Small Charr Research Articles

Habitat segregation by sympatric juvenile Arctic charr and brown trout in shallow lake areas: a consequence of interspecific differences in predator avoidance?

In sympatry, juvenile brown trout (Salmo trutta) usually occupy the shallow and most productive areas (littoral zone) of lakes, while juveniles of Arctic charr (Salvelinus alpinus) are found in deeper, less productive parts. In contrast, when Arctic charr juveniles occur in allopatry, they often occupy shallow littoral areas as well. Habitat segregation has traditionally been interpreted as a trade-off between predation risk and energy gain, while the segregation of these two species has been explained by brown trout being more aggressive and competitively superior to Arctic charr. We hypothesize, however, that the marked habitat segregation between the two species may also be due to differences in predator avoidance. Accordingly, we conducted several laboratory tests, using Arctic charr and brown trout as potential predators. Live fish of the same species were offered as prey, either as small charr only, small trout only, or both small charr and small trout together. Artificial shelters were then introduced to examine the avoidance ability of prey fish against predatory fish. Our results showed that under these circumstances, access to shelters strongly decreased mortality in juvenile brown trout, but had no effect on juvenile Arctic charr mortality. Thus, the habitat segregation shown by sympatric juvenile Arctic charr and brown trout in lakes may be a consequence of interspecific differences in predator avoidance.

Three sympatric forms of Arctic charr Salvelinus alpinus complex (Salmoniformes, Salmonidae) from Lake Kamkanda, Northern Transbaikalia

We studied morphology, size and age structure, growth, feeding, and variation at microsatellite loci of three forms of Arctic charr Salvelinus alpinus complex (dwarf, small, large) from mountain Lake Kamkanda in River Olekma basin, northern Transbaikalia. The forms differ in meristic and morphometric characters, external appearance and size. The small form distinctly differs from the dwarf and large forms in higher number and length of gill rakers. The forms differ in growth rate; however, differences in growth between the dwarf and the small forms are not as large as between sympatric dwarf and small charr from other Transbaikalian lakes. The large form is heterogeneous in growth rate. The small form matures one year earlier than the dwarf form and has a shorter life span. The dwarf form is a benthophage, the small form is a planktophage, and the large form is a predator. The dwarf form spawns in September, while the small form spawns in November-December, and there is no overlap in their spawning time. The three forms have clear genetic differences, which support their reproductive isolation. It is assumed that the three forms of Arctic charr originated within Lake Kamkanda on the basis of trophic polymorphism and spawning time displacement and attained a high degree of morphological and genetic divergence.

Extant and extinct forms of arctic charr Salvelinus alpinus (L.) complex from the Leprindo lake system (Transbaikalia): Differentiation in life history, morphology, and genetics

Interconnected lakes Bol’shoe Leprindo and Maloe Leprindo in Transbaikalia hosted large (extinct) and dwarf charr forms. Rarely “small” individuals intermediate in size between these forms are caught. In order to assess morphological, ecological, and genetic differentiation of sympatric charr forms and parapatric charr populations we studied their meristic and morphometric characters, feeding, breeding, and growth; we also investigated variation at 8 microsatellite loci using DNA isolated both from contemporary and historic samples. Profound differences were found between large and dwarf charr in growth rate, feeding (piscivores and highly specialized zooplanktivores, respectively), spawning time, and morphology. Dwarf charr from the two lakes demonstrate minor differences in morphology and growth rate. “Small” individuals are morphologically similar with dwarf charr and spawn together with them, they are recruited from dwarf form in late ontogeny as the result of transition to piscivorous feeding and growth acceleration. Microsatellite analysis showed that: (1) large and dwarf charr forms display high degree of genetic differentiation and reproductive isolation; (2) dwarf charr from interconnected lakes belong to different isolted populations; (3) “small charr” are genetically identical with dwarfs. The degree of ecomorphological and genetic differentiation between large and dwarf forms places charr from Leprindo Lakes among the most strongly differentiated Arctic charr forms’ flocks known at the vast range of S. alpinus complex.

Plasticity in probabilistic reaction norms for maturation in a salmonid fish

The relationship between body size and the probability of maturing, often referred to as the probabilistic maturation reaction norm (PMRN), has been increasingly used to infer genetic variation in maturation schedule. Despite this trend, few studies have directly evaluated plasticity in the PMRN. A transplant experiment using white-spotted charr demonstrated that the PMRN for precocious males exhibited plasticity. A smaller threshold size at maturity occurred in charr inhabiting narrow streams where more refuges are probably available for small charr, which in turn might enhance the reproductive success of sneaker precocious males. Our findings suggested that plastic effects should clearly be included in investigations of variation in PMRNs.

Cannibalism in Arctic charr: do all individuals have the same propensity to be cannibals?

By comparing large Arctic charrSalvelinus alpinus, which had shown a persistent cannibalistic response varying from zero to very high in succeeding laboratory trials, with their individual cannibalistic behaviour after release into a natural lake inhabited by small Arctic charr, it was found that all Arctic charr had the potential to become cannibalistic, irrespective of their laboratory behaviour. More specifically, Arctic charr that never fed on prey fishes when offered them in the tank experiments turned to cannibalism when released in the lake, highlighting the potential difficulties in extrapolating laboratory results to natural settings. This was also true for naive fish that had no prior experience of eating live food. Since no significant increase in the number of prey consumed during each of the succeeding laboratory trials was found, and naive fish showed a response under natural conditions similar to that of their counterparts, the training of the Arctic charr (or experience or learning) probably had no effect upon the piscivorous or cannibalistic response after stocking. Thus, the study appeared to demonstrate that most variations in cannibalism in Arctic charr was simply a function of environmental conditions, depending on the density of conspecificsv. alternative prey, and the relative size difference between predator and prey, rather than any genetic influence.

Seasonal and ontogenetic patterns in the migration of anadromous brook charr (Salvelinus fontinalis)

Migration patterns of brook charr (Salvelinus fontinalis) from the Sainte-Marguerite River, Québec, Canada, were investigated to explore the hypothesis that migratory behaviour changes according to size during the critical period of first downstream migration, when survival is likely to be related to size, and during subsequent seasonal movements. We hypothesized that as fish grow, they should adopt more conservative behaviours to protect the reproductive assets that they have accumulated. First downstream migration occurred over a month in spring. Larger juvenile charr migrated early, whereas smaller charr seemed to delay offshore migration. As predicted, migratory patterns of charr changed through ontogeny. Sea age 0 juveniles stayed in estuarine areas until October and overwintered outside their natal river. Sea age 1 juveniles returned to their natal river earlier in the fall and some of them overwintered there. Adults (some sea age 1 migrants and older migrants) undertook their upstream migration to spawning areas from July to September, larger ones migrating earlier than smaller ones. Postspawners migrated downstream after reproduction or overwintered in the river. Environmental differences related to geographical location may be responsible for the variation of migration patterns and other life-history traits observed among brook charr populations, emphasizing the co-evolution of anadromy and life history.

Takvatn Through 20 Years: Long-term Effects of an Experimental Mass Removal of Arctic Charr, Salvelinus Alpinus, From a Subarctic Lake

Between 1984 and 1989, the experimental removal of 31 tons (666 000 fish) of stunted Arctic charr, Salvelinus alpinus, from Takvatn in northern Norway, had strong effects on the populations of Arctic charr, brown trout, Salmo trutta, and three-spined sticklebacks, Gasterosteus aculeatus. The littoral catch per unit effort (CPUE) of charr had decreased by 90% in 1990 and then increased to about 50% of the initial level by 1994 while the pelagic CPUE had decreased to zero. Growth in both charr and trout greatly improved when the charr density had decreased, and large fish of both species appeared in the catches. These large fish became predators on small charr in the littoral zone. The incidence of trout increased from below 1% to 15% from 1988 to 1999 after a brief peak at 30% in 1992 and 1993. The charr population attained a bimodal size distribution and did not return to the stunted state during the 10 years following the intensive fishing period. The mass removal experiment showed that it is possible to change the structure of a charr population by intensive fishing. Predation on small charr from cannibals and large trout was probably essential for maintaining the new population structure. An increase in the growth of young charr from 1995 to 1997 was related to a high consumption of Daphnia and Eurycercus. Rapid changes in the growth of charr followed the density fluctuations in sticklebacks, which show large annual variations in this system; the rapid changes in charr growth were probably caused by variations in the competition intensity for cladoceran prey between young charr and sticklebacks. Twenty years of data has provided important information, but even more time is needed to follow the long-term trends in northern lakes such as Takvatn.

Behavioural responses of naive Arctic charr young to chemical cues from salmonid and non‐salmonid fish

The ability to distinguish among chemical cues from multiple predators is of key adaptive value for many prey fish. We examined the attractiveness and repulsiveness of chemical stimuli from different coexisting fish species fed on different diets on the behaviour of hatchery reared Arctic charr young in a Y‐maze fluviarum, where the charr could choose between two sides either with control water or stimulus water with fish odour. We used stimuli from (1) matching sized conspecifics, large (2) Arctic charr, (3) salmon, (4) brown trout and (5) brown trout fed on Arctic charr fry. Other salmonids were given pellet food. Additional fish odour treatments included piscivorous (6) pike and (7) burbot. In the control trials both sides received control water. Arctic charr young were expected to respond adaptively to the stimuli from coexisting piscivorous fish. The charr most strongly preferred water with the odour of their matching sized conspecifics, which was the only fish odour they were familiar with before the experiments. They also showed significant preference for other salmonid odours, even though these fish are potential predators on small charr. Chemical stimuli from pike and burbot, on the contrary, were strongly avoided, and burbot odour even prevented the charr to swim and enter the lateral halves of the fluviarum. Moreover, odour from brown trout fed on Arctic charr fry was avoided when compared to stimuli from trout fed on pellets. Although the Arctic charr young were completely naive regarding piscivores, the fact that they could distinguish between different predator taxa and diets on the basis of chemical cues only reflects the long coevolutionary history of these fish populations.

Experimental evidence of cannibalism and prey specialization in Arctic charr, Salvelinus alpinus

Use of a radiographic technique enabled the study of prey selection and individual specialization in Arctic charr, Salvelinus alpinus, fed with small charr and dry pellets under laboratory conditions. Both naive and experienced fish (mean weight 475 g, mean length 34.9 cm), selected the smallest individuals when offered juvenile charr (6–16 cm) as prey. The selected prey were, on average, 22% of the predator length. Cannibalism appeared to involve individual specialization, since when groups of large charr were given the opportunity to feed on juveniles one day every two weeks, the same individuals were cannibalistic throughout the sampling period of two months. When large charr were presented with alternate cycles of different food types consisting of dry pellets and fish prey, the charr exhibited a strong and consistent feeding specialization with three distinct groups being recognised: cannibals, pellet eaters and non-feeding fish.

Food resource partitioning of Arctic charr, Salvelinus alpinus (L.) and three‐spined stickleback, Gasterosteus aculeatus L., in the littoral zone of lake Takvatn in northern Norway

AbstractThe food resource partitioning of Arctic charr (Salvelinus alpinus L.) and three‐spined stickleback (Gasterosteus aculeatus L.) were investigated in the littoral zone of lake Takvatn in northern Norway in the ice‐free period June–November. Charr and sticklebacks had different feeding habits. Sticklebacks ate several small benthic prey items that were never eaten by charr, and the sticklebacks' diet were dominated by the benthic microcrustaceans Chydoridae and Ostracoda, chironomid larvae and stickleback eggs. Small charr (<17 cm) consumed a wide spectrum of chironomid pupae, terrestrial insects and zooplankton. Intermediate (17–20 cm) and small charr had quite similar feeding habits, while large charr (>20 cm) frequently ate both benthos, pelagic and terrestrial food. The diet overlap between small charr and sticklebacks was never larger than 0.6 (Schoener's index). The segregation in feeding habits indicates that small charr and sticklebacks are segregated in microhabitat when they are both in the littoral zone.

Salinity tolerance of freshwater acclimated, small‐sized Arctic charr, Salvelinus alpinus from northern Labrador

Arctic charr, Salvelinus alpinus, less than 150 mm in size were frequently captured at sea in northern Labrador in areas where salinities of 30‰ or higher had been recorded. These captures were inconsistent with many earlier reports for other areas that indicated Arctic charr less than 150 mm in size were not found at sea. A series of salinity challenge tests was carried out in the field, using wild Ikarut River charr, and in the laboratory, using cultured Fraser River charr, to understand more about the potential fate of these small fish. The results of challenge tests with small Arctic charr (< 120 mm) indicated that at intermediate salinities (10–20‰), these fish can readily survive. In laboratory tests with salinities at 30‰, survival was size dependent and would suggest that in natural situations, small charr would require periodic access to fresh or brackish water to stay alive. The influence of water temperature on salinity tolerance may be important when fish are exposed to temperatures that are below 0° C.

Bénéfices à court terme des mouvements anadromes saisonniers pour une population d'omble de fontaine (Salvelinus fontinalis) du Nouveau Québec

This study characterizes the seasonal anadromous movements of a brook charr population and compares its biological and energetic characteristics with charr spending summer in freshwaters. Downstream movements monitored at a counting fence over 3 yr were most intense in spring but occurred until fall and were positively correlated with rapid increases of water level. The timing of movements varied from year to year. Smaller charr were most subject to being swept downstream compared with freshwater residents, and most trout were concentrated near the mouth of the river. These patterns suggest that the downstream movements of charr in this system are passive. Upstream migrants had a higher condition factor and a lower tissue water content than freshwater residents, indicating that downstream movements result in a faster accumulation of energetic reserves during summer. However, the fortuitous character of anadromous migrations as well as the absence of differences in the biological characteristics (growth, size at maturity, fecundity, egg size) suggests that anadromous and resident fish belong to a single population whose yearly migrant component could be randomly determined.

The population, survival, growth, reproduction and food of arctic charr, Salvelinus alpinus (L.), in four unexploited lakes in Greenland

The material comprised 1205 arctic charr caught by gillnets and electrofishing in the ice‐free season 1982 in four interconnected lakes. The lakes were similar in biotic and abiotic factors and the arctic charr populations were therefore treated as one population. Two size groups of fish older than three years, called ‘small charr’ and ‘large charr’, were found. The two groups differed in feeding habits, growth rates, age of maturity and spawning frequencies. However, they did not differ in the frequencies of the F‐ and S‐ serum esterase alleles, and were in accord with the model proposed by Johnson (1976) which states that the ‘small charr’ and ‘large charr’ are two different forms of the same population. ‘Small charr’ recruit to the ‘large charr’ by entering a period of fast growth. In the investigated lakes this occurred when the ‘small charr’ were 3–10 years old. Some indications of rematuration of the ‘small charr’ when entering the group of ‘large charr’ were found.

Life history and movements of anadromous brook charr, Salvelinus fontinalis, in the St-Jean River, Gaspé, Quebec

A comparison between an anadromous and a freshwater lake population of brook charr showed that anadromous charr had a lower mean length at age 2+ and 3+, a greater longevity, a greater maximal length and a greater length and age at first maturity than the freshwater population. A biased sex ratio towards females occurred only in the anadromous population. The first 2 or 3 years in the life cycle of anadromous charr is spent in the river, followed by an intermediate period of a year in the salt wedge area and then by a 2- or 3-month period in salt water before returning to the river. Bigger charr started upstream migration earlier in the season than smaller charr. Migration peaks in 1979 were synchronized with the new moon. Fish movements in the estuary were greater during spring tides than neap tides. Diel activity was highest in the day in the estuary whereas the inverse situation occurred in the river. From tags returns, it was concluded that anadromous brook charr had a strong homing tendency.