Gray Triggerfish Reproductive Biology, Age, and Growth off the Atlantic Coast of the Southeastern USA

<p>The Gray Triggerfish <i>Balistes capriscus</i> supports fisheries on both sides of the Atlantic Ocean. We utilized fishery-independent samples to assess the age structure, growth, sex ratio, size and age at maturity, spawning season, and spawning frequency of the Gray Triggerfish population off the southeastern U.S. Atlantic coast. From 1991 to 2012, 7,685 samples were collected, ranging in FL from 82 to 578 mm and ranging in age from 0 to 13 years. Our study provides key life history information for an exploited population and is the first to comprehensively describe age, growth, and reproduction for a <i>Balistes</i> species. We documented that the Gray Triggerfish is sexually dimorphic, with adult males attaining larger sizes at age and a larger maximum size than females. Sex-specific growth curves were fitted, yielding the following von Bertalanffy equations: FL<i>_t</i> = 419[1 – <i>e</i>^{–0.54(<i>t</i>} ^{+ 0.61)}] for males and FL<i>_t</i> = 352[1 – <i>e</i>^{–0.94(<i>t</i>} ^{+ 0.22)}] for females. This species is characterized by a medium size at maturity (the smallest mature female was 179 mm FL; the smallest mature male was 183 mm FL) and relatively early age at maturity (the youngest mature female and male were age 0). Some shifts in population attributes coincided with a period of increased fishing pressure. Due to tighter regulations on snapper and grouper fisheries, the Gray Triggerfish has become a more targeted species. Fisheries biologists and managers should continue to evaluate potential impacts and establish management regulations that consider the region-specific reproductive season, size and age at maturity, and sex-specific differences in growth documented in this study.</p> <p>Received April 20, 2016; accepted January 9, 2017 Published online March 30, 2017</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

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

Fishery-independent sampling and multispecies spawning locations.

<p>On left, fishery-independent samples of female fish within 48 hours of spawning, by species. Gray shapes denote histological samples, black shapes denote collections of spawning condition females, with triangles denoting chevron traps, diamonds denoting short bottom longline, and circles denoting long bottom longline. On right, sites where females of multiple species have been captured in spawning location at the same time (labeled by collection year). Green boxes denote no-take marine protected areas. Basemap courtesy ESRI and National Park Service.</p

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

Input variables considered in logistic regression model.

<p>Input variables considered in logistic regression model.</p

Summary statistics for water depth (m), salinity (ppt), and temperature (°C) during SERFS observations of spawning condition females.

<p>Summary statistics for water depth (m), salinity (ppt), and temperature (°C) during SERFS observations of spawning condition females.</p

Vermilion Snapper spawning.

<p>Maps of Edisto MPA (green) square and surrounding shelf edge showing <b>A)</b> Depth from multibeam bathymetry and SERFS samples with spawning condition (stars) and non-spawning condition (Xs) female vermilion snapper, <b>B)</b> BPI from Benthic Terrain Modeler and squares denoting habitat type (HB: hardbottom, NH: not hardbottom, PH: potential hardbottom) from SEAMAP-SA, <b>C)</b> Model predictions of spawning locations at month and lunar phase of peak spawning and MARMAP fishery-dependent samples of spawning condition female Vermilion Snapper (crosses), and <b>D)</b> standard error in model predictions of peak spawning.</p

Summary statistics (mean ± standard deviation) for apparent use of multi-year spawning locations.

<p>Multi-year spawning location size computed as minimum convex polygon containing all collections within a site.</p

Number of collections from MARMAP/SERFS and FWC fishery-independent data with histological sampling (Samples), with number of sets containing females within 48 hours of spawning (Female Spawners), number of sets containing females and males within 48 hours of spawning (All Spawners), number of sets with three or more histologically-sampled fish for the species (Valid Sets), and number Valid Sets within the high-resolution multibeam bathymetry (MB Valid Sets).

<p>Number of collections from MARMAP/SERFS and FWC fishery-independent data with histological sampling (Samples), with number of sets containing females within 48 hours of spawning (Female Spawners), number of sets containing females and males within 48 hours of spawning (All Spawners), number of sets with three or more histologically-sampled fish for the species (Valid Sets), and number Valid Sets within the high-resolution multibeam bathymetry (MB Valid Sets).</p