Current Research

Escapement Rate of Red Drum (Sciaenops ocellatus) Stock in Mississippi

This objective of this research effort is to estimate mortality components and escapement rate of Red Drum stock in Mississippi. This project consists of determinations of instantaneous natural mortality rate, evaluation of overall and year-specific instantaneous total mortality rates, and calculation of the overall and year-specific instantaneous fishing mortality rates of Red Drum in Mississippi. Mortality estimates are then used to calculate an escapement rate. Alternative natural mortality estimations and fishery recruitment criteria are also evaluated to elucidate the impact of model misspecification and how these decisions affect the escapement rate.

Figure 1.CB

Escapement rate (%) estimations for each of the methods evaluated. The catch-curve truncation points to determine total mortality are indicated by the color and are labeled in the legend .  Each quadrant uses the natural mortality estimation method indicated by the quadrant title to calculate the escapement rate. The asterisks (*) symbol represents previous escapement rate estimates as determined by  Powers and Burns (2010, Tab L No. 3 (a)).

Figure 2.CB

Escapement rate (%) estimations under incremental catch-curve truncation points to determine total mortality.

 Sex-specific Age and Growth Characteristics of Red Drum (Sciaenops ocellatus) in the North-central Gulf of Mexico

The objective of this research effort is to evaluate the length-at-age and weight-at-length relationships of Red Drum. Sex-specific length-at-age and sex-specific weight-at-length relationships are quantified using multiple candidate models to determine the best supported model. Sex-specific relationships were examined for significant differences in male and female Red Drum.

Figure 3.CB

Seven candidate models were used to describe the length-at-age relationship of Red Drum in the northern Gulf of Mexico (n = 451). The candidate models included four variations of a von Bertalanffy growth function (VBGF), including the three-parameter (3-Param VBGF), the two-parameter (2-Param VBGF), the double (DVBGF), and the linear (LVBGF). The other three models evaluated include the Gompertz function, the three-parameter logistic function, and a seasonal a damped model described by Porch et al. (2002).

 

Reproductive Biology of Red Drum (Sciaenops ocellatus) in the North-central Gulf of Mexico

The objective of this research effort is to use the most accurate and current methods available to determine the reproductive characteristics of Red Drum, including (1) the spawning season, (2) the sex-specific age and length at maturity, and (3) the spawning interval.

Figure 4.CB
Percent reproductive phase by month of female and male Red Drum (n = 671) captured in the northern Gulf of Mexico. The phases were identified using the terminology defined by Brown-Peterson et al. (2011), and are: immature (IMM), developing (DEV), early developing (EDEV, subphase of developing), spawning capable (SC), actively spawning (AS, subphase of spawning capable) regressing (RGR), and regenerating (RGN). The number of samples collected each month is indicated by the number near the top of each bar.
Figure 5.CB

Photomicrograph of female histology sample imaged at 10x magnification, illustrating the early developing reproductive phase. Early developing females were identified by predominance of primary growth (PG) and the presence of some cortical alveolar (CA) oocytes.

 

Detecting Residency and Emigration of Red Drum (Sciaenops ocellatus) in the North-central Gulf of Mexico Using Stable Isotope Analysis

The objective of this research effort is to use tissue specific carbon (δ13C) and nitrogen (δ13N) isotope composition to determine ontogenetic movement of Red Drum through coastal and marine systems. Differences in stable isotope composition across year age classes with respect to reproductive phase and location of catch will help better determine ontogenetic movement of Red Drum between estuarine and marine systems.

Figure 6.CB

Size and Age Distribution of Gulf Menhaden (Brevoortia patronus) across the Northern Gulf of Mexico

The objective of this research effort is to use the Gulf of Mexico states’ monthly fishery independent data collection efforts to understand temporal and spatial dynamics of the Gulf Menhaden fishery. Length and weight data are examined for individuals collected by state agencies in Texas, Louisiana, Mississippi, and Alabama. Age of Gulf Menhaden is determined blindly using whole, polished otoliths and scale samples. This work will also be used to form recommendations for methodology improvements to enhance ageing precision.

Figure 5.KP

Gulf Menhaden sampling stations by state agencies in Texas (red), Louisiana (blue), Mississippi (green), and Alabama (yellow). Louisiana is separated into five Coastal Study Areas (CSAs)

 

Figure 6.KP

 

Spatially grouped densities of Gulf Menhaden fork lengths within sub-basins of TX, CSAs of Louisiana, Mississippi, and Alabama.

 

Network Analysis of Trophic Dynamics in the Northern Gulf of Mexico

The objectives of this research effort are to create a trophic network for the northern Gulf of Mexico using historical literature. Network analysis techniques are used to test the resilience of the trophic dynamics to perturbations. We also will use these techniques to examine how predator feeding effort may be reallocated among other prey when prey items are reduced. This work will provide and understanding of the complex trophic dynamics in the Gulf and highlight the cascading effects of perturbations in the system.

Figure 1.MO

A visual representation of a subset of the trophic network in the northern Gulf of Mexico. The arrows connect predator and prey and the thickness represents the relative weight of that connection.

 

Figure 2.MO

Changes in feeding pressure on prey items when the feeding effort on Gulf Menhaden (A) or Blue Crab (B) were reduced. The dark bars represent when Menhaden were reduced and the light bars represent when Blue Crab were reduced.

 

Heirarchical Bayesian Surplus Production Model for Blue Crab

The objectives of this research effort are to develop a heirarchical Bayesian surplus production model in the northern Gulf of Mexico to assist with stock assessments of Blue Crab. Currently, inshore Blue Crab are assessed and managed at a state level, however, there is evidence that there is only one stock. This model model uses indices of abundance and catch data from different basins or states across the Gulf to estimate a total abundance of Blue Crab in the northern Gulf of Mexico. The heirarchical Bayesian framework is flexible, allows easy incorporation of multiple data sets, and allows for the direct estimation of missing data or errors. The sensitivity of the analysis is tested to the exclusion of each index of abundance.

Figure 3.MO

The posterior distributions of key parameters estimated with the surplus production model, carrying capacity (K), intrinsic population growth rate (r), and initial biomass (B0). The red lines represent the 95% credible intervals. The top row shows parameter estimates from the model run using only adult indices of abundance and the bottom row shows parameter estimates from the model run using only juvenile indices of abundance.

 

Figure 4.MO

Estimated biomass trajectories for the Blue Crab stock when using only adult indices of abundance or only juvenile indices of abundance. Biomass/BMSY is a commonly used fishery reference point to assess the state of a stock. BMSY represents the biomass at which maximum sustainable yield is achieved.

 

Age and Growth Characteristics of Atlantic Chub Mackerel (Scomber colias) in the Northwest Atlantic

The objective of this research effort is to describe age and growth characteristics of Atlantic Chub Mackerel from the coastal Mid-Atlantic and New England region of the United States. Age estimates from both whole and sectioned otoliths are evaluated to determine which method results in highest precision. Otolith-derived age estimates are then used to evaluate the length-at-age relationship using a suite of non-linear growth models. The weight-at-length relationship is modeled using a power function. Median growth parameter estimates of Atlantic Chub Mackerel from the northwest Atlantic are compared with mean parameter estimates reported from other regions in the Atlantic and Mediterranean.

Figure 1.TD
Non-linear candidate models fit using a Bayesian approach to describe the length-at-age relationship for Atlantic Chub Mackerel in the northwest Atlantic.

Figure 2.TD
Predicted lengths at ages calculate from parameter estimates reported for studies in other regions. Predictions are averaged for each region and then a curve fit to compare average growth among regions.

Figure 3.TD
Weight-at-length relationship of Atlantic Chub Mackerel in the northwest Atlantic. The line is a power function fit to observed total length (cm) and weight (g).

Reproductive Dynamics of Atlantic Chub Mackerel (Scomber colias) in the Northwestern Atlantic

The objective of this research effort is to describe elements of the reproductive biology of Atlantic Chub Mackerel in the northwest Atlantic. Histological techniques are used to determine sex and length- and age-specific sexual maturity. The approximate spawning season is identified using histological indicators and evidence of spawning from analysis of historical data on larval fish collections and commercial catch. These data will be used to inform the effective management of Atlantic Chub Mackerel stock.

Figure 4.TD
Histology sample imaged at 10x magnification from a mature female Atlantic Chub Mackerel (35.8 cm TL) caught in October 2017. Mature females were identified by the presence of blood vessels, loosely packed primary growth oocytes (PG), diversity of PG size, and a thick ovarian wall.

Figure 5.TD
Logistic model describing the length at maturity for female Atlantic Chub Mackerel (n=151) from the northwest Atlantic, where the inflection point L50 represents the mean parameter estimate for total length-at-50% maturity. Individuals were assigned a binomial maturity code indicating immature (0) or mature (1) status.

Evaluating Enhancement Strategies for Spotted Seatrout (Cynoscion nebulosus) in the North-central Gulf of Mexico

The objective of this research effort is to use a simulation-based analysis to evaluate the efficacy of stock enhancement for Spotted Seatrout in the north-central Gulf of Mexico. An operating model is developed to represent the biological characteristics of the stocks and attributes of the associated recreational fisheries. The results from this work will provide insight into the magnitude of effort needed to enhance Spotted Seatrout stocks and the associated costs.

Flow model1
 

Visual representation of the operating model used in the Spotted Seatrout simulation-based analysis.

 

 

Management Strategy Evaluation for Vermilion Snapper (Rhomboplites aurorubens)

The objectives of this research effort are to develop a management strategy evaluation for Vermilion Snapper in the northern Gulf of Mexico. A suite of operating models will be used to represent the true underlying population dynamics of the stock and the major uncertainties associated with that stock, such as stock-recruit relationship. The operating models will be used to test a set of proposed management strategies and performance statistics will be used to evaluate how well or poorly the stock responded to each strategy. This methodology can be used to evaluate trade-offs of different management regulations and how variable the outcome may be prior to implementing any regulations. It will provide a tool for informing future management and identifying areas where more research effort and improved data would enhance assessment efforts.

Figure 5.MO

Visual representation of the MSE loop to be projected 40 years into the future to assess long-term impacts of management decisions.