A comparison of reproductive potential of red snapper, Lutjanus campechanus: natural and artificial habitats in the northern Gulf of Mexico

Abstract

From the Extended Abstract: "This study compares reproductive potential of red snapper from AH and from NHB. The natural hard bottom habitats in the GOM are thought by some to be historical centers of abundance for this species, given that red snapper are a relief associated fish and the existence of the banks precedes artificial reef in the GOM. Red snapper were collected in the summer (June-August) of 2009 and 2010 and then again twice quarterly from 2011 to 2013. Three NHB sites (Jakkula, McGrail, and Bright Banks) and two AH sites (East Cameron and Eugene Island) were sampled. Red snapper were collected opportunistically with vertical long lines and single hook lines. All female red snapper were measured for total length, total weight, and eviscerated body weight. Ovaries were removed and frozen at sea. In the lab, ovaries were weighed and fixed in 10% formalin for a minimum of two weeks. Histological slides from sectioned ovaries were then prepared either at the LSU Vetinary School or in our laboratory. Mean gonadosomatic index (GSI) values were plotted by month to examine seasonal changes in red snapper reproductive potential among sites. The GSI is indicative of the energy a fish has invested in reproduction, thus a larger GSI corresponds with a greater potential reproductive output.

Red snapper GSI at all sites was significantly higher in June, July, and August, during peak spawning season, than for other months (Figure 1, ANOVA, p<0.0001). The GSI were not significantly different among sites in other non-peak spawning months (September-May). Data from summer samples were graphed individually and showed red snapper mean GSI was higher at the three natural habitats than at artificial habitats. When the sites were pooled by habitat type the data show that red snapper from NHB sites exhibited higher mean GSI than red snapper from AH sites (Figure 2, ANOVA, p < 0.0001) during all peak spawning months."

We hypothesize these differences may be attributed to more abundant older fish at NHB sites that invest more energy to reproduction and less energy to growth. These results corroborate previous studies, which found age 2-3 red snapper dominate AHs, whereas older individuals are normally found inhabiting NHBs (Gallaway et al. 2009). Habitat differences in red snapper mean GSI could be the result of disparate age structure of red snapper between the habitats. Moving forward, age and growth data from fish collected in this study will be used to help elucidate possible mechanisms driving the large disparity in red snapper mean GSI between the habitat types.