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Assessing marine fish community size spectra with hydroacoustics is challenging, as communities are diverse, schooling and swim-bladder-less fishes are common, and fish orientation is variable. We developed an approach to examine these challenges and applied it to data from 51 optic–acoustic surveys of fishes at petroleum platforms throughout the US Gulf of Mexico. When in situ target strength (TS; dB re 1 m2) distributions were used to calculate the density (and subsequently abundance) of schooling fishes, fish lengths and size spectra slopes were significantly smaller than in simulated communities and fish community censuses at platforms (i.e., reference datasets). However, acoustic slopes were comparable to reference slopes when simulated TS values (based on species composition) were used to calculate schooling fish abundance. These findings held regardless of whether specific or general models were used to convert TS to length. Fish orientation was not a useful predictor of TS or slope, but may explain why in situ TS measurements from small groups of fishes around schools were unsuitable for abundance calculations. By examining the challenges associated with assessing size spectra with acoustics, this study aids progress towards using acoustic size spectra metrics for ecological inferences.

Per-recruit models have been widely used since the onset of modern fisheries science, particularly in data-limited situations. When the study fishery is a pulse fishery, namely a fishery operating over a brief period followed by a long fallow period, exploitation rates rather than fishing mortality rates are employed to calculate per-recruit quantities. The literature suggests that a discrete per-recruit model is more appropriate than a continuous per-recruit model when per-recruit quantities are expressed as a function of exploitation rates. For this reason, Erisman et al. [Erisman, B. E., Grüss, A., Mascarenas-Osorio, I., Lícon-González, H., Johnson, A. F., and López-Sagástegui, C. 2020. Balancing conservation and utilization in spawning aggregation fisheries: a trade-off analysis of an overexploited marine fish. ICES Journal of Marine Science, 77: 148–161.] recently developed a discrete per-recruit model to examine the impacts of altering exploitation rates for the Gulf corvina (Cynoscion othonopterus) pulse fishery. Using Erisman et al.’s (Erisman, B. E., Grüss, A., Mascarenas-Osorio, I., Lícon-González, H., Johnson, A. F., and López-Sagástegui, C. 2020. Balancing conservation and utilization in spawning aggregation fisheries: a trade-off analysis of an overexploited marine fish. ICES Journal of Marine Science, 77: 148–161.) data, we demonstrate in detail that, under certain conditions, it is reasonable to employ a continuous per-recruit model for a pulse fishery system. We then use the designed continuous per-recruit model to demonstrate how the timing of the pulse fishery within the year relative to the timing of reproduction can be accounted for in a per-recruit model, and we explore the impacts of these model developments. This article serves as a strong basis for future studies that model pulse fishery systems in data-limited situations.

We conducted a meta-analysis to summarize current knowledge on the effects of environmental and ecological drivers on the abundance of red snapper (Lutjanus campechanus) within the U.S. Gulf of Mexico. We reviewed 1252 published research articles and extracted or calculated effect sizes for 12 drivers from 82 independent studies within 26 articles that met our inclusion criteria. We used a fixed-effect model to calculate the absolute value of the mean effect size of each driver by age class studied and pooled across age classes to estimate effects on the overall abundance of red snapper. Habitat complexity and intra-specific competition had large effects on overall abundance and juvenile abundance, while habitat type and protection from predators showed medium to large effects on age 0 recruits and juvenile red snapper, and the mean effect of all drivers studied for adult red snapper were small or had no effect on abundance. Our results provide systematic support for the role of density-dependent mechanisms (habitat quality and availability, competition, predation) in shaping the regional abundance of red snapper, particularly during the juvenile stages. Sensitivity analyses indicated that issues with non-independence (e.g. within-article correlation), between-study heterogeneity, and publication bias influenced the magnitude and certainty of effect size estimates in a subset of drivers. Thus, our meta-analytical review also highlights the need for more empirical research on certain drivers (e.g. temperature, hypoxia) to improve our understanding of the factors that shape the regional abundance of red snapper.

In light of rapid shifts in biodiversity associated with human impacts, there is an urgent need to understand how changing patterns in biodiversity impact ecosystem function. Functional redundancy is hypothesized to promote ecological resilience and stability, as ecosystem function of communities with more redundant species (those that perform similar functions) should be buffered against the loss of individual species. While functional redundancy is being increasingly quantified, few studies have linked differences in redundancy across communities to ecological outcomes. We conducted a review and meta‐analysis to determine whether empirical evidence supports the asserted link between functional redundancy and ecosystem stability and resilience. We reviewed 423 research articles and assembled a data set of 32 studies from 15 articles across aquatic and terrestrial ecosystems. Overall, the mean correlation between functional redundancy and ecological stability/resilience was positive. The mean positive effect of functional redundancy was greater for studies in which redundancy was measured as species richness within functional groups (vs. metrics independent of species richness), but species richness itself was not correlated with effect size. The results of this meta‐analysis indicate that functional redundancy may positively affect community stability and resilience to disturbance, but more empirical work is needed including more experimental studies, partitioning of richness and redundancy effects, and links to ecosystem functions.

Hydroacoustic surveys were conducted at 56 different oil and gas platforms in the U.S. Gulf of Mexico (GOM), along with a commensurate collection of physio-chemical data, in order to characterize patterns of fish distribution around platforms. Relative acoustic measurements of Mean Volume Backscatter “MVBS”, Target Strength “TS” and fish density were examined. These acoustic variables were employed to test if patterns of MVBS, TS and density around GOM platforms differed among seabed depth-based categories (Coastal: 0-30 m; Offshore: 31-60 m; Bluewater: >60 m), and how these patterns varied as a function of the distance to platforms. The acoustic measurements were also examined across the study area to determine the influence of specific environmental factors and platform features (using generalized additive mixed models (GAMMs)), and whether hypoxic waters compressed fish distribution in the water column. Significantly greater mean fish densities and MVBS occurred at Coastal sites and these variables decreased with increasing seabed depth, whilst mean TS was highest at Offshore sites. Greatest values of fish MVBS and density were found at the shortest distances (0-25 m) from platforms. GAMMs suggested that salinity and temperature had a significant effect on fish density, TS, and MVBS. The number of other platforms within 5 km also had a significant effect on MVBS. Dissolved oxygen concentration has a significant effect on fish density. Finally, we found that fish densities and MVBS were significantly higher in the depth layers immediately above hypoxic layers, demonstrating vertical compression of fishes in the water column when hypoxia occurs. Our findings provide further evidence of the influence of environmental conditions and platform features on the regional patterns of fish density, TS and MVBS around platforms, and the influence of platforms on these metrics on a local scale across the GOM. The study highlights the applicability of using hydroacoustics in conjunction with modelling to assess fish distributions around artificial habitats.

Chemical contaminants present in the environment can affect mitochondrial bioenergetics in aquatic organisms and can have substantial effects on individual fitness. As early life stages of fish are particularly vulnerable to environmental contaminants, they are ideal models for examining the relationship between impaired mitochondrial bioenergetics (ATP-dependent respiration, basal oxidative respiration) and apical endpoints such as growth. Here, early life stages of the fathead minnow (Pimephales promelas), an ecologically relevant North American species, were used to investigate the relationship between mitochondrial bioenergetics and growth following perturbation with model mitochondrial toxicants 2,4-dinitrophenol and octylamine. Fathead minnows were exposed to 2,4-dinitrophenol and octylamine at 3 concentrations for 24 h and endpoints related to mitochondrial bioenergetics were measured with the Agilent Seahorse XFe24 Bioanalyzer. In order to link changes in mitochondrial bioenergetics to growth, fathead minnows were exposed to the same chemical contaminants for 7–14 days and growth was measured by measuring total length on a weekly basis. There was a significant correlation between decrease in average length at 14 days and basal respiration (r = 0.997, p = 0.050, n = 3), as well as maximal respiration (r = 0.998, p-value = 0.043, n = 3) for embryos exposed to 2,4 dinitrophenol. For octylamine, ATP production was highly correlated with average length at 7 days (p-value = 0.1) and spare respiratory capacity and average length at 14 days were highly correlated (p-value = 0.1). These data improve understanding of how mitochondrial toxicants impair growth in fish larvae and may be useful for developing an adverse outcome pathway for growth.

Phenols are classified as polar narcotics, which are thought to cause toxicity by non-specific mechanisms, possibly by disrupting membrane structure and function. Here we test three phenolic chemicals, phenol, 2,4-dichlorphenol and pentachlorophenol on embryo development, heartbeat rate and mitochondrial respiration in fathead minnow (Pimephales promelas). While these chemicals have been used on isolated mitochondria, they have not yet been used to verify respiration in intact embryos. Mitochondrial respiration in intact embryos was measured after optimizing the Seahorse XFe24 Extracellular Flux Analyzer. Heartbeat rate and mitochondrial respiration patterns of fathead minnow embryos at different developmental stages were also characterized. Exposures of embryos at developmental stage 20 occurred for 24 h with five concentrations of each phenolic compound ranging from 0.85 to 255 μM for phenol, 0.49 to 147 μM for 2,4-dichlorophenol and 0.3 to 90 μM for pentachlorophenol. Exposure to phenol at the concentrations tested had no effects on development, heartbeat or mitochondrial respiration. However, both 2,4-dichlorophenol and pentachlorophenol showed dose-dependent effects on development, heartbeat rate, and mitochondrial respiration, with the effects occurring at lower concentrations of pentachlorophenol, compared to 2,4-dichlorophenol, highlighting the higher toxicity of the more chlorinated phenols. Both 2,4-dichlorophenol and pentachlorophenol decreased basal mitochondrial respiration of embryos and ATP production. These results indicate that higher chlorinated phenolic chemicals cause developmental toxicity in fathead minnow embryos by decreasing mitochondrial respiration and heartbeat rate.