1. Cultural and economic demands for queen conch, Lobatus gigas (Linnaeus, 1758), have led to the overexploitation of this iconic species throughout its range in the wider Caribbean. Fisheries managers have responded in many ways, from remaining idle to placing moratoriums on conch harvest, yet heavily harvested conch populations have been slow to recover, and descriptions of natural baselines are missing.2. The study describes a population of conch surveyed on the isolated, partially submerged, carbonate platform known as the Cay Sal Bank, The Bahamas, using traditional and interpolation techniques. Counts and shell measurements of conch within six study areas were obtained using 118 timed dive surveys over shallow water habitat (<20 m).3. The density and standing stock of adult conch were calculated using raw estimates, estimates retroactively standardized by distance, and estimates from Geographic Information Systems (GIS) kriging interpolation. All methods result in similar abundance estimates and include one of the highest abundances of conch found for decades in legally fishable waters within the Caribbean. 4. Shell measurements revealed multiple-year cohorts within the nurseries encountered, suggesting consistent recruitment. Lip thickness, a proxy for age, significantly increased with distance to Nassau in unprotected areas within The Bahamas, and Cay Sal Bank contains the second oldest average population observed in legally fishable waters. 5. Media reports show that remote Bahamian banks are increasingly threatened by poaching as fishers deplete accessible stocks. Biophysical models demonstrate potential larval connectivity from Cay Sal Bank to both the Grand and Little Bahamas banks. We suggest protecting Cay Sal Bank as a modern baseline for conservation management and as a larval source located upstream of major Bahamian fishing grounds.

Human-fortified ship channel inlets can represent the only connection between estuarine and coastal waters for tens of kilometers in some areas of the Northern Gulf of Mexico, making them bottlenecks for fish movement. A variety of fishes associate with the jetties that fortify ship channel inlets, and the deep depths of channel inlets relative to surrounding waters may provide a unique type of habitat. To understand variability in fish biomass in these vital areas, 49 hydroacoustic surveys of the Aransas Channel Inlet, Texas were conducted and paired with environmental (e.g., temperature) and meteorological (e.g., barometric pressure) data between January 2018 and February 2020. Fishery-independent and fishery-dependent data from the surrounding area were employed to provide context to variability in fish backscatter (i.e., volume backscattering strength, s v , a proxy for fish biomass). Generalized additive models indicated that variation in fish backscatter was best explained by variation in temperature, change in barometric pressure, and salinity (adj.-R 2 = 0.71). There were two dimensions to these effects. In the first, variation in temperature tracked seasonal shifts in the relative abundance of pelagic fishes, which were well sampled by acoustic technologies relative to demersal fishes. In the second, episodic cold fronts (i.e., high pressure systems) were associated with high values of fish backscatter -likely because the Aransas Channel Inlet is far deeper than surrounding areas and protected by jetties, making it less affected by physical disturbances and rapidly changing air temperatures or precipitation. Thus, disturbances in the Aransas Channel Inlet (e.g., dredging and construction, shipping traffic) are likely to be most impactful to non-demersal fishes when temperature and salinity are low (< c.a. 15 °C and < c.a. 28 psu) and frontal systems are likely to affect the area (barometric pressure increase > c.a. 3 mb or decrease > 7 mb over 24 h).

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 U.S. 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.

Estuaries worldwide provide critical habitat to many ecologically and socioeconomically important fish species. However, the high turbidity and strong environmental gradients inherent to many estuaries make the monitoring of fish populations a challenging task. To assess the health and diversity of local fish populations, resource managers often employ fisheries-independent sampling methods, which result in valuable population assessments, but suffer from low-temporal resolution and high rates of mortality. Passive acoustic monitoring (PAM) provides a near-continuous, non-invasive means for monitoring soniferous fish activity over extended periods, but its utility for quantifying entire fish communities is largely untested, especially in turbid estuaries. Here, we use synchronized acoustic and gillnet sampling at 51 locations in the Mission-Aransas Estuary (TX), across two sampling seasons to test correlations between acoustic indices and gillnet catch. Positive correlations were observed between gillnet catch and sound pressure levels in both broadband (50–22050 Hz) and low-frequency (50–2500 Hz) bands. Additionally, sciaenid calling activity was positively correlated with sciaenid catch during the spring, when most spawning activity occurs. Our results indicate that PAM can be used to monitor the relative abundances of fish in Gulf of Mexico estuaries and beyond, although this is subject to species identity and seasonal dynamics.

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