Spatial Variability in the Growth of Sheepshead (\u3ci\u3eArchosargus probatocephalus\u3c/i\u3e) in the Southeast US: Implications for Assessment and Management

Understanding geographic variation in growth dynamics is essential for the management of exploited fish populations because such variation can be used to define stock structure and influence perceptions of stock productivity. Sheepshead (Archosargus probatocephalus) is a species targeted by both commercial and recreational fisheries, and is distributed throughout the north and central Atlantic Ocean and Gulf of Mexico. We analyzed fishery-dependent and –independent length-at-age and weight-at-length data from Texas, Louisiana, Mississippi, Alabama, Florida, South Carolina, North Carolina, and Virginia to investigate the geographic variation in growth of Sheepshead. We constructed a series of von Bertalanffy growth functions (VBGF) and length-weight power equations using a Bayesian framework that included sex, latitudinal, and regional effects. Median posterior VBGF parameter estimates of asymptotic length (L∞) for females ranged from 561 mm fork length in the Virginia Chesapeake Bay to 418 mm in Florida Gulf coast, while the posterior median growth coefficient (k) ranged from 0.42 yr−1 in Texas to 0.20 yr−1 in the Florida Atlantic. Predicted length-at-age and weight-at-length varied considerably among States. Predicted length-at-age for age-1 and -5 individuals was greater in the Gulf of Mexico than the Atlantic. However, predicted length-at-age for older age classes was greater in the Atlantic. Predicted weight-at-length decreased along latitudinal gradients in the Atlantic and the lowest values were found in Mississippi. Given the impact of growth on fisheries reference points, such geographic variation in growth can inform the development of assessment efforts for Sheepshead in the Gulf of Mexico and Atlantic

Timing and locations of reef fish spawning off the southeastern United States

<div><p>Managed reef fish in the Atlantic Ocean of the southeastern United States (SEUS) support a multi-billion dollar industry. There is a broad interest in locating and protecting spawning fish from harvest, to enhance productivity and reduce the potential for overfishing. We assessed spatiotemporal cues for spawning for six species from four reef fish families, using data on individual spawning condition collected by over three decades of regional fishery-independent reef fish surveys, combined with a series of predictors derived from bathymetric features. We quantified the size of spawning areas used by reef fish across many years and identified several multispecies spawning locations. We quantitatively identified cues for peak spawning and generated predictive maps for Gray Triggerfish (<i>Balistes capriscus</i>), White Grunt (<i>Haemulon plumierii</i>), Red Snapper (<i>Lutjanus campechanus</i>), Vermilion Snapper (<i>Rhomboplites aurorubens</i>), Black Sea Bass (<i>Centropristis striata</i>), and Scamp (<i>Mycteroperca phenax</i>). For example, Red Snapper peak spawning was predicted in 24.7–29.0°C water prior to the new moon at locations with high curvature in the 24–30 m depth range off northeast Florida during June and July. External validation using scientific and fishery-dependent data collections strongly supported the predictive utility of our models. We identified locations where reconfiguration or expansion of existing marine protected areas would protect spawning reef fish. We recommend increased sampling off southern Florida (south of 27° N), during winter months, and in high-relief, high current habitats to improve our understanding of timing and location of reef fish spawning off the southeastern United States.</p></div

External validation of spawning predictions.

<p>Boxplots of model-predicted Z-score standardized probabilities of collecting a spawning female underlying locations where spawning females were collected by Florida Fish and Wildlife Conservation Commission (FWC; Lowerre-Barbieri et al. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0172968#pone.0172968.ref039" target="_blank">39</a>]), LGL Ecological Research Associates ([<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0172968#pone.0172968.ref067" target="_blank">67</a>]), MARMAP Fishery Dependent Sampling (MMFD), and anecdotal reports from fishers (‘Tishler’) collected by Tishler-Meadows [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0172968#pone.0172968.ref066" target="_blank">66</a>]. Z-Scores above zero were interpreted as providing support for model predictions. Inset numbers denote sample sizes.</p

Probability of encountering a spawning condition female Vermilion Snapper.

<p>Predicted mean (left) and standard error (right) probabilities of observing spawning condition female Vermilion Snapper at time and conditions of peak spawning, relative to external validation observations (+). Raster color-coding based on 2.5 standard deviations from the mean. Green boxes denote no-take marine protected areas and SMZs. Basemap courtesy ESRI Ocean Basemap and partners.</p

Number of gear deployments with multispecies observations of spawning females from SERFS.

<p>Number of gear deployments with multispecies observations of spawning females from SERFS.</p

Spawning condition females and valid sets by month.

<p>Percentage of SERFS samples of females within 48 hours of spawning (<i>left</i>) and number of sets (<i>right</i>) where a histological sample was taken, by species and sampling month.</p

Logistic regression model fit statistics for probability of encountering a fish within 48 hours of spawning, with percent deviance explained (i.e. percent variability explained by inclusion of additional variable); cross-validation results for Area Under the Curve (AUC), False Positive Rate (FPR) and False Negative Rate (FNR); and percentage of 500 runs where random variable inclusion in model outperformed model-selected bathymetric variable (‘Random test’).

<p>See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0172968#sec002" target="_blank">Methods</a> for additional details.</p