Temporal Variability In Growth Research Articles

Incorporating distribution shifts and spatio-temporal variation when estimating weight-at-age for stock assessments: a case study involving the Bering Sea pollock (Gadus chalcogrammus)

AbstractEnvironmental conditions can create spatial and temporal variability in growth and distribution processes, yet contemporary stock assessment methods often do not explicitly address the consequences of these patterns. For example, stock assessments often assume that body weight-at-age (i.e. size) is constant across the stocks’ range, and may thereby miss important spatio-temporal patterns. This is becoming increasingly relevant given climate-driven distributional shifts, because samples for estimating size-at-age can be spatially unbalanced and lead to biases when extrapolating into unsampled areas. Here, we jointly analysed data on the local abundance and size of walleye pollock (Gadus chalcogrammus) in the Bering Sea, to demonstrate a tractable first step in expanding spatially unbalanced size-at-age samples, while incorporating fine-scale spatial and temporal variation for inclusion in stock assessments. The data come from NOAA’s bottom trawl survey data and were evaluated using a multivariate spatio-temporal statistical model. We found extensive variation in size-at-age at fine spatial scales, though specific patterns differed between age classes. In addition to persistent spatial patterns, we also documented year-to-year differences in the spatial patterning of size-at-age. Intra-annual variation in the population-level size-at-age (used to generate the size-at-age matrix in the stock assessment) was largely driven by localized changes in fish size, while shifts in species distribution had a smaller effect. The spatio-temporal size-at-age matrix led to marginal improvement in the stock assessment fit to the survey biomass index. Results from our case study suggest that accounting for spatially unbalanced sampling improved stock assessment consistency. Additionally, it improved our understanding on the dynamics of how local and population-level demographic processes interact. As climate change affects fish distribution and growth, integrating spatiotemporally explicit size-at-age processes with anticipated environmental conditions may improve stock-assessment forecasts used to set annual harvest limits.

Spatial and Temporal Variability in Growth of Giant Gartersnakes: Plasticity, Precipitation, and Prey

Abstract The growth rate of reptiles is plastic and often varies among individuals, populations, and years in response to environmental conditions. For an imperiled species, the growth rate of individual animals is an important component of demographic models, and changes in individual growth rates might precede changes in abundance. We analyzed a long-term dataset on the growth of Giant Gartersnakes (Thamnophis gigas) to characterize spatial and temporal variability and evaluate potential environmental predictors of growth. We collected data on the growth in snout–vent length (SVL) of Giant Gartersnakes over 22 yr (1995–2016) from eight sites distributed throughout the Sacramento Valley of California, USA. The von Bertalanffy growth curves indicated male Giant Gartersnakes grew faster toward shorter, asymptotic SVL than did females. Nearly equal variability in growth was attributable to differences among years and among sites. From 2003–2016 we collected data on precipitation, temperature, and the abunda...

Evaluating spatial and temporal variability in growth and mortality for recreational fisheries with limited catch data

Understanding the spatial and temporal variability in life-history traits among populations is essential for the management of recreational fisheries. However, valuable freshwater recreational fish species often suffer from a lack of catch information. In this study, we demonstrated the use of an approach to estimate the spatial and temporal variability in growth and mortality in the absence of catch data and apply the method to riverine smallmouth bass (Micropterus dolomieu) populations in Pennsylvania, USA. Our approach included a growth analysis and a length-based analysis that estimates mortality. Using a hierarchical Bayesian approach, we examined spatial variability in growth and mortality by assuming parameters vary spatially but remain constant over time and temporal variability by assuming parameters vary spatially and temporally. The estimated growth and mortality of smallmouth bass showed substantial variability over time and across rivers. We explored the relationships of the estimated growth and mortality with spring water temperature and spring flow. Growth rate was likely to be positively correlated with these two factors, while young mortality was likely to be positively correlated with spring flow. The spatially and temporally varying growth and mortality suggest that smallmouth bass populations across rivers may respond differently to management plans and disturbance such as environmental contamination and land-use change. The analytical approach can be extended to other freshwater recreational species that also lack of catch data. The approach could also be useful in developing population assessments with erroneous catch data or be used as a model sensitivity scenario to verify traditional models even when catch data are available.

Non-genetic sources of variation and temporal variability in growth and feed efficiency traits among phylogenetically distinct clusters of indigenous chicken in Kenya.

This study aims to investigate the influence of non-genetic factors on feed efficiency in indigenous chicken. Residual feed intake (RFI), residual gain (RG) and residual intake and gain (RIG) were used as measures of feed efficiency. Feed intake and body weight data were collected on 107 experimental birds on a daily and weekly basis, respectively, from ages 11 to 20weeks. A general linear model was fitted to determine the effect of sex, cluster, genotype and hatch group on mean performance and to assess temporal variation across clusters. The overall mean performance for daily gain (ADG), daily feed intake (ADFI), weekly metabolic body weight (MBW), RFI, RG and RIG was 10.38g/day, 133.01g/day, 164.12g/day, 0.00 (±14.23), 0.00 (±1.83) and 0.00 (±14.64), respectively. Sex significantly influenced variation in ADG and RG while hatch group influenced all traits except ADFI. Cluster and genotype had no effect on the traits. Interaction between sex and cluster significantly influenced ADFI, RFI and RIG. There was a significant temporal variation within and among clusters resulting in re-ranking of the phylogenetic groups in efficiency across the test period. Results indicate that growth and feed efficiency traits are influenced by non-genetic factors which should be accounted for, to reduce bias and improve accuracy of performance evaluations in the indigenous chicken.

Spatial and temporal variability in growth of southern flounder (Paralichthys lethostigma)

Delineation of stock structure is important for understanding the ecology and management of many fish populations, particularly those with wide-ranging distributions and high levels of harvest. Southern flounder (Paralichthys lethostigma) is a popular commercial and recreational species along the southeast Atlantic coast and Gulf of Mexico, USA. Recent studies have provided genetic and otolith morphology evidence that the Gulf of Mexico and Atlantic Ocean stocks differ. Using age and growth data from four states (Texas, Alabama, South Carolina, and North Carolina) we expanded upon the traditional von Bertalanffy model in order to compare growth rates of putative geographic stocks of southern flounder. We improved the model fitting process by adding a hierarchical Bayesian framework to allow each parameter to vary spatially or temporally as a random effect, as well as log transforming the three model parameters (L∞, K, and t0). Multiple comparisons of parameters showed that growth rates varied (even within states) for females, but less for males. Growth rates were also consistent through time, when long-term data were available. Since within-basin populations are thought to be genetically well-mixed, our results suggest that consistent small-scale environmental conditions (i.e., within estuaries) likely drive growth rates and should be considered when developing broader scale management plans.

And yet it shrinks: A novel method for correcting bias in forest tree growth estimates caused by water-induced fluctuations

Accuracy in tree woody growth estimates is important to global carbon budget estimation and climate-change science. Tree growth in permanent sampling plots (PSPs) is commonly estimated by measuring stem diameter changes, but this method is susceptible to bias resulting from water-induced reversible stem shrinkage. In the absence of bias correction, temporal variability in growth is likely to be overestimated and incorrectly attributed to fluctuations in resource availability, especially in forests with high seasonal and inter-annual variability in water. We propose and test a novel approach for estimating and correcting this bias at the community level.In a 50-ha PSP from a seasonally dry tropical forest in southern India, where tape measurements have been taken every four years from 1988 to 2012, for nine trees we estimated bias due to reversible stem shrinkage as the difference between woody growth measured using tree rings and that estimated from tape. We tested if the bias estimated from these trees could be used as a proxy to correct bias in tape-based growth estimates at the PSP scale.We observed significant shrinkage-related bias in the growth estimates of the nine trees in some censuses. This bias was strongly linearly related to tape-based growth estimates at the level of the PSP, and could be used as a proxy. After bias was corrected, the temporal variance in growth rates of the PSP decreased, while the effect of exceptionally dry or wet periods was retained, indicating that at least a part of the temporal variability arose from reversible shrinkage-related bias. We also suggest that the efficacy of the bias correction could be improved by measuring the proxy on trees that belong to different size classes and census timing, but not necessarily to different species.Our approach allows for reanalysis – and possible reinterpretation – of temporal trends in tree growth, above ground biomass change, or carbon fluxes in forests, and their relationships with resource availability in the context of climate change.

Effects of Temperature on Age‐0 Atlantic Menhaden Growth in Chesapeake Bay

AbstractAtlantic Menhaden Brevoortia tyrannus is an economically and ecologically important forage fish in the western Atlantic Ocean. In the Chesapeake Bay, its recruitment has been low since the late 1980s, prompting questions on how environmental factors may affect its productivity. Growth is an important component of production, but causes of spatial and temporal variability in growth of age‐0 Atlantic Menhaden are not fully understood. Our objective was to quantify the effect of temperature on spatial and temporal variability in growth of age‐0 Atlantic Menhaden in Chesapeake Bay. We analyzed data on mean length and temperature for years 1962–2011 from nine regions of Chesapeake Bay. We developed a linear model that relates mean total length of Atlantic Menhaden to cumulative growing degree‐days (GDDs) in Chesapeake Bay and validated the model using data that were withheld from the initial parameter estimation. The temperature threshold that best described variability in growth was 14°C, a temperature substantially higher than the physiological threshold for growth. The GDD model explained almost 80% of the variability in mean length over time (within and among years) and among regions. In a model validation exercise, it accurately predicted mean length in tributary subregions of the bay not included in the original model fitting. The GDD model requires only temperature data to effectively predict growth, making it simpler to apply than models requiring more complex approaches.Received August 22, 2013; accepted May 30, 2014

Estimation of regional sheep abundance based on group sizes

ABSTRACTWe used sightability models with aerial counts to estimate regional abundance of desert bighorn sheep (Ovis canadensis) in southwestern Arizona during 1992–2012. Because of incomplete spatial and temporal coverage of surveys, we integrated sightability estimates using Bayesian state‐space models. Although some game management units (GMUs) exhibited negative average growth rates during this period, temporal variability in growth was large. The combination of temporal variability and statistical uncertainty in the sightability estimates led to the selection of a regional model having zero mean growth from initial abundance. Hence, the model indicated a relatively stable population of desert bighorn sheep in southern Arizona, beginning with approximately 2,900 bighorn sheep in 1992 to the current number of approximately 2,300 sheep (2012). Our method provides statistically valid estimates of overall regional abundance not otherwise possible given the incomplete spatial coverage of surveys. Additionally, results have implications for other studies, common in wildlife management, where managers seek to integrate information across surveys with partial time‐series. © 2014 The Wildlife Society.

Thinning prolongs growth duration of European beech (Fagus sylvatica L.) across a valley in southwestern Germany

Analyses of seasonal growth patterns of trees permit an increased understanding on growth responses to year-to-year weather variability and site-specific conditions. In this study, growth responses of European beech (Fagus sylvatica L.) to thinning were analyzed in a narrow valley in southwestern Germany over a six-year study period (2001–2006). We considered three thinning treatments (unthinned control, intermediate thinning and heavy thinning), two aspects (north-east and south-west) and three social classes (predominant, dominant and co-dominant).The growth of 72 beech trees was monitored using automatic point dendrometers. To obtain seasonal curve parameters for statistical analyses, we fitted cumulative Weibull functions to standardized annual dendrometer series. The scale and shape parameter of this function, T and m, were used as indicators of timing and duration of growth, respectively. Together with annual radial growth, ir, they were analyzed in linear mixed models. Temporal variability in growth reflected inter-annual weather fluctuations; with generally lower growth levels and shorter growth duration in dry years. Further, the extreme dry year 2003 showed a remarkable early growth onset, followed by a late onset in 2004. Effects of thinning treatment highlighted the importance of resource limitation, e.g., water availability, as lowest growth levels were found in trees subjected to high competition in control plots. In addition, results indicated growing season prolongation with thinning. Effects of tree social class and aspect upon ir, T and m were absent or of minor importance, respectively.For both wet and dry years, reduced competition through thinning was found to stimulate growth and to prolong growth duration. Hence, thinning may be suggested as an adaptive forest management tool that may reduce stand vulnerability to drought. Further, this study illustrates that comparable growth levels can be achieved through very different seasonal growth patterns, thereby stressing the importance of intra-annual studies to increase the understanding on growth determinism of beech.

Age-dependency, climate, and environmental controls of recent tree growth trends at subarctic and alpine treelines

Spatial and temporal variability in growth and climate response of trees at and near treeline was investigated in the western Mackenzie Mountains, Northwest Territories, and the Hudson Bay Lowlands of northern Manitoba. Residual ring width chronologies were constructed using cores extracted from 108 trees in the mountains and 170 from the lowlands, and compared to historical climate data. Growth of most trees exhibited significant correlations with summer and autumn temperatures, and the growth–climate relationship did not differ noticeably between trees at and distal to treeline. Most mountain trees had significant positive growth trends from 1851 to 2006 that corresponded with warming over the same period, while growth trends varied among sites and species in the lowlands. Regionally, growth of all species responded positively to warming during the 20th century with the exception of lowland Picea mariana, which exhibited little response. Growth response for most trees was age-dependent, with trees established after 1920 demonstrating improved growth and sensitivity to temperature than older individuals, and growth of most species since the 1990s was greater than any time during the last 250 years, particularly for lowland Larix laricina. This study suggests that site factors and tree age can be more important drivers of local-scale growth trends than regional climate at arctic treelines where temperature is often assumed to be the main constraint on tree growth.

Combining a Bayesian nonparametric method with a hierarchical framework to estimate individual and temporal variation in growth

Growth modeling has long played an important role in ecology, conservation and management of many species. However, adopting a statistical framework that includes both temporal and individual variability in the growth dynamics has proven challenging. In this paper, we use a Bayesian state space framework (BSSF) to estimate parameters of a discrete time model from a mark-recapture data set of age-1 juvenile Atlantic salmon. We use a Gaussian process (GP) based approach to model variation in seasonal growth potential. In addition, we use auxiliary information on the food environment as prior knowledge of seasonal fluctuations in growth. Parameters for the GP prior and measurement error variances were fixed to speed convergence. Posterior estimates of model parameters were relatively insensitive to these choices. Our model captures the seasonal growth dynamics of juvenile Atlantic salmon as evidenced by close agreement between observed and predicted lengths (r2=0.98). In addition, the relatively narrow confidence intervals indicated significant learning in the parameters of interest. Finally, our model approach was able to accurately recover missing data points. Although this model was applied to a mark-recapture dataset of Atlantic salmon, the generality of the approach should make it applicable to a wide variety of size trajectory datasets, and thus, provides a useful tool to estimate individual and temporal variability in growth from datasets with repeated measurements.

Smolt Transformation in Two California Steelhead Populations: Effects of Temporal Variability in Growth

AbstractWe tested the effect of temporal patterns in food supply on life history decisions in coastal steelhead Oncorhynchus mykiss irideus from a Central California coastal (CCC) population (Scott Creek) and a Northern California Central Valley (NCCV) population (upper Sacramento River basin). We manipulated growth through feeding experiments conducted from May to the following March using warm (2006 cohort) and cool (2007 cohort) temperature regimes. Survival in seawater challenges just before the time of typical juvenile emigration provided an index of steelhead smolt versus nonsmolt life history pathways. Survival varied significantly with fish size (with larger fish being more likely to survive than smaller fish) and by source population (with CCC steelhead being more likely to survive than NCCV steelhead of the same size). The timing of increased food supply (treatment group) did not significantly affect seawater survival rates in either NCCV or CCC steelhead. For both strains, the eventual survivors of seawater challenges (putative smolts) diverged from the eventual mortalities (putative nonsmolts) in both size and growth rate by June in both years, suggesting that the initial growth advantages were maintained throughout the experiments. A significant divergence in condition factor between smolts and nonsmolts by December matched the expected morphological transition of smolts, which showed faster growth in length than weight compared with nonsmolts. The apparent timing of the decision window, several months before the typical period of smolt emigration, matches the patterns observed for other salmonids. In coastal California, this decision must occur before fish have had the opportunity to take advantage of improved winter–early spring feeding conditions. These results support the role of early growth opportunity in life history decisions and provide insight into the applicability of life history models for managing California steelhead.

Spatial and Temporal Variability in Growth of Hawaiian Spiny Lobsters in the Northwestern Hawaiian Islands

AbstractGrowth rates were estimated for recaptured Hawaiian spiny lobsters Panulirus marginatus tagged between 2002 and 2007 at Necker Island (23°30′N; 164°35′W), Gardner Pinnacles (25°00′N; 168°50′W), and Maro Reef (25°30′N; 170°45′W) in the Northwestern Hawaiian Islands (NWHI). The location and year‐specific nature of the tag–recapture cruises enabled investigation of spatial and temporal variability in growth. Mean growth rates, estimated by using the von Bertalanffy and Schnute growth models and fitted via a maximum likelihood technique, differed between sexes and particularly among locations and years. Male lobster growth rates at Necker Island were, in general, one‐third those at Gardner Pinnacles and one‐half those at Maro Reef. Female lobsters exhibited the same pattern with less‐pronounced differences. Maro Reef lobsters exhibited several abrupt, significant growth reductions among years, while Necker Island lobster growth rates increased significantly from 2004 to 2005. Model results also indicated substantial individual variability in growth. Neither density nor temperature could account for the differences in growth rates. No palinurid species studied to date has shown such spatial variability in growth, and only one panilurid species has exhibited similar variability on a temporal scale. Recognition of and accounting for the mean and individual variability in a life history trait of this endemic species will result in more accurate stock assessments and, ultimately, a better understanding of lobster dynamics and the NWHI coral reef ecosystem.

Experimental investigation of spatial and temporal variation in estuarine growth of age-0 juvenile red drum ( Sciaenops ocellatus)

Many ecological processes that occur during fish early life history stages are influenced by body size and multiple factors often work synergistically across space and through time to generate variation in body size among individuals. We conducted a replicated field experiment that was designed to quantify the level of spatial and temporal variation in growth of age-0 juvenile red drum during the 2–3 month estuarine recruitment period. The experiment was conducted over 53 consecutive days during fall (Oct–Dec) 2004 in a southeastern North Carolina estuary that has demonstrated consistent annual recruitment of red drum juveniles. After field capture and laboratory acclimatization, fish (30–52 mm TL; 0.19–1.11 g wet weight) were placed in pairs into one of three replicated field cages positioned at six sites along the estuarine salinity gradient. Growth was monitored for five consecutive 10–11 day intervals, with fish replaced between each interval. Time (experimental interval), space (estuary region), and the time × space interaction were evaluated for their effect on juvenile red drum growth. Results demonstrated a significant decrease in growth rates through time and significantly faster growth rates in the central region of the estuary with no significant interaction. The temporal variation in growth appeared to be mostly driven by declining fall water temperatures throughout the estuary. The consistent spatial variation in growth, with fastest growth realized in the central region, regardless of time, may have been partially due to consistent salinity differences among estuary regions. Moderate salinities (15–25 ppt) may enhance osmoregulatory efficiency in juvenile red drum and allow greater scope for growth. The degree of spatial and temporal variability in growth observed in this study implies that the timing of estuarine arrival and initial settlement habitat may have a strong influence on size at age patterns of first year red drum in North Carolina, and thus may impact early juvenile survival and eventual year-class success.

Spatial and Temporal Variability in Growth of Rhizophora Mangle Saplings on Coral Cays: Links with Variation in Insolation, Herbivory, and Local Sedimentation Rate

1 We used demographic growth analysis to quantify seasonal and annual patterns of shoot and root module production by Rhizophora mangle saplings growing on three coral cays in Belize, Central America. We investigated scaling relationships among root and shoot modules, leaf life-span, effects of herbivores on module and whole plant growth, and differences in growth under different sedimentation regimes. 2 Production of new shoots and aerial roots occurred seasonally. Annual peaks in solar insolation occurred in May; relative rates of change in numbers of shoot meristems and leaves, and stem length peaked one month following. Relative rate of change in numbers of aerial roots peaked one month following this shoot flush, and roots elongated primarily during the dry season. 3 Increased water depth was positively correlated with the ratio of root length to shoot length in saplings. Mean shoot growth rate was significantly lower at cays exhibiting relatively low sedimentation rates, as well as at similar locales within cays. 4 Average leaf life-span was 9 months. During an outbreak of the mangrove skipper Phocides pigmalion, insect herbivores shortened leaf life-span by increasing leaf abscission rate. Insect folivores reduced above-ground net primary production available for export to adjacent marine ecosystems by 5-20%. Up to seven-fold increases in percentage of roots bored by isopods occurred concomitantly with annual peaks in new root production. Relative elongation rate of roots decreased five-fold following isopod attack. However, whilst both insects and isopods tracked production of and consumed new modules, neither consumer contributed significantly to variance in whole-plant growth. 5 Demographic growth analysis is a powerful tool with which to predict dynamic responses of module production and whole-plant growth in response to local environmental conditions. Our analyses illustrate that growth of mangroves are sensitive to seasonal patterns of insolation, to decreasing sedimentation and to increasing water depth. Given that growth of mangrove saplings on coral cays declines significantly with sedimentation rate, persistence of these forests is unlikely if sea level in the Caribbean increases as predicted.