Day–night change in fish community structure in a seagrass bed in subarctic waters

The day–night change in fish community structure over a year was examined in a seagrass bed in Lake Notoro, Hokkaido, northern Japan, to examine nocturnal increases in predation risk. This seagrass bed has previously been considered a predation refuge for juvenile and small-sized fishes. Species richness, abundance and biomass of piscivorous fishes during nighttime were higher than those during daytime on all sample dates surveyed (May, August and November 2013), indicating an increase in predation risk for juvenile and small-sized fishes during nighttime. The mean biomass-weighted trophic level of fish communities in the seagrass bed was also higher at night than in the day. The piscivorous fishes collected in the seagrass bed during the night included important fishery species. These may obtain energy through nocturnal feeding in the seagrass bed. Therefore, the function of seagrass beds as fish habitats should be re-evaluated by considering two possible characteristics contributing to fishery production: as a daytime predation refuge for juvenile and small-sized fishes, and as a nighttime foraging ground for piscivorous fishes.     

Seasoned Sprat Products’ Acceptance in Estonia and in Thailand

The aim of the study was to describe and evaluate competitiveness of Estonian spice-cured sprat products in Estonia and Thailand. Sample A was saltiest, Sample B had lowest overall spiciness, and Sample C had highest pepper flavor and sour taste intensity. The main drivers of consumer acceptance for the spice-cured sprat products were different: flavor and appearance in Estonia and appearance and odor in Thailand. In Estonia, one cluster of consumers liked the traditional (Sample A) and lightly spiced (Sample B) sprat products, while the other cluster liked the traditional (Sample A) and the marinated (Sample C) sprat products. In Thailand, all samples scored low, but manual clustering indicated that marinated (Sample C) sprat products are most acceptable. The current study showed that spice-cured sprat products in general can be accepted by Thai consumers, especially as part of meals, if further flavor development is carried out with the products.     

Socio-cultural context of fishers’ participation in coastal resources management in Anini-y,Antique in west central Philippines

The vicious cycle of poverty, overfishing and resource degradation in coastal communities in the Philippines calls for action that will address the problem of declining fish catch and degraded fish habitats. The literature has shown that an efficient and effective coastal management program can be instrumental in approaching this problem. In order to secure food and livelihood of fishers, the Southeast Asian Fisheries Development Center/Aquaculture Department collaborated with the local government of Anini-y, Antique to develop a sustainable utilization of natural marine resources through sea ranching of abalone within the Nogas Island marine protected area. Establishing a marine protected area is a means of conserving natural stocks while sea ranching is considered an effective strategy that can increase fishery resources. The two management schemes are considered as effective coastal resources management strategies. The success of a sea-ranching project is dependent not only on biophysical but also on socioeconomic factors as determinants of community participation and cooperation. A social assessment was conducted to determine the fishers’ socio-cultural characteristics, their perceptions of their coastal resources and knowledge on how to effectively manage these coastal resources. The fishers’ awareness on fishing regulations and the extent of their participation in community's coastal resources management activities were also determined. Data were collected from a household survey using a semi-structured questionnaire, focus group discussions and in-depth interviews with key informants. The fishers generally scored low in almost all aspects of their socioeconomic wellbeing. Most fishers perceived that their coastal resources were in a bad condition which they attributed to illegal and commercial fishing, increasing number of fishers and the poor enforcement of fishery regulations. However, the weighted mean scores of their knowledge on coastal resources management, awareness to fishery regulations and participation in community coastal resource management activities were average. This implied that fishers when trained and developed can become potential partners for effective coastal resources management programs.     

When in life does density dependence occur in fish populations?

Fisheries advice is based on demographic calculations, which assume that density‐dependent processes regulating recruitment occur only in early life. This assumption is challenged by laboratory and lake studies and some recent indications from marine systems that demonstrate density‐dependent regulation late in life. By accounting for spatial dynamics of a population, something that has previously been ignored in models of fish, we show that density‐dependent regulation is determined by the size of the habitat: in small habitats, for example small lakes, regulation occurs late in life, while it can occur early in large habitats. When regulation happens late in life, fisheries yield is maximized by exploitation of mainly juvenile fish, while exploiting mature fish maximizes yield if regulation happens early. We review and interpret observations of density dependence in the light of the theory. Our results challenge the current assumption that density dependence always occurs early in life and highlights the need for an increased understanding of density‐dependent processes. This can only come about by a change of focus from determining stock‐recruitment relationships towards understanding when and how density‐dependent regulation occurs in nature.     

Risk in aquaculture: farmers’ perceptions and management strategies in Bangladesh

Abstract

This study examines Bangladesh fish farmers’ perception for risk sources, risk management strategies, and the relationship with socio-demographic variables. Data were collected from a sample of 350 farmers in Bangladesh. Exploratory factor analysis of a set of perception measurement items was used to assess farmers’ attitudes towards risk and their risk management strategies. The results reveal that fish-diseases, fish price variability, low quality of feed and fingerlings, flood and credit constraints were perceived as the most important sources of risk. For risk management, supply of good quality feed and fingerlings, diseases prevention, crop insurance, increasing personal savings, and assurance of bank loans were considered as the most important strategies to mitigate risks. Empirical evidence shows that farmers engage in multiple management strategies to reduce production risk.     

Cage fish culture in Lake Victoria: A boon or a disaster in waiting?

Fish catches in Lake Victoria have been on the decline while demand for fish has been increasing. Cage culture with >3,000 cages, over 3 million tilapias and valued at US$ 12 million is trying to fill the gap. This study reviews the development of cages and the need to develop a decision support tool for effective management. Existing literature and data on fisheries and cage culture held by the Kenya Marine and Fisheries Research Institute (KMFRI) were used in the analysis. Cage culture is a promising venture that may increase productivity, offer employment and enhance economic well‐being. However, site suitability for the installation of cages is poorly regulated with most developments (>45%) located within 200 m of the shoreline that are breeding grounds of fish and conflict with other lake users. Waste feed increases eutrophication, and enhances growth of algae and water hyacinth in the lake. Recent isolated fish kills were attributed to low dissolved oxygen concentrations (<0.64 mg/L), and an increasing occurrence of fish disease are signs of poor management practices among cage farmers. Cage culture may turn into an environmental disaster if not managed well, and there is need for robust policies and increased awareness to reduce environmental impacts.     

Maximum economic yield in crisis?

We examine the claim in Christensen that Maximum Economic Yield (MEY) is equal to Maximum Sustainable Yield (MSY). The basis for this claim is that MEY considers only the ‘catching’ of fish and that when the full value‐chain is considered; it is the MSY level that maximizes economic value. We argue that to maximize society’s benefit from a given sector of an economy, resources need to be allocated across all sectors such that additional net benefits from employing one more unit of society’s resources are equalized across all sectors of the economy. In this way, the opportunity cost of employing society’s resources across all economic sectors is minimized. In an economy where all resources are fully utilized, further value added in the value chain for fish is an additional cost and has the effect of reducing fishing effort and optimum yield rather than the opposite. In a less developed economy or a developed one in recession where all resources are not fully used, the multiplier effect could be important, and if it is high for fisheries it would be an argument to maximize sustainable yield and effort. We show, using current input‐output data, that this is not the case. Furthermore, from a simple principle of optimization, we know that to optimize a sector that consists of many segments through time, one has to optimize every portion of the chain through time.     

Can management practices in rice fields contribute to amphibian conservation in southern Brazilian wetlands?

• 1. Rice field expansion is one of the activities associated with the disappearance of 90% of the wetlands in southern Brazil. Worldwide, rice agriculture has been recognized as having considerable potential value for many aquatic species. Nevertheless, management practices in such systems must be ameliorated and better investigated.
• 2. This study evaluated the potential role of rice fields as refugia for amphibians, and whether different hydrologic management practices after rice cultivation could contribute to wetland amphibian conservation in southern Brazil.
• 3. Six collections were made in six rice fields with different management practices after cultivation (three dry and three flooded) and three natural wetlands. The amphibians were sampled through six random 15‐min visual transects per collection in each rice field and the natural wetlands.
• 4. In total, 2139 anuran individuals were observed in rice fields (798) and Reserva Lake (1341), comprising 12 anuran species distributed among five anuran families. Anuran richness and abundance varied over the rice cultivating cycle, and they were higher in the growing phases than in the fallow phases. The mean anuran richness and abundance was higher in Reserva Lake than in flooded and dry rice fields.
• 5. The different management practices adopted after the harvesting period (presence or lack of surface water) did not influence the anuran richness and abundance. It did, however, influence species composition.
• 6. The difference in species composition between the management practices adopted is an interesting result in terms of biodiversity conservation. Rice producers could maintain part of their agricultural land flooded during the fallow phase as a strategy to preserve a higher diversity of anurans. These results should be taken into consideration in wetland conservation plans in southern Brazil; however, the percentage of each agricultural land that should be kept flooded should be decided by Brazilian agricultural and conservation policies. Such a strategy would reconcile agricultural/economic needs with the conservation of biodiversity in southern Brazil, where more than 90% of wetland systems have already been lost. Copyright © 2009 John Wiley & Sons, Ltd.

     

Thyroid hormones down-regulate thyrotropin β mRNA level in vivo in the turbot (Psetta maxima)

Thyroid stimulating hormone (TSH) is a vertebrate pituitary heterodimeric hormone that stimulates the thyroid gland to produce the thyroid hormones, T3 and T4. We report here the cloning, by PCR on reverse-transcribed pituitary RNAs, of a 180 bp fragment of the cDNA encoding TSH subunit in the turbot (Psetta maxima). The deduced amino acid sequence displayed 66 and 75% identity with the corresponding sequence from the European eel (Anguilla anguilla) and the rainbow trout (Oncorchyncus mykiss), respectively. This cDNA was then used as a probe for densitometric analysis of individual pituitary Northern blots. TSH mRNA levels were quantified in turbot where circulating thyroid hormones were modified by dietary treatments or hormone supplementation. Recombinant rainbow trout growth hormone had no effect on circulating thyroid hormone levels or on pituitary TSH mRNA level. In turbot fed heat-treated rapeseed meal, plasma T4 levels were lowered and TSH mRNA increased more than two fold. In contrast, when turbot were fed a standard fish-meal supplemented with T3, circulating T3 levels were elevated and there was a dramatic decrease in TSH mRNA level. It is concluded that both thyroid hormones are able to down-regulate TSH mRNA level in vivo in the turbot. These results are discussed in the context of the evolution of the TH feed-back on TSH production.     

Do surrogates describe patterns in marine macroalgal diversity in the Recherche Archipelago,temperate Australia?

• 1. Surrogates aim to predict species diversity and to minimize sampling effort. Here the value of surrogates for marine macroalgae is tested.
• 2. Higher taxonomic levels and dominant taxa were evaluated as surrogates for detecting patterns in macroalgal species diversity (derived from species‐level biomass data) in the Recherche Archipelago, Western Australia.
• 3. Data were stratified by two island groups (inshore and offshore), three depth intervals (<10 m, 10–20 m, >20 m), and two exposures to wave energy. Correlations between similarity matrices from surrogate and species diversity data matrices were analysed using a modified Spearman rank correlation (r_s). The ability of surrogates to detect differences between exposures to wave energy was also investigated using analysis of similarity. Species diversity data were aggregated to higher taxonomic levels and were either fourth‐root or presence/absence (richness) transformed.
• 4. Species richness was the most consistent surrogate (r_s‐values>0.69, P=0.001). Genus‐level richness was also strongly correlated to species diversity in the Recherche Archipelago, except in depths <10 m where patterns in diversity were characterized by species turnover.
• 5. At offshore islands in depths 10–20 m and >20 m, family‐ and order‐level biomass data were suitable surrogates owing to the abundance of Alariaceae (Order Laminariales) represented by a single genus and species. Surrogates using biomass data from the orders Laminariales, Ceramiales, Dictyotales and Fucales were also successful at offshore islands in middle to deeper depths.
• 6. At inshore islands in depths 10–20 m and >20 m, genera from the orders Gigartinales, Fucales and Ceramiales were strongly correlated to species biomass data.
• 7. Surrogates, like species richness, that were strongly correlated to species biomass data were also able to distinguish between exposures to wave energy, based on analysis of similarity tests.
• 8. Sampling effort would be reduced if collecting richness data in species‐rich macroalgal assemblages such as those found in temperate Australia.

Copyright © 2006 John Wiley & Sons, Ltd.     

Trends in import and export of fishery products in the Czech Republic during 2010–2015

There has been a worldwide increase in consumption of fish from open waters and aquaculture during the last decades. In 2013, the Czech Republic was the sixth largest producer of fish within the EU, with annual production of 20,135 tonnes. However, during the period 2010–2015 import of fishery products to the Czech Republic increased from 39,098 to 43,399 tonnes. The monetary value of import increased by 81 % from 90.2 million EUR in 2010 to 169.9 million EUR in 2015. In 2010, the major imported fishery product was frozen fillets of sutchi catfish (Pangasianodon hypophthalmus) from Vietnam (8872 tonnes). In 2015, the most imported fishery product was whole chilled salmon (Salmo salar) from Norway (6897 tonnes). During 2010–2015, the export of fishery products increased from 18,167 to 22,134 tonnes, which is an increase by 21.8 %. The value of export has increased by 80 % from 54.5 million EUR in 2010 to 98.1 million EUR in 2015. The major exported fish was live common carp (Cyprinus carpio) at volume of 7545–9075 tonnes. This study looks at changes in market, volume and value of fish imported and exported during the last 6 years.     

Did volcanic ash from Mt. Kasatoshi in 2008 contribute to a phenomenal increase in Fraser River sockeye salmon (Oncorhynchus nerka) in 2010?

The effect of a widely distributed phytoplankton bloom triggered by volcanic ash from Alaska (Hamme et al., 2010. Geophys. Res. Lett. 37) on juvenile Fraser River sockeye is discussed in terms of the timing of ocean migration and trophic structure of the Gulf of Alaska. Our hypothesis is that the occurrence of a massive diatom bloom in the Gulf greatly enhanced energy ascendancy in the ocean at a time of year when adolescent sockeye migrated from the coast in 2008. We contend this increase in food availability was an important factor for the survival and growth of juvenile sockeye which led to one of the strongest sockeye returns on record in 2010 of 34 million, compared with perhaps the weakest return on record of 1.7 million the previous year.     

Are environmental conditions in Finnish streams limiting to early life-history survival in the nonnative rainbow trout?

The nonnative rainbow trout Oncorhynchus mykiss has been an unsuccessful invader in North European streams, although it has been widely introduced. Here we studied whether early life history stages (egg incubation and hatching, first overwintering) act as filters for the establishment of hatchery rainbow trout. Survival of hatched alevins was approximately 80%, whereas only 47% of the embryos survived. However, the latter value was impacted by the high number of unfertilized eggs. Correlation coefficients with embryo survival rate and environmental variables (pH and temperature) were statistically insignificant. In the overwintering experiments, the survival of rainbow trout was 93%. The growth was generally slowed during the winter, but in the spring the growth of rainbow trout exceeded that of the native brown trout. Our data demonstrated that the survival and growth of rainbow trout during early life-history stages were relatively high and comparable to those of the native brown trout. Based on the variables considered in our study, our results suggest that environmental conditions during early life-history stages are not detrimental for rainbow trout in the study streams.     

Plenty more fish in the sea?

Only in the last century did humans overwhelmingly accept that fisheries resources are finite. Consequently, ‘there are more fish still in the sea than ever came out of it’ served as a popular metaphor for unbounded expectations for half a millennium, expectations that also extended to use of the planet in general. By reconstructing historical fishing back 1200 years, we identify when this metaphor actually ceased to be true. For some of our most important stocks, it has not been true for centuries, although surprisingly, for fishes globally, it applied until the last century. We demonstrate, however, that there can still be ‘plenty more fish in the sea’ and that with effective management they provide a continuous flow of benefits for our future.     

Chemical alarm cues in juvenile African catfish,Clarias gariepinus Burchell: A potential stressor in aquaculture?

Previous studies on the effects of stocking density on the behaviour of African catfish have shown that at low densities, especially directly after restocking of tanks, increased aggression might occur. This aggression may directly affect the welfare of the fish. In addition, the resulting skin damage may also lead to the release of chemical alarm cues from the skin of the fish, possibly acting as a secondary stressor in a farming situation. Moreover, in a recirculation aquaculture system, a build-up of chemical alarm cues might occur. The objective of this study was to examine the effects of a single chemical alarm cue administration on the behaviour and growth performance of group-housed African catfish. Furthermore, the effects of a single passage over a biofilter on the behavioural response of African catfish to chemical alarm cues were tested. Although African catfish responded to chemical alarm cues with a short-term 35% increase in the number of active fish, no long-term effects were observed on both behaviour and growth performance of the fish. Furthermore, the results indicated that a single passage over a biofilter did not strongly alter the response of African catfish to the alarm cue, indicated by a 25% increase in the number of active fish. In conclusion, the results of this study indicate that chemical alarm cues, at the concentration applied in this study, cannot be considered a stressor for African catfish, although the effects of higher cue concentrations need further study. In addition, further study into the effects of chemical alarm cues on other, non-predatory, farmed fish is recommended.     

Short-Term Dinoflagellate Bloom in a Shrimp Pond in Bahía de La Paz,Gulf of California

From mid-August to mid-September 1998, a dinoflagellate bloom in a shrimp pond near La Paz, Baja California Sur, was studied. Daily samples were taken of phytoplankton, dissolved oxygen, nutrient concentrations, photosynthetic pigments and proteins. The bloom occurred at temperatures of 29.7 to 33.2?°C. High densities of a Scrippsiella-like dinoflagellate (15.9?×?10⁶ cells/L) occurred on the first day of sampling, reaching a peak of 249?×?10⁶ cells/L on Day 13, and declining to 4 to 7?×?10⁶ cells/L by Day 26. Chlorophyll a varied from 8.63 mg/m³ on Day 4 to 141.38 mg/m³ on Day 13. Total nitrogen varied widely (0.2–11.50 μM) while phosphates peaked only once on Day 13 (4.14 μM). Proteins ranged from 523 to 6387 μg/L; the latter value occurred two days after the maximal peak of nitrates and coinciding with the highest level of phosphates. Fertilizers added to the ponds increased nutrient concentration and stimulated phytoplankton growth. In turn, the food supply to cultured shrimp noticeably increased throughout the bloom.     

Are circle hooks effective in reducing incidental captures of loggerhead sea turtles in a Mediterranean longline fishery?

• 1. A known fishing hot spot for loggerhead sea turtles (Caretta caretta) in the Mediterranean Sea is in the waters of the Strait of Sicily where interactions with fish hooks and branchlines are believed to be a major cause of mortality for sea turtles.
• 2. Hooks with different shapes but a similar gape width (circle hook size 16/0 vs J hook size 2) were tested in order to determine the potential effectiveness of the hook design to both reduce sea turtle capture as well as to maintain acceptable levels of target species capture rates in a shallow‐set longline swordfish fishery in the Mediterranean.
• 3. Seven experimental fishing trips, 30 000 hooks total, were conducted on a single commercial fishing vessel (18 m in length) in the Strait of Sicily during the months of July through October over a period of three years from 2005 to 2007. Circle and J hooks were alternated along the mainline.
• 4. A total of 26 sea turtles were hooked, all immature‐size Caretta caretta. Turtles were caught at a statistically greater frequency on J hooks than on circle hooks. The capture rate, weight, and upper jaw fork length of the target species were not significantly different between the two types of hooks employed.
• 5. Five sea turtles swallowed the hook and in all such cases these were J type. Circle hooks tended to be located externally and were more easily detected by fishermen, and could be removed with the correct dehooking action before returning the turtle to the sea.
• 6. These findings suggest that 16/0 circle hooks can effectively reduce the incidental capture of immature loggerhead sea turtles in a Mediterranean swordfish longline fishery without affecting the catch size of the target species.

Copyright © 2009 John Wiley & Sons, Ltd.     

Is batch variability in hatching time related to size heterogeneity and cannibalism in pikeperch (Sander lucioperca)?

Larval size heterogeneity is known to induce cannibalism, and procedures to avoid larval size differences are consequently implemented already during egg incubation and hatching. We investigated the relation between larval development variability, size heterogeneity and cannibalism in pikeperch. Larvae were sorted into five groups according to the time of hatching during a 65‐h period. The larvae with different times of hatch were then reared separately or together during an 18‐day period. Late hatched larvae were longer (P=0.003) and had less yolk remaining (P<0.001) than early hatched individuals at the time of hatching. However, on 11 days post fertilization, the late‐hatching larvae tended to have larger yolk reserves than earlier hatched individuals (P=0.07). Furthermore, the next day, a lower proportion in the late fraction had switched to exogenous feeding (P=0.024). That larvae with a late hatching time developed slower suggests a positive relationship between the hatching time and the embryonic developmental rate. However, differences in the length and available yolk reserves at hatching between larval fractions with different hatching times suggest that hatching is not strictly associated with a specific developmental stage, and that factors other than the development rate of the embryo are involved in the timing of hatching.     

Numerical simulation of circulation in the Laizhou Bay

IntroductionAs part of the Bei Dou Fisheries Research and Managements project(1997- 2 0 0 0 ) ,the Institute of MarineResearch participated in a collaborative study with the Yellow Seas Fisheries Institute on approaches to thedevelopment of theoretical models as tools for assessing the carrying capacity of bivalve production.The In-stitute of Marine Research has in recent years engaged in relatively extensive activity on numerical modellingof coastal oceans. To demonstrate some of the po…     

Marteiliosis in mussels: a rare disease?

Among 1280 cultured and wild adult Mediterranean mussels, Mytilus galloprovincialis, collected over a 1 ‐ year surveillance period from the Slovene Adriatic Sea, 0.3% were histologically positive for the presence of Marteilia spp. The infection was concentrated in winter. Employing the molecular methods of PCR, cloning, DNA restriction and sequencing, only Marteilia refringens type M was detected in all the infected mussels. Although all life‐cycle stages of M. refringens severely infected digestive glands, only sporadic disruption of epithelial cells of digestive tubules and focal destruction of digestive tubules were observed in the infected mussels. This was the first detection of M. refringens in M. galloprovincialis from the Slovene Adriatic Sea with the lowest prevalence reported to date. In addition, our results highlight the need for sequencing to complement the established PCR‐RFLP analysis for correct parasite typing.