Optic–acoustic Analysis of Fish Assemblages at Petroleum Platforms

Abstract

Petroleum platforms provide high‐relief reef habitat in several ocean basins and are important to fishes and fishers alike. To determine which variables were important for shaping platform‐associated fish assemblages on a basin‐wide scale in the U.S. Gulf of Mexico, we employed optic and acoustic methods to measure fish distribution (geographic and water‐column), abundance, biomass, density, size, diversity, and richness at 54 platforms. We found that variables related to freshwater inflow and meso‐scale circulation patterns (e.g., salinity) affected more metrics than platform characteristics (e.g., platform depth). Platform fish assemblages varied gradually along gradients of these variables instead of exhibiting distinct assemblage groupings in non‐metric multidimensional scaling space. These effects contributed to the presence of biomass, density, diversity, and richness “hotspots” at platforms offshore of the Atchafalaya River. Our findings underscore the importance of freshwater inflow and circulation patterns in explaining variation in reef fish assemblages in the U.S. Gulf of Mexico.

Fish distribution in three dimensions around the Block Island Wind Farm as observed with conventional and volumetric echosounders

“…2014; Bolser et al. 2021). This phenomenon does not appear to be related to the number of turbines, but the size (Stanley and Wilson 1991) or configuration (Reynolds et al.…”

“…2019; Bolser et al. 2021) would be ideal for estimating abundance by echo or target counting within turbine structures and potentially along cables. All of the above systems operate at acoustic frequencies greater than 12 kHz, with most operating above 38 kHz.…”

“…Acoustic sampling within the boundaries of the turbine/platform and support structure will require submeter resolution so that biological targets can be separated from the solid structure. Acoustic lens technology (van Hal et al 2017), side-looking multibeam or volumetric sonars, and optical systems (Becker et al 2019;Bolser et al 2021) would be ideal for estimating abundance by echo or target counting turbine structures and potentially along cables. All of the above systems operate at acoustic frequencies greater than 12 kHz, with most operating above 38 kHz.…”

“…Turbines or other structures are commonly observed to have limited effects on fish distribution at scales of hundreds of meters to kilometers (Bergström et al 2013;Wilber et al 2022b). The attraction of natural or artificial structure appears to be limited to close proximity, where fish have refuge from predation an increased food supply (Bohnsack 1989;Claisse et al 2014;Bolser et al 2021). This phenomenon does not appear to be related to the number of turbines, but the size (Stanley and Wilson 1991) or configuration (Reynolds et al 2018;Becker et al 2019) of the structures may influence the abundance associated with it.…”

Integrating assemblage structure and habitat mapping data into the design of a multispecies reef fish survey

“…Unlike the eastern Gulf of Mexico, survey efforts in the western Gulf have been restricted primarily to deep reefs near the shelf break (Campbell et al 2019), so data needed to delineate spatial strata, especially in relation to depth, is limited. Data needed to delineate artificial reef habitat strata are also lacking because long‐term surveys in the western Gulf have exclusively targeted natural reef habitats, although some insights could be gleaned from focused studies (Bolser et al 2020, 2021). Finally, available habitat mapping data are restricted largely to multibeam sonar data collected in association with well‐known reef features (i.e., not collected under a randomized design) and so cannot be used to provide the unbiased estimates of habitat quantity and composition necessary for allocating sampling effort, particularly for natural reef habitats.…”