Variation in the trophic position of common stream fishes and its relationship to the presence of a rare fish,northern leatherside chub (Lepidomeda copei)

Variation in trophic position can be caused by structural changes in food webs that may affect the presence of, or be affected by the presence of, individual species. We examined variation in the trophic position of fishes across 14 stream sites in the Bear River drainage, WY, USA. This drainage is the focus of ongoing conservation of northern leatherside chub (Lepidomeda copei). Our goals were (i) to describe variation in trophic position of individual species and (ii) to determine whether these measures differed between sites with and without northern leatherside chub. Mean trophic position of individual fish species varied between 0 and 3 trophic positions across sites. For two of these species, trophic position declined at sites without northern leatherside chub. Importantly, habitat surveys from a previous study at 10 of these sites revealed no differences in habitat suitability for northern leatherside chub. This suggests that trophic position revealed systematic differences among sites that were not apparent based on traditional species‐habitat modelling. We outline possible mechanisms behind these patterns and argue that monitoring variation in trophic position can complement traditional, habitat‐based methods for understanding species distributions.     

Fisher accessibility and habitat complexity influence the distribution of adult Cherax cainii (Decapoda: Parastacidae) in a water supply reservoir

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Spatial association between northern fur seal (Callorhinus ursinus) and potential prey distribution during the wintering period in the northern Sea of Japan

Elucidating the response of marine predators to oceanographic features helps in understanding their foraging strategies and the cause of their spatial overlap and interference with fishery activities. Northern fur seal is a highly pelagic species during the wintering period. In recent years, fur seals have consistently been found distributed near the coast of southwest Hokkaido, Japan. Because interference by fur seals with coastal fishery activities has become a serious concern, an understanding is sought as to why fur seals come ashore in this area. We conducted ship‐based observations and estimated fur seal density. To elucidate the spatial and seasonal association of fur seal distribution and ocean environments, we constructed statistical models to describe how potential prey distribution and oceanographic features influenced the fur seal spatial distribution during the wintering period. Fur seal distribution corresponded markedly to potential prey distribution, and they tended to aggregate along the narrow continental shelf that is the main geographic feature of this area, which is 2000 m deep and approximately 10 km from the coast. Walleye pollock [Gadus chαlcogrαmmα (Theragra chαlcogrαmmα)] and arabesque greenling (Pleurogrammus azonus), which are one of the main prey for fur seals, move to the shallow area to spawn on the continental shelf seasonally, so potential prey abundance could be higher in coastal areas than offshore. Moreover, the absence of a mesopelagic biotic community may be one of the main factors in the coastal distribution of the fur seal.     

Preliminary study of the endangered populations of pearl mussel Margaritifera margaritifera (L.) in the River Tera (north‐west Spain): habitat analysis and management considerations

• 1. During 2001 and 2002, 12 tributaries of the River Duero basin, north‐west Spain, were sampled. Pearl mussels Margaritifera margaritifera (L.) were located in two of them. Isolated individuals were found in the River Tera, a tributary of the River Esla; and only a few colonies with more than 20 mussels were found in the River Negro.
• 2. All of the specimens found were adults (mean length 95 mm), with juveniles being absent in the river bed. The River Negro plots showed a low median mussel density (0.11 m^?2), and that of greatest size consisted of 164 ageing individuals.
• 3. Mussels were mainly located in permanent rivers and in shallow stretches with little flow of water, with heterogeneous substrates and heavily shaded by the riparian woods. The whole basin has well‐conserved rivers with cold oligotrophic water and poor mineralization due to the insolubility of the rocks.
• 4. This relic population has a severely restricted distribution because of a series of large reservoirs in a hydropower complex of the rivers Duero and Esla (caused by the construction of the Ricobayo Dam in 1947) and their negative impact on the rheophilous fish. The mussels of the River Tera have been isolated from the rest of the Duero basin since 1969 (Cernadilla Dam), whereas in the River Negro they have been isolated since 1995 (Agavanzal Dam).

Copyright © 2004 John Wiley & Sons, Ltd.     

Determinants of large-scale spatial distribution and seasonal microhabitat selection patterns of the endangered freshwater blenny Salaria fluviatilis in the Ebro River basin,Spain

1. The freshwater blenny Salaria fluviatilis is an endangered fish species with populations that are in rapid decline, largely owing to habitat degradation caused by human activity. This situation highlights the urgent need to develop measures for the conservation and recovery of the species based on a deep understanding of its specific habitat requirements.
2. In this study, spatial distribution and habitat selection patterns were investigated to determine the limiting factors for the species at different times of the year and at different spatial scales, from macro to microhabitats.
3. The presence of the freshwater blenny was assessed at 127 sites in the Ebro River basin, Spain, between 2002 and 2012. It was only detected at 25 sites, corresponding to the intermediate and lower reaches of medium-sized tributaries and in the main river, in accordance with the ecology of the species. Whether the species was present depended on the physicochemical, habitat and biological conditions of the study sites. Freshwater blenny was very sensitive to organic pollution and eutrophication, the deterioration of substrate composition and channel structure, and the degradation of aquatic and riparian vegetation.
4. Freshwater blenny showed a selective use of microhabitat locations with high current velocity, linked to gravel or cobble substrate. It was also observed that the species is capable of adapting its selection behaviour to the flow-mediated seasonal changes in its physical environment.
5. Although the results presented indicate that the species is not a microhabitat specialist, individual survival is likely to be dependent on the availability of key microhabitats, which must be protected against detrimental human activity.

     

Copepods and salmon: characterizing the spatial distribution of juvenile salmon along the Washington and Oregon coast,USA

Yearling Chinook (Oncorhynchus tshawytscha) and coho salmon (Oncorhynchus kisutch) were sampled concurrently with physical variables (temperature, salinity, depth) and biological variables (chlorophyll a concentration and copepod abundance) along the Washington and Oregon coast in June 1998–2008. Copepod species were divided into four different groups based on their water‐type affinities: cold neritic, subarctic oceanic, warm neritic, and warm oceanic. Generalized linear mixed models were used to quantify the relationship between the abundance of these four different copepod groups and the abundance of juvenile salmon. The relationships between juvenile salmon and different copepod groups were further validated using regression analysis of annual mean juvenile salmon abundance versus the mean abundance of the copepod groups. Yearling Chinook salmon abundance was negatively correlated with warm oceanic copepods, warm neritic copepods, and bottom depth, and positively correlated with cold neritic copepods, subarctic copepods, and chlorophyll a concentration. The selected habitat variables explained 67% of the variation in yearling Chinook abundance. Yearling coho salmon abundance was negatively correlated with warm oceanic copepods, warm neritic copepods, and bottom depth, and positively correlated with temperature. The selected habitat variables explained 40% of the variation in yearling coho abundance. Results suggest that copepod communities can be used to characterize spatio‐temporal patterns of abundance of juvenile salmon, i.e., large‐scale interannual variations in ocean conditions (warm versus cold years) and inshore‐offshore (cross‐shelf) gradients in the abundance of juvenile salmon can be characterized by differences in the abundance of copepod species with various water mass affinities.     

Preferential distribution of fish larvae in the California Current System: Time,space, and temperature

The preferential larval distributions of 22 fish species in the California Current System were identified in their temporal, spatial, and thermal domains using single parameter quotient analysis. This analysis allowed the characterization of their reproductive habitats based on ranges of preference, tolerance, and avoidance. In the temporal domain, the species’ preference intervals were wider than those previously reported, and all species showed preferences during two or more seasons of the year. In the spatial domain, the preferential distributions of the species were also wider, and some of them had different preferred zones from those described in previous works. Because one group of species was preferably distributed in coastal zones, and the other group was preferably distributed in oceanic zones, the biological production mechanisms sustaining these groups differ, namely, coastal upwelling and geostrophic fluxes of subarctic origin, respectively. In the thermal domain, the larval distribution preferences of 20 of 22 species have been determined for the first time, providing important information on their thermal tolerance window during the larval stage, a window that changes in width throughout each of the ontogenetic stages of fish. The distribution in each domain suggests association patterns between species, but additional studies are necessary to validate these patterns.     

金沙江下游与长江上游珍稀、特有鱼类国家级自然保护区鱼类物种多样性比较

为探讨长江上游珍稀、特有鱼类国家级自然保护区对金沙江下游现有鱼类资源可能发挥的替代生境保护作用,在对金沙江下游鱼类进行多次实地采样调查基础上,结合历史文献记载,梳理了金沙江下游的鱼类名录,并与“保护区”内的鱼类物种多样性进行了对比。结果表明,分布于金沙江下游的鱼类共有194种,其中土著鱼类162种,隶属于5目15科79属;分布于“保护区”内的鱼类197种,其中土著鱼类187种,隶属于6目21科94属。进一步分析显示,既见于金沙江下游又见于“保护区”的土著鱼类129种,反映出两者在鱼类种类组成上有较大的相似性;“保护区”内未能包括的仅见于金沙江下游的鱼类多为金沙江下游支流或附属高原湖泊中生活的种类,“保护区”在一定程度上可以发挥金沙江下游替代生境的作用。     

Ocean distribution and habitat associations of yearling coho (Oncorhynchus kisutch) and Chinook (O. tshawytscha) salmon in the northern California Current

Yearling juvenile coho and Chinook salmon were sampled on 28 cruises in June and September 1981–85 and 1998–07 in continental shelf and oceanic waters off the Pacific Northwest. Oceanographic variables measured included temperature, salinity, water depth, and chlorophyll concentration (all cruises) and copepod biomass during the cruises from 1998–07. Juvenile salmonids were found almost exclusively in continental shelf waters, and showed a patchy distribution: half were collected in ～5% of the collections and none were collected in ～40% of the collections. Variance‐to‐mean ratios of the catches were high, also indicating patchy spatial distributions for both species. The salmon were most abundant in the vicinity of the Columbia River and the Washington coast in June; by September, both were less abundant, although still found mainly off Washington. In June, the geographic center‐of‐mass of the distribution for each species was located off Grays Harbor, WA, near the northern end of our sampling grid, but in September, it shifted southward and inshore. Coho salmon ranged further offshore than Chinook salmon: in June, the average median depth where they were caught was 85.6 and 55.0 m, respectively, and in September it was 65.5 and 43.7 m, respectively. Abundances of both species were significantly correlated with water depth (negatively), chlorophyll (positively) and copepod biomass (positively). Abundances of yearling Chinook salmon, but not of yearling coho salmon, were correlated with temperature (negatively). We discuss the potential role of coastal upwelling, submarine canyons and krill in determining the spatial distributions of the salmon.     

Influences of local habitat and stream spatial position on fish assemblages in a dammed watershed,the Qingyi Stream,China

Abstract – Identifying the underlying mechanisms that explain the spatial variation in stream fish assemblages is crucial for the protection of species diversity. The influences of local habitat and stream spatial position on fish assemblages were examined from first‐order through third‐order streams within a dammed watershed, the Qingyi Stream, China. Based on linear regression models, the most important environmental variables influencing fish species richness were water temperature and wetted width, but stream spatial position variables were less important. Using canonical correspondence analysis, five environmental variables were identified to significantly influence fish assemblages, including three habitats (elevation, substrate and water depth) and two spatial variables (C‐link and Link). Our results suggest that, in a heavily dammed watershed, by blocking the migration routes of fishes, dams weaken the influence of stream spatial position on fish species richness. However, fish species compositions are significantly influenced by both local habitat environment and stream spatial position, which is perhaps owing to the distribution of fish species according to ecological requirements not related to spatial processes.     

Spatial distribution of fishing effort in relation to seafloor habitats in the Kattegat,a GIS analysis

• 1. High‐resolution fishing effort data from the Kattegat, an important fishing ground for Swedish and Danish fishermen, was analysed in a Geographical Information System (GIS). Data were based on position data for individual tows reported by Swedish fishermen during 2001–2003.
• 2. Gear dimension and towing speed data were used to calculate an index for area swept per hour for each main gear type in use in the area. These indexes were multiplied by fishing effort and a grid theme of fishing intensity was created after GIS analysis.
• 3. Around 44% of the entire area was affected by Swedish fisheries during the study period, hence 56% was not affected.
• 4. Effort was highly concentrated in certain areas and 10% of the total area was covered more than twice per year.
• 5. Overlaying the effort data set with habitat maps classified according to the European Nature Information System (EUNIS) showed that the fishing pressure differed between habitats. For deep rocky and muddy habitats, almost the entire area was affected by fisheries during the study period, while both intensity and proportion affected were lower in sandy sediments and gravels.
• 6. Around 55% of the deep rocky habitats were trawled more than twice per year. Of the muddy seafloor areas, 41% were covered more than twice per year and 4% more than once a month by trawls.
• 7. The biological effects of the fishing intensities found were analysed using a database (MarLIN) containing assessments of marine habitat recoverability. All habitats except muds are probably in a nearly or fully recovered condition (as defined by MarLIN). A considerable part of the muddy habitats are in a permanently altered condition owing to fishing disturbance taking place more frequently than the indicated recovery time.
• 8. Danish fishermen report more fishing effort in the area than do Swedes. Owing to differences in reporting fishing positions, Danish fisheries could not be included in the present study. Scaling up the results to include Danish fisheries is discussed.
• 9. The results of the present study could be used to target habitat management goals more precisely, while minimizing the negative impact of restrictions on the fishing sector.
• 10. A prerequisite for performing similar studies is the availability of high‐resolution fishing effort data and high‐resolution benthic habitat maps.

Copyright © 2006 John Wiley & Sons, Ltd.     

Spatial distribution analysis of the North Pacific spiny dogfish,Squalus suckleyi,in the North Pacific using generalized additive models

The North Pacific spiny dogfish (SPD), Squalus suckleyi, is a commercially exploited shark species that plays an important role in the ecosystem. To elucidate the distribution of the SPD in the North Pacific and to evaluate the effects of sea surface temperature (SST) and prey availability on its distribution, we estimated the probability of SPD presence using a generalized additive model with a binomial error distribution from SPD presence/absence data on 14,824 operations in fishery‐independent gillnet surveys between 1972 and 2011. The habitat model was structured in the east and west to reflect differences in the North Pacific oceanic environments. In the east, a higher probability of SPD presence was identified along the coast from the eastern Gulf of Alaska to Queen Charlotte Sound. In the west, it was identified around northern Japan. The estimated distribution was continuous between the two areas, whereas the probability of SPD presence was relatively low. Although the probability of SPD presence was higher at SSTs between 6°C and 12°C, the SST at the peak probability of SPD presence differed between the west and east. The prey species, Japanese sardine, Sardinops melanostictus, and walleye pollock, Gadus chalcogrammus, in the west and boreal clubhook squid, Onychoteuthis borealijaponica, in the east significantly affected the probability of SPD presence, which was higher if the prey species co‐existed with SPD. Therefore, SPD might adapt their distribution to that of available prey species. SPD stock assessment and management in these two important areas are required for its sustainable utilization.     

Environmental DNA reveals the temporal and spatial extent of spawning migrations of European shad in a highly fragmented river basin

1. Artificial barriers on lowland rivers impede the spawning migrations of anadromous fishes, preventing access to historical spawning areas. In the cryptic European shads Alosa alosa and Alosa fallax (‘shad’ hereafter), this has resulted in population declines across their range. Conservation programmes aim to facilitate the passage of migrators over these barriers and so require baseline information on the spatial and temporal extent of current migrations.
2. Here, a shad-specific environmental DNA (eDNA) assay was used to quantify the spatial extent of shad spawning migrations in the River Severn basin, western England. This basin is characterized by the presence of multiple barriers in the lower catchment. In 2017, the eDNA assay was piloted in the River Teme, an important shad spawning tributary, and then applied in 2018 and 2019 across the lower Severn basin.
3. In all years, shad DNA was detected between mid-May and mid-June, with the maximum spatial extent of shad distribution being in early June when shad eDNA was detected upstream of weirs that were generally considered as impassable. In 2018, this included the detection of shad above the most upstream weir on the main River Severn that required individual fish to have passed six weirs.
4. Although barriers inhibit the spawning migrations of shad, this eDNA assay showed that some highly vagile individuals might be able to ascend these barriers and migrate considerable distances upstream. This suggests that efforts to increase the permeability of these barriers could result in relatively high numbers of migrating shad reaching upstream spawning areas. These results demonstrate that this eDNA assay could also be used across their range, to further quantify the spatial extent of their spawning, including in highly fragmented rivers and those where shad are believed to spawn only occasionally and are rarely observed.

     

Quantifying the influence of geography and environment on the northeast Atlantic mackerel spawning distribution

Mackerel (Scomber scombrus) in the northeast Atlantic have shown changes in distribution at certain times of the year, which have impacted their exploitation and management. In this study, mackerel spawning habitat over 21 recent years was characterised using generalised additive modelling, based on spatial egg density data collected every third year during targeted ichthyoplankton surveys. Mackerel spawning distribution was found to depend primarily on geographical variables (coordinates and bottom depth), with preferred spawning locations on the shelf‐edge from the north of the Iberian peninsula to the west of Scotland, with a maximum west of Ireland. Environmental drivers had a lesser influence on egg distribution. Dome shaped relationships were found with temperature and mixed layer depth, with respective optimum at 13°C and around –300 m. The model was used to reconstruct maps of the potential habitat (areas where conditions were suitable, but not necessarily used, for spawning). Little changes were observed over the years in the potential habitat, suggesting that the expansion of the egg distribution (realised habitat) was not triggered by changes in the environmental variables investigated. Little evidence was found for density‐dependent habitat selection. There was a tendency for mackerel to make more use of areas of lesser suitability in years with large stock size (1992 and 2010). This pattern, however, broke down in 2013, when stock size was the highest, as spawning occurred very south and concentrated in the most suitable habitat.     

苏北浅滩生态监控区鱼卵的种类组成和数量分布

2004、2005年5月,在苏北浅滩生态监控区采用水平和垂直拖网两种方式进行了鱼卵调查,从南至北共设8个断面,范围为121°17′~121°55′E、32°00′~32°28′N。结果显示,第3~6断面(121°25′~121°36′E、32°08′~32°20′N)为鱼卵的密集区,密度最高的站位分别为2004年的7断面1站位(121°25′E、32°24′N)和2005年的5断面3站位(121°27′E、32°16′N)。主要的种类组成有多鳞鱚、鳀、斑鰶、远东拟沙丁鱼等。2004、2005年第一优势种均为多鳞鱚,2004年的第二、三位优势种分别为鳀和远东拟沙丁鱼,而2005年的第二位优势种则为斑鰶。     

Size influences the spatial distribution and fish‐aggregating device use of five Mediterranean fish species

Abstract Fish‐aggregating devices are floating objects used worldwide to improve pelagic fishery yield. Fish‐aggregating devices use the natural attraction exerted by floating objects on juveniles and adults of both pelagic and demersal fish. In this study, it was hypothesised that fish change their degree and type of interaction with moored floating objects depending on size. This is because fishes in early life stage remain close to floating objects, using them as a shelter, but as they grow they move further away from floating objects spending their time swimming to seek food. To test this hypothesis, the spatial distribution and habitat use of five Mediterranean fish species were quantified. The results enabled the hypothesis to be accepted for all species, except Balistes carolinensis Gmelin. For this species, a shelter from predator model was applicable, but for the other species, the generalised meeting point model was more adaptable.     

Degree of feeding niche overlap uniformises the distribution of interspecific territories in a Malawian cichlid community

Cichlid fishes in the rocky littoral zones of Lake Malawi are among the most diverse endemic fish communities of the world. They segregate food resources, but considerable niche overlaps have been reported by numerous studies in this field. If their niches largely overlap, the heterospecific individuals are expected to behave like conspecific individuals. Instead of studying their niche segregation, we investigated the spatial distribution patterns of adult males of nine abundant cichlid species by point process analysis, with due attention to niche partitioning, as measured by stable isotope analysis. Because their feeding habitats are restricted by intra‐ and interspecific interferences over the mating and feeding territories respectively, we hypothesised that the interspecific feeding territories of species with nearly similar niche tended to be distributed uniformly. Although the typical territorial animals are expected to be distributed uniformly, the distribution pattern of intraspecific mating territory was judged to be uniform only for two out of nine species. This result suggests that each species has its specific preference for territorial locations or their locations are restricted by interspecific interactions. The latter explanation was partially supported by the agreed locations of gravity centres between intraspecific mating and interspecific feeding territories. Species pairs with similar isotope ratios tended to show a uniform distribution of interspecific feeding territories. Thus, individual species pairs keep a certain distance from each other by using nearly similar food resources. This result suggests that some cichlid species coexist not only through niche segregation but also through territorial interactions, like conspecific individuals.     

Brook trout (Salvelinus fontinalis) movement and survival after removal of two dams on the West Branch of the Wolf River,Wisconsin

Dam removals allow fish to access habitats that may provide ecological benefits and risks, but the extent of fish movements through former dam sites has not been thoroughly evaluated for many species. We installed stationary PIT antennas in 2016 and 2017 to evaluate movements and survival of brook trout Salvelinus fontinalis in the West Branch of the Wolf River (WBWR) in central Wisconsin following removal of two dams and channel modifications designed to promote fish movement. These changes provided access to lacustrine habitats that might provide suitable winter habitat or act as ecological sinks. We used multistate models to estimate transition probabilities between river sections, to determine whether brook trout: (a) moved between multiple river sections and (b) entered lacustrine habitats as seasonal refuges, but eventually returned to lotic habitat. We also used a Cormack-Jolly-Seber model to evaluate whether apparent survival of brook trout in the WBWR was comparable to other populations. Few fish moved among river sections or used lacustrine habitat (<5% of tagged fish); most brook trout remained in sections where they were initially tagged, potentially due to quality habitat located throughout the river. Like other studies, brook trout in the WBWR appear to experience high mortality based on low number of detections, few physical recaptures and an estimated eight-month apparent survival rate of 0.27. In scenarios where fish can already access suitable habitat, removal of dams may not result in substantial increases in fish movement and colonisation of newly accessible habitat may not occur immediately.