Fauna of polyhaline subtidal marsh creeks in Southern New Jersey: Composition,abundance and biomass

Three polyhaline subtidal marsh creeks in southern New Jersey were sampled with weirs and seines to determine seasonal patterns of utilization by fishes and macroinvertebrates. Sixty-four species of fish, 13 invertebrates, and the diamondback terrapin were collected in 69 weir and 57 seine samples from April to November 1988 and April to October 1989. Average abundance, biomass, and faunal composition were strongly seasonal with greatest abundances during spring and summer, and peaks in May and August. Sixteen species were represented by all life-history stages, including the five most important species by combined ranks of percent frequency, mean abundance, and mean biomass. These five species were important during spring, summer, and fall and included the fishes Menidia menidia and Fundulus heteroclitus, the shrimps Palaemonetes vulgaris and Crangon septemspinosa, and the crab Callinectes sapidus. In addition, there were distinct seasonal assemblages of other species which utilized the creeks primarily as young-of-the-year. Importnat species in spring collections included the fishes Clupea harengus, Alosa aestivalis, Alosa pseudoharengus, Pollachius virens, and Urophysics regia, while Leiostomus xanthurus, Pomatomus saltatrix, Paralichthys dentatus, Mugil curema, and Strongylura marina were important in the summer. Fall samples were best characterized by declining abundances of summer species. Thus, subtidal marsh creeks in southern New Jersey appear to be valuable nurseries for a variety of species which spawn over the continental shelf, as well as one of the most important habitats for estuarine residents.     

Fish assemblage stability over fifty years in the Lake Pontchartrain estuary; Comparisons among habitats using canonical correspondence analysis

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.     

Assessing the use of saltmarsh flats by fish in a temperate Australian embayment

Little is known about the importance of salmarshes to juvenile and adult fishes in temperate Australia. We assessed diel and feeding patterns of fish inhabiting saltmarsh in a sheltered embayment along the coast of Victoria, Australia, between October 2002 and May 2003. The saltmarsh flat was generally only inundated during low-pressure weather systems (barometric pressure <1,013 hP). Fish were sampled over the saltmarsh flats using fyke and seine nets. A total of 2,047 individuals (10 species, including juveniles and adults) were caught.Atherinasoma microstoma was most abundant (fyke [F], μ=1.6 fish h⁻¹; seine [S], μ=28.2 fish shot⁻¹), followed byFavonigobius, lateralis (F: 0.5; S: 0.6),Galaxias maculatus (F: 0.1),Heteroclinus adelaide (F:<0.1),Kestratherina esox (F: <0.1; S: 1.6),Leptatherina presbyteroides (F: <0.1; S: 7.1) andTetractenos glaber (F: 1). Commercial species, includingAldrichetta forsteri (F: <0.1; S: 3.2),Sillaginodes punctata (F: <0.1; S: 0.9), andRhombosolea tapirina (F: 0.4), were commonly sampled. Variability in species richness or fish abundance was not explained by water temperature, salinity, depth, or barometric pressure. Significantly more species were sampled with the seine during nocturnal periods (p=0.002); fish abundance did not vary between diel periods, nor did fish abundance and species richness in fyke net samples. Diets of the most abundant species (A. microstoma, A. forsteri, andF. lateralis) were primarily composed of gammaridean amphipods and hemipteran insects. There was no correlation between fish diets and the composition of benthic invertebrates as sampled at 3 different regions of the saltmarsh flat. The saltmarsh flats in our study region are inhabited by several species normally associated with alternative habitat types such as seagrass, and the patterns of habitat use observed appear to be partially attributed to foraging behavior.     

Interannual and long-term variation in the nearshore fish community of the mesohaline Hudson River estuary

The detection of long-term shifts in species composition and spatial structuring of aquatic communities may be obscured by high levels of interannual variation. Estuarine fish communities are likely to exhibit high levels of variation owing to the influence of riverine forcing and the importance of anadromous and transient species, whose abundances may not be locally controlled. We describe patterns of interannual variation and long-term shifts in the nearshore fish community of the mesohaline Hudson River estuary based on 21 yr of beach seine sampling conducted annually between late August and mid November. Of the 60 species encountered, the most abundant were Atlantic silversides (Menidia menidia), striped bass (Morone saxatilis), white perch (Morone americana), American shad (Alosa sapidissima), and blueback herring (Alosa aestivalis). Relationships between annual community composition and seasonal flow and temperature regimes were examined with canonical correspondence analysis. Annual variation was most closely correlated with river flows in the 3-mo period preceding fish sampling, indicating a persistent effect of environmental conditions on community structure. Despite significant interannual variation in composition, longer-term trends in community structure were observed. These included declines in catch rates of freshwater and estuarine species and a dramatic increase in the catch of Atlantic silversides, an annual marine species. Associated with these changes were declines in community diversity and increased compositional variation. These results indicate that analyses of temporal changes in community structure need to account for the multiple time scales under which forcing factors and community composition vary.     

The influence of contiguous shoreline type, distance from shore, and vegetation biomass on nekton community structure in eelgrass beds

Three factors affecting the structure of nekton communities 9fishes and decapod crustaceans) in eelgrass beds were identified and evaluated: contiguous shoreline type, distance from shore, and macrophyte biomass. Throw traps (1 m²) were used to sample eelgrass nekton at seven locations in Great South Bay (New York, U.S.) along Fire Island National Seashore from May through October 1995. Abundances ofGobiosoma ginsburgi, Apeltes quadracus, andOpsanus tau were significantly higher in eelgrass beds adjacent to salt marshes.Menidia menidia, Syngnathus fuscus, Pseudopleuronectes americanus, andPalaemonetes pugio were significantly more abundant in eelgrass adjacent to beaches. Regression analyses indicated thatSyngnathus fuscus, Pseudopleuronectes americanus, andAnguilla rostrata abundances were positively related to eelgrass biomass, andApeltes quadracus andGobiosoma ginsburgi abundances were highest at moderate levels of macroalgae biomass. The distance of an eelgrass bed from shore was also important. Species generally associated with salt marshes (Fundulus heteroclitus, Cyprinodon variegatus, Lucania parva, andPalaemonetes pugio) were more abundant in eelgrass near the marsh shore. Abundances ofApeltes quadracus, Syngnathus fuscus, Menidia menidia, Hippolyte pleuracanthus, andCrangon septemspinosa increased with distance from the shoreline. Shoreline type, distance from shore, and macrophyte biomass appear to affect the abundance and distribution of some nekton species. The effect of shoreline type may be related to the distribution of macrophyte biomass; the biomasses of eelgrass and macroalgae were significantly higher along beach and marsh shorelines, respectively. Explaining within-habitat variability and identifying microhabitat preferences for nekton will aid in the proper design of future studies and habitat restoration efforts.     

Long-term declines in two apex predators,bull sharks (<Emphasis Type="Italic">Carcharhinus leucas</Emphasis>) and alligator gar (<Emphasis Type="Italic">Atractosteus spatula</Emphasis>), in Lake Pontchartrain,an oligohaline estuary in southeastern Louisiana

We analyzed historic and current fishery independent data to determine if the abundance of two apex predators, bull sharks (Carcharhinus leucas) and alligator gar (Atractosteus spatula), in Lake Pontchartrain had changed significantly over the last half century. Lake Pontchartrain is an environmentally degraded oligohaline estuary in southeastern Louisiana that has experienced considerable changes in fish assemblage composition over this interval. Using gillnet, beach seine, and trawl data collected during three time periods (1953–1955, 1977–1978, and 1996–2005), we analyzed trends in abundance forC. leucas andA. spatula using generalized linear models with a negative binomial error structure and a log link. Lake Pontchartrain data were divided into four spatial locations (northwest, northeast, southwest, southeast) since each region represents a unique combination of anthropogenic and natural influences that could affect catches. For each species and gear type, we produced log-likelihood profiles for the instantaneous rate of change in relative abundance through time. Raw catches were generally lower for both species in the later surveys.C. leucas were not captured in beach seines since the 1950s andA. spatula were rarely captured in trawls or seines since the 1970s. Likelihood profiles of changes in abundance forC. leucas andA. spatula showed very large declines in both species since 1953.C. leucas declined by 98.6% (95% CI: 73.4–99.9%) in gillnets and became functionally extirpated in beach seines with a decline of 99.9% (95% CI: 23–99.9%). Among all gears,C. leucas declined by the same rate as in gillnets. The decline inA. spatula was also large with a decrease of 98.6% (95% CI: 73.4–99.9%) in beach seines and a decline of 99.2% (95% CI: 54.8–99.9%) in trawls since 1953. Catches ofA. spatula in gillnets did not show a significant change over the study period. The continued decline of these two apex predators could seriously affect efforts to restore this degraded estuarine ecosystem.     

The abundance of fish larvae in estuaries: Within-tide variability at inlet and immigration

The larvae of winter spawning fishes immigrating through Beaufort Inlet into the Pamlico Sound estuarine system (North Carolina, United States) were passively sampled during 14 flood tides and nine of the following ebb tides. Five taxa were abundant in the catches. Pelagic species were represented by Atlantic menhaden, Brevoortia tyrannus. Nonpelagic taxa were represented by Atlantic croaker, Micropogonias undulatus, spot, Leiostomus xanthurus, pinfish, Lagodon rhomboides, and flatfishes of the genus Paralichthys. The sampling was continuous and the sample duration varied between 4 min and 32 min. The longest samples furnished the most accurate and precise estimates of the mean tidal abundance. Sampling 10 min each hour of the tide was the most efficient protocol for determining the mean tidal abundance. The abundance patterns was shown to differ according to the pelagic or nonpelagic behavior of the larvae. Analyses suggested the nonpelagic taxa rely on astronomical tides and vertical migrations synchronous with the direction of the tide flow to be transported upstream in the estuary. These larvae were not dependent upon the strength of the tide to penetrate the inlet. In contrast, menhaden larvae seemed to rely primarily on strong food tides to enter the estuarine area, probably because the vertical positioning of the species within the water column is not dependent upon the direction of the tide. However, if larvae were present outside of the inlet, strong flood tides indiscriminately brought pelagic and nonpelagic species into the estuary.     

Fish community ecology in an Altered River delta: Spatial patterns in species composition, life history strategies, and biomass

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.     

Diel Variation in the Pelagic Fish Assemblage in a Temperate Estuary

The pelagic fish assemblage within a temperate estuary was examined to determine if there were diel differences in species richness, total abundance, biomass, and species composition. These comparisons were made over both seasonal (January–December 1996) and annual (August–November 1995; August–December 1996) scales with pop net collections in a shallow (<2 m MLW) embayment within Great Bay in southern New Jersey, USA. In the complete year of sampling in 1996, more than 335,000 pelagic fish, representing 13 families (23 species), were collected during diel sampling with 12 species constituting over 99.9% of the total catch including Clupea harengus (84%), Menidia menidia (10%), and Anchoa mitchilli (4%). A detailed examination determined that nighttime species richness, total abundance and biomass may have been enhanced during some seasons by using artificial light. Diel variation in species composition was similar regardless of the use of the artificial light in all seasons but fall. Annual comparisons between 1995 and 1996 during late summer and fall found these results to be consistent. In general, these findings point out the importance of sampling during both day and night to understand the movement and abundance patterns of estuarine pelagic fishes and their ecological significance in temperate estuaries.     

Experimental evaluation of biases associated with sampling estuarine fishes with seines

Beach seines are widely used to estimate the density and species richness of fishes in estuaries. We evaluated the causes and extent of bias in estimates from seines using a series of field experiments in small estuaries in southern California, USA. Seining in spatially paired areas that were either enclosed by block nets or not, revealed that seines used without block nets und erestimated density by more than 4-fold and species richness by more than 2-fold relative to blocked areas. Seining in paired blocked areas with seines of two lengths revealed that net length affected estimates of density, but not species richness; a 7.6-m long seine produced 1.6-fold higher estimates of total density than did a 15.2-m long seine due to increased catches of demersal fishes, but not midwater species. Paired sampling in blocked areas also revealed that many fishes initially evaded capture by the seine. Estimates of density but not species richness were significantly higher in areas through which a seine was swept 5 times compared to once. This was due to higher catches of demersal fishes but not midwater fishes in areas seined 5 times. Repeated seining through blocked areas revealed that the vast majority (90% or more) of species and individuals of midwater fishes were captured within the first 5 sweeps, compared to only about 50% of the individuals of demersal species. A mark-recapture study in blocked areas revealed lower probabilities of capture for demersal species relative to midwater species.     

The value of salt marsh edge vs interior as a habitat for fish and decapod crustaceans in a Louisiana tidal marsh

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.     

Response of Lake Pontchartrain Fish Assemblages to Hurricanes Katrina and Rita

To assess possible impacts on Lake Pontchartrain fishes from the 2005 hurricanes, we compared trawl, beach seine, and gillnet collections taken before (2000–2003, 2005) and after (2006–2009) to determine if significant assemblage changes occurred. We also compared basic environmental variables to test for hurricane-related changes. Significant post-hurricane changes in fish assemblages occurred in trawl (analysis of similarity (ANOSIM), R?<?0.090, p?<?0.05) and beach seine (ANOSIM, R?<?0.120, p?<?0.05) collections across all seasons. Gillnet assemblages exhibited changes in only one season (ANOSIM, R?=?0.045, p?<?0.05). These consistently low global R values (all R?<?0.120) across all gears suggest only minor compositional changes in species. When peak abundance periods were compared for individual species, Gulf menhaden (Brevoortia patronus) declined in trawl collections after the hurricanes (Friedman's test, χ ²?=?6.00, p?=?0.014) but increased in gillnet collections (Friedman's test, χ ²?=?5.00, p?=?0.025). Hardhead catfish (Ariopsis felis) increased in trawl collections, but Gulf pipefish (Syngnathus scovelli), naked gobies (Gobiosoma bosc), and rough silverside (Membras martinica) all declined in beach seine samples and Atlantic croakers (Micropogonias undulatus), Spanish mackerel (Scomberomorus maculatus), and sand seatrout (Cynoscion arenarius) all declined in gillnet samples. In general, salinity increased and water clarity and dissolved oxygen decreased after the hurricanes. While the overall composition of Lake Pontchartrain fish assemblages remains stable, the significant decline of some species and changes in certain environmental variables are cause for concern. Future monitoring should determine if all elements of this estuary will recover from these impacts.     

Comparison of habitat use by estuarine fish assemblages in the Acadian and Virginian zoogeographic provinces

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.     

Mainstem and Backwater Fish Assemblages in the Tidal Caloosahatchee River: Implications for Freshwater Inflow Studies

Research strategies for investigating the freshwater-inflow requirements of estuarine fishes often integrate life-history information and correlative analyses of inflow and fish abundance. In tidal rivers, however, some fish have affinities for embayments, oxbows, and smaller tributaries, often referred to collectively as river “backwaters”. The objective of this study was to determine whether freshwater and estuarine fish assemblages differed between backwaters and the mainstem of the tidal Caloosahatchee River, a highly managed river system located in an urban setting in southwest Florida. Nonmetric multidimensional scaling of 21.3-m seine data revealed that fish assemblages did indeed differ between the backwater and mainstem habitats in each of three river sections. Univariate analyses identified species that differed in abundance between the habitats, which included ecologically and economically important fishes in the region. For example, striped mullet Mugil cephalus and pinfish Lagodon rhomboides were more abundant along the river's mainstem; common snook Centropomus undecimalis and bluegill Lepomis macrochirus were more abundant in the river's backwaters. For those species that were more abundant along the mainstem of the river or showed no difference, studies that measure changes in the distribution and abundance of these species with varying inflow along the mainstem of the river are justified. However, for species that were more abundant in backwater areas, geomorphological features should be considered in the design of studies that assess factors affecting fish use.     

Evaluating salt marsh restoration in Delaware Bay: Analysis of Fish response at former salt hay farms

In a continuing effort to monitor the fish response to marsh restoration (resumed tidal flow, creation of creeks), we compared qualitative and quantitative data on species richness, abundance, assemblage structure and growth between pre-restoration and post-restoration conditions at two former salt hay farms relative to a reference marsh in the mesohaline portion of Delaware Bay. The most extensive comparison, during April–November 1998, sampled fish populations in large marsh creeks with otter trawls and in small marsh creeks with weirs. Species richness and abundance increased dramatically after restoration. Subsequent comparisons indicated that fish size, assemblage structure, and growth of one of the dominant species,Micropogonias undulatus, was similar between reference and restored marshes 1 and 2 yr post-restoration. Total fish abundance and abundance of the dominant species was greater, often by an order of magnitude, in one of the older restored sites (2 yr post-restoration), while the other restored site (1 yr post-restoration) had values similar to the reference marsh. The success of the restoration at the time of this study suggests that return of the tidal flow and increased marsh area and edge in intertidal and subtidal creeks relative to the former salt hay farms contributed to the quick response of resident and transient young-of-the-year fishes.     

Distribution and abundance patterns of flatfishes in the Sado estuary, Portugal

The flatfish community of the Sado estuary was studied based on beam trawl catches in six sampling areas. Temperature and salinity were recorded during surveys and sediment composition was determined at each sampling area. A total of 12 species were identified (1 Bothidae, 1 Pleuronectidae, and 10 Soleidae).Dicologoglossa hexophthalma (Bennett 1831),Microchirus ocellatus (Linnaeus 1758), andSynaptura lusitanica (Capello 1868) were new records to this estuarine system.Monochirus hispidus Rafinesque, 1814, was the most abundant species (about 80% of the total individuals caught). Community structure reflected both spatial and temporal patterns. A longitudinal abundance pattern was noticed with some species much more abundant in outer estuarine areas, namelyM. hispidus, Arnoglossus laterna (Walbaum 1792), andBuglossidium luteum (Risso 1810), while others, such asSolea solea (Linnaeus 1758) andSolea senegalensis Kaup, 1858, presented the highest densities in inner areas. Besides temperature and salinity gradients, species distribution was also influenced by sediment composition. Seasonal variation was mainly determined by the different periods of juvenile peak abundance according to the species which emphasize the role of the estuary as a nursery ground for several flatfish species.     

Nekton use of salt marsh creeks in the upper Tejo estuary

The use of the Tejo estuary, Portugal, salt marsh creeks by nekton was examined based on sampling surveys with a fyke net from September 1998 until August 2001. From the 20 taxa (14 fish species, 5 decapod crustacean species, and 1 cephalopod species) identified in the studied creeks, 16 were regularly caught throughout the sampling period. The shrimpPalaemonetes varians was the most numerically abundant species in the creeks, while the biomass was dominated by the mulletLiza ramada. The nekton assemblage was mainly represented by marine-estuarine opportunist species, comprising 85% of the total. A high seasonality was detected on the species abundance patterns: the most abundant species (P. varians, Crangon crangon, L. ramada, Pomatoschistus microps, Syngnathus sp., andAnguilla anguilla) occurred throughout the sampling period,Sardina pilchardus, Dicentrarchus, labrax, andAtherina boyeri were particularly abundant in spring and summer, andEngraulis encrasicholus, Liza aurata, Gambusia holbrooki, Palaemon longirostris, andPalaemon serratus were most abundant in autumn and winter.L. ramada occurred in the tidal creeks in high numbers during neap tides, while the majority of the remaining taxa were most abundant during spring tides, suggesting a differential pattern of habitat use occording to species.     

Preliminary investigation of the effects of purse seine size on estimates of density and species richness of estuarine fishes

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.     

Use of tidal freshwater marshes by fishes and macrofaunal crustaceans along a marsh stream-order gradient

Fishes and invertebrate macrofauna (nekton) were sampled biweekly (July through October 1985) from the surface of tidal freshwater marshes. Samples were collected with flume nets at three different stream orders (orders 2, 3 and 4+) along a marsh stream order gradient. Twenty-five species of fishes (5,610 individuals, 17.072 kg preserved wet weight) representing 13 families, and three species of invertebrates (19,570 individuals, 13.026 kg preserved wet weight) were collected. The most abundant species were grass shrimp (Palaemonetes pugio), mummichogs (Fundulus heteroclitus), banded killifish (F. diaphanus), inland silversides (Menidia beryllina), and blue crabs (Callinectes sapidus). Invertebrate catches (mostly grass shrimp and blue crabs) were not significantly different among stations. Total numbers of fishes were significantly greater at both headwater (order 2) and main creek (order 3) stations than river (order 4+) stations, but catches of headwater and main creek stations were not significantly different. The relationship between marsh stream order and fish abundance may partly be related to the distribution of submerged aquatic vegetation (SAV) within marsh tidal creeks. Submerged aquatic vegetation decreases in abundance with increasing stream order. Some species may use SAV as a refuge from predators or as a foraging area during low tide when the marsh surface is inaccessible. The presence of SAV in tidal creeks may enhance the habitat value of adjacent marshes.     

Temporal and spatial patterns in abundance and diversity of fish assemblages in Elkhorn Slough,California

Assemblages of ichthyofauna of shallow inshore habitats along Californía’s central coast are described in terms of species composition, abundance, and life-style categories. A total of 22,334 fishes from 65 species and 27 families was collected with otter trawls at six sites in the main channel and tidal creeks of Elkhorn Slough, a tidal embayment and seasonal estuary, and two nearshore ocean stations in Monterey Bay during 44 months between August 1974 and June 1980. Greater than 90% of the catch comprised 10 species. The four dominant species,Cymatogaster aggregata, Leptocottus armatus, Phanerodon furcatus, andEmbiotoca jacksoni, occurred during most or all seasons and were classified as residents or partial residents. Several abundant species were marine immigrants that seasonally use the slough as spawning and nursery grounds; this resulted in higher abundance and species richness during summer. Species collected during winter largely were slough residents. Species compsosition and richness varied with distance from the slough entrance. The ocean assemblage was most different, and its similarity to other stations decreased progressively with distance inland and into the tidal creeks. During our study, 5,074 fishes were collected by beach seine in Bennett Slough, a remote shallow marsh basin adjacent to the entrance of Elkhorn Slough. Species richness was relatively low and three euryhaline species accounted for >80% of the total catch. The species assemblage was most similar to those at the tidal creek and most shallow stations of Elkhorn Slough. Resident species numerically dominated assemblages in Bennett Slough and the most inland areas of Elkhorn Slough. The high relative abundance of marine-related fishes (classified as marine, marine immigrant, and partial resident), entering Elkhorn Slough early in life or as spawning adults indicates the importance of this habitat to nearshore fish assemblages.