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1.
Small purse seines are well suited to sampling open water habitats in estuaries, yet little is known about how variation in their design affects estimates of density and species richness of estuarine fishes. We tested whether purse seine size (length and depth) affected estimates of density or species richness of fishes in San Dieguito Lagoon, southern California, U.S.A. Twenty-one species were captured, with the open water speciesAtherinops affinis dominating the catch. The larger net (36.4 m long × 3.6 m deep) produced higher estimates of density than the smaller net (18.2 m long × 2.4 m deep). The average number of species captured per sample was lower for the smaller net than the larger net, but species accumulation curves for the small and large nets were similar, indicating that the difference in the number of species per sample was primarily caused by the larger area sampled by the larger purse seine. Sampling with the larger purse seine was more time efficient than the smaller seine. We found small purse seines to be useful tools for sampling fishes in open water habitats in a small estuary, but we recommend that care be taken in selecting the size of a purse seine.  相似文献   

2.
Flume nets of various lengths and a 3-m seine were used to sample the fishes and macrocrustaceans using a flooded Louisiana salt marsh and the adjacent tidal creek. The experiment allowed for species-specific comparisons of the flooded marsh at the creek edge versus the interior. Of the 37,667 organisms collected in flume nets from January through November 1989, 89% were decapods (nine species) and 11% were fish (29 species). An additional 18,539 organisms (75% decapods and 25% fish) were collected from concurrent seine samples taken from July through November. Comparison of catches among different flume lengths and low tide versus high tide seine collections revealed distinct patterns of marsh habitat utilization. Densities of most organisms were highest within 3 m of the water’s edge, but significant numbers of marsh-resident fish species used the interior marshes. The edge marshes appeared to be used by both transient and resident species; however, the interior marshes were used primarily by marsh-resident species (Cyprinodontiformes andPalaemonetes sp.) that are excellent food sources for adult transient-species. Four zonations of marsh use are described for transients, residents, and rare species.  相似文献   

3.
Efficiency, defined as the percentage of the total number of individuals captured from a known area of tidal creek (blocked with seines), was studied on six occasions from December 1976 through August 1978. Sampling was conducted at two stations near the Cape Fear River, Southport, North Carolina using either seines or rotenone. For the three most abundant species collected by each method, the range for seine efficiencies (60.6±19.4 to 78.0±9.4%) was generally narrower than that for rotenone (29.6±9.5 to 57.7±14.8%). However, overall species richness was better represented by rotenone, the mean percentage of species captured for all samples was 92.1% versus 70.3% for seines. Consistent patterns in efficiency for individual species with regard to size, age, or water temperature were absent. A comparison of individual collections with that of the sample “universe” trapped between the block nets indicated that a representative sample of the extant nekton community was taken by each method.  相似文献   

4.
Species richness and abundance of epibenthic fishes and decapod crustaceans were quantified with day-time beam trawl tows and throw traps to provide information on nekton assemblages inZostera marina and unvegetated sandy habitats in northern latitudes. Sampling at randomly selected stations with a 1.0-m beam trawl occurred in eelgrass (Zostera marina) and unvegetated sandy substrates of two mid-coastal Maine estuaries: Casco Bay and Weskeag River. Random 1.0-m throw trap samples were collected inZostera and adjacent unvegetated sandy substrates in Casco Bay and Weskeag River as well. Species richness and faunal abundances were positively associated with the occurrence ofZostera within Weskeag River and Casco Bay estuaries using both gear types. A total of 17 species of fishes and 6 species of decapods were collected in the two estuaries using both gears. Populations of most species were dominated by young-of-the-year and juvenile life history stages. Number and densities of fishes were higher inZostera, due primarily to the abundances of eelgrass residents such as threespine,Gasterosteus aculeatus, and fourspine sticklebacks,Apeltes quadracus, grubby,Myoxocephalus aenaeus, and cunner,Tautogolabrus adspersus. Crangon septemspinosa dominated decapod catch per unit effort and density in both estuaries and habitats.  相似文献   

5.
We evaluated the sampling characteristics of enclosure traps in estuaries in southern California, USA. Using enclosure traps that sampled 0.25, 0.5, and 1-m2 footprints, we found that enclosure trap size significantly affected estimates of fish density and the precision of these estimates. The highest estimates were produced by the 0.5-m2 trap and the lowest by the 0.25-m2 trap. Precision of the density estimates improved with increasing trap size, while the proportion of zero values in the data sets decreased and estimates of species richness increased. The largest trap was difficult to use in the field and often did not function properly; thus we concluded that intermediate enclosure trap sizes offered the best compromise between statistical and logistical considerations. By examination of burrows in sediment cores taken in fished out enclosure traps, we found no evidence to support the widely held view that burrow-dwelling fishes evaded capture by hiding in burrows. We also used mark-recapture techniques to estimate recovery efficiency in 0.43-m2 enclosure traps. Recovery efficiency averaged 91% and did not differ significantly among estuaries or sampling stations within estuaries. Based on extensive netting within enclosure traps, we determined that in areas with dense fish populations (>90 fish 0.43-m−2), netting could be ceased after the first sweep that captured no fish with only a trivial effect on the estimate of density. In more sparsely populated areas, netting had to continue until 2–3 sweeps had captured no fish in order to obtain estimates of density that were within 90% of the actual values present. Overall, we found enclosure traps to be effective tools for sampling small, abundant fishes in shallow estuaries in southern California, but we recommend that care be taken when choosing trap size and sampling (netting) effort within traps in order to optimize their sampling characteristics.  相似文献   

6.
We assessed fish assemblage stability over the last half century in Lake Pontchartrain, an environmentally degraded oligohaline estuary in southeastern Louisiana. Because assemblage instability over time has been consistently associated with severe habitat degradation, we attempted to determine whether fish assemblages in demersal, nearshore, and pelagic habitats exhibited change that was unrelated to natural fluctuations in environmental variables (e.g., assemblage changes between wet and dry periods). Collection data from three gear types (trawl, beach seine, and gill nets) and monthly environmental data (salinity, temperature, and Secchi depth) were compared for four collecting periods: 1954 (dry period), 1978 (wet period), 1996–1998 (wet period), and 1998–2000 (dry period). Canonical correspondence analysis (CCA) revealed that although the three environmental variables were significantly associated with the distribution and abundance patterns of fish assemblages in all habitats (with the exception of Secchi depth for pelagic samples), most fish assemblage change occurred among sampling periods (i.e., along a temporal gradient unrelated to changing environmental variables). Assemblage instability was the most pronounced for fishes collected by trawls from demersal habitats. A marked lack of cyclicity in the trawl data CCA diagram indicated a shift away from a baseline demersal assemblage of 50 yr ago. Centroid positions for the five most collected species indicated that three benthic fishes, Atlantic croaker (Micropogonias undulatus), spot (Leiostomus xanthurus), and hardhead catfish (Arius felis), were more dominant in past demersal assemblages (1954 and 1978). A different situation was shown for planktivorous species collected by trawls with bay anchovy (Anchoa mitchilli) becoming more dominant in recent assemblage and Gulf menhaden (Brevoortia patromus) remaining equally represented in assemblages over time. Changes in fish assemblages from nearshore (beach seine) and pelagic (gill net) habitats were more closely related to environmental fluctuations, though the CCA for beach seine data also indicated a decrease in the dominance ofM. undulatus and an increase in the proportion ofA. mitchilli over time. The reduced assemblage role of benthic fishes and the marked assemblage change indicated by trawl data suggest that over the last half century demersal habitats in Lake Pontchartrain have been impacted more by multiple anthropogenic stressors than nearshore or pelagic habitats.  相似文献   

7.
Catchability coefficients (q) of 366-m and 732-m trammel nets set along the shore in a rectangular shape were determined for selected fish species, utilizing noise and sublethal rotenone strike methods. Catachbility coefficients ranged from 0 to 1 for both trammel nets; 65% and 75% of the values for the 366-m and 732-m nets, respectively, were less than 0.1. Only the perpendicular strike method may have affected the catch efficiency of the nets, but the effect was not consistent among all species. Catchability coefficients were slightly higher when fish too small to be caught in the net were removed from the calculations. Despite the wide range of catchability coefficients among species, trammel nets struck with noise can be used to detect gross changes in abundance (standing stock) of many estuarine fishes. Increases in trammel net efficiency may be obtained by improvement in striking techniques or changes in net design, such as use of less visible monofilament webbing.  相似文献   

8.
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9.
Many studies compare utilization of different marine habitats by fish and decapod crustaceans; few compare multiple vegetated habitats, especially using the same sampling equipment. Fish and invertebrates in seagrass, mangrove, saltmarsh, and nonvegetated habitats were sampled during May–August (Austral winter) and December–January (Austral summer) in the Barker Inlet-Port River estuary, South Australia. Sampling was undertaken using pop nets in all habitats and seine nets in seagrass and nonvegetated areas. A total of 7,895 fish and invertebrates spanning 3 classes, 9 orders, and at least 23 families were collected. Only one fish species,Atherinosoma microstoma, was collected in all 4 habitats, 11 species were found in 3 habitats (mangroves, seagrass, and nonvegetated), and 13 species were only caught in seagrass and nonvegetated habitats. Seagrass generally supported the highest numbers of fish and invertebrates and had the greatest species richness. Saltmarsh was at the other extreme with 29 individuals caught from two species. Mangroves and nonvegetated habitats generally had more fish, invertebrates, and species than saltmarsh, but less than seagrass. Analyses of abundances of individual species generally showed an interaction between habitat and month indicating that the same patterns were not found through time in all habitats. All habitats supported distinct assemlages although seagrass and nonvegetated assemblages were similar in some months. The generality of these patterns requires further investigation at other estuaries. Loss of vegetated habitats, particularly seagrass, could result in loss of species richness and abundance, especially for organisms that were not found in other habitats. Although low abundances were found in saltmarsh and mangroves, species may use these habitats for varying reasons, such as spawning, and such use should not be ignored.  相似文献   

10.
The relative capture efficiencies for fish in 732-m trammel nets using three striking methods were compared using nets set in open-water and along the shoreline in Texas bays in fall and spring. When compared to noise, sublethal concentrations of rotenone and KMnO4 did not increase the catches of 9 of the 12 species tested at either shoreline or open-water stations in either the fall or spring. Some effect of strike type was noted for hardhead catfish (Arius felis), gizzard shad (Dorosoma cepedianum), and striped mullet (Mugil cephalus) at stations struck with noise or rotenone, but catches were not consistently greater for either striking method. The catches of some species were different between station types and seasons. However, the total catch at shoreline stations was the same as at open-water stations in both the fall and spring.  相似文献   

11.
Species richness declines to a minimum (artenminimum) in the oligohaline reach of estuaries and other large bodies of brackish water. To date, observations of this feature in temperate estuaries have been largely restricted to benthic macroinvertebrates. Five years of seine data collected during the summers of 1990–1995 in the major tidal tributaries to the lower Chesapeake Bay were examined to see if this feature arose in estuarine fish assemblages. Estimates of numerical species richness (alpha diversity) and rates of species turnover between sites (beta diversity) were generated via rarefaction and detrended correspondence analysis. Two spatial attributes of the distribution of littoral fish species along salinity gradients in the tributaries of the lower Chesapeake Bay were revealed: (1) a species richness depression in salinities of 8–10% and (2) a peak in the rate of species turnover associated with the tidal freshwater interface (salinities of 0–2%). Expression of the minimum is influenced by the physical length of the salinity gradient and the interaction between a species’ salinity preferences and tendency to make long excursions from favorable habitats.  相似文献   

12.
Subtidal accumulations of oyster shell have been largely overlooked as essential habitat for estuarine nekton. In southeastern U.S. estuaries, where oyster reef development is mostly confined to the intertidal zone, eastern oyster (Crassostrea virginica) shell covered bottoms are often the only significant source of hard subtidal structure. We characterized and quantified nekton use of submerged shell rubble bottoms, and compared it to use of intertidal reefs and other subtidal bottoms in the North Inlet estuary, South Carolina. Replicate trays (0.8 m2) filled with shell rubble were deployed in shallow salt marsh creeks, and were retrieved after soak times of 1 to 25 days from May 1998 to March 2000. Thirty six species of fishes, representing 21 families, were identified from the 455 tray collections. Water temperature, salinity, soak time and the presence of a shell substrate all affected the catch of fishes in the trays. Catches during the warmer months were two to five times greater than those during the winter. Fishes were present in 98% of the trays with an overall average of 5.7 fish m?2. The assemblage was numerically dominated by small resident species including naked goby (Gobiosoma bose), oyster toadfish (Opsanus tau), and crested blenny (Hypleurochilus geminatus). Transient species accounted for 23% of all individuals and 62% of the total biomass due to the presence of relatively large sheepshead (Archosargus probatocephalus) and black sea bass (Centropristis striata). Both the transient and resident species displayed distinct periods of recruitment and rapid growth from April to October. Lower abundances of juvenile gobies and blennies during 1998 were attributed to long periods of depressed salinity caused by high rainfall associated with El Niño conditions in spring. Crabs and shrimps, which were often more abundant than the fishes, accounted for comparable biomass in the tray collections. In comparisons of subtidal tray and trawl catches, trays yielded 10 to 1,000 fold higher densities of some demersal fish groups. Comparisons of intertidal and subtidal gear catches indicated that many species remain in the subtidal shell bottom at all stages of the tide. This study suggests that subtidal shell bottom may be essential fish habitat for juvenile seabass, groupers, and snappers and that it may be the primary habitat for a diverse assemblage of ecologically important resident fishes and crustaceans. Given the high levels of nekton use and the areal extent of oyster shell bottoms in eastern U.S. and Gulf estuaries, increased attention to protection and restoration of these areas appears justified.  相似文献   

13.
We sampled nearshore fishes in the Sacramento-San Joaquin Delta, California, United States, during 2001 and 2003 with beach seines and gill nets. We addressed three questions. How and why did fish assemblages vary, and what local habitat features best explained the variation? Did spatial variation in assemblages reflect greater success of particular life history strategies? Did fish biomass vary among years or, across habitats? Nonmetric multidimensional scaling showed that habitat variables had more influence on fish assemblages than temporal variables. Results from both gear types indicated fish assemblages varied between Sacramento and San Joaquin River sampling sites. Results from gill net sampling were less pronounced than those from beach seine sampling. The Sacramento and San Joaquin river sites differed most notably in terms of water clarity and abundance of submerged aquatic vegetation (SAV), suggesting a link between these habitat characteristics and fish relative abundance. Among-site differences in the relative abundance of periodic and equilibrium strategist species suggested a gradient in the importance of abiotic versus biotic community structuring mechanisms. Fish biomass varied among years, but was generally higher in SAV-dominated habitats than the turbid, open habitats in which we found highest abundances of striped bassMorone saxatilis and special-status native fishes such as delta smeltHypomesus transpacificus, Chinook salmonOncorhyncus tschawytscha, and splittailPogonichthys macrolepidotus. The low abundance of special-status fishes in the comparatively productive SAV-dominated habitats suggests these species would benefit more from large-scale restoration actions that result in abiotic variability that mirrors natural river-estuary habitat than from actions that emphasize local (site-specific) productivity.  相似文献   

14.
Once viewed as an inexhaustible fishery resource, eastern oyster reefs (Crassostrea virginica) have been dramatically depleted. In North Carolina alone, eastern oyster harvests have declined by 90% since the early 1900s. However, eastern oyster restoration and management efforts have substantially increased since the 1970s. Oyster reefs provide habitat and refuge for organisms, improve water quality, and decrease erosion. Oyster restoration projects aim to construct reefs that function similarly to their natural counterparts. Therefore, post-creation monitoring of these reefs is crucial in determining restoration success. However, monitoring is often lacking or focused only on oyster density and size rather than ecosystem functions such as nekton utilization. This study examines nekton utilization among created reefs compared to natural reefs in an estuary in Wilmington, North Carolina. The objective was to determine whether the created reefs function similarly to the natural reefs in abundance, species richness, and fish size. Using seine nets and Breder traps, reefs were sampled over a 5-month period. No significant difference was detected among reefs for nekton abundance, species richness, and standard length. This is a promising result for future management, indicating that created and natural reefs can support similar communities of fishes and shrimp.  相似文献   

15.
We explain a new method of quantifying seagrass cover and describing seagrass species composition during fisheries-independent monitoring. This new method is similar to a point-intercept method developed to estimate arboreal crown cover, but it uses an aquascope designed for shallow water. The method does not require a diver. Seagrass cover (cover ratio) distinguished different percentage cover categories in 0.25-m2 seagrass plots. Estimates of species composition determined by using the new method were most similar to those obtained by using estimates of aboveground biomass. Within each 141-m2 area sampled with a 21.3-m fish seine, we accurately estimated seagrass cover ratio and species composition with six observations that typically required less than 6 total minutes. Within such areas, 42 trials were conducted to evaluate the precision with which different observers estimated seagrass cover ratio and species composition. In 98% of the trials, observers attained statistically similar estimates of cover ratio, and in 100% of the trials in areas with multiple seagrass species, observers attained statistically similar estimates of species composition. We conclude that the new method provided efficient and reasonably accurate means to quantify seagrass cover and species composition.  相似文献   

16.
Development and validation of an estuarine biotic integrity index   总被引：1，自引：0，他引：1  
We tested hypotheses about how estuarine fish assemblages respond to habitat degradation and then integrated these responses into an overall index, the Estuarine Biotic Integrity Index (EBI), which summarized observed changes. Fish assemblages (based on trawl catches) and habitat quality were measured monthly or biweekly at nine sites in two estuaries from March 1988 to June 1990. Submerged aquatic vegetation habitats were classified as low or medium quality based on year-round measurements of chemical and physical characteristics (phytoplankton blooms; macroalgae; dissolved oxygen; nutrients; dredged channels). We tested 15 metrics and selected 8 for inclusion in the EBI: total number of species, dominance, fish abundance (number or biomass), number of nursery species, number of estuarine spawning species, number of resident species, proportion of benthic-associated fishes, and proportion abnormal or diseased. Fish assemblages in low-quality sites had lower number of species, density, biomass, and dominance compared with medium-quality sites. Fish abundance peaked in July and August, and was lowest in January to March. The seasonal cycle in low-quality sites was damped compared with medium-quality sites. Abundances of fishes using estuaries as a spawning and nursery area and of benthic species were lower in low-quality sites compared to medium-quality sites. The individual metrics and the overall index correlated with habitat degradation. The EBI based on biomass did not do better than the EBI based on number, indicating that the extra effort to obtain biomass may not be warranted. We suggest the EBI is a useful indicator of estuarine ecosystem status because it reflects the relationship between anthropogenic alterations in estuarine ecosystems and the status of higher trophic levels.  相似文献   

17.
Comparison of the relative abundance of fish species from different life-history groups and their temporal patterns of estuarine habitat use from two estuaries north and south of Cape Cod indicates that the Cape acts as a zoogeographic boundary. Between April 1988 and December 1989, monthly seine and trawl samples were collected from nearshore, shallow-water marsh, and beach and deeper open-water habitats in Wells Harbor, Maine, and Waquoit Bay, Massachusetts. Forty-eight species and 80,341 individuals were collected from Waquoit Bay compared to 24 species and 22,561 individuals from Wells Harbor. Waquoit Bay had proportionally fewer resident species and more marine, nursery, and occasional species than Wells Harbor. Annual density and biomass values were greater across all habitats in Waquoit Bay, with the summer values from the marsh habitat an order of magnitude higher than comparable summer data from the Wells habitats. We suggest that marsh and beach habitats provide a nursery area for young-of-the-year fishes, while deeper, open-water habitats serve as a corridor for fishes moving to nearshore habitats or serve as a refuge during low tide.  相似文献   

18.
This study evaluated the use by fish of restored tidal wetlands and identified links between fish species composition and habitat characteristics. We compared the attributes of natural and constructed channel habitats in Sweetwater Marsh National Wildlife Refuge, San Diego Bay, California, by using fish monitoring data to explore the relationships between channel environmental characteristics and fish species composition. Fishes were sampled annually for 8 yr (1989–1996) at eight sampling sites, four in constructed marshes and four in natural marshes, using beach seines and blocking nets. We also measured channel habitat characteristics, including channel hydrology (stream order), width and maximum depth, bank slope, water quality (DO, temperature, salinity), and sediment composition. Fish colonization was rapid in constructed channels, and there was no obvious relationship between channel age and species richness or density. Total richness and total density did not differ significantly between constructed and natural channels, although California killifish (Fundulus parvipinnis) were found in significantly higher densities in constructed channels. Multivariate analyses showed fish assemblage composition was related to channel habitat characteristics, suggesting a channel’s physical properties were more important in determining fish use than its restoration status. This relationship highlights the importance of designing restoration projects with natural hydrologic features and choosing proper assessment criteria in order to avoid misleading interpretations of constructed channel success. We recommend that future projects be designed to mimic natural marsh hydrogeomorphology and diversity more closely, the assessment process utilize better estimates of fish habitat function (e.g., individual and community-based species trends, residence time, feeding, growth) and reference site choice, and experimental research be further incorporated into the restoration process.  相似文献   

19.
Trends in global and United States fish catches were examined to determine the status of estuarine fisheries yields relative to those from other ecosystems. Potential marine fish production, based upon primary production relationships, was estimated globally and for specific marine ecosystems, including estuaries. While global fish catches increased substantially during the past two decades and continued to increase through 1989, catches of estuarine-dependent species have peaked or stabilized. In the United States, total catches have increased but many estuarine-dependent fisheries have declined, although the declines in catches are no more dramatic than those of heavily-fished continental shelf species. Overfishing probably is the primary cause of declines in estuarine and shelf fisheries. A few estuarine-dependent species of the United States have experienced substantial increases in harvests since 1970, for example, Pacific salmons, menhaden, and penaeid shrimps. The percentage contribution of major estuarine fisheries to the United States commercial catch declined between 1970 and 1990, although the yield of these species increased substantially. Global marine fisheries production at trophic level 2.5 was estimated to be 1,359 million tons. Potential yield was estimated to be 307 million tons, but the 1989 world marine catch was only 86.5 million tons. The major fraction, 196 million tons, of the estimated potential yeild was for the open ocean where technological constraints may prevent its full realization. Of the remaining 111 million tons of the potential, 18.0 million tons (16.2%) may come from estuaries and probably already is fully exploited. The potential catches from shelves, 68.5 million tons (61.6%), and upwelling areas, 24.8 million tons (22.2%), while considerably larger than those from estuaries, are lower in a relative sense (per unit area) than fisheries production and potential catch in estuarine zones. Relationships between fish production, fish harvest, and primary production were examined in specific estuaries. The developing role of aquaculture and its effect on estuarine fisheries are discussed.  相似文献   

20.
We describe the use of flume nets for passively, quantitatively, and nondestructively sampling fishes and macrocrustaceans on tidal marsh surfaces. We captured 3,765 organisms of 23 species in 118 samples using six such nets in a Virginia tidal freshwater marsh in 1984. Efficiency estimates for four common species of fishes range from 53 to 80%. Flume nets are most suited to the collection of long-term data and are particularly useful in elucidating seasonal trends in species composition and relative abundance. These nets are also useful in comparing different microhabitats within and between marshes. This method is most applicable to intertidal habitats with predictable lunar tides, including mud flats, mangrove swamps, and other wetlands.  相似文献   

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