Abstract
AbstractFor the economically and ecologically important Red Snapper Lutjanus campechanus, depth distribution patterns across ontogeny are not well understood, particularly in the southeastern U.S. Atlantic Ocean (SEUSA). Using data derived from two fishery‐independent surveys targeting hardbottom habitats, we examined patterns of age‐ and length‐specific depth distributions of postjuvenile (age 1+) Red Snapper in the SEUSA. We also compared age and length distributions between fishery‐independent surveys and commercial hook‐and‐line catches to make inferences about gear‐specific age and size selectivity, which could have implications for gear‐specific interpretations of Red Snapper depth distribution patterns and for determining selectivity functions used in stock assessments. Older, larger Red Snapper were generally distributed throughout all depths, whereas the younger and smaller Red Snapper occurred disproportionately in relatively shallow waters. For Red Snapper equal to or larger than 50 cm FL, we found no evidence of a positive relationship between depth and age or length. Additionally, age and length distributions of Red Snapper ≥ 50 cm FL did not differ between fishery‐independent surveys and the commercial hook‐and‐line fishery. These results provide no support for assertions of greater abundances of older and larger Red Snapper in deeper SEUSA waters. As observed in this study for Red Snapper in SEUSA waters, we suggest that patterns of increasing age and size with depth for multiple reef‐associated fish species in SEUSA and Gulf of Mexico waters may be driven by younger and smaller fish occurring in shallower waters, and older and larger fish being distributed more equally across depths. Analyses to test this hypothesis for multiple species would be informative for their assessment and management and are recommended.Received October 21, 2013; accepted March 11, 2014
Highlights
Foraging requirements, competitive interactions, and predation risk vary throughout an animal’s lifetime due to increases in body size and changes in behavior (Werner and Gilliam 1984; Ludwig and Rowe 1990)
As observed in this study for Red Snapper in southeastern U.S Atlantic Ocean waters (SEUSA) waters, we suggest that patterns of increasing age and size with depth for multiple reef-associated fish species in SEUSA and Gulf of Mexico waters may be driven by younger and smaller fish occurring in shallower waters, and older and larger fish being distributed more across depths
Some SEUSA stakeholders have asserted that relatively old and large Red Snapper are disproportionately distributed in relatively deep waters, which has implications for fishing sector-specific selectivity functions used in recent Red Snapper stock assessments
Summary
Competitive interactions, and predation risk vary throughout an animal’s lifetime (i.e., ontogeny) due to increases in body size and changes in behavior (Werner and Gilliam 1984; Ludwig and Rowe 1990). Successful assessment and management of marine fish species is predicated in part upon a clear understanding of ontogenic shifts in distribution patterns, driven, for example, by changing habitat affinities with ontogeny. If older and larger Red Snapper were disproportionately distributed in relatively deep waters, but the recreational or commercial hook-and-line fishery was centered in shallower waters, a dome-shaped selectivity pattern (which assumes that the largest, most fecund fish escape capture), as used for Red Snapper in the GOM (Cowan 2011), might be more appropriate than a flat-top selectivity pattern (in which selectivity plateaus with increasing age or length; Thorson and Prager 2011). We examine patterns of age- and length-specific depth distributions of postjuvenile (age 1+) Red Snapper in the SEUSA to inform future Red Snapper stock assessments and, more generally, broaden understanding of the ecology of this economically and ecologically important species. Because relatively old and large Red Snapper are thought to become progressively less associated with hardbottom habitats (Szedlmayer 2007; Gallaway et al 2009; Cowan 2011), we assessed the sparse Red Snapper catch history and depth information available from a fishery-independent survey that included sampling of unstructured (nonhardbottom) habitats in SEUSA waters
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