Life history invariants,age at maturity and the ferox trout

Summary Data on brown trout in Norway and on Arctic char in Norway, Iceland, Greenland or Canada are used to make three points about life-history invariants. First, invariants constructed from adaptive programmes of development that are conditioned on growth and mortality rates are more complicated than those constructed solely on the basis of dimensional analysis, but are more consistent with the data. Second, if one allows the possibility of escaping a size ceiling (e.g. by switching from planktivory to piscivory) ferox trout — brown trout that are exceptionally large and long lived — are predicted with the theory only if mortality is size dependent and the growth rate on food sources with different asymptotic sizes differs. Third, a successful empirical approach for finding life-history invariants can be more fully understood as the result of adaptive programmes of development.     

Habitat use and life history of brown trout (Salmo trutta) and Arctic charr (Salvelinus alpinus) in some low acidity lakes in central Norway

Habitat utilization and the life history of browntrout Salmo trutta and Arctic charr Salvelinus alpinus were investigated in fivesympatric populations and five allopatric brown troutpopulations in Høylandet catchment, a atmosphaericlow deposition area in Mid Norway. There was asignificant inverse correlation in abundance ofepibenthic Arctic charr and brown trout in theselakes, indicating that the latter species is dominant.The largest numbers of sympatric brown trout andArctic charr were caught in epibenthic habitat. In twolakes, brown trout to some extent also occurredpelagically, while pelagic individuals of Arctic charrwere found in all five lakes. The main food items forboth epibenthic and pelagic brown trout wereterrestrial surface insects and chironomid pupae.Zooplankton was the primary food item for Arctic charrin both habitats. Although the age distribution wasvery different in the populations, neither speciesseem to suffer from recruitment failure. There was nosignificant difference in survival rates betweensympatric populations of brown trout and Arctic charr.We found a significant inverse correlation betweenepibenthic catches of brown trout and the mean weightof 4+ fish, the most abundant age group. However, ifusing weight data for three-year-old fish, no suchrelationship was found for Arctic charr. Brown troutand Arctic charr reached asymptotic lengths of197–364 mm and 259–321 mm, respectively. Both speciestypically reached sexual maturity at age 2–3, and nomaturation-induced mortality was evident. We concludethat fish populations in Høylandet lakes areregulated throughout their lifes by inter- andintraspecific competition.     

Seasonal patterns of growth, lipid deposition and lipid depletion in anadromous Arctic charr

Seasonal patterns of growth, lipid deposition and lipid depletion were studied in anadromous Arctic charr from a north Norwegian population. Samples were collected in late May when fish were migrating between fresh water and the sea, and in mid-July when the fish re-entered fresh water. A sample of maturing fish captured in mid-July was held in captivity until late September to assess lipid mobilization linked to the final stages of maturation. The fish increased substantially in weight during their 40–50-day summer residence in sea water (immatures from c . 300 to 600 g; maturing fish from c . 500 to 800 g), and body lipid stores were increased approximately fivefold. The carcass (head, skeleton and skin) was the major lipid depot, accounting for c . 50% of the total lipid content when the fish re-entered fresh water from the sea. The muscle of the ascending charr contained 35–40% of the body lipids, whereas the gut and liver each held 4–5%. Body lipid decreased 30–40% during the period between the re-entry of the fish to fresh water and spawning; although lipids were depleted from all depots the carcass and muscle were quantitatively the most important. By the time of spawning, the gonads of the females held almost 25% of the body lipid, whereas in the males the gonads accounted for <3% of the total lipids. Females lost c . 80% of their body lipid during spawning and overwintering, and, consequently, the lipid depots were severely depleted by the early spring. By contrast, lipid depletion in the males amounted to 50–55% of total lipid in the same period. These data suggest that the combination of spawning and overwintering in fresh water imposes a greater load on the females than on the males. It may be that the severity of the depletion prevents females from spawning in successive years.     

Development of spinal deformities in Atlantic salmon and Arctic charr fed diets supplemented with oxytetracycline

Some individuals within populations of Atlantic salmon Salmo salar and Arctic charr Salvelinus alpinus fed diets supplemented with oxytetracycline (OTC) developed spinal deformations. Possible differences in feed intake and growth of spinally deformed fish relative to fish without any deformities were investigated. Amongst Atlantic salmon, 17% of the fish fed OTC-supplemented feed developed spinal fractures, whereas none of the fish receiving the basic feed did so. Despite deformation of the spinal column, the injured fish continued to feed and grow, but at lower rates than unaffected individuals. In contrast to Atlantic salmon, Arctic charr showed no signs of spinal fractures at any time during the 65-day experiment.     

Forage digestibility and intake by lesser snow geese: effects of dominance and resource heterogeneity

We measured forage intake, digestibility, and retention time for 11 free-ranging, human-imprinted lesser snow geese (Chen caerulescens caerulescens) as they consumed underground stembases of tall cotton-grass (Eriophorum angustifolium) on an arctic staging area in northeastern Alaska. Geese fed in small patches ( =21.5 m²) of forage that made up 3% of the study area and consisted of high-quality aquatic graminoid and intermediate-quality wet sedge vegetation types. Dominant geese spent more time feeding in aquatic graminoid areas (r=0.61), but less total time feeding and more time resting than subdominant geese. Subdominant geese were displaced to areas of wet sedge where cotton-grass was a smaller proportion of underground biomass. Geese metabolized an average of 48% of the organic matter in stembases and there was a positive correlation between dominance and organic matter metabolizability (r=0.61). Total mean retention time of forage was 1.37 h and dry matter intake was 14.3 g/h. Snow geese that stage on the coastal plain of the Beaufort Sea likely use an extensive area because they consume a large mass of forage and exploit habitats that are patchily distributed and make up a small percentage of the landscape. Individual variation in nutrient absorption may result from agonistic interactions in an environment where resources are heterogeneously distributed.     

The combined effects of ambient temperature and enforced sustained swimming activity on body temperatures of arctic charr (Salvelinus alpinus L.)

1. 1.|The difference between tissue temperatures and ambient water temperatures (ΔT) of the ectothermic Arctic charr (Salvelinus alpinus L.) ranged between 0.2 and 0.6°C.

2. 2.|For fish held at 5.7°C there were no significant differences in ΔT of exercising fish and those of controls.

3. 3.|By contrast, for fish held at 1.7°C sustained exercise led to a significant increase in ΔT of all body compartments compared with fish held in standing water (controls).

4. 4.|It is suggested that Arctic charr are capable of a limited control of metabolic heat exchange between body compartments and surrounding water when subjected to sustained exercise and ambient temperatures <2°C.

The analysis of plant-herbivore interactions between ungulates and vegetation on alpine grasslands in the Himalayan region of Nepal

During FAO Project NEP/85/011 a methodology was developed for His Majesties Government Department of National Parks and Wildlife Conservation (HMG DNPWC) to determine the impact of lifestock and wild ungulates on condition and physiognomy of alpine grasslands and to derive parametrical relationships between livestock/wildlife distribution and grassland condition.Between Nov. 1986 and March 1988 eight surveys, lasting from 2–9 weeks were undertaken in various regions of central and eastern Nepal. The comparison of three climatically similar areas (Hinku-Hongu, Sagarmatha, Langtang) showed significant differences in the condition (e.g. grass cover, grass height, bare topsoil, biomass) and physiognomy (vegetation composition) of alpine grasslands. These differences seemed to be not so much a function of ungulate density, but were mainly determined by grazing duration, i.e. winter grazing as well as topographical features.Overgrazed areas with a decrease of graminees and an increase of unpalatable shrubs (e.g. Rhododendron anthopogon, Berberis sp.) and herbs (Euphorbia wallichii and E. longifolia, Iris sp.) were particularly abundant in the vicinity of villages. Productivity of grasslands seemed to be highest at altitudes between 3400 and 4000 m ab. S.L. Here grass species showed highest coverage, shrubs and herbs only moderate values. Habitat utilisation of lifestock (cattle, water buffalo, yak, hybrids, goats and sheep) as well as of wild ungulates, such as thar (Hemitragus jemlahicus), bharal (Pseudois nayaur), goral (Nemorhaedus goral goral) and serau (Capricornis sumatraensis tahr) were compared. Productivity (biomass and grass coverage) of grasslands could be correlated with thar density.Differences of utilisation patterns between wild ungulates e.g. bharal and thar, but also between livestock and thar suggested, that some form of competitive exclusion is operating. With the increase of wild ungulates in Sagarmatha N.P., due to protection, conflicts with livestock grazing were evident.In tourist areas, changes in the structure of lifestock populations-mainly as a response to tourism-, have lead to decreasing utilisation of high alpine pastures (>4000 m a S.L.). This pattern also reflects human emigration rates of up to 12% annually. Whereas this does not necessarily benefit the upper regions, it does increase grazing problems in lower regions, in particular the grazing of forests.Two examples of stepwise multiple regression analysis are given to detect parametrical relationships between different numbers and combinations of independent variables. Biomass as well as lifestock numbers could be predicted accurately (r=0.70 (0.84), 0.001相似文献   

Protein digestion, growth and food conversion in Atlantic salmon and Arctic charr with different trypsin-like isozyme patterns

Protein digestibility and food conversion were determined in groups of Atlantic salmon ( Salmo salar L.) and Arctic charr ( Salvelinus alpinus L.) with or without the trypsin-like isozyme TRP-2*92 . Determinations were made at two salinities, 0 and 27 ppt; at two temperatures, 6 and 10° C and on large (200 g) and small (30–90 g) fish. The overall digestibility of protein was found to be 81.4±0.2% and was unaffected by the presence of the isozyme or the other variables. The feed conversion ratio of Atlantic salmon possessing TRP-2*92 was observed to be significantly lower with significantly higher specific growth rate than in fish without this isozyme.     

The effect of temperature fluctuations on oxygen consumption and ammonia excretion of underyearling Lake Inari Arctic charr

Underyearling Lake Inari Arctic charr Salvelinus alpinus were acclimated to 11·0) C for 3 weeks, and then one group was maintained at 11·0) C and others were exposed to 14·4) Cconst, 17·7) C_const or a diel fluctuating temperature of 14·3° C ± 1° C (14·3° C_fluc). Routine rates of oxygen consumption and ammonia excretion were measured over 10 days before the temperature change and over 31 days following the change. Measurements were made on fish that were feeding and growing. The temperature increase produced an immediate increase in oxygen consumption. There was then a decline over the next few days, suggesting that thermal acclimation was rapid. For groups exposed to constant temperature there was an increase in oxygen consumption ( M _accl, mg kg⁻¹ h⁻¹) with increasing temperature ( T ), the relationship being approximated by an exponential model: M _accl= 46·53e0·^{086 T} . At 14·3° C_fluc oxygen consumption declined during the 3–4 days following the temperature shift, but remained higher than at 14·4° C_const. This indicates that small temperature fluctuations have some additional influences that increase metabolic rate. Ammonia excretion rates showed diel variations. Excretion was lower at 11° C_const than at other temperatures, and increases in temperature had a significant effect on ammonia excretion rate. Fluctuating (14·3° C_fluc) temperature did not influence ammonia excretion relative to constant temperature (14·4° C_const).     

Sex steroids, growth and condition of Arctic charr broodstock during an annual cycle

Changes in plasma concentrations of sex steroids, growth rate and condition of repeat spawning (3+) male and female Arctic charr were studied throughout an annual reproductive cycle. Individually marked fish (mean weight approx. 500 g) were held under conditions of liberal food supply, constant temperature (4° C) and simulated natural photoperiod (Tromsø, 70° N). Once each month fish were weighed, measured and blood samples taken for steroid analysis. Plasma concentrations of testosterone (T), 11-ketotestosterone (11-KT) and oestradiol-17β (E₂) were determined using radioimmunoassay (RIA). Both male and female fish displayed distinct seasonal changes in plasma concentrations of sex steroids, growth rate and condition. From February (minimal concentrations) to March all sex steroids increased slightly and these elevated concentrations were maintained until May. Thereafter, there was a second, and far more pronounced, increase in plasma steroid concentrations which culminated in peak steroid concentrations in September–October. There was then a rapid decline during the spawning period. In winter, growth rate and condition were generally low, then increased during the spring, reached a peak during the summer, and then declined with the onset of autumn. During spring (March–May), the frequency distributions of plasma testosterone concentrations in both male and female fish were bimodal. The fish of the upper modal group of the distribution had significantly higher growth rates and condition than those in the lower modal group. In summer and early autumn (June–September) the association between T and growth rate changed. Significant negative correlations between T and growth rates were observed in females. There was an increase in endocrine activity, indicated by elevated plasma sex steroid concentrations in March, 7–8 months prior to maturation. It is suggested that this may be one factor influencing the onset of spring growth and energy deposition among maturing charr.