Water Stocks Research Articles

Modelled effects of primary and secondary production enhancement by seamounts on local fish stocks

Abstract This paper addresses how large aggregations of fish found on many seamounts are sustained. We used a generic seamount ecosystem model from the Northeast Atlantic to examine the impact of a potential increase of local primary production on higher trophic levels, to quantify the immigration of allochthonous micronekton that would be required to maintain a “typical” seamount community, and to quantify if the necessary immigration ratios could be supported by local oceanographic conditions. Our simulation predictions indicate a lack of autochthonous resources in the system to support large amounts of seamount aggregating fish. In other words, autochthonous seamount production may be responsible for sustaining only a small amount of its total biomass. Additionally, our study supports the idea that enhancement of primary productivity also cannot sustain large aggregations of seamount fish. Our seamount model, which took into account high abundances of fish, marine mammals, seabirds and tuna, required a total immigration of allochthonous micronekton of 95.2 t km−2 yr−1 less than the potential available biomass after considering the immigration of prey based upon average current velocities and prey standing stocks in oceanic waters. Our model predicted that the horizontal flux of prey would be sufficient to sustain the rich communities living on seamounts.

Paraglacial and paraperiglacial landsystems: concepts, temporal scales and spatial distribution

The Pleistocene Earth history has been characterized by major climatic fluctuations. During glacial periods, ice may have covered around 30 per cent of the Earth surface compared to approximately 10 per cent nowadays. With global change, polar environments and other montainous glacial environments of the world are presently undergoing the most important changes since the end of the Last Glacial Maximum and are experiencing paraglacial and paraperiglacial geomorphological readjustments. Paraglacial and paraperiglacial landsystems consist of several subsystems including gravitational, fluvial, coastal, aeolian and lacustrine environments. Paraglacial and paraperiglacial landsystems can be analysed as open and complex landsystems characterized by energy, water and sediment fluxes and exchange with surrounding environments, especially with glacial and periglacial landsystems as inputs. Those cascading landsystems are likely to react to climate change because they rely on an ice-cold water stock (glacier and permafrost) that developed during a previous cold sequence (glaciation). The response of paraglacial and paraperiglacial systems to climatic forcing takes place over a long time span ranging from an immediate reaction to several millennia. The spatial limits of paraglacial and paraperiglacial landsystems are inherently dependant on the time scale over which the system is analyzed. During the Pleistocene, glaciations widely affected the high latitudes and the high altitudes of the Earth and were followed by inherited paraglacial sequences. Glacier forelands in Arctic and alpine areas experience paraglacial processes with the present warming. The expected global warming for the twenty-first century will result in significant impacts on present glacier areas in mountains and could result in the appearance of new areas for paraglacial dynamics. In permafrost terrain, landscapes underwent a similar paraperiglacial geomorphological adjustment in mountainous, continental and coastal areas, with permafrost thaw-degradation and thermokarst processes.

Potenciais de rendimento dos alvos da pesca de arrasto de talude do sudeste e sul do Brasil estimados a partir de parâmetros do ciclo de vida.

Trawl fishing in slope waters of southern and southeastern sectors of Brazilian coast has been sustained by important concentrations of the gulf hake (Urophycis mystacea), argentine hake (Merluccius hubbsi), silver John dory (Zenopsis conchifera), monkfish (Lophius gastrophysus) and, seasonally, the argentine squid (Illex argentinus). Potential yields were estimated for the former four species using growth, natural mortality and selectivity parameters available in the literature or calculated from empirical relationships and length frequency distributions of the trawl catches. These potentials oscillated between 8 and 10% of the total virginal biomass (Bo ) and the total virginal exploitable biomass (ExBo ,) for the gulf hake and the argentine hake. In relation to the siver John dory estimated maximum catches corresponded to 12.5% of ExBo , and 9.5% of Bo , whereas in the monkfish these catches were limited to 6% of both ExBo , and Bo ,. Because the available biomass estimated for these stocks in the slope waters of southeastern and southern Brazil cannot be considered as virginal, at least for the gulf hake and the argentine hake, the estimated potential yields may be generally regarded as conservative reference points. They suggest that precautionary annual catches of the main targets combined (gulf hake, the argentine hake and the silver John dory) should be under 10% of their total biomass available. Additionally, regarding the monkfish, an important component of the trawl bycatch and the main target of a gill net fishery in the same area, the TAC (Total Allowable Catch) adopted for management purposes is well bellow (2,5%) the maximum levels estimated by life-history parameters.

Flow injection analysis system based on amperometric thin-film transducers for free chlorine detection in swimming pool waters

This work reports on the performance of a user-friendly flow injection analysis (FIA) system for the monitoring of free chlorine. A methacrylate flow cell integrating a gold thin-film microelectrode, together with an on-chip gold counter electrode, both fabricated by microfabrication technology, provided robustness, low output impedance, rapid response and low cost to the proposed flow system. An external Ag/AgCl reference electrode placed downstream the chip completes the electrochemical cell. Amperometric detection of chlorine was carried out at a set potential of +350 mV, without oxygen interference. The proposed flow system responded linearly to chlorine concentrations in a range from 0.2 to 5 mg l −1, with a sensitivity of 0.23 μA l mg −1, the estimated limit of detection being 0.02 mg l −1. In addition, the system response was kept stable for at least 10 days (±3 σ criterion), by keeping the flow system in an inert atmosphere when not in use. Fifteen samples of swimming pool waters were analyzed and no matrix effects were detected. Also, results were in good agreement with those obtained by a standard method. The excellent analytical performance of the system together with its good working stability would also enable its application for the detection of chlorine in other matrices such as tap water or chlorine stock solutions.

Bringing competition to urban water supply*

This paper proposes a market‐based reform that would introduce competition into the provision of urban water. This proposal calls for a decoupling of infrastructure control and ownership of water whereby the property rights to water would be transferred to private hands. The proposal involves periodically allocation (e.g. by auction) of existing water stock held in urban catchments to virtual suppliers who then compete in providing bulk water. This change when coupled with effective third party access and retail competition would lead to a competitive market for the provision of urban water. The approach aims to address concerns over inefficient pricing and infrastructure provision under the current arrangement.

Testing the Hydrological Landscape Unit Classification System and Other Terrain Analysis Measures for Predicting Low-Flow Nitrate and Chloride in Watersheds

Elevated nitrate concentrations in streamwater are a major environmental management problem. While land use exerts a large control on stream nitrate, hydrology often plays an equally important role. To date, predictions of low-flow nitrate in ungauged watersheds have been poor because of the difficulty in describing the uniqueness of watershed hydrology over large areas. Clearly, hydrologic response varies depending on the states and stocks of water, flow pathways, and residence times. How to capture the dominant hydrological controls that combine with land use to define streamwater nitrate concentration is a major research challenge. This paper tests the new Hydrologic Landscape Regions (HLRs) watershed classification scheme of Wolock and others (Environmental Management 34:S71-S88, 2004) to address the question: Can HLRs be used as a way to predict low-flow nitrate? We also test a number of other indexes including inverse-distance weighting of land use and the well-known topographic index (TI) to address the question: How do other terrain and land use measures compare to HLR in terms of their ability to predict low-flow nitrate concentration? We test this for 76 watersheds in western Oregon using the U.S. Environmental Protection Agency's Environmental Monitoring and Assessment Program and Regional Environmental Monitoring and Assessment Program data. We found that HLRs did not significantly improve nitrate predictions beyond the standard TI and land-use metrics. Using TI and inverse-distance weighting did not improve nitrate predictions; the best models were the percentage land use-elevation models. We did, however, see an improvement of chloride predictions using HLRs, TI, and inverse-distance weighting; adding HLRs and TI significantly improved model predictions and the best models used inverse-distance weighting and elevation. One interesting result of this study is elevation consistently predicted nitrate better than TI or the hydrologic classification scheme.

Synoptic assessment of water resource variability in reservoirs by remote sensing: General approach and application to the runoff harvesting systems of south India

This paper presents a methodological procedure based on remote sensing and image analysis techniques designed to map and quantify water stocks in small irrigation reservoirs over vast, user‐defined regions. Because the method is based on unsupervised pixel classification schemes, it is analytically transparent and entirely replicable and can therefore be used in most settings as a tool for integrated water resource management, planning, or policy making, with benefits to irrigation, land use, agriculture, and water‐related social issues. Satellite images of semiarid south India are used here to quantify fluctuating water volumes in ∼2500 reservoirs. In this pilot study, the detection of temporal trends and spatial discontinuities in land use at successive dates within reservoir beds is a proxy for assessing the performance of reservoirs and for formulating hypotheses on the environmental, socioeconomic, or anthropological reasons behind the inferred levels of infrastructural maintenance or disuse. The synoptic approach paves the way for future efforts as better ground truth data become available.

Desempenho produtivo da tilápia do Nilo (<em>Oreochromis niloticus</em> L.) em diferentes densidades e trocas de água em “raceway”

Nile tilapia, Oreochromis niloticus L. (Perciformes Cichlidae) fingerlings were stocked at 90, 120 and 150 fishes in 24 circular tanks (0,5 m³), submitted to two full water exchanges, in a 30 and 60 minutes, in raceway system, to evaluate productive performance. The performance results were analyzed through a completely randomized design, in a 3x2 factorial scheme. After 128 days, the final weight and the weight gain were higher in larger water exchange and lower stocking density. The feed conversion ratio with non-significant statistical differences. The total biomass increased with the water exchange and stocking density increasing for 120 and 150 fishes/m³; the specific growth ratio increased with water exchange increasing; the fillet yield and the carcass yield decreased significantly with lower water exchange and bigger stocking density. In this research, it was concluded that the best performance parameters were obtained with full water exchange in 30 minutes, at bigger stocking densities.

Combined effects of water quality and stocking density on welfare and growth of rainbow trout (Oncorhynchus mykiss)

An 84-day experiment assessed the combined effects of two fresh water quality levels (H: 1.71 ± 0.15 mg O2l −1 and 0.28 ± 0.01 mg l −1 total ammonia nitrogen (T-AN), L: 5.15 ± 0.07 mg O2l −1 and 0.54 ± 0.01 mg T-AN l −1 ) and 3 stabilized stocking densities: 24.8 ± 0.2, 74.2 ± 0.5 and 120.0 ± 0.9 kg m −3 ) on rainbow trout. Fish were fed using demand feeders with rewards proportional to stocking density. Mass increase was significantly affected by water quality and stocking density, being highest in H water and the lowest at 120 kg m −3 . There was no significant difference in final weight between 25 and 74 kg m −3 , but at 120 kg m −3 it was 27% and 19% lower in H and L water respectively than at 25 kg m −3 . Feed intake (FI) from day 0-85 was significantly affected by water quality, 1.5% in H compared to 1.1-1.0 in L, but there were no significant differences in apparent feed conversion (AFC). FI was not significantly affected by stocking density but AFC was impaired, it increased with stocking density. Marked changes in fish morphology and composition were related to water quality: Condition K factor and fillet fat content were significantly higher in H than in L groups. Dorsal and pectoral fin condition was affected by stocking density and water quality: fins were significantly longer and less eroded in L groups and at low stocking density. Physiological measures were within the usual ranges, but differed between treatments. Changes in plasma osmolarity, hydromineral balance (Na + ) and acid base balance (HCO − ) showed that fish were more affected by water quality than by stocking density. There was no sign of acute stress in acclimated fish as cortisol and glycemia were similar under all experimental conditions. This study highlights the importance of water quality and feeding conditions when considering the effects of stocking density on fish welfare.

Diel variations in particle stocks in the oligotrophic waters of the Ionian Sea (Mediterranean)

In order to assess the factors responsible for the variability in particle attenuation of light at a daily scale in the oligotrophic waters of the Ionian Sea (Eastern Mediterranean), optical and biogeochemical measurements were collected at high spatial and temporal frequency during late summer 1999. Over 5 days, repeated profiles were conducted in situ every 3 h using a spectral absorption–attenuation meter at 9 wavelengths (WETLabs ac-9) in a profiling mode, and were accompanied by a series of discrete biogeochemical measurements including particle size distribution and concentration, and flow cytometric determination of picophytoplankton and heterotrophic bacteria abundances. Temporal variations in the vertical distribution of the particle attenuation coefficient and particle concentration displayed clear daily oscillations, with an increase during daytime counter-balanced by a similar decrease at night. For the first time in in situ conditions, diel changes in the particle size were also evidenced through discrete measurements of the particle size distribution and in situ continuous ac-9 profiles of the spectral characteristics of particle attenuation coefficient. The diel variability in the concentration and size of the particle stock, and its impact on bulk particle attenuation, is discussed in relation to the composition of the autotrophic assemblage, the balance between algal and non-algal particles and the specific rhythms in biological processes. In Ionian Sea waters, heterotrophic bacteria appear to play a major role in the diel cycle in particle attenuation.

“Escapes” of Eggs from Farmed Cod Spawning in Net Pens: Recruitment to Wild Stocks

Escapes of farmed fish from aquaculture installations, as well as large scale stock enhancement and sea ranching activities, are regarded as risk factors for negative genetic impacts on native gene pools. These aspects have been discussed for several decades, and a number of recent experiments on Atlantic salmon have clearly demonstrated dramatically reduced overall fitness of farmed offspring compared with offspring of wild origin. The Atlantic cod (Gadus morhua L.) is now the most promising new marine species for large scale farming in Norway, and more than 500 commercial farming licenses have been issued, corresponding to a maximum annual production capacity of about 300,000 tonnes. In comparison with the environmental problems caused by escapes from the salmon farming industry, cod farming presents new challenges. As a marine species, cod are able to spawn in the net pens during the ongrowing period and thus release genetic material into the environment. Coastal cod stocks in Norwegian waters are depleted and therefore may be particularly vulnerable to genetic interaction with farmed cod. Thus, there is an urgent need for more detailed knowledge of potential hazards. A pilot experiment performed in Heimarkspollen in Austevoll (a practically landlocked fjord) demonstrated for the first time that farmed cod are capable of producing viable cod larvae that mix with larvae from wild cod. The farmed cod used in the pilot experiment were homozygotic for a rare allele (GPI-1*30), and mature fish were placed in a net pen to allow spawning and egg drift into the surrounding water to take place. Surveys of eggs found the highest densities in the vicinity of the net pen. Later larval surveys found that 20% to 25% of the larvae sampled in the area possessed the unique genetic marker and could therefore be traced to the spawning cod in the net cage. Numerous genetically marked larvae were also found outside Heimarkspollen, indicating a high degree of dispersal of eggs and larvae by tidal advection.

The Oligomeric State of the Active BM2 Ion Channel Protein of Influenza B Virus

Influenza A virus and influenza B virus particles both contain small integral membrane proteins (A/M2 and BM2, respectively) that function as a pH-sensitive proton channel and are essential for virus replication. The mechanism of action of the M2 channels is a subject of scientific interest particularly as A/M2 channel was shown to be a target for the action of the antiviral drug amantadine. Unfortunately, an inhibitor of the BM2 channel activity is not known. Thus, knowledge of the structural and functional properties of the BM2 channel is essential for the development of potent antiviral drugs. The characterization of the oligomeric state of the BM2 channel is an essential first step in the understanding of channel function. Here we describe determination of the stoichiometry of the BM2 proton channel by utilizing three different approaches. 1) We demonstrated that BM2 monomers can be chemically cross-linked to yield species consistent with dimers, trimers, and tetramers. 2) We studied electrophysiological and biochemical properties of mixed oligomers consisting of wild-type and mutated BM2 subunits and related these data to predicted binomial distribution models. 3) We used fluorescence resonance energy transfer (FRET) in combination with biochemical measurements to estimate the relationships between BM2 channel subunits expressed in the plasma membrane. Our experimental data are consistent with a tetrameric structure of the BM2 channel. Finally, we demonstrated that BM2 transmembrane domain is responsible for the channel oligomerization.

The price of lice

Wild salmon stocks in Canadian coastal waters are being severely affected by parasites from fish farms. So intense are these infestations that some populations of salmon are at risk of extinction.

Natural-gas-powered thermoelectricity as a reliability factor in the Brazilian electric sector

The introduction of natural-gas-powered thermoelectricity into the Brazilian generation sector can be considered as a very complex energy, economic, regulatory and institutional revision. Brazil is a country with very specific characteristics in electricity generation, as approximately 80% of the generating capacity is based on hydroelectricity, showing strong dependency on rain and management of water reservoirs. A low rate of investment in the Brazilian Electricity Industry in the period of 1995–2000, associated with periods of low rainfall, led to a dramatic lowering of the water stocks in the reservoirs. With this scenario and the growing supply of natural gas, both from within Brazil and imported, natural gas thermal electric plants became a good option to diversify the electrical supply system. In spite of the Brazilian Government's efforts to install such plants, the country was faced with severe electricity rationing in 2001. The objective of this work is to show the need to continue with the implementation of natural gas thermal electricity projects, in a manner that allows flexibility and guarantees greater working reliability for the entire Brazilian electricity sector. Taking into account the world trend towards renewable energy, the perspectives of usage of biofuels in the Brazilian Energy Matrix and in electrical energy generation are also analyzed. The very issue of electrical power efficiency in Brazil and its challenges and strategic proposals from the standpoint of Government Programs and results provided so far are presented. The technological constraints in order to put on stream the thermal electric plants are also analyzed. The article concludes with a positive perspective of the usage of natural gas as to be the third pillar in the Brazilian Energy Matrix for the years to come.

Thinking outside the framework: equitable research partnerships for environmental research in Australia

Many environmental science research programmes now adopt community‐based philosophies and designs, although there are few applications in Australian Indigenous communities. This research describes the development and testing of a framework of engagement to guide collaboration between Indigenous and non‐Indigenous Australians during an environmental sciences research project. That project aimed to assess trepang (sea cucumber) stocks in Aboriginal waters, and determine the commercial harvest potential of the resource to local people. Its objectives were to undertake trepang survey and mapping, integrate Indigenous knowledge about the resource, and model the existing catch data of commercial fishers operating in the region. The framework of engagement developed to guide the research process comprised a goal, research stages, and a number of guiding principles for collaboration, which were constructed from content analysis of available guidelines and literature and from data gathered during expert interviews. Further data were gathered using participant observation, while implementing the trepang research in accordance with this framework of engagement, and these data were analysed to test and evaluate the framework. Findings indicate discursive and reflective approaches such as action research or adaptive management may better facilitate equitable research partnerships for sustainable development.

Population dynamics of Parastromateus niger in Kuwaiti waters as assessed using length?frequency analysis

The population dynamics of the black pomfret, Parastromateus niger, sampled from commercial gill-net catches from Kuwaiti waters of the Arabian Gulf, were investigated from October 2003 to September 2005. Length-based stock assessment using the FiSAT software package showed an asymptotic length of 65 cm TL and growth curvature of 0.34 year−1. Raw data as well as that corrected for probability of capture indicated a recruitment from February to September. The total mortality coefficient was estimated to be 1.20, a natural mortality of 0.68 and fishing mortality of 0.52. The selectivity model based on the running average showed that 25% of 14.0 cm TL fish, 50% of specimens reaching 16.3 cm TL, and 75% of all specimens of 20.2 cm TL encountering the gear were retained. Relative yield-per-recruit analyses revealed a current exploitation rate of 0.43; this is below the maximum sustainable yield index, indicating for sustainable fishery of P. niger that the exploitation rate could be increased to 0.6, provided size of the fish at first capture, i.e. the legal size, is also increased to 32.5 cm TL. These results suggest that P. niger stocks in Kuwaiti waters, contrary to existing views, are moderately exploited. This conclusion, however, is critically dependent on the estimate of natural mortality, which requires further confirmation.

Sensitive profiling of chemically diverse bioactive lipids

Here, we present an improved method for sensitive profiling of lipids in a single high-performance liquid chromatography-electrospray ionization-quadrupole time of flight mass spectrometry experiment. The approach consists of i) sensitive isocratic elution, which takes advantage of C18 column material that is resistant to increased pH values induced by piperidine, ii) chemometric alignment of mass spectra followed by differential analysis of ion intensities, and iii) semiquantitative analysis of extracted ion chromatograms of interest. A key advantage of this method is its wide applicability to extracts that harbor lipids of considerable chemical complexity. The method allows qualitative and semiquantitative analysis of fatty acyls, glycerophospholipids (such as glycerophosphatidylinositols, glycerophosphatidylserines, and glycerophosphatidylcholines in brain extracts), phosphatidylinositol mannosides, acylated glycerophospholipids, sphingolipids (including ceramides and gangliosides in brain extracts), and, for the first time with ESI, prenols and mycolic acids (MAs). MAs are targets in antimycobacterial therapy, and they play an important immunomodulatory role during host-pathogen interactions. We compared high-resolution mass spectra of MAs derived from Mycobacterium bovis Bacille Camette-Guérin during entry into nonreplicative conditions induced by oxygen deprivation (hypoxic dormancy). Although the overall composition is not drastically altered, there are pronounced differences in individual MAs. alpha-MAs accumulate during entry into dormancy, whereas a subpopulation of keto-MAs is almost entirely eliminated. This effect is reversed upon resuscitation of dormant mycobacteria. These results provide detailed chemical information with relevance to drug development and immunobiology of mycobacteria.

Interaction of Water Alkalinity and Stocking Density on Survival and Growth of Silver Catfish, Rhamdia quelen, Juveniles

The use of lime to increase water pH, hardness, and alkalinity can decrease mortality of acidic-sensitive species (Weatherley 1988) because it reduces ion loss through the gills (Flik et al. 1996; Wilkie et al. 1999) and allows recovery of normal ion plasma levels (Rosseland et al. 1986). Enhancement of water quality also reduces incidence of diseases in fishes (Singhal et al. 1986) and improves active cellular transport during the embryonic phase as well as eggs hatching (Hwang et al. 1994). Alkalinity is a measure of the acid-neutralizing capacity of water, and it is important because it protects organisms from pH changes (Boyd 1990; Zweig et al. 1999). Alkalinity levels below 30 mg CaCO3/L limits primary production in well-fertilized ponds, and in unfertilized ponds, the primary production increased with alkalinity levels up to 120 mg CaCO3/L (Boyd 1990). According to Zweig et al. (1999), there are no direct effects of alkalinity on fish, but adequate values of water alkalinity can improve growth of Nile tilapia, Oreochromis niloticus, larvae (Rojas and Rocha 2004). The use of high stocking densities to maximize available space for production might impair water quality because of excess of nitrogen residues from fish excretion (Jobling 1994). In addition, some species try to establish territories and do not feed properly (Alanara 1994), compromising water quality. Silver catfish, Rhamdia quelen (Quoy and Gaimard, 1824; Heptapteridae), accepts artificial food and possesses high fertility, fast growth, and good acceptance in the fish market (Baldisserotto 2004), and consequently, its culture is increasing in Brazil. Juveniles of this species survive in soft water without problems within the 4.0–9.0 pH range (Zaions and Baldisserotto 2000), and the increase of water hardness to 100–150 mg CaCO3/L improves survival at very acidic and alkaline waters (Townsend and Baldisserotto 2001). Growth of this species is lower in acidic or alkaline soft water compared to neutral water (Copatti et al. 2005), but no studies with alkalinity were made. A previous study verified that stocking density of 0.5 fish/L in a closed system provided better growth of silver catfish juveniles than lower stocking densities (Piaia and Baldisserotto 2000), but higher densities were not tested. Therefore, this study investigated the influence of water alkalinity and stocking density for the culture of silver catfish juveniles in a closed system.

Red Coral Fishery at the Costa Brava (NW Mediterranean): Case Study of an Overharvested Precious Coral

The Mediterranean red coral (Corallium rubrum ,L . 1758) is a slow-growing longevous gorgonian that produces a red calcium carbonate skeleton, which is in high demand by the jewellery industry. Its long history of intensive commercial harvesting has resulted in a well-documented decline of its stocks throughout the Mediterranean, becoming especially apparent during the last two decades. Based on the extensive ecological data from the Costa Brava (NE Spain) stocks, this study reviews, for the first time, socioeconomic aspects and the impact of current fishing practices on the red coral population structure and reproductive biology. A comparison of the intensively harvested populations in shallow water with that of the infrequently harvested ones in deep water, along with a population in a marine reserve as well, reveals that 98% of all shallow water colonies show a juvenile size and branching pattern as a result of harvesting. Recent data on the reproductive biology of the species show that 91% of the colonies in shallow water populations (<60 m depth) are not 100% sexually mature. These populations are clearly at the limit of their recoverability potential. The maximum sustainable yield (estimated using the Beverton-Holt model) is reached at an age of first capture of 98 years, although the current regulations allow harvesting of approximately 11-year-old colonies (corresponding to a basal diameter of 7 mm). The presented data reveal how this renewable resource is being exploited in a clearly non-sustainable and inefficient way, changing significantly the underwater landscape of the Mediterranean coast. The review of all available data suggests that the shallow water stocks are depleted. Furthermore, recent trends in poaching of juvenile colonies and mass mortality events threaten the survival of the shallow water populations. A ban on reconstituted coral from the market appears to be the only option to control this form of poaching.

Groundwater use under incomplete information

This paper introduces a game theoretic model of groundwater extraction in a two-cell aquifer under incomplete information. A novel assumption is that individual users have incomplete knowledge of the speed of lateral flows in the aquifer: although a user is aware that his neighbor's water use has some influence on his future water stock, he is uncertain about the degree of this impact. We find that the lack of information may either increase or decrease the rate of water use and welfare. In a two-period framework, the relevant characteristic is the ratio of the periodic marginal benefits of water use. Depending on whether this ratio is convex or concave, the average speed with which the aquifer is depleted decreases or increases when users learn more about the local hydrologic properties of groundwater. In principle, welfare may decrease even in cases when the groundwater allocation is closer to the efficient groundwater allocation.