Movement patterns, habitat use and site fidelity of the white croaker (Genyonemus lineatus) in the Palos Verdes Superfund Site, Los Angeles, California

The persistent DDT footprint of ocean disposal, and ecological controls on bioaccumulation in fishes

Globally, ocean dumping of chemical waste is a common method of disposal and relies on the assumption that dilution, diffusion, and dispersion at ocean scales will mitigate human exposure and ecosystem impacts. In southern California, extensive dumping of agrochemical waste, particularly chlorinated hydrocarbon contaminants such as DDT, via sewage outfalls and permitted offshore barging occurred for most of the last century. This study compiled a database of existing sediment and fish DDT measurements to examine how this unique legacy of regional ocean disposal translates into the contemporary contamination of the coastal ocean. We used spatiotemporal modeling to derive continuous estimates of sediment DDT contamination and show that the spatial signature of disposal (i.e., high loadings near historic dumping sites) is highly conserved in sediments. Moreover, we demonstrate that the proximity of fish to areas of high sediment loadings explained over half of the variation in fish DDT concentrations. The relationship between sediment and fish contamination was mediated by ecological predictors (e.g., species, trophic ecology, habitat use), and the relative influence of each predictor was context-dependent, with habitat exhibiting greater importance in heavily contaminated areas. Thus, despite more than half a century since the cessation of industrial dumping in the region, local ecosystem contamination continues to mirror the spatial legacy of dumping, suggesting that sediment can serve as a robust predictor of fish contamination, and general ecological characteristics offer a predictive framework for unmeasured species or locations.

Dynamical analysis of a diffusive population-toxicant model with toxicant-taxis in polluted aquatic environments

This paper deals with a diffusive population-toxicant model in polluted aquatic environments, with a toxicant-taxis term describing a toxicant-induced behavior change, that is, the population tends to move away from locations with high-level toxicants. The global existence of solutions is established by the techniques of the semigroup estimation and Moser iteration. Based on a detailed study on the properties of the principal eigenvalue for non-self-adjoint eigenvalue problems, we investigated the local and global stability of the toxin-only steady-state solution and the existence of positive steady state, which yields sufficient conditions that lead to population persistence or extinction. Finally, by numerical simulations, we studied the effects of some key parameters, such as toxicant-taxis coefficient, advection rate, and effect coefficient of the toxicant on population growth, on population persistence. Both numerical and analytical results show that a weak chemotaxis effect, a small advection rate of the population, and a weak effect of the toxicant on population growth are favorable for population persistence.

A Morphometric Assessment of the Condition of White Croakers (Genyonemus Lineatus) and Queenfish (Seriphus Politus) with Access to a Wastewater Outfall and a DDT/Polychlorinated Biphenyl Superfund Site: A Los Angeles Outer Harbor Case Study

Sediments and water columns in the Los Angeles Outer Harbor (CA, USA), a major port behind a breakwater, contain DDTs and polychlorinated biphenyls (PCBs) from a nearby Superfund site, and contaminants brought in by ships, boats, stormwater, a river, and a wastewater outfall. White croaker and queenfish, a bottom feeder and a water column feeder, respectively, are two bioindicators for this marine ecosystem. Their condition as populations of fish is assumed to be robust for this role at all times. The present study tests this benign assumption amid progressively increasing DDT/PCB levels in their tissues. The results, as shown by progressively shrinking gonads, show a less than robust white croaker population particularly. Although the males are generally larger than the females, the length (standard [SL] or total [TL]) and body mass (BM) of 80 white croakers collected over 8 years were found to be similar irrespective of gender (177 mm, 212 mm, and 114 g, respectively). Queenfish (67) did not show such similarity over the same period (female: 152 mm SL, 177 mm TL, 56 g BM; male: 145 mm SL, 172 mm TL, 50 g BM). The site-specific expressions/values capturing the current conditions of these fish populations are SL = 0.835[TL] - 1.68 (r²  = 0.914, n = 68) and SL = 0.891[TL] - 8.88 (r²  = 0.961, n = 50) for white croaker and queenfish, respectively. In the allometric growth equation BM = a[SL]^b , a and b are 2.83 and 2.49 × 10^-4 (r²  = 0.817) for white croakers, and 6.10 and 2.73 × 10^-5 (r²  = 0.825) for queenfish, respectively. The relative coefficients of condition K_n are 0.97 ± 0.07 and 1.01 ± 0.12 for white croakers and queenfish, respectively. Molecular-level studies are needed to establish definitively the links between DDT/PCB bioaccumulation in fish tissues and the robustness of the fish populations. Environ Toxicol Chem 2022;41:410-425. © 2021 SETAC.

Using acoustic telemetry to quantify potential contaminant exposure of Vermilion Rockfish (Sebastes miniatus), Hornyhead Turbot (Pleuronichthys verticalis), and White Croaker (Genyonemus lineatus) at wastewater outfalls in southern California

Contaminant Exposure Models (CEMs) were developed to predict population-level tissue contaminant concentrations in fishes by pairing sediment-bound contaminant concentrations (DDTs, PCBs) and fine-scale acoustic telemetry data from a habitat-associated species (Vermilion Rockfish, Sebastes miniatus), nomadic flatfish species (Hornyhead Turbot, Pleuronichthys verticalis), and nomadic benthic/midwater schooling species (White Croaker, Genyonemus lineatus) tagged near wastewater outfalls in southern California. Model results were compared to contaminant concentrations in tissue samples. The CEMs developed require further refinement before implementation into management efforts but may act as steppingstones to help shift primary monitoring methods away from the regular field collection of fish for tissue contaminant analyses and towards behavioral modeling and habitat mapping. We also developed Kernel Density Estimates that can be used by managers immediately to identify regions that contribute most to contaminant exposure in species of concern. Prioritizing remediation efforts in these areas are likely to be most effective at improving fish health.

Sublethal, sex-specific, osmotic, and metabolic impairments in embryonic and adult round stingrays from a location exposed to environmental contamination in southern California, USA

Organic contaminants are known to affect a suite of physiological processes across vertebrate clades. However, despite their ancient lineage and important roles in maintaining healthy ecosystems, elasmobranchs (sharks, skates, and rays) are understudied with regard to sublethal effects of contaminant exposure on metabolic processes. Perturbations resulting from contaminant exposure can divert energy away from maintaining physiological homeostasis, particularly during energetically challenging life stages, such as pregnancy and embryonic development. Using the round stingray (Urobatis halleri) as a model elasmobranch species, we captured adult males and pregnant females (matrotrophic histotrophy) and their embryos from two populations differing in their environmental exposure to organic contaminants (primarily polychlorinated biphenyls (PCBs)). Pregnant females from the PCB-exposed population experienced significant decreases from early- to late-pregnancy in tissue mass and quality not seen in reference females. PCB-exposed pregnant females also failed to maintain plasma urea concentrations as pregnancy progressed, which was accompanied by a loss in muscle protein content. Despite the energetic demands of late-term pregnancy, females had significantly greater liver lipid content than reproductively inactive adult males. PCB-exposed adult males also had high metabolic capacity (i.e., enzyme activity) for most substrate groupings of all sex-site groups, suggesting that males may be even more negatively impacted by contaminant exposure than pregnant females. Evidence that in utero exposure to PCBs via maternal offloading impairs embryo outcomes is accumulating. Embryos from the PCB-contaminated site had lower tissue quality measures and indications that sex-based differences were manifesting in utero as males had higher metabolic capacities than females. This study indicates that accumulated PCB contaminants are not physiologically inert in the stingray.

Evaluation of dredged sediment for aquatic placement: interpreting contaminant bioaccumulation

The potential bioaccumulation of sediment-associated contaminants is one of the primary concerns associated with the aquatic placement of dredged sediment. Laboratory bioaccumulation tests with representative infaunal organisms exposed to dredged sediment and reference sediment are used to assess the potential for contaminant-related bioaccumulation impacts. Dredged sediment testing and evaluation guidance provides statistical inferences and numerous assessment factors (e.g., the magnitude of difference (MOD)) to interpret results; however, detailed information for applying these factors is lacking. Therefore, the focus of this work was to provide context for the application of the MOD as a line of evidence for evaluating bioaccumulation risk associated with dredged material placement in aquatic environments by considering variance (as coefficient of variation (CV)), MOD, and statistical differences associated with bioaccumulation bioassay tissue concentrations in three case studies. Based on peer-reviewed data and dredged material monitoring data, relatively low within-sample variability (CVs < 50%) of tissue concentrations can be achieved for commonly assessed constituents (e.g., polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), metals, and butyl tins). Thus, statistical comparisons were generally able to detect significant differences (p < 0.05; α = 0.05) across tissue concentrations with relatively low MODs (< 2-fold difference). Based on the observed variance, MOD, and statistical differences associated with bioaccumulation bioassay tissue concentrations, a 2-fold MOD can provide an additional line of evidence to evaluate bioaccumulative risk when statistical significance is observed. These results indicated that a judicious consideration of the sample variance and MOD is a useful factor when discerning meaningful differences among contaminant tissue concentrations.

Simultaneous observation of intermittent locomotion of multiple fish by fine-scale spatiotemporal three-dimensional positioning

Recent advances in biotelemetry techniques, especially positioning methods, have revealed the detailed behaviour and movement of aquatic organisms. Behavioural intermittence in animal locomotion, such as the Lévy walk, is a popular topic in the field of movement ecology. Previous attempts to describe intermittent locomotion quantitatively have been constrained by the spatial and temporal resolution possible with conventional biotelemetry systems. This study developed a fine-scale spatiotemporal three-dimensional positioning method using a new biotelemetry system with a positional precision of <10 cm and positioning interval of <10 s. Using this proposed positioning method, the intermittent stop-and-go locomotion of Siebold’s wrasses (Pseudolabrus sieboldi) was observed during travel from an unsuitable to a suitable location following displacement. The fish displayed behavioural intermittence in relocating to a suitable location. Initially, their movement halted for reorientation, after which they moved intermittently yet in a straight line to the suitable location. To test the positioning ability of the proposed method, data sets were resampled at intervals of 5, 10, 30, 60, and 300 s. Longer sampling intervals failed to identify reorientations and underestimated the number of stops, distance travelled, and speed. Overall, the results highlighted the adequacy and ability of the proposed positioning method to observe the intermittent locomotion of fish, such as stop-and-go behaviour, in a natural environment.

Applying acoustic telemetry to understand contaminant exposure and bioaccumulation patterns in mobile fishes

Contamination in urbanised estuaries presents a risk to human health, and to the viability of populations of exploited species. Assessing animal movements in relation to contaminated areas may help to explain patterns in bioaccumulation, and assist in the effective management of health risks associated with consumption of exploited species. Using polychlorinated dibenzodioxin and polychlorinated dibenzofuran (PCDD/Fs) contamination in Sydney Harbour estuary as a case study, we present a study that links movement patterns resolved using acoustic telemetry to the accumulation of contaminants in mobile fish on a multi-species basis. Fifty-four individuals across six exploited species (Sea Mullet Mugil cephalus; Luderick Girella tricuspidata; Yellowfin Bream Acanthopagrus australis; Silver Trevally Pseudocaranx georgianus; Mulloway Argyrosomus japonicus; Yellowtail Kingfish Seriola lalandi) were tagged with acoustic transmitters, and their movements tracked for up to 3years. There was substantial inter-specific variation in fish distribution along the estuary. The proportion of distribution that overlapped with contaminated areas explained 84-98% of the inter-specific variation in lipid-standardised biota PCDD/F concentration. There was some seasonal variation in distribution along the estuary, but movement patterns indicated that Sea Mullet, Yellowfin Bream, Silver Trevally, and Mulloway were likely to be exposed to contaminated areas during the period of gonadal maturation. Acoustic telemetry allows examination of spatial and temporal patterns in exposure to contamination. When used alongside biota sampling and testing, this offers a powerful approach to assess exposure, bioaccumulation, and potential risks faced by different species, as well as human health risks associated with their consumption.

Increase in predation risk and trophic level induced by nocturnal visits of piscivorous fishes in a temperate seagrass bed

The majority of surveys on food webs of aquatic ecosystems have been conducted during the day owning to difficulties in sampling animals at night. In this study, to examine diurnal changes in predator-prey interactions in a temperate seagrass Zostera marina bed, a quantitative day/night survey of fish, the dominant animal community, coupled with acoustic telemetry of their predators, was conducted. The number of species, abundance, and biomass of piscivorous predators and mean trophic level during the night were significantly higher than those in the day in all seasons. Analysis of the stomach contents of 182 piscivorous predators showed that no fish predation occurred during the day whereas predation occurred during the night in winter, spring, and summer. Acoustic telemetry demonstrated nocturnal visits by dominant piscivorous fish species (rockfishes and conger eel) to the seagrass bed. We conclude that the nocturnal visits by piscivorous fishes increased the predation risk and trophic level in the fish nursery. The ecological functions of seagrass beds should be reevaluated accounting for day/night changes in food webs; these areas serve as nurseries for juvenile and small-sized fishes during the day and as foraging grounds for predators during the night.

Historical record and fluxes of DDTs at the Palos Verdes Shelf Superfund site, California

Marine sediments at many locations in the world are contaminated with a wide range of persistent organic pollutants. The Palos Verdes Shelf (PVS) is located in the ocean off the coast of Los Angeles, California and has been listed as a Superfund site by the US EPA since 1997, because of heavy contamination of DDTs and PCBs. However, little is known about the historical trend in the deposition of DDTs as a result of decades-long discharge of wastewater effluents. In this study, sediment cores were taken from the PVS site and determined for DDT and its metabolites including DDE and DDD (denoted as DDTs). Individual DDTs were found in the majority (95%) of the samples analyzed. The highest ∑DDT concentrations were found in three cores along the 60-meter isobath with geometric means of 31300, 7490, and 5010ng/gdw and medians of 82400, 17300, and 5200ng/g dw, respectively. Among DDT congeners, p,p'-DDE, o,p'-DDE and p,p'-DDD were predominant, contributing to approximately 54%, 27%, and 14% of the ΣDDTs in sediment. The vertical profiles of concentrations of contaminants in the sediment cores were examined. For most of the cores, a steady increase in the concentrations of DDTs during 1940s to 1980s was observed, while the concentrations declined gradually toward the surficial layers. On the basis of the mass flux of DDTs calculated and the area of the PVS Superfund site, we estimated the total deposition amount of DDTs in sediment and the deposition amount of ΣDDTs in this region during 1947-1971 was 132 tons, which was fairly close to what was reported in earlier studies for industrial wastewater discharge in the PVS site (870-1450tons). Our findings suggest that the elevated levels of DDTs in sediment from the PVS site are linked to the discharge of these contaminants between the 1940s-1980s.

Strain differences in the collective behaviour of zebrafish (Danio rerio) in heterogeneous environment

Recent studies show differences in individual motion and shoaling tendency between strains of the same species. Here, we analyse collective motion and response to visual stimuli in two morphologically different strains (TL and AB) of zebrafish. For both strains, we observed 10 groups of 5 and 10 zebrafish swimming freely in a large experimental tank with two identical landmarks (cylinders or discs) for 1 h. We tracked the positions of the fish by an automated tracking method and compute several metrics at the group level. First, the probability of the presence shows that both strains avoid free space and are more likely to swim in the vicinity of the walls of the tank and the landmarks. Second, the analysis of landmarks occupancy shows that AB zebrafish are more present in their vicinity than TL ones and that both strains regularly transit from one to the other one with no preference on the long duration. Finally, TL zebrafish show a higher cohesion than AB zebrafish. Thus, environmental heterogeneity and duration of the trials allow to reveal individual and collective behavioural variabilities among different strains of zebrafish. These results provide a new insight into the need to take into account individual variability of zebrafish strains for studying collective behaviour.

Strain differences in the collective behaviour of zebrafish (Danio rerio) in heterogeneous environment

Recent studies show differences in individual motion and shoaling tendency between strains of the same species. Here, we analyse collective motion and response to visual stimuli in two morphologically different strains (TL and AB) of zebrafish. For both strains, we observed 10 groups of 5 and 10 zebrafish swimming freely in a large experimental tank with two identical landmarks (cylinders or discs) for 1 h. We tracked the positions of the fish by an automated tracking method and compute several metrics at the group level. First, the probability of the presence shows that both strains avoid free space and are more likely to swim in the vicinity of the walls of the tank and the landmarks. Second, the analysis of landmarks occupancy shows that AB zebrafish are more present in their vicinity than TL ones and that both strains regularly transit from one to the other one with no preference on the long duration. Finally, TL zebrafish show a higher cohesion than AB zebrafish. Thus, environmental heterogeneity and duration of the trials allow to reveal individual and collective behavioural variabilities among different strains of zebrafish. These results provide a new insight into the need to take into account individual variability of zebrafish strains for studying collective behaviour.

Area use and movements of the white croaker (Genyonemus lineatus) in the Los Angeles and Long Beach Harbors

Understanding the movements of fish in relation to areas of contaminated and urbanized habitats is crucial to fisheries management and habitat remediation. In this study, the movements of white croaker in the Los Angeles and Long Beach Harbors were examined using both active and passive acoustic telemetry tracking. Daily area use for 20 fish actively tracked over multiple days averaged 94,720 ± 78,720 m(2) (±SD), with daily activity spaces shifting over periods of up to 1 month. Long-term dispersal (up to 7 months) of 93 passively tracked white croaker followed significantly non-random patterns, with 55 individuals (59.1%) making inter-regional Harbor movements. Inter-regional movements took an average of 4.7 ± 4.1 weeks to complete. Dispersal was significantly faster than what was predicted by an individual-based random walk model generated from short-term white croaker movements recorded during active tracking within the Harbor. Longer-term dispersal is likely the result of intentional movements between patches of favorable habitat rather than random daily shifts in activity spaces, indicating that white croaker deliberately utilize different areas within the Harbor and over the course of a year utilize much of the favorable Harbor habitat.

Habitat selection and utilization of white croaker (Genyonemus lineatus) in the Los Angeles and Long Beach Harbors and the development of predictive habitat use models

White croaker (Genyonemus lineatus) are a sentinel fish species for contamination due to their direct interaction with contaminated sediments through benthic foraging. White croaker within the Los Angeles (LA) and Long Beach (LB) Harbor exhibited hierarchical habitat selection: avoiding dredged areas while selecting for areas of high sediment total organic carbon (4.8-8.1%), high polychaete density (406-700 polychaetes/0.1 m(2)), and small sediment grain size (<23.5 μm). Model results suggest that these fish are moving into shallower waters at night, which may be to forage and refuge more during the day presumably to avoid predation. The predictive model for white croaker habitat use indicated three important areas of use within the LA-LB Harbor: Consolidated Slip, Inner Long Beach Harbor, and Fish Harbor. The areas containing the most frequently selected habitats by white croaker are also often areas of high sediment contamination, and thus are likely locations where these fish are acquiring contaminants. While many sediment mitigation alternatives exist, identifying and remediating sediments in key white croaker habitat may lead to a decrease in white croaker tissue concentrations over time if the fish continue to utilize these areas post remediation.