Ecosystem benefits of floating offshore wind

Report produced for Simply Blue GroupThe offshore renewable energy (ORE) sector is at a crucial moment with multiple governments enacting policies and legislation that will decisively accelerate the expansion of offshore renewable energy globally. Floating offshore wind energy will become increasingly important over the next decade and this report seeks to elucidate the potential ecosystem benefits of floating offshore wind energy developments

Population Parameter Estimation and Stable Isotope Analysis of Gulf Sturgeon (Acipenser oxyrinchus desotoi) in the Pascagoula River

Gulf Sturgeon (GS), Acipenser oxyrinchus desotoi, are a threatened, anadromous fish species in the northern Gulf of Mexico. Their range is from the Pearl River, LA, in the west to the Suwannee River, FL, in the east with a longitudinal divide at Mobile Bay, AL, creating a western population unit (WPU) and an eastern population unit (EPU). Sturgeon belonging to the WPU exhibit lower abundances, higher mortality rates, and are overall less studied than their EPU counterparts. Notable data gaps for the WPU includes the absence of recent population parameter estimations and confirmed feeding habitat. My thesis aims to reduce our knowledge gaps for WPU sturgeon by estimating population parameters through mark-recapture modelling and describing feeding habitat by stable isotope analysis for GS natal to the Pascagoula River. Pascagoula River GS were captured with anchored gill nets, tagged, and had blood and muscle samples taken between April–November from 2013–2020. Mark-recapture modelling revealed a steadily increasing GS abundance between 2013–2020 and a higher survival than previously estimated for this population, but comparisons with the EPU are difficult. Stable isotope analysis revealed δ13C values of a majority of individuals indicated estuarine/marine feeding. Only young-of-year and age-1 individuals had δ13C values indicative of river feeding, and only some year ones seemed to also feed in the estuary. This project has helped close knowledge gaps that will be important for continued monitoring of the species

Proportions of demersal fish exposed to sublethal hypoxia revealed by otolith chemistry

Fishes exposed to hypoxia may experience sublethal effects that impair growth, reproductive fitness, and condition, with potential consequences for population sustainability. Characterizing sublethal effects of hypoxia exposure requires the ability to differentiate between exposed, and non-exposed individuals. Moreover, because sublethal effects may manifest well after exposure to hypoxia has ceased, long-term markers that facilitate retrospective identification of exposure are necessary. We used sagittal otoliths from 337 Atlantic croaker Micropogonias undulatus sampled at multiple stations in the northern Gulf of Mexico to characterize exposure to hypoxia during the first year of life. Otolith elemental profiles of Ba:Ca and Mn:Ca revealed 4 primary clusters of fish associated with residence in normoxic, hypoxic, and estuarine habitats. Croaker exposed to hypoxia in the first year of life constituted 34% of all individuals sampled in fall of 2014, and this pattern was consistent across the sampling region. Young-of-year croaker exposed to hypoxia were smaller in length and mass but had similar mean relative condition factors to croaker of the same year class experiencing normoxic conditions. These results indicate that in some years, one-third of the young-of-year croaker in the northern Gulf of Mexico experience hypoxic conditions and survive. The potential for sublethal effects of hypoxia on growth may be important for future efforts to forecast population sustainability under chronic seasonal hypoxia in the region