Spring Growth Rates Research Articles

Migration and growth potential of coho salmon smolts: implications for ecological impacts from growth-enhanced fish

Wild-genotype and growth hormone (GH) transgenic coho salmon (with dramatically enhanced growth potential) were used to examine the influence of genotype, age, body size, growth, and rearing conditions on the onset of seaward migration and to assess the potential consequences of the introduction of such transgenic fish on natural ecosystems and wild populations. When reared from the first feeding stage under naturalized stream conditions, there was no difference in survival or migratory timing between the two genotypes. However, larger fish migrated earlier in the season than smaller fish of both genotypes, and transgenic fish with higher specific spring growth rates migrated earlier in the season than slower-growing transgenic fish. Stream-reared fish of both genotypes also displayed increased migratory activity at dawn and dusk. Fish reared in the hatchery for 3 and 15 months before being released into the stream in August differed in onset of seaward migration due mainly to age (older fish migrated earlier in the season) and genotype (transgenic fish migrated before wild-type in younger fish). Further, hatchery-reared fish showed no diel pattern in activity during migration. In older fish, larger individuals migrated later in the season than small individuals, whereas there was no clear size effect in younger individuals. Thus, although small differences in spring migration timing were observed among groups, seaward migration in coho salmon was largely independent of major shifts in size and growth rate induced by GH transgenesis (i.e., transgenic fish migrated at approximately the normal time in the spring, rather than at the typical size). Further, early rearing conditions had a stronger effect on migratory behavior than did the growth-promoting transgene. Taking into account effects of migratory timing, growth, survival, and differential food conversion efficiencies, these data suggest that transgenic fish escaped from hatcheries would have a greater impact on stream ecosystems during early life compared to escaped wild-type fish. However, this difference may be reduced if rearing occurred in subsequent generations under wild conditions where growth rates of transgenic fish are reduced compared with hatchery conditions.

Context‐specific influence of water temperature on brook trout growth rates in the field

Summary1. Modelling the effects of climate change on freshwater fishes requires robust field‐based estimates accounting for interactions among multiple factors.2. We used data from an 8‐year individual‐based study of a wild brook trout (Salvelinus fontinalis) population to test the influence of water temperature on season‐specific growth in the context of variation in other environmental (i.e. season, stream flow) or biotic factors (local brook trout biomass density and fish age and size) in West Brook, a third‐order stream in western Massachusetts, U.S.A.3. Changes in ambient temperature influenced individual growth rates. In general, higher temperatures were associated with higher growth rates in winter and spring and lower growth rates in summer and autumn. However, the effect of temperature on growth was strongly context‐dependent, differing in both magnitude and direction as a function of season, stream flow and fish biomass density.4. We found that stream flow and temperature had strong and complex interactive effects on trout growth. At the coldest temperatures (in winter), high stream flows were associated with reduced trout growth rates. During spring and autumn and in typical summers (when water temperatures were close to growth optima), higher flows were associated with increased growth rates. In addition, the effect of flow at a given temperature (the flow‐temperature interaction) differed among seasons.5. Trout density negatively affected growth rate and had strong interactions with temperature in two of four seasons (i.e. spring and summer) with greater negative effects at high temperatures.6. Our study provided robust, integrative field‐based estimates of the effects of temperature on growth rates for a species which serves as a model organism for cold‐water adapted ectotherms facing the consequences of environmental change. Results of the study strongly suggest that failure to derive season‐specific estimates, or to explicitly consider interactions with flow regime and fish density, will seriously compromise our ability to predict the effects of climate change on stream fish growth rates. Further, the concordance we found between empirical observations and likely energetic mechanisms suggests that our general results should be relevant at broader spatial and temporal scales.

Arrowleaf clover improves lamb growth rates in late spring and early summer compared with subterranean clover pastures in south-west Victoria

The profitable production of lamb from pasture-based systems is dependent on high levels of pasture production being efficiently utilised by sheep of superior genetic merit. Pastures that can extend the pasture-growing season and provide high quality feed in late spring and summer have the potential to increase production efficiency and the proportion of lambs that meet market specifications. In this paper we tested the hypothesis that arrowleaf clover (cv. Arrotas), a cultivar selected for late maturity, would supply feed of higher nutritive value than conventional annual legumes and perennial ryegrass mixtures during December and January and this would improve lamb growth rates over this period. Two experiments were conducted to compare the nutritive value of pasture and growth rates of lambs grazing arrowleaf clover, subterranean clover (cv. Leura) or subterranean clover/perennial ryegrass mixtures at different stocking rates during late spring and early summer in south-west Victoria. In the second experiment an arrowleaf clover/perennial ryegrass treatment was also included. Lambs were removed from the plots when they could no longer maintain liveweight. Arrowleaf clover extended the growing season by 4–6 weeks and provided feed of significantly higher digestibility than subterranean clover during December and January. The digestibility of arrowleaf and perennial ryegrass was comparable, but arrowleaf had significantly higher crude protein content during this period. Lambs grazing arrowleaf clover at stocking rates up to 24 lambs/ha grew at or above 100 g/day until the end of January, whereas lambs grazing subterranean clover and perennial ryegrass mixed pastures could not maintain weight by mid-to-late December in both years and were removed from the pastures. At the highest stocking rates total lamb production from arrowleaf clover monoculture pastures in late spring and early summer was ~400 kg liveweight/ha, and was more than double that achieved from the subterranean clover and perennial ryegrass/subterranean clover mixed pastures. The perennial ryegrass/arrowleaf clover mixed pastures in the second experiment produced a similar quantity of lamb per hectare as the arrowleaf clover monoculture pastures at the same stocking rate. In this paper we demonstrated that late-maturing arrowleaf clover can be a profitable, special purpose lamb-finishing pasture. Arrowleaf clover was most suited to more elevated parts of the landscape where estimated carrying capacity was 20 to 40% greater than that from lower lying parts of the landscape that were more subject to water logging and weed infestation. The risks of including arrowleaf clover pastures into the farming system could be reduced by direct drilling arrowleaf clover, which has relatively poor winter production, into existing perennial ryegrass pastures.

Nitrogen fertilization of grass/clover swards under cutting or grazing by dairy cows

Intensively managed perennial ryegrass/white clover (Lolium perenne L. and Trifolium repens L.) swards receive relatively high levels of fertilizer N, and high N surpluses can subsequently be found. The N-fertilization effects on growth, yield, and herbage quality were therefore examined on three farms over a period of three years. Nitrogen was applied at four rates (0, 75, 150, and 225 kg N year−1) with cutting or grazing regime in Year 1 and Year 2, after establishment. A spring-only application of 150 kg N was compared with four applications during the season, which was the fertilization management in the rest of the experiment. N-response was greatly affected by management. Under cutting it was higher in Year 1 [16 kg dry matter (DM) kg−1 N] than in Year 2 (9 and 13 kg DM kg−1 N with and without residual effects of fertilization in Year 1). Under grazing with one or two rest periods for cuts the N-response was only approximately half that under cutting. Under grazing there was only a response at the beginning of the season (May–June), while under cutting there was a response throughout the season. N-response decreased with increasing clover content in herbage by 4 kg DM kg−1 N per 10%-units of clover content. A spring-only application of 150 N increased the growth rate in spring–early summer, and decreased the rate later in the season. The annual yield was unaffected by the application method in fields with good clover establishment, but the seasonal clover content was highly affected. The results indicate different possibilities for strategic fertilization both at farm and field level, and in swards with a high clover content it demonstrates how the clover content can be used as a buffer both for maximizing the N-response and for manipulating the production profile.

Growth ofHimantoglossum adriaticumandH. caprinumindividuals, and relationship between sizes and flowering

The long-term protection of plant species is impossible without a comprehensive and thorough knowledge of their biology. This paper deals with some of the important aspects of the biology of two strictly protected species, Himantoglossum adriaticum and H. caprinum. The changes of the leaf area of plants were measured with a non-destructive method and the growth pattern was investigated during the vegetation period. It was also studied how the plant size of individuals changed from year to year, and what kind of connection there was between the plant condition and the flowering. Large size plants of both species were characterised by intensive growth rates in autumn and spring, their growth stopped in winter. Often they lost some of their leaf areas because of damage from insects (mainly in the case of H. caprinum) , and frost (almost exclusively in the case of H. adriaticum ). In some years the medium and small size plants were characterised by similar growth pattern to those of large size ones, but more often their growth did not stop in winter, though their growth was not so fast. The medium and small size H. caprinum individuals showed an intense autumn growth only in one vegetation period, which characterised both large size individuals of H. caprinum and all individuals of H. adriaticum. The constant annual rate of growth, which may have been slowed meaning that the leaf number did not grow, but it did not stop either, was detected in hardly more than 10% of individuals with both species. In the case of H. adriaticum the critical size for flowering seemed to be 50 cm 2 , which was usually reached in the four-leaf stage of the rosettes. The same value was 100 cm 2 in the case of H. caprinum and it needed at least a six-leaf basal rosette. The leaf number and the leaf area of reproductive plants had been larger for already two years before flowering took place, than those of the plants that remained vegetative.

Size‐independent growth in fishes: patterns, models and metrics

A combination of a dynamic energy budget (DEB) model, field data on Atlantic salmon Salmo salar and brown trout Salmo trutta and laboratory data on Atlantic salmon was used to assess the underlying assumptions of three different metrics of growth including specific growth rate (G), standardized mass‐specific growth rate (GS) and absolute growth rate in length (GL) in salmonids. Close agreement was found between predictions of the DEB model and the assumptions of linear growth in length and parabolic growth in mass. Field data comparing spring growth rates of age 1+ year and 2+ year Atlantic salmon demonstrated that in all years the larger age 2+ year fish exhibited a significantly lower G, but differences in growth in terms of GS and GL depended on the year examined. For brown trout, larger age 2+ year fish also consistently exhibited slower growth rates in terms of G but grew at similar rates as age 1+ year fish in terms of GS and GL. Laboratory results revealed that during the age 0+ year (autumn) the divergence in growth between future Atlantic salmon smolts and non‐smolts was similar in terms of all three metrics with smolts displaying higher growth than non‐smolts, however, both GS and GL indicated that smolts maintain relatively fast growth into the late autumn where G suggested that both smolts and non‐smolts exhibit a sharp decrease in growth from October to November. During the spring, patterns of growth in length were significantly decoupled from patterns in growth in mass. Smolts maintained relatively fast growth though April in length but not in mass. These results suggest GS can be a useful alternative to G as a size‐independent measure of growth rate in immature salmonids. In addition, during certain growth stanzas, GS may be highly correlated with GL. The decoupling of growth in mass from growth in length over ontogeny, however, may necessitate a combination of metrics to adequately describe variation in growth depending on ontogenetic stage particularly if life histories differ.

Coevolution and the adaptive value of autumn tree colours: colour preference and growth rates of a southern beech aphid

The evolutionary explanation for the change in leaf colour during autumn is still debated. Autumn colours could be a signal of defensive commitment towards insects (coevolution) or an adaptation against physical damage because of light at low temperatures (photoprotection). These two hypotheses have different predictions: (1) under the coevolution hypothesis, insects should not prefer red leaves in autumn and grow better in spring on trees with green autumn leaves; and (2) under the photoprotection hypothesis, insects should prefer and grow better on trees with red leaves because they provide better nutrition. Studying colour preference in autumn and growth rates in spring of a southern beech aphid species (Neuquenaphis staryi) on Nothofagus alessandrii, we found preference for green leaves in autumn but no differential performance of aphids in spring. We suggest that aphid preference for green might have evolved to exploit better their host during the autumn rather than to improve their performance in spring.

Patrón de crecimiento de pasto buffel [Pennisetum ciliare L. (link.) sin. Cenchrus ciliaris l.] en Tamaulipas, México

The purpose of this research was to learn on the crop growth rate (CGR), leaf area index (LAI), leaf:stem (LS) ratio, and the dead tissue:live tissue (DL) ratio of buffelgrass [Pennisetum ciliare L. (Link.) Syn. Cenchrus ciliaris L.], as functions of rainfall (precipitation, i.e.: PREC), soil moisture at 20 (SM20) and 40 (SM40) cm, growing degree days (GDD), solar radiation, heliothermal units, and evapotranspiration. From July 1999 to December 2000, five time-overlapped cut programs were designed in order to perform weekly pasture harvests, under a 3-replicate, randomized block design. Multivariate analysis as principal components and conglomerate analyses together with regression analysis were performed. Eighty five (85) percent variability could be explained by three principal components. Three treatment groups were formed (P<0.01). Group 1: spring/late-fall harvests showing moderate CGR (16.36±14.38 kg ha-1 d-1) limited by SM20 and GDD. Group 2: summer harvests with 28.56±23.3 kg ha-1 d-1 (CGR), 1.49±0.7 (LS) and 0.64±0.4 (LAI) restricted by PREC. Group 3: winter harvests with 5.1±7.8 kg ha-1 d-1 (CGR), limited by GDD and SM20. SM20 explained 87 %, and PREC explained 92 % of CGR variation for Groups 1 and 2, respectively. Spring growth rates could not be predicted since no rainfall events were recorded in that time, during the studied period. Under the conditions of this study, it is possible to predict buffelgrass growth rates during summer and fall.

Reproductive ecology of Panicum turgidum Forssk.

P anicum turgidum Forssk. is a drought-resistant C 4 plant which exhibits high growth rates in late spring and summer months. Seed germination under different constant and alternating temperatures and the best time for propagation of this species were studied. The responses of the plant to different water regimes were also estimated. The present study revealed that the seed germination was successful under relatively high temperature. Propagation by transplants was favoured in months with moderate temperatures, so as not to cause excessive loss of water and drying of transplants. Cultivation of Panicum turgidum under different water treatments showed that its growth was greatly influenced by the amount of available water. The increase of growth was reflected mostly on the biomass, tillering capacity and the seed output.

Marine lakes of karst islands in Ha Long Bay (Vietnam)

Ha Long Bay in North Vietnam is characterized by karst towers and bigger islands totalling more than 3000 isles. Karst processes carved hundreds of caves out of the limestone and contributed to the formation of many enclosed and semi-enclosed saltwater lakes. Here, we report the results of a general survey of several lakes and the first data on the Hang Du I lake, a small basin devoid of any apparent communication with the surrounding sea. Hang Du I is characterized by the presence of Rhizostomeae, genus Mastigias, suggesting strong similarities with the famous lakes described from the archipelago of Palau. Among the benthic organisms sponges are the most important group. Temperature and abundance of the monsoon rains are the main factors influencing remarkable seasonal variations in physical–chemical parameters and the community structure of the lake. A thermal crisis with water temperatures up to 36 °C was recorded in September 2003. In this period, usually abundant medusae and sea anemones totally disappeared. Sponge populations showed fast growth rates in winter and spring and a partial degeneration to face the harsh conditions of the summer season. When isolated from the surrounding marine environment, the saltwater lakes share the condition of oceanic islands, representing spots of habitats surrounded by a completely different environment. The Ha Long Bay marine lakes are not easy to access, being surrounded by tropical forest, but local people usually exploit them for both fishery and oyster harvesting. There is an urgent need to develop measures of protection for these endangered and unique environments, natural laboratories that facilitate the study of evolution of marine organisms, where biodiversity has been until now totally unexplored.

Temporal life history plasticity of the Southern Ocean squid Todarodes filippovae from waters off Tasmania, Australia

Population dynamics and maturity parameters were analysed for seasonal samples of the oceanic ommastrephid squid Todarodes filippovae from off the coast of Tasmania Australia from 2002 to 2004. Based on assumed daily periodicity in statolith increments, T. filippovae had a life cycle of about a year with the sexually dimorphic females reaching their larger size by predominantly growing faster than males. Due to the small sample size of males, analysis was undertaken on female individuals only. Growth in all samples was best described by a power curve and varied annually, with significantly faster growth in 2001 compared to the subsequent 2 years. Seasonal growth rates also varied with autumn- and winter-hatched squid significantly faster than summer-hatched squid. Spring growth rates were intermediate but not significantly different to the other three seasons. Peak hatching periods occurred in late autumn and early winter. ANOVA revealed a season × year interaction for mantle length and total body weight. Pairwise comparisons showed that the annual differences were likely driven by smaller squid in autumn 2002 compared to autumn samples in the other 2 years. Pairwise comparisons also revealed seasonal differences with winter-caught squid smaller than those from the majority of other samples. There were no seasonal effects on mature female gonad weights but females caught in 2002 had significantly lighter gonad weights than females from the following 2 years. There were no consistent trends among seasons or years in the age structure of mature females. This study revealed the plasticity and flexibility in growth and maturity parameters in this species, with a preference for faster growth during cooler periods.

Biomass development and photosynthetic potential of intertidal Zostera capricorni in New Zealand estuaries

A 2-year study of structural (biomass, shoot density), morphological (rhizome morphometrics) and dynamic (photosynthetic potential, tissue nutrient content) characteristics of the seagrass Zostera capricorni Asch. on intertidal estuarine sand-flats was undertaken at four sites on the Coromandel Peninsula, New Zealand. Spatial (position within the bed, within and among estuaries), summer–winter and between year variations in almost all measured characteristics were observed, suggesting responses to varying environmental conditions at different scales. Mean above-ground biomass ranged from 46 to 81 g DW m −2 and mean below-ground biomass ranged from 133 to 542 g DW m −2, varying significantly among the four sites. The site with the lowest biomass also had the lowest and most variable photosynthetic potential, measured using the pulse amplitude modulated fluorescence parameter ( F v/ F m), ranging from an average of 0.35 to 0.78. Despite the differences in biomass, there was much greater similarity in shoot density (mean summer densities: 2700–3800 m −2) among the sites. At all sites, above- and below-ground biomass, shoot density and rhizome morphometrics differed between the edge of the beds and within the beds. While biomass was generally higher within the beds, the incidence of rhizome branching was higher and primary rhizome internode lengths were longer at the edge than within the beds. Differences in biomass and shoot density between summer and winter were similar at all the sites, consistent with high growth rates in spring–summer reported elsewhere for temperate intertidal seagrass. At some sites, the lengths of the primary rhizome internodes, the frequency of rhizome branching and leaf lengths at the edge of the bed were longer in winter than summer, and plants exhibited high F v/ F m values in winter 2001. Despite lower ambient temperatures than in summer, winter may still be an important period for growth in the temperate North Island New Zealand climate.

Rangewide provenance variation in Atlantic white-cedar ( Chamaecyparis thyoides): Early survival and growth in New Jersey and North Carolina plantations

Atlantic white-cedar, Chamaecyparis thyoides (L.) B.S.P., is an important wetland tree species occurring along the Atlantic coast of the United States, from Maine to Florida, and westward along the Gulf of Mexico coast to Mississippi. Within this range, its distribution is patchy and disjunct, due to the scattered occurrence of suitable wetland habitat, natural range disjunctions and historic declines. Much recent interest has focused on the species, its management and its restoration, but very little is known about its geographic pattern of phenotypic variation. This study presents second year results from the first rangewide white-cedar provenance test. Rooted cuttings were propagated from 34 source populations, encompassing the entire latitudinal range (29°12′–44°20′N) of the species, and planted in three common garden plantations, two in New Jersey and one in North Carolina. Survival was generally high for Atlantic coastal populations at all three planting locations, ranging from 72% to 100% for individual provenances, but many Florida and Gulf coast populations exhibited reduced survival and winter hardiness in New Jersey, with 44–94% survival and 11–67% of surviving trees experiencing winter dieback. Height growth varied significantly between planting sites and provenances, and a significant site by provenance interaction suggested that relative performance of provenances varied across sites. All populations grew significantly more at Hofmann Forest, North Carolina than at the two New Jersey plantations, with mean 2-year height growth ranging from 54 to 96 cm for individual provenances at this site. By comparison, mean height growth ranged from 23 to 63 cm at Richard Stockton College, and from 12 to 32 cm at Brendan T. Byrne State Forest, New Jersey. Within individual sites, we identified polynomial relationships between height growth and latitude of origin, with southern Atlantic coastal populations among the best performers at all sites. Patterns of growth phenology were significantly correlated with latitude of origin. Spring growth rate and the percent of total growth occurring during spring were positively correlated with latitude, while fall growth rate and the percent of growth occurring during fall were negatively correlated with latitude. These early results suggest that significant provenance variation exists among white-cedar populations, and that local sources should be preferred for regeneration and restoration purposes.

Determinação das condições climáticas que favorecem o desenvolvimento da ferrugem e da mancha angular do feijoeiro

Este trabalho objetivou estudar o efeito da temperatura e do molhamento foliar no desenvolvimento da ferrugem e da mancha angular do feijoeiro (Phaseolus vulgaris). Foram conduzidos ensaios em condições de campo durante os plantios das águas (outubro a dezembro), de inverno (maio a agosto) e da seca (fevereiro a maio). Os ensaios foram instalados em blocos casualizados com três repetições e dois tratamentos. Os tratamentos consistiram de: 1) inoculação com Uromyces appendiculatus e 2) inoculação com Phaeoisariopsis griseola. No inverno, a ferrugem ocorreu com maior intensidade, atingindo um valor máximo de severidade (Ymax) igual a 1,3 e as maiores taxas de crescimento (0,09, 0,04 e 0,07 aos 34, 55 e 62 dias, respectivamente), devido à predominância, nessa época, de temperaturas inferiores a 21,1 °C, e de maior número de horas diárias com temperaturas menores ou iguais a 16 °C, quando ocorreu molhamento foliar. Nos plantios das águas e da seca, a mancha angular ocorreu com maior intensidade, atingindo Ymax iguais a 2,6 e 3,5, respectivamente e as maiores taxas de crescimento (0,06, 0,02 e 0,15 aos 46, 60 e 67 dias, respectivamente, no plantio das águas, e 0,13 e 0,38 aos 51 e 58 dias, respectivamente, no plantio da seca), devido à predominância, nessa época, de temperaturas superiores a 21,1 °C, quando ocorreu molhamento foliar e não ocorrência de temperaturas menores ou iguais a 16 °C. Com esse estudo pôde-se caracterizar, em função das condições climáticas, o plantio de inverno como favorável à ocorrência da ferrugem e os plantios da água e da seca como favorável à ocorrência da mancha angular.

Changes in tissue concentrations of the vitamins B1 and B2 during reproductive cycle of bivalves: Part 2. The Pacific oyster Crassostrea gigas

Thiamin and riboflavin (vitamins B1 and B2) were measured in different organs of the Pacific oyster Crassostrea gigas over an annual cycle in Marennes Oleron (France), to study the natural accumulation and their possible transfer to gonads and eggs. We observed an annual cycle of vitamin concentration with low levels in winter and high levels in spring. The first increase was observed in the digestive gland (DG) in March with no change in the mantle plus gonad tissue or muscle, suggesting no immediate transfer to gonad tissue or a strong utilisation of these vitamins in the gonad in winter. A second peak was observed in the DG in spring, coinciding with an increase in the gonad plus mantle and muscle, suggesting that vitamin transfer was immediate in spring. The DG could be an intermediate compartment in vitamin transfer. Riboflavin was mainly concentrated in eggs and disappeared from the gonad during spawning. Thiamin was also concentrated in eggs but also in the gonad–mantle tissue. By artificial conditioning, it was possible to increase the thiamin concentration 2.5-fold in eggs in spring, but riboflavin concentrations remained similar to those in nature. No difference was evident in D-larval production from natural or hatchery spawnings, nor in larval growth rate in spring. Vitamins B1 and B2 in eggs were probably above D-larval requirements in spring (9 and 20 fg/egg (dry weight) for thiamin and riboflavin, respectively). Low vitamin concentrations observed in winter coinciding with gonadal mitoses and glycogen metabolism, could be explained by a high vitamin utilisation for these biological processes. These results may explain low levels of vitamins observed in eggs from winter conditioning of oysters as natural vitamin concentration in this period is low, and transfer to gonads seems limited.

Setting management limits for the production and utilization of herbage for out‐of‐season grazing

Three experiments were carried out on perennial ryegrass‐dominant swards to provide a basis for recommendations for the limits to (a) building up and timing of utilization of a herbage ‘bank’ for out‐of‐season grazing and (b) duration and intensity of early spring grazing in the United Kingdom and Ireland.In experiment 1, the effect of regrowth interval (from 7 September, 20 October, 17 November or 15 December) in autumn on herbage accumulation, leaf turnover and on subsequent spring growth was investigated. Swards regrown from early September reached maximum herbage mass (about 3 t ha–1 DM) and leaf lamina content in mid‐November, by which time senescence rate exceeded rate of production of new leaves. New leaf production and senescence rates were greater in swards remaining uncut until December than in those cut in October or November. Time of defoliation up to December had no effect on spring herbage mass in the subsequent spring. Defoliating in March reduced herbage mass in late May by less than 20%.Experiment 2 investigated the progress in herbage growth and senescence in swards regrowing from different times in late summer and autumn to produce herbage for utilization beyond the normal grazing season. Treatments in a randomized block design with three replicates were regrowths from 19 July, 8 August, 30 August and 20 September. Based on a lower ceiling of leaf and total herbage mass being reached with progressively later regrowths, beyond which leaf senescence generally exceeded leaf production and herbage mass declined, it was concluded that currently recommended rotation lengths for this period should extend from 3 weeks in late July to 8 weeks for swards previously grazed in mid‐September. In both experiments, leaf senescence commenced earlier (by one leaf‐age category) than previously published estimates and so brought forward the time at which senescence rates balanced leaf growth rates.In experiment 3, designed to evaluate the effect of daily grazing period and intensity in early spring on herbage regrowth, dairy cows grazed successive plots (replicates) for 2 or 4 h each day at two intensities (target residual heights of 5 or 7 cm) in March to mid‐April. Regrowth rate was similar in all treatments including the ungrazed control, despite soil moisture content being relatively high on occasions. Tiller density was significantly reduced in May by grazing plots in early or mid‐April.It is concluded that in autumn there are limits to which rotation lengths should be extended to produce herbage for out‐of‐season grazing owing to attainment of ceiling yields. Although utilization in early spring may reduce herbage availability in spring, out‐of‐season utilization need not reduce herbage growth rates in early spring.

Growth, Smoltification, and Smolt-to-Adult Return of Spring Chinook Salmon from Hatcheries on the Deschutes River, Oregon

The relationship between smoltification and smolt-to-adult return (SAR) of spring chinook salmon Oncorhynchus tshawytscha from the Deschutes River, Oregon, was examined for four release groups in each of three successive years. Fish were reared, marked with coded wire tags, and released from Round Butte Hatchery, Pelton Ladder rearing facility, and Warm Springs National Fish Hatchery. Smolt releases occurred in nearly the same place at similar times, allowing a direct comparison of SAR to several characters representing smolt quality. Return rates varied significantly among facilities, varying over an order of magnitude each year. The highest average SAR was from Pelton Ladder, the lowest was from Warm Springs. Each of the characters used as metrics of smoltification—fish size, spring growth rate (February–April), condition factor, plasma hormone concentration (thyroxine, cortisol, and insulin-like growth factor-I [IGF-I]), stress challenge, gill Na+, K+-ATPase activity, and liver glycogen concentration—varied significantly among facilities and seasonally within hatchery groups. However, only spring growth rate, gill ATPase activity, and plasma IGF-I concentration showed significant relationships to SAR. These characters and SAR itself were consistently lower for fish released from Warm Springs Hatchery than for fish from Round Butte Hatchery and Pelton Ladder. This demonstrates that differences in the quality of fish released by facilities may have profound effects on subsequent survival and suggests that manipulations of spring growth rate may be used to influence the quality of smolts released from facilities.

Influence of seagrass habitat patch size on growth and survival of juvenile bay scallops, Argopecten irradians concentricus (Say)

Patchy seagrass meadows are common features on high energy sand shoals in temperate coastal waters. We tested the effect of seagrass patch size within patchy seagrass meadows on growth and survival of juvenile bay scallops, Argopecten irradians concentricus (Say), during spring (two sites) and fall (one site) settlement periods in Back Sound, North Carolina, USA. Because plant characteristics such as density and species composition (proportion of Zostera marina L. and Halodule wrightii Aschers) may influence growth and predation rates, we also quantified these variables during each time period. Weekly growth rates of scallops in the spring were more than twice that of the fall (∼1.5 vs. 0.6 mm per week). Spring growth rates were statistically greater at Cape Lookout than at Oscar Shoal. The actual difference in growth, however, was <1 mm (7.34±0.13 mm and 6.45±0.19 mm over 5 weeks, respectively), and most likely would not have produced significant biological effects such as differential predation rates. Average growth of juvenile scallops placed in the center (0.75×0.75 m area) of replicate small (∼1 m across) patches was faster than in large (>8 m across) patches over 5–7 week periods during both seasons. The difference in growth, however, was small (∼1 mm) and would probably have little biological significance. In the spring, scallop survivorship after 2 weeks did not differ between sites or among seagrass patches of varying size. After an additional 3 weeks however, scallop survivorship was approximately 30% greater at the site dominated by Zostera marina with lower shoot density, but there was no difference in survivorship among seagrass patch sizes. The same pattern was observed over the cumulative 5-week period. In the fall, predation rates on juvenile scallops were significantly higher in small patches than in large over very short time intervals (e.g., 24 h). Over 3-, 4- and 7-week time intervals, however, there was no effect of patch size on scallop survival, even though shoot densities were significantly greater in medium- and large-sized patches than in small. Lack of a long-term patch size and/or seagrass density effect on scallop survivorship may be due to differential responses to patch size by the many potential predators that prey on juvenile scallops.

Temperature responses and nuclear DNA amounts of seven white clover populations which differ in early spring growth rates

The growth of seven white clover populations differing in morphology, geographic origin, and seasonality of growth was measured at constant temperatures ranging from 5°C to 25°C in controlled environment chambers. All populations showed increased growth up to a maximum of 20–25°C, but there were significant shifts in the relative performance of the populations at different temperatures. Leaf appearance rates, leaf sizes, and stolon extension rates were all differentially affected by temperature. Growth potential in the late winter to early spring period in the warm‐temperate New Zealand climate appeared to be strongly related to the ability of plants to grow at 5°C. The most rapid growing populations at 5°C ('Daeno’, ML‐48–65) originated from continental climates. Differences of up to 21% in 2C nuclear DNA amounts were measured between the white clover populations by microdensitometry. The results were generally consistent with the prediction that large genome size is associated with capacity for growth at low temperatures, whereas small genome size is associated with superior growth at higher temperatures. The two closely‐related Pitau and G49 populations were an exception to this trend.

Relation of Fish Size and Growth Rate to Migration of Spring Chinook Salmon Smolts

Abstract We examined the relation of size and growth rate to downstream migration in yearling spring chinook salmon Oncorhynchus tshawytscha. A group of juvenile chinook salmon was graded by size into small and large categories; half the fish in each category were reared at an elevated temperature beginning in mid-February, resulting in four distinct treatment groups: large–warm, large–cool, small–warm, and small–cool. Fish from warmwater treatment groups displayed significantly higher growth rates through the spring than coolwater groups. Fish were released into a natural creek on two dates (25 March, release 1 and 12 April, release 2), and downstream movement was monitored. For each release, fish that migrated past a weir within the first 5 d postrelease had significantly higher spring growth rates than fish that did not migrate within that period. A similar comparison of release length to migration demonstrated significant differences only in release 2. Also for release 2, fish from the large–warm and ...