Estuarine-dependent Fish Research Articles

Intake modifications to reduce entrainment and impingement at Carolina Power & Light Company’s Brunswick Steam Electric Plant, Southport, North Carolina

The Brunswick Steam Electric Plant (BSEP) is a two-unit nuclear station located in the lower Cape Fear River Estuary (CFE) near Southport, NC. Once-through cooling water is withdrawn from the CFE and discharged to the Atlantic Ocean. Estuarine-dependent fish and shellfish species are potentially subject to entrainment and impingement during cooling-water withdrawal. Mitigation technologies include a fish diversion structure (9.4-mm mesh screens) at the mouth of the intake canal to reduce impingement of large organisms, 1-mm fine-mesh traveling screens to reduce entrainment of larvae, a fish return system to return impinged organisms alive back to the estuary, and flow minimization. Installation of the fish diversion structure resulted in a 40% reduction in number and 70% reduction in the weight of larger organisms impinged. Use of fine-mesh screens successfully reduced the number of organisms entrained by as much as 80% depending upon species present. Survival of organisms returned to the CFE ranged from <1% to approximately 92% depending upon species and size class. In addition to monitoring the effectiveness of the intake modifications, over 20 years of extensive environmental studies in the estuary indicate that operation of the BSEP has had no measurable adverse effect on the fisheries of the CFE. The species composition, seasonality, and abundance of organisms using the CFE have not changed as a result of operation of the BSEP.

Does salinity affect somatic growth in early juvenile Atlantic croaker, Micropogonias undulatus (L.)?

Factors affecting recruitment of fishes remain one of the most studied but least understood issues of fisheries science. Understanding the causes of recruitment variability remains elusive because factors that affect the growth and survivorship of young fishes are complex and dynamic. Here we focus on the influence of salinity on growth of early juvenile Atlantic croaker, Micropogonias undulatus under laboratory conditions as part of a larger study to relate short-term fluctuations in growth rates of young estuarine-dependent fishes with variability in abiotic environmental factors. Body growth of juvenile Atlantic croaker was significantly (P<0.001) different among all of the three salinity treatments with growth in 5‰>20–5‰=20‰. A linear response to the changing treatment suggests an additive effect of changing salinity on body wet weight (WW) growth. Juvenile Atlantic croaker in the 5‰ treatment grew in WW by a factor of 3.88 relative to initial WW. Fish in the 20–5‰ treatment grew in WW by a factor of 2.90, while fish in the 20‰ treatment grew in WW by a factor of 2.17. Otolith diameter also varied significantly with salinity, and there was a significant positive relationship between changes in body WW and changes in otolith diameter growth (r=0.68, P<0.02, n=12). The correlation between body and otolith growth justified our use of otolith data to infer that substantial fluctuation in the early growth of early juvenile Atlantic croaker from field collections was inversely cross-correlated with salinity and water temperature. Assuming that the probability of survival during the nursery period increases as postlarval fish grow, salinity-induced plasticity in growth rates implies that the site and habitat into which post-larval fish settle can potentially influence recruitment dynamics. This study demonstrates that there is the potential for fluctuations and spatial variability in salinity to cause significant variability in short-term growth rates for juvenile fishes within estuarine nursery areas.

Abundance and Size of Larval Fishes outside the Entrance to Beaufort Inlet, North Carolina

Synoptic ichthyoplankton sampling was conducted on two transects, one on either side of Beaufort Inlet, North Carolina, during the winter immigration season of seven ocean-spawned, estuarine-dependent fishes;Brevoortia tyrannus (Atlantic menhaden),Leiostomus xanthurus (spot),Micropogonias undulatus (Atlantic croaker),Lagodon rhomboides (pinfish),Paralichthys albigutta (Gulf flounder),P. dentatus (summer flounder), andP. lethostigma (southern flounder). Densities and lengths of larvae were significantly different among sampling dates, with distance offshore, and between sides of the inlet. Flood-tide stage had minimal effect on larval densities and lengths except forP. albigutta andP. lethostigma. Changes in larval densities with distance offshore were not coherent among species; densities ofB. tyrammus increased offshore whereas densities of the other species decreased offshore. Average larval densities on a sampling date were coherent among species. Patterns in larval lengths were also coherent among the four non-flounder species. Larval densities outside of Beaufort Inlet were correlated with larval densities inside of Beaufort Inlet. Larval densities outside of Beaufort Inlet were also correlated with the north component of the wind, nearshore water temperature, and distance to the mid-shelf front. Differences in larval density across the inlet were significantly correlated with the east component of the wind. The patterns in larval densities outside of Beaufort Inlet were complex and apparently influenced by both the physical processes that supply larvae to the nearshore region and nearshore physical dynamics.

A PRELIMINARY SURVEY OF COASTAL RIVER SYSTEMS ON THE SOUTH AFRICAN WEST COAST, ORANGE RIVER—GROOT BERG, WITH PARTICULAR REFERENCE TO THE FISH FAUNA

SUMMARY The coastal river systems on the west coast of South Africa from the Orange River to the Groot Berg were surveyed during the period September to October 1993. The ichthyofaunal and physicochemical characteristics of each system are discussed in relation to their suitability as estuarine nursery areas. Of the fifteen systems sampled, only three appeared to exhibit any estuarine characteristics in terms of their fish fauna. Of the remainder, one system was a coastal lake system which had been severely altered and eleven were either dry river beds or semi-permanent waterbodies which are normally isolated from the sea and appear to be of little value as habitat for either resident or estuarine-dependent marine fishes. The systems on this arid coast are, however, very important habitats for migratory and resident waterbirds.

A PRELIMINARY SURVEY OF THE COASTAL RIVER SYSTEMS OF FALSE BAY, SOUTH-WEST COAST OF SOUTH AFRICA, WITH PARTICULAR REFERENCE TO THE FISH FAUNA

SUMMARY The estuaries of False Bay were surveyed during the period October to November 1993. The ichthyofaunal and physico-chemical characteristics of each system are presented and their suitability as estuarine nursery areas is discussed. Eleven systems drain into False Bay and most of these have, in one way or another, been impacted and modified by human activities. Two systems, the Buffels (Wes) and Elsies appear to be little more than coastal streams which only flow during the winter rainy period and offer little habitat for either resident or estuarine-dependent marine fishes. One system, the Seekoe, has been reduced to an outfall for treated sewage effluent and does not appear to support any fish fauna. A further two systems, the Silwermyn and Sir Lowry's Pass, have been severely altered and their fish fauna appears to be limited. The remaining six systems still appear to serve a viable estuarine nursery function and estuarine and estuarine-dependent marine species were a dominant component of their fish fauna.

Rapid Growth, High Feeding Rates, and Early Piscivory in Young-of-the-Year Bluefish (Pomatomus saltatrix)

The bluefish (Pomatomus saltatrix) is an offshore-spawning estuarine-dependent fish that is abundant along the east coast of North America. Young-of-the-year bluefish undergo a habitat shift from offshore waters to inshore nursery areas at about 40–70 mm total length which coincides with an increased growth rate and a diet shift from planktivory to piscivory. Here, we measure growth of young-of-the-year bluefish on different diets and estimate consumption rates both in the field and in the laboratory. Growth on a fish diet is significantly higher than that on a zooplanktivorous diet. Bluefish have among the highest evacuation (5–7 h), consumption (20–30% body weight/d), and specific growth rates (1–2 mm/d) reported for temperate fishes and are similar to those for pelagic tropical species. These results suggest that bluefish may exhibit a tropical feeding physiology in temperate estuarine nurseries as a way to achieve rapid growth rates.

Microhabitat use by marsh-edge fishes in a Louisiana estuary

We used a drop sampler to characterize use of the marsh-edge ecotone by small fishes along two transects running inland from the Gulf of Mexico for ca. 25 km in Louisiana's Barataria-Caminada Bay System. Monthly sampling was stratified among upper, middle, and lower reaches and within reaches to characterize fish responses to salinity, depth, distance from shore, substrate, dissolved oxygen concentration, temperature, turbidity, velocity, and emergent stem density. In 681 quantitative samples, covering 658 m2, collected between October 1987 and October 1989, we collected 57 fish species and 16 864 individuals, primarily larvae and juveniles. The 15 most abundant fishes, comprising 97.7% of all individuals, were concentrated near the marsh edge (i.e., 0 to 1.25 m distance). Some significant differences within species for seasonal variables (e.g., temperature and dissolved oxygen concentration) reflected the ephemeral duration of early life history stages. Other differences reflected ontogenetic microhabitat shifts (e.g., depth and distance from shore). Within ecological groups, characterized as demersal residents, nektonic transients, and demersal transients, spatial and temporal segregation reflected the particular habitat requirements of each species. In a principal component analysis of microhabitat use, the first three components were interpreted as seasonal, depth-and-distance, and salinity axes, respectively. The array of species and size classes in principal component space reflected the complex dimensionality of microhabitat use. The high density of fish larvae and juveniles near the marsh edge confirmed the importance of the marsh-edge ecotone as a nursery for many estuarine-dependent fishes.

Effects of Semi-impoundment of Louisiana Marsh on Fish and Crustacean Nursery Use and Export

Abstract About 200,000 hectares of Louisiana marsh are, or soon will be, semi-impounded by private landowners. Additional large acreages have been semi-impounded by public agencies, and the trend is expected to continue, To determine quantitatively the effect of semi-impoundment on fisheries export, a 70-hectare marsh pond was leveed to create two nearly identical 35-hectare ponds. A weir (low dam) was placed on the outlet to semi-impound one of the ponds. All fishes and crustaceans emigrating from the two ponds were trapped continuously and the traps were emptied daily. The trapping continued for 2 years, the weir being switched to the outlet of the other pond after the first year. Comparisons of catches from the weired and unweired ponds showed that the weir caused substantial reductions in both number and total weight of most of the important estuarine-dependent fishes and crustaceans migrating back toward the Gulf of Mexico. A subsequent test indicated semi-impoundment by a vertically slotted weir wou...

Dynamics of littoral fishes and decapods along a coastal river-estuarine gradient

We examined community dynamics of nekton along a coastal river-estuarine gradient in Old Fort Bayou Mississippi, U.S.A. Distribution, abundance and similarity of nekton varied spatially and seasonally along the gradient in concert with varying physical-chemical conditions. The tidal freshwater (TFW) and oligohaline (OH) habitats had greater diversity and evenness than the mesohaline (MH) habitat, due to the interfacing of the dominant freshwater and the estuarine/marine faunas. Stepwise multiple regression indicated that water temperature was the most important predictor of species richness within TFW and MH when the entire species complement was considered. However, separation of freshwater and estuarine/marine species suggested that water temperature (positive relationship) and salinity (negative relationship) were the best predictors of freshwater species at TFW while the estuarine/marine species complement was best predicted by salinity and water temperature at TFW and MH. Models based on abundance data indicated that there was a significant negative relationship between salinity and turbidity and freshwater species abundance while a positive relationship was documented between estuarine/marine species abundance and salinity and turbidity. The dynamic nature of saline marsh nekton depends, in part, on the species complement, the salinity, and the rate of salinity fluctuation within various sections along the estuarine gradient. Although it is dogmatic that many estuarine habitats are physiologically ‘harsh’ due to fluctuating physical-chemical conditions, low-salinity nekton were found to tolerate greater fluctuations in salinity and pH than higher-salinity nekton. These habitats act as conduits between freshwater and estuarine habitats and serve a nursery function for estuarine-dependent fishes and decapods; they are thus functional components of the estuarine system.

Fish Population Responses to Chronic and Acute Pollution: The Influence of Life History Strategies

We have developed a simulation model to estimate pollution effects on economically important estuarine-dependent fish populations. Traditionally, pollution studies have focused upon impacts on individual organisms; however, wise management of marine resources depends upon an understanding of dynamics at the population level. As a required first step toward conducting relevant pollution studies, we have compiled available life history data on eight species (14 spatial-temporal stocks), concentrating on age-specific rates of growth, survival, and fecundity. Leslie matrix models of species population dynamics were used to predict pollutant impacts—mediate through changes in 1st-year survival. On average, and without compensation, these modelled stocks respond to a one-time-50% reduction in first-year survival by taking ten years to equilibrate at 88% of their preimpact abundance. Our synthesis of the data included a search for derived (standardized) population parameters to evaluate differences in susceptibility among and within fish populations to pollutant stresses. We demonstrated that knowledge of a species’ age-specific fecundity pattern provides additional predictive power of its response to pollution perturbation.

Meiofaunal Densities and Copepod Species Composition in a Louisiana, U.S.A., Estuary

Meiofaunal Densities and Copepod Species Composition in a Louisiana, U.S.A., Estuary

Comprehensive Estuarine Nursery Study Completed

Abstract Louisiana coastal marsh is eroding rapidly to open water. Water control structures are being used in an attempt to slow this erosion. Many estuarine-dependent fishes and crustaceans must be able to pass from the Gulf to the marsh, and back again to the Gulf, to complete their life cycle. Much still needs to be learned of their habits during these migrations so that the structures can be operated for efficient passage of organisms. We briefly describe the methods used in a 4-year study to determine seasonal presence, relative abundance, timing and depth of movements, and the effect of cold fronts.

A preliminary report on the assessment of wetland productive capacity from a remote-sensing-based model — A NASA/NMFS joint research project

The NASA and the NMFS have undertaken a joint research project to develop Landsat Thematic Mapper (TM) technology for the determination of the value of wetlands to estuarine fish and shellfish production. NASA has developed the remote-sensing-based model to predict wetland productive capacity, a measure of the organic carbon exported to the estuarine food chain. The productive capacity (PC) model uses satellite remotely sensed determinations of vegetation, as the source of carbon, and distance-to-water, shoreline density, and water body type as hydrographic factors influencing carbon export. Regression analyses of aircraft simulated TM (TMS) data showed a stronger relationship with percent vegetation cover than with biomass for estimating the source of organic detritus. Land/water discrimination, fundamental to the measurement of the hydrographic variables, was accomplished more accurately with TMS than with Landsat Multispectral Scanner (MSS) data as compared to a photographic standard. The PC model generates detrital export measurements as input to an estuarine ecosystem model being developed by NMFS. Initial findings show that salinity patterns along with animal interactions affect the utilization of detritus by benthic organisms. The coupling of the two models establishes a technique for estimating the economic value of wetlands with respect to estuarine-dependent fish and shellfish production.

Comparison of, and the effects of altered freshwater inflow on, fish assemblages of two contrasting South African estuaries: the cool-temperate Olifants and the warm-temperate Breede

This study compares the fish assemblages of the permanently open cool-temperate Olifants and warm-temperate Breede estuaries on the west and south coasts of South Africa respectively, and their responses to altered freshwater flows. Both estuaries have experienced a >35% reduction in mean annual runoff (MAR) from a historical reference condition to the present day with a >60% reduction possible under future flow scenarios. With the exception of species that have both marine and estuarine breeding populations, the Olifants Estuary fish assemblage has experienced an overall 20% decrease in abundance from reference (pristine state) to the present day and will gradually decline to 55% of reference with a predicted future 60% reduction in MAR. Consequently, future reductions in flow are likely to result in the Olifants Estuary progressing towards a low biomass, low diversity, marine-dominated system. In contrast, reduced freshwater flows in the Breede Estuary are likely to experience an overall reduction in the abundance of species that breed only in estuaries, and in freshwater and catadromous species. Collectively, entirely estuarine-dependent fish will increase in abundance, but considered individually some important exploited species such as Argyrosomus japonicus and Pomadasys commersonnii will collapse to 50% of historical numbers once there has been a 64% reduction in MAR. Overall, fish abundance in the estuary has increased by 6% from reference to the present day and is likely to increase to 115% of reference with future reductions in flow. Some species with a preference for fresh and brackish water will be all but lost from the system, but overall diversity is likely to increase with the range expansion of warm-temperate and subtropical marine species westward. In all, the fish assemblage of the Breede Estuary will experience a gradual change from a relatively high-diversity, low-abundance, freshwater rich system under historical flow conditions to a high diversity, high-abundance, marine-dominated system with future reductions in flow.