22 research outputs found
Environmental influences on growth, maturation and smoltification in Atlantic salmon parr, Salmo salar
The maturation of Atlantic salmon (Safmo safar) parr, and its effects on growth and
smoltification, causes significant economic losses to commercial aquaculture. The
current thesis investigates the role of environmental factors on freshwater
development, with the aim of providing information which would help reduce the
currently observed levels of maturation in farmed salmon.
The effects of short day "winter" photoperiods were investigated by exposing three
replicated groups of fish to an 8 week "winter" photoperiod (LDlO:14) commencing
in May, August or September, in an otherwise continuous light (LD24:0) regime. A
further group was held on LD24:0 throughout. 200 to 300 individuals were PIT
tagged in each group in order to follow the growth of fish undergoing different
developmental strategies, with the retrospective analysis of such development also
possible. The highest incidence of maturation (>20%) was observed in the May winter
photoperiod group, with low levels recorded in the August and September fish «4%),
suggesting that maturation may be influenced during a "critical" period in early
development. Maturation levels were intermediate «9%) in the continuous light
group indicating that seasonally-changing photoperiodic cues are not necessarily
required for gonadal development. The size of mature fish was initially the same as
both immature parr and smolts, although the growth of mature individuals
subsequently declined, and at the conclusion of the experiment they were significantly
smaller. The August photoperiod resulted in the highest incidence of smoltification,
with all other treatments resulting in low levels.
In a second experiment, PIT tagged fish were reared under an 8 or 12 week ''winter''
photoperiod (LD 10: 14) starting in Mayor June, in an otherwise continuous light
(LD24:0) regime. The highest incidence of maturation (> 11 %) was found in the 12
week May fish, with intennediate levels in the 8 week May and 8 week June groups
«8%). Low levels were found within the 12 week June group «0.6%) and it is
suggested that a critical period when maturation is influenced may occur during a
specific, short period in early development. Throughout the experiments, mature
individuals maintained the same size as their immature siblings. The 12 week June
photoperiod appeared to result in the highest level of smoltification, although those
exposed to the 12 week May photoperiod showed the greatest seawater survival.
In both photoperiod experiments, fish showing some signs of smoltification were also
found to be undergoing gonadal development, indicating that maturation and
smoltification are not completely mutually exclusive processes.
Possible nutritional effects were considered using different dietary lipid inclusions
(either 12.5% or 25%) and variable rations of feed (either full, 2/3 or 113 rations).
Different dietary lipid inclusions had no effect on growth, although the whole body fat
content of individuals was affected, with a switch in dietary fat content during
development resulting in a rapid change in body composition. Fish size increased with
ration and, although at the lowest ration of feed whole body fat levels were reduced,
they were maintained at a set level under the high and intennediate rations, implying a
lipostatic control of growth. Maturation levels were low throughout the nutrition
experiments, suggesting that genetic influences may have been important. Dietary
lipid level had a negligible effect on smoltification, although increases in ration
resulted in a greater incidence of smoltification. Using a 0+ photoperiod regime (i.e.
LD24:0 applied from March until December, with the exception of an 8 week period
of LD17:7 applied from August), smolting individuals showed a reduction in smolt
status when compared to those developed under a natural photoperiod. It is suggested
that such regimes restrict the mobilisation of long-tenn energy stores, with the
subsequent development of seawater tolerance affected. However, it was noted that
the 0+ regime had increased the incidence of smolts.
In summary, it has been shown that environmental factors such as photoperiod,
nutrition and temperature can play an important role in the developmental strategies
taken by juvenile Atlantic salmon. Such factors are likely to greatly influence the
attainment of size and/or nutritional thresholds necessary for various developmental
strategies, in particular if such thresholds occur during seasonally-sensitive "critical"
periods when development can be influenced. Furthermore, the life history strategy
undertaken by an individual may be affected by endogenous rhythms, cued by
seasonally-changing environmental factors. However, there are clear indications that
the underlying genetic control of maturation may also be of importance
Bark Thickness in Coast Redwood (Sequoia sempervirens (D.Don) Endl.) Varies According to Tree- and Crown Size, Stand Structure, Latitude and Genotype
Research Highlights: Bark thickness (BT) in coastal redwood (Sequoia sempervirens (D.Don) Endl.) varies in accordance with tree size, crown ratio, position within the canopy, height along the tree stem, genetic identity and latitude. However, current BT predictive equations do not account for such variability, leading to inaccurate BT estimations. We present improved BT models to increase the accuracy of BT estimates for coastal redwood in northern California. Background and Objectives: BT is an important metric that has many practical applications in forest management. However, BT varies substantially across species and environments, as well as across individuals and populations. Our objectives were to investigate BT along various gradients of change, with factors accounting for genetics, tapering of BT along the tree bole, differences in BT according to tree crown position within the stand, and the latitude. Materials and Methods: We collected BT data throughout most of redwood’s natural range along a north–south latitudinal gradient. Subsets of these data were used to examine the influence of particular variables on BT while holding the other variables constant. Results: Regionally, the bark was thicker among more xeric southern redwoods and thinner among more mesic northern redwoods. We found that the BT of codominant, intermediate and suppressed trees was around 8%, 14%, and 18% thicker, respectively, than bark of the same size dominant tree. Redwood trees growing in the partial shade of an overstory had thicker bark than trees growing in even-aged stands and incorporating genetic identity yielded major improvements in the BT model estimates, suggesting that BT is under genetic control. Bark thickness decreased with increasing height along the tree stem, with notable differences in the BT above and below breast height. Conclusions: We recommend utilizing the best available BT equations (over standard ‘bark factors’) in forest science, modeling and management applications. We also recommend the adoption of our drilling method for BT measurement on larger trees due to the potential for error associated with traditional bark gauge measurements
76-Year Decline and Recovery of Aspen Mediated by Contrasting Fire Regimes: Long-Unburned, Infrequent and Frequent Mixed-Severity Wildfire
Quaking aspen (Populus tremuloides) is a valued, minor component on northeastern California landscapes. It provides a wide range of ecosystem services and has been in decline throughout the region for the last century. This decline may be explained partially by the lack of fire on the landscape due to heavier fire suppression, as aspen benefit from fire that eliminates conifer competition and stimulates reproduction through root suckering. However, there is little known about how aspen stand area changes in response to overlapping fire. Our study area in northeastern California on the Lassen, Modoc and Plumas National Forests has experienced recent large mixed-severity wildfires where aspen was present, providing an opportunity to study the re-introduction of fire. We observed two time periods; a 52-year absence of fire from 1941 to 1993 preceding a 24-year period of wildfire activity from 1993 to 2017. We utilized aerial photos and satellite imagery to delineate aspen stands and assess conifer cover percent. We chose aspen stands in areas where wildfires overlapped (twice-burned), where only a single wildfire burned, and areas that did not burn within the recent 24-year period. We observed these same stands within the first period of fire exclusion for comparison (i.e., 1941–1993). In the absence of fire, all aspen stand areas declined and all stands experienced increases in conifer composition. After wildfire, stands that burned experienced a release from conifer competition and increased in stand area. Stands that burned twice or at high severity experienced a larger removal of conifer competition than stands that burned once at low severity, promoting expansion of aspen stand area. Stands with less edge:area ratio also expanded in area more with fire present. Across both time periods, stand movement, where aspen stand footprints were mostly in new areas compared to footprints of previous years, was highest in smaller stands. In the fire exclusion period, smaller stands exhibited greater loss of area and changes in location (movement) than in the return of fire period, highlighting their vulnerability to loss via succession to conifers in the absence of disturbances that provide adequate growing space for aspen over time
Integrated Radiation Transport and Nuclear Fuel Performance for Assembly-Level Simulations
The Advanced Multi-Physics (AMP) Nuclear Fuel Performance code (AMPFuel) is focused on predicting the temperature and strain within a nuclear fuel assembly to evaluate the performance and safety of existing and advanced nuclear fuel bundles within existing and advanced nuclear reactors. AMPFuel was extended to include an integrated nuclear fuel assembly capability for (one-way) coupled radiation transport and nuclear fuel assembly thermo-mechanics. This capability is the initial step toward incorporating an improved predictive nuclear fuel assembly modeling capability to accurately account for source-terms and boundary conditions of traditional (single-pin) nuclear fuel performance simulation, such as the neutron flux distribution, coolant conditions, and assembly mechanical stresses. A novel scheme is introduced for transferring the power distribution from the Scale/Denovo (Denovo) radiation transport code (structured, Cartesian mesh with smeared materials within each cell) to AMPFuel (unstructured, hexagonal mesh with a single material within each cell), allowing the use of a relatively coarse spatial mesh (10 million elements) for the radiation transport and a fine spatial mesh (3.3 billion elements) for thermo-mechanics with very little loss of accuracy. In addition, a new nuclear fuel-specific preconditioner was developed to account for the high aspect ratio of each fuel pin (12 feet axially, but 1 4 inches in diameter) with many individual fuel regions (pellets). With this novel capability, AMPFuel was used to model an entire 17 17 pressurized water reactor fuel assembly with many of the features resolved in three dimensions (for thermo-mechanics and/or neutronics), including the fuel, gap, and cladding of each of the 264 fuel pins; the 25 guide tubes; the top and bottom structural regions; and the upper and lower (neutron) reflector regions. The final, full assembly calculation was executed on Jaguar using 40,000 cores in under 10 hours to model over 162 billion degrees of freedom for 10 loading steps. The single radiation transport calculation required about 50% of the time required to solve the thermo-mechanics with a single loading step, which demonstrates that it is feasible to incorporate, in a single code, a high-fidelity radiation transport capability with a high-fidelity nuclear fuel thermo-mechanics capability and anticipate acceptable computational requirements. The results of the full assembly simulation clearly show the axial, radial, and azimuthal variation of the neutron flux, power, temperature, and deformation of the assembly, highlighting behavior that is neglected in traditional axisymmetric fuel performance codes that do not account for assembly features, such as guide tubes and control rods
Epicormic sprout development in pruned coast redwood: pruning severity, genotype, and sprouting characteristics
• Young coast redwood (Sequoia sempervirens (D. Don.) Endl.) trees were pruned to various heights
to examine the effect of pruning severity on epicormic sprouting. Seven
separate stands were used with as many as six treatments per stand in
coastal Humboldt County, California, USA.
• Epicormic sprout development was affected by pruning severity but primarily
at the most severe pruning treatments that removed all but the branches in
the top 15% of tree height. Less severe treatments produced sprouts
but the number and size of these sprouts were comparable to unpruned trees.
• Natural clonal patterns were also used to explore patterns of sprouting
between genotypes. Linear mixed-effects models were developed to predict
sprouting frequency as a function of pruning severity while accounting for
the nested data structure (i.e., stem sections sampled nested within
genotypes within treatments within sites).
• Comparing variances attributed to each of these random effects indicated
that at any level of pruning severity, differences in epicormic sprouting
between genotypes and sites expressed soon after pruning had disappeared
after six growing seasons. Epicormic branches were more common two years
after pruning than six years indicating many branches were dying. Branches
were more common in the middle of the pruned bole, possibly because of
competition from basal sprouts and the expanding tree crown.Développement de rejets épicormiques sur
des séquoias californiens : intensité de l'élagage,
génotype, caractéristiques des rejets. • De jeunes séquoias de Californie (Sequoia sempervirens (D. Don.) Endl.) ont été
élagués à différentes hauteurs afin d'examiner l'effet de
l'intensité de l'élagage sur les rejets épicormiques. Sept
peuplements ont été utilisés avec jusqu'à six traitements
par peuplement dans la région côtière du Comté de Humboldt
en Californie (USA).
• Le développement des rejets épicormiques a été affecté
par l'intensité de l'élagage, mais surtout par les traitements les
plus sévères qui ont presque supprimé toutes les branches au
sommet sur 15 % de la hauteur des arbres. Des traitements moins
sévères ont produit des rejets, mais le nombre et la dimension de
ces rejets étaient comparables à ceux des arbres non
élagués.
• Des clones naturels ont également été utilisés pour explorer
les modèles de rejet entre génotypes. Des modèles linéaires
a effets mixtes ont été développés pour prédire la
fréquence des rejets en fonction de l'intensité de l'élagage, en
prenant en compte la structure imbriquée des données
(c'est-à -dire, les sections du tronc échantillonnées,
imbriquées avec les génotypes, les traitements et les stations).
• La comparaison des variances attribuées à chacun de ces effets
aléatoires a indiqué qu'à tout niveau d'intensité
d'élagage, les différences de rejets épicormiques entre les
génotypes et les stations exprimées peu de temps après la taille
avaient disparu au bout de six saisons de croissance.
• Les branches épicormiques ont été plus fréquentes deux ans
après l'élagage que six ans plus tard indiquant que de nombreuses
branches sont en train de mourir. Les branches ont été plus
fréquentes dans le milieu de la partie du tronc élaguée,
peut-être en raison de la concurrence des rejets de la base et de
l'expansion du houppier
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Bark Thickness in Coast Redwood (Sequoia sempervirens (D.Don) Endl.) Varies According to Tree- and Crown Size, Stand Structure, Latitude and Genotype
Research Highlights: Bark thickness (BT) in coastal redwood (Sequoia sempervirens (D.Don) Endl.) varies in accordance with tree size, crown ratio, position within the canopy, height along the tree stem, genetic identity and latitude. However, current BT predictive equations do not account for such variability, leading to inaccurate BT estimations. We present improved BT models to increase the accuracy of BT estimates for coastal redwood in northern California. Background and Objectives: BT is an important metric that has many practical applications in forest management. However, BT varies substantially across species and environments, as well as across individuals and populations. Our objectives were to investigate BT along various gradients of change, with factors accounting for genetics, tapering of BT along the tree bole, differences in BT according to tree crown position within the stand, and the latitude. Materials and Methods: We collected BT data throughout most of redwood’s natural range along a north–south latitudinal gradient. Subsets of these data were used to examine the influence of particular variables on BT while holding the other variables constant. Results: Regionally, the bark was thicker among more xeric southern redwoods and thinner among more mesic northern redwoods. We found that the BT of codominant, intermediate and suppressed trees was around 8%, 14%, and 18% thicker, respectively, than bark of the same size dominant tree. Redwood trees growing in the partial shade of an overstory had thicker bark than trees growing in even-aged stands and incorporating genetic identity yielded major improvements in the BT model estimates, suggesting that BT is under genetic control. Bark thickness decreased with increasing height along the tree stem, with notable differences in the BT above and below breast height. Conclusions: We recommend utilizing the best available BT equations (over standard ‘bark factors’) in forest science, modeling and management applications. We also recommend the adoption of our drilling method for BT measurement on larger trees due to the potential for error associated with traditional bark gauge measurements