A comparison of the size and age distribution of red snapper Lutjanus campechanus to the age of artificial reefs in the northern Gulf of Mexico

Abstract

Size and age of red snapper, Lutjanus campechanus, were sampled from April through November 2010 and compared with the age of the artificial reef at the site of capture. Artificial reefs were deployed in 2006 (n=20, 4 year old reefs), 2009 (n=10, 1 year old reefs), and 2010 (n=10, 0.5 year old reefs). Red snapper were sampled using hook-and-line and a fish trap. After sampling was completed, SCUBA divers estimated the remaining red snapper densities at sample reefs using visual surveys, photographs, and video recordings. Red snapper total densities per reef were estimated from both captured and diver counted fish. In the laboratory, all captured red snapper were weighed (0.1 g), measured (mm), and the otoliths removed for age estimation. Annual growth increments on each otolith were counted independently four times. After four readings, two readers examined any otoliths with counts that differed and attempted to reach a consensus on age. If an agreement on age could not be reached the otolith was rejected. All otoliths were counted whole if age < 7, while all older otoliths were sectioned for counting. Mean ± SD age of red snapper showed significant differences when compared across reef age, with older reefs yielding older fish: 2006-reefs = 3.6 ± 1.2 years, 2009-reefs = 2.0 ± 1.7 years, 2010-reefs = 1.7 ± 1.0 years (ANOVA: F2, 1025 = 194.23, P < 0.0001). A significant positive correlation between fish age and reef age was detected with 37% (r2 = 0.37, P < 0.0001) of the variance of fish age explained by reef age. Comparisons of a subset (n = 8) of 2006 and 2010 reefs, all at the same depth (30 m) also showed a significant reef age effect on fish age, that negated possible depth difference effects (t-test:228 = 9.29 P < 0.0001). Also, comparisons of known distances to other “public” reefs failed to detect a significant effect on fish age and density, and negated possible reef proximity effects (fish age: Pearson’s r = 0.160, P = 0.345; density: Pearson’s r = -0.061, P = 0.721). Growth rates were not significantly different among reef ages for all fish < 10 years, indicating that older reefs did not provide “better” habitat (ANCOVA: F3,1018 = 2.98, P = 0.085). These results suggest that new artificial reefs are quickly colonized by young fish, and older reefs are more important for older red snapper. This scenario supports the contention that artificial reefs in the northern Gulf of Mexico are producing red snapper and not just acting as attractants.