Juvenile Survival Rates Research Articles

Broodstock cultivation of the yellow seahorse, Hippocampus kuda Bleeker, in the aquarium culture system

To improve the yield and survival rate of the offspring, the broodstock cultivation methods of the yellow seahorse, Hippocampus kuda Bleeker, were assessed, including the temperature conditions, diets, culture density and mono-or mixed-sex culture. Feeding parent seahorses with live food increased fecundity, and culture density of more than two pairs of parents during mating improved the survival rate of both sexes and decreased the production cycle. Additionally, separate culture of males and females prior to mating improved fecundity as well as the survival rate of juveniles. A higher number of larvae per batch was produced at 26 °C than at 30°C and 22°C, whereas seahorse production occurred at a higher frequency at 30 °C than in the lower temperature treatments. These results suggest that the optimal culture conditions for H. kuda are as follows: provide live food when cultivating seahorse broodstock, use equal proportions of males and females during mating, use monosex culture at other times, and maintain seawater temperature of 26 °C.

Improving the quality of tridacnid clam juveniles through crossbreeding broodstock from different zones across the Spermonde Archipelago

Tridacnid clam populations have declined, and they are considered as endangered. There is increasing concern over their status in the Spermonde archipelago, South Sulawesi, where some species can no longer be found, including larger species such as Tridacna gigas and T. derasa as well as the shallow-water clam Hippopus hippopus. This research aimed to produce high-quality juvenile tridacnid clams by crossbreeding distantly related broodstock from different zones as a contribution to the effective conservation of endangered species. The research was conducted in the Spermonde archipelago and at the Hasanuddin University Marine Station Hatchery in Barrang Lompo Island. Broodstock of T derasa and T. squamosa were collected from zones III and IV of the Spermonde Archipelago. Juvenile clam production followed established methods for inducing spawning and larval rearing through trocophore, veliger, and pediveliger stages to produce juveniles that were reared in land-based and ocean nurseries. Parameters measured were the juvenile survival rate and the quality of zooxanthellae (density, chlorophyll content, and mitotic index). Data were analyzed descriptively. The mean density of zooxanthellae in juvenile clams was 3.17 x 106 cells/ind (range 3.15x106 - 5.27x106 cells/in). The mean chlorophyll-a content of these zooxanthellae was 2.7 mg/m3 (range 1.1 mg/m3 - 4.1 mg/m3), which is consistent with the mean phaeopigment concentration of 5.5 mg/m3 (range 4.2 mg/m3 - 6.2 mg/m). The mitotic index peaked at 8.5% between 09:00 and 12:00.

Low carrying capacity a risk for threatened Chinook Salmon

Since they were listed under the U. S. Endangered Species Act of 1973, Snake River spring-summer Chinook Salmon (Oncorhynchus tshawytscha) have been the subject of numerous population viability analyses (PVAs). In all of the previous PVAs that we are aware of, management actions to improve the species’ status have focused on increasing survival rates of juveniles and adults. These PVAs did not explicitly treat carry capacity; instead, they assumed that survival rate improvements increased intrinsic productivity, and implicitly assumed that this would also increase carrying capacity. In a novel alternative approach, we instead examined how carrying capacity itself was related to extinction risk. We estimated three alternative multi-population PVAs using maximum likelihood estimation and chose the model with the best fit to the spawner-recruit data from 26 populations in the Snake River Spring/Summer Chinook Salmon evolutionarily significant unit. We then estimated carrying capacity and 24-year extinction probability for each of these populations using alternative quasi-extinction thresholds. We found that carrying capacities estimates were low in several of the populations and that extinction probability increases sharply with decreasing carrying capacity. A sensitivity analysis with fixed carrying capacities and increasing intrinsic productivity illustrated that unless actions increase carrying capacity, little change in extinction risk can occur.

Survey of survival rate and histological alterations of gills and hepatopancreas of the Litopenaeus vannamei juveniles caused by exposure of Margalefidinium / Cochlodinium polykrikoides isolated from the Persian Gulf

Harmful algal blooms (HABs) have had harmful effects on the health of a wide range of organisms and are becoming a noteworthy risk to fisheries, human health and wildlife around the globe. Although the lethal influences of dinoflagellate Margalefidinium / Cochlodinium polykrikoides have been well-documented for finfish, the impacts on decapod crustacean species, especially, Litopenaeus vannamei are poorly understood. Here, we examined the exposure of L. vannamei juveniles with different M. polykrikoides densities (T1: 1 × 103, T2: 2 × 103, T3: 3 × 103, T4: 9 × 103 and T5: 30 × 103 cells ml−1), in order to observe possible histological alterations in gills and hepatopancreas. After 96 h exposure, shrimp exhibited increased mortality and survival rate of juveniles in control group were meaningfully (P < 0.05) higher than treatments exposed to 9 × 103 and 30 × 103 cells ml−1 of M. polykrikoides. The lowest survival observed in treatments T4 (95.56%) and T5 (82.20 %), respectively. The juveniles exposed to high densities of M. polykrikoides had flaccid bodies and gills were yellow in color with some black spots (melanization) in pereiopods. At the end of the experiment, shrimps’ hepatopancreas and gills exhibited various histological alterations. The irregular appearance of the tubular structure of the hepatopancreas, R- and B-cells reduction, separation of epithelium and myoepithelial layer, ruptured epithelial cells and degeneration of tubules were detected in the hepatopancreas of shrimps exposed to 30 × 103 cells ml−1. In gills of shrimp exposed to 30 × 103 cells ml−1, alterations in epithelial structure, increases in the number of intercellular hemocytes, and changes in tissue structure were observed. Finally, findings suggest that M. polykrikoides blooms can lead to significant impacts on survival and major histological alterations in gills and hepatopancreas organs when the density of M. polykrikoides was over 9 × 103 cells ml−1.

Life on the edge: habitat fragmentation limits expansion of a restored carnivore

AbstractThe successful recovery of imperiled species is dependent on knowledge of how demographic drivers mediate population growth and expansion. One of the largest species restoration projects has been the reintroduction of swift foxes Vulpes velox to southern Canada, where 947 foxes were released between 1983 and 1997. Swift foxes have since increased and expanded their range into northern Montana (USA), but have experienced a population decline and stall in recolonization over the past 10 years. The objective of this study was to estimate the survival and reproductive rates of swift foxes in northern Montana, which constitutes the southern edge of this population. In addition, we evaluated support for two different hypotheses of how environmental factors and several demographic factors influence survival. Although our length of monitoring was relatively short, we found that adult and juvenile annual survival rates were 54% and 74%, respectively, and fecundity was 0.85. We found the most support for the hypothesis that the percentage of native grassland at the 1‐km scale influenced survival and found that survival increased, on average, 2.1% for every 5% increase in grassland. Compared to previous estimates of swift fox population growth immediately following the release, our data suggest the population is currently stable. The long‐term successful recolonization and connectivity of swift fox populations in this region will likely be dependent on maintaining large tracts of contiguous grassland. Comparing the estimates of demographic rates among different points in space and time should help managers better understand the population dynamics and inform restoration strategies for recovering populations.

The Emergence of Complex Dynamics during the Evolution of a Structured Limited Population

The paper considers a microevolution model of two-stage population with limitation under the influence of natural selection that regulates juvenile survival rate. An analytical and numerical study of the model is performed; the parametric areas of various dynamic modes are determined. It is shown that an emergence of new alleles (for example, as a result of mutations) providing a greater reproductive potential of individuals leads to a natural selection of these alleles and evolutionary growth of the average value of the reproductive potential in the population. However, in the case of density dependent regulation of birth rate, the increase in the average value of reproductive potential leads to destabilization of the dynamics for the age group sizes. Scenarios of changes in the dynamics are various and depend on the parameter values of the model, but the main result is always the same: the dynamics become more and more complex and, as a rule, chaotic.

Estimating Reproduction and Survival of Unmarked Juveniles Using Aerial Images and Marked Adults

Methods for estimating juvenile survival of wildlife populations often rely on intensive data collection efforts to capture and uniquely mark individual juveniles and observe them through time. Capturing juveniles in a time frame sufficient to estimate survival can be challenging due to narrow and stochastic windows of opportunity. For many animals, juvenile survival depends on postnatal parental care (e.g., lactating mammals). When a marked adult gives birth to, and provides care for, juvenile animals, investigators can use the adult mark to locate and count unmarked juveniles. Our objective was to leverage the dependency between juveniles and adults and develop a framework for estimating reproductive rates, juvenile survival, and detection probability using repeated observations of marked adult animals with known fates, but imperfect detection probability, and unmarked juveniles with unknown fates. Our methods assume population closure for adults and that no juvenile births or adoptions take place after monitoring has begun. We conducted simulations to evaluate methods and then developed a field study to examine our methods using real data consisting of a population of mule deer in a remote area in central Nevada. Using simulations, we found that our methods were able to recover the true values used to generate the data well. Estimates of juvenile survival rates from our field study were 0.96, (95% CRI 0.83–0.99) for approximately 32-day periods between late June and late August. The methods we describe show promise for many applications and study systems with similar data types, and our methods can be easily extended to unmanned aerial platforms and cameras that are already commercially available for the types of images we used.Supplementary materials accompanying this paper appear online.

Effects of food, salinity, and ammonia-nitrogen on the physiology of juvenile seahorse (Hippocampus erectus) in two typical culture models in China

Food and water environments are key factors affecting juvenile survival rate in seahorse aquaculture. In order to adjust to local conditions, different seahorse (Hippocampus erectus) breeding models were developed in North and South China. Seahorses in North China were commonly fed Artemia in indoor containers with a stable water environment, while most seahorses in South China were fed copepods in outdoor concrete ponds. Firstly, we compared the effect of food type on juvenile seahorses based on a one-month feeding experiment and found no significant difference in body length. However, the insulin-like growth factor 1 (IGF-1) gene expression was significantly higher in the liver of seahorses fed copepods than in the lever of seahorses fed Artemia, suggesting that copepods promoted better growth. A high expression of stress-related genes, namely, heat shock proteins 70 (HSP70) and Mn superoxide dismutase (Mn-SOD), in the liver of the seahorses that were fed copepods suggested that copepods might cause more stress on juveniles. Lower leptin gene expression in the liver of seahorses fed Artemia than in those fed copepods proved that Artemia was better for satiating the juveniles. Furthermore, the potential effects of salinity (15 and 30 ppt) and ammonia‑nitrogen (0, 5, and 15 mg/L) on juvenile seahorse physiological stress were studied through a 5-d orthogonal experiment. Both lower salinity and higher ammonia‑nitrogen increased the ventilation rate significantly. Low salinity caused a rapid increase in the ventilation rate on day 1, while high ammonia‑nitrogen was the main factor during the later period (days 2–5). Significant changes in the mRNA expression of genes, including Na+: K+:2Cl− cotransporter 1 (NKCC1) and Na, K-ATPase (NKA) in the gill, HSP70, Mn-SOD, glutamate dehydrogenase (GDH), and glutamyl synthase (GS) in the liver, indicated that seahorses are sensitive to acute salinity decline. In addition, high ammonia‑nitrogen exposure significantly changed the expression of genes (i.e., Mn-SOD, GDH, and GS) in seahorses exposed to low salinity level, while no significant variation was observed in seahorses exposed to normal salinity, suggesting that salinity decline might increase the negative effects of ammonia‑nitrogen stress. The present study provides a better understanding of how food, salinity, and ammonia‑nitrogen affect juvenile seahorses, and will be potentially important to improve animal welfare and increase production efficiency.

Variation in the microbiome of the spider mite Tetranychus truncatus with sex, instar and endosymbiont infection.

Most arthropod-associated bacterial communities play a crucial role in host functional traits, whose structure could be dominated by endosymbionts. The spider mite Tetranychus truncatus is a notorious agricultural pest harboring various endosymbionts, yet the effects of endosymbionts on spider mite microbiota remain largely unknown. Here, using deep sequencing of the 16S rRNA gene, we characterized the microbiota of male and female T. truncatus with different endosymbionts (Wolbachia and Spiroplasma) across different developmental stages. Although the spider mite microbiota composition varied across the different developmental stages, Proteobacteria were the most dominant bacteria harbored in all samples. Positive relationships among related operational taxonomic units dominated the significant coassociation networks among bacteria. Moreover, the spider mites coinfected with Wolbachia and Spiroplasma had a significantly higher daily fecundity and juvenile survival rate than the singly infected or uninfected spider mites. The possible function of spider-mite associated bacteria was discussed. Our results highlight the dynamics of spider mite microbiotas across different life stages, and the potential role of endosymbionts in shaping the microbiota of spider mites and improving host fitness.

Estimating Survival for Elusive Juvenile Pond‐Breeding Salamanders

ABSTRACTJuvenile vital rates have important effects on population dynamics for many species, but this demographic is often difficult to locate and track. As such, we frequently lack reliable estimates of juvenile survival, which are necessary for accurately assessing population stability and potential management approaches to conserve biodiversity. We estimated survival rates for elusive juveniles of 3 species, the ringed salamander (Ambystoma annulatum), spotted salamander (A. maculatum), and small‐mouthed salamander (A. texanum), using 2 approaches. First, we conducted an 11‐month (2016–2017) mark‐recapture study within semi‐natural enclosures and used Bayesian Cormack‐Jolly‐Seber models to estimate survival and recapture probabilities. Second, we inferred the expected annual juvenile survival rate given published vital rates for pre‐metamorphic and adult ambystomatids assuming stable population growth. For all 3 species, juvenile survival probabilities were constant across recapture occasions, whereas recapture probability estimates were time‐dependent. Further, survival and recapture probabilities among study species were similar. Post‐study sampling revealed that the initial study period median estimate of annual survival probability (0.39) underestimated the number of salamanders known alive at 11 months. We therefore appended approximately 1 year of opportunistic data, which produced a median annual survival probability of 0.50, encompassing salamanders that we knew to have been alive. Calculation from literature values suggested a mean annual terrestrial juvenile ambystomatid survival probability of 0.49. Similar results among our approaches indicated that juvenile survival estimates for the study species were robust and likely comparable to rates in nature. These estimates can now be confidently applied to research, monitoring, and management efforts for the study species and ecologically similar taxa. Our findings indicated that similarly robust vital rate estimates for subsets of ecologically and phylogenetically similar species can provide reasonable surrogate demographic information that can be used to reveal key factors influencing population viability for data‐deficient species. © 2020 The Wildlife Society.

EFFECT OF SALINITY ON THE SURVIVAL, GROWTH AND IMMUNITY RATE OF JUVENILE SEA CUCUMBERS (Holothuria scabra)

Sea cucumber (Holothuria scabra) is important species as food and medicine especially for Chinese market. It  is a stenohaline and osmoconforming organism with a low level of tolerance to salinity change. Salinity of the medium is one of the environmental factors that affect the physiology and survival of juvenile sea cucumbers. This study was aimed at assessing the effect of different salinities on the growth, survival and immunity rate of juvenile sea cucumbers (Holothuria scabra) and also determining the suitable salinity level for the optimal growth, survival and immunity rate of the sea cucumbers. This experiment  used a completely randomized design with 5 salinity treatments: 24, 29, 34, 39, and 44 ppt with 3 replications using fifteen30 L-fiber glass tanks. The juvenile sea cucumbers measured 4.4 ± 0.2 cm in total length and 5.6 ± 0.3 g in body weight. The juveniles were raised at 15 individuals/tank, fed with cultured fresh benthos once a day in the afternoon. Coelomate was taken from the sea cucumber juveniles from each tank  and used to determinie the immunity rate and also for the osmolality. The data were analyzed using ANOVA followed by Tukey’s test at 5% level of significance. The salinity of the medium significantly affected (P &lt; 0.05) the growth, survival rate and immunity rate of sea cucumber juveniles. The 24 - 34 ppt salinity can support survival rate up to 100%, high growth (6.47 – 7.10 g) and immunity rate (27 – 76 x 104phagocytic cell/mL), while the 44 ppt salinity has resulted in not only a low survival rate (55.6%), but also had a bad effect on osmolality (303 ± 3.5 mOs-mol kg-1), growth (3.12 ± 0.34 g), and immunity (209 x 104 phagocytic cell/mL).

Estimating correlations among demographic parameters in population models.

Estimating correlations among demographic parameters is critical to understanding population dynamics and life‐history evolution, where correlations among parameters can inform our understanding of life‐history trade‐offs, result in effective applied conservation actions, and shed light on evolutionary ecology. The most common approaches rely on the multivariate normal distribution, and its conjugate inverse Wishart prior distribution. However, the inverse Wishart prior for the covariance matrix of multivariate normal distributions has a strong influence on posterior distributions. As an alternative to the inverse Wishart distribution, we individually parameterize the covariance matrix of a multivariate normal distribution to accurately estimate variances (σ 2) of, and process correlations (ρ) between, demographic parameters. We evaluate this approach using simulated capture–mark–recapture data. We then use this method to examine process correlations between adult and juvenile survival of black brent geese marked on the Yukon–Kuskokwim River Delta, Alaska (1988–2014). Our parameterization consistently outperformed the conjugate inverse Wishart prior for simulated data, where the means of posterior distributions estimated using an inverse Wishart prior were substantially different from the values used to simulate the data. Brent adult and juvenile annual apparent survival rates were strongly positively correlated (ρ = 0.563, 95% CRI 0.181–0.823), suggesting that habitat conditions have significant effects on both adult and juvenile survival. We provide robust simulation tools, and our methods can readily be expanded for use in other capture–recapture or capture‐recovery frameworks. Further, our work reveals limits on the utility of these approaches when study duration or sample sizes are small.

Survival of Douglas-fir provenances in Austria: site-specific late and early frost events are more important than provenance origin

Autumn and spring frost events caused wide variation in the survival of juvenile Douglas-fir in Austrian forest sites located in the transition zone from Atlantic to continental climate. Survival rate can be optimized by planting provenances originating from an altitudinal belt of 500–1400 m in North America. Neither the variety nor the climate of origin of planted Douglas-fir provenances influence its response to frost events. Understanding the risks of frost during late spring and early autumn is crucial for planting non-native Douglas-fir (Pseudotsuga menziesii [Mirbel] Franco) as an alternative tree species under climate change in Europe. We investigate the role of early and late frost events on the survival of juvenile Douglas-fir and tested whether survival depends on seed origin. With data from 19 provenance trials across Austria, we modeled the effects of early and late frost events on juvenile survival rate, accounting for random variations due to site condition and provenance origin. Wide variations (37–93%) in the juvenile survival rate of Douglas-fir were mainly driven by early and late frost events (daily Tmin < 0 °C), summer drought, and continentality. Juvenile survival declined with an increasing number of frost events within the observation period and prevailing warm spells preceding the frost events. The seed origin of the tested provenances had a minor effect and was related to the altitude, but not to the variety or the climate of provenance origin. For planting Douglas-fir in the transition zone from Atlantic to continental climates, typical in Austrian forests, the local site conditions and the probability of the occurrence of early and late frosts should be considered, while provenance selection should rather focus on productivity.

Incorporating habitat suitability and demographic data for developing a reintroduction plan for the critically endangered yellow spotted mountain newt, Neurergus derjugini

In reintroduction programmes for amphibians, data on age structure in hosting populations and choices of life stage or age groups in releasing captive bred individuals are often missing. Similarly, employing site selection procedures for selecting appropriate reintroduction locations are often neglected. Here, we obtained data on longevity, age at maturation, and age structure from skeletochronological data in a free living population of the yellow spotted mountain newt, Neurergus derjugini. A maximum longevity of 13 years for males and 12 years for females showed that N. derjugini is a long living newt with a stable age structure. We also employed maximum entropy modelling, geographic information system, and multicriteria decision analysis to obtain ranked suitability scores for reintroduction sites. Finally, we determined post-release survival rates for different life stage and age groups of N. derjugini including 30 eggs and 60 individuals of six-months old larvae, one and three-year old juveniles, and six-year old adults (15 each) born and raised in a captive-breeding facility and released into mesh enclosures in a selected stream. Over 10 visits to the site before and after overwintering, the survival rates for eggs, larvae, one and three-year juveniles and six-year old adults were 25, 80, 86.66, 93.33 and 53.33 % respectively. Applying survival rates obtained from current experimental reintroductions through a static life table suggest that an optimal release strategy to arrive at a numerical target of 100 adults aged three can be achieved by reintroduction of 650 fertilised eggs and fostering them in meshed enclosures in the selected stream.

Breeding Behavior of Mara [Dolichotis patagonum (Zimmermann, 1780)] in the Monte-Chaco Ecotone of Argentina

Phylogenetic constraints and ecological factors have been suggested as alternative key factors in the evolution of animal sociality. The mara (Dolichotis patagonum) is a cavid rodent endemic to Argentina that has the particularity of being monogamous with a communal breeding system. Researches on reproductive behavior of mara in its natural habitat have been restricted to Peninsula de Valdes (PV). In this work, we studied the breeding behavior of the mara in Sierra de las Quijadas National Park (SQNP). A census to locate mara's dens in 230 ha, was conducted through adjacent line transects of five meters width. After locating the dens, we followed their reproductive activity using camera traps. A density of 4.34 randomly distributed dens/ha was found. No communal breeding was observed. Breeding season extended from October to June. Estimated density was from 0.16 to 0.24 reproductive adults/ha. The survival rate of juveniles was 31.3%. These observations differ from those reported for the species. Resource dispersion hypothesis could explain both reproductive strategies prevailing in the extremes of its distribution, SQNP (solitary breeding) and PV (communal breeding). The intraspecific variability registered enhances the importance of ecological factors in determining sociality traits for the mara.

Review of California sea lion (Zalophus californianus) abundance, and population dynamics in the Gulf of California

Abstract: The life history of California sea lion (Zalophus californianus) in the California Gulf is marked by a series of important events influencing and modifying its population growth, evolution and distribution.&#x0D; Despite the fact that the population has been studied since the 1950s, research has been have been rather punctual and fragmentary, before 2010, there are a very few censuses conducted simultaneously in all rookeries, which prevent obtaining information on key aspects of life cycle, population trend and potential threats. In the present work we conducted a thorough review encompassing the last 37 years of California sea lion life history and environment in the Gulf of California. This allowed an opportunity to focus on short- and long-term processes acting on the population and hopefully improve knowledge about the population trend and status and unveil some latent aspects hardly recognizable using a partial vision. We collected and analyzed data from different sources since the 1970s to 2018: published papers, master’s and doctoral thesis, in addition to technical reports. The data is organized in sections corresponding with crucial population life history events. Considering a long-time frame period the population could appear stable with zero growth due to the cyclic interannual fluctuation that could denote a certain dependence with climatic factors, not directly with El Niño event, but with sea surface temperature anomalies that determine a change in prey availability. However, many doubts persist about the incidence of different local environmental factors on gender and age, particularly related with juvenile recruitment and female survival rate. More information is required based on seasonal censuses, life cycle, regional environmental variation; statistical errors need to be assessed and monitoring methods should be standardized and must be considered to ascertain short- and long-term population and colony spatial-temporal patterns.

Applying science to pressing conservation needs for penguins.

More than half of the world's 18 penguin species are declining. We, the Steering Committee of the International Union for Conservation of Nature Species Survival Commission Penguin Specialist Group, determined that the penguin species in most critical need of conservation action are African penguin (Spheniscus demersus), Galápagos penguin (Spheniscus mendiculus), and Yellow‐eyed penguin (Megadyptes antipodes). Due to small or rapidly declining populations, these species require immediate scientific collaboration and policy intervention. We also used a pairwise‐ranking approach to prioritize research and conservation needs for all penguins. Among the 12 cross‐taxa research areas we identified, we ranked quantifying population trends, estimating demographic rates, forecasting environmental patterns of change, and improving the knowledge of fisheries interactions as the highest priorities. The highest ranked conservation needs were to enhance marine spatial planning, improve stakeholder engagement, and develop disaster‐management and species‐specific action plans. We concurred that, to improve the translation of science into effective conservation for penguins, the scientific community and funding bodies must recognize the importance of and support long‐term research; research on and conservation of penguins must expand its focus to include the nonbreeding season and juvenile stage; marine reserves must be designed at ecologically appropriate spatial and temporal scales; and communication between scientists and decision makers must be improved with the help of individual scientists and interdisciplinary working groups.

Environmental water flow can boost foraging success of the juvenile rapa whelk Rapana venosa (Muricidae) in aquaculture tanks with still or flowing water: Indication of chemosensory foraging

Artificial breeding of Rapana venosa has been attempted in China, but the high mortality rate of rapa whelk juveniles (10–40 mm) seriously restricts the breeding success of this species in artificial cultivation and the overall aquaculture industry, and thus the scale of industrialization is far from being realized. One main factor was found to contribute to this high mortality rate: the low predation efficiency of juveniles. We studied the foraging behavior of various sized R. venosa juveniles in still, flowing, and circulating water, with the juveniles being positioned either upstream or downstream from the prey in the flowing water experiments. Our findings demonstrated that the distance between juveniles and prey in still water significantly restricted the ability of juveniles to locate food, but water flow significantly enhanced this ability. In addition, the small-sized juveniles were found to be more active predators than the larger sized juveniles. Our findings demonstrated that circulating water flow is important to improve the survival and growth rate of juveniles in R. venosa cultures. Our results broaden the understanding of chemical orientation in gastropods and can be used to develop or improve commercial breeding strategies for R. venosa.

FIRST EXPERIENCE OF CAGE CULTIVATION OF HATCHERY-PRODUCED JUVENILE SCALLOP MIZUHOPECTEN YESSOENSIS AT EASTERN COAST OF PRIMORYE

Yesso scallop Mizuhopecten yessoensis is the main object of aquaculture in Primorye with annual yield measured in hundreds ton. However, further development of its farming could be restricted by lack of the spat. Availability of the spat imported from China using for the scallop cultivation at the coast of Primorye is explored. The spat from Chinese hatchery located in Shandong province was supplied for one aquaculture company in Primorye in the volume of 660 . 106 ind. in 2018 and settled to hanging collectors (1000 ind. per bag), then to cages in the marine farm located north-eastward from the Moryak-Rybolov Bay. Survival and growth rate of the scallop juveniles were examined in early November 2018, when the water temperature was from 10.3–10.4 оС at the sea surface to 9.7–9.9 оС at the bottom, salinity was about 33.60 psu in the whole water column, chlorophyll a concentration varied in the range 0.4–0.8 mg/L with the maximum in the layer 8–24 m. The spat mortality during transportation was estimated as 15 %, but it increased to 56–90 % during its growing up in cages. This level of mortality is much higher than mortality of the spat collected from the coastal waters at southern Primorye. The highest mortality of artificial spat was observed for large-sized mollusks, whereas it was satisfactory for the small-sized ones. Possible reason of high mortality is too high density of juveniles and damaging of their soft tissues by other shells. The spat shells height did not exceed 5–10 mm in the collectors but increased during their growing in cages to 20–25 mm. This size is similar to the size of scallop growing from natural spat in southern Primorye. However, growth rate of the scallop growing at the Moryak-Rybolov Bay (2.0–2.7 mm/month) is lower than in Peter the Great Bay (3.0–3.5 mm/month) though higher than in the Vladimir Bay and Aniva Bay. Mean body weight of the cultivated scallop in November was 1.5 ± 0.1 g.

Bistability and Bifurcations in Modified Nicholson-Bailey Model with Age-Structure for Prey

The paper investigates dynamic modes of the predator-prey model with age structure for prey. We use a slight modification of the Nicholson-Bailey model to describe the interaction between predator and prey. We assume the population size is regulated by decreasing juvenile survival rate with growth of age class sizes. Conditions for sustainable coexistence of interacting species are described. It is shown that the coexistence of species becomes possible if there are a transcritical or saddle-node (tangential) bifurcations. Due to the saddle-node bifurcation there is bistability in the system of interacting species: predator either coexists with prey or dies depending on the initial conditions. It is shown that the range of demographic parameters, for which the prey and predator coexist, can significantly increase with growth of survival of adult prey or the proportion of predators born or the prey consumption rate of the predator. We studied the oscillation scenarios of interacting population, influences of reproduction, survival and self-regulation rates of population prey and age-dependent predation as well as variations in the current number on transitions between different dynamic modes. It is shown that an increase in the birth rate of the prey under intraspecific competition can lead to a dynamics destabilization and to oscillations appearance in numbers. Age-dependent predation is shown to be a stabilizing influence. At the same time, with a high birth rate of the prey, the system stability is ensured by the high survival rate of adult prey. It was found that in the model parametric space, both bistability and multistability arises, which are not related to each other. Consequently, even a small variation of the current population size leads to more complex behavior of the interacting species, and can give a significant change in both the observed dynamic mode and the coexistence scenario of the species.