Can timing of spawning explain the increase in egg size with female size in salmonid fish?

A common observation is that egg size increases with maternal size within populations. Several hypotheses have been proposed to explain this phenomenon. Most recently, it was suggested that the optimal egg size depends on female size due to correlations between (i) breeding time and egg size selection and (ii) female size and breeding time, and as such, the positive egg size–maternal size relationship represents an adaptive strategy. Here, we test the second of these two premises in two salmonid species, Atlantic salmon (Salmo salar) and coho salmon (Oncorhynchus kisutch) for which we have detailed breeding and egg size data. The body size of spawning females decreased throughout the season in coho salmon, but not in Atlantic salmon. Furthermore, we did not find a direct correlation between egg size and breeding time, which would also be expected if this premise was correct. Accordingly, breeding date does not appear to be as important as other factors in shaping among female differences in egg size.     

Fish stock assessment of the northern New Caledonian lagoons:2 – Stocks of lagoon bottom and reef-associated fishes

Fish stocks found on lagoon bottoms and near reefs are characterized by a high diversity and heterogeneous habitat which make stock estimation difficult. In particular, it is necessary to combine several methods in order to evaluate the major components of these stocks. The present study aimed at estimating reef fish stocks in the Northern Province of New Caledonia, a region where they represent a major target for the local fishermen. These estimates were based on experimental fishing with handlines and bottom longlines. Handlines were used to assess the stocks near reefs, and longlines for those in areas away from reefs and on lagoon soft bottoms. Handline stations (363) were sampled in three different regions (west, north and east lagoons) and three biotopes (nearshore, middle lagoon and barrier reef). A total of 104 species were caught, the major families being Lethrinidae, Lutjanidae and Serranidae. Species composition and catch per unit of effort (CPUE) varied among regions and biotopes. In particular, the north zone showed characteristics of an unexploited area with very high yields. An increase in CPUE and fish size from the coast towards the barrier reef and with increasing depth was observed in all regions. Correlations between CPUE from handlines and the numerical density and biomass estimates from underwater visual censuses (UVC) performed on nearby reefs were significant. A total of 206 longline stations were sampled in the west and east regions. A total of 80 species were caught, the major families being the same as those caught in stations with handlines with the addition of Carangidae. The CPUE of longlines was significantly correlated with numerical density and biomass estimates made by UVC along the longlines. Stock estimates based on the correlations between CPUE from handlines or longlines and UVC estimates indicate that 90 % of the lagoon stock were found on soft bottoms and near reefs. Reefs, despite biomasses that were five times larger than soft-bottom and near-reef areas, made only a small contribution to total stock. The ratio between density and CPUE was highest for the lowest densities, thus indicating that fishing efficiency increased with density. Comparison of handline catch performed around reefs and UVC data from nearby reefs suggests that there were strong relationships between the fish assemblages of these two biotopes.     

Habitat and prey selection of common minke,sei, and Bryde’s whales in mesoscale during summer in the subarctic and transition regions of the western North Pacific

This study represents the first quantitative analysis of the characteristics of the distribution areas and stomach contents of common minke whale Balaenoptera acutorostrata, sei whale B. borealis, and Bryde’s whale B. edeni in relation to oceanographic and prey environments in mid summer in the western North Pacific. Common minke whales were distributed within subarctic regions and the northernmost region of the transitional domain, coinciding with the main habitat of their preferred prey, Pacific saury Cololabis saira. Sei whales were mainly found in the northernmost part of the transition zone and showed prey preference for Japanese anchovy Engraulis japonica, which was significantly more abundant in the main distribution area of the whale than in its adjacent areas. “Hot spots” of Bryde’s whales were found in several regions of the transition zone between the subarctic boundary and the Kuroshio front. This whale species preferred Japanese anchovy as prey, for which the distribution density was significantly higher in the main distribution area of the whale than in the adjacent areas. These results indicate that the summer distributions of Pacific saury and Japanese anchovy greatly influence the distributions of these whale species, suggesting that the whales’ habitat selection is closely related to their prey selection.     

Gametogenesis, reproductive investment, and spawning behavior of the Pacific giant oyster Crassostrea gigas: evidence of an environment-dependent strategy

The progress of gametogenesis was studied in oysters Crassostrea gigas having the same origin (Tremblade), but cultured during 1 year in two distinctive French marine areas, the Baie des Veys and Marennes-Oléron. We assessed seasonal changes in the reproduction cycle on the basis of stereological techniques to estimate reproductive investment and measurement of gonad evolution area by quantitative histology. From a qualitative point of view, both oyster groups presented typical reproductive stages, but showed differential timing, in particular during the sequence of spawning and duration of the re-absorption stage. Oysters in Baie des Veys had a single partial spawning in August and a re-absorption stage that extended until winter. Oysters in Merennes-Oléron had a partial spawning in July and massive release of gametes during August. Spawnings in both the areas were related to maximum temperature (19°C). The quantitative analysis showed, on an annual basis, a higher reproductive investment by oysters from Baie des Veys, 86% against 53% in the other group. Larger gonads, higher gamete production, and more intensive spawning were the characteristics of oysters in Baie des Veys. Recently, the reproduction pattern and investment has been related with summer mortalities; therefore, a quantitative understanding of reproductive processes becomes necessary for C. gigas. Environmental conditions at each site may explain differences in the progress and intensity of gametogenesis. While temperature regulated the time and speed of gametogenesis, results suggest that the intensity was influenced by the quantity of available food but may need further research. However, nutrient recycling from unreleased gametes in the gonads of oysters from Baie des Vey is a factor to be considered in the results of this study.     

Fish stock assessment of the northern New Caledonian lagoons:1 – Structure and stocks of coral reef fish communities

Lagoon fish in New Caledonia are mainly caught by artisanal fisheries and subsistence fishing. Reef fish are the major component of this catch. The present study aimed at estimating these reef fish standing stocks and at finding the main factors influencing the distribution of these fish. Sampling of 904 stations was stratified according to three zones (north, east and west) and three reef types (barrier, intermediate and fringing). Fish communities exhibited strong heterogeneity in their distribution, showing higher biomass (maximum of 447 g·m^–2) and total standing stock (43 000 tonnes) in the north zone than in the east and west zones. Similarly, observed patterns were dependent on reef types: higher biomass and total standing stock being observed on barrier reefs than on intermediate or fringing reefs. The total standing stocks, which were about 65 000 t, were mainly composed of herbivorous fish families such as the Acanthuridae and Scaridae. The differences in the patterns of distribution of species, individuals and standing stocks between reef types may be explained by variations in terrestrial influences and reef morphology, whereas differences among zones were most likely due to accessibility of fishing areas and fishing pressure. The latter is almost non-existent in the north zone, which can thus be considered to be almost unexploited commercially. This most likely explains the high proportion, 77 %, of long-lived species in the biomass of this zone. The results might have implications in management of reefs elsewhere in the South Pacific, for which similar data are only scarcely available.     

Islands in the ice stream: were spawning habitats for native salmonids in the Great Lakes created by paleo‐ice streams?

Lake trout Salvelinus namaycush, lake whitefish Coregonus clupeaformis and cisco Coregonus artedi are salmonid fishes native to the Laurentian Great Lakes that spawn on rocky substrates in the fall and early winter. After comparing the locations of spawning habitat for these species in the main basin of Lake Huron with surficial substrates and the hypothesized locations of fast‐flowing Late Wisconsinan paleo‐ice streams, we hypothesize that much of the spawning habitat for these species in Lake Huron is the result of deposition and erosion by paleo‐ice streams. This hypothesis may represent a new framework for the identification and protection of spawning habitat for these native species, some of which are currently rare or extirpated in some of the Great Lakes. We further suggest that paleo‐ice streams may have been responsible for the creation of native salmonid spawning habitat elsewhere in the Great Lakes and in other glaciated landscapes.     

Egg drift and hatching success in European river lamprey Lampetra fluviatilis: is egg deposition in gravel vital to spawning success?

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When aquaculture restores and replaces an overfished stock:Is the conservation of the Species assured? The case of the scallop Argopecten purpuratus in Northern Chile

The fishery for Argopecten purpuratus in northern Chile, whichcollapsed because of overfishing, has been replaced by aquaculture of thespecies. In 1998, cultures produced 16,474 t, while the highest landings recorded inthe entire history of the fishery was in 1984 (one year after the 1983 ElNiño) with 5275 t. The figures for stock size of the species in the pastand at present, show that the wild stock of scallops today represents notmore than 10–15% of the total stock of the species within Chile, with mostof the individuals being kept in sea farms. Thus it is concluded that thescallop already represents a domestic species and, considering theoccurrence and development of selection practices in sea farms,biodiversity within the species appears to be at risk. With the developmentof culture practices over its entire range, there is little use in trying torecover a wild fishery for this scallop. It is urgent, however, that selectednatural beds be protected in order to preserve genetic diversity.     

Fish stock assessment of the northern New Caledonian lagoons:3 – Fishing pressure,potential yields and impact on management options

The potential yields of demersal reefal and lagoonal finfish, which are valuable for trade or consumption in the Northern Province of New Caledonia, are unknown. Fishing pressure was estimated from tally-sheets of professional fishermen to assess trade fishing and a household consumption survey to assess subsistence fishing. Total yield was estimated to be 1 326 tonnes in 1995, 94 % of which correspond to subsistence fishing. Most of the catches were taken from the east and west coasts; in the north zone (Bélep Archipelago) catches were very low. From this fishing pressure and the total stock values, the maximum sustainable yield (MSY) was estimated to be 12 600 t, which was about 10 % of the total stocks assessed in the Northern Province (138 300 t). This MSY was dominated by five families, namely Lethrinidae, Acanthuridae, Scaridae, Serranidae and Lutjanidae. The results suggest that fishing effort in the Northern Province of New Caledonia could increase without endangering the stock. However, on a smaller geographical scale, some locations (Koné and Népoui on the west coast), reef habitats (near-reef areas) or species groups (fish caught by line) were already being intensively fished. Fishing techniques should be diversified so that part of the fishing effort be redirected toward the least heavily exploited groups of species and biotopes.     

Threatened aquatic Andean frogs and mining activity in the Lithium Triangle of South America: Can both coexist?

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Decline and fall of the salmon fisheries in the Netherlands: is restocking the Rhine a reality?

Abstract. The Atlantic salmon, Salmo salar L., was once of major importance to the fishing industry along the River Rhine. This paper discusses the Dutch and German salmon catches over the years 1863–1950. Even up to the end of the last century, it was not uncommon for Dutch and German fishermen to land 100000 salmon a year. However, factors such as the increased use of locks and weirs along the Rhine, coupled with growth in pollution, soon led to a rapid decline in numbers. By 1933, the salmon fishing industry in the Netherlands had virtually ceased to exist. Analysis of the available catch statistics suggests that the decline in the salmon population could have started before official records began. Although the degree of scatter in the data and uncertainties in the assumptions preclude the possibility of drawing firm conclusions about the survival rate of salmon, these figures illustrate how difficult it will be to maintain a stable population in the Rhine. Moreover, a number of changes have taken place since the heyday of salmon in western Europe, which could compound the problem. Of particular importance in the context of the Rhine are:

• 1 the closure of two of the major migration routes to the sea (Haringvliet and Zuiderzee);
• 2 morphological changes in the river;
• 3 chemical and thermal pollution;
• 4 the loss of accessible spawning and nursery areas of the required quality;
• 5 the disappearance of salmon from other rivers that flow into the North Sea such as the Rivers Elbe, Weser and Ems. If salmon were only reintroduced into the Rhine, a certain proportion would probably stray and infiltrate these other rivers.

The fact that the impact of these changes is difficult to quantify increases the uncertainty associated with maintaining a stable stock of salmon in the Rhine.     

Isolation and characterization of an atypical Siberian sturgeon herpesvirus strain in Russia: novel North American Acipenserid herpesvirus 2 strain in Europe?

Siberian sturgeon herpesvirus (SbSHV) was isolated in Russia for the first time in 2006. Nine SbSHV isolates were recovered from different fish hatcheries producing the same cytopathic effect in cell cultures, the same clinical signs and mortality kinetics in virus‐infected fish and the same virus neutralization pattern and shared identical nucleotide sequences. In 2011, a new isolate was recovered from juvenile sturgeon, which caused completely different cytopathic effect. That isolate was not readily neutralized by Siberian sturgeon hyperimmune antisera, and its DNA was not recognized by the routine PCR developed for SbSHV detection. Molecular study of the novel isolate revealed that it was more closely related to North American Acipenserid herpesvirus 2 (AciHV‐2) isolates from white sturgeon, while the genome sequences of the former SbSHV isolates showed high similarity to the AciHV‐2 isolated from shortnose sturgeon. While clinical signs and mortality caused by the novel isolate in infected Siberian sturgeon were similar to those of the formerly described SbSHV isolates, the incubation period and mean time to death produced by the novel isolate were twice as long. The differences between the former isolates and the recent one suggest that a novel SbSHV strain emerged in Europe and the molecular findings imply its North American origin.     

Can pH and Water-to-Protein Ratio be Good Instruments to Evaluate the Abusive Water Added in Seafood by Phosphate Addition?

The aim of the present study was to evaluate the effect of the phosphates on tuna meat pH, and water-to-protein ratio. Tuna fillets were soaked in cold (5 °C) tripolyphosphate solution (STPP) and blend phosphate (CARNAL® 961) at 3, 5 and 10% for 30, 60 and 120 min. The control group was represented by cold distilled water. After soaking, the samples were drained, weighed, frozen, stored (-35 °C, for 15 days), thawed, drained, and grilled. After each step, samples were withdrawn for the following analysis: pH, phosphate (as P2O5), moisture and protein. A gradual increase in pH and residual phosphate was observed, which remained below the limits established by national (for pH) and international (for phosphate) legislation. A moderate positive correlation between pH and phosphate values was observed. An increase in moisture content and the water-to-protein ratio were observed, and still below to the legislation limit (i.e., 6.0). We suggest a critical review and possible changes in the parameters which are used as indicators of abusive use of the phosphate additive in seafood to combat the economic fraud in the frozen seafood products. It should be emphasized that these suggestions should be the focus of the collaborative study for its validation.     

Salmon prices in France and the UK: Does origin or market place matter?

Abstract

There have been several attempts to distinguish farmed Atlantic salmon by origin using trademarks. Whether there exist different regional markets for salmon, and in particular whether the UK market is separate from the market in continental Europe, is also an issue that has received attention. To address these questions, we investigate the relationship between Norwegian and Scottish salmon both in France and the UK, and between Scottish salmon in France and the UK. The analysis is carried out by investigating how the development of prices is related using co‐integration tests.     

Reconciling sustainability,economic efficiency and equity in fisheries: the one that got away?

Concern about the global state of fisheries and fish resources has highlighted the three primary considerations in fisheries management: sustainable utilisation, economic efficiency and equity in access to resources. We appear to be failing in pursuit of all three goals. Living marine resources are particularly threatened by overfishing, leading to many of the world’s fish stocks being heavily, fully or over exploited. Similarly, the economic diagnosis is that costs of fishing exceeded the value of the world’s catch by about US$ 40 billion at the beginning of the decade. Statistics on equity are less available, but the necessary spread of limited access to fisheries frequently has the greatest impact on the small scale, traditional fisher. This paper considers the reasons underlying the general failure of fisheries management and the solutions that are being proposed. Factors contributing to the problems include high biological uncertainty, conflict between the constraint of sustainability and social and economic priorities, poorly defined objectives, and institutional failures related to access rights and participation in management by the users. These issues point to the real complexity of fisheries management. It is argued that this complexity can be abused by all interest groups to avoid responsibility and to suit their own objectives. It is suggested that there are eight simple principles controlling fisheries management that are generally well‐understood and, if properly considered in fisheries management systems, would lead to improved performances. Responsible management will, however, only be effective if there is a genuine desire to achieve the objectives. Fishing capacity, frequently reflecting dependency of users on fisheries resources, is commonly in excess of the sustainable production of the resources. Excess dependency can preclude the political will to consider alternative strategies and only once it has been overcome, probably requiring solutions borrowed from outside fisheries, is effective management likely to be considered seriously. Thereafter, responsible management requires setting unambiguous objectives and management measures in co‐operation with users and other interest groups. The agreed strategy must be included in legislation to ensure transparency and accountability and to constrain decision‐makers. The performance of the strategy must be monitored and revised as necessary.     

Where once the eel and the elephant were together: decline of the European eel because of changing hydrology in southwest Europe and northwest Africa?

The collapse in recruitment of the European eel (Anguilla anguilla) since the early 1980s has been ascribed to possible overfishing, poisoning, parasitism, habitat loss and changes in ocean circulation. It is unclear which mechanism is most important, and firm data are lacking to make an assessment of the factors that apply over the full continental range. On the other hand, the recruitment of the American eel (A. rostrata) has declined along the western Atlantic at about the same time. This suggests a candidate mechanism that can affect both species together. A change in ocean climate may be a likely explanation, which is supported by a possible link between the North Atlantic Oscillation and one important recruitment index. However, it is unsafe to discard the other possible mechanisms because of lack of evidence. Habitat loss, in particular, may be important. We review over a century of evidence to suggest how the eel may have declined through progressive habitat loss that accelerated in the early 1980s as the result of economic development linked with hydrological changes. Although no single line of evidence can definitely prove one hypothesis for the eel decline, the total body of information may indicate a pronounced susceptibility in the southwest corner of the continental range closest to the Sargasso Sea that has been particularly affected by drought and dam construction. The sexual dimorphism of the species together with the energy requirements of the spawning migration may provide insight to explain the population collapse.     

Environmental and spatial processes: what controls the functional structure of fish assemblages in tropical rivers and headwater streams?

In this study, we investigated functional structure patterns of tropical headwater and river fish assemblages. We hypothesised that environmental conditions are primarily structuring headwater streams leading to functionally clustered assemblages, whereas processes that favour functional overdispersion would guide river assemblages. For 27 headwater streams and 22 rivers, we used eight functional traits for calculating two functional indexes: mean pairwise distance (MPD) and net relatedness index (NRI). We performed linear regressions between indexes and species richness, a multiple regression between NRI and eight environmental variables and a variation partitioning to disentangle the role of environment and space on NRI. Our findings indicate that fish assemblages of headwaters are structured by environmental conditions as most assemblages in this habitat displayed a tendency to clustering and MPD/NRI were not correlated with species diversity, whereas the opposite pattern was observed for river habitat. Four environmental variables (channel depth, water velocity, dissolved oxygen and turbidity) explain 56% of functional structure variation. These variables seem to function as selective filters in headwaters, whereas channel depth may be determinant for functional overdispersion of river fish assemblages. Components associated with space are also influencing the functional structure. Limitations of species dispersal through space (between both habitat types) appear as a possible cause to this. In this sense, both environmental conditions and processes linked with space are capable of influencing the functional structure of tropical headwater streams and river fish assemblages.     

Marine capture fisheries in the Arctic: winners or losers under climate change and ocean acidification?

Climate change, ocean acidification (OA) and the subsequent changes in marine productivity may affect fisheries and eventually the whole economy in the Arctic. We analysed how changes in climate and ocean pH under scenarios of anthropogenic CO₂ emissions are likely to affect the economics of marine fisheries in the Arctic. We applied a Dynamic Bioclimate Envelope Model (DBEM) and outputs from four different Earth System Models (ESMs) to project future changes in the distribution and maximum catch potential of exploited marine fishes and invertebrates. We projected that total fisheries revenue in the Arctic region may increase by 39% (14–59%) by 2050 relative to 2000 under the Special Reports on Emission Scenario (SRES) A2. Simultaneously, total fishing costs, fishers’ incomes, household incomes and economy‐wide impacts in the Arctic are also projected to increase. Climate change with OA is expected to reduce the potential increases in catch and the economic indicators studied herein. Although the projections suggest that Arctic countries are likely to be ‘winners’ under climate change in comparison with tropical developing countries, the effects of OA will lower the expected future benefits in the Arctic. The predicted impacts are likely to be conservative as we consider only the direct effects of OA on fishes and calcifiers, of which there are only a few in the Arctic. Results of this study would be useful for designing effective adaptation strategies to climate change and measures to mitigate the potential negative impacts of OA in the Arctic.     

Aphanomyces astaci presence in Japan: a threat to the endemic and endangered crayfish species Cambaroides japonicus?

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