The Mississippi River is one of the world's 10 largest rivers, with average freshwater discharge ... more The Mississippi River is one of the world's 10 largest rivers, with average freshwater discharge into the northern Gulf of Mexico (GOM) of 380 km 3 year − 1 . In the northern GOM, anthropogenic nitrogen is primarily derived from agricultural fertilizer and delivered via the Mississippi River. The general consensus is that hypoxia in the northern Gulf of Mexico is caused primarily by algal production stimulated by excess nitrogen delivered from the Mississippi-Atchafalaya River Basin and seasonal vertical stratification of incoming stream flow and Gulf waters, which restricts replenishment of oxygen from the atmosphere. In this paper, we review the controversial aspects of the largely nutrient-centric view of the hypoxic region, and introduce the role of non-riverine organic matter inputs as other oxygen-consuming mechanisms. Similarly, we discuss non-nutrient physically-controlled impacts of freshwater stratification as an alternative mechanism for controlling in part, the seasonality of hypoxia. We then explore why hypoxia in this dynamic river-dominated margin (RiOMar) is not comparable to many of the other traditional estuarine systems (e.g., Chesapeake Bay, Baltic Sea, and Long Island Sound). The presence of mobile muds and the proximity of the Mississippi Canyon are discussed as possible reasons for the amelioration of hypoxia (e.g., healthy fisheries) in this region. The most recent prediction of hypoxia area for 2009, using the current nutrient-centric models, failed due to the limited scope of these simple models and the complexity of this system. Predictive models should not be the main driver for management decisions. We postulate that a better management plan for this region can only be reached through a more comprehensive understanding of this RiOMar system-not just more information on river fluxes (e.g., nutrients) and coastal hypoxia monitoring programs.
We conducted hydroacoustic, gill-net, and push trawl surveys to quantify changes in habitatspecif... more We conducted hydroacoustic, gill-net, and push trawl surveys to quantify changes in habitatspecific fish size and biomass in shallow (,2-m) estuarine waters of Barataria Bay, Louisiana, in order to evaluate essential fish habitat. Surveys were conducted monthly between June 2003 and May 2004 among regions located along a north-south salinity gradient. The fish length distributions derived from the gill-net and push trawl catches showed moderate concordance with the measured target strength distributions, indicating that our integrated approach more effectively characterized the fish community than using only a single gear type would have. Acoustic estimates showed that biomass was highest during fall (mean 6 SE; 2.30 6 0.27 g/m 3 ) and next highest in spring (1.49 6 0.20 g/m 3 ), with relatively low biomass during summer (0.70 6 0.14 g/m 3 ) and winter (0.86 6 0.14 g/m 3 ); pelagic fish biomass from nets was low during winter (53.9 6 14.9 grams per unit effort [gpue]) but relatively high in fall (846.1 6 207.2 gpue), spring (774.3 6 175.5 gpue), and summer (620.3 6 140.7 gpue). Oyster habitat supported a greater biomass of pelagic fish (acoustic survey: 1.54 6 0.15 g/m 3 ; gill-net survey: 467.3 6 81.0 gpue) than soft-bottom habitat (acoustic: 0.94 6 0.11 g/m 3 ; gill-net: 315.2 6 54.8 gpue). Among regions, the greatest biomass of pelagic fish was observed at polyhaline stations (acoustic: 1.78 6 0.19 g/m 3 ; gill-net: 654.3 6 136.5 gpue), followed by mesohaline (acoustic: 1.18 6 0.15 g/m 3 ; gill-net: 378.5 6 79.1 gpue) and oligohaline stations (acoustic: 0.82 6 0.12 g/m 3 ; gill-net: 228.3 6 50.2 gpue). Gill-net biomass was linearly related to the acoustic biomass estimates of small pelagic fish. The complementary, multigear approach proved to be useful in evaluating habitat use and may be particularly helpful in identifying and monitoring ecosystem reference points to evaluate change and in standardizing ecosystem-based assessment approaches.
... Patricia Sánchez-Gil a , Corresponding Author Contact Information , E-mail The Corresponding ... more ... Patricia Sánchez-Gil a , Corresponding Author Contact Information , E-mail The Corresponding Author , Alejandro Yáñez-Arancibia b , E-mail The Corresponding Author , Margarito Tapia a , E-mail The Corresponding Author , John W. Day c , E-mail The Corresponding Author ...
Eos, Transactions American Geophysical Union, 2010
Coastal water hypoxia, where dissolved oxygen is less than 2 milligrams per liter, is a global en... more Coastal water hypoxia, where dissolved oxygen is less than 2 milligrams per liter, is a global environmental problem [e.g., Diaz and Rosenberg, 2008]. It is largely associated with eutrophication, whereby nutrient inputs (nitrogen and phosphorous) to coastal waters lead to elevated primary production and accelerated rates of microbial respiration, which results in oxygen depletion. Despite more than 25 years of monitoring [Rabalais et al., 2007] (see also Figure S1 in the online supplement to this Eos issue (http://www.agu.org/eos_elec/)), the relative importance of the various processes that control hypoxia in bottom waters of the northern Gulf of Mexico (GOM)—in particular, those beyond the direct influence of river plumes [Dagg et al., 2007; Bianchi et al., 2008, 2010, and references therein]—remains uncertain. For example, a prediction last June pronounced that the 2009 hypoxic area would be the largest on record (˜23,000 square kilometers; see http://www.gulfhypoxia.net/Research/Shelfwide%20Cruises/2009/Files/2009_Hypoxia_Forecast.pdf). However, the most recent annual surveys estimated its size at 8000 square kilometers, only 35% of that predicted. This occurred in the absence of a significant hurricane impact on this margin in 2009—hurricanes tend to dissipate hypoxia.
Production of bay anchovy Anchoa mitchilli is highest in the larval and juvenile stages. The inte... more Production of bay anchovy Anchoa mitchilli is highest in the larval and juvenile stages. The interplay between vital rates, stage durations, prey resources, and anchovy abundance ultimately determines the relative magnitude of recruitment (which in the model varies by about three-fold) and of stage-specific production. Changes in adult seasonal spawning patterns that increase the number of larval survivors result in only a slight increase in overall production due to density-dependent decreases in growth rates of later life stages. Bay anchovy in the mid-Chesapeake Bay may reach a compensatory threshold during late summer-autumn as fish growth is affected by competition for food resources. Density dependence in the population is evident in the relationships between spawner-recruit, size-recruit, and production of larval or juvenile to young-of-the-year life stages. Density-dependent growth acts differentially upon the early life stage that exceeds the compensatory threshold in any given year, due either to environmental variability or population size, or both. This could explain partially the relatively low recruitment variability observed for this anchovy.
2009. Simulating the effects of side-aspect fish orientation on acoustic biomass estimates. -ICES... more 2009. Simulating the effects of side-aspect fish orientation on acoustic biomass estimates. -ICES Journal of Marine Science, 66: 000 -000.
Vol. 185: 133-146.1999 MARINE ECOLOGY PROGRESS SERIES Mar Ecol Prog Ser Published August 20 ... J... more Vol. 185: 133-146.1999 MARINE ECOLOGY PROGRESS SERIES Mar Ecol Prog Ser Published August 20 ... James H. Cowan Jr'l*, Kenneth A. ~ ose ~ , ... Edward D. Houde3, Shyh-Bin Wangl, John Young4 ... 'University of South Alabama, Dauphin Island Sea Lab, 101 ...
Ovaries of red snapper Lutjanus campechanus were examined histologically to determine rates of oo... more Ovaries of red snapper Lutjanus campechanus were examined histologically to determine rates of oocyte maturation, diel spawning periodicity and whether lunar cycle influenced spawning rhythm. Hydration of red snapper oocytes began during the mid-morning hours; c. 5 h was necessary for oocytes to become fully hydrated and ovulation occurred no more than 5 h after oocytes attained full hydration. Appearance of fresh postovulatory follicles after 1330 hours and the absence of hydrated oocytes after 1830 hours signified that red snapper spawning occurred during this 5 h period. In addition, evidence of a peak in spawning was seen near 1600 hours. Postovulatory follicles degenerated within a 24 h time period. A lunar spawning cycle was not evident.
Bay anchovy Anchoa mitichilli population dynamics in the mesohaline region of Chesapeake Bay are ... more Bay anchovy Anchoa mitichilli population dynamics in the mesohaline region of Chesapeake Bay are descnbed and analyzed with an individual-based model. The model begins with spawning by individual females and simulates the daily growth and mortality of each female's progeny as they develop through the egg, yolk-sac larva, (feeding) larval, juvenile, and adult Stages in a single, well-mixed compartment. The model runs for 50 yr. Eggs and yolk-sac larvae develop at rates dependent on temperature, and die at fixed daily rates. All feeding individuals (larvae, juveniles, and adults) consume zooplankton and grow according to defined bioenergetics relationships. Encounters, attacks and captures of prey, and the probability that feeding individuals will die are treated stochastically using Monte Carlo techniques Net immigration of spawners into the modeiied box each year is simulated in 2 ways: multiplier of survivors and as a constant number. Model predictions of stage-specific growth and survival rates, and diets were sirnilar for multiplier and constant immigration simulations, and both were similar to observed values. Density-dependent growth of larvae and juveniles led to a negative relationship between mean length and number of recruits and to density-dependent survival of larvae and juveniles. Density-dependent growth was due to anchovy consumption reducing prey densities, and not due to temperature effects on numbers surviving and growth. First-year su,mivorship was lower in years of high egg production than in years of low egg production. Larval growth and survival rates were positively related to recruitment, but the reverse was true for juveniles. Years of high recruitment were not years of high first-feeder production, but rather were years of high larval survival. The model simulates a single spatial box with a forced net immigration of spawners and assumes density-independent spawning and mortality processes. The model quantifies the basic processes leading to recruitinent of bay anchovy and Sets the Stage to explore potential compensatory responses of anchovy. KEY WORDS: Bay anchovy . Chesapeake Bay . Population dynamics . Individual-based model O Inter-Research 1999 Resale of full article not perrnitted T = ßo -ßlcos(0.0172 day) -ß,sin(0.0172 day) (1)
Chronographic tethering devices were used to investigate the effects of habitat type, prey type, ... more Chronographic tethering devices were used to investigate the effects of habitat type, prey type, tidal state and time of day on predation in the Damariscotta River, Maine (43°57' N, 69°3 5' W) and in St. Joseph Bay, Florida (30°00' N, 85°30' W). Traditional tethering data (presence/ absence) revealed that there were significant differences in the number of predation events between sites (p = 0.037) with more predation events occurring at the St. Joseph Bay site. In addition, there were significant differences in predation between prey types (p < 0.001). Regardless of site, significantly more 'soft' bodied prey types (shrimp) were removed than 'hard' bodied prey types (brachyuran crabs). Separating the data by site revealed that there were significant differences between habitat types (seagrass interior, seagrass edge and unvegetated substrate) at the Damariscotta River site (p = 0.027), but not at the St. Joseph Bay site (p = 0.943). Using the time to predation recorded on the chronographic tethering devices, survival times were calculated. Based on prey survival time, comparisons were made between predation intensity in monotypic stands of the seagrasses Zostera marina L. (Damariscotta River) and Thalassia testudinum (St. Joseph Bay), and bare substrate and the grass edge at both study sites. There were no significant differences in survival time between habitats at the Damariscotta River site (p = 0874). However, the average prey survival time was significantly less for the seagrass bed edge at the St. Joseph Bay site than for the T. testudinum bed interior and unvegetated habitats (p = 0.019). In addition, the time to predation allowed the effect of tidal state and light versus dark on predation to be assessed. While neither tidal state nor light versus dark had any effect on predation at the Damariscotta River site (p = 0.096 and p = 0.481 respectively), at the St. Joseph Bay site, there were significantly more predation events during the day than at night (p < 0.001), regardless of tidal state (p = 0.664). The use of the chronographic tethering devices revealed that while there was no significant difference in the number of predation events or rate of predation at the St. Joseph Bay site, the interface (i.e. 'edge') between bare or unvegetated substrates and seagrass assemblages was associated with the highest predation risks.
Proceedings of The National Academy of Sciences, 2008
We used two high profile articles as cases to demonstrate that use of fishery landings data can l... more We used two high profile articles as cases to demonstrate that use of fishery landings data can lead to faulty interpretations about the condition of fishery ecosystems. One case uses the mean trophic level index and its changes, and the other uses estimates of fishery collapses. In earlier analyses by other authors, marine ecosystems in the Gulf of Mexico (GOM) and U.S. Atlantic Ocean south of Chesapeake Bay were deemed to be severely overfished and the food webs badly deteriorated using these criteria. In our reanalyses, the low mean trophic level index for the GOM actually resulted from large catches of two groups of low trophic level species, menhaden and shrimp, and the mean trophic level was slowly increasing rather than decreasing. Commercial targeting and high landings of shrimps and menhaden, especially in the GOM, drove the index as previously calculated. Reanalyses of fishery collapses incorporating criteria that included targeting, variability in fishing effort, and market forces discovered many false cases of collapse based simply upon a decline of catches to 10% of previous maximum levels. Consequently, we suggest that the low mean trophic level index calculated in the earlier article for the GOM did not reflect the overall condition of the fishery ecosystem, and that the 10% rule for collapse should not be interpreted out of context in the GOM or elsewhere. In both cases, problems lay in the assumption that commercial landings data alone adequately reflect the fish populations and communities. landings data ͉ mean trophic level index
Factors that affect sunrival and growth of bay anchovy Anchoa mitchilli larvae in the Chesapeake ... more Factors that affect sunrival and growth of bay anchovy Anchoa mitchilli larvae in the Chesapeake Bay, USA, were studied in situ in 3.2 m3 mesocosm enclosures. Experiments tested the effects of variable prey level and anchovy egg and larvae densities on growth and survival of larvae to at least 16 d post-hatching. Eggs were stocked at 100 m-3 with microzooplankton (< 150 ~m ) prey added at nominal levels of 50, 500, 1500, or 5000 1-l. In a second series of experiments, eggs were stocked at 10, 100, or 2 1000 m-3 and prey level was maintained near 500 1-l. Larvae growth was rapid (0.39 to 0.63 mm d-l), even at the lowest prey levels and highest initial egg stocking densities. Growth rates tended to decrease as egg density increased. Instantaneous mortality rates were high (0.08 to 0.23 d-l) but lower than those reported for bay anchovy larvae from estuaries with gelatinous zooplankton and fish predators present. Highest mortality unexpectedly occurred in mesocosms with the highest prey level and lowest mortality occurred in enclosures with the highest initial egg stocking densities. Relative production decreased as prey level increased but Gw:Z ratios were above unity for all except the highest prey level experiment. In the stocking density experiments, highest production occurred in enclosures with the lowest initial egg densities. Some unexpected results may have been induced by effects of the mesocosm enclosures.
Low dissolved oxygen concentrations can affect growth rates, distribut~ons and predatorprey inter... more Low dissolved oxygen concentrations can affect growth rates, distribut~ons and predatorprey interactions of aquatic organisms. Each of these potential effects is generally examined separately in laboratory and field studies. As a result, it is often difficult to determine the net influence of low oxygen on survival and which individual effect of low oxygen contributes most to mortality. We used a spatially explicit individual-based predation model to predict how effects of low dissolved oxygen on vertical distributions, predation rates, and larval growth combine to influence survival of estuarine fish larvae in a water colun~n where the subpycnocline (bottom) and pycnocline layers are subject to oxygen depletion We analyzed simulations involving 3 predators (scyphomedusae based on Chrysaora quinquecirrha, and fish that were relatively sensitive to, or tolerant of, low dissolved oxygen), water columns that dlffered in the relative thickness of the subpycnocline layer, and bottom dissolved oxygen concentrations ranging from < l mg 1-' to no-effect concentrations. The effect of dissolved oxygen on larval and predator vertical &stributions, predator capture success and larval growth rates In simulations were based on previous experiments and field sampling in the Patuxent River, a tributary of the Chesapeake Bay. USA. Simulations indicated that bottom dissolved oxygen can strongly affect predation mortality of fish larvae. Thus, there is the potential for eutrophication to have a large effect on larval fish survival, and possibly recruitment, even in the absence of direct effects of low oxygen-induced mortality of larvae or the effects of nutrient enrichment on the abundance of larval prey or predators. Depending on predator characteristics and water column depth, lowest larval survival occurred when oxygen concentrations were either < l mg I-' or sufficiently high that oxygen concentratlon had no effect on distributions or capture rates; hlghest survival generally occurred with hypoxic bottom layers (1 to 2 mg 1-' dissolved oxygen). Bottom dissolved oxygen concentration also strongly affected the relative importance of fish and sea nettle predation in simulations that included both types of predators. Differences among predator types had important consequences for the magnitude and location of predation. Bottom-layer oxygen depletion shifted the focus of trophic interactions into the pycnocline and surface layers. Additional simulations indicated that distributional and capture success effects on larval survival were more important than growth rate effects, and that the direction of effects depended on the predator type and dissolved oxygen concentrations. Limitations of the model as well as implications of results for efforts to reduce nutrient loadings into estuaries are discussed.
The relative predation potentials on ichthyoplankton of the scyphomedusa Chrysaora quinquecjrrha,... more The relative predation potentials on ichthyoplankton of the scyphomedusa Chrysaora quinquecjrrha, the ctenophore Mnemiops~s leidyi and the bay anchovy Anchoa mjtchllli from Chesapeake Bay, USA, were estimated in 3.2 m3 in situ mesocosm enclosures and in 1.0 m3 laboratory tanks. For all 3 predators, averaged predation mortality (d-') and volume-specific clearance rates (1 d-' ml-') were higher and less variable when bay anchovy eggs were prey than when goby Gobiosoma bosci larvae 13.0 to ca 10.0 mm standard length (SL)] were prey. The smallest larvae (3.0 to <5.5 mm SL) were more vulnerable than eggs or larger larvae. Averaged mortality rates per scyphomedusa (0.78 and 0.32 d-' on eggs and larvae respectively) were 7 times higher than those per ctenophore (0.11 and 0.04 d-l), and almost 2 times higher than those per bay anchovy (0.37 and 0.21 d-l). However, volume-specific clearance rates by the relatively small bay anchovy predators were higher (ca 500 1 d-' ml-l) than those of the gelatinous predators. The volume-specific clearance rates of the ctenophore and medusa were only 4 and 7 % respectively of that for the anchovy. Combined species results suggest that these predators may consume 20 to 40 % daily of the fish eggs and larvae in mid-Chesapeake Bay. The scyphomedusa potentially is the most important predator on summer ichthyoplankton due to its overall abundance, high clearance rates and temporal CO-occurrence with vulnerable life stages of fish. 0 Inter-Research 1993
Journal of Experimental Marine Biology and Ecology, 2010
Water control structures (WCSs) installed to regulate water levels can alter both the hydrology a... more Water control structures (WCSs) installed to regulate water levels can alter both the hydrology and ecology of salt marshes. WCSs are thought to limit nekton ingress into, and egress from, managed marshes. Slots (vertical openings that span most of the water column) incorporated into WCSs are thought to facilitate nekton passage through structures, but little research has directly examined how slot size affects passage rates. We used dual-frequency identification sonar (DIDSON) acoustic imaging to examine the effect of slot width (10, 15, 30, or 60 cm), tidal cycle, diel period, and season on nekton passage at a WCS located in a tidal salt marsh canal. Few individuals (total numbers and relative percentages) used the slots for passage through the structure during any stage of the tidal cycle, day or night, or seasonally. The number and size of migrants were similar for all four slot sizes examined. Nekton used the slots most often on flood tides to access the managed marsh (i.e., swim inside), primarily at night. Individuals entering the managed marsh were larger than those observed leaving the managed marsh. Whereas the majority of migrants were observed during winter months, season did not affect nekton passage in our study. Acoustic imaging allowed a unique and comprehensive evaluation of nekton passage by permitting an examination of factors such as swimming direction and proportion of migrants that are unobservable with other sampling techniques.
The ability to estimate fish abundance accurately over a particular habitat is contingent upon th... more The ability to estimate fish abundance accurately over a particular habitat is contingent upon the use of appropriate sampling methods. The objectives of this study were to compare the catch per unit area (A), length-specific bias, and relative catchability (q-ratio) of four different gear types for sampling red snapper (Lutjanus campechanus) over natural low-relief reef habitats on the inner continental shelf of the northern Gulf of Mexico. Specifically, our goal was to assess the overall performance of a standard otter trawl, a small fish trap, a chevron trap, and a stationary 4-camera underwater video array during six quarterly sampling cruises performed in 2004 and 2005. The sizes of snapper captured by trawls ranged from 30 to 250 mm total length (TL) (ages 0 and 1 yr). Trawls captured the most red snapper per unit area and had q-ratios of 3:1 to 5:1 relative to small fish traps for juvenile red snapper. The chevron trap collected the second highest number of red snapper and proved most useful at collecting red snapper from 150 to 440 mm TL (ages 1–5 yr). The q-ratio of the chevron trap relative to the underwater video array was approximately 3:1. Our comparison demonstrated the chevron trap is most effective for sampling adults, while trawls were the most effective gear for sampling age-0 yr fish.
Differences in the biological and ecological strategies of two tropical flatfishes, Etropus cross... more Differences in the biological and ecological strategies of two tropical flatfishes, Etropus crossotus (fringed flounder) and Citharichthys spilopterus (bay whiff) are discussed. The comparative analysis was based on the seasonal distribution of relative abundance of the two species and flatfish movements utilizing estuarine plume influenced areas as part of their life cycles. Growth parameters of the von Bertalanffy equation and recruitment were estimated (FISAT software) to compare life cycle patterns. The recruitment patterns illustrate the key difference between “estuarine-dependent” and “estuarine-related” nekton strategies. Both species have a short life cycle with a continuous recruitment activity. E. crossotus is an estuarine-related species, with two recruitment pulses (winter frontal season), in the estuarine plume on the shelf. C. spilopterus is an estuarine-dependent species, with a main recruitment pulse during the rainy season in the estuarine plume, and a residual secondary pulse inside the adjacent estuarine system (Terminos Lagoon). The results show that the ecological success of these tropical coastal marine flatfish, with similar biological patterns, is based upon the sequential use (in time and space) of estuarine plume influenced habitats, suggesting that fish migration to shallow waters is related to food availability changes as a strategy towards optimum recruitment.
The Mississippi River is one of the world's 10 largest rivers, with average freshwater discharge ... more The Mississippi River is one of the world's 10 largest rivers, with average freshwater discharge into the northern Gulf of Mexico (GOM) of 380 km 3 year − 1 . In the northern GOM, anthropogenic nitrogen is primarily derived from agricultural fertilizer and delivered via the Mississippi River. The general consensus is that hypoxia in the northern Gulf of Mexico is caused primarily by algal production stimulated by excess nitrogen delivered from the Mississippi-Atchafalaya River Basin and seasonal vertical stratification of incoming stream flow and Gulf waters, which restricts replenishment of oxygen from the atmosphere. In this paper, we review the controversial aspects of the largely nutrient-centric view of the hypoxic region, and introduce the role of non-riverine organic matter inputs as other oxygen-consuming mechanisms. Similarly, we discuss non-nutrient physically-controlled impacts of freshwater stratification as an alternative mechanism for controlling in part, the seasonality of hypoxia. We then explore why hypoxia in this dynamic river-dominated margin (RiOMar) is not comparable to many of the other traditional estuarine systems (e.g., Chesapeake Bay, Baltic Sea, and Long Island Sound). The presence of mobile muds and the proximity of the Mississippi Canyon are discussed as possible reasons for the amelioration of hypoxia (e.g., healthy fisheries) in this region. The most recent prediction of hypoxia area for 2009, using the current nutrient-centric models, failed due to the limited scope of these simple models and the complexity of this system. Predictive models should not be the main driver for management decisions. We postulate that a better management plan for this region can only be reached through a more comprehensive understanding of this RiOMar system-not just more information on river fluxes (e.g., nutrients) and coastal hypoxia monitoring programs.
We conducted hydroacoustic, gill-net, and push trawl surveys to quantify changes in habitatspecif... more We conducted hydroacoustic, gill-net, and push trawl surveys to quantify changes in habitatspecific fish size and biomass in shallow (,2-m) estuarine waters of Barataria Bay, Louisiana, in order to evaluate essential fish habitat. Surveys were conducted monthly between June 2003 and May 2004 among regions located along a north-south salinity gradient. The fish length distributions derived from the gill-net and push trawl catches showed moderate concordance with the measured target strength distributions, indicating that our integrated approach more effectively characterized the fish community than using only a single gear type would have. Acoustic estimates showed that biomass was highest during fall (mean 6 SE; 2.30 6 0.27 g/m 3 ) and next highest in spring (1.49 6 0.20 g/m 3 ), with relatively low biomass during summer (0.70 6 0.14 g/m 3 ) and winter (0.86 6 0.14 g/m 3 ); pelagic fish biomass from nets was low during winter (53.9 6 14.9 grams per unit effort [gpue]) but relatively high in fall (846.1 6 207.2 gpue), spring (774.3 6 175.5 gpue), and summer (620.3 6 140.7 gpue). Oyster habitat supported a greater biomass of pelagic fish (acoustic survey: 1.54 6 0.15 g/m 3 ; gill-net survey: 467.3 6 81.0 gpue) than soft-bottom habitat (acoustic: 0.94 6 0.11 g/m 3 ; gill-net: 315.2 6 54.8 gpue). Among regions, the greatest biomass of pelagic fish was observed at polyhaline stations (acoustic: 1.78 6 0.19 g/m 3 ; gill-net: 654.3 6 136.5 gpue), followed by mesohaline (acoustic: 1.18 6 0.15 g/m 3 ; gill-net: 378.5 6 79.1 gpue) and oligohaline stations (acoustic: 0.82 6 0.12 g/m 3 ; gill-net: 228.3 6 50.2 gpue). Gill-net biomass was linearly related to the acoustic biomass estimates of small pelagic fish. The complementary, multigear approach proved to be useful in evaluating habitat use and may be particularly helpful in identifying and monitoring ecosystem reference points to evaluate change and in standardizing ecosystem-based assessment approaches.
... Patricia Sánchez-Gil a , Corresponding Author Contact Information , E-mail The Corresponding ... more ... Patricia Sánchez-Gil a , Corresponding Author Contact Information , E-mail The Corresponding Author , Alejandro Yáñez-Arancibia b , E-mail The Corresponding Author , Margarito Tapia a , E-mail The Corresponding Author , John W. Day c , E-mail The Corresponding Author ...
Eos, Transactions American Geophysical Union, 2010
Coastal water hypoxia, where dissolved oxygen is less than 2 milligrams per liter, is a global en... more Coastal water hypoxia, where dissolved oxygen is less than 2 milligrams per liter, is a global environmental problem [e.g., Diaz and Rosenberg, 2008]. It is largely associated with eutrophication, whereby nutrient inputs (nitrogen and phosphorous) to coastal waters lead to elevated primary production and accelerated rates of microbial respiration, which results in oxygen depletion. Despite more than 25 years of monitoring [Rabalais et al., 2007] (see also Figure S1 in the online supplement to this Eos issue (http://www.agu.org/eos_elec/)), the relative importance of the various processes that control hypoxia in bottom waters of the northern Gulf of Mexico (GOM)—in particular, those beyond the direct influence of river plumes [Dagg et al., 2007; Bianchi et al., 2008, 2010, and references therein]—remains uncertain. For example, a prediction last June pronounced that the 2009 hypoxic area would be the largest on record (˜23,000 square kilometers; see http://www.gulfhypoxia.net/Research/Shelfwide%20Cruises/2009/Files/2009_Hypoxia_Forecast.pdf). However, the most recent annual surveys estimated its size at 8000 square kilometers, only 35% of that predicted. This occurred in the absence of a significant hurricane impact on this margin in 2009—hurricanes tend to dissipate hypoxia.
Production of bay anchovy Anchoa mitchilli is highest in the larval and juvenile stages. The inte... more Production of bay anchovy Anchoa mitchilli is highest in the larval and juvenile stages. The interplay between vital rates, stage durations, prey resources, and anchovy abundance ultimately determines the relative magnitude of recruitment (which in the model varies by about three-fold) and of stage-specific production. Changes in adult seasonal spawning patterns that increase the number of larval survivors result in only a slight increase in overall production due to density-dependent decreases in growth rates of later life stages. Bay anchovy in the mid-Chesapeake Bay may reach a compensatory threshold during late summer-autumn as fish growth is affected by competition for food resources. Density dependence in the population is evident in the relationships between spawner-recruit, size-recruit, and production of larval or juvenile to young-of-the-year life stages. Density-dependent growth acts differentially upon the early life stage that exceeds the compensatory threshold in any given year, due either to environmental variability or population size, or both. This could explain partially the relatively low recruitment variability observed for this anchovy.
2009. Simulating the effects of side-aspect fish orientation on acoustic biomass estimates. -ICES... more 2009. Simulating the effects of side-aspect fish orientation on acoustic biomass estimates. -ICES Journal of Marine Science, 66: 000 -000.
Vol. 185: 133-146.1999 MARINE ECOLOGY PROGRESS SERIES Mar Ecol Prog Ser Published August 20 ... J... more Vol. 185: 133-146.1999 MARINE ECOLOGY PROGRESS SERIES Mar Ecol Prog Ser Published August 20 ... James H. Cowan Jr'l*, Kenneth A. ~ ose ~ , ... Edward D. Houde3, Shyh-Bin Wangl, John Young4 ... 'University of South Alabama, Dauphin Island Sea Lab, 101 ...
Ovaries of red snapper Lutjanus campechanus were examined histologically to determine rates of oo... more Ovaries of red snapper Lutjanus campechanus were examined histologically to determine rates of oocyte maturation, diel spawning periodicity and whether lunar cycle influenced spawning rhythm. Hydration of red snapper oocytes began during the mid-morning hours; c. 5 h was necessary for oocytes to become fully hydrated and ovulation occurred no more than 5 h after oocytes attained full hydration. Appearance of fresh postovulatory follicles after 1330 hours and the absence of hydrated oocytes after 1830 hours signified that red snapper spawning occurred during this 5 h period. In addition, evidence of a peak in spawning was seen near 1600 hours. Postovulatory follicles degenerated within a 24 h time period. A lunar spawning cycle was not evident.
Bay anchovy Anchoa mitichilli population dynamics in the mesohaline region of Chesapeake Bay are ... more Bay anchovy Anchoa mitichilli population dynamics in the mesohaline region of Chesapeake Bay are descnbed and analyzed with an individual-based model. The model begins with spawning by individual females and simulates the daily growth and mortality of each female's progeny as they develop through the egg, yolk-sac larva, (feeding) larval, juvenile, and adult Stages in a single, well-mixed compartment. The model runs for 50 yr. Eggs and yolk-sac larvae develop at rates dependent on temperature, and die at fixed daily rates. All feeding individuals (larvae, juveniles, and adults) consume zooplankton and grow according to defined bioenergetics relationships. Encounters, attacks and captures of prey, and the probability that feeding individuals will die are treated stochastically using Monte Carlo techniques Net immigration of spawners into the modeiied box each year is simulated in 2 ways: multiplier of survivors and as a constant number. Model predictions of stage-specific growth and survival rates, and diets were sirnilar for multiplier and constant immigration simulations, and both were similar to observed values. Density-dependent growth of larvae and juveniles led to a negative relationship between mean length and number of recruits and to density-dependent survival of larvae and juveniles. Density-dependent growth was due to anchovy consumption reducing prey densities, and not due to temperature effects on numbers surviving and growth. First-year su,mivorship was lower in years of high egg production than in years of low egg production. Larval growth and survival rates were positively related to recruitment, but the reverse was true for juveniles. Years of high recruitment were not years of high first-feeder production, but rather were years of high larval survival. The model simulates a single spatial box with a forced net immigration of spawners and assumes density-independent spawning and mortality processes. The model quantifies the basic processes leading to recruitinent of bay anchovy and Sets the Stage to explore potential compensatory responses of anchovy. KEY WORDS: Bay anchovy . Chesapeake Bay . Population dynamics . Individual-based model O Inter-Research 1999 Resale of full article not perrnitted T = ßo -ßlcos(0.0172 day) -ß,sin(0.0172 day) (1)
Chronographic tethering devices were used to investigate the effects of habitat type, prey type, ... more Chronographic tethering devices were used to investigate the effects of habitat type, prey type, tidal state and time of day on predation in the Damariscotta River, Maine (43°57' N, 69°3 5' W) and in St. Joseph Bay, Florida (30°00' N, 85°30' W). Traditional tethering data (presence/ absence) revealed that there were significant differences in the number of predation events between sites (p = 0.037) with more predation events occurring at the St. Joseph Bay site. In addition, there were significant differences in predation between prey types (p < 0.001). Regardless of site, significantly more 'soft' bodied prey types (shrimp) were removed than 'hard' bodied prey types (brachyuran crabs). Separating the data by site revealed that there were significant differences between habitat types (seagrass interior, seagrass edge and unvegetated substrate) at the Damariscotta River site (p = 0.027), but not at the St. Joseph Bay site (p = 0.943). Using the time to predation recorded on the chronographic tethering devices, survival times were calculated. Based on prey survival time, comparisons were made between predation intensity in monotypic stands of the seagrasses Zostera marina L. (Damariscotta River) and Thalassia testudinum (St. Joseph Bay), and bare substrate and the grass edge at both study sites. There were no significant differences in survival time between habitats at the Damariscotta River site (p = 0874). However, the average prey survival time was significantly less for the seagrass bed edge at the St. Joseph Bay site than for the T. testudinum bed interior and unvegetated habitats (p = 0.019). In addition, the time to predation allowed the effect of tidal state and light versus dark on predation to be assessed. While neither tidal state nor light versus dark had any effect on predation at the Damariscotta River site (p = 0.096 and p = 0.481 respectively), at the St. Joseph Bay site, there were significantly more predation events during the day than at night (p < 0.001), regardless of tidal state (p = 0.664). The use of the chronographic tethering devices revealed that while there was no significant difference in the number of predation events or rate of predation at the St. Joseph Bay site, the interface (i.e. 'edge') between bare or unvegetated substrates and seagrass assemblages was associated with the highest predation risks.
Proceedings of The National Academy of Sciences, 2008
We used two high profile articles as cases to demonstrate that use of fishery landings data can l... more We used two high profile articles as cases to demonstrate that use of fishery landings data can lead to faulty interpretations about the condition of fishery ecosystems. One case uses the mean trophic level index and its changes, and the other uses estimates of fishery collapses. In earlier analyses by other authors, marine ecosystems in the Gulf of Mexico (GOM) and U.S. Atlantic Ocean south of Chesapeake Bay were deemed to be severely overfished and the food webs badly deteriorated using these criteria. In our reanalyses, the low mean trophic level index for the GOM actually resulted from large catches of two groups of low trophic level species, menhaden and shrimp, and the mean trophic level was slowly increasing rather than decreasing. Commercial targeting and high landings of shrimps and menhaden, especially in the GOM, drove the index as previously calculated. Reanalyses of fishery collapses incorporating criteria that included targeting, variability in fishing effort, and market forces discovered many false cases of collapse based simply upon a decline of catches to 10% of previous maximum levels. Consequently, we suggest that the low mean trophic level index calculated in the earlier article for the GOM did not reflect the overall condition of the fishery ecosystem, and that the 10% rule for collapse should not be interpreted out of context in the GOM or elsewhere. In both cases, problems lay in the assumption that commercial landings data alone adequately reflect the fish populations and communities. landings data ͉ mean trophic level index
Factors that affect sunrival and growth of bay anchovy Anchoa mitchilli larvae in the Chesapeake ... more Factors that affect sunrival and growth of bay anchovy Anchoa mitchilli larvae in the Chesapeake Bay, USA, were studied in situ in 3.2 m3 mesocosm enclosures. Experiments tested the effects of variable prey level and anchovy egg and larvae densities on growth and survival of larvae to at least 16 d post-hatching. Eggs were stocked at 100 m-3 with microzooplankton (< 150 ~m ) prey added at nominal levels of 50, 500, 1500, or 5000 1-l. In a second series of experiments, eggs were stocked at 10, 100, or 2 1000 m-3 and prey level was maintained near 500 1-l. Larvae growth was rapid (0.39 to 0.63 mm d-l), even at the lowest prey levels and highest initial egg stocking densities. Growth rates tended to decrease as egg density increased. Instantaneous mortality rates were high (0.08 to 0.23 d-l) but lower than those reported for bay anchovy larvae from estuaries with gelatinous zooplankton and fish predators present. Highest mortality unexpectedly occurred in mesocosms with the highest prey level and lowest mortality occurred in enclosures with the highest initial egg stocking densities. Relative production decreased as prey level increased but Gw:Z ratios were above unity for all except the highest prey level experiment. In the stocking density experiments, highest production occurred in enclosures with the lowest initial egg densities. Some unexpected results may have been induced by effects of the mesocosm enclosures.
Low dissolved oxygen concentrations can affect growth rates, distribut~ons and predatorprey inter... more Low dissolved oxygen concentrations can affect growth rates, distribut~ons and predatorprey interactions of aquatic organisms. Each of these potential effects is generally examined separately in laboratory and field studies. As a result, it is often difficult to determine the net influence of low oxygen on survival and which individual effect of low oxygen contributes most to mortality. We used a spatially explicit individual-based predation model to predict how effects of low dissolved oxygen on vertical distributions, predation rates, and larval growth combine to influence survival of estuarine fish larvae in a water colun~n where the subpycnocline (bottom) and pycnocline layers are subject to oxygen depletion We analyzed simulations involving 3 predators (scyphomedusae based on Chrysaora quinquecirrha, and fish that were relatively sensitive to, or tolerant of, low dissolved oxygen), water columns that dlffered in the relative thickness of the subpycnocline layer, and bottom dissolved oxygen concentrations ranging from < l mg 1-' to no-effect concentrations. The effect of dissolved oxygen on larval and predator vertical &stributions, predator capture success and larval growth rates In simulations were based on previous experiments and field sampling in the Patuxent River, a tributary of the Chesapeake Bay. USA. Simulations indicated that bottom dissolved oxygen can strongly affect predation mortality of fish larvae. Thus, there is the potential for eutrophication to have a large effect on larval fish survival, and possibly recruitment, even in the absence of direct effects of low oxygen-induced mortality of larvae or the effects of nutrient enrichment on the abundance of larval prey or predators. Depending on predator characteristics and water column depth, lowest larval survival occurred when oxygen concentrations were either < l mg I-' or sufficiently high that oxygen concentratlon had no effect on distributions or capture rates; hlghest survival generally occurred with hypoxic bottom layers (1 to 2 mg 1-' dissolved oxygen). Bottom dissolved oxygen concentration also strongly affected the relative importance of fish and sea nettle predation in simulations that included both types of predators. Differences among predator types had important consequences for the magnitude and location of predation. Bottom-layer oxygen depletion shifted the focus of trophic interactions into the pycnocline and surface layers. Additional simulations indicated that distributional and capture success effects on larval survival were more important than growth rate effects, and that the direction of effects depended on the predator type and dissolved oxygen concentrations. Limitations of the model as well as implications of results for efforts to reduce nutrient loadings into estuaries are discussed.
The relative predation potentials on ichthyoplankton of the scyphomedusa Chrysaora quinquecjrrha,... more The relative predation potentials on ichthyoplankton of the scyphomedusa Chrysaora quinquecjrrha, the ctenophore Mnemiops~s leidyi and the bay anchovy Anchoa mjtchllli from Chesapeake Bay, USA, were estimated in 3.2 m3 in situ mesocosm enclosures and in 1.0 m3 laboratory tanks. For all 3 predators, averaged predation mortality (d-') and volume-specific clearance rates (1 d-' ml-') were higher and less variable when bay anchovy eggs were prey than when goby Gobiosoma bosci larvae 13.0 to ca 10.0 mm standard length (SL)] were prey. The smallest larvae (3.0 to <5.5 mm SL) were more vulnerable than eggs or larger larvae. Averaged mortality rates per scyphomedusa (0.78 and 0.32 d-' on eggs and larvae respectively) were 7 times higher than those per ctenophore (0.11 and 0.04 d-l), and almost 2 times higher than those per bay anchovy (0.37 and 0.21 d-l). However, volume-specific clearance rates by the relatively small bay anchovy predators were higher (ca 500 1 d-' ml-l) than those of the gelatinous predators. The volume-specific clearance rates of the ctenophore and medusa were only 4 and 7 % respectively of that for the anchovy. Combined species results suggest that these predators may consume 20 to 40 % daily of the fish eggs and larvae in mid-Chesapeake Bay. The scyphomedusa potentially is the most important predator on summer ichthyoplankton due to its overall abundance, high clearance rates and temporal CO-occurrence with vulnerable life stages of fish. 0 Inter-Research 1993
Journal of Experimental Marine Biology and Ecology, 2010
Water control structures (WCSs) installed to regulate water levels can alter both the hydrology a... more Water control structures (WCSs) installed to regulate water levels can alter both the hydrology and ecology of salt marshes. WCSs are thought to limit nekton ingress into, and egress from, managed marshes. Slots (vertical openings that span most of the water column) incorporated into WCSs are thought to facilitate nekton passage through structures, but little research has directly examined how slot size affects passage rates. We used dual-frequency identification sonar (DIDSON) acoustic imaging to examine the effect of slot width (10, 15, 30, or 60 cm), tidal cycle, diel period, and season on nekton passage at a WCS located in a tidal salt marsh canal. Few individuals (total numbers and relative percentages) used the slots for passage through the structure during any stage of the tidal cycle, day or night, or seasonally. The number and size of migrants were similar for all four slot sizes examined. Nekton used the slots most often on flood tides to access the managed marsh (i.e., swim inside), primarily at night. Individuals entering the managed marsh were larger than those observed leaving the managed marsh. Whereas the majority of migrants were observed during winter months, season did not affect nekton passage in our study. Acoustic imaging allowed a unique and comprehensive evaluation of nekton passage by permitting an examination of factors such as swimming direction and proportion of migrants that are unobservable with other sampling techniques.
The ability to estimate fish abundance accurately over a particular habitat is contingent upon th... more The ability to estimate fish abundance accurately over a particular habitat is contingent upon the use of appropriate sampling methods. The objectives of this study were to compare the catch per unit area (A), length-specific bias, and relative catchability (q-ratio) of four different gear types for sampling red snapper (Lutjanus campechanus) over natural low-relief reef habitats on the inner continental shelf of the northern Gulf of Mexico. Specifically, our goal was to assess the overall performance of a standard otter trawl, a small fish trap, a chevron trap, and a stationary 4-camera underwater video array during six quarterly sampling cruises performed in 2004 and 2005. The sizes of snapper captured by trawls ranged from 30 to 250 mm total length (TL) (ages 0 and 1 yr). Trawls captured the most red snapper per unit area and had q-ratios of 3:1 to 5:1 relative to small fish traps for juvenile red snapper. The chevron trap collected the second highest number of red snapper and proved most useful at collecting red snapper from 150 to 440 mm TL (ages 1–5 yr). The q-ratio of the chevron trap relative to the underwater video array was approximately 3:1. Our comparison demonstrated the chevron trap is most effective for sampling adults, while trawls were the most effective gear for sampling age-0 yr fish.
Differences in the biological and ecological strategies of two tropical flatfishes, Etropus cross... more Differences in the biological and ecological strategies of two tropical flatfishes, Etropus crossotus (fringed flounder) and Citharichthys spilopterus (bay whiff) are discussed. The comparative analysis was based on the seasonal distribution of relative abundance of the two species and flatfish movements utilizing estuarine plume influenced areas as part of their life cycles. Growth parameters of the von Bertalanffy equation and recruitment were estimated (FISAT software) to compare life cycle patterns. The recruitment patterns illustrate the key difference between “estuarine-dependent” and “estuarine-related” nekton strategies. Both species have a short life cycle with a continuous recruitment activity. E. crossotus is an estuarine-related species, with two recruitment pulses (winter frontal season), in the estuarine plume on the shelf. C. spilopterus is an estuarine-dependent species, with a main recruitment pulse during the rainy season in the estuarine plume, and a residual secondary pulse inside the adjacent estuarine system (Terminos Lagoon). The results show that the ecological success of these tropical coastal marine flatfish, with similar biological patterns, is based upon the sequential use (in time and space) of estuarine plume influenced habitats, suggesting that fish migration to shallow waters is related to food availability changes as a strategy towards optimum recruitment.
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