Juvenile Stocking Research Articles

Temperature and Maternal Age Effects on Burbot Reproduction

AbstractRiver regulation alters the thermal regime of many freshwater ecosystems, and impoundments are known to negatively impact the recruitment of fluvial Burbot Lota lota populations. Some conservation programs in North America and Eurasia have begun to incorporate stocking of hatchery Burbot to mitigate extirpation risks. Anthropogenic modification of river temperatures and population structure has unknown implications for Burbot reproduction. This study evaluated the effects of elevated water temperatures and different maternal ages on spawning and embryo development of hatchery Burbot. Juveniles stocked downstream of a hydroelectric dam were found to naturally mature in a warmer postdam regime. The river‐adapted hatchery adults volitionally spawned in a broodstock facility at 2, 4, and 6°C. The spawning period spanned 18 d at 2°C but was shortened to 6−7 d at 4°C and 6°C. Survival of embryos to the eyed stage was 86.7, 47.9, and 0.1% at incubation temperatures of 2, 4, and 6°C, respectively. Embryo deformity increased dramatically between 4°C and 6°C. Young (age‐3) and old (age‐7 and older) females spawned 4−12 d later than 5‐ and 6‐year‐old females. Age‐3 females spawned smaller eggs, but no relationship was found between maternal age and embryo vital rates. It was concluded that juvenile stocking supplemented the abundance of reproductive adults in the highly altered ecosystem of the lower Kootenai River. Spawning temperatures above 4°C potentially underlie Burbot recruitment bottlenecks in systems affected by impoundments, climate warming, or other barriers to coldwater spawning habitat. Contraction of the spawning period by warmer temperatures, a truncated population age structure, or both could synchronize spawning to coincide with suboptimal conditions for normal embryo development.

Separating wild versus stocking components in fish recruitment without identification data: a hierarchical modelling approach

Salmonid juvenile stocking programs are often poorly monitored due to the lack of identification between stocked and wild fish. In this study, a hierarchical Bayesian model is developed to take advantage of spatiotemporal variations of stocking and wild recruitment for estimating these two components despite the absence of identification data. It is first tested by means of simulated data and then applied to the 37 year abundance data set of the Atlantic salmon (Salmo salar) population of the Allier catchment (France). Despite the absence of identification data, juvenile densities could be estimated and split into wild and stocked components. We found that the stocked juveniles contributed significantly to the total juvenile production, while the wild reproduction continued to provide an important contribution. This approach is encouraging and promising from a management advice perspective. It is flexible enough to accommodate for case study specificities and shows that long-term monitoring abundances can be useful to assess the impact of stocking programs even in the absence of direct means of identifying stocked versus wild fish.

Population Status Assessment and Restoration Modeling of White AbaloneHaliotis sorenseniin California

White abalone Haliotis sorenseni was listed as endangered in 2001 because of severe declines throughout southern California due to overfishing. Populations continue to decline despite the closure of the fishery in 1996. There has been little to no evidence of recruitment in southern California from population surveys and in artificial reefs targeting white abalone recruitment since the listing of the species. A 13-y time series of white abalone abundance in prime habitat, surveyed with a remote-operated vehicle, was used in a population viability analysis to quantify: (1) the population decline and (2) the time to reach a quasi-extinction threshold. The annual decline in the population is 12%, which is comparable to adult natural mortality rates for abalone species. The quasi-extinction threshold of 1,000 individuals is met within 15 y. These results confirm that the white abalone populations in southern California are at high risk of extinction, and highlight the importance of active stocking and restoration for the species. To inform restoration, a deterministic density-dependent size-based matrix model was developed to investigate different stocking scenarios, incorporating an innovative method for modeling low populations by setting the reproductive term as a function of adult density to mimic a reproductive Allee effect. A minimum density of 0.14 abalone/m2 of stocked juveniles led to a maximum population growth rate (λ) of more than or equal to 1 for the model population within 10 y but that recovery was poor (mean λ15–20 ≤ 1.0) over time if the level of juvenile stocking was less than 0.23 abalone/m2 in the model population. The innovative approach of incorporating adult density into the reproductive term in the model quantitatively shows how low population densities can impact threatened and endangered species, and may be widely used for other species. These results can not only help guide stocking strategies but also allow for the quantitative evaluation of white abalone under the guidance of the IUCN Red List of Threatened Species, suggesting that white abalone should be considered Critically Endangered.

Fecundity, survival, and growth of the seahorse Hippocampus ingens (Pisces: Syngnathidae) under semi-controlled conditions

We studied fecundity, survival, and growth of the seahorse Hippocampus ingens under semi-controlled conditions. Three wild brood stock mature males of 14.8, 24.5, and 32.0 g released 1,598, 1,703, and 1,658 juveniles. Juvenile stocking densities of 12 were settled in 60-1 aquariums in groups of 1, 12, and 20 days old organisms. The rate of survival was 21.5, 61.9, and 59.0%, respectively, in 35 days. Juveniles were fed a mix diet of rotifers B. plicatilis and Artemia nauplii, then they were transferred to a cement tank of 100,000 1 at a density of 50/1,000 1 and fed with live adult Artemia for 60 days more. They grew from an average of 0.7, 1.5, and 2.7 to 4.5, 5.4, and 6.7 cm, respectively, in 95 days. The seawater temperature varied from 17 to 23 degrees C.

Assessing Red Drum Juvenile Stocking in a South Carolina Estuary Using Genetic Identification

AbstractThe South Carolina Department of Natural Resources has been stocking red drum Sciaenops ocellatus since 1988 to evaluate parameters critical to their successful survival and recruitment in South Carolina estuaries. From 1999 to 2002, between 600,000 and 1,000,000 juvenile red drum were stocked each year in two tributaries of Charleston Harbor. The harbor and each tributary were partitioned into three independent strata and randomly sampled monthly for two decades, allowing population trends before, during, and after stocking to be evaluated. Using microsatellite‐based parentage analysis, we examined the contribution of stocked age‐0 juvenile red drum (15–60 mm total length) to the local population 1 year after release by using fishery‐independent sampling. Analysis of these data showed that the highest contributions (88.9%) were close to the stocking site in years with low natural recruitment, whereas in years with high natural recruitment, contributions were lower and stocking was less effective in increasing catch per unit effort. The results of stocking 600,000 small juveniles/year from 1999 to 2001 in one of the study tributaries (Ashley River) indicated that stocked fish did not displace wild fish but had an additive effect on their abundance, supporting the hypothesis that trophic resources are not limiting for postlarval age‐0 red drum within Charleston Harbor. The high observed variability in contribution among years of stocking similar‐sized red drum suggests that (1) interpretation on a year‐class‐specific basis is necessary to fully understand the effects of stocking and (2) marine stock enhancement programs would benefit substantially from evaluation in the context of wild annual recruitment patterns.Received June 3, 2010; accepted August 18, 2011

Use of Zero Water Discharge Technology through the Application of Nitrifying Bacteria and Textile Vertical Substrate in Grow-Out Phase of Macrobrachium rosenbergii De Man

This study was conducted to develop a zero water discharge technology for Macrobrachium rosenbergii growth in order to solve the unpredictability of prawn production during grow-out phase.The system consists of three major compartments: (1) Prawn culture tank, (2) Trickling biofilter for nitrification process, and (3) Textile vertical substrate for prawn territory expansion. The trial was conducted in three diferent stages: (1) nitrifying bacteria of 105 Colony Forming Units.mL-1(CFU.mL-1) was inoculated into the culture 24 hours prior to juvenile stocking and every 10 days during culture period, (2) the culture was grouped into five treatments: 30 individuals.m2 (control), 40 individuals.m2, 50 individuals.m2, 60 individuals.m2, and 70 individuals.m2, and (3) measurements of biological, physicochemical, and microbiological culture parameters. Optimum culture performance was obtained in the culture with initial stocking density of 30 individuals.m-2 (control) with final metabolic body weight, length, specific growth rate (SGR), survival rate (SR), feed conversion rate (FCR) of (11.37 ± 4.92) g, (10.69 ± 1.45) cm, 2.569%.day-1, 78.3%, and 0.99, respectively. However, from an economic perspective, stocking with 70 individuals.m-2 (treatment IV) produced the highest total final biomass (975 g) and highest profit (Rp. 19.285 per kg) compared to the other treatments. Results indicate that use of the developed zero-water discharge rearing system with the application of nitrifying bacteria and textile vertical substrate can maintain good water quality to support a higher stocking density, better growth and larval survival rate and profit of prawn M. rosenbergii de Man grow-out culture.

Growing, losing or introducing? Cage aquaculture as a vector for the introduction of non-native fish in Furnas Reservoir, Minas Gerais, Brazil

Cage aquaculture has been developed in many countries, including Brazil. This form of production, although economically productive, may cause several impacts to the environment. Considering the historical relationship between aquaculture and species introduction, our study investigated the potential of cage aquaculture in spreading non-native species into hydroelectric reservoirs. We interviewed 19 fish farmers in Furnas Reservoir, Grande River basin. All producers have grown exclusively Nile tilapia (Oreochromis niloticus), an African fish, and all producers reported the occurrence of fish escapes. Releases were mainly accidental, but highly frequent during some management procedures, such as length classification, fish capture and juvenile stocking. Escapes were also reported due to cage damage and deliberate releases. These results indicate that, in cage aquaculture facilities, fish are frequently released to the external environment. When raising non-native species (e.g. Furnas Reservoir), these facilities constitute an important vector for fish introductions.

An estimate of the historic population size of adult pallid sturgeon in the upper Missouri River Basin, Montana and North Dakota

Summary Juvenile pallid sturgeon Scaphirhynchus albus raised in hatcheries and stocked in the wild are used to augment critically imperiled populations of this federally endangered species in the United States. For pallid sturgeon in recovery priority management area 2 (RPMA 2) of the Missouri River and lower Yellowstone River where natural recruitment has not occurred for decades, restoration programs aim to stock an annual minimum of 9000 juvenile pallid sturgeon for 20 years to re-establish a minimum population of 1700 adults. However, establishment of this target was based on general guidelines for maintaining the genetic integrity of populations rather than pallid sturgeon–specific demographic information because data on the historical population size was lacking. In this study, information from a recent population estimate (158 wild adults in 2004, 95% confidence interval 129–193 adults) and an empirically derived adult mortality rate (5%) was used in a cohort population model to back-estimate the historic abundance of adult pallid sturgeon in RPMA 2. Three back-estimation age models were developed, and assumed that adults alive during 2004 were 30-, 40-, or 50-years old. Based on these age assumptions, population sizes [±95% confidence intervals; (CI)] were back-estimated to 1989, 1979, and 1969 to approximate size of the population when individuals would have been sexually mature (15 years old) and capable of spawning. Back-estimations yielded predictions of 344 adults in 1989 (95% CI 281–420), 577 adults in 1979 (95% CI 471–704), and 968 adults in 1969 (95% CI 790–1182) for the 30-, 40-, and 50-year age models, respectively. Although several assumptions are inherent in the back-estimation models, results suggest the juvenile stocking program for pallid sturgeon will likely re-establish an adult population that equals in the short-term and exceeds in the long-term the predicted population numbers that occurred during past decades in RPMA 2. However, re-establishment of a large population in RPMA 2 that exceeds populations present 40+ years ago should be considered conservatively, as this strategy will increase the number of reproductive adults and thereby increase the likelihood for natural recruitment in this recruitment-limited system.

Genetic Assessment of Walleye ( Sander vitreus) Restoration Efforts and Options in Nipigon Bay and Black Bay, Lake Superior

Walleye ( Sander vitreus) stocks in Nipigon Bay and Black Bay historically numbered as the largest stocks in Lake Superior, but collapsed in the 1960s due to overfishing, habitat loss, and other pressures. We used microsatellite DNA analyses to assess the success and relative contributions of past rehabilitation stocking to walleye in Nipigon Bay, and to investigate the relationship between historical and contemporary populations in Black Bay. Based on the genetic data, juvenile stocking and adult transfers from four source populations into Nipigon Bay differed substantially in their contributions to the reestablished population. The genetic data also indicated that natural reproduction was occurring and identified survivors from the former Nipigon Bay population. Similar genetic analysis of scale samples from the historical Black Bay fishery and present-day walleye from a major tributary (Black Sturgeon River) showed that the historical and contemporary samples comprise one genetic stock, which is significantly different from neighboring native and introduced populations. These findings suggest that walleye restoration efforts in Lake Superior are working, and highlight the utility of and options for adaptive management approaches for restoring extirpated populations.

Linking juvenile white spruce density, dispersion, stocking, and mortality to future yield

We examined methods of linking density, dispersion, and stocking information from juvenile regeneration surveys with mortality estimates to predict future yield of white spruce (Picea glauca (Moench) Voss) in boreal mixedwoods. The study focused on data from 709 stands (7–150 years) and defined a stocked plot (10 m2) as having one or more acceptable trees. In juvenile surveys, ingress of natural spruce overwhelmed the regular planting pattern, creating clumped dispersion patterns, as indicated by the Morisita index. A function was developed to describe the relationship between stocking, density, and dispersion. In mature, permanent sample plots, only 30%–40% stocking of 10 m2 plots (700 stems·ha–1) was needed to achieve full yields. Mortality rates for planted spruce varied from 0.1% to 0.8% per year for juvenile stands and from 1.7% to 3.3% per year for mature stands. For rotation-length predictions in Alberta, 0.7% per year is likely a mean mortality loss. These findings were combined to generate stocking versus time curves at a range of mortality rates. The tallest spruce measured in each juvenile survey plot had the same mortality rate regardless of absolute size, and spruce mortality was reduced when associated with aspen. These findings call into question minimum height requirements and free-to-grow criteria in regeneration standards.

Fecundity, survival, and growth of the seahorse Hippocampus ingens (Pisces: Syngnathidae) under semi-controlled conditions

We studied fecundity, survival, and growth of the seahorse Hippocampus ingens under semi-controlled conditions. Three wild brood stock mature males of 14.8, 24.5, and 32.0 g released 1 598, 1 703, and 1 658 juveniles. Juvenile stocking densities of 12 were settled in 60-l aquariums in groups of 1, 12, and 20 days old organisms. The rate of survival was 21.5, 61.9, and 59.0 %, respectively, in 35 days. Juveniles were fed a mix diet of rotifers B. plicatilis and Artemia nauplii, then they were transferred to a cement tank of 100 000 l at a density of 50/1 000 l and fed with live adult Artemia for 60 days more. They grew from an average of 0.7, 1.5, and 2.7 to 4.5, 5.4, and 6.7 cm, respectively, in 95 days. The seawater temperature varied from 17 to 23 C°.

希少種ウミガメ類の産卵，ふ化管理および放流技術の開発

希少種ウミガメ類の産卵，ふ化管理および放流技術の開発

Impact of Juvenile Stocking Size on the Major Carp Production in a Minor Reservoir, Bibinagar, India

The present study deals with the impact of juvenile stocking sizes of the major carp on production in a minor reservoir, Bibinagar, Nalgonda, India. Reservoir surface area equaled over 23.8 ha and water from the reservoir was used for irrigation and fisheries. Four experiments were conducted for 4 years from 2000–2001 to 2003–2004. The experiments were planned in such a way that every year juvenile stocking size was held constant and subsequent fish production analyzed. During the first year’s experiment (2000–2001) a stocking size of 25–30 mm (fry) was maintained. Similarly 50–55 (advanced fry), 75–80 mm (fingerling) and 100–105 mm (advanced fingerling) were stocked during 2001–2002, 2002–2003 and 2003–2004 respectively. Uniform yearly stocking densities (2000/ha) were established in each experiment in the month of July and fish were harvested in June of the subsequent year. Major carp production was enhanced with larger stocking size. Yearly productions equaled 144.00, 231.48, 632.91 and 1005.03 kg/ha/year with the above stocking sizes. Variation in stocking sizes had significant (P<0.05) effects on fish production. The number of fish per kg production decreased gradually with increases in stocking size with an average value of 3.97. Reservoir production of catla was the most abundant species, followed by rohu, common carp, mrigal and grass carp. These results show that stocking size has a great impact on fish production and the stocking of advanced fingerlings will provide maximum carp production in minor reservoirs in India.

Estimating the influence of prawn stocking density and seagrass type on the growth of juvenile tiger prawns ( Penaeus semisulcatus ): results from field experiments in small enclosures

Fine mesh enclosures (0.9 m 2 in basal area, 1 m high, with 100 μm mesh) and a jet-net retrieval system were developed to test the influence of juvenile prawn stocking density on growth rates in (1) different months (April and October/November) and (2) different types of intertidal seagrass beds in the Embley River estuary of tropical Australia. Small juvenile tiger prawns (3-6 mm in carapace length, CL) were stocked in enclosures at densities of 4-32 prawns per enclosure (4.4-35.5 prawns m -2) on a high biomass seagrass bed (about 70 g m -2 of mostly Enhalus acoroides) and one with low biomass (about 10 g m -2 of mostly Halodule uninervis). After 2-3 weeks in the enclosures, recovery rates, and hence possibly survival, were greater on the high biomass Enhalus than on the low biomass Halodule. However, not all fish and crustaceans could be excluded from the enclosures. Growth rates were twice as fast on the high biomass Enhalus than on the low biomass Halodule. It is likely that the high biomass Enhalus, with its greater surface area, supported more epiphytic flora and fauna and reduced the potential for interference competition between prawns, compared with the low biomass Halodule. Growth rates on Enhalus were significantly faster at a stocking density of 4 prawns per enclosure (1.3 mm CL week -1) than at a stocking density of 16 and 32 prawns per enclosure (both 0.8 mm CL week -1), and did not differ significantly between April and October/November (temperatures were about 30°C at both times). The mean growth rate at 8 prawns per enclosure (1.1 mm CL week -1) did not differ significantly from those at 4, 16 and 32 prawns per enclosure. These results from two seagrass beds suggest that the carrying capacity for juvenile tiger prawns was greater in the high biomass Enhalus than the low biomass Halodule bed.

Biology and conservation of sturgeon and paddlefish

The Acipenseriformes (sturgeon and paddlefish)live in the Northern Hemisphere; half of thesespecies live in Europe, mostly in thePonto-Caspian region, one third in NorthAmerica, and the rest in East Asia and Siberia.They reproduce in freshwater and most of themmigrate to the sea, either living in brackishwater (Caspian, Azov, Black and Baltic Seas) orin full seawater on the oceanic continentalshelf. Most species feed on benthic organisms.Puberty usually occurs late in life (5–30 yearsof age) and adult males and females do notspawn on an annual basis. Adults continue togrow and some species such as the beluga (Huso huso) have reached 100 years of age andmore than 1,000 kg weight. Stocks of sturgeonsare dramatically decreasing, particularly inEurasia; the world sturgeon catch was nearly28,000 t in 1982 and less than 2,000 t by 1999.This decline resulted from overfishing andenvironmental degradation such as: accumulationof pollutants in sediments, damming of rivers,and restricting water flows, which becomeunfavorable to migration and reproduction.Several protective measures have beeninstituted; for example, fishing regulation,habitat restoration, juvenile stocking, and theCITES listing of all sturgeon productsincluding caviar. In addition, sturgeon farmingpresently yields more than 2,000 t per year(equivalent to wild sturgeon landings) andabout 15 t of caviar. Hopefully, thisartificial production will contribute to areduction of fishing pressure and lead to therehabilitation of wild stocks.