Shark bycatch in the experimental tuna longline fishery in Lakshadweep Sea,India

Bycatch from the experimental longline operations in the Lakshadweep Sea were studied. The experiments were conducted on converted Pablo boats, originally used for pole and line fishing operations, to capture skipjack tuna in the Lakshadweep Islands. The overall bycatch rate was very high, with a mean hooking rate of 8.05/1000 hooks compared to the targeted tuna catch (1.75/1000 hooks). Bycatch contributed 82.4% of the catch in comparison to the tuna (17.6%) Thunnus albacares, in the longline operations. Silky shark (Carcharhinus falciformes) with 89.9% was the dominant shark species followed by C. amblyrhynchos, Galeocerdo cuvier, Alopias pelagicus, Negapriion acutedens and Sphyrna lewinii with 4.7, 2.7, 1.4, 0.7 and 0.7%, respectively. Sharks contributed to 74.1% of the catch, followed by 15.7% sailfishes and 10.2% miscellaneous fishes. Higher bycatch rates were evident during evening hours compared to mornings, but the results were not significant statistically. Studies on the effects of depth on the overall fishing performance and species selectivity failed to establish any significant relationship at a depth range of 35–100 m. Soaking time had a significant effect on bycatch rates. The hooking rate of sharks declined with an increase in soaking time. Considering the high shark bycatch in the fishery, an accurate monitoring of the longline fish catches in the Lakshadweep waters is an important step towards ensuring the sustainability of other populations, especially sharks.     

Gear selectivity of functional traits in coral reef fisheries in Brazil

Small-scale reef fisheries are important commercial and subsistence activities that support the livelihoods of millions of people in tropical regions. Tropical marine fisheries typically target a diversity of species caught with a matching diversity of fishing gears and practices. Here, we explored how multiple fishing gears select for distinct functional traits of fish assemblages inside a large multiple use marine environmental protected area off northeastern Brazil. In 1833 landing interviews with local fishers, we identified 101 species, which were categorized according to six traits: body size, schooling behavior, mobility, position in the water column, diet and period of activity. Our research is the first to explore the broad patterns of gear selectivity with regards to fish functional traits for different habitat types. While gears used in reef habitats were highly selective of sedentary and benthic species that form schools with few individuals, gears used in coastal lagoons were selective of highly mobile pelagic species that form large schools. We found a low competitive interaction between different gear types, meaning there was a low overlap in trait selectivity between fishing gears. We also found direct associations between gears and fish functional traits: hooks and line targeted species that exhibit limited mobility capabilities, making these species more vulnerable to local levels of fishing effort. In contrast, nets and fish corrals targeted mobile species that exhibited a greater diversity of functional traits. Some of our results contrasted with the current literature on the topic, with differences highlighting the need for more research to clarify global patterns of trait selectivity by gear type. Our results have implications for fisheries management in northeastern Brazil: gear bans and effort caps are commonly used management measures that can foster fisheries sustainability by minimizing impacts to fish assemblage functions.

     

Sustainability in single-species population models

In this paper, we review the concept of sustainability with regard to a single-species, age-structured fish population with density dependence at some stage of its life history. We trace the development of the view of sustainability through four periods.The classical view of sustainability, prevalent in the 1970s and earlier, developed from deterministic production models, in which equilibrium abundance or biomass is derived as a function of fishing mortality. When there is no fishing mortality, the population equilibrates about its carrying capacity. We show that carrying capacity is the result of reproductive and mortality processes and is not a fixed constant unless these processes are constant. There is usually a fishing mortality, F(MSY), which results in MSY, and a higher value, F(ext), for which the population is eventually driven to extinction. For each F between 0 and F(ext), there is a corresponding sustainable population. From this viewpoint, the primary tool for achieving sustainability is the control of fishing mortality.The neoclassical view of sustainability, developed in the 1980s, involved population models with depensation and stochasticity. This view point is in accord with the perception that a population at a low level is susceptible to collapse or to a lack of rebuilding regardless of fishing. Sustainability occurs in a more restricted range from that in the classical view and includes an abundance threshold. A variety of studies has suggested that fishing mortality should not let a population drop below a threshold at 10-20% of carrying capacity.The modern view of sustainability in the 1990s moves further in the direction of precaution. The fishing mortality limit is the former target of F(MSY) (or some proxy), and the target fishing mortality is set lower. This viewpoint further reduces the range of permissible fishing mortalities and resultant desired population sizes. The objective has shifted from optimizing long-term catch to preserving spawning biomass and egg production for the future. The use of discount rates in objective functions involving catch is not a suitable alternative to protecting reproductive value.As we move into the post-modern time period, new definitions of sustainability will attempt to incorporate he economic and social aspects of fisheries and/or ecosystem and habitat requirements. These definitions now involve "warm and fuzzy" notions (healthy ecosystems and fishing communities, the needs of future generations, diverse fish communities) and value judgements of desired outcomes. Additional work is needed to make these definitions operational and to specify quantitative objectives to be achieved. In addition, multiple objectives may be incompatible, so trade-offs in what constitutes sustainability must be made. The advances made under the single-species approach should not be abandoned in the post-modern era, but rather enhanced and combined with new approaches in the multi-species and economic realms.     

A Review of Catch-and-Release Angling Mortality with Implications for No-take Reserves

Management agencies have increasingly relied on size limits, daily bag or trip limits, quotas, and seasonal closures to manage fishing in recreational and commercial fisheries. Another trend is to establish aquatic protected areas, including no-take reserves (NTRs), to promote sustainable fisheries and protect aquatic ecosystems. Some anglers, assuming that no serious harm befalls the fish, advocate allowing catch-and-release (C&R) angling in aquatic protected areas. The ultimate success of these regulations and C&R angling depends on ensuring high release survival rates by minimizing injury and mortality. To evaluate the potential effectiveness of these practices, we review trends in C&R fishing and factors that influence release mortality. Analysis of Marine Recreational Fishery Statistic Survey (MRFSS) data for 1981–1999 showed no statistically significant U.S. trends for total number of anglers (mean 7.7 × 10⁶), total catch in numbers (mean 362 × 10⁶), or total annual catch/angler (mean 42.6 fish). However, mean total annual landings declined 28% (188.5 to 135.7 × 10⁶), mean total catch/angler/trip declined 22.1% (0.95 to 0.74 fish), and mean landings/angler/trip declined 27% (0.42 to 0.31 fish). The total number of recreational releases or discards increased 97.1% (98.0 to 193.2 × 10⁶) and as a proportion of total catch from 34.2% in 1981 to 58.0% in 1999. Evidence indicates that the increased releases and discards are primarily in response to mandatory regulations and to a lesser extent, voluntary releases. Total annual catch and mean annual catch/angler were maintained despite declines in catch per trip because anglers took 30.8% more fishing trips (43.5 to 56.9 × 10⁶), perhaps to compensate for greater use of bag and size limits. We reviewed 53 release mortality studies, doubling the number of estimates since Muoneke and Childress (1994) reviewed catch and release fishing. A meta-analysis of combined data (n=274) showed a skewed distribution of release mortality (median 11%, mean 18%, range 0–95%). Mortality distributions were similar for salmonids, marine, and freshwater species. Mean mortality varied greatly by species and within species, anatomical hooking location was the most important mortality factor. Other significant mortality factors were: use of natural bait, removing hooks from deeply hooked fish, use of J-hooks (vs. circle hooks), deeper depth of capture, warm water temperatures, and extended playing and handling times. Barbed hooks had marginally higher mortality than barbless hooks. Based on numbers of estimates, no statistically significant overall effects were found for fish size, hook size, venting to deflate fish caught at depth, or use of treble vs. single hooks. Catch and release fishing is a growing and an increasingly important activity. The common occurrence of release mortality, however, requires careful evaluation for achieving fishery management goals and in some cases, disturbance, injury, or mortality may conflict with some goals of NTRs. Research is needed to develop better technology and techniques to reduce release mortality, to assess mortality from predation during capture and after release, to determine cumulative mortality from multiple hooking and release events, and to measure sub-lethal effects on behavior, physical condition, growth, and reproduction.     

An overview of historical changes in the fishing gear and practices of pelagic longliners,with particular reference to Japan’s Pacific fleet

We identify changes in pelagic longline fishing gear and practices that need to be accounted for in stock assessments. Pelagic longline fishers have continuously modified their fishing gear and practices to improve fishing power and catchability, which has altered the relationship between catch rates and abundance. Advances in technology resulted in the introduction of many electronic devices to assist in navigation, communication and finding target species. The development of synthetic materials allowed improvements to lines and hooks that increased the probability of hooking target species and landing them. Other changes increased fishing power by improving searching efficiency (e.g., satellite imagery) or the time spent on fishing grounds (e.g., freezers). The number of hooks deployed in daily longlining operations has steadily increased since 1950. However, mean soak time did not change significantly because faster longline retrieval and deployment speeds balanced the increased hook numbers. There has been a shift from having all baits available at dawn, to having more available at dusk and at night. In the 1970s, several longline fleets began to exploit a much greater depth range, resulting in increased catchability for deep-dwelling species (e.g., bigeye tuna, Thunnus obesus) and reduced catchability for epipelagic species like blue marlin (Makaira nigricans). Research has been mostly limited to the effects of longline depth on the catchability of target species. Recent experiments have quantified the effects of bycatch mitigation measures on fishing power and catchability. Progressive improvements in expertise and technological improvements in the gear will also affect fishing power, but are particularly difficult to quantify.     

Characterizing fishing effort and spatial extent of coastal fisheries

Biodiverse coastal zones are often areas of intense fishing pressure due to the high relative density of fishing capacity in these nearshore regions. Although overcapacity is one of the central challenges to fisheries sustainability in coastal zones, accurate estimates of fishing pressure in coastal zones are limited, hampering the assessment of the direct and collateral impacts (e.g., habitat degradation, bycatch) of fishing. We compiled a comprehensive database of fishing effort metrics and the corresponding spatial limits of fisheries and used a spatial analysis program (FEET) to map fishing effort density (measured as boat-meters per km2) in the coastal zones of six ocean regions. We also considered the utility of a number of socioeconomic variables as indicators of fishing pressure at the national level; fishing density increased as a function of population size and decreased as a function of coastline length. Our mapping exercise points to intra and interregional 'hotspots' of coastal fishing pressure. The significant and intuitive relationships we found between fishing density and population size and coastline length may help with coarse regional characterizations of fishing pressure. However, spatially-delimited fishing effort data are needed to accurately map fishing hotspots, i.e., areas of intense fishing activity. We suggest that estimates of fishing effort, not just target catch or yield, serve as a necessary measure of fishing activity, which is a key link to evaluating sustainability and environmental impacts of coastal fisheries.     

Hook performance and selectivity of Eurasian perch,Perca fluviatilis (Linnaeus, 1758) in the Åland Archipelago,Finland

The effects of two hook‐types (circle or J hook) fished with two different baits (red worms Eisenia spp., or cyprinid fishes) were examined for deep‐hooking, catch rate, mean total length, and selectivity of Eurasian perch, Perca fluviatilis, in the Åland Archipelago, Finland. The perch population available to hook‐and‐line gear was sampled with multipanel gillnets, with panels ranging from 10 to 60 mm in stretched mesh diameter. The effect of each hook then was examined for each bait by conditioning the size distributions of hook‐and‐line catches on the size distribution of perch collected with gillnets to estimate selectivity. The proportion of deeply‐hooked perch was 4.8 times greater for J hooks (0.21) than circle hooks (0.04) baited with worms and 3.7 times greater for J hooks (0.33) than circle hooks (0.09) baited with fish. Catch rates were significantly different between the two baits but not between the two hooks, with the greatest catch rate observed for the circle hook baited with worms. There was no significant difference in perch total length between the two hooks, but there was a significant difference between the two baits, with the fish bait catching significantly larger perch. Perch selection peaks between the two hooks differed by only 13.8 mm, but the selection peak with fish bait (236.4 mm TL) was 119.9 mm greater than the selection peak with the worm bait (116.5 mm TL). A substantially lesser incidence of deep hooking support the conservation benefits of circle hook use for perch, especially when catch‐and‐release is practiced. Using fish baits similar in size to those used in this experiment can avoid potentially harmful interactions between relatively small perch and anglers who place little importance on catch motives but whose satisfaction is still catch‐dependent.     

Co-management and Spatial Features Contribute to Secure Fish Abundance and Fishing Yields in Tropical Floodplain Lakes

Empirical data are needed to show the efficacy of co-management, which is regarded as a promising approach to achieve conservation goals. In this study, we addressed the potential influence of fisheries co-management to increase fish abundance and fishing yields in the lower Tocantins River Basin (Brazilian Amazon), downstream from a large dam. We analyzed 590 fish landings (6.7 t of fish) from five fishing villages and 48 fish samples obtained using gillnets (10,378 fish from 101 species) in 12 floodplain lakes in four regions: two with incipient co-management and two unmanaged. The fish species richness did not differ among the regions, but the lakes in the regions that were co-managed had higher fish abundance (biomass and number of individuals) and a higher mean proportion of fish reproducing during the high water season. Fishers had higher catches per unit of effort in the co-managed regions than fishers in the non-managed regions. These results were also influenced by geographic factors (distance and accessibility of lakes), as fish biomass was higher in lakes that were distant from the main river and from the main city in the region. Managers should thus consider strategic selection of the geographic locations of managed sites, even in remote areas. However, the fish biomass sampled in lakes was more related to region than to the lakes’ geographical location. Therefore, co-management has at least partially contributed to increased fish abundance and fishing yields in the studied region, through the protection of an important fish habitat (lakes). We provide empirical evidence that co-management can contribute to the maintenance of fish abundance, sustainability of fisheries, and food security in large tropical rivers impacted by damming.     

Connectivity,persistence, and loss of high abundance areas of a recovering marine fish population in the Northwest Atlantic Ocean

In the early 1990s, the Northwest Atlantic Ocean underwent a fisheries‐driven ecosystem shift. Today, the iconic cod (Gadus morhua) remains at low levels, while Atlantic halibut (Hippoglossus hippoglossus) has been increasing since the mid‐2000s, concomitant with increasing interest from the fishing industry. Currently, our knowledge about halibut ecology is limited, and the lack of recovery in other collapsed groundfish populations has highlighted the danger of overfishing local concentrations. Here, we apply a Bayesian hierarchical spatiotemporal approach to model the spatial structure of juvenile Atlantic halibut over 36 years and three fisheries management regimes using three model parameters to characterize the resulting spatiotemporal abundance structure: persistence (similarity of spatial structure over time), connectivity (coherence of temporal pattern over space), and spatial variance (variation across the seascape). Two areas of high juvenile abundance persisted through three decades whereas two in the northeast are now diminished, despite the increased abundance and landings throughout the management units. The persistent areas overlap with full and seasonal area closures, which may act as refuges from fishing. Connectivity was estimated to be 250 km, an order of magnitude less than the distance assumed by the definition of the Canadian management units (~2,000 km). The underlying question of whether there are distinct populations within the southern stock unit cannot be answered with this model, but the smaller ~250 km scale of coherent temporal patterns suggests more complex population structure than previously thought, which should be taken into consideration by fishery management.     

Distance from a Fishing Community Explains Fish Abundance in a No-Take Zone with Weak Compliance

There are numerous examples of no-take marine reserves effectively conserving fish stocks within their boundaries. However, no-take reserves can be rendered ineffective and turned into ‘paper parks’ through poor compliance and weak enforcement of reserve regulations. Long-term monitoring is thus essential to assess the effectiveness of marine reserves in meeting conservation and management objectives. This study documents the present state of the 15-year old no-take zone (NTZ) of South El Ghargana within the Nabq Managed Resource Protected Area, South Sinai, Egyptian Red Sea. Previous studies credited willing compliance by the local fishing community for the increased abundances of targeted fish within the designated NTZ boundaries compared to adjacent fished or take-zones. We compared benthic habitat and fish abundance within the NTZ and the adjacent take sites open to fishing, but found no significant effect of the reserve. Instead, the strongest evidence was for a simple negative relationship between fishing pressure and distance from the closest fishing village. The abundance of targeted piscivorous fish increased significantly with increasing distance from the village, while herbivorous fish showed the opposite trend. This gradient was supported by a corresponding negative correlation between the amount of discarded fishing gear observed on the reef and increasing distance from the village. Discarded fishing gear within the NTZ suggested decreased compliance with the no-take regulations. Our findings indicate that due to non-compliance the no-take reserve is no longer functioning effectively, despite its apparent initial successes and instead a gradient of fishing pressure exists with distance from the nearest fishing community.     

Hook selectivity of the pacu Piaractus mesopotamicus (Holmberg, 1887) in the Pantanal, the state of Mato Grosso do Sul, Brazil.

The Pacu Piaractus mesopotamicus is the most captured fish species in the Pantanal, Mato Grosso do Sul State, and since 1994, its maximum sustainable yield had already been exceeded. Its capture is carried out only by hooks, as mesh gears are forbidden either for professional or for recreational fishing. The aim of this study was to determine selectivity for different hook sizes used in P. mesopotamicus fishing and to verify which sizes capture only adults. Data were collected in the rivers Miranda, Aquidauana, and Vermelho, in January, March, and April 2002. Six longlines with eight hook sizes were used and we adopted the hook opening as a measure related to selectivity. Different hooks captured individuals of the same length and their medians were similar, evidencing the great overlap among sizes. Regression results showed no significant relationship between ln[c2(l)/c1(l)] and total length of captured individuals. In addition, the Kolmogorov-Smirnov test also did not detect significant differences in the size of captured fish. Several hypotheses, such as the selectivity models, shape of selection curves, scarcity of large fishes, and behavior are used in order to explain the absence of hook selectivity for this species. Size of recruitment for this gear was 28 cm of total length, when individuals are still immature.     

Assessing Fishers' Support of Striped Bass Management Strategies

Incorporating the perspectives and insights of stakeholders is an essential component of ecosystem-based fisheries management, such that policy strategies should account for the diverse interests of various groups of anglers to enhance their efficacy. Here we assessed fishing stakeholders’ perceptions on the management of Atlantic striped bass (Morone saxatilis) and receptiveness to potential future regulations using an online survey of recreational and commercial fishers in Massachusetts and Connecticut (USA). Our results indicate that most fishers harbored adequate to positive perceptions of current striped bass management policies when asked to grade their state’s management regime. Yet, subtle differences in perceptions existed between recreational and commercial fishers, as well as across individuals with differing levels of fishing experience, resource dependency, and tournament participation. Recreational fishers in both states were generally supportive or neutral towards potential management actions including slot limits (71%) and mandated circle hooks to reduce mortality of released fish (74%), but less supportive of reduced recreational bag limits (51%). Although commercial anglers were typically less supportive of management changes than their recreational counterparts, the majority were still supportive of slot limits (54%) and mandated use of circle hooks (56%). Our study suggests that both recreational and commercial fishers are generally supportive of additional management strategies aimed at sustaining healthy striped bass populations and agree on a variety of strategies. However, both stakeholder groups were less supportive of harvest reductions, which is the most direct measure of reducing mortality available to fisheries managers. By revealing factors that influence stakeholders’ support or willingness to comply with management strategies, studies such as ours can help managers identify potential stakeholder support for or conflicts that may result from regulation changes.     

Fishing destabilizes the biomass flow in the marine size spectrum

Fishing impacts on marine food webs are predicted by simulations of a size spectrum community model. In this model, predation is determined by predator and prey size and abundance, and drives predator growth and prey mortality. Fishing amplifies temporal oscillations in the biomass flow. Oscillations appear at lower fishing intensity and have wider amplitude when fishing is selective (removes a narrow size range) and/or when large fish are targeted, than when fishing is more balanced (catching a larger size range) or when small fish are targeted. A novel index of size diversity is developed, and is shown to be sensitive to both fishing intensity and selectivity. To avoid unstable food web dynamics with potential harmful consequences for fisheries, limiting both fishing intensity and selectivity might be an appropriate exploitation strategy.     

Navigating Over Space and Time: Fishing Effort Allocation and the Development of Customary Norms in an Open-Access Mangrove Estuary in Ecuador

Fisheries are increasingly understood as complex adaptive systems; but the cultural, behavioral, and cognitive factors that explain spatial and temporal dynamics of fishing effort allocation remain poorly understood. Using Geographic Information Systems (GIS) as a visualization tool, this paper combines catch-per-unit-effort (CPUE) and ethnographic data on the Ecuadorian mangrove cockle fishery to explore patterns in fishing effort and the social production of fishing space. I argue that individual decisions about where, when, and how to fish result in spatial and temporal patterns in effort allocation, ultimately regulating open-access fisheries that typically operate on a first-come, first-served basis. These emergent patterns in the fishing effort are explained by individual-level preferences and adaptations; the development of knowledge and customary norms through the habitual use of resource space by individuals and groups; ecological conditions; and access. New adaptive challenges threaten to undermine such self-organization of open-access systems on larger spatial and temporal scales prompting a likely re-allocation of the fishing effort in the future.     

Multidimensional analysis of fishery production systems in the state of Pernambuco, Brazil

A total of 17 fishery systems covering gillnets, traps and seines targeting fish and crustaceans as well as hand-collected mussels in the state of Pernambuco (Brazil) were compared and analyzed in the present study using the RAPFISH method and 57 attributes to qualify five evaluation dimensions: economic, social, ecological, technological and management. The aim was to determine the sustainability of each field from the fishery (i.e. stocks) and social standpoint (i.e. fishermen). With regard to sustainability, it was generally apparent that the fisheries analyzed are far from any ideal that would permit long-term exploitation, but are nonetheless also distant from the extremes of non-sustainability in the environments investigated. The low degree of organization demonstrated in most fisheries of Pernambuco and the low level of schooling among the fishermen contribute toward maintaining the status quo, with an increase in situations of conflict and a lack of valorization regarding the activities. The shrimp system is the least sustainable, mainly due to its environmental impact; however, this is compensated by the relatively higher quality of living provided stakeholders through its exploitation. The evaluation dimensions showed the most sustainable system in Pernambuco to be the stationary 'uncovered pound net', followed by the line system. Alternative procedures for integrated fishery management, such as an increase in statistical data, coastal zoning to limit shrimp farms and establishing protected areas are proposed and discussed. Such procedures may contribute toward the formulation of public policies for the fishery industry of the state, which is essentially made up of artisanal fisheries with low yields and exercised by the 11 926 fishermen affiliated with coastal fishing colonies.     

A review of biology,fisheries and population structure of Dentex dentex (Sparidae)

The common dentex Dentex dentex (Linnaeus, 1758) is an iconic marine coastal fish in the Mediterranean Sea. It is a demersal sparid fish (0–200 m), that grows to a maximum length of 100 cm and a weight of 13 kg, with a relatively long life span (more than 20 years). As a high trophic level predator, it holds a key position in coastal marine food webs. The common dentex is of great economic importance for both artisanal (small-scale coastal fisheries) and recreational fishing. Despite its economic and ecological importance, scientific data on this species in its natural environment are still very scant. The global commercial catch of common dentex has fluctuated over the last 60 years on an interannual time scale, and has declined significantly since the 1990s. There are few data regarding fishing effort and total catch from recreational fishing for common dentex, but it appears that this species is particularly targeted by this activity. The common dentex is now classified as “vulnerable” in the Red List of Threatened Species in the Mediterranean Sea. This review summarizes the current literature on D. dentex in regard to biology, ecology, parasitology, population structure, commercial and recreational fishing, and management regulations. Future research directions to fill gaps in current knowledge are suggested.     

An individual-based model applied to the study of different fishing strategies of Pintado Pseudoplatystoma corruscans (Agassiz, 1829)

The decline in stocks of commercial fish species has been documented in several regions of the world. This decline is due partially to the effect of evolutionary pressure caused by the management of fishing activity, which reduces the size of fish after a few generations. In this paper, the population dynamics of the Pintado Pseudoplatystoma corruscans, one of the main commercial species of freshwater fish in Brazil, were simulated considering different scenarios of fishing mortality and different minimum and maximum lengths of capture. The results show that selective fishing based on the different proposed selectivity curves can result in an evolution-mediated increase in the growth rate of the fish, the biomass and the catch. This suggests that appropriate changes in Brazilian legislation can contribute to the sustainability of fisheries and to conservation of the fish stocks exploited by man.     

Pathology associated with an aquareovirus in captive juvenile Atlantic halibut Hippoglossus hippoglossus and an experimental treatment strategy for a concurrent bacterial infection

A large-scale mortality of larval and juvenile halibut Hippoglossus hippoglossus occurred at a semi-commercial halibut farm in Atlantic Canada. Investigation of the cause revealed aquareovirus particles in necrotic liver tissue of affected fish. Cytopathic effect on CHSE-214 cell lines occurred from all fish cultured for viruses, and the viral morphology of the particles in culture was consistent with that observed in necrotic host tissue. The virus was placed in the family of Reoviridae, genus Aquareovirus based on morphology and RT-PCR results. Multifocal hepatocellular necrosis was a consistent finding in all fish as well as acute necrosis of proximal renal tubules. Concurrent bacterial infections were present in some specimens. Fish experimentally treated with oxytetracycline or a combination of oxytetracycline and chloramine-T had a significantly lower mortality rate than untreated fish. Fish treated with chloramine-T alone had a significantly elevated mortality rate compared to controls. Despite supportive medical therapy, mortality levels in treated and untreated groups remained elevated, supporting the hypothesis that the primary pathogen was of viral origin. This is the first report of elevated mortalities in Atlantic halibut associated with an aquareovirus.     

Indicators of AEI applied to the Delaware Estuary

We evaluated the impacts of entrainment and impingement at the Salem Generating Station on fish populations and communities in the Delaware Estuary. In the absence of an agreed-upon regulatory definition of "adverse environmental impact" (AEI), we developed three independent benchmarks of AEI based on observed or predicted changes that could threaten the sustainability of a population or the integrity of a community. Our benchmarks of AEI included: (1) disruption of the balanced indigenous community of fish in the vicinity of Salem (the "BIC" analysis); (2) a continued downward trend in the abundance of one or more susceptible fish species (the "Trends" analysis); and (3) occurrence of entrainment/impingement mortality sufficient, in combination with fishing mortality, to jeopardize the future sustainability of one or more populations (the "Stock Jeopardy" analysis). The BIC analysis utilized nearly 30 years of species presence/absence data collected in the immediate vicinity of Salem. The Trends analysis examined three independent data sets that document trends in the abundance of juvenile fish throughout the estuary over the past 20 years. The Stock Jeopardy analysis used two different assessment models to quantify potential long-term impacts of entrainment and impingement on susceptible fish populations. For one of these models, the compensatory capacities of the modeled species were quantified through meta-analysis of spawner-recruit data available for several hundred fish stocks. All three analyses indicated that the fish populations and communities of the Delaware Estuary are healthy and show no evidence of an adverse impact due to Salem. Although the specific models and analyses used at Salem are not applicable to every facility, we believe that a weight of evidence approach that evaluates multiple benchmarks of AEI using both retrospective and predictive methods is the best approach for assessing entrainment and impingement impacts at existing facilities.