A review of seed production and stock enhancement for commercially important portunid crabs in Japan

We reviewed the present status of seed production for stock enhancement and evaluated the impact of stocking on commercial catches in Japan, of portunid crabs particularly Portunus trituberculatus and Scylla paramamosain. The mean survival rate from hatching to first-stage crabs was around 10%, and 20–30% of the larval culture trials conducted in recent years could not harvest juveniles during seed production. To achieve reliable mass seed production technologies, measures for controlling disease and the nutritional condition of larvae in seed production tanks are required to be developed. The main spawning season extends from April/May to July. Reflecting their life cycle characteristics such as high growth rates, crabs recruit to the fishery after September and largely contribute to the commercial landings until December in the hatching year. The main release season of juveniles is from June to July. Consequently, released juveniles are expected to contribute to commercial landings in the release year. Analyses of catch and release statistics in two small bays estimated the yield from released individuals (YPR, yield per release) at 2.4 g for P. trituberculatus and 3.3–7.7 g for S. paramamosain, which were similar to values reported from tagging surveys. On a major regional basis, catch and release histories of P. trituberculatus highlighted the impact of hatchery releases on commercial landings as 33.6 g YPR in the Seto Inland Sea, where catches and releases have been greatest. Although the YPR estimates were different between small bays and major regional seas, Japanese stock enhancement programmes should have had an impact on portunid crab production, dependent on the magnitude of the releases.     

Assessment of recapture rates after hatchery release of Chinese shrimp Fenneropenaeus chinensis in Jiaozhou Bay and Bohai Bay in 2012 using pedigree tracing based on SSR markers

We calculated the recapture rates for Chinese shrimp Fenneropenaeus chinensis following hatchery release in Jiaozhou Bay and Bohai Bay in 2012 based on parentage identification using simple sequence repeat (SSR) markers. The results and process were as follows: In total, 3 × 10⁵ postlarval Chinese shrimp (inner marker), comprising six full-sib families, were released into Jiaozhou Bay with a hatchery release of approximately 9 × 10⁷ same-sized stock in the spring. Eight shrimp (inner marker) were identified from 2,507 recapture catches in the autumn, with information about eight SSR loci available by using Cervus 3.0. Similarly, another six full-sib families, comprising 2.04 × 10⁵ postlarvae, were released into Bohai Bay with a hatchery release of approximately 1.6 × 10⁸ same-sized Chinese shrimp of postlarval stock, and four shrimp were identified from 3,232 recapture catches in the autumn. Furthermore, we calculated the number of released stock in the recapture catches, i.e., 2,400 and 3,137 in Jiaozhou Bay and Bohai Bay, respectively. Combined with statistics for Chinese shrimp resources during the autumn fishing season, we calculated that the recapture rates for Jiaozhou Bay and Bohai Bay were 2.70 and 2.59 %, respectively, being slightly lower but more precise compared with results obtained using traditional methods (2.81 and 2.67 %).     

The enhancement of cod stocks

Atlantic cod have been a primary target for marine stock enhancement since the 1880s. In the early part of this period, hatched larvae were released in Norway, the USA and Canada. The last larval releases were conducted in Norway in 1971, and a century of cod larvae releases were halted without any clear evidence of benefit. Since the early 1980s, the focus has been on production of larger, more viable juvenile cod. Emphasis has been given to the design of tag–release programmes involving large-scale releases and ecosystem analysis in selected ecosystems. Most of this research has been carried out in Norway, where more than one million tagged juvenile cod have been released. Smaller stocking experiments have also been performed in Denmark, Sweden, the Faroe Islands and the USA.
This paper reviews the major findings from these programmes. We include summaries and evaluations of rearing techniques for juvenile cod, methods of tagging and recapture, experimental fishing, migration, mortality and growth rates in the different habitats, genetic analysis, and ecosystem studies that have tried to describe the variation in the cod carrying capacity of selected release areas.
Despite relatively large variation in environmental conditions, in cod production and in fishing mortality along the Norwegian coast, results indicate that, under the conditions experienced during the 1980s and 1990s, releases of juvenile cod did not significantly increase cod production and catches. The biological limitations and future prospects of Atlantic cod stock enhancement are addressed.     

Economic,ecological and genetic impacts of marine stock enhancement and sea ranching: A systematic review

Hatchery release is one of the most popular management tools in fisheries, forestry and wild life management, while its negative impacts on wild populations are a global concern. Research and monitoring of its impacts are generally lacking, and the usefulness of hatchery release for fisheries and conservation objectives is unclear. Here, I evaluated positive and negative impacts of worldwide marine stock enhancement and sea ranching programmes in a systematic review associated with meta‐analyses with the goal of reducing bias of the review. Vast numbers of individuals of more than 180 species are released into the wild each year, but most studies are at experimental stages to assess its potential, and empirical studies are sparse for evaluating the impact on fishery production. Most cases are economically unprofitable except for a few successful cases or unevaluated. The effects of releasing juveniles can be dwarfed by the magnitude of natural recruitment when the spawning stock produces much larger recruitment than released juveniles. Density‐dependent growth caused by competition of food can be substantial, and growth rates of hatchery and wild fish and other competitive species can simultaneously be reduced when stocking exceeded the carrying capacity. Relative reproductive success can vary depending on the species, seed quality and environmental factors. Empirical studies show evidence of substantial gene flow from hatcheries, but fitness reduction in stocked populations has not been reported. The results represent the current state of worldwide marine stock enhancement and sea ranching activity and provide key information for growing fields of artificial propagation and conservation.     

象山港黄姑鱼增殖放流效果评估及增殖群体利用方式优化

以回捕渔获重量和对繁殖群体的补充能力为评价指标,借助标志放流-回捕实验,利用模型模拟分析方法,定量评估浙江象山港黄姑鱼(Nibea albiflora)的增殖放流效果;同时,结合其增殖目标定位,探索构建生态高效的增殖群体利用方式。研究结果表明,象山港黄姑鱼增殖群体的捕捞死亡系数为1.31,在该捕捞强度下,11055尾增殖放流鱼苗可产生737 kg回捕渔获收益,同时还向增殖水域补充了554尾初次性成熟个体,增殖放流活动在一定程度上起到了修复象山港黄姑鱼资源、促进渔民增产增收的效果。结果表明,捕捞强度过大是制约象山港黄姑鱼增殖放流功效发挥的重要因素,捕捞死亡系数应降至0.46,同批次黄姑鱼增殖放流所能提供的回捕渔获重量和性成熟个体尾数可分别较现行捕捞强度提升41.49%和326.90%。综上述,象山港黄姑鱼增殖放流的生态和经济功效较为显著,合理降低对增殖群体的捕捞强度是进一步提升其增殖放流效果的必要措施。     

Increased harvest of anadromous hatchery steelhead,Oncorhynchus mykiss (Walbaum), through return timing manipulation

Harvest hatchery programmes serve to augment fisheries but should also minimise impacts to wild populations. In an experiment to increase harvest in an anadromous hatchery steelhead, Oncorhynchus mykiss (Walbaum), terminal river fishery, a new hatchery strain, was created using selective breeding of early arriving adults to the river. First‐generation progeny of the new early arriving strain were reared and released over 4 years concurrent with releases of the standard hatchery strain. This study compares adult return timing, terminal harvest and straying behaviour of progeny of the early arriving and standard hatchery strains. The new strain migrated towards the terminal river fishery earlier, they were harvested earlier in the eight‐month fishing season and their overall harvest was 17% greater, but 7.7% of the new strain strayed to other rivers compared to 5.0% of the standard strain. Selective breeding to match adult return timing with fishing effort may help bolster harvest, but a paired release evaluation, such as was conducted in this study, would be prudent before switching all hatchery production to a selectively bred strain.     

Shell marking by artificial feeding of the tropical abalone Haliotis asinina Linne juveniles for sea ranching and stock enhancement

A method of marking abalone (Haliotis asinina Linne) for sea ranching and stock enhancement purposes was developed. Three‐month‐old abalone juveniles (11.8‐mm shell length, 0.28 g) were fed artificial diets for 1, 2, or 3 weeks. The width of the bluish‐green shell band produced by abalone juveniles was 1.7, 2.6, and 4.2 mm after 1, 2, or 3 weeks of feeding respectively. The growth and survival of juveniles fed artificial diets did not differ from that of juveniles fed the seaweed Gracilariopsis bailinae (control). Feeding the diet‐fed juveniles with the seaweed thereafter produced the natural brownish shell, thus forming a sandwiched bluish‐green band. An experimental release in outdoor tanks with natural growth of seaweeds and diatoms, and in a marine reserve showed that the shell band remained clear and distinct, indicating the usefulness of this shell marking method in sea ranching and stock enhancement of abalone.     

Stock enhancement in a commercial mullet,Mugil cephalus L., fishery in Hawaii

Abstract This study showed that cultured striped mullet, Mugil cephalus L., released as juveniles can make a significant contribution to landings in an island commercial fishery. Following pilot hatchery releases from 1990 to 1993, striped mullet fisheries in Kaneohe Bay, Hawaii, USA, were sampled to recover cultured fish from the bay-wide catch. Direct sampling of 181 fishing trips resulted in recovery of 211 cultured striped mullet. By autumn 1994, cultured fish comprised 13.0% (2.8%) of the commercial mullet catch in Kaneohe Bay, and the percentage was increasing logarithmically. This study corroborated predictions from previous studies of juveniles about effects of release strategies on survival of cultured mullet. Following summer releases, recapture rates were strongly affected by fish size-at-release, with a critical release size of 60 mm total length (the smallest size released that was subsequently detected in the fishery). Over 30 000 juveniles stocked in 1990 (but not in a nursery habitat preferred by striped mullet) apparently suffered complete mortality.     

The survival of hatchery‐origin pinto abalone Haliotis kamtschatkana released into Washington waters

1. Wild populations of pinto abalone (Haliotis kamtschatkana) in Washington State have declined by 97% since 1992, despite a fishery closure since 1994. No recruitment has been detected recently, indicating probable reproductive failure due to low densities. A pilot programme placed a total of over 11,000 hatchery‐origin juveniles, age 18–22 months, at 10 sites in the San Juan Islands.
2. Observed (naive) year 1 survival averaged 10.2% (0–23% range) and was most influenced by site compared with lineage or size‐at‐outplant. Families survived in the approximate proportions that they were outplanted, and there was little support for an effect of size‐at‐outplant on survival.
3. Detection was low due to the small chance of sighting individuals on complex substrate. When derived from repeated sampling, an upper bound on naive detection rate averaged 0.38 and increased with size. When derived from a closed capture–recapture model, average detection was estimated at 0.19.
4. Growth was highly variable and confounded with detection, but an average 3.4% of detected outplants across all sites (0–7.5% range) had reached reproductive size in 2017.
5. A state‐space model of exponential population growth was modified to account for imperfect detection and yielded an estimated density of abalone for each survey. Seven out of eight sites included in the model remained above a target abalone density of 0.3 m^?2 throughout the project.
6. The majority of tagged abalone made little net movement over weekly and annual timescales, although some emigration likely reduced survival estimates.
7. The restoration programme is transitioning from a pilot phase to a production phase, including optimization of hatchery and outplant processes. Existing well‐performing sites will receive additional cohorts every 4–5 years to maintain aggregation densities. New sites will replace poorly performing ones, although this is hampered by a poor understanding of the mechanisms behind site performance.

     

Use of Microsatellite DNA Profiling to Identify Japanese Flounder,Paralichthys olivaceus of Hatchery Origin

Japanese flounder, Paralichthys olivaceus, is an economically important marine fish species in Asia. A suite of 18 microsatellite markers chosen from published genetic linkage maps was used to carry out parentage assignments of 188 hatchery‐reared juveniles from a small number of breeders. The probabilities of exclusion for the 18 microsatellite markers were 0.604–0.913, and the effectiveness of combined probability of exclusion reached 100% when using the eight microsatellite markers with higher Excl 1 probabilities. The cultured and wild stocks (WSs) were differentiated in a release‐recapture population based on these markers. Of the 321 recaptured offspring, 28.34% were assigned to their parental pairs in our broodstock, whereas the remaining offspring could not be traced back to a possible sire or dam. Significant reduction in genetic diversity of the cultured stock (CS) had not been found compared with that of the WS. The results suggest that CSs released into the wild will not adversely affect the genetic structure of natural populations. Our results demonstrate that these markers provide an efficient tool for parentage assignments and genetic analysis of Japanese flounder.     

Classifying tagging experiments for commercial fisheries into three fundamental types based on design,data requirements and estimable population parameters

Mark–recapture experiments have the potential to provide direct estimates of fundamental parameters required for fishery stock assessment and provision of subsequent management advice in fisheries. The literature on mark–recapture experiments is enormous, with a variety of different experimental designs and estimation models; thus, it can be difficult to grasp the primary features of different approaches, the inter‐relationship among them and their potential utility in different situations. Here, we present an overview of the tagging experimental designs that are appropriate for use in commercial fishery situations. We suggest that most mark–recapture experiments in a large‐scale fishery context can be classified into one of three basic types – Petersen, tag‐attrition or Brownie – based on the fundamental design employed for releases and recaptures. The release and recapture strategy (e.g. the number of release events, whether the size of the sample examined for recaptured tags is known) determines which parameters can be estimated and from where the information for estimating them arises. We conclude that an integrated Brownie and Petersen approach is the most powerful of the different approaches in terms of the range of parameters that can be estimated without underlying assumptions or constraints on parameters. Such an approach can provide direct estimates of fishing mortality, natural mortality and population size, which are the main population dynamics parameters that traditional fishery stock assessments attempt to estimate.     

Microsatellite DNA markers of Ezo abalone (Haliotis discus hannai): a preliminary assessment of natural populations sampled from heavily stocked areas

Reproductive success of released animals becomes a growing interest in the context of stock enhancement program and conservation biology. In the case of the Ezo abalone (Pacific abalone; Haliotis discus hannai), limited information is available about the extent of interbreeding between natural and released hatchery populations. This study aimed to develop microsatellite DNA markers from Ezo abalone to address the issue. We developed 38 microsatellite markers that worked well in three full-sib families established from wild caught abalone. Of these, nine markers, with which alleles could be scored easily and accurately, were applied to two population samples derived from coastal areas where intensive releases of hatchery-produced abalone seedlings have been carried out. Multilocus estimates of genetic population differentiation calculated based on the nine markers (F_ST analogue θ and R_ST analogue ρ) rejected a null hypothesis of genetic homogeneity between the populations (θ=0.048, P<0.00001; ρ=0.029, P=0.0051). Although both populations conformed to Hardy Weinberg's equilibrium at almost all of the nine loci, the results of simulation analysis for variance of relatedness coefficient provided evidence of nonrandom mating in each population, possibly caused by the cumulative effect of stocking on the genetic make-up. The population analysis presented here is preliminary; but we consider that the microsatellite markers are potentially an efficient means to examine the reproductive contribution of released abalone to natural resources.     

Significance of Fish Size-At-Release on Enhancement of Striped Mullet Fisheries in Hawaii

A tag-release-recapture study was conducted to evaluate size-at-release impacts upon recruitment of cultured, juvenile striped mullet, Mugil cepahlus released in inshore habitats of Oahu, Hawaii, USA. In June and July 1990, 85,848 juvenile mullet were graded into five size groups (ranging from 45 to 120 mm in length), identified with binary-coded wire tags, and released into two estuaries (2×5 factorial design). Of the tagged fish, 42,822 were released into Kaneohe Bay on the east (windward) coast of Oahu; 43,026 were released into Maunalua Bay on Oahu's dryer south shore. The fish were released into both bays simultaneously. Releases were blocked in time across 5 release lots. To evaluate growth and survival rates of released mullet, both bay systems were sampled monthly with cast nets over a ten-month period after release. Overall, 733 tagged M. cephalus were recaptured, 277 from Kaneohe Bay and 456 from Maunalua Bay. Overall proportions of tagged fish in samples declined from 33.4% (±25.2%) of the total M. cephalus catch at week 5 to 1.88% (±0.95%) by week 23. From week 23 on, tagged fish averaged 2.09% (±0.23%) of the striped mullet in monthly samples. Within 9 wk after releases, recapture frequencies were clearly skewed in favor of fish that were larger at the time of release. Fish smaller than 70 mm when released were rare or absent in collections within 18 wk after release. This confirms results of a smaller-scale pilot study in Maunalua Bay and shows that fish size-at-release can have a major impact on the success of hatchery releases in marine habitats. Pilot studies to identify minimum fish size-at-release should be conducted at all sites targeted for full-scale marine hatchery releases.     

Evaluation of the effect of stock enhancement in the coastal waters of Guangdong,China

A total of 14.573 million fish fry and 96.32 million shrimp larvae were released across 31 locations into the coastal waters off Guangdong, China, in 2010. The released fish and shrimp were sampled through a combination of market and fishing log‐book surveys. The combined fishery production reached 362 868 kg. The input–output ratio was 1:5.99 for released fish (over 3 years) and 1:11.01 for released shrimp (over 2 years). The average increase in income was 721 RMB per capita. Approximately 240 thousand fish (after 3 years) and 1.2 million shrimp (after 2 years) survived to sexual maturity and could contribute to the spawning stock. The stockings were approximately one‐seventh of the fish and one‐half of the shrimp stocking carrying capacities, respectively. Based on these results, the intensity of stocking could be increased. Stocking and recapture strategies should be adjusted to align with the optimal stocking carrying capacity determined from this study.     

Stocking of brown trout, Salmo trutta L.: effects of acclimatization

One-year-old hatchery brown trout, Salmo trutta L., ( n  = 16 520) from a sea-run, local brood stock were marked and released (scatter-planted) into the River Laisälven in northern Sweden. Eight different groups were created using Alcian blue and Visible Implant Elastomer tags. Half the fish were kept in small enclosures in four stocking areas for 6 days before release. The other half were released just after transportation. To evaluate the effect of acclimatization on post-stocking performance, the areas were electric fished 2 months later. During the electric fishing survey, a higher number of the acclimatized hatchery fish were recaptured than those released immediately. The growth rate of stocked fish differed significantly between stocking areas and fish held in enclosures grew more than those released directly. The rate of recapture of hatchery fish varied between stocking areas (6.4–17.4%). Movements of juveniles within and between the stocking areas were low, and only 3.6% of the recaptured fish were found in an area not originally stocked. These results showed that acclimatization of fish before release increases the number and size at recapture within a stocking area.     

Are hatchery‐reared abalone naïve of predators? Comparing the behaviours of wild and hatchery‐reared northern abalone,Haliotis kamtschatkana (Jonas, 1845)

Abalone populations have declined worldwide, generating interest in enhancement using hatchery‐reared individuals. In many cases, such restoration efforts have met with limited success due to high predator‐induced mortality rates. Furthermore, the mortality rates of outplanted hatchery abalone are often considerably higher than for wild individuals. This study uses northern abalone (Haliotis kamtschatkana) as a case study to determine whether hatchery‐reared abalone behave differently than their wild counterparts. In the field, outplanted hatchery‐reared abalone were significantly less responsive than wild abalone, in terms of number of abalone responding and intensity of response, to nearby movement and to physical contact with an inert probe. Also, when encountering a cue to which all abalone responded (a seastar predator), hatchery‐reared individuals remained subdued. Anti‐predator behavioural deficits in hatchery‐reared abalone were more pronounced in 4‐year‐old individuals than in 1‐year‐old individuals, suggesting an influence of either age or amount of time spent in the hatchery environment. These behavioural differences are expected to increase the vulnerability of hatchery‐reared abalone to predators, and are likely a major cause of their elevated predator‐induced mortality when outplanted.     

Suitability of cage culture for Pacific abalone Haliotis discus hannai Ino production in China

Pacific abalone (Haliotis discus hannai Ino) aquaculture is a thriving industry in China. This study describes a novel submerged cage culture system for abalone rearing in Fujian, South China. The cage consisted of five vertical slots that were oriented perpendicular to the flow of water. The slots were separated by six vertically connected plastic plates for abalone attachment and shelter at the bottom of the cage. Experiment 1 was designed to determine the appropriate stocking density at the start of the abalone sea‐based production cycle. Eight‐month‐old hatchery reared and size‐graded juveniles were transferred to the sea‐based culture system. For different stocking densities, shell length of juveniles obtained in this novel culture system on 2, 3.5 and 5 months, respectively, was compared with shell lengths obtained in a traditionally multi‐tier basket culture system. In Experiment 2, daily growth rates (DGRs) in shell length and biomass in terms of wet weight of 2‐year‐old abalones reared in cage and tiered basket culture systems were compared over a 6‐month period. Results of Experiment 1 showed that growth of abalone in the cage culture system is density‐dependent; the mean final shell length of juveniles obtained was 6.7–15.9% higher than in tiered baskets system even at the same initial stocking density. In Experiment 2, DGRs in shell length of 53.83–78.38 μm day^?1 obtained in cage system were significantly higher than that in tiered baskets (P < 0.01). And in terms of wet weight biomass, it was 1.48–3.01 times higher in the cage system compared with the traditional system. Abalone survival was more than 87.5% in both culture systems in both experiments. Advantages of the newly established cage culture system included better growth performance of the animals reared and potential improvement of rearing conditions, such as improved water flow velocity and dissolved oxygen.     

A comparison of no-take zones and traditional fishery management tools for managing site-attached species with a mixed larval pool

No‐take zones (NTZs) can generate higher larval production by sessile, sedentary and site‐attached species per unit area than in exploited areas, and may increase recruitment and yield compared to status quo management. Whilst NTZs may be considered an essential part of optimal management, few studies have specifically compared the effects of NTZs with those of correctly applied gear and effort controls. A yield‐per‐recruit (YPR) population model, based on the sedentary abalone Haliotis laevigata, was used to compare the effects of management by minimum landing size (MLS), effort limitation and NTZs, either singularly or in combination. Initially, a minimum basic YPR model was used. Three additional assumptions were sequentially added to the model to see if they affected conclusions drawn from the model. The additional assumptions were the inclusion of: (i) a length–fecundity relationship; (ii) an age‐dependent natural mortality function; and (iii) mortality of undersized individuals due to fishery operations. In the absence of undersized mortality caused by fishing, under virtually all conditions the population is best managed with a combination of MLS and effort control, without any NTZs. For simulations that included mortality of undersized individuals in the fished area, under nearly all circumstances NTZs were considered an essential part of optimal fishery management, and management incorporating NTZs greatly increased the sustainable yield that could be taken.