Anchoa Mitchilli Research Articles

Reproductive biology and egg mortality of bay anchovy, Anchoa mitchilli, in the Hudson River estuary

Bay anchovy, Anchoa mitchilli, is an ecologically important species in coastal systems, acting as predators on zooplankton while serving as prey for many birds and economically important finfish species. Despite the importance of bay anchovy, limited information exists concerning reproductive biology and egg mortality from the northern parts of its range. Spawner demographics suggested Hudson River fish were older and larger than reported elsewhere. Egg mortality rates were higher in the Hudson River than reported in more southerly systems. Differences in the reproductive biology of bay anchovy suggest either anthropogenic factors or latitudinal differences between populations exist and therefore should warrant further investigations on this species in the northern portions of its range

Fish biomass size spectra in Chesapeake Bay

Biomass size spectra of pelagic fish were modeled to describe community structure, estimate potential fish production, and delineate trophic relationships in Chesapeake Bay. Spectra were constructed from midwater trawl collections each year in April, June–August, and October 1995–2000. The size spectra were bimodal: the first spectral dome corresponded to small zooplanktivorous fish, primarily bay anchovyAnchoa mitchilli; the second dome consisted of larger fish from several feeding guilds that are supported by multiple prey-predator linkages. Annual production estimates of pelagic fish, derived from a mean production to biomass ratio, varied nearly three-fold, ranging from 162 × 109 kcal (125 × 103 tons) in 1996 to 457 × 109 kcal (352 × 103 tons) in 2000. Seasonally, the biomass level and mean individual sizes of fish in the first dome increased from April to October, while the biomass level of the second dome was relatively stable. Regionally, biomass levels in the second dome were higher than biomasses in the first dome for the upper and lower Bay, but were minimal in the middle Bay where seasonal and episodic hypoxia occurs. To test a benthic-pelagic coupling hypothesis that could explain the higher biomass in the second domes for the lower and upper Bay, a cyclic size-spectrum model was fit that included only species in the zooplanktivorous-piscivorous fish guilds. The mean, normalized slope equaled −1, indicating that zooplanktivorous fish may support piscivore production, but that a benthic-pelagic linkage is required to fully support fish production in the second dome. Interannual variability in slopes and intercepts of modeled size spectra was related to salinity, recruitment level of bay anchovy, and the primary axis of a correspondence analysis (salinity effect) on fish community structure. The spectral slope and intercept of normalized spectra were lowest in 1996, a near-record wet year. Results suggest that fish size spectra can be developed as useful indicators of ecosystem state and response to perturbations, especially if prey-predator relationships are explicitly represented.

Seasonal Variation in Fish Assemblages Within the Estuarine Portions of the Myakka and Peace Rivers, Southwest Florida

Juvenile and small adult fish were sampled monthly from 1996 to 2002 in the estuarine portions of the Myakka and Peace rivers, at the northern end of Charlotte Harbor (a relatively pristine estuarine system in southwest Florida). We provide a detailed description of the fish faunas in these areas, including seasonal assemblage structure. Seasonal cycles in assemblage structure were evident. Nearshore (to ~5 m) fish assemblages sampled by seine were separated into three main seasonal groups by cluster analysis (January-April, May-September, September-January). The ichthyofauna collected from deeper (≥1.8 m) areas by otter trawl formed two seasonal groups (June-October and November-March). Small schooling taxa such as Anchoa mitchilli, Menidia spp. and Eucinostomus spp. dominated seine catches, and variations in their abundances contributed greatly to dissimilarities between seasons, as did seasonal recruitment of young-of-the-year (YOY) estuary-dependent species such as Mugil cephalus, Lagodon rhomboides, Leiostomus xanthurus, and Bairdiella chrysoura. Estuarine residents (e.g., A. mitchilli and Trinectes maculatus) and YOY estuary-dependent species (e.g., Cynoscion arenarius and Menticirrhus americanus) were important in defining seasonal dissimilarities in fish assemblages from the trawled areas. Correlations between biotic patterns and environmental factors (water temperature, salinity, dissolved oxygen, precipitation, and river discharge) were relatively low, perhaps reflecting the euryhaline nature of the fish present and their intrinsic spawning periods. The present study provides a detailed description of temporal ichthyofaunal patterns in the estuarine portions of two tidal rivers in southwest Florida and provides a baseline with which future fish populations in this area can be compared.

Species-specific avoidance responses by blue crabs and fish to chronic and episodic hypoxia

Although both chronic and episodic hypoxia (O2<2 mg l−1) alter the distribution and abundance patterns of mobile animals within estuaries, recent evidence suggests that some animals may be more likely to remain within hypoxic or anoxic water than others, due to differences in physiological tolerance and movement responses to the dynamics of hypoxia. Determining avoidance responses to hypoxia is important for identifying the species most susceptible to the direct and indirect impacts of these events. A trawl survey was used to examine the avoidance responses of blue crabs (Callinectes sapidus) and several fish [pinfish (Lagodon rhomboides), spot (Leiostomus xanthurus), Atlantic croaker (Micropogonias undulatus), bay anchovy (Anchoa mitchilli), and paralichthid flounders (Paralichthys dentatus and Paralichthys lethostigma)] to chronic hypoxia and episodic hypoxic upwelling events in the Neuse River Estuary, North Carolina, USA. Trawl collections were made in three depth strata (3.0–4.6 m, 1.7–3.0 m, and 0.9–1.7 m depth) to quantify changes in the depth-specific distribution and abundance patterns of the six most common estuarine taxa during three dissolved oxygen conditions: normoxia, chronic hypoxia, and episodic hypoxic upwelling events. Pinfish, anchovies, blue crabs, and paralichthid flounder abundance increased with increasing dissolved oxygen concentrations. The two taxa most closely associated with the bottom (blue crabs and flounder) showed the strongest avoidance response to hypoxia. All taxa showed a stronger avoidance response to chronic hypoxia as compared to episodic hypoxic upwelling events. This difference is attributed to a reduced ability to avoid the rapid intrusions of hypoxic water during episodic events, or to increased risks of injury and predation in shallow refuge habitats, which may force some individuals back into hypoxic water.

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.

Reproductive characteristics of Japanese anchovy, Engraulis japonicus, in two bays of Japan

Abstract The reproductive characteristics of Japanese anchovy, Engraulis japonicus , were studied in Osaka Bay and Wakasa Bay, which are located on each side of Japan. The length of spawning season varied between two bays: 8 months (between April and November) in Osaka Bay and 4 months (between May and August) in Wakasa Bay. The seasonal temperature profiles suggested that not only the onset of spawning in both bays but also the end of spawning in Osaka Bay are highly temperature-dependent, and that the critical temperature is about 15 °C. On the other hand, Osaka Bay anchovy collected after July were composed of only small ones (smaller than 10.5 cm body length). A comparison of length–weight relationships revealed a better body condition of small Osaka Bay fish than Wakasa Bay fish. It is likely that the Japanese anchovy in Wakasa Bay ceases spawning as early as September in spite of a high temperature, due to their poor nutritional condition. Estimated spawning frequency ranged from 0.40 to 0.88 for Osaka Bay females and from 0.22 to 0.62 for Wakasa Bay females. These values indicate that the Japanese anchovy from two bays spawn at similar intervals of 1.13–2.50 and 1.61–4.55 days. The sizes at first maturity in Osaka Bay and Wakasa Bay were estimated as 7.38 and 8.53 cm, respectively. These reproductive characteristics are compared and contrasted with those described for the Japanese anchovy in Sagami Bay.

Effects of environmental variables upon the spatial and temporal structure of a fish community in a small, freshwater tributary of the Indian River Lagoon, Florida

A survey to monitor the distribution and abundance of fishes and selected invertebrates in the St. Sebastian River, Florida, was conducted from March 1999 through June 2000. We recorded a total of 181,854 individuals (representing 77 taxa) in 128 seine samples, and a single species, bay anchovy ( Anchoa mitchilli), accounted for 84.4% of the animals collected. Seasonally, the species compositions of spring and fall samples were most similar (percent similarity index (PSI)=95.3%), whereas those of summer and winter samples were most dissimilar (PSI=54.0%). The spring samples contained the greatest mean number of taxa (N0=59 taxa), and the fall samples had the fewest (N0=38). In addition, spring samples had the highest index of abundant taxa (Hill's N1=10.6) and summer samples had the lowest (Hill's N1=6.4), suggesting that approximately four more taxa were caught in greater abundance during spring than during summer. Community composition determined via canonical correspondence analysis revealed four assemblages: two seasonal groupings and two spatial groupings. Seasonal species assemblages were composed of a spring-summer group characterized by recruits of Irish pompano ( Diapterus auratus), snook ( Centropomus undecimalis), and naked goby ( Gobiosoma bosc), and a fall–winter group characterized by recruits of mullet ( Mugil cephalus), spot ( Leiostomus xanthurus), and croaker ( Micropogonias undulatus). Spatial groupings were composed of a north prong group which included taxa with estuarine affinities, and a south prong group which included taxa with freshwater affinities. Community composition recorded during periods of controlled water releases and during periods of naturally high-water-flow differed, primarily because abundant estuarine taxa disappeared during the controlled release. The loss of these taxa suggests that when large amounts of fresh water enter the system during relatively short periods of time, the estuarine component of the community does not have time to adjust to the rapid decrease in salinity.

Diet and Daily Ration of Bay Anchovy in the Hudson River, New York

AbstractAlong the U.S. Atlantic coast, bay anchovy Anchoa mitchilli form an important component of estuarine and coastal food webs. The combination of its trophic position and abundance makes the diet and ration of this fish important in the study of estuarine systems. Diet and ration have been studied in this species in the middle and southern parts of its range, but information is lacking for the northern parts. Therefore, this study sought to quantify the diets and daily ration of bay anchovy on a seasonal basis within the Hudson River, New York, estuary. Diets of bay anchovy in the Hudson River were similar to those reported in other parts of their range. Bay anchovy ate mostly copepods, barnacle Balanas spp. nauplii, and mysid shrimp Neomysis americana. Mysids were seasonally important, contributing up to 81% (by weight) for adult fish in August. No differences were detected in diet composition or prey length between age‐0 and adult bay anchovy within months, but age‐0 fish did have an estimated ration up to 2.7 times as high as that of adults. The adult ration ranged from 0.061 g per gram of body weight per day in May to 0.252 g g−1 d−1 in August. The ration of age‐0 fish ranged from 0.449 to 0.684 g g−1 d−1 in August and September. The daily ration of bay anchovy was higher than reported for the mid‐Chesapeake Bay. This was surprising, as the Hudson River fish are older and larger than those studied in the Chesapeake Bay and physiological allometry indicates that larger individuals should have lower specific rates than smaller ones. This counterintuitive finding suggests that food availability was higher in the Hudson River than in the Chesapeake Bay studies.

Distribution and transport of bay anchovy ( Anchoa mitchilli) eggs and larvae in Chesapeake Bay

Mechanisms and processes that influence small-scale depth distribution and dispersal of bay anchovy ( Anchoa mitchilli) early-life stages are linked to physical and biological conditions and to larval developmental stage. A combination of fixed-station sampling, an axial abundance survey, and environmental monitoring data was used to determine how wind, currents, time of day, physics, developmental stage, and prey and predator abundances interacted to affect the distribution and potential transport of eggs and larvae. Wind-forced circulation patterns altered the depth-specific physical conditions at a fixed station and significantly influenced organism distributions and potential transport. The pycnocline was an important physical feature that structured the depth distribution of the planktonic community: most bay anchovy early-life stages (77%), ctenophores (72%), copepod nauplii (>76%), and Acartia tonsa copepodites (69%) occurred above it. In contrast, 90% of sciaenid eggs, tentatively weakfish ( Cynoscion regalis), were found below the pycnocline in waters where dissolved oxygen concentrations were <2.0 mg l −1. The day–night cycle also influenced organism abundances and distributions. Observed diel periodicity in concentrations of bay anchovy and sciaenid eggs, and of bay anchovy larvae >6 mm, probably were consequences of nighttime spawning (eggs) and net evasion during the day (larvae). Diel periodicity in bay anchovy swimbladder inflation also was observed, indicating that larvae apparently migrate to surface waters at dusk to fill their swimbladders. Overall results suggest that wind-forced circulation patterns, below-pycnocline dissolved oxygen conditions, and diel changes in vertical distribution of larvae and their copepod prey have important implications for potential transport of bay anchovy early-life stages.

Production of bay anchovy Anchoa mitchilli in Chesapeake Bay: application of size-based theory

To evaluate and quantify productivity of abundant bay anchovy Anchoa mitchilli in the Chesapeake Bay ecosystem, daily stock biomass, production, and contribution to predators of young- of-the-year (YOY) bay anchovy were estimated from May 1995 to October 2000, based on tri-annual midwater trawl collections. Empirical allometric relationships were applied to develop size-depen- dent growth and mortality estimates. Estimated annual mean stock biomass of YOY bay anchovy was lowest in 1996 (17 × 10 3 metric tons (t) wet weight) and highest in 2000 (64 × 10 3 t). Estimated YOY production varied inter-annually by a factor of 4, ranging from 167 × 10 3 t in 1996 to 697 × 10 3 t in 2000. Daily stock biomass levels usually peaked in mid September, while daily production and con- tribution to predators peaked from mid July to late September. The annual production to mean bio- mass (P/ - B) ratio, which included the very productive larval stage, was high and ranged from 9.02 to 13.23. Analysis of environmental factors indicated that water temperature and dissolved oxygen were important controllers of growth rate. Inter-annual variability in length-specific mortality was inversely related to mean salinity in the summer and fall, suggesting that salinity controls abun- dances and spatial distributions of predators on bay anchovy. Results imply that annually variable hydrological conditions and secondary productivity may drive observed variability in recruitment and production of YOY bay anchovy by inducing small but decisive differences in growth and predation mortality on early-life stages.

Response of clupeid fish to ultrasound: a review

AbstractA number of species of clupeid fish, including blueback herring, American shad, and gulf menhaden, can detect and respond to ultrasonic sounds up to at least 180 kHz, whereas other clupeids, including bay anchovies and Spanish sardines, do not appear to detect sounds above about 4 kHz. Although the location for ultrasound detection has not been proven conclusively, there is a growing body of physiological, developmental, and anatomical evidence suggesting that one end organ of the inner ear, the utricle, is likely to be the detector. The utricle is a region of the inner ear that is very similar in all vertebrates studied to date, except for clupeid fish, where it is highly specialized. Behavioural studies of the responses of American shad to ultrasound demonstrate that they show a graded series of responses depending on the sound level and, to a lesser degree, on the frequency of the stimulus. Low-intensity stimuli elicit a non-directional movement of the fish, whereas somewhat higher sound levels elicit a directional movement away from the sound source. Still higher level sounds produce a “wild” chaotic movement of the fish. These responses do not occur until shad have developed the adult utricle that has a three-part sensory epithelium. We speculate that the response of the American shad (and, presumably, other clupeids that can detect ultrasound) to ultrasound evolved to help these species detect and avoid a major predator – echolocating cetaceans. As dolphins echolocate, the fish are able to hear the sound at over 100 m. If the dolphins detect the fish and come closer, the nature of the behavioural response of the fish changes in order to exploit different avoidance strategies and lower the chance of being eaten by the predators.

The diet of Chesapeake Bay striped bass in the late 1950s

AbstractThe diet of Chesapeake Bay striped bass, (Morone saxatilis) Walbaum, based on unpublished stomach content data from 916 fish collected between 1955 and 1959 was described. The diet in the late 1950s, quantified using an index of relative importance (IRI), was dominated by Atlantic menhaden, Brevoortia tyrannus Latrobe. Atlantic menhaden (66%) and bay anchovy, Anchoa mitchilli Valenciennes, (19%) had the highest IRI value overall. Small striped bass (&lt;600 mm total length) ate predominantly bay anchovy (IRI = 67%). Large striped bass (≥ 600 mm total length) ate predominantly Atlantic menhaden (IRI = 93%). Since 1990 small striped bass rely more on invertebrate prey and larger fish now rely more on small pelagic prey, such as bay anchovy and 0‐age clupeids. Analysis of historical data using current techniques provided a valuable tool for comparison to help in understanding the current striped bass predator–prey relationship in Chesapeake Bay.

Spatial and temporal variabilities of pelagic fish community structure and distribution in Chesapeake Bay, USA

Spatio-temporal variability in assemblages of pelagic fish in Chesapeake Bay from 1995 to 2000 was documented based on midwater trawl surveys conducted three times annually (April, July, and October). Numerically dominant pelagic and benthopelagic fishes, 30–256 mm TL, were included in the analysis. Species assemblages, diversity indices, biomass distributions, and a correspondence analysis revealed that physical forcing, primarily driven by freshwater input, shaped the structure of fish communities, both annually and regionally. But, seasonal succession occurred, with adults dominating in the spring and recruited juveniles dominating in the fall. The dominant species were bay anchovy ( Anchoa mitchilli), Atlantic croaker ( Micropogonias undulatus), white perch ( Morone americana), spot ( Leiostomus xanthurus), weakfish ( Cynoscion regalis), and Atlantic menhaden ( Brevoortia tyrannus). Young-of-the-year (YOY) and age-1+ fish were concentrated in different regions and different seasons. A correspondence analysis showed that salinity was the most important environmental factor explaining annual differences in the upbay–downbay gradients in fish community structure. In 1997–2000, following a surge of freshwater input and nutrient loadings in 1996, October baywide fish biomass increased by 120% and mean baywide dissolved oxygen (DO) concentration below the pycnocline in summer decreased by 30%. These interannual variabilities in baywide fish biomass and mean DO suggest a relationship between bay plankton productivity and fish production. Species composition shifted markedly in 1996 when YOY and age-1+ anadromous fishes became dominant, but returned progressively in subsequent years to the usual structure in which bay anchovy and other polyhaline species were dominant.

Vulnerability of marine forage fishes to piscivory: effects of prey behavior on susceptibility to attack and capture

We conducted a series of size-structured laboratory experiments to quantify and compare the susceptibility of several estuarine and marine forage fishes to attack and capture by piscivorous predators. Size-dependent estimates of capture success, handling time, and prey profitability were generated from single-species experiments offering bay anchovy, Atlantic menhaden, Atlantic silverside, and age-0 striped bass to piscivores. Bay anchovy and Atlantic menhaden were most susceptible to capture and yielded high profitability compared to Atlantic silverside and age-0 striped bass prey. Variation in capture success among forage species was particularly influential in generating disparate profitability functions. Although morphological differences among forage species contributed to variation in susceptibility to predation, behavioral analyses indicated that variable reaction distances to approaching predators and activity levels of prey may explain a large fraction of the observed differences in susceptibility. When several forage species were offered to predators simultaneously in larger enclosures, mortality was highest and occurred earlier for bay anchovy and Atlantic menhaden compared to other prey, which points to the strong influence of predator capture success on overall forage fish vulnerability. Our results demonstrate species-specific differences among forage fishes in the ability to avoid attack and capture by piscivores, and we conclude that the expression of antipredator behaviors contributes significantly to variation in forage species vulnerability.

The pattern and influence of low dissolved oxygen in the Patuxent River, a seasonally hypoxic estuary

Increased nutrient loadings have resulted in low dissolved oxygen (DO) concentrations in bottom waters of the Patuxent River, a tributary of Chesapeake Bay. We synthesize existing and newly collected data to examine spatial and temporal variation in bottom DO, the prevalence of hypoxia-induced mortality of fishes, the tolerance of Patuxent River biota to low DO, and the influence of bottom DO on the vertical distributions and spatial overlap of larval fish and fish eggs with their gelatinous predators and zooplankton prey. We use this information, as well as output from watershed-quality and water-quality models, to configure a spatially-explicit individual-based model to predict how chang- ing land use within the Patuxent watershed may affect survival of early life stages of summer breeding fishes through its effect on DO. Bottom waters in much of the mesohaline Patuxent River are below 50% DO saturation during summer. The system is characterized by high spatial and temporal variation in DO concentrations, and the current severity and extent of hypoxia are sufficient to alter distributions of organisms and trophic interactions in the river. Gelatinous zooplankton are among the most tolerant species of hypoxia, while several of the ecologically and economically important finfish are among the most sensitive. This variation in DO tolerances may make the Patuxent River, and similar estuaries, particularly susceptible to hypoxia-induced alterations in food web dynamics. Model simulations consistently predict high mortality of planktonic bay anchovy eggs (Anchoa mitchilli) under current DO, and increasing survival of fish eggs with increasing DO. Changes in land use that reduce nutrient loadings may either increase or decrease predation mortality of larval fish depending on the baseline DO conditions at any point in space and time. A precautionary approach towards fisheries and ecosystem management would recommend reducing nutrients to levels at which low oxygen effects on estuarine habitat are reduced and, where possible, eliminated.

Life history strategies of estuarine nekton: The role of marsh macrophytes, benthic microalgae, and phytoplankton in the trophic spectrum

The stable isotope signatures of marine transient and resident nekton were used to investigate trophic linkages between primary producers, marsh macrophytes, phytoplankton, benthic microalgae, and consumers within the Delaware Bay. A whole estuary approach was used to compare the flux of nutrients from primary producers to juvenile weakfish (Cynoscion regalis), bay anchovy (Anchoa mitchilli), and white perch (Morone americana) in open waters of the lower and upper Bay and adjacent salt marshes dominated by either Spartina alterniflora or Phragmites australis. Our results suggest that trophic linkages vary significantly along the salinity gradient, reflecting the transition from Spartina to Phragmites-dominated marshes, and secondarily, in a marsh to open water (offshore) direction at a given salinity. Superimposed on this pattern was a gradient in the proximate use of organic matter that depended on life history traits of each species ranging from pelagic to benthic in the order bay anchovy > weakfish > white perch.

Spatial and temporal variability in surf zone fish assemblages on the coast of northern New Jersey

The surf zone fish community along 15 km of northern New Jersey shoreline was sampled every 2 weeks by beach seine in the late summers and early falls of 1995–1999 in conjunction with monitoring of a beach nourishment project. Fifty-seven species representing 30 families were collected during the course of the study. Over 90% of each sampling period's catch was composed of five taxa or less. These taxa included Atlantic and rough silversides, Menidia menidia and Membras martinica, bluefish, Pomatomus saltatrix, and bay and striped anchovies, Anchoa mitchilli and Anchoa hepsetus, with the relative contributions of these taxa varying among years. Both bluefish and anchovy abundances varied by an order of magnitude among years. Size-frequency distributions indicate summer-spawned bluefish recruit to the surf zone habitat as two cohorts in August and October, respectively. Fish abundance and richness were greater at substations closest to rock groins. Taxonomic richness declined along with decreasing water temperature in the fall, but was not correlated with turbidity or tide stage (measured as minutes before or after low tide). The extensive sampling effort undertaken in this study, 2190 seine hauls that captured 295 868 fish, was examined in relation to the number and relative proportions of taxa collected. Species accumulation curves and percent similarity calculations were used to investigate the adequacy of a reduced sampling protocol in characterizing the taxonomic composition of the surf zone fish community. Calculations from eight complete sampling periods (84 seine hauls each) indicate that a reduction in sampling effort by one-half would have yielded on average 75% of the total number of species captured with approximately 85% similarity in relative species composition.

Seasonal changes of the pelagic fish assemblage in a temperate estuary

The pelagic (i.e. fishes that spend most of their time swimming and feeding in the water column) fish assemblage was examined within a temperate estuary to determine the seasonal patterns of abundance, biomass, richness, and species composition. These measures were related to abiotic measures including temperature, salinity, water transparency, and depth. Pelagic fish (n<350 000) were sampled weekly from August 1995 through December 1996 in Great Bay in New Jersey, USA, with a pop net (5 m diameter, 5 m length, 3 mm cod end). The most frequently occurring and abundant species included Clupea harengus (frequency of occurrence, 27.4%; abundance, 80.5% of total catch), Menidia menidia (frequency of occurrence, 83.5%; abundance, 10.6% of total catch), Anchoa mitchilli (frequency of occurrence, 66.5%; abundance, 6.0% of total catch), and Anchoa hepsetus (frequency of occurrence, 23.1%; abundance, 1.9% of total catch). There were strong seasonal trends in species richness, total abundance, and total biomass with peaks in spring, summer, and autumn, and very low values for these parameters in winter. In addition, there were five seasonal groupings within this pelagic fish assemblage that were primarily, but not exclusively, represented by young-of-the-year (age 0+). Winter (December–March) was represented by adult Gasterosteus aculeatus and age 1+ by M. menidia. Spring (April–early June) was overwhelmingly dominated by age 0+ C. harengus. Early summer (late June–early July) was relatively species rich and characterized by age 0+ of Brevoortia tyrannus, Pomatomus saltatrix, Alosa pseudoharengus, and age 1+ of A. mitchilli. Late summer (late July–August) remained relatively species rich and included mostly age 0+ of A. mitchilli, A. hepsetus, and M. menidia. Autumn (September–November) continued to have high catches of age 0+ of M. menidia and A. mitchilli. As expected for temperate estuaries, the best of the measured abiotic predictors of these groupings included temperature, salinity, and degree of change in temperature. However, timing of life history characteristics, such as location, and timing of reproduction and migration also influenced the seasonal occurrence of these pelagic species. The large abundance and biomass of a relatively few species, as observed in this study, are typical of estuaries, although this is one of the few studies that have focused solely on the pelagic component of estuarine fish assemblages.

Diurnal Fish Density in Relation to Seagrass and Drift Algae Cover in Tampa Bay, Florida

To assess the relationship between fish density and seagrass and drift algae cover on a small geographic scale, we collected quantitative data on fish and vegetation communities during daylight hours near the mouth of the Little Manatee River, Tampa Bay, Florida. In 1991, fish were collected with two types of sampling gear, a 120-m long-haul seine and 1-m2 roving dropnets. Seagrass and drift algae cover in each sampled area was categorized as none, sparse, moderate, or dense. Despite evident gear bias, sampling with both types of gear produced similar overall fish densities. Anchoa mitchilli, Lagodon rhomboides, and Syngnathus scovelli were the most abundant or frequently collected species, regardless of gear type. Densities of 12 of the 20 most abundant species were significantly related to either seagrass or drift algae cover or both. When fish density-vegetation cover relationships were significant, the greatest fish densities always occurred in either dense or moderate covers of seagrass or drift algae. Densities of L. rhomboides and Orthopristis chrysoptera were positively related to the level of seagrass and drift algae cover in samples collected with both types of gear, but significant relationships between the densities of other species and the level of vegetation cover generally varied by vegetation or gear type (or both). Density of Eucinostomus gula peaked in moderate seagrass and declined at higher and lower levels of cover. Total fish density was similar at sites dominated by either drift algae or seagrass but was significantly reduced at sites with little cover from either vegetation type. We conclude that both seagrass and drift algae are essential habitats for juvenile and small adult fish in Tampa Bay and that fish density on a small geographic scale is strongly related to vegetation cover. Drift algae may form an important alternate habitat for fish during winter months, when levels of seagrass cover are lowest and those of drift algae are highest.

The Effects of Season and Proximity to Fringing Mangroves on Seagrass-Associated Fish Communities in Charlotte Harbor, Florida

Little has been published on habitat use by fishes in Charlotte Harbor, one of Florida's largest-and still relatively pristine-estuaries. Multivariate analyses of data from 21.3-m-seine samples (1996-2000) were used to examine spatiotemporal patterns of seagrass habitat use by Charlotte Harbor fishes. Two habitats (mangrove-associated seagrass shorelines and offshore seagrass flats) were examined. Throughout the year, the mangrove-seagrass habitat was distinguished by Menidia spp., Mugil gyrans, Eucinostomus harengulus, and Floridichthys carpio, and the offshore seagrass flats habitat was distinguished by Bairdiella chrysoura, Orthopristis chrysoptera, and Cynoscion nebulosus. The dry season (Dec.-May) was distinguished by Lagodon rhomboides, Leiostomus xanthurus, and O. chrysoptera in both habitats and by Mugil cephalus in the mangrove-seagrass habitat. The wet season (June-Nov.) was distinguished by Lucania parva, F. carpio, and Fundulus grandis in the mangrove-seagrass habitat and by Eucinostomus gula, Microgobius gulosus, C. nebulosus, and E. harengulus in the offshore seagrass flats habitat. Eucinostomus spp., Anchoa mitchilli, and Strongylura notata were abundant in both habitats during the wet season. In general, many species were collected in both habitats and were widely distributed in the estuary. Various combinations of four environmental variables (i.e., water temperature, salinity, dissolved oxygen, water depth) and their coefficients of variation were well correlated with the biotic community patterns. These results show that different fish communities use different seagrass habitats in Charlotte Harbor, depending on the season and the proximity of the seagrasses to fringing mangroves.