelling cyprinodontid fishes, 90% of which are imperilled by habitat destruction within limited or shrinking ranges. Constructing habitats that mimic natural habitat form and function may provide a tool for species conservation, especially within freshwater protected areas. However, pupfish population assessments within degraded compared with restored habitats are infrequent, and few comparisons among survey methods exist.
2. Density estimates were developed for Endangered Comanche Springs pupfish Cyprinodon elegans throughout altered and restored habitats in a freshwater protected area by using mark–recapture and N-mixture models fitted to data collected using minnow trap and visual count survey methods. This allowed comparison of habitats, survey methods, and statistical methods commonly used to generate population size estimates for imperilled pupfish.
3. Population estimates varied across major habitat types and were largest among habitats constructed to mimic naturally occurring ciénegas. Estimates using visual counts were higher than estimates from minnow traps where water was deeper and where macroalgae cover was highest. N-mixture models generally estimated higher abundances than mark–recapture and were not limited by recapture ability.
4. The results provide strong evidence that restored habitats house greater abundances of pupfish, but survey and statistical methods commonly used to detect these differences have trade-offs in performance according to the habitats surveyed. This work benefits the field of conservation biology by providing guidance for existing and emerging monitoring programmes assessing abundance-based fish responses to habitat improvements.

     

Spatial organisation of European eel (Anguilla anguilla L.) in a small catchment

Abstract –  Modelling-governing patterns of European eel ( Anguilla anguilla L.) distribution of four eel size classes (<150, 150–300, 300–450 and >450 mm) in the Frémur basin (northwest France) was done using artificial neural network (ANN) techniques and ecological profiles. Our results demonstrate the high predictive power of the ANN models. Some macro- and microscale factors, such as distance from the sea, depth and flow velocity, have the most significant influence on the models. Influence of distance from the sea appears to be very different from the spatial organisation usually described in river systems. In fact, the general tendencies of total eel densities according to the distance from the sea showed that densities increase weakly upstream. Another outcome was the variations in habitat preference according to the eel size, even if this species is spread over practically every type of microhabitat. Small eels were mainly found in shallow habitats with strong abundance of aquatic vegetation, whereas large eels tend to be found in intermediate to high depth with small to intermediate abundance of aquatic vegetation. Finally, we hypothesise that European eels change behaviour and microhabitat characteristic preference around a size of 300 mm.     

Effects of improving longitudinal connectivity on colonisation and distribution of European eel in the Loire catchment, France

Abstract –  Major migration barriers have been identified as an important factor in the drastic reduction of freshwater eel stocks at the catchment scale. In this study, we developed a way to assist decision making in the management of migration barriers so as to increase eel presence throughout the Loire catchment (France). Models were developed according to eel size-class and various different management strategies to improve accessibility, taking into account: (i) all the migration barriers from the tidal limit to different upstream limits (downstream–upstream strategy), (ii) all the migration barriers with a given degree of passability (migration barrier passability class strategy), (iii) all the migration barriers in a given sub-catchment area (sub-catchment strategy) and (iv) all the migration barriers in the entire Loire catchment (global strategy). Eel were actually found to occur in the Loire at about 50% of the sites sampled. The improvement of habitat accessibility by removing all obstacles to colonisation or installing fish passes, for example (global strategy), would lead to eels being found throughout the whole river. If this management strategy is impossible because the high cost, two others, also producing significant eel continental colonisation must be implemented. Either all barriers from the tidal limit with medium passability and/or migration barriers in the sub-catchment area which is closest to the sea and least accessible must be managed. In both cases, the area significantly exploited by eels and the probability that this species will be present will be doubled. However, these results can only be counted on if the fluvial recruitment increases significantly.     

Coastal river connectivity and the distribution of ascending juvenile European eel (Anguilla anguilla L.): Implications for conservation strategies regarding fish‐passage solutions

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Determining the consistency of thermal habitat segregation within and among Arctic charr morphotypes in Gander Lake,Newfoundland

Abstract – Otolith carbon and oxygen isotope data obtained from distinct genetic and ecological groups of lacustrine Arctic charr, Salvelinus alpinus L., from Gander Lake, Newfoundland, were used to examine hypotheses regarding the consistency of differential habitat use among the groups. Results indicated thermal habitat separation by group, with small ‘pale’ individuals consistently remaining in cooler profundal habitats and larger ‘dark’ individuals more frequently occupying warmer upper water column habitats. Theoretical measures of resource separation and competition indicated lower thermal habitat overlap among the forms and greater within‐form competition. Depth at capture data indicated more varied short‐term use of available lake habitats by ‘dark’ form Arctic charr, possibly as a result of cannibalistic foraging on profundal ‘pale’ form fish. Nominal capture depth data only partially explained observed variation in the mean temperature of occupied thermal habitat, suggesting that capture depth can only be used as a rough index of thermal habitat use. Provided that sufficient thermal gradients exist in the environments being studied, otolith oxygen isotopes provide a useful means of establishing the significance of niche differentiation among individuals.     

Projecting future habitat quality of three midwestern reservoir fishes under warming conditions

Rising temperatures caused by climate change are likely to affect cool‐water and warm‐water fishes differently. Yet, forecasts of anticipated temperature effects on fishes of different thermal guilds are lacking, especially in freshwater ecosystems. Towards this end, we used spatially explicit, growth rate potential (GRP) models to project changes in seasonal habitat quality for a warm‐water piscivore (largemouth bass Micropterus salmoides), a cool‐water piscivore (walleye Sander vitreus) and a hybrid piscivore (saugeye S. vitreus × S. canadensis) in two Midwestern reservoirs. We assessed habitat quality for two periods (early and middle 21st century) under two realistic greenhouse gas emission scenarios (a mid‐century emissions peak and a rapid continuous increase in emissions). Largemouth bass were projected to experience enhanced or slightly reduced habitat during all seasons, and throughout the mid‐21st century. By contrast, walleye habitat was projected to decline with anticipated warming, except during the spring in the smaller of our two study reservoirs and during the fall in the larger of our two study reservoirs. Saugeye habitat was projected to either increase modestly or decline slightly during the spring and fall and declines in habitat quality and quantity that were smaller than those for walleye were identified during summer. Collectively, our findings indicate that climate warming will differentially alter habitat suitability for reservoir piscivores, favouring warm‐water species over cool‐water species. We expect these changes in habitat quality to impact the dynamics of reservoir fish populations to varying degrees necessitating the consideration of climate when making future management decisions.     

Assessment of a catchmentwide salmon habitat rehabilitation scheme on a drained river system in Northern Ireland

A catchment‐scale salmon, Salmo salar L., habitat enhancement scheme was developed for the River Main (Northern Ireland) with reference to baseline habitat and electric fishing surveys. In total, 19 separate sites were enhanced using flow deflectors or random boulder addition. Habitat suitability for juvenile salmon increased at enhanced sites following the scheme, and significant changes in underlying physical habitat characteristics (particle size, depth and flow) were detected after the installation of flow deflectors. The overall index of salmon fry recruitment, monitored across the catchment, showed no change between pre‐ and post‐enhancement periods. The mean biomass of salmon evident at individual enhancement sites (5.1 g m^?2) was significantly higher than the mean biomass at control sites (1.2 g m^?2). Increased densities of >0+ juvenile salmon were associated with enhanced sites relative to controls. Marking studies indicated the potential for long‐range dispersal of juvenile salmon between 0+ (summer) and 1+ (summer) age classes. The potential of the scheme to enhance the local salmon stock was discussed.     

Habitat configuration for an obligate shallow‐water delphinid: The Indo‐Pacific humpback dolphin,Sousa chinensis,in the Beibu Gulf (Gulf of Tonkin)

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Where once the eel and the elephant were together: decline of the European eel because of changing hydrology in southwest Europe and northwest Africa?

The collapse in recruitment of the European eel (Anguilla anguilla) since the early 1980s has been ascribed to possible overfishing, poisoning, parasitism, habitat loss and changes in ocean circulation. It is unclear which mechanism is most important, and firm data are lacking to make an assessment of the factors that apply over the full continental range. On the other hand, the recruitment of the American eel (A. rostrata) has declined along the western Atlantic at about the same time. This suggests a candidate mechanism that can affect both species together. A change in ocean climate may be a likely explanation, which is supported by a possible link between the North Atlantic Oscillation and one important recruitment index. However, it is unsafe to discard the other possible mechanisms because of lack of evidence. Habitat loss, in particular, may be important. We review over a century of evidence to suggest how the eel may have declined through progressive habitat loss that accelerated in the early 1980s as the result of economic development linked with hydrological changes. Although no single line of evidence can definitely prove one hypothesis for the eel decline, the total body of information may indicate a pronounced susceptibility in the southwest corner of the continental range closest to the Sargasso Sea that has been particularly affected by drought and dam construction. The sexual dimorphism of the species together with the energy requirements of the spawning migration may provide insight to explain the population collapse.