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Diet segregation between introduced bullhead (Cottus gobio L.) and Atlantic salmon parr (Salmo salar L.) in a sub-Arctic river
Abstract
The diets of accidentally introduced bullhead and native salmon parr were studied in River Utsjoki, a tributary to the watercourse River Tana, one of the most important river habitats in Europe for the declining Atlantic salmon. Food resource partitioning was studied in sympatry during the summer and autumn seasons and compared with allopatric situations. We found a consistent segregation in food niche between the two species. Both salmon parr and bullhead predominantly utilised the benthic feeding habitat, but the bullhead mostly ate interstitial prey whereas salmon parr mainly consumed prey associated with the substrate surface. Furthermore, the salmon parr fed more on drift than the obligate benthivore bullhead. This study documents a selective segregation in food niche between a benthic and a drift-feeding fish in running water. At present there is little evidence of competition between the species, but potential competition for food is discussed.
... Les macroinvertébrés sont capturés sur le fond ou au moment de la dérive et la proportion de formes adultes prises en surface ou d'insectes terrestres reste assez faible (Muje et al. 1989, Desvilettes et al. 1997b. Malgré une grande diversité de proies potentiellement ingérables au niveau des zones de radier, les tacons semblent se focaliser sur un petit nombre d'unités taxonomiques (Diptères, Ephéméroptères, Plécoptères et Trichoptères), que ce soit dans les rivières tempérées (Maitland 1965, Stradmeyer et Thorpe 1987a, Vignes 1995 ou subarctiques (Thonney et Gibson 1989, Keeley et Grant 1997, Amundsen et al. 2001 (Vignes 1995, Amundsen et al. 2001, tandis que d'autres comme les nymphes de Baetidae (Ephéméroptères) et les larves de Chironomidae (Diptères) sont majoritairement capturées au cours de leur dérive dans la masse d'eau (Forrester 1994, Rader 1997, Gabler et al. 2001. Le régime alimentaire du tacon peut également varier en fonction de son stade de développement (Keeley et Grant 1997, Erkinaro et Erkinaro 1998. ...
... Les macroinvertébrés sont capturés sur le fond ou au moment de la dérive et la proportion de formes adultes prises en surface ou d'insectes terrestres reste assez faible (Muje et al. 1989, Desvilettes et al. 1997b. Malgré une grande diversité de proies potentiellement ingérables au niveau des zones de radier, les tacons semblent se focaliser sur un petit nombre d'unités taxonomiques (Diptères, Ephéméroptères, Plécoptères et Trichoptères), que ce soit dans les rivières tempérées (Maitland 1965, Stradmeyer et Thorpe 1987a, Vignes 1995 ou subarctiques (Thonney et Gibson 1989, Keeley et Grant 1997, Amundsen et al. 2001 (Vignes 1995, Amundsen et al. 2001, tandis que d'autres comme les nymphes de Baetidae (Ephéméroptères) et les larves de Chironomidae (Diptères) sont majoritairement capturées au cours de leur dérive dans la masse d'eau (Forrester 1994, Rader 1997, Gabler et al. 2001. Le régime alimentaire du tacon peut également varier en fonction de son stade de développement (Keeley et Grant 1997, Erkinaro et Erkinaro 1998. ...
... Les macroinvertébrés sont capturés sur le fond ou au moment de la dérive et la proportion de formes adultes prises en surface ou d'insectes terrestres reste assez faible (Muje et al. 1989, Desvilettes et al. 1997b. Malgré une grande diversité de proies potentiellement ingérables au niveau des zones de radier, les tacons semblent se focaliser sur un petit nombre d'unités taxonomiques (Diptères, Ephéméroptères, Plécoptères et Trichoptères), que ce soit dans les rivières tempérées (Maitland 1965, Stradmeyer et Thorpe 1987a, Vignes 1995 ou subarctiques (Thonney et Gibson 1989, Keeley et Grant 1997, Amundsen et al. 2001 (Vignes 1995, Amundsen et al. 2001, tandis que d'autres comme les nymphes de Baetidae (Ephéméroptères) et les larves de Chironomidae (Diptères) sont majoritairement capturées au cours de leur dérive dans la masse d'eau (Forrester 1994, Rader 1997, Gabler et al. 2001. Le régime alimentaire du tacon peut également varier en fonction de son stade de développement (Keeley et Grant 1997, Erkinaro et Erkinaro 1998. ...
This project was conducted in the overall context of enhancing the natural salmon population of the River Allier and focused on growth performances of their juveniles and parr in a large temperate river. We focused on the development of juveniles Atlantic salmon released at fry stage into the wild and we integrated them in the context of the food chain. Our work had several objectives: (i) conduct a detailed analysis of diet, growth and nutritional status of parr raised in a salmon farm, released and recaptured along the continuum of the River Allier, (ii) assess whether, due to different fatty acid composition (FA), macroinvertebrates could affect parr growth and their overwintering survival, (iii) determine, through an approach based on FA biomarkers, the origins of lipid compounds found in macroinvertebrates and specify the sources of carbon assimilated by them along the river continuum. Sampling took place from June 2006 to October 2006 at monthly intervals. Samples of salmon, macroinvertebrates and different sources of organic matter were collected in five riffles along the river continuum (rhithron-epipotamon). Significant variations in growth, condition factor and lipid accumulation have been observed in restocked parr along the upstream-downstream gradient. The transition zone of rhithron-epipotamon appeared to be of great interest for salmon growth because of favourable environmental (temperature and flow) and trophic (preys composition and abundance) parameters. The values recorded in these areas were close to those achieved by the hatchery-reared salmon. In addition, growth performances seemed to result from dietary inputs of polar lipids (PL) from Baetids and Simuliids preferentially consumed by salmon in these downstream riffles. In contrast, the rhithron areas mainly located in trout zone, can be considered as the extreme upstream limit for 0+ salmon restocking. The low growth and lipid storage observed in this area appeared to result from lower dietary inputs in PL compared to the other riffles, not compensated by a significant input of neutral lipids from Chironomids. Thus, Simuliids and Baetids, preferentially consumed in downstream riffles, constituted an interesting type of food compared to Chironomids for parr overwintering survival and smoltification. The FA biomarkers approach showed that despite different feeding modes and whatever the localization of sites along the river continuum, macroinvertebrates consumed by parr receive their carbon from autochthonous production, more specifically on diatoms. A complementary approach by isotopic analysis of FA could confirm these origins of essential FAs in salmon and the relevance in the studied ecosystem of some FAs considered as biomarkers.
... Salmo salar is the dominant species in the main river and no potential interspecific food competitors are present in significant abundance (Erkinaro, 1995;Amundsen et al., 2001). In the River Utsjoki, the S. salar parr coexist with introduced bullheads Cottus gobio L. Previous studies have concluded that the C. gobio do not have any significant effect on S. salar production in the River Utsjoki, as the S. salar parr and C. gobio are selectively segregated (Nilsson, 1967) in both habitat and food niche utilization (Pihlaja et al., 1998;Jørgensen et al., 1999;Gabler et al., 2001). Hence, based on the assumption that the dense C. poecilopus population in River Reisa negatively influences the food resources of juvenile S. salar through interspecific competition Gabler, 2000), it was hypothesized that the S. salar parr in this river system should experience reduced food consumption and S. salar somatic growth rates compared to the S. salar populations in the other two systems. ...
... Despite the accidental introduction and successful establishment of C. gobio in this watercourse, the S. salar population does not appear to suffer from interspecific competition. This has also been the conclusion of other studies in the River Utsjoki, which have demonstrated different habitat and diet preferences of the two species, with the bullheads primarily being located in and near the many lake localities in this watercourse (Pihlaja et al., 1998;Jørgensen et al., 1999;Gabler et al., 2001). Apparently, the S. salar parr have ample food resources at this river site, an assumption that is also supported by high invertebrate densities found in zoobenthos and drift studies in the river Gabler et al., 2001). ...
... This has also been the conclusion of other studies in the River Utsjoki, which have demonstrated different habitat and diet preferences of the two species, with the bullheads primarily being located in and near the many lake localities in this watercourse (Pihlaja et al., 1998;Jørgensen et al., 1999;Gabler et al., 2001). Apparently, the S. salar parr have ample food resources at this river site, an assumption that is also supported by high invertebrate densities found in zoobenthos and drift studies in the river Gabler et al., 2001). The population density of S. salar parr is moreover relatively low in the upper parts of this tributary (Jørgensen et al., 1999) and intraspecific competition appears to be low or absent. ...
The quantitative food consumption and somatic growth of Atlantic salmon Salmo salar parr were compared between three sub-Arctic rivers in northern Norway and Finland, addressing the potential occurrence of resource limitation and interspecific competition. In one of the rivers, previous resource partitioning studies have suggested severe dietary competition between juvenile S. salar and a dense population of alpine bullheads Cottus poecilopus. It was hypothesized that S. salar parr in this river would have restricted food consumption and growth rates compared to the S. salar populations in the other two rivers where interspecific competition was less likely to occur. The feeding and growth performance differed significantly between the S. salar populations. The lowest food acquisition and growth rates were in the S. salar parr population living in sympatry with C. poecilopus, confirming a restricted food supply for the S. salar parr and providing empirical support for the presence of resource limitation and interspecific food competition in this river system. The study reveals that S. salar parr in sub-Arctic rivers may experience food limitations resulting in diminished growth rates.
... There was a negative correlation between prey diversity and dietary overlap of salmon and bullhead, supporting the hypothesis that high prey diversity may enhance food resource partitioning between sympatric species and thereby facilitate their coexistence. In previous studies, high dietary overlap was observed between salmon and bullhead at a homogeneous river site with a low diversity of zoobenthos (Gabler & Amundsen, 1999), whereas strong dietary segregation was observed between salmon and European bullhead (Cottus gobio Linnaeus, 1758) in a more heterogeneous river that had relatively high diversity of zoobenthos (Gabler, Amundsen, & Herfindal, 2001). ...
... Thus, resource partitioning between salmon and bullhead species may be related to between-river differences in prey diversity and habitat characteristics (Gabler & Amundsen, 1999;Gabler et al., 2001). The present study reveals that food resource partitioning between salmon and bullhead can vary within a river system, between sites at relatively short distances from each other, and between seasons at a given site, with resource partitioning being strongly dependent on prey diversity at different sites. ...
Although food resource partitioning among sympatric species has often been explored in riverine systems, the potential influence of prey diversity on resource partitioning is little known. Using empirical data, we modeled food resource partitioning (assessed as dietary overlap) of coexisting juvenile Atlantic salmon (Salmo salar) and alpine bullhead (Cottus poecilopus). Explanatory variables incorporated into the model were fish abundance, benthic prey diversity and abundance, and several dietary metrics to give a total of seventeen potential explanatory variables. First, a forward stepwise procedure based on the Akaike information criterion was used to select explanatory variables with significant effects on food resource partitioning. Then, linear mixed-effect models were constructed using the selected explanatory variables and with sampling site as a random factor. Food resource partitioning between salmon and bullhead increased significantly with increasing prey diversity, and the variation in food resource partitioning was best described by the model that included prey diversity as the only explanatory variable. This study provides empirical support for the notion that prey diversity is a key driver of resource partitioning among competing species.
... Both zoobenthos abundance and drift rates at the sampling site were low compared to densities found in tributaries to the river Tana (Erkinaro and Erkinaro, 1998). Flying insects made up the bulk of the surface drift, whereas chironomid larvae dominated both the suspended drift and the benthos, which has also commonly been observed in other subarctic rivers (Bergersen, 1989;Gabler et al., 2001;Huru, 1986). ...
... The drift feeding feature of Atlantic salmon thus appears to be strongly dependent on the drift rates, and in subarctic rivers like the river Tana, the invertebrate production and drift rates may be so low that drift feeding by salmon parr is feasible only during a short mid-summer period. Similar conclusions have also been reached in studies from other large subarctic rivers (Bergersen, 1989;Gabler and Amundsen, 1999;Amundsen et al., 2000;Gabler et al., 2001). ...
The food utilisation and partitioning between three age-groups of Atlantic salmon parr were studied in the subarctic river Tana (70° N, 27° E) by analysis of fish stomach contents and invertebrate composition in the three main lotic feeding habitats: bottom substratum, water column and surface. The salmon parr exhibited large seasonal variation in their food choice, but the different age-groups had a similar diet, dominated by mayfly and stonefly nymphs in May, flying insects and simuliid larvae and pupae in July, and caddis fly larvae in August and September. Some differences in the food resource use of the three age-groups were however also observed, mainly related to size-dependent differences in feeding abilities, but partly also to different use of feeding habitats. Small-sized stonefly and mayfly nymphs and simuliid larvae and pupae decreased in importance with increasing fish age, whereas Trichoptera larvae and flying insects increased. The low resource partitioning between the different age-groups of salmon parr suggests that intraspecific competition for food may occur. All age-groups mostly fed on prey types associated with the bottom habitat, and substantial drift feeding was only observed in July, probably due to low drift rates throughout most of the summer season in this subarctic river.RésuméL’utilisation et le partage de la nourriture entre trois groupes d’âge de tacons (stade « parr ») du saumon Atlantique du fleuve Tana (70° N, 27° E) ont été étudiés par analyse des contenus stomacaux et par la composition en invertébrés pour trois types d’habitats principaux : sur le fond, dans la colonne d’eau et en surface. Les tacons montrent une grande variation saisonnière dans leur choix de nourriture mais les différents groupes d’âge ont un régime alimentaire similaire, dominé par des nymphes d’insectes éphémèroptères et des nymphes de plécoptères en mai, des insectes volants et des larves et pupes de simuliidés en juillet, et des larves de trichoptères à fourreau, en août et septembre. Quelques différences dans l’usage des ressources alimentaires des trois groupes d’âge sont également observées, principalement relatives aux différences de taille dans la capacité alimentaire, mais aussi en partie liées aux différents types d’habitat. Les nymphes de plécoptères de petites tailles, et celles d’éphémèroptères et les larves et pupes de simuliidés diminuent en importance avec l’augmentation de l’âge, alors que les larves de trichoptères et les insectes volants augmentent. La faible partition des ressources entre les différents groupes d’âge des tacons montre que la compétition intraspécifique pour la nourriture peut se présenter. La plupart des groupes d’âge se nourrit de proies associées à l’habitat situé sur le fond, et une alimentation substantielle basée sur des proies dérivant dans le courant est seulement observée en juillet, probablement due aux faibles taux de proies dérivant en été, durant la majeure partie de la saison estivale dans ce fleuve subarctique.
... They are mostly associated with the bottom and are therefore easy to capture because of their low mobility (Vignes 1998; Amundsen et al. 2001). This would imply that benthic feeding could prevail in these upstream riffles, which has also been demonstrated in other studies of juvenile salmon (Sosiak et al. 1979;Keeley & Grant 1995;Gabler et al. 2001). In downstream riffles (Sites 4 and 5), Simuliid larvae dominated the benthic fauna, whereas Baetid nymphs were preferentially chosen by parr. ...
... Baetidae species are frequently regarded as intentional drifters, particularly when subject to Salmonid predation (Forrester 1994;Rader 1997). Consequently, their strong abundance in salmon parr diet can reflect an increasing drift feeding, as shown in some studies conducted in sub-arctic Norwegian rivers Gabler et al. 2001). Prey size was also an important factor in prey choice (Wankowski 1979). ...
Abstract – The feeding, growth and nutritional status of salmon parr (0+) released at fry stage in different riffles were studied in a large temperate river (Allier, France) throughout the active feeding period. Significant differences were observed along the upstream–downstream gradient. Parr growth performance and energy storage were higher in downstream riffles and low in the most upstream one. These longitudinal growth variations are discussed in the context of diet and food availability differences, habitat variables and intra- and inter-species competition. The most favourable site for optimum growth and nutritional status appeared to be the intermediary riffle located in the grayling zone.
... Introduced populations exist in the Clyde, Forth and Tweed catchments and there is concern that competition, both for food and space, between bullheads and juvenile Atlantic salmon may result in an overall negative impact on Atlantic salmon production. Empirical evidence to support this is limited to basic inference, however Gabler et al. (2001) in one of the few studies to explore the interaction between Atlantic salmon parr and bullhead reported selective segregation in prey choice between species. It remains possible, however, that higher levels of dietary and spatial overlap exist between Atlantic salmon fry and bullhead at varying stages in their life history. ...
The International Union for the Conservation of Nature (IUCN) assert that the spread of Invasive Alien Species (IAS) is, after habitats loss, the second most significant threat to global biodiversity. The most recent global assessment report on biodiversity and ecosystem services carried out by the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) concluded that nearly one fifth of the Earth’s surface is at risk of plant and animal invasions, impacting native species, ecosystem functions and nature’s contributions to people, as well as economies and human health.This paper reviews the ways in which INNS may impact Atlantic salmon.
... Alpine bullhead share the same microenvironment (shelter between gravel and stones, depth and river velocity) as salmon fry and parr, resulting in competition for both space and food. In fact, alpine bullhead may be the dominant of these two species, especially in high density populations Amundsen 1999, Svenning 2000) as also observed for Cottus gobio Linnaeus (see Gabler et al. 2001). The sympatry and niche overlap with salmon provides ideal conditions for G. salaris transmission and host switching (see Bakke et al. 2007). ...
The notifiable freshwater pathogen Gyrodactylus salaris Malmberg, 1957 tends to be a generalist in contrast to other monogeneans. Whilst it causes most damage to its primary host, the Atlantic salmon (Salmo salar Linnaeus), transport and reservoir hosts likely play a key role in maintaining the parasite in the environment. Here, we tested the ability of G. salaris (strain River Lierelva, southern Norway) to infect and reproduce on a population of wild caught alpine bullhead (Cottus poecilopus Heckel). Exposure of alpine bullhead yearlings (0+) to G. salaris for 24 h at low (6.5 °C) or high temperature (11.5 °C) resulted in the establishment of 1 to 104 parasites per fish. Eight to nine days post-infection at high temperature, the infection of G. salaris was eliminated, indicative of innate host immunity. In contrast, at low temperature G. salaris infections persisted for 47-48 days. The relative lengthy infection of alpine bullhead with G. salaris compared to other non-salmonids tested may be due to low temperature and high initial infection load in combination with an epibiont infection. The present results suggest that this non-salmonid may function as a temperature-dependent transport or reservoir host for G. salaris.
... By contrast, the effect of sculpin predation on salmonids in Europe appears to differ. Several studies found interactions between one of the most common European sculpin species, Cottus gobio L., and salmonids, but as a result of habitat and diet overlap and not predation (Pihlaja et al. 1998; Jørgensen et al. 1999; Gabler et al. 2001; Elliott 2006). However, field observations of C. gobio in interstitial spaces of spawning redds of brown trout, Salmo trutta L., together with experimental studies where C. gobio has been shown to predate on brown trout, Salmo trutta L., fry (Gaudin & Heland 1984; Gaudin 1985; Bardonnet & Heland 1994; Gaudin & Caillere 2000) Correspondence: Daniel Palm, Department of Wildlife, Fish and Environmental Studies, Swedish University of Agricultural Sciences, SE-901 83 Umea˚,Umea˚, Sweden (e-mail: daniel.palm@vfm.slu.se) ...
Abstract The study examined if recruitment of juvenile Atlantic salmon, Salmo salar L., was influenced by the presence of European sculpin, Cottus gobio L., and if the spawning substrate size used by salmon influences sculpin predation on salmon eggs. A combination of information on spawning site selection by female salmon and associated densities of juvenile salmon indicated that recruitment of juvenile salmon was 10 times lower in areas where sculpin was present than areas without sculpin. Predation rate on salmon eggs was found to be dependent on substrate size in artificial redds created in stream aquaria using four different sizes of substrate (13, 23, 37 and 62 mm). Predation rate averaged 83% in the aquaria with the largest substrate size, whereas a rate of only 2–3% was observed using smaller substrate sizes. Sculpin may thus be an important factor influencing the recruitment of juvenile salmon. Selecting small enough gravel sizes during restoration of salmon spawning habitat could therefore be important to minimise egg predation.
... Finally, one may argue that some interspecific interactions may have accounted for the observed distributions. Bullhead commonly coexists with other lotic fish species (e.g., trout, salmon, minnow, loach), but with no (or little) competitive interactions (WELTON et al., 1983;WELTON et al., 1991;JØR-GENSEN et al., 1999;GABLER et al., 2001). Bullhead's distribution and density at a site can be significantly influenced by the presence of predators such as the trout, the pike or the burbot (DEGERMAN and SERS, 1994), but such predatory species did not occur at our study site, and were not likely to influence the observed distributions. ...
We investigated differences in microhabitat preference curves for bullheads, Cottus gobio L., of different size-classes during low flow periods, and evaluated the influence of such differences on habitat use through Weighted Usable Area (WUA) predictions in relation to river flow in a piedmont stream in Southwest France. Water depth, current velocity, and substratum composition were used to calculate proportional use values for each size-class (SC), and to quantify size-specific microhabitat preferences. Bullhead used non-cohesive and coarse mineral particles (pebbles, cobbles, boulders), but there was a spatial segregation of individuals from different size classes (SC1–SC4). Smaller bullhead (SC1, total length <60 mm) took refuge under cobbles, significantly preferred shallower areas, and were less prone to select high current velocities than larger bullhead (SC 2 to 4, >60 mm), the latter occurring below (or under) the largest particles, where current velocity is weakened and sand accumulates. SC1 bullhead had a more restricted range for each habitat descriptors, and were thus likely to require a more specific habitat type than other bullhead. The maximum WUA values and the related preferred discharges (0.15–0.75 m3 s–1) depended on the considered size-class. Our results suggest that ontogenetic niche shifts may play a role in the structure and dynamics of populations, by adjusting species' requirements to the spatial and temporal dynamics of environmental conditions, including abiotic and biotic conditions. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
... They found no evidence of competition, but rather a positive relationship between abundance of non-salmonids, overall ecological productivity and salmon growth. From comparisons among populations inhabiting a small number of streams, it has been suggested that demersal fishes in the family Cottidae (known commonly as sculpins in North America and bullheads in Europe) have a potentially negative influence on populations of salmon (Amundsen & Gabler 2008), although diet studies suggest little competition for food (Gabler et al. 2001). It is evident, however, that cottids may be vigorous predators of salmon at early life stages with substantial consequences for population processes (Ward et al. 2008), making it difficult to attribute negative effects to competitive interactions. ...
IntroductionIntraspecific competitionInterspecific competitionConclusions
References
... And although 0+ bullhead and salmon parr share common microhabitat preferences, as suggested by their close ordinations in the composite CCA for Ellingham side-channel (Figure 3(a)), in the Hampshire Avon they occurred together more often than expected in autumn only. Bullhead is known to influence salmonid distribution through predation of the salmonid eggs in locations where the densities of 51+ bullhead are elevated (Gaudin and H! e eland, 1984;Gaudin and Caille`re, 1985), but evidence of competition for food is equivocal (Pihlaja et al., 1998a,b;Gabler et al., 2001). This study found mainly 0+ bullhead, which could explain the low level of statistical association between bullhead and salmon parr. ...
Five side‐channels and small tributaries of the River Avon (Hampshire, UK) were examined between spring 1999 and spring 2000 using point abundance sampling by electrofishing to determine the status of fish listed in Annex II of the EC Habitats Directive prior to habitat management works to enhance spring feeding habitat of wading birds.
Seasonal patterns of abundance and microhabitat use of bullhead Cottus gobio and accompanying fish species were examined. Parr of Atlantic salmon Salmo salar were sufficiently abundant for microhabitat analysis at one site only. Only two specimens of brook lamprey Lampetra fluviatilis were observed, one at each of two sites. Bullhead was amongst the most abundant fish species at all five sites, 0+ bullhead predominating.
Bullhead microhabitat preferences were generally similar at all five sites, but seasonal variations were observed, as was the case for the accompanying fish species, which included dace Leuciscus leuciscus , chub Leuciscus cephalus , stone loach Barbatula barbatula , roach Rutilus rutilus , and threespine stickleback Gasterosteus aculeatus .
Bullhead conservation status is discussed, in particular the possible exemption of British bullhead populations, such as already granted for those of Finland, from Annex II of the Habitats Directive.
© Crown Copyright 2004 Reproduced with the permission of Her Majesty's Stationary Office. Published by John Wiley & Sons, Ltd.
... This has also been observed in other salmonids (reviewed in Carlson et al. 2008), where mortality seems more closely linked to the level of energy storages (Finstad et al. 2004;Pangle et al. 2004). The overall density of charr in the experimental brook was lower compared to fish density in other subarctic rivers and streams (Gabler & Amundsen 1999;Gabler et al. 2001;Jensen 2004), and generally, stream-dwelling salmonids have low antagonistic behaviour during winter with low temperatures and light intensities typically for under ice conditions (reviewed by Huusko et al. 2007). In addition, Arctic charr are considered less aggressive than many other salmonids (Heggberget 1984). ...
Abstract – Winter growth and survival of wild individually tagged juvenile Arctic charr (1+ age) from a riverine anadromous stock, were studied in a small ice-covered (∼6 months) ground water brook (temperature ∼1 °C) connected to Skibotnelva in subarctic northern Norway. The overall winter survival was estimated to be 68% from late October 2005 to early May 2006. The recaptured charr were not significantly different in initial length or weight compared with the nonrecaptured fish suggesting low size-dependent mortality. The majority (98%) of the recaptured charr showed significant increase in size, with a mean increment of 62% from their initial bodyweight and 12% of the charr parr had more than doubled their weight. The mean specific growth rate was calculated to be slightly lower (0.27) than estimated values from a growth model (∼0.35). In addition, the condition factor increased significantly during the field experiment. These results are the first individual growth data on riverine anadromous Arctic charr parr under natural winter conditions, and indicate that charr can grow relatively fast during periods with low temperature and also that ground water brooks can be good over-wintering habitat for juvenile Arctic charr. These results suggest that the winter period is perhaps a less severe bottleneck than previously recognised for the cold-adapted Arctic charr.
... Bullheads commonly coexist with these species with no or little competitive interactions (Welton et al. 1983;Jørgensen et al. 1999). Coexistence is favoured by the behavioural and morphological characteristics of this benthic fish (small-bodied and benthic-dwelling fish, usually living under cobbles and rocks, sedentary and territorial behaviour) (Welton et al. 1983;Gaudin andCaillè re 1990, 2000Welton et al. 1991;Gabler et al. 2001). Nevertheless, bullhead's density and microdistribution at a site was reported to be significantly influenced by the presence of predators such as the pike or the burbot in Swedish rivers (Degerman and Sers 1994), or by the presence of competitors such as Signal crayfish in a British lowland river (Guan and Wiles 1997). ...
We used general linear modelling to assess the influence of environmental variables on the spatial distribution patterns of the bullhead (Cottus gobio) at stream system, site, and microhabitat scales in southwestern France. Bullheads occurred at 67 sites (out of 554 sampling sites), chiefly close to the source, in small and shallow streams. Population density at a site was primarily influenced by thermal conditions. Stream width was negatively related to the probability of presence of bullheads within the stream system, but positively related to local density, showing that bullhead density could increase within a range of stream width, but that wider rivers were unsuitable. Slope was negatively correlated to bullhead’s occurrence and local density, and depth was negatively correlated to local density and microhabitat use, suggesting that bullhead’s shimming performance was weak under greater erosive forces. Therefore, the most significant results suggested that the distribution of populations and individuals was first governed by the suitability of physical and hydraulic habitat, then population dynamics at a site was mainly governed by the thermal regime. Multi-scale studies of factors influencing a species’ distribution thus allow to integrate patterns observed at different scales, and enhance our understanding of interactions between animals and their environment. Such models are essential in the exploratory phase of fundamental and applied investigations, because they help to target further research, and they should influence the measures to be taken in field surveys or conservation plans.
... More recently, some studies have suggested that various sculpin species are associated with reduced recruitment of juvenile salmonids in other systems in North America and Europe (Olsen and Vollestad, 2001; Pender and Kwak, 2002; Elliott, 2006 ). However, no comparable previous work has addressed the interaction between slimy sculpin and Atlantic salmon (see Pihlaja et al., 1998; Gabler and Amundsen, 1999; Gabler et al., 2001 for other sculpin species). The effects of sculpins on salmonids are probably most severe for population reintroductions or for populations already suppressed by other factors, as sculpins regularly coexist with healthy salmonid populations (Moyle, 1977). ...
Reintroduction of extirpated populations creates a unique context that can exacerbate the effects of interactions among species. Thus, reintroduced populations may be particularly vulnerable to predators and competitors, including native species with which they historically coexisted. In this study, we evaluated the effect of native fishes on survival of reintroduced Atlantic salmon (Salmo salar) in the Connecticut River basin, where the native salmon population is extinct. Juvenile salmon are stocked annually in many Connecticut River tributaries. We sampled salmon reintroduction sites across tributaries with different fish communities to determine whether native fish reduce the success of salmon reintroductions (N = 19 site-years). Increased density of slimy sculpin (Cottus cognatus), a native generalist predator, was associated with reduced recruitment of reintroduced salmon. Salmon first-summer survival declined with increased sculpin density across sites, and low first-summer survival led to reduced densities of overyearling salmon the subsequent year. Hierarchical partitioning analysis showed that the negative relationship between sculpin and salmon was independent of potentially confounding variation in other fish community or habitat characteristics. Negative effects of native, historically-sympatric species, particularly generalist predators, can impede restoration of extirpated populations.
... Cottus gobio commonly coexists with other fish species (chiefly salmonids and loach) with no or little competitive interactions (Jørgensen et al. 1999, Welton et al. 1983. Coexistence is allowed by resources partitioning (mainly food and shel-ters), and certainly favoured by the behavioural and morphological characteristics of this fish species (Welton et al. 1991, Gaudin & Caillère 1990, Gabler et al. 2001. However, bullhead's distribution and density at a site was reported to be significantly influenced by the presence of predators such as the pike (Esox lucius L.) or the burbot (Lota lota L.) in Swedish rivers (Degerman & Sers 1994), or by the presence of competitors / predators such as signal crayfish (P. ...
White-clawed crayfish, bullhead, and freshwater pearl mussel are different model organisms in terms of biological traits. Analysing their distribution patterns, habitat demands, and causes of decline may thus help to derive broader frameworks for conservation projects. This paper includes a wide-ranging literature review for these three threatened freshwater animals, then uses general patterns to make suggestions about broader protection measures for freshwater species. Each species has a patchy distribution, from local to broad spatial scales. However, we point out the difficulty to summarise such knowledge, because many variables were not consistently and/or accurately recorded by workers, and because the range of colonised habitats depends on the environmental heterogeneity within study areas. Causes of decline are chiefly related to human activities which modify the biological, chemical, and physical features of the aquatic environment, and can be classified into four types: physical habitat alterations, interspecific interactions, overfishing and poaching, and natural disturbance. By analysing causes of decline and possible actions, we develop seven general trends that could be adopted for a wider array of species. However, protection plans cannot be effective without actual collaborations between river managers, local inhabitants, and authorities. Finally, the re-introduction procedure itself (if needed) depends on the biology of the species under survey, and remains specific. At the same time, further fundamental research is needed to generalise relationships between population and habitat dynamics at different spatial and temporal scales.
... Bullheads introduced into a river in northern Finland sometime before 1979 had no significant effects on juvenile salmon densities (Pihlaja et al. 1998). Gabler, Amundsen & Herfindal (2001) examined the diets of the two species in the same river and concluded that there was little evidence for competition between them. Similarly, bullheads were found to have no detectable effects on densities of accompanying fish species, including juvenile salmon and trout, in the River Avon in southern England (Carter et al. 2004). ...
Changes in the population density of juvenile sea trout Salmo trutta L. and bullheads Cottus gobio L. were compared in a small stream over 34 years. Both species have a similar diet and obviously live in the same general habitat. Habitat loss was most marked in seven summer droughts: severest in 1976, 1983, 1984, 1995, and less severe but followed by autumn droughts in 1969, 1989 and 1993. The contrasting effects of habitat loss on the two species were examined.
For both species, the Ricker curvilinear model significantly fit ( P < 0·001) the relationship between initial egg density and survivor density for successive life stages, even though egg densities were much lower for bullheads than trout. These analyses provided evidence for density‐dependent population regulation and also identified extreme outliers, most being for year‐classes affected by summer droughts.
The variable effects of changes in habitable area (= % wettable area in sampling section) were quantified by using the residuals, each residual being the absolute value expressed as a percentage of the expected value from the Ricker curve. Significant relationships between the residuals and habitable area showed that habitat loss had a marked effect on survivor density, this being negative for 0+ and 1+ trout, and positive for 0+, 1+ and 2+/3+ bullheads.
Therefore, during periods of habitat loss in the summer months, bullhead density increased at the expense of trout density. Low flows and a decrease in wettable area were associated with a marked reduction in habitat quality for drift‐feeding trout and an increase in habitat quality, and perhaps also quantity, for benthic‐feeding bullheads. This case study shows that, during a major perturbation, the relationship between the densities of two species can change markedly in favour of the less numerous species. The competitive coexistence between the two species is therefore a dynamic process that changes through time with periodic changes in the environment.
This review summarises the current state of knowledge on salmon freshwater feeding, emphasising the issues of what to eat, and when and where feeding activity occurs. It also provides a brief introduction to optimal foraging theory and drift - feeding models. We focus primarily on juvenile salmon freshwater feeding, as the adult salmon feed very little while in fresh water. The juveniles actively select prey items both in terms of prey types and sizes, with large - sized prey types usually being preferred. The diet composition, both in terms of taxa and average prey size, changes with fish size. Most of the diet consists of invertebrates, but there are also some records of juvenile salmon eating fish. In running water, the salmon can feed from invertebrates drifting either on the water surface or in the water column, or from benthic invertebrates on the streambed surface. In temperate areas, juveniles are predominantly daytime drift - feeders, whereas they spend more time feeding on the benthos at night in northern areas. The relative extent of benthic feeding also increases with decreasing light and temperature through the season. The highest feeding rates are observed during spring and early summer. However, although feeding rates decrease with falling water temperatures in the autumn, juveniles also feed during the winter. Thus, juvenile salmon are versatile fish, being able to feed successfully in different habitats ranging from small streams to large lakes and under different conditions (e.g. changing light levels and seasons).
The food utilisation and partitioning between three age-groups of Atlantic salmon parr were studied in the subarctic river Tana (70° N, 27° E) by analysis of fish stomach contents and invertebrate composition in the three main lotic feeding habitats: bottom substratum, water column and surface. The salmon parr exhibited large seasonal variation in their food choice, but the different age-groups had a similar diet, dominated by mayfly and stonefly nymphs in May, flying insects and simuliid larvae and pupae in July, and caddis fly larvae in August and September. Some differences in the food resource use of the three age-groups were however also observed, mainly related to size-dependent differences in feeding abilities, but partly also to different use of feeding habitats. Small-sized stonefly and mayfly nymphs and simuliid larvae and pupae decreased in importance with increasing fish age, whereas Trichoptera larvae and flying insects increased. The low resource partitioning between the different age-groups of salmon parr suggests that intraspecific competition for food may occur. All age-groups mostly fed on prey types associated with the bottom habitat, and substantial drift feeding was only observed in July, probably due to low drift rates throughout most of the summer season in this subarctic river.
The diel and seasonal food habits of young-of-year (YOY) and post-young-of-year (PYOY) Atlantic salmon (Salmo salar) parr were assayed over the course of 11 months in the West Brook, Massachusetts USA. Gut fullness of YOY salmon did not vary significantly among months. PYOY salmon exhibited significant seasonal differences in gut fullness, with peak fullness occurring in the spring and late fall. Significant diel differences in PYOY gut fullness occurred in June and April, with peak fullness always occurring at dawn. Prey composition varied substantially among months. Dominant prey items of PYOY salmon were baetid mayflies in June, July, and August, limnephilid caddisflies in October and November, and ephemerellid mayflies in February and April. Few differences in prey composition between PYOY and YOY salmon were observed. Fish growth was unrelated to prey availability, but gut fullness explained up to 97% of growth variation across seasons. Results suggest that spring and fall are critical periods of feeding for PYOY salmon and that diel feeding intensity shifts seasonally.
Habitat competition in brown trout Salmo trutta and Siberian sculpin Cottus poecilopus was investigated by varying density, fish size, and species composition in stream channels providing areas of different substratum particle sizes. In allopatry, both small (52 ± 4 mm LT) and large (86 ± 6 mm LT) brown trout exhibited strong preference for the intermediate (8–11 cm diameter) and large (17–21 cm) gravel substrata. There was a tendency for more brown trout to occupy finer (2–4 cm) substrata with increasing density, in particular for large brown trout. Also, more small brown trout were observed on finer substrata when tested with large brown trout, suggesting interspecific competition for restricted space. Both small (56 ± 6 mm LT) and large (88 ± 10 mm LT) Siberian sculpin preferred the large gravel in all tests, and did not change their substratum preferences much with increasing densities, suggesting higher tolerance for ‘crowding’. The large Siberian sculpin preferred the coarser substratum, and the largest individuals were consistently found on it. In sympatry with large Siberian sculpin, habitat displacement of brown trout occurred, indicative of interspecific competition. A higher proportion of small and large brown trout occupied the finer substrata than in allopatry. Habitat selection by large Siberian sculpin appeared to be unaffected by species composition and density. Small Siberian sculpin were displaced to finer substrata when tested with large Siberian sculpin, suggesting intraspecific competition. The results indicate that Siberian sculpin are potential habitat competitors for young brown trout.
The density, diet and habitat use of brown trout (Salmo trutta) and Siberian sculpin (Cottus poecilopus) were studied in the subalpine River Atna in southeastern Norway in the autumn during a six year period (1986–1991). There was an inverse relationship between the density of brown trout and Siberian sculpin. Diet overlap, as indicated by the Schoener index, was high between the two species, ranging between 0.48 and 0.86. Chironomid larvae and other aquatic insects were the most common food items for both species. Brown trout also consumed substantive amounts of surface insects. Siberian sculpin typically occupied sites with finer substrates and greater water depths than brown trout, even though there was considerable overlap in habitat use between the two species. Because the two species shared similar habitats, we suggest that the potential for species interactions exists, particularly at sites where density of sculpin is high.
Increased mortality of juvenile Atlantic salmon (Salmo salar L.), related to lowered levels of stored energy following the loss of ice cover during winter, has been observed after hydropower development in the subarctic River Alta, northern Norway. Drift samples were compared to examine if drift densities, and thus drift prey availabilities for juvenile salmon, were lower in the ice-free than the ice-covered area. In addition, juvenile salmon stomach contents were compared to benthos and drift in the ice-free area to examine salmon winter feeding habitat. Zooplankton, originating from the reservoir, dominated drift at the ice-free site but had lower densities at the downstream ice-covered site. Excluding zooplankton, Chironomidae comprised most of the remaining drift at both the ice-free and ice-covered site, followed by Ephemeroptera, Plecoptera and Simuliidae. No Trichoptera were found in the drift samples. There was no consistent diel periodicity in drift. Benthos was dominated by Chironomidae, followed by Ephemeroptera, Plecoptera and Trichoptera. Other invertebrates occurred in low numbers. Juvenile salmon demonstrated size-selective feeding and fed mainly on Ephemeroptera, followed by Trichoptera and Plecoptera. No zooplankton and few Chironomidae were found in the stomach samples. Stomach content was more similar to benthos than to drift, indicating a larger extent of benthic than drift feeding. No evidence was found for the hypothesis that lack of ice cover reduced the invertebrate drift or caused diel periodicity in the drift. Differences in drift between areas with and without ice could not account for the observed differences in mortality of juvenile salmon during the winter in these areas.
p> Frilund GE, Koksvik J, Rikstad A and Berger HM. 20092009. Cottus gobio (Linnaeus, 1758), a new fish-species in Nord-Trøndelag County, Norway. Fauna Norvegica 29: 55-60.
Cottus gobio, a freshwater sculpin, was discovered by electrical fishing in rivers draining to Murusjøen in Lierne, Nord-Trøndelag County in the middle of Norway. Until now, this sculpin has only been found in a few river systems in the south-eastern and north-eastern parts of Norway. Species specific characters (glands and fins) were used to distinguish C. gobio from the close relative C. poecilopus. The sculpin dominated the catches in all the investigated rivers. In August 2008 in the River Fiskløysa, a total of 194 specimens were collected. Their length varied from 37 mm to 105 mm, indicating the presence of both juvenile (age 0) and adult individuals. In September 2008, qualitative sampling was conducted in another part of Fiskløysa and in the rivers Kveelva and Murubekken. In River Fiskløysa, the species was not registered above a presumably impassable waterfall about 1.6 km from Lake Murusjøen. In River Kveelva sculpins were caught below a nine meters moderate waterfall, close to the outlet of Lake Kvesjøen, but no sculpins were registered above the waterfall. This indicates that the waterfall is a possible barrier for further upstream dispersal into Lake Kvesjøen. Sculpins were also registered in River Murubekken.The paper discusses possibilities for C. gobio being spread naturally or artificially into the river systems in Lierne. It is predicted that the dispersal most likely has been natural from populations in Sweden, as there are no distinct barriers preventing the sculpin from spreading westwards. The time-period of the dispersal, however, is still unknown, and the sculpin may still be expanding its home range in these water systems.
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Mottled sculpins (Cottus bairdi) have a strong negative effect on the ability of the stonefly Agnetina capitata to capture some types of mayfly prey. To determine the mechanism for this interference effect, behavior of Agnetina in the presence and absence of sculpins was observed over 24 h periods (12 h light, 12 h dark), using an infra-red sensitive camera and a time-lapse video recorder. Agnetina larvae reacted to the presence of sculpins by significantly reducing the time they spent off the bottom of the substrate, and by significantly decreasing the amount of time spent moving on the substrate. These experiments suggest that in the presence of fish, stonefly diets may contain a smaller proportion of prey that tend to frequent tops and sides of stones. This behavioral flexibility may be important in streams in that it allows stoneflies to advantageously shift their diets when fish population densities are low.
This paper reviews the literature on invertebrate drift in running waters, emphasising papers published during the last 10–15 years. The terms constant drift, catastrophic drift, behavioural drift, active drift and distributional drift are defined, but their use should be limited as much confusion has arisen. Sampling methods are briefly reviewed.
The composition of drift in streams and rivers is assessed, especially with respect to temporal variation, drift densities and drift distances. This body of descriptive literature is subsequently analysed in relation to both abiotic and biotic variables, such as current/discharge, photoperiod, temperature, benthic densities, predators and life cycle stage.
The ecosystem significance of drift in terms of colonization and distribution, population dynamics and its importance as a food resource are then reviewed and discussed. Drift enables organisms to escape unfavourable conditions and gives them the potential to colonize new habitats. However, mortality poses a constant threat. The drift community is composed of components whose presence in the drift may be due to widely differing reasons. This renders unsuccessful most attempts to explain drift in terms of one or even a few factors, except in extreme cases, such as floods or pollution. The question whether drifting organisms are alive, dead, or “ecologically dead” is seldom addressed, as is variation at the level of the individual.
The drift literature is dominated by large numbers of discriptive papers and there is a need for laboratory and field studies aimed at testing specific hypotheses.
Introduction of sculpins into a stream previously devoid of these predators significantly reduced drift rate of Gammarus pulex. The drift of insect larvae was not affected. High amounts of exudates after implantation of sculpins were probably responsible for the low number of drifting G. pulex specimens. Laboratory experiments confirmed reduced locomotory activity of G. pulex when exposed to caged sculpins, an observation that excludes reduced drift activity as a result only of predation.
The average size of drifting G. pulex specimens was larger during the night than during the day. This result is in accordance with the hypothesis that large individuals should, in relation to small ones, turn nocturnal because of greater predation risk during daytime. Presence of sculpins did not alter the size composition of drifting G. pulex.
Intraspecific and interspecific competition for food were studied in simple communities in laboratory streams stocked with reticulate sculpins (Cottus perplexus), cutthroat trout (Salmo clarki), and carnivorous stoneflies of the genus Acroneuria. Herbivorous midge larvae were the principal prey organisms. Different combinations and densities of the carnivorous species were used in different streams and experiments. The rates of food consumption, respiration, and growth of sculpins and trout in the laboratory stream communities were found to be functions of prey density. Measurements of prey density thus may be useful measures of food availability for certain predators in some aquatic systems. Prey density in the streams was a function of predator density. These findings together suggest possible ways of modeling the production of a predator by using functions of the densities of the predator, its competitors, and its prey. Such models may make it possible to identify the seasonal or ecosystem changes that alter the relationships between the biomass and production of a predator and may be useful for predicting the biomass of a predator that would maximize its production.
(1) Survival, growth and annual production of six species of fish were measured in one soft water and five hard water stream sites in southern England, the species studied being trout (Salmo trutta), salmon parr (S. salar), bullhead (Cottus gobio), stone-loach (Nemacheilus barbatula), three spined stickleback (Gasterosteus aculeatus) and minnow (Phoxinus phoxinus). (2) There were only minor differences in the growth rates of fish at the five hard water sites, but these rates were higher than those for the same fish species in the softer Docken's Water. At all sites growth was most rapid in the spring and early summer and though growth continued throughout the year there was a considerable decrease in the rate during the winter months. (3) Annual bullhead production ranged from 6.2 to 43.1 g/m2 (fresh weight) in the hard-water streams and this represented from 43 to 83% of total fish production. Bullhead production was greatest during the first few months of life and was correlated directly with the density of the 0 group population. (4) Trout production ranged from 2.6 to 12.9 g/m2/annum (fresh weight) at the hard water sites and contributed from 7 to 37% to the total fish production at each site. There was a more even distribution of production among the age groups than in the bullhead, and trout production at each site was affected by the proportion of each age group present. (5) In the soft water stream trout contributed 87% (12.1 g/m2) of annual fish production, with most of the remainder coming from the minnow population. Bullheads did not occur in this stream.
From an investigation in the trout-zone of the Morávka stream, results were obtained showing a differentiation of the niches from which the three commonest co-existing species of fish obtained their food. The brown-trout takes larger animals that move freely or sit upon the bottom, the minnow feeds on smaller animals inhabiting the bottom surface or plants, and the sculpin obtains its food from under stones and among gravel. There was thus little evidence of competition for food among these species. This is contrary to the conclusion generally accepted in the literature from data which, in most instances, have been too limited to be conclusive.
In Black Brows Beck, earliest and latest spawning dates were 3 November and 7 December; larger females spawned earlier than smaller females. Eggs per redd and mean egg weight increased with female size and decreased with time from the start of the spawning period. Migratory trout produced more and larger eggs per unit length of fish than did resident trout in a neighbouring stream. In laboratory and stream experiments, 50% of eggs hatched and 50% of alevins emerged after 444o days and 852o days from fertilization, respectively. Population densities of eggs and alevins were very similar within but differed between year-classes (range: 12-133 eggs m-2). The dominant factor affecting population densities of young trout was the population density of eggs, and hence alevins, at the start of each year-class. Maximum recruitment was 7.2 fish m-2 (95% CL = 6.5-8.0) soon after the fry stage ended in May/early June and 2.0 (+ or -0.5) fish m-2 in late August/September. Optimum egg densities for these values were 40.0 m-2 (95% CL = 38.5-41.7) and 62.5 m-2 (55.6-71.4) respectively. Mortality was very low for eggs and alevins but high for young trout trying to establish feeding territories. The instantaneous mortality rate was linearly related to egg density. The mortality rate for June to August was also negatively related to, and appeared to compensate for, the high mortality rate in May/early June. Density-dependent mortality appeared to be the chief mechanism for population regulation of the young trout.-from Author
1. The differences in local distribution of Myrmica rubra L. and M. scabrinodis Nyl. have been considered in western Scotland and compared with other regions. 2. Three examples of the partition of habitats between the two species have been described and evidence that they result from interactive segregation has been advanced. 3. Certain adaptive differences that prevent one species replacing the other entirely have been discussed and this situation compared with that in other animals.
The locomotory activity of the closely related freshwater sculpins Cottus poecilopus Heckel and C. gobio L. was investigated in South Sweden (55° 35′N, 13° 30′E). Three physical factors were considered: light intensity, day-length and temperature. 1. The activity of both species was lower in winter than in summer. Short-time variations in activity followed variations in temperature at low temperature. The annual cycle of level of activity seemed to be correlated to temperature as far as influenced by exogenous factors. 2. In natural light conditions the diel activity of both species was synchronized to light throughout the year with a maximum peak after sunset. On overcast days in winter C. poecilopus began its activity earlier than C. gobio, being also active in the afternoon. 3. Spawning caused a temporary desynchronization for some days. 4. In artificial light low intensity released a phase shift in C. poecilopus which became light-active, while C. gobio remained dark-active. Seasonal phase shifts are known for C. poecilopus in North Sweden (at the Arctic Circle), where the species is light-active in winter but dark-active in summer. 5. Feeding of the fishes did not affect the diel activity pattern. 6. The different response to low light intensity may diminish competition between the two species, as they utilize different periods of the day for activity. /// Регистрация активности передвижения исследовалась у близко стоящих видов пресноводных подкаменщиковых Cottus poecilopus Heckel у C. gobio в Южной Швеции (55° 35′N, 13° 30′E) Учитывалось три физических фактора: сила света, света, продолжительность дня и температура. 1. Активность у обоих видов была меньше зимой чем летом. Кратковременные измененения активности следовали колебаниям температуры при низкой температуре. Годовой цикл активности тоже завичит от температуры, когда она контролируется экзогенными факторами. 2. При природных световых усдовиях оба вида имеют почти тот-же круглосуточный образ жизни. Они были синхронизованы с силой света на протяжении целого года с максимальной активностью после захода солнца. Зимой, с пасмурные дни начинал C. poecilopus раньше свою активность, чем C. gobio и был активным также в послеобеденное время. 3. Нерест вызывал временную десинхронизацию в течение несколвко суток. 4. При искусственном свете вызывала слабая сила света смещение фаз у C. poecilopus который становился светоактивным тогда, когда C. gobio оставался темноактивным. Смещения фаз связанны с временами года встречаются у C. poecilopus в Северной Швеции (вблизи Полярного круга), где вид является светоактивным зимой и темноактивным летом. 5. Кормление рыб не оказывало никакого влияния на суточную активность. 6. Разная реакция на слабый свет повидимому уменьшает конкуренцию между видами, так как они используют разное время суток для своей активности.
The distribution, social behaviour, and feeding behaviour of juvenile Atlantic salmon were studied in a selection of stream and river habitats in northern Scotland using Scuba diving techniques. The results are discussed with respect to food acquisition and choice of feeding site. It is concluded that juvenile salmon feed predominantly on drifting material and that their daytime distribution reflects the current velocity related abundance of drift.
The bullhead, Cottus gobio L., was observed in the River Utsjoki in the far north of Finland for the first time in 1979. This river is a tributary of the sub-Arctic River Teno, which flows into the Arctic Ocean and is one of the most important salmon rivers in northern Europe. The bullhead does not belong to the natural fish fauna of the Finnish river systems flowing into the Arctic. It was probably introduced by anglers as bait or accidentally during the water exchange activities as salmon fry were transferred from Finnish hatcheries to northern Norway. A viable bullhead population has dispersed through the River Utsjoki catchment. In 1995 its range extended from the lowest part of the river to a point 43 km upstream. It is highly probable that it has also entered the mainstem of the River Teno.
In 1979, bullheads (Cottus gobio L.) were registered for the first time in the River Utsjoki (70°N, 27°E), a large tributary of the River Tana, which is one of the most important Atlantic salmon (Salmo salar L.) rivers in the world. The bullhead was probably introduced into the river by man. The occurrence of bullheads in the River Utsjoki has raised the question of whether their presence may reduce the production of salmon smolts by occupying, e.g., favourable salmon habitats. The spatial distribution of bullheads and salmon parr was investigated by electrofishing in different river habitats and by gillnetting in 13 lakes in the watercourse. Salmon and bullheads were segregated predominantly along the river reaches, and there was an inverse relationship between the densities of the two species at individual localities. Almost all bullheads (98%) were caught within 50 m of a lake, while they were almost completely absent from typical river reaches which were the principal habitat of salmon parr. Different physical conditions seemed to explain the different densities of salmon parr in the different parts of the watercourse, while the presence of bullheads appeared to have little or no influence. Both salmon parr and bullheads inhabited a number of lakes in the watercourse, coexisting with grayling (Thymallus thymallus (L.)), whitefish (Coregonus spp. ) and burbot (Lota lota (L.)), among other species.
Annual production by the slimy sculpin, Cottus cognatus Richardson, was estimated at 59.4 kg/hectare wet weight for the period July, 1970, to July, 1971, in Valley Creek, Minnesota. Mark-and-recapture population estimates made by electrofishing and aging with otoliths were the bases for determining mean biomass and instantaneous growth rates. Annual turnover ratio, i.e., ratio of annual production to mean standing crop, was 1.2. Unusual silt and turbidity conditions, occurring in 1971, reduced the 1971 year class drastically, but had less serious effects on total production by all age groups. Food of the sculpins was similar in most respects to that of the brook trout inhabiting the same stream. Young sculpins fed heavily on small dipterans, mainly chironomids; older sculpins fed mainly on Gammarus and Trichoptera larvae. Comparisons with annual production estimates for brook (Salvelinus fontinalis) and rainbow trout (Salmo gairdneri), made previously in Valley Creek for comparable time periods, suggested a normal total annual production for all fishes of about 200 kg/hectare, with sculpins contributing about 1/3 and trout about 2/3.
A newly introduced species, the bullhead, Cottus gobio L., was observed for the first time in the River Utsjoki, a tributary of the River Teno, in 1979. The River Teno is one of the most important Atlantic salmon, Salmo salar L., rivers in Northern Europe and its tributary the River Utsjoki is an important salmon spawning and nursery area. The densities of bullhead were lowest in the areas to which the species has spread most recently and highest in the areas downstream of its introduction point. Densities were markedly lower upstream. Statistical analysis showed that the presence of the bullhead had not affected juvenile salmon densities in the River Utsjoki.
Some 72 different animal taxa were recorded in the stomachs of Gadus morhua. Of these 11 taxa made up the principal prey. Deep water prawn Pandalus borealis, capelin Mallotus villosus and small krill Thysanoessa spp. were the most important. The others were the polychaete Nephtys sp., the mysids Erythrops sp. and Michteimysis mixta, the amphipods Arrhis phyllonyx, Halirages fulvocinctus and Rhachotropis macropus, the krill Meganyctiphanes norvegica, and herring Clupea harengus. Krill was probably the only prey taken in midwater. Food diversity was lowest at the mid-fjord station, probably due to smaller environmental variations, a lesser edge effect, and less influence of adjacent prey communities on this large and deep trawling ground.-from Author Gadus morhua prawn Pandalus borealis capelin Mallotus
When relative frequencies of resource kinds in the diet are known, the competition coefficient giving the effect of competitor j on i may be computed as\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage{wasysym} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document}$\alpha_{ij}=\left(\frac{T_{j}}{T_{i}}\right)\left[\frac{{\sum\limits_{k=1}^{m}}(d_{ik}/f_{k})\:(d_{jk}/f_{k})\:b_{ik}}{\sum\limits_{k=1}^{m}(d_{ik}/f_{k})^{2}\:b_{ik}}\right],$\end{document}where Tj/Ti= the ratio of the number of items consumed by an individual of competitor j to that consumed by an individual of competitor i, measured over an interval of time that includes all regular fluctuations in consumption for both species; dik = the frequency of resource k in the diet of competitor i (and similarly for djk); fk = the stan...
At three localities in central Swedish Lapland (approx. 66"N, 16"E), areas of stream bottom were mapped with regard to depth, current and substrate conditions, and the benthic fauna of Ephemeroptera, Plecoptera, Trichoptera and Diptera Simuliidae was sampled in spring and autumn. The three environmental factors were found to be variously associated with each other, three combinations being dominant. The distri- bution of the benthic species was compared with these combinations, and it was found that most species showed a significant over-representation at sites characterized by one of these complexes. An attempt was made to establish which of the three factors was the most important for the different species. This analysis was complicated by the association between the environmental factors, but certain conclusions could be drawn from interspecific comparisons. Substrate is an especially important determinant of the life conditions of the fauna; besides other functions it usually has to provide food for the animals. Benthic species select their habitats on the basis of factor combinations, rather than isolated factors; in this interplay of environmental factors food was found to have a dominant influence in the biotope investigated. B TpeX M~CTOO~UT~HURX ueHTpanbH08 UB~A- CKOP nanna~nzi~ (npU~epH0 66" C.m. U 16"B.&) YTaCTKU C IIpUnOHHbIM TeYeHUeM KapTklpOBaHbI; y~asaab~ rny6u~a, TereHuR u xaparcrep cy6c~- pala. Bec~oP u oceHbm Uccnenosanacb ~~HTO- cHas @ay~a Ephemeroptera. Plecoptera, Trich- optera U Diptera-Simdiidae. Tpw w3yre~~ble @aKTopa CpenbI TeCHO CBR3aHbI MeXnY ~0608. B UCCJIenOBaHHbIX TO9KaX BbIneneHO TpU TUna ~ec~oo6~~a~u8, pa3JIUYaIoLLlEiXCR KOMnJIeKCOM ycno~u8 cywecTBosaHuR. El3y~e~~e pacnpenene- HUR ~~HTOCHO~ nOKa3an0, 'lTO ~OJI~LTIUH- 4ay~b1 CTBO BUnOB IIPUYPOqeHO K YYaCTKaM C OnHUM
Dietary components of Mississippi silversides (Menidia audens) and juvenile largemouth bass (Micropterus salmoides) were tabulated by the percentage of occurrence, the percentage of total number, the percentage of total volume, the average of the volume percentages, and the relative importance index. Each of these diet measures was then applied to three published overlap indexes and a correlation method (Spearman rank correlation coefficient). Each measure of diet resulted in different values for a particular overlap index (0.04 to 1.06) and for the Spearman rank correlation coefficient (0.06 to −0.30). Likewise, each index gave different values for different diet measures. Of these indexes and diet measures, the Schoener index based on the average of volume percentages is recommended with reservations.
The impact that predators have on invertebrate prey density in running waters is the subject of debate. Some studies show strong effects of fish predation on benthic prey density whereas others show little or no effects. Recent reviews discuss different factors that affect interactions between predators and invertebrate prey. These include differences in enclosure size, mesh size, predator densities, small sample sizes and the role of invertebrate predators. We suggest the complementary hypothesis that vertebrate predators used in experiments differ in foraging methods. Some predators feed primarily on benthic prey (e.g. sculpins, blacknose dace, creek chub, darters) whereas other predators feed on both drift and benthic prey (predominantly salmonids). Potentially, if the amount of drifting terrestrial animals is large, the impact of drift-feeding fish on the benthic community should be low. We conducted a mete-analysis on the results of field studies that manipulated these two types of predators and found that benthic feeding predators have significantly larger impacts on benthic prey than drift feeding predators. Four methodological variables, mesh size, size of enclosures, duration of experiments, and predator density were analysed to determine whether these could explain the differences between studies involving benthic and drift feeding predators. No correlations existed between any of these four methodological variables and predator impact, indicating that the difference was not due to methodological differences between experiments.
Populations of sculpin (Cottus cognatus) were altered to create stream sites with increased and decreased fish density. Subsequently, the response of benthic insect species was observed. Sculpin predation appeared to have little or no effect on size distributions and secondary production of most benthic invertebrates. However, densities of some trophic groups increased by two- or three-fold following reductions of sculpin densities. Within sites of sculpin removal, densities of gatherer/scrapers were twice those of addition or reference sites. Densities of total insect populations in reduction or reference sites were two to three times greater than those in the addition sites. Several trophic groups, particularly scraper/gatherers, showed the highest densities in sites of unaltered sculpin densities. Filter-feeders presented a third response to the manpulated sculpin populations; their densities increased with increased sculpin density. This suggests a negative sculpin influence on competitors of filterers.
From 25 July to 11 September 1984 Atlantic salmon, Satmo salar L., parr were observed underwater between 0800 and 1600 h, feeding actively from defended territories at two sites in the River Tilt, Perthshire, Scotland. Territories comprised one or more preferred stations on or just above the substrate, from which the fish intercepted drifting particles (75% of feeding), or foraged on the substrate (25%). Drift feeding occurred 36% at the surface, 35% in mid-water and the remainder at the feeding station. 35% of prey particles were attacked directly from the feeding station, and 65% indirectly after preliminary inspection, sometimes involving a drift downstream by the fish. 20% of captures were made upstream of the station and 80% downstream. 12–15-cm fish fed more frequently at the surface, while 10-cm fish fed in mid-water or at their stations. Surface feeding decreased proportionately during rainfall. Frequency of feeding increased with temperature. Feeding was depressed in the presence of large salmonids.
Abstract– Food resource partitioning between Siberian sculpin (Cottus poecilopus) and Atlantic salmon parr (Salmo salar) was investigated throughout a summer season in the subarctic River Reisa, northern Norway. The two species had almost identical diets, feeding primarily on benthic invertebrates and selecting the same prey species. There was no strong segregation in the diel feeding rhythms of the two species, although the salmon parr consumed a large proportion of their food at night during August and September. The results suggest that the two species compete for food, and that interspecific competition for limited food resources may explain the low production of Atlantic salmon in this river. The observation of a high degree of dietary overlap between the sculpin and the salmon parr contrasts with expectation of interactive segregation. Further, the findings conflict with general niche and competition theories, being inconsistent with the competitive exclusion principle.
Abstract— Available food and feeding of Atlantic salmon parr were studied in different parts of a subarctic river in northernmost Finland, the River Teno: in the large main stem, in a major tributary influenced by lakes, and in two minor tributaries. The highest density of benthic organisms was found in an outlet of a lake, but drifting organisms were the most abundant in the small tributaries. Migrant parr that move to the small tributaries from the main stem have better food resources in their new habitat. Plecoptera nymphs were the most important prey for salmon parr early in the spring. Later in the summer dipterans were usually the dominant prey group. In September the importance of Plecoptera was emphasized in the small tributaries and the lake outlet, and that of Trichoptera in other sites. Drifting prey was used more by large than by small parr. The utilization of drifting food appeared to be related to the water temperature rather than to the availability of the drift.
During the ice-free season in three subarctic rivers in northern Norway and Finland, Atlantic salmon parr Salmo salar exhibited significant diel fluctuations in stomach content weights in August and September, the largest weights being recorded consistently at 0300 hours. Accordingly, the feeding rate of the parr was highest during the night and lowest in daytime, whereas during the other periods of the ice-free season, no pronounced diel fluctuations in food intake occurred. The consistent nocturnal feeding periodicity in early autumn in subarctic rivers may be associated with benthic feeding and an increased availability of benthic prey at night.
Stream fish faunas are being increasingly subjected to non-native fishes. Successful establishment of non-native forms varies widely between geographic regions (38–77%), but is generally greater in areas that are either altered by man or initially depauperate in fish species. While such introductions have generally had undesirable effects on native fish species, they show no signs of decreasing. Thus, this essay is an attempt to determine if the introduction of non-native fishes may provide insights into processes structuring stream fish assemblages. There are, unfortunately, few detailed ecological studies documenting the response of stream fish assemblages to introduced fishes. Of the 31 studies included in my analysis, the majority (77%) documents a decline in native fishes following the introduction of exotic or transplanted forms. Only 10 studies examined shifts in resource use, of which 5 documented or suggested shifts in habitat. Overall, the responses of native stream fish assemblages to non-native fishes suggest that biotic interactions are important in structuring the impacted assemblages, being implicated in 62% of the studies. Proposed or demonstrated mechanisms are divided equally between competition and predation. Unfortunately, pre-disturbance data are generally lacking so that processes important in structuring native fish assemblages cannot be determined.
I assessed the impact of both drift-feeding (Salmo trutta, brown trout) and benthic-feeding (Cottus gobio, bullhead) fish on a benthic assemblage during a 1-month-long field experiment. I used enclosures containing cobble/gravel
substrata with 6-mm mesh net that allowed invertebrates to drift freely in and out of enclosures. Four treatments, arranged
in a factorial design, were tested: a predator-free control, bullheads only (2.67 bullheads/m2, two per enclosure), brown trout only (2.67 brown trout/m2, two per enclosure), and bullheads and brown trout together (2.67 fish/m2, one of each). Bullheads reduced the densities of seven invertebrate taxa (Gammarus pulex amphipods, Baetis rhodani mayfly nymphs, Leuctra spp. stonefly nymphs, Polycentropus spp. caddis larvae, Pacifastacus leniusculus signal crayfishes, Simuliidae, blackfly larvae, and Limnephilidae, caddis larvae) whereas brown trout only affected one taxon
(B. rhodani). The weaker effect of brown trout on benthic prey was probably related to its heavy reliance on terrestrial prey. Dietary
analyses showed that more than 80% of prey consumed by brown trout were terrestrial animals, whereas bullhead only consumed
benthic prey. Neither bullhead nor brown trout affected the absolute number of immigrating or emigrating invertebrates in
enclosures, but bullhead affected the per capita emigration rates of G. pulex. Direct predation by bullhead was more important than avoidance behaviour (drift) in determining densities of six of the
seven taxa; only G. pulex densities were equally affected by avoidance behaviour and direct predation. Direct predation by brown trout was also more
important in determining densities of B. rhodani. The presence of bullhead raised periphyton biomass, presumably mediated via their consumption of grazers. Brown trout had
no effect on periphyton biomass and these results indicate that the presence of alternative prey, in this case terrestrial
animals, may have repercussions for fish-benthic macroinvertebrate-periphyton interactions and may potentially explain some
of the variable impacts of fish on benthic macroinvertebrates that have been reported in the literature.
Brown trout (Salmo trutta L.) and sculpin (Cottus gobio L.) predation on the cased limnephilid larvae Glyphotaelius pellucidus (Retz.) (weak, broad leaf case), Limnephilus pantodapus McLachl. (weak, long cylindrical leaf case), L. rhombicus (L.) (rigid, hedgehog case) and Potamophylax cingulatus (Steph.) (rigid, cylindrical mineral case) was studied in the laboratory. The proportion of larvae ingested was significantly higher in brown trout than in sculpin for all four prey species. Brown trout captured larvae of all four species with equal success, but the higher number of unsuccessful captures resulted in a higher survival rate for P. cingulatus. It was significantly more difficult for sculpin than for brown trout to capture L. pantodapus larvae and to ingest all species except L. rhombicus. P. cingulatus larvae were never ingested by sculpins, and had the highest survival rate after capture by both fish species. In brown trout, the handling time of L. pantodapus was significantly longer than that of P. cingulatus. Sculpin had a significantly longer handling time of G. pellucidus than brown trout. L. pantodapus and L. rhombicus larvae feigned dead significantly longer than did those of G. pellucidus and P. cingulatus upon attacks from sculpins. L. rhombicus larvae also feigned dead for a long time upon attacks from brown trout. The survival rate of a larva attacked by sculpin or brown trout depends on both case rigidity as well as its behaviour. Brown trout was a more successful predator of cased caddis larvae than sculpin.
We tested the role of the slimy sculpin (Cottus cognatus), a benthic fish, in structuring the rocky littoral invertebrate community in Toolik Lake, Alaska. Comparisons of sculpin
gut contents and prey community structure indicated that these fish forage selectively, eating proportionally more large and
motile prey, and proportionally fewer small and sessile forms. Field experiments compared the effects of natural, reduced
and elevated sculpin densities on benthic community structure. At natural levels of sculpin density, biomass of trichopteran
larvae were reduced by more than 50%, and predatory chironomid larvae by 27%, in comparison to areas where sculpin were excluded.
Tube-dwelling and small free living chironomid larvae were unaffected at normal sculpin densities. Under artificially high
sculpin densities, there was some reduction of tube-dwelling chironomids, but the small free living ones remained unaffected.
There appears to be a threshold length of about 3.5 mm, below which chironomid larvae are free form sculpin predation. Tube-dwelling
chironomids may be longer than this threshold, but still avoid predation by having most of their body hidden in their tubes.