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1.
Vincenzi S, Crivelli AJ, Jesensek D, De Leo GA. Detection of density‐dependent growth at two spatial scales in marble trout (Salmo marmoratus) populations.
Ecology of Freshwater Fish 2010: 19: 338–347. © 2010 John Wiley & Sons A/S Abstract – Density‐dependent body growth has often been observed in freshwater salmonid populations. Several studies suggest this compensatory pattern as a potential mechanism of population regulation. The choice of the spatial scale is important for the detection of density‐dependent growth, as study areas need to be of the appropriate size to capture the density of conspecifics actually experienced by individuals over the preceding growth period. Here, we used four marble trout (Salmo marmoratus) populations (Gatsnik, Gorska, Huda and Zakojska) living in Slovenian stream to study the relationships between early density of marble trout and subsequent body growth. As streams are divided in sectors delimited by natural barriers that prevent or strongly limit movement of individuals, we tested the relationship between early density and body size through the lifetime at two spatial scales, that is, sector level (for Gatsnik and Zakojska) and whole stream level (the four populations were pooled). Sector length in Gatsnik and Zakojska ranged from 113 to 516 m. At both sector and whole stream level, temporal data were pooled. Growth declined significantly with increasing density both at the sector and whole stream levels, and the density‐dependent relationship was described by negative power curves. However, at the sector level the density‐dependent pattern was stronger in Gatsnik, a stream in which fish could move across sectors, than in Zakojska, where upstream movement across sectors is prevented by waterfalls.  相似文献   

2.
Abstract –  The role of endogenous and exogenous factors in regulating population dynamics of freshwater salmonids is still a matter of debate. The aim of the present work was to assess the relative importance of density-dependent and -independent factors in determining the survival of marble trout ( Salmo marmoratus ) yearlings in two populations living in Slovenian streams (Zakojska and Gorska). The investigation was performed by combining a classical life table analysis with Monte Carlo simulation. Size-dependent fecundity was estimated by stripping wild adults in the fish farm. A significant positive relationship was found between length of marble trout females and the number of eggs produced. Egg density was the major determinant of survival from eggs to age 1+ ( σ 0) in both streams. Residuals of the relationship between σ 0 and egg density were positively correlated with rainfall only in Zakojska, probably because, within a certain range, more intense rainfalls increases stream flow and, consequently, suitable habitat for trout. Our study shows how density-dependent and environmental factors can interact to determine the survival of marble trout during the first year of life.  相似文献   

3.
Abstract. A brown trout, Salmo trutta fario L., population in homeothermous stream conditions was investigated in terms of age, length-weight relationship, annual and seasonal growth, changes in seasonal condition and specific growth rates, as management variables. The growth of this species in the stream studied was very good, with the most rapid growth in the first year of its life (15·9cm) when the juvenile trout emerged early (April) from the stream bed. The greatest specific growth rate in length was between birth and the first year of life (182·6%). There was an agreement between the condition factor (K) and the growth rate. The values of K, for the juvenile trout, increased continuously because these mainly resulted from their growth through the year. The growth of the two sexes was similar except for the period from October to February when the growth of males was higher than that of females. Also the growth for both sexes was well described by the Von Bertalanffy growth model. No effect was found on the growth rate of tagged and untagged fish. The density and biomass were low, ranging between 0·008 and 0·035 fish.m?2 and 1·25 and 5·63 g.m2 respectively.  相似文献   

4.
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5.
Determination of the occurrence and importance of densitydependent responses is central to understanding stream trout population dynamics. I propose a conceptual model of growth, based on a distribution of feeding site quality, that considers the effects of density on growth. The site quality model assumes that trout select the best feeding sites available and, as the number of trout increases, they will be forced to use less energetically profitable sites, resulting in decreased growth, but also an increase in variance of size or growth. Results from a 3-year study of a brown trout (Salmo trutta) population show that growth to age 1 was significantly reduced for the 1981 year class, which was about 4 times more dense than other year classes. The reduction in growth was not due to a decrease in the growth of all trout but rather an increase in the number of slower growing fish. These results are consistent with my site quality distribution model and suggest that individual fish growth, the distribution of growth, and the variance of growth rates should be considered in addition to mean size and growth.  相似文献   

6.
We examined individual growth and fatness in the 1975–2002 year classes of Japanese sardine. Samples were collected at the feeding grounds in the Pacific waters off northern Japan during drastic fluctuations in the population in the 1970s to 2000s. Growth rates for ages 1–3 of the 1979–1988 year classes, which included low-recruitment year classes subsisting during the high population levels of the 1980s, were apparently slower than for other year classes. There was no obvious trend when comparing year classes, growth during the first year of life (age 0), and maximum body length (BL) at age ≥5. The condition factors (CF, indicating fatness) for adult sardines of BL ≥19 cm in the 1979–1983 year classes during the maximum population level of the mid-1980s were significantly lower than for other year classes. However, there were no apparent trends in CF variations for small sardines of BL <19 cm. The apparent decreases in growth rate and fatness were strongly related to the cumulative sum of population abundance that each year class experienced. It is thought that insufficient food owing to the density-dependent effect of an abundant population at feeding grounds resulted in a decrease in the growth rate for small-bodied sardines that are investing their energy intake in body growth, and a decrease in fatness for large-bodied adults that are accumulating fat for the next reproduction.  相似文献   

7.
The non‐native rainbow trout (Oncorhynchus mykiss) has been introduced worldwide for angling purposes and has established self‐reproducing populations in many parts of the world. Introduced rainbow trout often have negative effects on the native salmonid species, ranging from decrease abundance, growth and survival, to their local extinction. Assessing the effects of introduced rainbow trout on the native species is thus crucial to better set up conservation programmes. In this study, we investigated the effects of non‐native rainbow trout on the diet of native marble trout (Salmo marmoratus) living in the Idrijca River (Slovenia). An impassable waterfall separates the stream in two sectors only a few hundred metres apart: a downstream sector (treatment) in which marble trout live in sympatry (MTs) with rainbow trout (RTs) and an upstream sector (control) in which marble trout live in allopatry (MTa). Specifically, we investigated using stable isotopes the effects of rainbow trout on dietary niche, diet composition, body condition, and lipid content of marble trout. We found dietary niche expansion and niche shift in marble trout living in sympatry with rainbow trout. Compared to MTa, MTs had higher piscivory rate and showed higher body condition and prereproduction lipid content. Our results indicate that the presence of rainbow trout did not have negative effects on marble trout diet and condition and that changes in dietary niche of marble trout are likely to be an adaptive response to the presence of rainbow trout, and further research is needed to better understand.  相似文献   

8.
The effects of biotic (density‐dependent) and environmental (flow and temperature) factors on the apparent survival, mean length and size variation of a low‐density brown trout population in the juvenile stage, that is, from their first summer (0+) to the end of the second year (1+), were determined. Apparent survival was negatively related to the age class density during the three periods (first summer, first winter and second summer). A significant interaction between the mean flow and 0+ density highlighted a gradient towards strong density dependence acting on fish loss (i.e., mortality or migration) with decreasing summer flow. Conversely, no density dependence was reported at higher mean flows. The mean length was determined by density‐dependent and density‐independent (temperature and flow) factors throughout the study period. The negative relationship between fish length and intracohort density was highly significant during the three periods. The yearling (1+) density was negatively related to 0+ fish length measured after the first summer, suggesting intercohort effects. A positive effect of temperature on fish length was observed. Mean length after the summer seasons (0+ and 1+ fish) was also positively related to mean flow. Fish size variation around the mean measured with the coefficient of variation (CV) increased with increasing 0+ densities, both at the end of the first summer and the first winter. Results suggested that density‐dependent and density‐independent factors acted jointly on apparent survival and growth with a predominance of biotic processes. We discussed the potential implications of density‐dependent regulations on growth and survival for population resilience after catastrophic events.  相似文献   

9.
The importance of survival and growth variations early in life for population dynamics depends on the degrees of compensatory density dependence and size dependence in survival at later life stages. Quantifying density‐ and size‐dependent mortality at different juvenile stages is therefore important to understand and potentially predict the recruitment to the population. We applied a statistical state‐space modelling approach to analyse time series of abundance and mean body size of larval and juvenile fish. The focus was to identify the importance of abundance and body size for growth and survival through successive larval and juvenile age intervals, and to quantify how the dynamics propagate through the early life to influence recruitment. We thus identified both relevant ages and mechanisms (i.e. density dependence and size dependence in survival and growth) linking recruitment variability to early life dynamics. The analysis was conducted on six economically and ecologically important fish populations from cold temperate and sub‐arctic marine ecosystems. Our results underscore the importance of size for survival early in life. The comparative analysis suggests that size‐dependent mortality and density‐dependent growth frequently occur at a transition from pelagic to demersal habitats, which may be linked to competition for suitable habitat. The generality of this hypothesis warrants testing in future research.  相似文献   

10.
Variation in growth and body size during critical life history stages can have important implications for life history schedules and survivorship. For Pacific herring (Clupea pallasii), there is still debate as to whether juvenile body size is governed by density‐dependent or ‐independent processes and few have evaluated whether the relative importance of either process shifts over the course of early ontogeny. We used a unique data set consisting of seasonal measurements of abundance, body size, and spatial distribution within a semi‐enclosed basin of Puget Sound (Washington State, U.S.A.) to measure the relative importance of temperature and cohort abundance on body size at distinct time periods, and evaluated whether density‐dependent habitat shifts might be responsible for density‐dependent growth. Over the 9 years of sampling (2001–2010) midsummer body size was positively related to temperatures experienced during the egg/yolk sac and larval stages and unrelated to cohort abundance. However, fall body size was negatively correlated with abundance and uncorrelated with both midsummer body size and temperature, indicating a shift from density‐independent to density‐dependent control over the course of the growing season. Thus, density‐dependent effects may supplant density‐independent effects exhibited early in herring life history. Our data on spatial distributions of herring and their zooplankton prey indicate that density‐dependent reductions in growth may be explained by density‐dependent habitat shifts that lead to reduce overlap of herring with zooplankton. Evidence of density‐dependent growth in marine fish populations is often attributed to exploitative competition, but our results suggest that these patterns may partly be mediated by density‐dependent distribution expansions in to prey‐poor habitat.  相似文献   

11.
Juvenile walleye pollock of the Japanese Pacific population were collected from the Funka Bay [spawning ground; 16–64 mm fork length (FL)] in spring and the Doto area (nursery ground; 70–146 mm FL) in summer. Hatch dates were estimated by subtracting the number of otolith daily increments from sampling dates, and their early growth was back‐calculated using otolith radius–somatic length relationships. Interannual change of the hatching period was observed during 2000–02, and the peaks ranged from mid‐February in 2000 to early‐April in 2002. In 2000, when a strong year class occurred, early life history of the surviving juveniles could be characterized by early hatching and slower growth in the larval stage (<22 mm length). Higher growth rate in 2001 and 2002 did not always lead to good survival and recruitment success. Even though their growth was slow in 2000, the larvae hatched early in the season had larger body size on a given date than faster‐growing larvae hatched in later season in 2001 and 2002. Bigger individuals at a certain moment may have advantage for survival. The delay of hatching period may result in higher size‐selective mortality, and as a necessary consequence, back‐calculated growth in 2001 and 2002 could shift towards higher growth rate, although abundance of such a year class would be at the lower level. Variability in spawning period, early growth and their interaction might have a strong relation to larval survival through cumulative predation pressure or ontogenetic changes in food availability.  相似文献   

12.
Management agencies in several western states of the United States are implementing suppression programmes to control non‐native lake trout, Salvelinus namaycush (Walbaum), for the conservation of native species. This study was implemented to ascertain the population demographics of an expanding lake trout population and use those data to construct an age‐structured model to inform suppression efforts. Population projection matrices were used to model population growth and identify age or stage classes with the greatest influence on population growth. The size and age structure of lake trout sampled was skewed towards juveniles, indicating strong recruitment and a growing population. Matrix‐model simulations corroborated the observed size and age structure, as the lake trout population was predicted to grow exponentially (λ = 1.35, 95% CL: 1.25–1.43) with no suppression efforts. Elasticity analysis of matrix models indicated the relative contribution of survival rates to population growth among immature age classes was equal from age 0 to age at first maturity, but immature survival rates contributed more than adult survival and fertility rates. These results emphasise the importance of targeting juvenile lake trout for suppression efforts during exponential growth in recently established populations.  相似文献   

13.
Large and long‐lived piscivorous brown trout, Salmo trutta, colloquially known as ferox trout, have been described from a number of oligotrophic lakes in Britain and Ireland. The “ferox” life history strategy is associated with accelerated growth following an ontogenetic switch to piscivory and extended longevity (up to 23 years in the UK). Thus, ferox trout often reach much larger sizes and older ages than sympatric lacustrine invertebrate‐feeding trout. Conventional models suggest that S. trutta adopting this life history strategy grow slowly before a size threshold is reached, after which, this gape‐limited predator undergoes a diet switch to a highly nutritional prey source (fish) resulting in a measurable growth acceleration. This conventional model of ferox trout growth was tested by comparing growth trajectories and age structures of ferox trout and sympatric invertebrate‐feeding trout in multiple lake systems in Scotland. In two of the three lakes examined, fish displaying alternative life history strategies, but living in sympatry, exhibited distinctly different growth trajectories. In the third lake, a similar pattern of growth was observed between trophic groups. Piscivorous trout were significantly older than sympatric invertebrate‐feeding trout at all sites, but ultimate body size was greater in only two of three sites. This study demonstrates that there are multiple ontogenetic growth pathways to achieving piscivory in S. trutta and that the adoption of a piscivorous diet may be a factor contributing to the extension of lifespan.  相似文献   

14.
Habitat use, food composition and growth of stocked and native brown trout, Salmo trutta L., were studied in the subarctic Lake Muddusjärvi in northern Finland. Stocked brown trout and native brown trout preferred littoral and pelagic areas. Trout were stocked in October. In June stocked trout fed primarily on invertebrates while native fish were piscivorous. From July onwards the composition of the diet of both stocked and native trout was similar and consisted almost entirely of small‐sized whitefish. Brown trout were already piscivorous at a length of about 20 cm. The mean length of prey consumed was about 12 cm. Mean length‐at‐age was similar from the second year in the lake despite of the larger size of stocked fish during the first year in the lake.  相似文献   

15.
Seasonal patterns in growth, survival and movement of brook trout Salvelinus fontinalis were monitored in two southeastern Minnesota streams divided into study reaches based on brown trout Salmo trutta abundance. We estimated survival and movement while testing for effects of stream reach and time using a multistrata Cormack–Jolly–Seber model in Program MARK. Multistrata models were analysed for three age groups (age‐0, age‐1 and age‐2+) to estimate apparent survival, capture probability and movement. Survival varied by time period, but not brown trout abundance and was lower during flood events. Age‐0 brook trout emigrated from reaches with low brown trout abundance, whereas adult brook trout emigrated from downstream brown trout‐dominated reaches. Growth was highest in spring and summer and did not differ across streams or reaches for the youngest age classes. For age‐2+ brook trout, however, growth was lower in reaches where brown trout were abundant. Interspecific interactions can be age or size dependent; our results show evidence for adult interactions, but not for age‐0. Our results suggest that brook trout can be limited by both environmental and brown trout interactions that can vary by season and life stage.  相似文献   

16.
Many investigators have examined the importance of suitable in‐stream habitat and flow regime to salmonid fishes. However, there is much less known about the use of small (<5 l·s?1 discharge) first‐order streams within a larger stream network by salmonids. The purpose of this study was to evaluate the use of small headwater streams by juvenile brown trout Salmo trutta in the Emmons Creek stream network in Wisconsin, USA, and to determine whether abundance was related to habitat variables in these streams. Fishes in eight spring‐fed first‐order streams were sampled during a 7‐month period using a backpack electroshocker and measured for total length. Habitat variables assessed included stream discharge, water velocity, sediment composition and the abundance of cover items (woody debris and macrophytes). Densities of YOY trout ranged from 0 to 1 per m2 over the course of the study and differed among first‐order streams. Stepwise multiple regression revealed discharge to be negatively associated with trout density in spring but not in summer. All other habitat variables were not significantly related to trout density. Our results demonstrate the viability of small first‐order streams as nursery habitat for brown trout and support the inclusion of headwater streams in conservation and stream restoration efforts.  相似文献   

17.
Arantes CC, Castello L, Stewart DJ, Cetra M, Queiroz HL. Population density, growth and reproduction of arapaima in an Amazonian river‐floodplain. Ecology of Freshwater Fish 2010: 19: 455–465. © 2010 John Wiley & Sons A/S Abstract – Compensatory density effects are key features of fish population dynamics that remain poorly understood in tropical river‐floodplains. We investigated possible compensatory growth and reproductive processes for a river‐floodplain population of Arapaima sp., an extinction‐prone fish species of South America. Body growth was studied through analysis of ring patterns on the scales, and size and age at sexual maturity was studied through analysis of female gonads. Growth and maturity were compared for unmanaged conditions with relatively low population density (in 1990s) versus managed conditions with markedly higher density (in 2005–2006); between 1999 and 2005–2006, abundance increased 7.3 fold. Results contradict theoretical expectations for slower growth and delayed reproduction at higher population density. Total lengths of arapaima at low population density were significantly shorter for age classes 1–5 compared with lengths of those age classes at high population density (ancova , P < 0.0001 for both slopes and intercepts). Total length at 50% maturity (L50) only declined about 4% with increasing density (e.g., 164 cm at low density vs. 157 cm at high density). Apparent faster growth at high density and only a slight change in size at maturity resulted in fishes spawning at an earlier age with high density conditions (age 3 vs. age 4–5). We hypothesise that these patterns reflect compliance with minimum size limits of catch during the high density (managed) situation, where there was no harvest of immature fishes. Compliance with minimum size limits, thus, may have led to faster average body growth rate and earlier reproduction, which has greatly promoted population recovery.  相似文献   

18.
Abstract –  The population density of brown trout ( Salmo trutta ) in a small natural system was manipulated in six equal-length stream sections by stocking hatchery-reared 1+ brown trout (unstocked, tripled and quintupled) over two consecutive years. The results showed that hatchery-reared trout grew more slowly and were more mobile than resident trout, and that their growth was inversely density dependent. In contrast, growth of the resident trout was density independent. The recapture of 1+ resident and hatchery-reared trout was inversely density dependent. This is most likely a consequence of increased competition. However, after a single winter the population density returned to its base level prior stocking and older resident trout showed no density-dependent recapture. Thus, the advantage of stocking, here higher biomass, may have the detrimental effect of decreasing resident stocks of the same size class during summer.  相似文献   

19.
Wood in streams functions as fish habitat, but relationships between fish abundance (or size) and large wood in streams are not consistent. One possible reason for variable relationships between fish and wood in streams is that the association of fish with wood habitat may depend on ecological context such as large‐scale geomorphology. We studied the relationship between salmonid assemblages and large wood jams (LWJ) in four settings that differed geomorphically at the scale of the stream corridor along a tributary to Lake Superior in old‐growth conifer–hardwood forest in northern Michigan. The focal fish species of this study were brook trout (Salvelinus fontinalis), which were wild in the stream. Relocation efforts for coaster brook trout (an adfluvial life history variant of brook trout) were ongoing in the study stream. We measured fish abundance and length in pairs of pools of similar size and substrate, but varying in the presence of LWJ; this allowed us to evaluate associations of fish simply with the presence of LWJ rather than with other channel or flow‐shaping functions of LWJ. The length of Oncorhynchus spp. and young introduced brook trout was not strongly correlated with LWJ presence; however, the presence of LWJ in pools was positively correlated with larger wild brook trout. We also found that the correspondence of LWJ with the abundance of salmonids appears to be moderated by the presence of alternative habitat in this relatively natural, old‐growth forest stream.  相似文献   

20.
Growth rate variation of three age groups of brown trout, Salmo trutta L. (age‐0, 1 and 2, and 3+), was quantified from recaptured, individually tagged brown trout and related to season, stream reach, relative abundance, initial length and movement to examine factors influencing growth in length in three streams in the Midwestern United States. Total variation in growth was almost five times greater for age‐0 than for age‐3+ trout. Individual trout accounted for about 13% of total variation in age‐0 growth, season about 57%, and trout initial length and relative abundance combined another 2%. The 2006 age‐0 cohort had the fastest growth rates in their second spring and summer (2007) and slowest growth in their first winter (2006–2007). About 53% of total growth variation of age‐1 and age‐2 trout was accounted for by individual trout, season, initial length and stream reach. Predicted growth rates indicated strong effects of season and initial length. A significant interaction between these two factors indicated that, although smaller trout grew faster than larger trout, this length effect was most pronounced in spring and summer. About 35% of total growth variation of age‐3+ trout was accounted for by individual trout and season. Together, season and individual trout characteristics were identified as the most important factors influencing brown trout growth in these streams.  相似文献   

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