Juvenile Red Snapper Lutjanus Campechanus Research Articles

Fourier-transform near infrared spectroscopy (FT-NIRS) rapidly and non-destructively predicts daily age and growth in otoliths of juvenile red snapper Lutjanus campechanus (Poey, 1860)

Fourier Transform Near Infrared Spectroscopy (FT-NIRS) has shown great promise as a rapid and non-destructive method for predicting age in years from a variety of ageing structures in fish. Herein we assess the utility of FT-NIRS to predict both daily age and otolith weight from whole otoliths of juvenile red snapper Lutjanus campechanus collected from the US Gulf of Mexico and southeastern US Atlantic Ocean. Spectral data from whole otoliths (n = 153) were collected with a FT-NIR spectrometer while manipulating otolith presentation with an external aperture to maximize signal to noise. Traditional daily age estimates and otolith weights were correlated to spectral data via partial least-squares regression to create age and otolith weight prediction models that were compared across aperture treatments and geographic region. FT-NIRS calibration models using apertured spectra were significantly better at predicting age than models using non-apertured spectra (model rank = 5 and 10, respectively) and yielded predicted age to within an average of six days relative to traditional estimates (R2 = 0.91, RMSECV = 6.08 days, bias = −0.04). Exponential growth models produced from FT-NIRS-predicted ages (Lt = 28.3*e0.01t) were not significantly different (likelihood ratio χ2 = 1.05, df = 2, p = 0.59) from those derived from traditional ages (Lt = 30.7*e0.009t). Additionally, FT-NIRS models were capable of predicting otolith weights that were not significantly different from direct measurements (t = 1.75, df = 147, p = 0.08). This study is the first to demonstrate successfully the potential of FT-NIRS to predict daily age and otolith weight in juvenile fishes, as well as the first to manipulate external apertures to optimize signal to noise. These findings support the potential for broad application of FT-NIRS in fisheries biology.

Comment: Accounting for Fishing Mortality When Comparing Density‐Dependent with Density‐Independent Mortality in Gulf of Mexico Red Snapper

Gazey et al. (2008) investigated the potential for density-dependent total mortality to act on the population of juvenile Red Snapper Lutjanus campechanus in the western Gulf of Mexico. Their analy...

Distinguishing Wild from Hatchery‐Produced Juvenile Red Snapper with Otolith Chemical Signatures

AbstractOtolith chemical signatures were evaluated as natural tags to distinguish wild from hatchery‐produced juvenile red snapper Lutjanus campechanus. Otoliths were sampled from 59 hatchery‐reared fish and 146 wild fish collected over the continental shelf from northwest Florida to Texas. One sagitta from each fish was cleaned, dissolved in ultrapure nitric acid, and analyzed with sector field inductively coupled plasma mass spectrometry to test for differences in otolith element:Ca ratios (Ba:Ca, Li:Ca, Mg:Ca, Mn:Ca, and Sr:Ca) between wild and hatchery fish. The second sagitta was cleaned, ground to a fine powder, and analyzed with stable isotope ratio mass spectrometry to test for differences in delta (δ) values of the stable isotopes 13C and 18O. Significant differences existed in otolith chemical signatures between hatchery and wild juveniles (multivariate analysis of variance, Pillai's trace: P < 0.001). Jackknifed classification accuracies from linear discriminant function analysis indicated that hatchery fish could be distinguished from wild fish with 100% accuracy based on otolith chemical signatures. The most important otolith chemistry feature in distinguishing hatchery from wild fish was δ13C, with the mean difference in δ13C between hatchery and wild fish (−2.6‰) being similar to the mean difference in δ13C between hatchery feeds and the predominant food of wild juveniles (−2.8‰). Overall, results suggest that otolith chemical signatures may be employed as effective natural tags for mass marking of future stockings of red snapper or other marine fishes to estimate the hatchery contribution to wild populations.

Effect of Trawling and Habitat on Mercury Concentration in Juvenile Red Snapper from the Northern Gulf of Mexico

AbstractWe evaluated mercury (Hg) contamination in juvenile red snapper Lutjanus campechanus (<250 mm total length) as an indicator of Hg pollution on the northern Gulf of Mexico (GOM) continental shelf. Specifically, we examined the effects of fish size, commercial shrimp trawling, and habitat type on total Hg concentrations and stable nitrogen isotope ratios (δ15N; a proxy for trophic position) in red snapper. Red snapper Hg concentrations and δ15N values were positively and significantly correlated with fish size. In addition, red snapper collected over trawled habitats had significantly higher Hg concentrations and δ15N values than did red snapper collected from similar, nontrawled habitats. Red snapper also exhibited habitat‐specific differences in Hg concentrations and δ15N values, but differences were size dependent and generally small. Our study suggests that the Hg concentrations of juvenile red snapper in the northern GOM are elevated in areas where commercial shrimp trawling occurs, possibly due to increases in both red snapper trophic position and bioavailable Hg in trawled areas. Additional studies are needed to determine whether Hg concentrations are elevated in fish from trawled areas in other marine ecosystems.

Effects of habitat complexity and predator exclusion on the abundance of juvenile red snapper

Predator exclusion and habitat complexity factors that may affect juvenile red snapper Lutjanus campechanus habitat selection were examined in field and laboratory experiments. A significant predator exclusion effect was detected. Uncaged shell habitats showed significantly lower numbers of age 0 year red snapper, and both uncaged shell and block‐shell habitats showed significantly lower numbers of age 1 year red snapper compared with caged habitats (P < 0·001). Habitat complexity also affected age 0 year red snapper, as mean abundance significantly decreased with decreased habitat complexity (P < 0·001). In the laboratory, age 0 year red snapper association with complex habitats significantly increased with exposure to a predator Gulf flounder Paralichthys albigutta (P < 0·001). This study showed that predator exclusion and habitat complexity were significant factors that affected the abundance of juvenile red snapper in nursery areas of the northern Gulf of Mexico. Predation may affect juvenile red snapper abundance directly through mortality and indirectly by influencing habitat selection.

Use of coded-wire and visible implant elastomer tags for marine stock enhancement with juvenile red snapper Lutjanus campechanus

As part of a stock enhancement research project in the Gulf of Mexico, we evaluated optimal tag placement sites, retention, and detection in hatchery-reared juvenile red snapper Lutjanus campechanus (46–110 mm standard length) with coded-wire tags (CWT) and visible implant elastomer tags. Coded-wire tags were implanted in nose cartilage, left cheek muscle, the nape, dorsal musculature, and the caudal peduncle. Three weeks after tagging, all implant locations tested showed tag retention over 97% except for those implanted in the dorsal musculature (90%). No additional tag loss was found between 3 and 6 weeks after tagging regardless of implant location or fish size. We selected the nape musculature for larger-scale tagging because of high tag retention and ease of tagging. Retention of CWTs in the nape after 6 months was 99% ( n = 285). Visible implant elastomer (VIE) tags were implanted in muscular and fin tissue of juvenile snapper and retention rates were ≥95% (after 6 weeks) for all implant locations except for anal fin muscles (87% tag retention). In a separate study, 6 months after tagging, fish size-at-tagging and the number of VIE marks implanted in the caudal fin significantly influenced tag retention (two-way analysis of variance, P = 0.026). After experimental stock enhancement releases, divers 17–20 m deep, found that VIEs in caudal fins were highly visible, but those in the nose area were difficult to see due to pigmentation over the tags and fish orientation. Tag color influenced tag visibility and red and orange elastomer tags were the most visible among eight colors tested (red, orange, yellow, green, pink, black, blue, and purple). Divers commonly confused green elastomer tags for yellow, and sometimes confused red, pink and orange. No color confusion occurred when similar colors were observed side-by-side however.

Delineation of Essential Habitat for Juvenile Red Snapper in the Northwestern Gulf of Mexico

Seasonal habitat suitability index models were developed for juvenile red snapper Lutjanus campechanus in the western Gulf of Mexico. Habitat factors considered in the analysis included water temperature, salinity, and dissolved oxygen at the bottom; depth and density of offshore petroleum platforms; and low-relief bottom structures. High-value habitat for juvenile red snapper is characterized by depths between 18 and 64 m, water temperatures of 24–26°C, salinities around 35%, and dissolved oxygen levels of at least 5 mg/L. Density of low-relief structures was not a significant habitat element, and an inverse association was found between juvenile red snapper abundance and the density of offshore platforms. Results of the model analysis suggest that the step-like expansion of the hypoxic area (dissolved oxygen ≤ 2 mg/L) offshore of the mouth of the Mississippi River and west to the Louisiana–Texas border, which first occurred in 1993, has reduced habitat carrying capacity for juvenile red snapper in this region by up to 25%, averaging 19%. This environmental change may limit the level to which overfished Gulf red snapper stocks can be rebuilt to historical levels.

Reduction of Juvenile Red Snapper Bycatch in the U.S. Gulf of Mexico Shrimp Trawl Fishery

Bycatch reduction devices (BRDs) have been mandated for use in the U.S. Gulf of Mexico shrimp fishery to reduce shrimp trawl mortality of juvenile red snapper Lutjanus campechanus. Conditional survival of juvenile red snapper from shrimp trawl bycatch has been estimated to be on the order of 12%. The BRDs have been estimated to reduce shrimp trawl bycatch mortality by more than the 50% reduction that has been estimated as necessary to rebuild the stock by the target date of 2019. Results from analyses in this study that used observer data collected during 1992–1996 do not support this contention. A low fraction of the annual bycatch occurs during times of the year when BRDs effectively exclude juvenile red snapper at the sizes encountered. Maximum potential exclusion of juvenile red snapper with the use of BRDs is only about 25–27%, not 59% as has been previously estimated. If rebuilding requires a 50% reduction in age-0 and age-1 red snapper bycatch mortality to achieve the stock recovery targets, this study's results clearly demonstrate that the BRD by itself will not produce the mortality reductions necessary to meet this objective.