Rice fields to prawn farms: a blue revolution in southwest Bangladesh?

This paper examines freshwater prawn (Macrobrachium rosenbergii) farming in southwest Bangladesh where a large number of farmers have converted their rice fields to export oriented prawn farms, locally known as gher. The gher design potentially provides good opportunities for diversified production of prawn, fish, rice and dike crops, that has brought about a ‘blue revolution’. The average annual yield of prawn, fish and rice was estimated at 467, 986 and 2,257 kg ha⁻¹, respectively. Large farmers produced higher production due to more inputs, larger farm size and longer experience of prawn farming than others. All farmers in different gher size categories (i.e., small, medium and large) made a profit, with seed and feed dominating variable costs. Despite a higher production costs per hectare, the average annual net return was higher in large farms (US2,426), compared with medium (US2,426), compared with medium (US1,798) and small (US$1,420) farms. Prawn production in gher systems has been accompanied by a great deal of social and economic benefits. Most farmers associate the blue revolution with increases in income and living standards. Socio-economic benefits of the households of prawn farmers depend on resource ownership (i.e., farm size) and are very apparent. Nevertheless, a number of significant challenges, particularly social and environmental issues, are vital in translating its benefits effectively to the thousands of rural poor.     

Is cod lekking or a promiscuous group spawner?

The mating system of cod ( Gadus morhua ) has been described as promiscuous with few options for exercising mate choice. We, on the other hand, argue that cod fulfil the prerequisites of a conventional lekking mating system. A review of papers on cod mating behaviour suggests that mature males aggregate and possibly defend small territories on the spawning grounds, where male–male interactions are common. Females visit males at the aggregations when ready to spawn and males show an extensive courtship display including dance, fin display, and acoustic calls. This may allow females to discriminate between males and both fin size and mass of drumming muscles, the cod's acoustic organ, are related to a male's fertilisation potential. This, together with the presence of sexual dimorphism in drumming muscles, suggests that sexual selection by females is at work. Different courtship display combined with different mate preferences may be important premating mechanisms reducing or preventing interbreeding between groups of cod.     

Is European catfish a threat to eels in southern France?

• 1. European eel (Anguilla anguilla) is recognized as a critically endangered species in the northern hemisphere. Threats such as overfishing or pollution are well known as risks for eel populations. However, much less is known about the impact of introduced fish on European eels. In particular, introduced large‐bodied predators could become new predators to eels.
• 2. The potential impact of European catfish (Silurus glanis L) on an eel population in the Camargue, southern France was studied using a combination of stable isotope and gut content analyses.
• 3. Only large‐bodied catfish (>500 mm) can consume numerous fish prey. However, catfish mostly consumed crayfish (Procambarus clarkii), these prey items being found in 79% of the guts of the largest individuals. Eel was absent from the dissected catfish guts. A mixing model based on Bayesian inference revealed that catfish diet included only 5% (0–8.5%) of marine sources (both eel and mullet).
• 4. While local economic interests prompted ecological studies to assess whether catfish exerted a new and strong predatory pressure on eel, this study found that European catfish behaved as an opportunistic omnivore, and as such was not a direct threat as a predator on eel populations in the Camargue. Copyright © 2011 John Wiley & Sons, Ltd.

     

Is spawning stock biomass a robust proxy for reproductive potential?

Reference points based on fishing mortality (F) and spawning stock biomass (SSB) are a requirement of many fisheries management frameworks. SSB is assumed to be a proxy for stock reproductive potential (SRP). Limit reference points based on SSB are used to indicate the level of biomass below which productivity is affected. SSB fails to account for changes in fecundity, egg viability and sex ratio, and it has been argued that total egg production (TEP) provides a better reflection of SRP. We explore how accounting for TEP impacts limit reference points and evidence for a relationship between stock and recruit. Time series of SSB and TEP are compared for three North Sea stocks: cod (Gadus morhua), herring (Clupea harengus) and plaice (Pleuronectes platessa). Dynamics based on TEP are different from those based on SSB for cod and plaice, but the stock–recruit relationships were not ‘improved’ using TEP. Shifts in productivity (spawner per recruit) occur in all three time series and SSB underestimated uncertainty. Yet again, it was shown that assumptions of stationarity about fish population productivity are incorrect. We argue that the use of TEP does improve the realism in our understanding of stock dynamics, and demographically, more complex management strategy evaluation is required to develop management procedures that are robust to uncertainty and integrate F and the demographic health of a stock. Empirical feedback control systems based on fisheries independent indices including surveys of eggs, larvae, recruits, juveniles or spawning adults should be evaluated and compared to traditional approaches.     

Is fisheries governance possible?

Are there limits to the governability of a fishery? The establishment of a 200 nautical mile economic zone in Norway in 1977 made it possible to change from an open‐access regime to a more closed one. In this process, the former self‐regulating Norwegian fishing industry, to a large extent, accepted and adapted an explicit, hierarchical form of state‐run governance. However, the process of change did not stop there. Since the turn of the millennium, we have seen the creation of a cybernetically organized fishing industry, where control, regulation and governance have become re‐embedded in the industry. This article explores this radical new development and perspective on fisheries governance and governability based on lessons learned from technological and organizational changes in the Norwegian fishing industry.     

Is the crown-of-thorns starfish a threat to the reefs of Lord Howe Island?

• 1 Lord Howe Island, a World Heritage Area which lies in the southern Pacific Ocean, has the most southern true coral reefs in the world.
• 2 In the past decade, populations of Acanthaster planci, the crown-of-thorns starfish, have significantly reduced coral cover at Elizabeth and Middleton Reefs, approximately 200 km to the north of Lord Howe Island, and a small population has been reported from Lord Howe Island.
• 3 The abundance and distribution of A. planci was evaluated using surveys by the local recreational diving industry and video-transects, and the potential rate of recovery of the coral community following predation was assessed by analysing coral recruitment patterns.
• 4 The starfish population at Lord Howe Island remained relatively small and localized between 1984 and 1993.
• 5 Coral recruitment was dominated by the juveniles of brooding corals, and these same species dominated the established coral community. There was limited recruitment of broadcast-spawning coral species during the study period, suggesting that southern dispersal of coral larvae from more northern sites may be a rare or sporadic event.
• 6 The results indicate that there is only a small probability that the present starfish population will result in a major starfish outbreak. However, the recovery of the coral community from a major outbreak would be slow because of the apparently low rate of input of coral larvae from sources external to the reef.
• 7 Management agencies need to consider whether the present small and localized starfish population should be removed, given the likely ramifications of an infestation and the economic importance of the reef to tourism.

     

Is the winter period a severe bottleneck of anadromous riverine Arctic charr parr?

Abstract –  Winter growth and survival of wild individually tagged juvenile Arctic charr (1+ age) from a riverine anadromous stock, were studied in a small ice-covered (∼6 months) ground water brook (temperature ∼1 °C) connected to Skibotnelva in subarctic northern Norway. The overall winter survival was estimated to be 68% from late October 2005 to early May 2006. The recaptured charr were not significantly different in initial length or weight compared with the nonrecaptured fish suggesting low size-dependent mortality. The majority (98%) of the recaptured charr showed significant increase in size, with a mean increment of 62% from their initial bodyweight and 12% of the charr parr had more than doubled their weight. The mean specific growth rate was calculated to be slightly lower (0.27) than estimated values from a growth model (∼0.35). In addition, the condition factor increased significantly during the field experiment. These results are the first individual growth data on riverine anadromous Arctic charr parr under natural winter conditions, and indicate that charr can grow relatively fast during periods with low temperature and also that ground water brooks can be good over-wintering habitat for juvenile Arctic charr. These results suggest that the winter period is perhaps a less severe bottleneck than previously recognised for the cold-adapted Arctic charr.     

The benthic impacts of a large cod farm — Are there indicators for environmental sustainability?

A cod farm in Vidlin Voe, Shetland was at the time of the study the largest cod farm in Europe, and was started in 2003. Run according to organic principles, the farm consisted of 17  32 m diameter cages in the 3 km long sea loch (locally known as voe), which though extremely exposed at the mouth, is sheltered near the cages.Benthic macrofauna and physical/chemical sediment parameters were measured in the summer months of 2004, 2005 and 2006 as biomass increased in the growing cycle. A range of biotic indices showed the benthic environment was enriched at peak biomass of the farm, but by contrast, surficial CHN levels and organic matter were low and uniform. The commonly used sediment indicators redox, total organic carbon and total organic nitrogen did not correlate well with biotic indicators at this site. Predictions from a near-field particle tracking and resuspension model (CODMOD) and a simple nutrient enhancement box model of the voe system (Equilibrium Concentration Enhancement (ECE) model), were used to assess the assimilative capacity of the system.     

Is it a hindrance for an invasive aquatic species to spread across scattered habitat patches?

1. Despite their importance for aquatic biodiversity, ponds are among the most vulnerable freshwater habitats. Owing to their isolation in terrestrial environments, ponds are expected to be relatively well protected from biological invasions, but this depends on many factors. 2. The purpose of this study was to examine the influence of a range of variables (water quality, habitat, and landscape attributes) on the colonization of discrete ponds by a widespread aquatic invader, the red swamp crayfish Procambarus clarkii, which can disperse overland. 3. Investigations were conducted in two networks of ponds, each located in close proximity to a large invaded marsh. The two marshes under study differed in the length of time since the crayfish were introduced. 4. The proportions of colonized ponds and crayfish abundances were moderate in both networks, but higher in the network that had been invaded first. In both networks the distance to the marsh was the main predictor of pond colonization, considering similar energy costs to cross aquatic and terrestrial habitats for the recently invaded network, but assuming that dispersal was 25 times costlier across the terrestrial matrix than via streams for the earlier invaded network. Pond characteristics had no influence on crayfish occurrence in either network. Furthermore, predictions of pond invasion were lower for the recently invaded network. 5. The importance of the distance to the marsh indicates that natural dispersal was the main process of pond colonization by crayfish. Findings also suggested that overland dispersal was rare and costly. By contrast, streams were probably significant in facilitating crayfish dispersal. Differences between the two networks might arise from an invasion process still in progress in the recently invaded network. 6. From a management viewpoint, local actions are encouraged to prevent the spread of crayfish via streams. In addition, broader‐scale actions to mitigate other human disturbances would improve the outlook for pond biodiversity.     

Assessing cetacean body condition: Is total lipid content in blubber biopsies a useful monitoring tool?

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Is behaviour in a novel environment associated with bodily state in brown trout Salmo trutta fry?

Energetic status and body size are inconstant bodily states often considered to have feedback effects on behaviour. Feedbacks can be negative, like starvation‐threshold feedbacks (lower state values = increased risk taking due to higher energy need, and vice versa), or positive, like state‐dependent safety feedbacks (higher state values = lower vulnerability when expressing risky behaviours, and vice versa). Few studies have investigated feedback effects during the early‐life survival bottleneck of territorial species, when rapid growth is particularly important to maintain competitive ability. We investigated effects of body size and energetic status on the emergence latency into an unknown environment in highly territorial brown trout fry. We manipulated energetic status using high and low food rations in different combinations over two consecutive periods. In contrast to results from other small‐sized fishes, no general behavioural effects of energetic state were detected, but larger fish had on average shorter emergence latency. Starvation‐threshold feedbacks were not supported, but the size effect favours the presence of a state‐dependent safety feedback. When individuals were split into clusters characterised by long (>34 s) and short (<34 s) emergence latency, a state‐dependent safety feedback, based on energetic status, was found in the short‐latency cluster. Positive state‐dependent feedbacks may reflect the high level of competition among wild trout fry during the first summer, particularly among the more active individuals (i.e., from the short latency cluster). High state levels could be utilised to gain advantages over lesser competitors (e.g., to establish territories), particularly if the overall risk of starvation is higher than the risk of predation.     

Is the decline of birds and amphibians in a steppe lake of northern Patagonia a consequence of limnological changes following fish introduction?

• 1. Laguna Blanca, in Laguna Blanca National Park, is a lake in Patagonia which has been designated as a Ramsar site since 1971 because of bird diversity and abundance and importance for nesting, particularly for the black neck swan, Cygnus melanocoryphus. It is also valued for its populations of endemic amphibians, Atelognathus patagonicus and Atelognathus praebasalticus.
• 2. Avian and amphibian populations have decreased dramatically in recent years. Percichthys colhuapiensis, Percichthys trucha (Pisces, Percichthyidae), Salmo trutta and Oncorhynchus mykiss (Pisces, Salmonidae) were introduced into Laguna Blanca in 1965. Since 1986, no Atelognathus frogs have been found. The abundance of swans and coots, which are strongly associated with macrophytes for nesting and feeding, has diminished drastically, whereas piscivorous birds have increased.
• 3. The fishless condition of some neighbouring small lakes with abundant pond weeds, aquatic birds and endemic amphibians, was assessed in order to compare the physical and chemical characteristics and the quantitative composition of the benthos among lakes. Fish presence at Laguna Blanca and its absence at El Burro, Antiñir and Jabón lakes, were confirmed. Compared with previous results, it seems that the abundance of Amphipoda (Hyalella), Copepoda and Cladocera at Laguna Blanca has decreased, while Acari has increased and Notostraca has disappeared. Water transparency has diminished in Laguna Blanca and now is lower than that of fishless lakes.
• 4. P. colhuapiensis were captured only in Laguna Blanca, with the highest captures in the littoral zone. The population shows rapid individual growth in the early years and an absence of fish older than 6 years. The preponderance of benthos and the presence of macrophytes in the gut contents of adult P. colhuapiensis appear to indicate that they are important consumers of these resources.
• 5. This paper concludes that fish introduction in Laguna Blanca led to a complex trophic cascade effect (fish predation on tadpoles, fish competition for avian food, bottom disturbance, zooplankton reduction) producing deleterious effects on the amphibian and bird populations.

Copyright © 2006 John Wiley & Sons, Ltd.     

Is current floodplain management a cause for concern for fish and bird conservation in Bangladesh's largest wetland?

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Is observed variability in the long-term results of the Continuous Plankton Recorder survey a response to climate change?

In the more than 50 years that the Continuous Plankton Recorder (CPR) survey has operated on a regular monthly basis in the north-east Atlantic and North Sea, large changes have been witnessed in the planktonic ecosystem. These changes have taken the form of long-term trends in abundance for certain species or stepwise changes for others, and in many cases are correlated with a mode of climatic variability in the North Atlantic, either: (1) the North Atlantic Oscillation (NAO), a basin-scale atmospheric alteration of the pressure field between the Azores high pressure cell and the Icelandic Low; or (2) the Gulf Stream Index (GSI), which measures the latitudinal position of the north wall of the Gulf Stream. Recent work has shown that the changes in the GSI are coupled with the NAO and Pacific Southern Oscillation with a 2 year lag. The plankton variability is also possibly linked to changes observed in the distribution and flux of water masses in the surface, intermediate and deep waters of the North Atlantic. For example, in the last two decades, the extent and location of the formation of North Atlantic Deep Water, Labrador Sea Intermediate Water and Norwegian Sea intermediate and upper-layer water has altered considerably. This paper discusses the extent to which observed changes in plankton abundance and distribution may be linked to this basin-scale variability in hydrodynamics. The results are also placed within the context of global climate warming and the possible effects of the observed melting of Arctic permafrost and sea ice on the subpolar North Atlantic.     

A size-based stock assessment model for invasive blue catfish in a Chesapeake Bay sub-estuary during 2001–2016

Stock assessment modeling provides a means to estimate the population dynamics of invasive fishes and may do so despite data limitations. Blue catfish (Ictalurus furcatus) were introduced to the Chesapeake Bay watershed to support recreational fisheries but also consume species of conservation need and economic importance. To assess management tradeoffs, managers need to understand the current status of the population and anticipate future population abundance and trends. A Bayesian size-based stock assessment model was used to estimate blue catfish abundance, fishing mortality, and size structure over time (2001–2016) in the tidal James River. The model estimated population size increases until around 2006, with declines in total abundance after 2011 and large blue catfish (≥80 cm total length) after 2001. These first estimates of blue catfish population dynamics in the Chesapeake Bay region provide inputs for projection models to evaluate prospective management actions and identify monitoring needs.     

Is Guam a regional source,destination, or stepping‐stone for larvae of three fisheries species?

The pelagic larval duration (PLD) period of fish can influence dispersal, recruitment, and population connectivity, thereby potentially informing best strategies for fisheries management. Computer models were used to simulate the dispersal of larvae of three species, representing a range of PLDs, from the Pacific island of Guam and neighboring islands for a 9‐year period (2004–2012) to gain insight into the best management strategies for these species. The species included two springtime spawners with shorter and longer PLDs, scribbled rabbitfish (Siganus spinus; 33 days) and yellowfin goatfish (Mulloidichthys flavolineatus; ~90 days maximum), and a fall spawner with a similarly long PLD, bluespine unicornfish (Naso unicornis; ~94 days maximum). An ocean circulation model coupled with a particle dispersal model provided simulated numbers of larvae settling at each island in relation to the island where they were spawned. Graph analysis was used to examine generational connections between islands. For S. spinus, self‐seeding was the dominant means of replenishment at Guam. Local management actions to maintain adequate spawning stock may be a primary control on long‐term sustainability for that fishery. In contrast, N. unicornis and M. flavolineatus populations at Guam were reliant on outside sources for 92%–98% of larval supply. For them, identifying and negotiating the preservation of upstream spawning potential in the Marshall Islands and Federated States of Micronesia will be needed. Guam played a relatively minor role in generational connectivity across the region. Shortest paths spanning the region often did not pass through Guam, or there were equally short paths through other islands.     

Is serotonin uptake by peripheral tissues sensitive to hypoxia exposure?

Fish Physiology and Biochemistry - In the Gulf toadfish (Opsanus beta), the serotonin (5-HT) transporter (SERT) is highly expressed in the heart, and the heart and gill both demonstrate the...