The response of otters to environmental changes imposed by the construction of large dams

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Evaluation and impact assessment of culture‐based fisheries to enhance fish yield in small reservoirs in Odisha State,India

The present study investigates the success of stocking fingerlings of Indian major carps ‐Gibelion catla (Hamilton), Labeo rohita Hamilton and Cirrhinus mrigala Hamilton – to enhance fish yield in 58 small reservoirs in Odisha State, India. Fish stocking and yield data were collected from State Fisheries Department, Odisha. The relationships between area, stocking density and fish yield of different size groups of reservoirs were assessed using the Pearson correlation coefficient (r). Fish yield increased significantly (p < 0.05, t‐test) from 204 kg/ha/year in 2012–13 to 323 kg/ha/year in 2013–14 due to adoption of CBF. The corresponding per capita fish production increased from 398 kg fisher^?1 year^?1 to 702 kg fisher^?1 year^?1 benefitting more than 8,000 fisher households. Reservoirs in the size group 100–500 ha showed the highest response of fish yield with respect to stocking of fingerlings. The size of fingerlings at stocking and area of the reservoir had greater impact on enhancing fish yield. Stocking had a profound positive impact on fish yield. This study forms a baseline evaluation of the impact of stocking on small tropical reservoirs in India. It also recommends management measures and discusses issues, and the way forward for sustainable fisheries enhancement in small tropical reservoirs in eastern India.     

Elevated CO2 does not exacerbate nutritional stress in larvae of a Pacific flatfish

Multiple aspects of climate change are expected to co‐occur such that ocean acidification will take place in conjunction with warming and a range of trophic changes. Previous studies have demonstrated that nutritional condition plays a significant role in the responses of invertebrates to ocean acidification, but similar studies have yet to be conducted with marine fishes. In this study, we examined the potential interactive effects of elevated CO₂ levels and nutritional stress on the growth and development of northern rock sole (Lepidopsetta polyxystra). Separate experiments examined the effects of these two environmental stressors during the pre‐flexion (3–31 days) and post‐flexion (31–87 days) larval stages. In both stages, the larval feeding regime has a much larger impact on growth rates than did the CO₂ level, and there was no observed interaction between stressors. By 31 days post‐hatch, larvae in the high‐feeding treatment were 84.2% heavier than the fish in the low‐feeding treatments, but there was no significant effect of CO₂ level on body size or condition. While overall growth rates were faster during the pre‐flexion stage, the effects of food limitation were greater for post‐flexion larvae undergoing metamorphosis, with the high‐feeding treatment fish being 3.3 times as heavy as fish in the low‐feeding treatments. These results have important implications for understanding the impacts of the multi‐faceted nature of climate change on population productivity of commercial fish species in the North Pacific.     

Effect of supplementary stocking of juvenile brown trout,Salmo trutta,on yield in a Norwegian mountain reservoir

Abstract The effect of supplementary stocking of juvenile (age 0+), hatchery‐reared, brown trout, Salmo trutta L., on annual yields was assessed in a Norwegian mountain reservoir between 1979 and 2007. Fishing was mainly carried out by local fishermen with benthic gillnets. During the study period, annual stocking ranged from 0 to 52 500 fish (19.8 ha^?1). No stocking has been carried out since 1997. Annual yield varied from 1650 to 5653 kg, corresponding to 0.62–2.13 kg ha^?1. Exploitation rate in terms of number of gillnets and mean weight of 6+ fish (age when catchable size was reached) explained 64% of the variability in catches. Stocked fish contributed very little to the yield or catch‐per‐unit‐effort, exhibiting no positive correlation with stocking density. The lack of contribution from stocked fish was probably caused by a competitive bottleneck in the eroded epibenthic zone, causing high juvenile mortality. If stocking continues, it is recommended that fish with body lengths >15–20 cm are used.     

Grow‐out culture of abalone Haliotis tuberculata coccinea Reeve,fed land‐based IMTA produced macroalgae,in a combined fish/abalone offshore mariculture system: effect of stocking density

Haliotis tuberculata coccinea has been identified as a target species for European aquaculture development, in order to fulfil the rising demand for abalone. The effects of different stocking densities on the growth performance, feed utilization and survival of two different initial size groups (30 and 40 mm) of abalones, during the final grow‐out to cocktail/market size (45–60 mm), were determined over a 6‐month period. Trials were performed in abalone cages installed in a commercial open‐sea cages fish farm. Animals were fed the red algae Gracilaria cornea and the green one Ulva rigida, both obtained from a land‐based integrated multi‐trophic aquaculture system. Survival rates were very high (94–98%) regardless the density employed. Sustained high linear growth was recorded both in shell and weight. However, a 17–19% reduction in weight gain was obtained by doubling the initial stocking density, suggesting a higher competition for space or food. Nevertheless, the high growth performance (70–94   μm day^?1; 250–372% weight gain) and survival attained, even at high densities, denoted the suitability of the offshore mariculture system as well as the biofilter produced macroalgae for grow‐out culture of H. tuberculata coccinea that overall could reach cocktail/commercial size in only 18–22 months.     

A comparison of randomized intervention analysis and two-factor analysis of variance for analysis of angler effort in a floodplain river fishery

Probability values were compared among randomized intervention analysis (RIA) and untransformed and log_e‐transformed two‐factor analyses of variance (anova ) to test effects of fish stocking and a public relations programme on angler effort. The data set consisted of a time series of angler vehicle counts at single control and impact locations in a before–after‐control‐impact (BACI) experimental design. A randomized complete block anova indicated that probability values from RIA and the untransformed and log_e‐transformed two‐factor anova did not differ significantly (P = 0.345), and that they did not result in different conclusions concerning angler effort. Randomized intervention analysis is superior to two‐factor anova in not having to conform with assumptions of parametric statistics, and it tests for temporal autocorrelation. Two‐factor anova is superior to RIA in providing statistical inferences about possible differences in main effects, i.e. control and impact locations and pre‐ and post‐treatment periods, if the interaction term is non‐significant. To achieve the most comprehensive analysis, it is recommended that both RIA and two‐factor anova (whether untransformed or transformed) be performed during field experiments of angler effort when using a BACI design at single control and treatment locations.     

Response of estuarine consumer communities following the stocking of a juvenile penaeid (Penaeus plebejus) over two consecutive years

Research programmes that monitor and evaluate the impact of stocking activities are essential to quantify effects of stocking and provide information for adaptive management of future releases. The consumer communities in two estuaries stocked with 5.8 million post‐larvae eastern king prawn Penaeus plebejus (Hess) were monitored, both before and after stocking, and relative to two similar reference estuaries. Following stocking, there was evidence of increases in the abundances of prawns within stocked estuaries. Communities in all four estuaries showed significant levels of variation over time as well as among the systems themselves. Changes in overall diversity were similarly observed. The presence or absence of vegetation and other seasonal effects were found to explain most of the observed variation in the community assemblage, while prawn stocking appeared to have a little detectable influence. While this study points to minimal impacts of prawn stocking on the consumer community at the densities used, research into potential shifts in resource use by competitors and the growth and survival of prawns is required to fully understand post‐release changes in stocked systems.     

Just a FAD? Ecosystem impacts of tuna purse‐seine fishing associated with fish aggregating devices in the western Pacific Warm Pool Province

The western and central Pacific Ocean supports the world's largest tuna fisheries. Since the 1990s, the purse‐seine fishery has increasingly fished in association with fish aggregating devices (FADs), which has increased catches of juvenile bigeye and yellowfin tunas and vulnerable bycatch species (e.g., sharks). This has raised concerns regarding the sustainability of these species’ populations and the supporting ecosystem, but may provide improved food security of Pacific Island nations through utilisation of FAD‐associated byproduct species (e.g., wahoo). An ecosystem model of the western Pacific Warm Pool Province was used to explore the potential ecological impacts of varying FAD fishing effort (±50% or 100%) over 30 years. The ecosystem has undergone a significant change in structure since 1980 from heavy exploitation of top predators (e.g., tunas) and “fishing up the food web” of high‐trophic‐level non‐target species. The ecosystem appeared resistant to simulated fishing perturbations, with only modest changes (<10%) in the biomass of most groups, although some less productive shark bycatch species decreased by up to 43%, which had a subsequent positive effect on several byproduct species, the prey of sharks. Reduction of FAD effort by at least 50% was predicted to increase the biomass of tuna species and sharks and return the ecosystem structure to a pre‐industrial‐fishing state within 10 years. Spatial disaggregation of the model and integration of economic information are recommended to better capture ecological and economic changes that may result from fishing and/or climate impacts and to develop appropriate management measures in response.     

Trophic relationships and ecosystem characteristics in a newly-impounded man-made lake in Thailand

Abstract  The trophic dynamics of a newly-impounded south east Asian reservoir, Pasak Jolasid, Thailand, monitored from its creation, were constructed using ecopath , a mass-balanced model. The trophic levels (TLs) of 36 ecological groups varied between 1.0 and 3.2. The majority of fish biomass was at the second TL, where the fishery is concentrated. Some food resources (benthic organisms and zooplankton) were not fully used, whereas phytoplankton and benthic algae were important components of the food web, which is based on phytoplankton and detritus. The implications of these findings are discussed in terms of ecological maturity of the ecosystem and possible fishery management of this multi-purpose reservoir.     

嵊泗人工鱼礁海区生态系统能量流动模型初探

主要根据从2005年1月开始投放人工鱼礁至11月在嵊泗人工鱼礁海区进行的环境、资源和生态调查资料,应用Ecopath withEcosim(EwE)软件,构建嵊泗人工鱼礁海区生态系统初步能量流动模型。模型由13个功能组构成,每一组都代表在生态系统中具有相似地位的有机体,基本覆盖了嵊泗人工鱼礁海区生态系统能量流动的主要过程。模型分析表明,嵊泗人工鱼礁海区生态系统的能量流动主要以捕食食物链途径为主,各功能组的营养级范围为1.00~4.18。生态网络分析表明,系统的能量流动主要有6级,来自初级生产者的能流效率为13.8%,来自碎屑的转换效率为13.4%,平均能量转换效率为13.6%。     

Effects of pre-rigour filleting on quality aspects of Atlantic cod (Gadus morhua L.)

Aquaculture is promising in increasing the amount of fresh Atlantic cod available all year around. The aim of this study was to investigate the effects of pre‐rigour filleting on fillet quality of wild and farmed cod. Pre‐rigour filleting resulted in significantly less fillet gaping than in fillets produced post rigour. The pre‐rigour fillets were, however, 12–13% shorter post rigour. In spite of the significantly lower water content of the muscle 6 days post mortem, a significantly higher liquid loss was seen in the pre‐rigour group. Differences in gaping score and muscle pH were dependent on whether the fish were wild or fed. Fillet gaping increased with storage time and was particularly pronounced for well‐fed cod. Fed cod had a significantly higher hydroxyproline (Hyp) content and significantly lower amount of glycosaminoglycans (GAGs) than wild cod. The ratio between GAGs and Hyp was thus significantly lower in fed cod. A connection between connective tissue components and fillet gaping may exist. However, further investigations are required.     

Optimization of the stocking parameters for mud spiny lobster Panulirus polyphagus (Herbst, 1793) capture‐based aquaculture in tropical open sea floating net cages

Mud spiny lobsters, Panulirus polyphagus (Herbst, 1793), were reared at four different stocking sizes and stocking densities in open sea cages to evaluate their effects on growth performance. To evaluate the effect of stocking size on the growth performance, the lobsters were segregated into four different treatment groups according to size and were stocked at a density of 300 animals per cage. To evaluate the effect of stocking density on the growth performance, lobsters of 81–100 g were stocked in four different stocking densities, i.e. 16/m², 24/m², 32/m² and 40/m². The results showed that the growth rate of (60–80 g) size group, was significantly higher compared to the size groups, i.e. 101–120 g and 121–140 g comprising of larger individuals. The final body weight, though significantly higher in 81–100 g as compared to 60–80 g, the growth performance (i.e. weight gain percentage (WG %) and specific growth rate (SGR)) were not significantly different. The density‐dependent influence on growth performance was evident in this study. The WG % and SGR during 90 days’ culture period was significantly higher in 24/m² compared to other groups. This study provides crucial information about the appropriate stocking density and stocking size of lobsters at the field level, which would help to promote sustainable lobster cage farming by maximizing the production potential of the system.     

Spawning behaviour of Penaeus (Fenneropenaeus) merguiensis de Man and the effect of light intensity on spawning

An experiment was conducted to investigate the effect of light intensity just prior to and during spawning of Penaeus (Fenneropenaeus) merguiensis de Man in the laboratory. Neither the presence of light nor light intensity (0, 10 and 1100 lux) had a significant effect on the spawning process or hatching rate in P. merguiensis. Difference in the percentage of spawners, percentage of incomplete spawning, fecundity and hatching rate were all insignificant (P > 0.05) among the three light treatments. However, spawning was delayed (up to 21 min on average) under 1100 lux with a high percentage of incomplete spawning, compared with the Control (0 lux). For the first time, spawning behaviour of P. merguiensis was observed and fully described. The spawning process can be divided into four phases: dormant, pre‐spawning, spawning and post‐spawning by distinct behaviour of prawn broodstock. The dormant phase was characterized by a quiescent and non‐feeding period, whereas movement of prawn broodstock was active during the pre‐spawning and post‐spawning phases. Depending on the individual, spawning was completed within 3–5 min. Prawns often stayed still on the water surface during spawning with occasional manoeuvres to change the position. After a short rest at the termination of the spawning phase, prawn broodstock re‐exhibited active movement as in the pre‐spawning phase, but showing conspicuous care to the deposited eggs. The role of light in controlling ovarian development and spawning, and the behaviour of prawn broodstock in relation to maximizing fertilization rate are discussed.     

Can satellite ponds buffer the impact of introduced fish on newts in a mountain pond network?

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Increased spawning activity of female Nile tilapia (Oreochromis niloticus) (L.) after stocking density and photoperiod manipulation

This study was conducted to evaluate the effects of stocking density and photoperiod in increasing the reproductive performance of Oreochromis niloticus. In experiment 1, a change in stocking density (from 47.7 to 6.8 kg m^?3) was performed, with groups of 48 females moved to single compartments. In experiment 2, 36 females experienced a 6L:18D photoperiod for 21 or 28 days (stocking density: 31.3 kg m^?3) before being placed in individual compartments (stocking density of 6.9 kg m^?3, 12L:12D photoperiod). The spawning rates in experiment 1 (32.2%) and in experiment 2 (21 days: 65.2%, 28 days: 36.1%) were significantly higher than those in the control (17.7%). On the other hand, hatching and swim‐up fry rates were significantly lower in experiment 2 – 21 days (41.3%, 40.4%) but not in experiment 1 (64.0%, 56.3%) compared with the control (67.0%, 62.3%). The spawning rate in experiment 2 – 21‐day treatment group was the highest, while the number of eggs collected per female was significantly lower than that in the control. In experiments 1 (20.8%) and 2 (21 days: 44.4%, 28 days: 19.4%), the daily spawning rates were the highest 3 days after maintaining females in single compartments. The current experiment demonstrates how specific stocking density changes can be used to induce higher spawning rates in Nile tilapia.     

Effect of timing of count events on estimates of sea lice abundance and interpretation of effectiveness following bath treatments

Effectiveness of sea lice bath treatment is often assessed by comparing pre‐ and post‐treatment counts. However, in practice, the post‐treatment counting window varies from the day of treatment to several days after treatment. In this study, we assess the effect of post‐treatment lag time on sea lice abundance estimates after chemical bath treatment using data from the sea lice data management program (Fish‐iTrends) between 2010 and 2014. Data on two life stages, (i) adult female (AF) and (ii) pre‐adult and adult male (PAAM), were aggregated at the cage level and log‐transformed. Average sea lice counts by post‐treatment lag time were computed for AF and PAAM and compared relative to treatment day, using linear mixed models. There were 720 observations (treatment events) that uniquely matched pre‐ and post‐treatment counts from 53 farms. Lag time had a significant effect on the estimated sea lice abundance, which was influenced by season and pre‐treatment sea lice levels. During summer, sea lice were at a minimum when counted 1 day post‐treatment irrespective of pre‐treatment sea lice levels, whereas in the spring and autumn, low levels were observed for PAAM over a longer interval of time, provided the pre‐treatment sea lice levels were >5–10.     

A new classification of pre‐ovulatory oocyte maturation stages in pikeperch,Sander lucioperca (L.), and its application during artificial reproduction

This study aimed at improving the reproduction effectiveness and synchronization of ovulation in the pikeperch, Sander lucioperca (L.), during induced spawning, which is one of the main bottlenecks in the aquaculture of this species. For this purpose, a new categorization of maturation stages in pre‐ovulatory oocytes was applied. It is generally based on two morphological indicators: germinal vesicle migration or its breakdown (GVBD) and different oil droplet coalescence rates. This categorization covered seven stages (from I to VII) – from the end of vitellogenesis to ovulation. The categorization was verified by controlled reproduction with the use of hormonal stimulation (500 IU of hCG per kg of female body weight) and low spawning temperature (12 °C), which extended the latency time. In addition, some morphological indicators (pseudo‐gonadosomatic index, Fulton's condition coefficient) of females were calculated in order to determine their usability in determining the maturation stage. However, these indicators proved to be ineffective for this purpose, further highlighting the need to determine the maturational stages in pre‐ovulatory oocytes to synchronize ovulation in pikeperch. During the experiment, ovulation seemed to be synchronized among the experimental treatments. Statistical differences were found in terms of latency time between experimental groups at different maturity stages (II – 78–98 h; III – 57–78 h; IV – 48–58 h; V – 32–49 h; VI – 5–30 h) according to the proposed classification. This classification and the results presented in the study significantly improved the synchronization of ovulation, which may positively affect the effectiveness of pikeperch production under controlled conditions.     

基于营养通道模型的海州湾中国明对虾生态容纳量

通过增殖放流,增加优质渔业资源、改善种群结构是渔业资源养护的重要手段,而增殖生态容量的研究是科学实施增殖放流的前提。为确定海州湾中国明对虾的生态容纳量,根据2013年连云港海州湾渔业生态修复水域的调查资料,应用Ecopath with Ecosim(EwE)软件中的Ecopath模块,构建了该区域的生态系统能量流动简易模型,计算了放流种类中国明对虾的增殖生态容纳量。结果表明:系统各功能组营养级范围在1~4.42。系统总流量9335.191 t·km~(–2)·a~(–1),系统总初级生产力3892.630 t·km~(–2)·a~(–1),系统初级生产力与总呼吸量的比值为1.331,连接指数为0.415,杂食指数为0.174,Finn循环指数为11.4%,平均能流路径为2.8系统尚处于由衰竭状态向恢复状态转变,还未恢复到成熟态。中国明对虾不是本海域的关键种,当前中国明对虾的生物量为0.04 t·km–2·a–1,中国明对虾的生态容纳量为0.846 t·km~(–2)·a~(–1)。     

Remaining questions in the case for balanced harvesting

Balanced harvesting – harvesting all species and sizes in an ecosystem in proportion to their productivity – is a fisheries management strategy that has been suggested recently to increase yields, while reducing overall ecosystem impact. However, some aspects of balanced harvesting are controversial, including its call for extensive harvesting of juveniles and forage fish. Balanced harvesting also calls for targeting species and size‐classes that are not currently marketable, possibly at a significant economic cost. Some have argued that this cost is outweighed by the ecological benefits of maintaining the ecosystem size and trophic structures and by the benefits of extra yield for food security. There is broad consensus that balanced harvesting would require major changes to fishery management institutions and consumer behaviour, and it is unclear to what extent it is physically possible with current technologies. For this reason, we argue that steps to implement balanced harvesting are difficult to justify until the case for it is more clearly resolved. We outline some of the pivotal questions that must be answered to make a convincing case for or against balanced harvesting, many of which can be answered empirically. In identifying these questions, we hope to offer a constructive path forward in resolving some of the key issues in the balanced harvesting debate.     

Stages of gonad development during the reproductive cycle of the blackfin snook, Centropomus medius Günther

The reproductive biology of the Blackfin snook Centropomus medius was studied to expand our current knowledge on its aquaculture potential. From April 2001 to November 2002, 301 females and 193 males were captured. A 1:1.6 (male:female) ratio was found. Gonadosomatic (GSI) and hepatosomatic (HSI) indices suggested that the spawning period (SP) extended from September to November, with peak spawning activity in September (GSI=0.98% and HSI=0.7%). The period of pre‐gametogenesis extended from January to June. During the post‐SP in December, 90% of oocytes were pre‐vitellogenic and 10% were atretic. Histological analysis of gonads (haematoxylin–eosin, Sudan black B, Alcian blue PAS, Cleveland Wolfe) showed five stages of oocyte development, each occurring at a characteristic range of oocyte diameters (μm): (I) pre‐vitellogenic (25–55); (II) cortical alveoli (56–250); (III) vitellogenic (251–340); (IV) maturation (341–645) and (V) atretic (21–100). Five reproductive stages were identified for testis morphology: (I) regressed; (II) early maturation; (III) mid‐maturation; (IV) full maturation and (V) regression. The type of ovarian development in C. medius was identified as a group synchronous.