Understanding and Managing Living Resources

The blacknose shark, Carcharhinus acronotus, is a small coastal shark found in the western Atlantic Ocean from Virginia to Brazil, including the Gulf of Mexico (GoM). Like other coastal sharks in the western Atlantic, blacknose sharks experienced historic overfishing throughout the 1970s and 1980s. The GoM blacknose shark stock status is currently unknown; however, studies have observed that GoM blacknose sharks have not shown signs of recovery, primarily due to susceptibility as bycatch. Although studies have evaluated the age, growth, and maturity of blacknose sharks throughout their range, the most recent study in the GoM used samples collected two decades ago, and updated data are needed to better understand the current population dynamics of the stock. Therefore, the objectives of this study are to 1) determine the sex-specific and overall growth parameters of GoM blacknose sharks and 2) determine the size and age at maturity of GoM blacknose sharks. From 2000 to 2023, blacknose sharks (n = 202) were collected from the northern GoM via bottom longline and gillnet surveys. A section of vertebrae was extracted from each fish for aging. Blacknose sharks ranged in size from 36-114 cm fork length, with females significantly larger than males (p = 0.005). This study is necessary for evaluating the health of the GoM blacknose shark stock and informing effective management measures that ensure population sustainability.

The tiger shark (Galeocerdo cuvier) is a large, highly migratory predator with a circumglobal distribution. In the western North Atlantic Ocean (WNA), tiger sharks can be found in the Gulf of Mexico (GoM) and southern U.S. Atlantic Ocean year-round and occasionally move as far north as Nova Scotia. Like many other shark species, WNA tiger sharks were heavily exploited throughout the 1970s and 1980s, leading to significant declines in abundance. Although several studies have suggested their numbers are increasing, tiger sharks have never been formally assessed in the U.S. as a single species and the stock status is unknown. Reliable, updated estimates of life history parameters are critical for informed management of this species in the WNA. Therefore, the objectives of this study are to 1) determine the combined and sex-specific growth parameters of WNA tiger sharks and 2) determine the size and age at maturity of WNA tiger sharks. Between 2005 and 2024, tiger sharks (n = 249) were collected from the U.S. GoM and Atlantic coast via fishery-independent and fishery-dependent sampling. Vertebral centra were extracted from each fish for aging. Tiger sharks ranged in size from 56-360 cm fork length, with females significantly larger than males (p = 0.003). Findings from this study will inform future management actions to ensure sustainability of the WNA tiger shark stock.

Fishery-independent video surveys are widely used to gather data on relative abundance and species composition of reef-associated fish. Video gears have advantages over traditional fisheries gears (e.g. trawls, longlines, gillnets) as they can be used over a wider range of habitat, are less selective of particular species and size-classes, are non-extractive, and are archival. Two important video gears used to collect data in the Gulf of Mexico are Remotely Operated Vehicles (ROVs) and Stereo Baited Remote Underwater Video systems with 360-degree camera arrays (360-BRUV). Mobile single-camera systems like the current ROV systems have a limited field of view, but are capable of maneuvering to focus on specific habitat patches. Whereas, stationary 360-degree camera systems benefit from a wider field of view, but are constrained to sample only the immediate area where they are deployed. Because of these discrepancies, abundance data generated from each gear could vary in terms of accuracy and precision across a range fish abundance. The standardization of these camera systems and comparison to each other helps increase the applicability of the data they collect. In this comparison study between the 360-BRUV and ROV we are quantifying the relative biases of each gear, determining the degree of correlation between the relative abundance (max Ns) of each camera system and assessing the effect of different methods on the relationship between the data from the two gears. Our current data shows the 360-BRUV and ROV have different probabilities of encountering certain species and measure different proportions of fish abundance. The data collected from this project will supplement Alabama's offshore Fisheries Independent Survey and the Greater Amberjack Count, a large independent study that aims to estimate the absolute abundance of greater amberjack in the coastal waters of the southeast United States.

Seagrasses and other submerged aquatic vegetation (SAV) provide critical nearshore habitats. Information on the location, extent, and condition of SAV resources in Mississippi (MS) and Alabama (AL) is often crucial in coastal management decision-making, like permitting for dock or pier construction, sediment dredging for navigation, living shoreline construction, and others. The benefits and challenges of using drones and sonar for detecting and mapping SAV in nearshore, shallow, and optically complex waters to support coastal management and permitting needs in the region were evaluated. These technologies are being tested to determine the conditions under which each method is most cost-effective, maximizes efficiency, and yields high-accuracy data that can improve management strategies and outcomes. Results indicate that drone platforms can detect most SAV in shallow waters at low tide. Sonar data is more difficult to extract and process, and further sampling is required to provide a sufficient database with which to compare against aerial imagery. Regression and ordination techniques will be needed to cross-validate aerial imagery with sonar maps. Having recommendations under which conditions each method is most suited can provide easier decision-making for natural resource managers.

Streamflow-recession indices are helpful in understanding surface-water and groundwater interactions, ecological niches, and the susceptibility of alteration to the hydrologic regime from anthropogenic influences. To improve low-flow calculations, Bingham (1982) calculated the "geologic factor" or gfactor which reflects the impact of surficial geology to streamflow recession. Bingham selected peak flows after a precipitation event at U.S. Geological Survey streamgages during a 20-year time period and hand plotted streamflow recession curves. The number of days needed for the streamflow to decrease one log cycle for each recession curve was averaged to calculate the gfactor for the streamgage. Bingham (1982) further regionalized the gfactor using a combination of the calculated gfactor, geologic maps, and decades of experience as a hydrologist in Alabama. Since then, the gfactor has been used not only for low-flow calculations, but also for regulatory and ecological research purposes. Although proven to be helpful, the time intensive and subjective process for calculating and regionalizing gfactor make it difficult to replicate Bingham's methodology in other regions or to include more recent hydrologic data. In this study, we present an automated methodology for reproducing Bingham's gfactor in Alabama using the R programming language. This new methodology will make it possible evaluate decadal impact of droughts, surface-water withdrawal, surface-water and groundwater connectivity as well as provide a basis for using machine-learning regionalization methods.