Patterns of estuarine use by juvenile English sole (Parophrys vetulus) and Dungeness crab (Cancer magister)

Extensive trawl surveys were conducted in two large estuaries (Grays Harbor and Willapa Bay) on the Washington coast during 1983–1987, and in adjacent areas of the open coast. These surveys have shown that both English sole and Dungeness crab rely heavily on these estuaries as nursery areas, although the pattern of utilization differs substantially. Juvenile migration patterns can show substantial interannual variability and can only be delineated by concurrent surveys in both coastal and estuarine areas, conducted over a period of several years. English sole eggs and Dungeness crab larvae are released in coastal waters. Larvae of both species transform to the benthic stage in both coastal and estuarine areas, but most English sole eventually migrate into the estuaries during the first year of life, even if initial settlement is along the open coast. By the time English sole have attained a length of 55 mm (TL), most of them are found in estuaries. English sole begin emigrating from the estuaries at about 75 mm, and few remain there during the second year of life. In contrast, Dungeness crab appear to remain in the area of initial settlement throughout the first year of life. Growth is substantially faster in estuaries where 0+ crab reach a mean size of about 40 mm carapace width (CW) by September, with those off the coast are only about 14 mm CW. Juveniles remain in the area of settlement over their first winter but, in contrast to English sole, most coastal 1+ crab immigrate to estuaries to join siblings that settled there the previous year. By September of the second year, crab at about 100 mm CW emigrate to the open coast where they reach maturity. Advantages to juvenile stages that reside in estuaries are discussed in terms of accelerated growth at higher temperatures and potentially greater food supplies than found nearshore along the coast.     

The necessity for intertidal foraging by estuarine populations of subadult dungeness crab,Cancer magister: Evidence from a bioenergetics model

Complex intertidal habitats characteristic of northeastern Pacific coastal estuaries provide critical nursery environments for young-of-the-year Dungeness crab,Cancer magister, yet their role in supporting subsequent year classes remains unclear. SubadultC. magister (40–130 mm; 1+ and >1+ year classes), which reach densities as high as 4,300 crabs ha^?1 in subtidal channels during low tides, migrate during flood tides from subtidal refuges into intertidal habitats to forage. As with other brachyuran species that undertake extensive tidally-driven migrations, intertidal foraging may contribute significantly to the energy budget of subadultC. magister. In order to explore the energetic incentive for intertidal migrations by subadult crabs, we developed an ontogenetically-based bioenergetics model for crabs within Willapa Bay, Washington. The model showed that energetic demand varied spatially across the bay, with the highest average energetic demand of a population of subadult crabs (2.13×10⁶ kJ ha^?1) occurring in a habitat stratum termed lower side channel (LSC) and characterized by relatively little subtidal area and extensive intertidal flats. Comparison of model results with subtidal prey production revealed that the latter could not satisfy subadultC. magister energetic demands, especially in LSC where modeled crab predation depleted subtidal prey biomass within 17 simulation days. We estimate that 1 ha of subtidal crabs from LSC would minimally require an additional 1.6 ha of intertidal area to satisfy energetic demands without depleting prey biomass. Our model results support the assertion thatC. magister make regular migrations to forage on productive intertidal flats, and suggest that intertidal foraging may contribute significantly to the diet of subadult crabs in coastal estuaries.     

Ocean distribution of dungeness crab megalopae and recruitment patterns to estuaries in Southern Washington State

We investigated the distribution of meroplankton and water properties off southern Washington and simultaneously measured time series of larval abundance and water properties in two adjacent estuaries, Grays Harbor and Willapa Bay. The cruise period, in late May 1999, coincided with large variation in the alongshore wind stress that caused dynamic change in the position of the Columbia River plume, coastal upelling and downwelling, and offshore phytoplankton production. In the coastal ocean, meroplankton groups responded differently to this wind event and the associated advection of water masses. Dungeness crab (Cancer magister) megalopae were largely indifferent to the wide salinity variation, and were found throughout the surveyed area in both plume and recently upwelled waters. Megalopae of kelp crab (Pugettia producta) and hermit crab (Pagurus spp). were more abundant in upwelled water and low numbers were caught in the plume water. Barnacle cyprids appeared to track the advective transport suggesting that they may be more passively dispersed. Within the estuaries, hydrography responded rapidly and synchronously to variation in wind stress. Intrusions of both plume and newly upwelled waters were detected at estuarine sites, depending on the type of water present at the coast, indicating a tight link between the estuaries and the coastal ocean in this region. A 90-d record ofC. magister megalopae abundance was made at 3 estuarine sites using light traps. The bulk of theC. magister recruitment was limited to a relatively brief period in late May through June. Within this window, megalopae occurred in distinct pulses of 3–5 d interspaced with periods of low or zero abundance.C. magister megalopae recruited to the estuaries over a wide range of wind forcing, and were transported into the estuary within varied water types. There were no periodic patterns indicative of spring-neap tidal variations in the abundance time series. Abundance was only weakly cross-correlated between the adjacent Grays Harbor and Willapa Bay estuaries, which contrasts with the more synchronous estuarine-coastal linkages measured for water properties. These results suggest the interaction of larval aggregation size in the ocean with estuary-ocean exchange processes likely controls patterns of estuarine recruitment.     

Swimming behavior of Dungeness crab,Cancer magister Dana,megalopae in still and moving water

In the Grays Harbor estuary, juvenile Dungeness crab (Cancer magister Dana) are found at higher densities in epibenthic shell deposits compared to open mud flat. Differences in predation rate between habitats have been suggested to be due to habitat preference and differential survival. Megalopae preferred shell over open space in still-water conditions. However, it is not known whether megalopae are able to select shell in flowing water since larval preference is known to differ between still and flowing water. Here we report the first experimental study of swimming behavior of Dungeness crab megalopae in a range of current velocities (0–40 cm s^?1) equivalent to natural flow in Grays Harbor estuary. Experiments were conducted in daylight using a recirculating flume. Megalopae swimming speeds ranged from 8.5 cm s^?1 (8 body lengths s^?1) in still water to 44.8 cm s^?1 (44 body lengths s^?1) at flow speeds of 40 cm s^?1, Neither swimming behavior nor sheltering behavior in shells showed any flow-related pattern. Megalopae spent a large proportion of time swimming against the current and made headway upstream against all current velocities tested. The results suggest that Dungeness crab megalopae are able to maneuver and actively search for settlement sites under current velocities found in natural habitats, including intertidal shell deposits, and support the hypothesis of active selection of shell by megalopae.     

Blue Crab (<Emphasis Type="Italic">Callinectes sapidus</Emphasis> Rathbun, 1896) Settlement at Three Georgia (USA) Estuarine Sites

The blue crab, Callinectes sapidus Rathbun, 1896, represents the second most important fishery for coastal Georgia; yet, little is known about environmental forces that affect planktonic postlarval settlement in the region. Here, we describe a study to examine the physical mechanisms responsible for blue crab settlement in the extensive salt marsh system of coastal Georgia. Bottom and surface samplers were placed at three sites along a salinity gradient from a low-salinity site in the Altamaha River to a high-salinity area of the Duplin River, Sapelo Island, GA, USA during 2005. Megalopae and juvenile monitoring occurred from July through December. The majority of both megalopae (86.8%) and juvenile (89.3%) blue crabs were recovered in bottom samplers at the low-salinity Altamaha River site during August and early September. Few megalopae were collected at the surface of the Altamaha River or at the two higher-salinity sites in the Duplin and North Rivers. Downwelling winds were unable to explain all settlement events; however, winds with an onshore component regularly preceded settlement events. The use of a multiple-regression model revealed a lagged relationship (r = 0.5461, $ lag = 0–2 days $ lag = 0–2 days ) between wind events, temperature, salinity, maximum tidal height, and settlement.     

Atmospheric deposition of nitrogen: Implications for nutrient over-enrichment of coastal waters

Atmospheric deposition of nitrogen (AD-N) is a significant source of nitrogen enrichment to nitrogen (N)-limited estuarine and coastal waters downwind of anthropogenic emissions. Along the eastern U.S. coast and eastern Gulf of Mexico, AD-N currently accounts for 10% to over 40% of new N loading to estuaries. Extension of the regional acid deposition model (RADM) to coastal shelf waters indicates that 11, 5.6, and 5.6 kg N ha⁻¹ may be deposited on the continental shelf areas of the northeastern U.S. coast, southeast U.S. coast, and eastern Gulf of Mexico, respectively. AD-N approximates or exceeds riverine N inputs in many coastal regions. From a spatial perspective, AD-N is a unique source of N enrichment to estuarine and coastal waters because, for a receiving water body, the airshed may exceed the watershed by 10–20 fold. AD-N may originate far outside of the currently managed watersheds. AD-N may increase in importance as a new N source by affecting waters downstream of the oligohaline and mesohaline estuarine nutrient filters where large amounts of terrestrially-supplied N are assimilated and denitrified. Regionally and globally, N deposition associated with urbanization (NO_x, peroxyacetyl nitrate, or PAN) and agricultural expansion (NH₄ ⁺ and possibly organic N) has increased in coastal airsheds. Recent growth and intensification of animal (poultry, swine, cattle) operations in the midwest and mid-Atlantic regions have led to increasing amounts of NH₄ ⁺ emission and deposition, according to a three decadal analysis of the National Acid Deposition Program network. In western Europe, where livestock operations have dominated agricultural production for the better part of this century, NH₄ ⁺ is the most abundant form of AD-N. AD-N deposition in the U.S. is still dominated by oxides of N (NO_x) emitted from fossil fuel combustion; annual NH₄ ⁺ deposition is increasing, and in some regions is approaching total NO₃ ⁻ deposition. In receiving estuarine and coastal waters, phytoplankton community structural and functional changes, associated water quality, and trophic and biogeochemical alterations (i.e, algal blooms, hypoxia, food web, and fisheries habitat disruption) are frequent consequences of N-driven eutrophication. Increases in and changing proportions of various new N sources regulate phytoplankton competitive interactions, dominance, and successional patterns. These quantitative and qualitative aspects of AD-N and other atmospheric nutrient sources (e.g., iron) may promote biotic changes now apparent in estuarine and coastal waters, including the proliferation of harmful algal blooms, with cascading impacts on water quality and fisheries.     

Patterns in use of estuarine habitat by juvenile English sole (Pleuronectes vetulus) in four Eastern North Pacific estuaries

English sole (Pleuronectes vetulus) is one of a few commercially important marine fishes on the Pacific coast of North America that use estuarine areas as nurseries for juvenile stages. Trawl surveys of four United States Pacific Northwest estuaries were conducted to determine spatial patterns of juvenile English sole residence in estuaries during 1998–2000. Additional data from 1983–1988 were also analyzed. Two size classes of juvenile English sole were identified during surveys, with densities of small (Total length [TL] <50 mm) sole ranging from 0 to 11,300 fish ha^?1 across all sites, and densities of large (TL 50–150 mm) sole ranging from 0 to 33,000 fish ha^?1 across all sites. Principal components analysis of static habitat data collected at each trawl survey site was used to define habitat types within each estuary, and discriminant function analysis was used to test the resulting classification scheme. Both small and large cohort English sole used lower side channel locations at significantly higher densities than other estuarine areas. Small English sole also showed significant relationships with both bottom temperature and depth. These patterns in habitat use were consistent across all estuaries and indicate that English sole used shallow depth areas surrounded by extensive tidal flats, where temperatures were optimal for growth. The analysis also suggested a carrying capacity may exist for large English sole in nursery estuaries.     

Contribution of estuaries to commercial fisheries in temperate Western Australia and the concept of estuarine dependence

Fisheries catch statistics for temperate Western Australia are considered in conjunction with life cycle data to elucidate the importance of estuaries to the commercial and recreational fisheries in this region. The data are used to discuss whether the term estuarine-dependent is strictly applicable to all species of finfish found in abundance in estuaries. Between 1976 and 1984, 96 species of finfish, 7 species of crustaceans and 12 species of mollusks contributed to the large commercial fishery in estuaries, protected coastal areas and open marine waters of temperate Western Australia. The mean annual weight and monetary value (in 1984 terms) of this fishery was 21,355 t and $A151.3×10⁶. The contribution of the weight (4,340 t) and value ($A3.7×10⁶) of the estuarine-dependent species to the total fishery was 20.3 and 2.4%, respectively. Estuarine-dependent marine species frequently use protected inshore waters in temperate Western Australia, and have to do so when they occur in subtropical regions in Western Australia where there are no permanent estuaries. Even the semi-anadromous Perth herring and some species which are estuarinesensu stricto in south-western Australia complete their life cycle within the marine waters of this latter more northern region. Since virtually none of the commercially important marine species in temperate Western Australia can be considered to be entirely dependent on estuaries, and a similar conclusion is valid for many species of marine teleosts found in abundance in estuaries in temperate waters elsewhere in the world, these marine species would be best regarded as estuarine opportunists rather than estuarine dependents.     

Methods for determining minimum freshwater inflow needs of Texas bays and estuaries

In response to legislative directives beginning in 1975, the Texas Water Development Board (TWDB) and the Texas Parks and Wildlife Department (TPWD) jointly established and currently maintain a data collection and analytical study program focused on determining the effects of and needs for freshwater inflows into the state's 10 bay and estuary systems. Study elements include hydrographic surveys, hydrodynamic modeling of circulation and salinity patterns, sediment analyses, nutrient analyses, fisheries analyses, freshwater inflow optimization modeling, and verification of needs. For determining the needs, statistical regression models are developed among freshwater inflows, salinities, and coastal fisheries. Results from the models and analyses are placed into the Texas Estuarine Mathematical Programming (TxEMP) model, along with information on salinity viability limits, nutrient budgets, fishery biomass ratios, and inflow bounds. The numerical relationships are solved within the constraints and limits, and optimized to meet state management objectives for maintenance of biological productivity and overall ecological health. Solution curves from the TxEMP model are verified by TWDB’s hydrodynamic simulation of estuarine circulation and salinity structure, which is evaluated against TPWD’s analysis of species abundance and distribution patterns in each bay and estuary system. An adequate system-wide match initially verifies the inflow solution. Long-term monitoring is recommended in order to verify that implementation of future water management strategies maintain ecological health of the estuaries and to provide an early warning of needs for adaptive management strategies.     

Matrix-based modeling of blue crab population dynamics with applications to the Chesapeake Bay

Blue crab (Callinectes sapidus) plays an important ecological and economic role in estuaries from South America to New England. It supports a large commercial fishery in the United States with approximately one third of the landings taken from Chesapeake Bay. I developed a stage-based matrix model of the blue crab population to address three key questions: What is the ability of blue crab populations to support sustainable exploitations? What stages of the life cycle are most important in regulating the dynamics of the populations? And specific of the Chesapeake Bay, what is the importance of a winter dredge fishery in determining long-term sustainability of the crab population? The model indicated that with the current pattern of exploitation blue crab populations are able to sustain a total instantaneous mortality rate (Z)～0.7. If the natural mortality rate is estimated for a maximum life expectancy of 8 yr, this translates to moderate levels of exploitation (F<0.32). This value is less than the current estimate of exploitation in Chesapeake Bay (0.9–1.1) indicating that the level of exploitation in this system needs to be reduced to avoid overfishing. Transitions to and from small age-1 crabs were shown to be important in regulating the overall dynamics of the population. The egg production realized by large adults was also shown to be an important regulatory process. The model indicated that reductions in the winter dredge fishery would have a substantial role in ensuring the long-term sustainability of the population. Reductions in other sectors of the fishery are also required to ensure sustainability.     

Influence of Environmental Variables and Fishing Pressure on Bivalve Fisheries in an Inshore Lagoon and Adjacent Nearshore Coastal Area

Climate changes affect marine ecosystems and the survival, growth, reproduction and distribution of species, including those targeted by commercial fisheries. The impact of climate change has been reported for many fish species, but studies focusing on the effects of climate on bivalve resources are lacking. In Portugal, the harvesting of bivalves is an old and artisanal activity, of special importance along the Algarve coast (South of Portugal). This study aims to evaluate the influence of climatic, environmental and fisheries factors on the landings of intertidal coastal lagoon and coastal bivalve species (subtidal nearshore species). The environmental and fisheries parameters considered to affect the landings of bivalves in the eastern Algarve were: fishing effort (number of fishing events), sea surface temperature, North Atlantic Oscillation (NAO) index, upwelling index, wind magnitude and direction and river discharges. Analysis of time series data using min/max autocorrelation factor analysis and dynamic factor analysis showed that, for most species, fishing effort was positively related with landings per unit effort trends in the following year. Lagoon bivalve species (Cerastoderma edule and Ruditapes decussatus) responded to different environmental variables than the coastal bivalve species (Chamelea gallina, Pharus legumen, Donax spp. and Spisula solida). Upwelling index had a significant effect on the lagoon bivalves while the NAO index, wind magnitude and direction, and river discharges only affected the coastal species. This study highlighted the need to adapt fishing effort regimes, while considering the background effects of environmental variability, in order to improve fisheries management.     

Relationships Between Meteorological and Water Quality Variables and Fisheries-Independent White Shrimp (<Emphasis Type="Italic">Litopenaeus setiferus</Emphasis>) Catch in the ACE Basin NERR,South Carolina

White shrimp (Litopenaeus setiferus) fisheries-independent and fisheries-dependent landings can be highly variable and may be related to environmental factors that influence growth, mortality, and survival. We used linear regression analysis to look for potential relationships between environmental and white shrimp catch-per-unit-effort (CPUE) data collected from the Ashepoo-Combahee-Edisto (ACE) Basin National Estuarine Research Reserve (NERR) for four critical months in the shrimp life cycle. This analysis used data from white shrimp fisheries-independent CPUE (2002 to 2014) and water quality and meteorological variables for August (juvenile), December (sub-adult), March (adult), and April (spawning adult). The results showed that shrimp CPUE was mainly correlated with water temperature, salinity, and dissolved oxygen concentration collected through the ACE Basin NERR’s System-Wide Monitoring Program (SWMP), but offshore wind, precipitation, and intra-annual CPUEs also partially explained the variability in monthly CPUEs. Black gill prevalence was correlated with water temperature and salinity. Additionally, our analysis found that winter water temperatures of ≤11 °C were correlated with reduced shrimp abundance the following spring. Ultimately, managers would like to successfully predict white shrimp stock abundance throughout fishing seasons based on environmental conditions. This study is a first step in identifying the environmental variables that may be useful in predicting white shrimp CPUE in the South Atlantic Bight. The techniques employed here can serve as a basis for predicting and managing other wild annual fisheries stocks.     

AnnouncingEstuaries and Coasts, Journal of the Estuarine Research Federation

This is the first issue ofEstuaries and Coasts (ISSN 1559-2723), which continues the Estuarine Research Federation's publication inEstuaries (1978–2005) (ISSN 0160-8347) of scientific reports, reviews, comments, and notes on estuarine and coastal scientific research from around the world. Numbering of volumes ofEstuaries and Coasts continues uninterrupted fromEstuaries since the expanded title was not intended to mark a change in the scope of the journal. It is our hope that the journal will continue to become more international in its coverage, and to include more coastal science than is sometimes associated with the single word nameEstuaries. In addition to the change of the journal's name there is also a new cover design that will change with each issue and highlight an estuary or coast associated with one or more articles in the issue. Another change to the journal is a new column entitled Perspectives in Estuarine and Coastal Science, which is intended to stimulate discussion about emerging topics in estuarine and coastal science. The H. T. Odum Synthesis Essay, initiated in 2005, will be continued on an annual basis.     

Evolution of Mid-Atlantic Coastal and Back-Barrier Estuary Environments in Response to a Hurricane: Implications for Barrier-Estuary Connectivity

Assessments of coupled barrier island-estuary storm response are rare. Hurricane Sandy made landfall during an investigation in Barnegat Bay-Little Egg Harbor estuary that included water quality monitoring, geomorphologic characterization, and numerical modeling; this provided an opportunity to characterize the storm response of the barrier island-estuary system. Barrier island morphologic response was characterized by significant changes in shoreline position, dune elevation, and beach volume; morphologic changes within the estuary were less dramatic with a net gain of only 200,000 m³ of sediment. When observed, estuarine deposition was adjacent to the back-barrier shoreline or collocated with maximum estuary depths. Estuarine sedimentologic changes correlated well with bed shear stresses derived from numerically simulated storm conditions, suggesting that change is linked to winnowing from elevated storm-related wave-current interactions rather than deposition. Rapid storm-related changes in estuarine water level, turbidity, and salinity were coincident with minima in island and estuarine widths, which may have influenced the location of two barrier island breaches. Barrier-estuary connectivity, or the transport of sediment from barrier island to estuary, was influenced by barrier island land use and width. Coupled assessments like this one provide critical information about storm-related coastal and estuarine sediment transport that may not be evident from investigations that consider only one component of the coastal system.     

Distribution and abundance of early life history stages of the blue crab,Callinectes sapidus,in tidal marsh creeks near Charleston,South Carolina

A 16-month study of estuarine habitats in poly-, meso-, and oligohaline salinity regimes near Charleston Harbor assessed the distribution and abundance of megalopae and early crab stages of the blue crab,Callinectes sapidus. Blue crab were sampled with a plankton net and a cylindrical drop sampler. Blue crab were most abundant in plankton collections at night, accounting for 68% of the megalopae and over 88% of the juveniles collected in day and night tows combined. At night, densities of megalopae were greatest in surface samples, whereas densities in daylight collections were greater on the bottom. Juvenile densities were greatest on the bottom in both day and night collections, although catch rates at night were more variable than those of the megalopae. This suggests that megalopae, and possibly juvenile stages, experience a diel vertical migration. Results indicate that ingress to estuarine nursery areas occurs at the megalopal stage. Megalopal densities were highest at the polyhaline site, while juvenile blue crab were most abundant in the oligohaline area. Habitat utilization by juvenile blue crab was estimated using a cylindrical drop sampler and Venturi suction pump on three bottom types in the intertidal zone. Densities were greatest over the sandy-mud substrate, although catch rates were much lower than those reported for other geographical areas. These results suggest that juvenile blue crab do not occur in abundance on the marsh surface but remain on the creek bottom, possibly because creek physiography and large tidal amplitudes may restrict accessibility to the marsh surface.     

Estuarine Ecosystem Response Captured Using a Synoptic Climatology

Estuarine and coastal ecosystems respond strongly to proximate climate forcing. In this study, we present a regional, synoptic climatology as an approach to classify weather patterns that generate interannual variability in coastal and estuarine ecosystems. Synoptic climatology is a method that classifies sea level pressure data into distinct patterns representing common weather features for a specified region. A synoptic climatology was developed for the eastern United States and used to quantify surface conditions affecting Chesapeake Bay during wet and dry years. In a synthesis analysis, several mechanisms were identified that explained the link between weather patterns and ecosystem structure, principal among them is the delivery of freshwater to the Bay during spring. Wet and dry years were characterized by shifts in biogeography of the Chesapeake Bay. The shifts resulted from habitat changes and trophic interactions and included the timing and magnitude of the spring phytoplankton bloom, the distribution/abundance of mesozooplankton and gelatinous zooplankton, and juvenile indices of fish. Synoptic climatology resolved regional weather variability at a spatial scale not strongly controlled by larger-scale climate indices and explained ecosystem responses in Chesapeake Bay.     

Seasonal Occurrence of Cownose Rays (Rhinoptera bonasus) in North Carolina’s Estuarine and Coastal Waters

The seasonal occurrence of cownose rays (Rhinoptera bonasus) within North Carolina’s estuarine and coastal waters was examined from aerial surveys conducted during 2004–2006. Generalized linear models were used to assess the influence of several variables (month, year, habitat type, sea surface temperature, and turbidity) on predicted counts of cownose rays. The spatial distributions of rays were compared by season, and differences in group size were tested as a function of season and habitat. Cownose ray data associated with the North Carolina Division of Marine Fisheries (NCDMF) fishery independent gill net sampling program in Pamlico Sound was also examined as a function of season and year, and compared with aerial observations. Rays immigrated into the region in mid-spring (April), dispersed throughout the estuary in the summer (June–August), and emigrated by late autumn (November). Predicted counts were highest in the spring (April, May) and autumn (September–November) for coastal habitats and highest in the summer for estuarine habitats. Predicted counts were also higher in the coastal region than estuarine and higher when sea surface temperatures were above average. Comparison of group size by habitat type revealed substantially larger group sizes in the coastal habitat than the estuarine. In addition, for the estuary, spring surveys had larger group sizes than summer surveys; for the coastal habitat, autumn group sizes were significantly larger than spring or summer group sizes. The NCDMF gill net sampling surveys indicated similar trends in monthly migration patterns as well as increased ray abundance in 2008 and 2009 compared with 2003–2007. These results suggest that North Carolina’s waters serve as important habitat during the seasonal migration of cownose rays, as well as during the summer when the species may utilize the estuarine region as a nursery and/or for foraging.     

Movement Patterns and Distributional Shifts of Dungeness Crab (Metacarcinus magister) and English Sole (Parophrys vetulus) During Seasonal Hypoxia

Hypoxia (dissolved oxygen?<?2 mg L^–1) has emerged as a worldwide threat to coastal and estuarine ecosystems. Beyond direct mortality, secondary ecological impacts caused by hypoxia-driven distributional shifts may be equally important. From July–November 2009 and June–September 2010, we quantified the movement patterns of Dungeness crab (Metacarcinus magister) and English sole (Parophrys vetulus) in Hood Canal, Washington USA, a seasonally hypoxic estuary. Although highly mobile (mean cumulative distance?±?SD?=?11.0?±?25.6 km, N?=?60), there was little evidence of either species exhibiting large-scale directional movement out of the hypoxic region. However, Dungeness crab showed significant shifts towards shallower waters and elevation in activity in the hypoxic region, potentially increasing their vulnerability to crabbing and other indirect ecological consequences. Our findings suggest hypoxia could have a more localized impact on the mobile fauna in Hood Canal. However, more detailed information concerning the local-scale oxygen dynamics and responses of these species, such as English sole vertical movement, is essential for grasping the population and community level effects of hypoxia.     

Impact of Farakka barrage on the hydrology and fishery of Hoogly estuary

Construction of the Farakka barrage on the Ganga River in April 1975 to augment water supply to the Calcutta port has brought about a significant increase in freshwater discharge in its distributary, the Hoogly estuary. This has naturally resulted in major changes in the ecology of this estuary, causing modifications in the structure of its fishery resources, fishing pattern, and fish production. This paper presents observations on salinity, plankton, bottom biota, fishery resource, and fish production of different zones of the Hooghly estuary during the period 1982–1992. Comparison with similar studies made before and immediately after commissioning of the Farakka barrage (1975–1977) has revealed that the increased freshwater discharge has resulted in considerable decrease in salinity throughout the estuary. The freshwater zone now extends toward the mouth of the estuary. The true estuarine zone has moved seaward and the marine zone has been restricted to the area near the mouth of the estuary. This has effected major changes in plankton dynamics, sharp decline in the fishery of marine and neritic species in the upper estuary, caused a significant increase in catch ofTenualosa ilisha and an over twofold increase in the average annual fish landings from the estuary as a whole. New zonations have been proposed based on the presently, observed salinity values, which are the most significant factor in determining the fishery of any estuary. An interdisciplinary study of the ecology of the new zones is needed to establish their correct biological characteristics.