Post-release Growth Research Articles

Life histories of Abies alba and Picea abies growing in old-growth forests driven by natural gap-phase dynamics

We analyzed growth trajectories recorded in the tree-ring series of Norway spruce Picea abies (L.) H. Karst. and silver fir Abies alba Mill. co-occuring with European beech Fagus sylvatica L. in old-growth forests driven by natural stand dynamics. The study sites were localized in five old-growth stands in the Western Carpathians (Central Europe). We characterized the life histories of 218 individual trees by using 25 metrics which refer to the age of the trees, number of release events, reaction to releases, radial increment and basal area increment. We found a large variation in the dbh-age relationship. The life histories of most trees included two or three (in single cases up to seven) release events. We did not find tree age as an important factor in determining post-release growth response. The maximal basal area increment was frequently registered at the terminal stage of tree life. The life histories of spruces and firs did not significantly differ. We concluded that in natural forests driven by gap-phase dynamics, the history of release events is the primary driver of tree growth and that tree age plays a secondary role. After reaching the overstory, trees can continue growing without significant symptoms of aging until extrinsic forces cause their death. Our results indicate that in the studied ecosystem the persistence of less shade-tolerant spruce is not attributable to the niche differentiation and site partitioning mechanism. An alternative hypothesis based on shifts in stand densities, species composition and climatic factors is more probable.

Post-release growth of captive-reared Gharial Gavialis gangeticus (Gmelin, 1789) (Reptilia: Crocodilia: Gavialidae) in Chitwan National Park, Nepal

Supplementation of wild populations of the Critically Endangered Gharial Gavailis gangeticus with individuals reared in captivity is a widely used conservation management tool in Nepal and India, although its efficacy is uncertain. Measuring post-release growth in Gharial can provide valuable information on acclimation of captive-reared Gharial to the wild and provide growth rates to inform population recovery models. We studied post-release growth of Gharial reared in the Gharial Conservation Breeding Centre, Nepal, following their release into the Chitwan National Park. We used recapture data from known individuals to determine growth and change of mass for 26 Gharial recaptured 0.5–10 years after release. We found that Gharial recaptured two or more years post-release had increased in mass and length despite being over six years old at release, however there was a triangular relationship between time since release and growth: some Gharial had grown very slowly, whilst others had grown much faster. All Gharial recaptured less than two years since release had lost mass and had negligible growth in total length. This data show that there is considerable variation in post-release growth rates, which will lead to some individuals being very old before they reach a potentially mature size class, with unknown implications for reproduction. This variation is important for predicting or modelling recovery in populations where the release of Gharial from captivity is a management tool. Our results also suggest the two years after release are an acclimation phase—when Gharial lose mass and do not grow—which should be considered by release strategies in order to give Gharial the best chance of survival after release.

Importance of experienced thermal history: Effect of acclimation temperatures on the high-temperature tolerance and growth performance of juvenile marbled flounder.

Experienced thermal history often affects the temperature tolerance of fish; however, the effect of thermal history on growth performance is unclear. To contribute to effective stocking (release of hatchery-reared juveniles in the field), we conducted four laboratory experiments using juvenile marbled flounder (Pseudopleuronectes yokohamae, around 30mm standard length and 0.3g body wet weight) acclimated at 12°C and 24°C for approximately 2 weeks to investigate the effects of acclimation temperature on high-temperature tolerance, food consumption, and growth performance. The acclimation to 24°C increased tolerance to high temperatures, as shown in a 24-h exposure experiment and in a temperature elevation experiment. The 50% lethal temperature (upper incipient lethal temperature) was estimated to be 25.9°C and 29.0°C for the 12°C and 24°C acclimation groups, respectively. In subsequent experiments, we tested the effects of high and low temperature acclimation on the food consumption and growth performance of two size groups of juveniles (28.7±2.0 and 34.5±2.9mm, mean±SD), that were reared at temperatures ranging from 14°C to 23°C. The optimal temperature for growth was 20°C and did not differ between the acclimation temperatures or between the size groups. However, food consumption and growth performance were suppressed by acute temperature changes. Specifically, feeding and growth were lower in the 24°C-acclimated group than in the 12°C-acclimated group when exposed to 14°C, which is close to the natural water temperature at release in the field. These results suggest that experienced thermal history does not affect the optimal temperature but can affect the growth performance of juveniles. To maximize the post-release growth of hatchery-reared juveniles, the influence of thermal history should be taken into consideration and acute thermal changes before release should be avoided.

Captive-rearing duration may be more important than environmental enrichment for enhancing turtle head-starting success

Raising captive animals past critical mortality stages for eventual release (head-starting) is a common conservation tactic. Counterintuitively, post-release survival can be low. Post-release behavior affecting survival could be influenced by captive-rearing duration and housing conditions. Practitioners have adopted environmental enrichment to promote natural behaviors during head-starting such as raising animals in naturalistic enclosures. Enrichment might be especially beneficial for animals held in captivity long-term to prevent degradation of adaptive behaviors. Using 32 captive-born turtles (Terrapene carolina), half of which were raised in enriched enclosures, we employed a factorial design to explore how enrichment and rearing duration affected post-release growth, behavior, and survival. Six turtles in each treatment (enriched or unenriched) were head-started for nine months (cohort one). Ten turtles in each treatment were head-started for 21 months (cohort two). At the conclusion of captive-rearing, turtles in cohort two were overall larger than cohort one, but unenriched turtles were generally larger than enriched turtles within each cohort. Once released, enriched turtles grew faster than unenriched turtles in cohort two, but we otherwise found minimal evidence suggesting enrichment affected post-release survival or behavior. Cohort two dispersed farther and had generally higher active season survival than cohort one (0.50 vs. 0.33). Body mass was positively associated with daily survival probability. Our findings suggest attaining larger body sizes from longer captive-rearing periods to enable greater movement and alleviate susceptibility to predation (the primary cause of death) could be more effective than environmental enrichment alone in chelonian head-starting programs where substantial predation could hinder success.

Environmental Characteristics Associated with Settlement of Reintroduced Chinese Giant Salamanders

Captive breeding and reintroduction have been increasingly used to restore endangered amphibians worldwide. Knowing habitat requirements for targeted species will help to enhance post release settlement and contribute to the success of reintroduction projects. To collect critical information on habitat requirements of the poorly documented Chinese Giant Salamanders (Andrias davidianus), we reintroduced 31 juveniles at two streams in central China and monitored them through radio telemetry from May 2013 to September 2014. We recorded 14 environmental variables twice a month (except during winter) at salamander locations and random locations. We also conducted transects systematically along streams to collect data on environmental variables and prey species. Habitat selection by salamanders was examined at two spatial scales: home-range scale and stream-reach scale. At the home-range scale, water quality variables were not different between salamander locations and random locations, although salamanders were found in deeper water, used larger boulders, and were closer to boulders. Regression models confirmed that presence of salamanders was positively associated with boulder size, river depth, and canopy cover but negatively associated with distance to boulders. At the stream-reach level, only the average water velocity was lower within home ranges than out of home ranges; however, no difference was found between core home ranges and out of home ranges. These results showed that large boulders were the most important variable selected by salamanders. Plenty of large boulders in the streams, together with evidences of postrelease growth of salamanders, indicate the two streams likely are providing suitable habitat for salamanders.

Effects of hatchery rearing on Florida largemouth bass Micropterus floridanus resource allocation and performance under semi-natural conditions.

This study examined the growth, activity, metabolism and post-release survival of three groups of Florida largemouth bass Micropterus floridanus: wild-caught fish, hatchery fish reared according to standard practice (hatchery standard) and hatchery fish reared under reduced and unpredictable food provisioning (hatchery manipulated). Hatchery-standard fish differed from wild-caught fish in all measured variables, including survival in semi-natural ponds. Hatchery-standard and hatchery-manipulated fish showed higher activity levels, faster growth and lower standard metabolic rates than wild-caught fish in the hatchery. Fish reared under the manipulated feeding regime showed increased metabolic rates and increased post-release growth, similar to wild-caught fish. Their activity levels and post-release survival, however, remained similar to those of hatchery-standard fish. Activity was negatively correlated with post-release survival and failure of the feed manipulation to reduce activity may have contributed to its failure to improve post-release survival. Activity and post-release survival may be influenced by characteristics of the rearing environment other than the feeding regime, such as stock density or water flow rates.

Boldness towards novelty and translocation success in captive‐raised, orphaned Tasmanian devils

Translocation of endangered animals is common, but success is often variable and/or poor. Despite its intuitive appeal, little is known with regards to how individual differences amongst translocated animals influence their post-release survival, growth, and reproduction. We measured consistent pre-release responses to novelty in a familiar environment (boldness; repeatability=0.55) and cortisol response in a group of captive-reared Tasmanian devils, currently listed as "Endangered" by the IUCN. The devils were then released at either a hard- or soft-release site within their mothers' population of origin, and individual growth, movement, reproduction (females only), and survival across 2-8 months post-release was measured. Sex, release method, cohort, behavior, and cortisol response did not affect post-release growth, nor did these factors influence the home range size of orphan devils. Final linear distances moved from the release site were impacted heavily by the release cohort, but translocated devils' movement overall was not different from that in the same-age wild devils. All orphan females of reproductive age were subsequently captured with offspring. Overall survival rates in translocated devils were moderate (∼42%), and were not affected by devil sex, release method, cohort, release weight, or pre-release cortisol response. Devils that survived during the study period were, however, 3.5 times more bold than those that did not (effect size r=0.76). Our results suggest that conservation managers may need to provide developmental conditions in captivity that promote a wide range of behaviors across individuals slated for wild release.

Post‐release feeding and growth of hatchery‐reared Japanese flounder Paralichthys olivaceus: relevance to stocking effectiveness

The feeding and growth of hatchery-reared (HR) Japanese flounder Paralichthys olivaceus of c. 100 mm total length (L(T) ) released off the coast of Fukushima, Japan, were investigated. From 2 to 15 days after release, the HR P. olivaceus frequently exhibited high empty-stomach frequency (>40%), low stomach-content mass (<1% of body mass), reduced somatic condition from release (c.-10%) and negligible growth. Thereafter, empty-stomach frequency decreased, the stomach-content mass of HR fish increased to 2-8% of body mass, the somatic condition recovered and growth rate increased to 0·5-1·5 mm day(-1) . Prey items were initially mysids, shifting thereafter to fishes such as the Japanese anchovy Engraulis japonica, as observed similarly in wild counterparts. The proportion of mysids decreased with time after release irrespective of size at release, indicating the importance of mysids for adaptation to natural food. Recapture rates at age 1 year, derived from fish market surveys, varied greatly among release years (4-11%). The variation in the recapture rates was largely accounted for by the post-release growth rates (r(2) = 0·5), suggesting a relationship between the post-release growth of HR fish and their survival and subsequent stocking effectiveness.

Reduced hatchery rearing density increases social dominance, postrelease growth, and survival in brown trout (Salmo trutta)

Hatchery fish reared for conservation or supplementation often have difficulties adapting to natural conditions, resulting in poor performance in the wild. In a standard hatchery, fish are confined at high densities, which creates a social environment different from that experienced after release. Here we investigated how rearing density influences social dominance, postrelease growth, and survival in brown trout ( Salmo trutta ). Fish were reared at three density treatments: conventional hatchery density, half of conventional hatchery density, and natural density. Four months after hatching, dominance status was determined, and 36 fish from each treatment were released into an enclosed stream and recaptured after 36 days. Trout reared at natural density had higher dominance status and grew faster, both in the hatchery and in the natural stream, than trout from higher densities. Moreover, trout reared at natural density were twice as likely to survive in the stream as trout from higher densities. These novel results suggest that more natural rearing densities would facilitate the development of adaptive behaviour in hatchery salmonids and, thereby, their contribution to natural production.

Response to canopy opening does not act as a filter to Fagus sylvatica and Acer sp. advance regeneration in a mixed temperate forest

• In mixed-species forest stands, large losses in tree species diversity often occur during the regeneration phase. In a former coppice-with-standards, we investigated whether the limiting stage in the recruitment process of advance regeneration is the immediate seedling response to canopy release. Experimental canopy gaps were opened and the survival and growth of advance seedlings (Fagus sylvatica, Acer pseudoplatanus, Acer campestre, Acer platanoides) growing in the gaps or under closed canopy were monitored for three years. • All species responded positively and rapidly to canopy release. Survival was not affected by gap opening. Diameter increment after gap opening was similar across species, and height increment was greater for Acer platanoides and for Acer pseudoplatanus. Post-release diameter and height growth were mainly determined by pre-release seedling size. Competition from neighbouring seedlings did not affect growth in the three years following canopy opening. • In the recruitment process of F. sylvatica and Acer sp. advance regeneration, the recovery from canopy release did not appear as a limiting step that would filter against some species. Pre-release size was the main factor accounting for post-release growth and is probably a major determinant of long-term seedling dominance.

Growth, Survival, and Habitat Use of Naturally Reared and Hatchery Steelhead Fry in Streams: Effects of an Enriched Hatchery Rearing Environment

AbstractAfter hatchery‐reared salmonids are released into the wild, their survival and performance are frequently lower than those of wild conspecifics. Additionally, negative effects of hatchery fish on wild fish are cited as factors affecting the recovery of salmonid populations. Alternative hatchery rearing environments and release practices have been proposed to mitigate both problems. We investigated the postrelease growth, survival, habitat use, and spatial distribution of hatchery steelhead Oncorhynchus mykiss fry reared in conventional and enriched environments and compared their performance with that of naturally reared steelhead fry from the same parent population in two streams. Average instantaneous growth rates differed between streams but not among the three rearing groups. The survival of naturally reared fry was significantly greater than that of both types of hatchery fry (relative survival = 0.33) but did not differ between the conventional and enriched environments. Naturally reared fry grew and survived equally well regardless of the type of hatchery fry with which they were stocked. Supplementation increased fry population size in all stream sections but produced hatchery‐biased populations. Steelhead fry preferred pool habitat within stream sections, but pool use was affected by an interaction between rearing environment and stream. Hatchery fry had more clumped spatial distributions than naturally reared fry, which were affected by a significant interaction between rearing type and stream. Hatchery rearing type and stream had no effect on the spatial distribution of naturally reared fry. We conclude that (1) hatchery steelhead fry released in streams grow as well as naturally reared fry but do not survive as well, (2) enriched hatchery environments do not improve postrelease growth or survival, and (3) upon release, fry raised in enriched hatchery environments affect the growth and survival of naturally reared fry in much the same way as fry reared in conventional hatchery environments.

Advance Regeneration in the Inland West

Advance conifer regeneration readily survives release from overstory competition in the Inland West, but foresters are concerned about the ability of released trees to attain normal growth rates. There are also concerns about forest health issues associated with managing advance regeneration. The best pre-release predictors of post-release growth response are pre-release vigor and crown ratio at release. The fastest growing trees before release grow the fastest following release. A general recommendation is that at least a 0.50 crown ratio at release is necessary for good response to release. A 0.50 crown ratio means that trees will have the necessary photosynthetic capability to respond to changes in stand conditions. The best time to release advance regeneration is after budset in the fall but before budbust in the spring. Release during this time period means needles that develop the first summer after release will be adapted to full sunlight. A conceptual framework of physiological response to release...

Adult Production of Chinook Salmon Reared at Different Densities and Released as Two Smolt Sizes

Abstract Chinook salmon (Oncorhynchus tshawytscha) were reared at densities of 6.6–24.3 kg/ m3 and released as small (9.7–10.3 g) or large (28.2–31.8 g) smolts to determine the effects of fish size at release and rearing density on postrelease growth and adult return rate. Density did not affect survival during rearing, but mean weights for both size-classes were significantly lower at the highest rearing densities (P < 0.05). Density and size at release affected adult return rates, which were lower for fish reared at high densities for both size-classes. However, the increased number of smolts produced at higher densities compensated for the reduced return rates by yielding a higher number of returning adults per unit volume of rearing space. The estimated costs for each adult produced were US$11.10–12.00 for small smolts and $13.10–23.80 for large smolts. The lowest costs were projected at the second-highest density (18.6 kg/m3) for small smolts and at the highest density (20.3 kg/m3) for large smolts.