Seasonal Growth Rates Research Articles

Stable isotope ratios in harbor seal Phoca vitulina vibrissae: effects of growth patterns on ecological records

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 281:267-273 (2004) - doi:10.3354/meps281267 Stable isotope ratios in harbor seal Phoca vitulina vibrissae: effects of growth patterns on ecological records Liying Zhao1,2,*, Donald M. Schell1 1Institute of Marine Science, School of Fisheries and Ocean Sciences, University of Alaska Fairbanks, PO Box 757220, Fairbanks, Alaska 99775, USA 2Present address: UC Davis Stable Isotope Facility, 3112 Plant & Environmental Sciences Bldg, University of California, Davis, California 95616, USA *Email: lyzhao@ucdavis.edu ABSTRACT: Growth rates and patterns of vibrissae (whiskers) in captive harbor seals Phoca vitulina were examined by intravenous infusion of 15N-labeled amino acid tracers to mark their keratinous tissues. The use of vibrissa segmental isotopic analysis as diet indicators was evaluated during controlled feeding trials. Harbor seals shed their vibrissae annually. Replacement of new vibrissae started in May or June, depending on individual seals. Growth rates of new vibrissae were very fast at up to 0.78 mm d-1 during summer and fall, and then changed to a much slower growth rate throughout winter and early spring. An average growth rate of 0.075 mm d-1 was obtained from 1 vibrissa from December to May. δ13C and δ15N values in vibrissae co-varied and reflected temporal variations of diet or habitat changes of seals, particularly over a rapid growth period from late spring to fall. Compared with other tissues such as blood components, vibrissae can be sampled less invasively and archive ecological records over a longer period. Vibrissa segmental isotopic analysis provides a more flexible tool for studying foraging ecology of wild seals, despite the varying seasonal growth rates and annual replacements. KEY WORDS: Vibrissae · Growth patterns · Foraging ecology · Stable isotopes · Pinnipeds Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 281. Online publication date: November 01, 2004 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2004 Inter-Research.

The effect of supplemental food on the growth rates of neonatal, young, and adult cotton rats (Sigmodon hispidus) in northeastern Kansas, USA

Abstract In food-limited populations, the presence of extra food resources can influence the way individuals allocate energy to growth and reproduction. We experimentally increased food available to cotton rats (Sigmodon hispidus) near the northern limit of their range over a 2-year period and tested the hypothesis that seasonal growth rates would be enhanced by supplemental food during winter and spring when natural food levels are low. We also examined whether additional food resources were allocated to somatic growth or reproductive effort by pregnant and lactating females. The effect of supplemental food on growth varied with mass and season, but did not influence the growth rates of most cotton rats during spring and winter. In winter, small animals on supplemented grids had higher growth rates than small animals on control grids, but females in spring had lower growth rates under supplemented conditions. Growth rates of supplemented cotton rats were enhanced in summer. Northern cotton rat populations may use season-specific foraging strategies, maximizing energy intake during the reproductive season and minimizing time spent foraging in winter. Adult females invest extra resources in reproduction rather than in somatic growth. Pregnant females receiving supplemental food had higher growth rates than control females, and dependent pups (≤ 1 month of age) born to supplemented mothers had higher growth rates than those born to control mothers. Increased body size seems to confer an advantage during the reproductive season, but has no concomitant advantage to overwinter survival.

Regulation of spatial and seasonal variation of macroalgal biomass in a brackish, eutrophic lake

Processes leading to biomass variation of Ulva were investigated at two contrasting sites in the eutrophic Veerse Meer (The Netherlands). Ulva species dominated at the Middelplaten site, while at the Kwistenburg site a mixture of Ulva spp. and Chaetomorpha linum dominated. Total summer macroalgal biomass was higher at Middelplaten than at Kwistenburg (282 and 79 g DW m–2, respectively). Growth rates of Ulva spp. were high at both sites in May 1992 (cage mean 0.28–0.30 day–1), but quickly dropped to lower values (0.05–0.10 day–1). In May, growth rates were significantly highest at Kwistenburg, while during the rest of the season growth rates were similar for both sites. Temperature, pH, dissolved oxygen, salinity, light attenuation, phytoplankton and nutrient concentrations did not differ between sites. The relation between variation in Ulva spp. growth rates and environmental parameters was analysed using stepwise multiple regression, showing that light and temperature were the main variables regulating Ulva spp. growth rates. As Ulva growth rates were similar for both sites but biomass was much lower at Kwistenburg it was concluded that a large amount of produced biomass was lost at Kwistenburg. Although the exact reason for this remains unclear, it seems most likely that transport of macroalgae by wind and waves is a very important factor. This study shows the importance of simultaneously measuring growth rates and biomass at a high temporal resolution to reveal the mechanisms responsible for spatial variation in macroalgal biomass in shallow coastal areas.

Rate of growth of isolated bubbles in sediments with a diagenetic source of methane

Observation of bubbles in estuarine and coastal sediments indicates that bubbles at or below 10 cm depth grow on seasonal time scales (May‐October). In order to determine the controls on this growth rate, we have constructed a diffusion‐reaction model that accounts for the dynamics of methane formation, its diffusion through pore waters, its incorporation into a bubble, and the consequent growth of the bubble. The model produces an explicit equation for the radius of a growing bubble, R(t), with time using mean parameter values and under the assumption that the mechanics of the sediment response to growth can be neglected: [equation]. where w is the porosity, D is the tortuosity‐corrected diffusivity, cg is the concentration of gas in the bubble, S is the rate of methanogenesis near the bubble, R1 is the half‐separation distance between bubbles (R1 k R), c1 is the ambient CH4 concentration, c0 is the pore‐water CH4 concentration at R, t is time, and R0 is the initial bubble radius, if not zero. The effects of the source S and supersaturation (c1 2 c0), thus, appear as separate contributing terms, and this formula can then be applied even in those cases where apparently c1 ≈ c0. The model is applied to three sediments where bubbles have been previously studied, i.e., Cape Lookout Bight (USA), White Oak River (USA) and Eckernfoörde Bay (Germany). In all three cases, using the site‐specific time‐averaged parameter values, the model predicts seasonal growth rates, consistent with the observations. Furthermore, the source term dominates the rate of growth at the first of these two sites, whereas diffusion from the ambient supersaturation dominates at the German location. Real bubbles may follow a more complicated growth history than predicted by the above equation because of the mechanical properties of sediments; nevertheless, the overall growth times are concordant with ultimate diffusion control. The effects of rectified diffusion, that is, the pumping of gas into a bubble by pressure oscillations, e.g., from waves and tides, were also examined. Existing models for that process suggest that it is negligible, due to the low frequency of these types of oscillations.

ENERGY ALLOCATION STRATEGY IN YOUNG FISH: ALLOMETRY AND SURVIVAL

We observed substantial variation in seasonal growth rates, autumn body size, and growing-season mortality among eight experimental cohorts of age-0 rainbow trout, Oncorhynchus mykiss. Wet mass, water, lipids (storage), and lipid-free dry mass (structure) had biphasic allometries with inflexions at ∼10 cm in length. Dry:wet mass and storage:structure ratios were positively related to fish length, indicating that the relative quantities of these constituents change with body size. Lipid concentration varied according to a sigmoid relationship with wet mass which also had a growth-rate dependence. Independent assessments of the allometry of growing-season survival and winter metabolism facilitated assessment of the costs and benefits of two alternate energy allocation strategies of young fish. For cohorts with low growth rates and small autumn body size, a somatic growth rate maximization strategy is optimum, producing a 5% net survival advantage over an energy storage maximization strategy. For cohorts with intermediate growth rates and autumn mass, somatic growth and energy storage strategies lead to similar first-year survival. The fastest growing cohorts are estimated to have a net survival advantage of 7%, by adopting an energy storage maximization strategy over a growth rate maximization strategy.

Predição da taxa de gestação de novilhas da raça Nelore acasaladas com um ano de idade

Os objetivos deste trabalho foram quantificar o relacionamento entre variáveis observadas antes da estação de monta e a fertilidade de 321 novilhas e usar tais variáveis no desenvolvimento de equações para predizer a fertilidade das novilhas usando-se metodologia de regressão logística. As variáveis foram: pesos ao nascer, à desmama e a um ano de idade, ganhos de peso diários na pré e pós-desmama e no total, taxas de crescimento relativo (TCR) na pré e pós-desmama e no total, idade da novilha no início da estação de monta (IDCOB) e idade da vaca ao parto. As novilhas que conceberam eram 18 dias mais velhas do que as que não conceberam na estação. As novilhas que ficaram gestantes eram 1,1kg mais leves ao nascer do que as que falharam em conceber. As que tiveram diagnóstico de gestação positivo apresentaram, em média, 0,01% a mais nas taxas de crescimento relativo pré-desmama e total do que as que falharam em conceber. Novilhas que ficaram gestantes eram filhas de vacas mais jovens ao parto e o modelo completo explicou 26,6% da variação na fertilidade delas. A combinação dos efeitos lineares da IDCOB e da TCR total foi o melhor modelo para predizer a fertilidade das novilhas.

Temporal variation in growth rates and reproductive parameters in the small near-shore tropical squid Loliolus noctiluca; is cooler better?

Seasonal growth rates and size- and age-at-maturity were analysed for the small near- shore tropical loliginid squid Loliolus noctiluca off North Queensland, Australia, over a period of 2 yr. Age of individuals was determined using daily statolith increments. The life cycle of L. noctiluca off North Queensland was just over 4 mo. Analysis of growth found that growth was non-asymptotic, and the form of the curve; exponential, linear or log-linear, depended on sex and season that individuals were caught. Winter-caught individuals were the fastest growing and achieved the largest size com- pared with summer or autumn-caught individuals. Furthermore, females grew faster than males dur- ing the winter. The patterns of growth of L. noctiluca were compared between tropical North Queensland and temperate New South Wales. The temperate individuals lived longer and had slower growth rates. There was also a marked seasonal influence on the onset of sexual maturity among the North Queensland population, with the fastest growing winter-caught individuals matur- ing later than the autumn or summer individuals. L. noctiluca has a large latitudinal range from New Guinea to Tasmania, this study, and published work, suggests a trend towards increased lifespan and decreased growth rate with increasing latitude.

Optimization of Dairy Heifer Management Decisions Based on Production Conditions of Pennsylvania

We used a dynamic programming model to determine optimum rearing decisions of dairy replacements. Heifers were described in the model by age, season, body weight, pregnancy state, and prepubertal growth rate. Prices and parameters were chosen to represent the dairy population of Pennsylvania. We calculated monthly costs and revenues from calf value, feed costs, veterinary costs, semen costs, carcass value, and fullgrown heifer value. The model considered a stochastic variation in the onset of puberty, conception, involuntary disposal, and a seasonal variation in the prices of calves, heifers, and feed.Based on a critical prepubertal average daily gain of 0.9 kg/d and a maximum achievable postpubertal growth rate of 1.1 kg/d, the optimum practice resulted in an average age at first calving of 20.5 mo at a body weight of 563kg. Discounted net returns equaled $107 per heifer per year. The optimum rearing practice was not sensitive to seasonal variation in prices. Nevertheless, the economic results per season of birth varied considerably; the highest income per heifer was obtained from heifers born in December ($142/yr), whereas those born in May yielded the lowest ($100/yr).Sensitivity analyses demonstrated a considerable influence of growth rate restrictions and variation in reproductive performance on both the optimal rearing practices as the expected net returns.Key words: heifer rearing, dynamic programming, optimization, Pennsylvania

A modelling study of tropospheric distributions of the trace gases CFCl<sub>3</sub> and CH<sub>3</sub>CCl<sub>3</sub> in the 1980s

Abstract. Interhemispheric transport is a key process affecting the accuracy of source quantification for species such as methane by inverse modelling, and is a source of difference among global three-dimensional chemistry transport models (CTMs). Here we use long-term observations of the atmospheric concentration of long-lived species such as CH3CCl3 and CFCl3 for testing three-dimensional chemistry transport models (CTMs); notably their ability to model the interhemispheric transport, distribution, trend, and variability of trace gases in the troposphere. The very striking contrast between the inhomogeneous source distribution and the nearly homogeneous trend, observed in the global ALE/GAGE experiments for both CH3CCl3 and CFCl3 illustrates an efficient interhemispheric transport of atmospherically long-lived chemical species. Analysis of the modelling data at two tropical stations, Barbados (13° N, 59° W) and Samoa (14° S, 124° W), show the close relationship between inter-hemispheric transport and cross-equator Hadley circulations. We found that cross-equator Hadley circulations play a key role in producing the globally homogeneous observed trends. Chemically, the most rapid interaction between CH3CCl3 and OH occurs in the northern summer troposphere; while the most rapid photolysis of CH3CCl3 and CFCl3, and the chemical reactions between CFCl3 and O(1D), take place in the southern summer stratosphere. Therefore, the cross-equator Hadley circulation plays a key role which regulates the southward flux of chemical species. The regulation by the Hadley circulations hence determines the amount of air to be processed by OH, O(1D), and ultraviolet photolysis, in both hemispheres. In summary, the dynamic regulation of the Hadley circulations, and the chemical processing (which crucially depends on the concentration of OH, O(1D), and on the intensity of solar insolation) of the air contribute to the seasonal variability and homogeneous growth rate of observed CH3CCl3 and CFCl3.Key words: Atmospheric composition and structure (middle atmosphere - composition and chemistry; pollution - urban and regional) - Meteorology and atmospheric dynamics (convective processes)

Mercury toxicity in plants

Mercury poisoning has become a problem of current interest as a result of environmental pollution on a global scale. Natural emissions of mercury form two-thirds of the input; manmade releases form about one-third. Considerable amounts of mercury may be added to agricultural land with sludge, fertilizers, lime, and manures. The most important sources of contaminating agricultural soil have been the use of organic mercurials as a seed-coat dressing to prevent fungal diseases in seeds. In general, the effect of treatment on germination is favorable when recommended dosages are used. Injury to the seed increases in direct proportion to increasing rates of application. The availability of soil mercury to plants is low, and there is a tendency for mercury to accumulate in roots, indicating that the roots serve as a barrier to mercury uptake. Mercury concentration in aboveground parts of plants appears to depend largely on foliar uptake of Hg0 volatilized from the soil. Uptake of mercury has been found to be plant specific in bryophytes, lichens, wetland plants, woody plants, and crop plants. Factors affecting plant uptake include soil or sediment organic content, carbon exchange capacity, oxide and carbonate content, redox potential, formulation used, and total metal content. In general, mercury uptake in plants could be related to pollution level. With lower levels of mercury pollution, the amounts in crops are below the permissible levels. Aquatic plants have shown to be bioaccumulators of mercury. Mercury concentrations in the plants (stems and leaves) are always greater when the metal is introduced in organic form. In freshwater aquatic vascular plants, differences in uptake rate depend on the species of plant, seasonal growthrate changes, and the metal ion being absorbed. Some of the mercury emitted from the source into the atmosphere is absorbed by plant leaves and migrates to humus through fallen leaves. Mercury-vapor uptake by leaves of the C3 speciesoats, barley, and wheat is five times greater than that by leaves of the C4 species corn, sorghum, and crabgrass. Such differential uptake by C3 and C4 species is largely attributable to internal resistance to mercury-vapor binding. Airborne mercury thus seems to contribute significantly to the mercury content of crops and thereby to its intake by humans as food. Accumulation, toxicity response, and mercury distribution differ between plants exposed through shoots or through roots, even when internal mercury concentrations in the treated plants are similar. Throughfall and litterfall play a significant role in the cycling and deposition of mercury. The possible causal mechanisms of mercury toxicity are changes in the permeability of the cell membrane, reactions of sulphydryl (-SH) groups with cations, affinity for reacting with phosphate groups and active groups of ADP or ATP, and replacement of essential ions, mainly major cations. In general, inorganic forms are thought to be more available to plants than are organic ones.

Site-Specific Factors Affecting Corn Response to Starter Fertilizer

The need for starter fertilizer (SF) in corn (Zea mays L.) production is questioned for economic and environmental reasons where soils have phosphorus (P) test levels above those needed to maximize yields. We evaluated corn yield response to SF at 100 on-farm sites, most having excessively high (EH) soil test P and K levels, over a 3-yr period in Wisconsin. Treatments (three replications) of none or an average rate of 15+26+32 (N+P 2 O 5 +K 2 O) lb/acre were placed 2 in, below and 2 in, laterally from the seed at planting. Statewide, SF significantly increased yields by about 4 bu/acre each year. For individual sites, yield response to SF ranged from -10 to +42 bu/acre and 40% of the sites had a positive economic response to SF. Economic response to SF increased with hybrid relative maturity (RM) and was more frequent at sites with soil K tests below 140 ppm. The percentage of responsive sites was linearly related (r 2 = 0.51) to the sum of RM and planting date (PD) in Julian days (PDRM). Results show that profitable responses to SF can occur on soils with EH test levels for P and K. Responses are most likely at later PDs using longer RM hybrids (PDRM >235) and where soil K levels are below 140 ppm. The SF response with late PDs and hybrids may be due to stimulation of early season growth rates by SF resulting in a realization of more of the crop's yield potential by the end of the growing season. The use of PDRM values in conjunction with soil test K information to predict response to SF will enable corn producers to evaluate the potential for economic return on a site-specific basis.

Development and Corroboration of a Bioenergetics Model for Northern Pikeminnow Feeding on Juvenile Salmonids in the Columbia River

A bioenergetics model was developed and corroborated for northern pikeminnow Ptychocheilus oregonensis, an important predator on juvenile salmonids in the Pacific Northwest. Predictions of modeled predation rate on salmonids were compared with field data from three areas of John Day Reservoir (Columbia River). To make bioenergetics model estimates of predation rate, three methods were used to approximate the change in mass of average predators during 30-d growth periods: Observed change in mass between the first and the second month, predicted change in mass calculated with seasonal growth rates, and predicted change in mass based on an annual growth model. For all reservoir areas combined, bioenergetics model predictions of predation on salmon were 19% lower than field estimates based on observed masses, 45% lower than estimates based on seasonal growth rates, and 15% lower than estimates based on the annual growth model. For each growth approach, the largest differences in field-versus-model predation occurred at the midreservoir area (−84% to −67% difference). Model predictions of the rate of predation on salmonids were examined for sensitivity to parameter variation, swimming speed, sampling bias caused by gear selectivity, and asymmetric size distributions of predators. The specific daily growth rate of northern pikeminnow predicted by the model was highest in July and October and decreased during August. The bioenergetics model for northern pikeminnow performed well compared with models for other fish species that have been tested with field data. This model should be a useful tool for evaluating management actions such as predator removal, examining the influence of temperature on predation rates, and exploring interactions between predators in the Columbia River basin.

Seasonal growth dynamics and overwintering of the aquatic carnivorous plantAldrovanda vesiculosa at experimental field sites

New potential sites for the critically-endangered, aquatic carnivorous plantAldrovanda vesiculosa L. (Droseraceae) were selected in North and South Bohemia (Czech Republic) and both its seasonal growth dynamics and overwintering rate were investigated. Groups of either 5 or 10 plants were planted in 1×1 m nylon enclosures in selected shallow, dystrophic waters at the end of May. Plant growth characteristics and water chemistry were investigated at 2 to 5 week intervals over the 1994 growing season inside ten enclosures placed at six sites. Within seven enclosures at three sites, the seasonal growth was very fast and 38–141 turions developed from the initial five plants. Water at these sites was mesotrophic with a high concentration of CO2 above 0.1 mmol.l−1 and pH between 6.2 and 7.6. At the other three sites, plant growth was very poor. The fastest plant propagation was found between late June and mid-August and corresponded with the warmest seasonal period. During this period, the doubling time of the total number of shoot apices was 16.4–34.9 days. Turions developed in mid-September and sank to the bottom by mid-October. In some enclosures, the turions overwintered on the wet bottom whereas they were submersed in the other ones. Though the turions were subject to frosts of up to −20°C, none died due to the frosts. Grazing of turions by ducks or small rodents was found at some sites. The overwintering rate of turions at sites varied from 0 to 70% and was not related to seasonal growth rate. Most turions floated to the surface and germinated during late April-early May. It is suggested that considerable turion losses in stable, naturalAldrovanda stands are compensated for by fast seasonal shoot growth and branching which leads to the recovery of an abundant plant population.

Age and growth of leaping grey mullet (<i>Liza saliens</i> (Risso, 1810)) in Minorca (Balearic Islands)

A population of leaping grey mullet (Liza saliens (Risso, 1810) was studied in order to measure seasonal and annual growth rates. The annual growth rates were similar to those reported for other populations from the central Western Mediterranean and intermediate between those living in northern and southern areas. As usual, the growth rate of adult males was slower than that of females. Males reached adulthood in their third summer. Females of the same age showed a moderate gonadal development, but did not ripen until the next summer. Mullets of all ages gained weight only when the water temperature was higher than 20°C. However adults and immature fish showed reduced growth in mid-summer, when that of the juveniles peaked. This difference is not a consequence of the reproductive cost, because the growth rate of immatures was greatly reduced although they did not spawn.

Growth of White Crappies in Response to Temperature and Dissolved Oxygen Conditions in a Kentucky Reservoir

Abstract Abiotic factors that may regulate growth, recruitment, and mortality of warmwater fishes in reservoirs of the Midwest and southeast United States are poorly understood. I examined the effect of reservoir temperature on the growth of white crappies Pomoxis annularis in a Kentucky reservoir to test the hypothesis that warm summer epilimnion temperatures may constrain white crappie growth and describe annual patterns of seasonal growth. Each year reservoir stratification reduced epilimnion volume as summer progressed and prevented white crappie use of cooler hypolimnetic waters due to low dissolved oxygen conditions below the thermocline. Water temperature at the 3-m depth explained significant portions of variability in growth of both juvenile (age-1) and adult (age-2) white crappies during 1989–1993. Higher temperatures resulted in slower instantaneous growth rates, and growth usually decreased during Jul and Aug. Seasonal growth rates differed between juvenile and adult white crappies. Juveniles ...

Effect of Rate, Timing, and Placement of Liquid Dairy Manure on Reed Canarygrass Yield

Perennial cool-season grasses in a crop rotation provide alternative land area for in-season manure applications. Reed canarygrass (Phalaris arundinacea L) might be suitable crop for manure application due to its consistently high yields and N uptake capacity. The primary objective of this research was to determine the agronomic responses to and feasibility of in-season manure application rates to reed canarygrass. Field studies were established at three locations with pure stands of reed canarygrass. Treatments included a series of liquid dairy manure and fertilizer N rates. In addition, broadcast or surface-band manure placement configurations and single or split manure application timings were compared with one manure rate. Manure application rates up to 40 000 gal/acre per yr (approximately 920 lb total N/acre per yr) were applied. A positive dry matter yield response was measured with increasing rates of manure or fertilizer N. Grass stand density generally increased with manure or fertilizer compared with the unfertilized control. With the 20 000 gal/acre rate, split applications with manure applied in early spring resulted in superior yields compared with split manure applications made after the second and third forage cuttings. For the 20 000 gal/acre manure application rate, split application of the manure after the second and third cuttings did not result in significantly greater forage yields than a single application made after the second cutting. Forage yield was similar for broadcast and surface-band manure placement configurations for the one manure rate investigated.

Continuous measurements of atmospheric CO2 at Jubany Station, Antarctica

The first 4 years (1994–1997) of continuous atmospheric CO2 measurements from Jubany station located on the Antarctic peninsula are presented. Details are given on the station environment, meteorological conditions, instrumentation, and data selection strategy. The average seasonal cycle and annual growth rate are characterized and compared with other independent Antarctic CO2 measurement records. An analysis of diurnal behaviour and local meteorology and statistical variability in the measurements suggests that Jubany is a suitable site for making systematic observations of CO2 that are representative of large well-mixed air masses.

Comparative seedling growth of five endemic New Zealand podocarp species under different light regimes

The comparative growth of seedlings of Dacrycarpus dacrydioides, Podocarpus totara, Dacrydium cupressinum, Prumnopitys ferruginea, and P. taxifolia was investigated at different light levels. Five light regimes were achieved using shade cloth for glasshouse seedlings (2–25% of full sunlight) and under different canopy vegetation types (5–30% of full sunlight) in dense lowland podocarp forest at Whirinaki Forest Sanctuary, Central North Island, New Zealand. Height growth, stem diameter growth, and dry weight increase were measured for a 15 month period over two spring seasons in both glasshouse and forest environments. The five podocarp species show significant differences in height growth, stem diameter growth, and dry weight increase under the different light regimes of both glasshouse and forest environments. Seasonal height growth rates were examined in the forest, and species exhibited different responses to the climatic parameters of rainfall, humidity, temperature, and solar radiation. Comparative growth rates are used to infer regeneration strategies of the five podocarp species, particularly in response to elevated light levels. Totara and kahikatea are considered to be light demanding and have the ability to respond to increased light levels. Both rimu and matai do not appear to have the ability to respond to elevated light levels and it may be more appropriate to consider these two species as consistently slow growers. Miro is often considered the most shade tolerant of the five podocarp species and in the present study it exhibited an increased growth response to elevated light levels, especially in the forest.

Seasonal and annual growth rates in the Antarctic fish Notothenia coriiceps Richardson

Growth in Antarctic fishes is assumed to be seasonal but quantitative data are scarce. Growth rates in juvenile Notothenia coriiceps, a typical Antarctic fish, were measured using mark–recapture techniques and found to be greater when periods of liberty included summer and early autumn months and least when liberty was restricted to winter months. Weight specific growth rates ranged from −0.08–0.26% body weight day −1. Year class analysis and cohort analysis were attempted on serial samples of the population but proved ineffective methods for detecting seasonal growth in these slow growing fishes. A tentative description of the seasonal growth profile is proposed. Seasonality in growth indicates that some form of growth limitation is active; competing hypotheses of temperature and resource limitation are discussed. Annual growth rates in three year classes showed an inverse relationship with age. Parameters of the Pütter-von Bertalanffy growth equation were estimated. Comparison with other studies show the growth characteristics of N. coriiceps differ with geographical location but have not changed substantially at Signy Island over the past 25 years.

A comparison of once- and twice-yearly weaning of an extensive herd in northern Australia

Summary. Continuous mating is common in northern Australian beef herds. The resulting calves are born throughout the year making weaning and herd management difficult. Calves born late in the wet season do not reach suitable liveweight for weaning until late in the year. Low liveweight and poor feed conditions make management of these animals for subsequent turnoff or breeding more difficult. We recorded the growth and survival of all progeny and reproductive performance of heifers from 2 groups of 250 Bos indicus-Bos taurus-cross cows grazing native pastures at Kidman Springs, Northern Territory, for 5 years from July 1985. Calves were weaned in June only (W1) or June and October (W2). Unweaned calves remained with their dams until June the following year and heifers entered the breeding herd as 2 year olds. Calves weaned in June (WJ) were heaviest (157.1 kg; P<0.05) but gained least (84.6 kg; P<0.05) over the following year. Unweaned (UW) calves were lighter (51.1 kg; P<0.05) at branding time, in June, than those weaned in October (WO; 66.8 kg). However, they gained more weight (144.5 v. 112.4 kg; P<0.05) over the following year than WO calves because of a superior wet season growth rate, so that WO calves were lightest (P<0.05) at the yearling muster. Mortality rates of all calf groups were low (2.5%). Liveweight at branding and liveweight gain to yearling stage affected whether heifers subsequently joined the breeding herd. More (P<0.05) heifers from WJ joined the herd than from WO and UW groups. Overall, 63.6% of heifers were selected as replacement breeders (no difference between W1 and W2). Bull control was difficult and many heifers (48%) conceived before the planned start of mating. Cumulative conception rate was 91.3% by 30 months post-branding. In the first year, 60% of heifers mated were confirmed pregnant, but reproductive losses of 25.6% from pregnancy diagnosis to branding contributed to a branding rate of 44.9%. The conception rate of heifers when lactating was 18.6%. Mortality during the first year in the herd was 11.7%. In general, WJ heifers had lower mortalities, higher conception, calving and weaning rates, and higher conception rates when lactating than WO or UW heifers. Animals weaned in October were identified as the most difficult group to manage because of lower liveweight as 2 year olds compared with WJ and UW calves. This affected the numbers of heifers suitable for joining. Cost-effective management systems are needed to improve growth rates or delay onset of oestrus in these animals.