Browsing by Author "Dr. Jeffrey Buckel, Committee Chair"

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    Developing an index of abundance for gag grouper in North Carolina
    (2009-08-12) Adamski, Kyle Michael; Dr. Jeffrey Buckel, Committee Chair; Dr. Joseph Hightower, Committee Member; Dr. Kenneth Pollock, Committee Member
    Gag grouper (Mycteroperca microlepis) are an economically important fish in the U.S. south Atlantic. Juvenile gag grouper utilize seagrass habitat soon after larval ingress into estuarine environments. The recent stock assessment for gag grouper indicated the need for a fishery-independent index of abundance. The goal of this study was to assess the potential for a post-larval and juvenile abundance index in North Carolina. Data on post-larval gag collected during the NOAA Beaufort Inlet Bridgenet Program (weekly samples from November – May of 1986 to 2008) were examined; additionally, ichthyoplankton were sampled nightly in spring of 2007 and 2008. A 5-m otter trawl was used to sample juvenile gag in seagrass beds at 15 to 20 randomly selected stations every two weeks from June through September in both 2007 and 2008; data on seagrass species and blade densities were determined before each trawl. Age at capture, pelagic larval duration (PLD, determined from transition mark), and fertilization dates were estimated from post-larval and juvenile otolith microstructure. A single cohort was produced each year; estimated fertilization dates ranged from February through April around full and new moons supporting planned January through April fishing closures for adult gag grouper. From 1986 to 2008, weekly concentrations of post-larval gag grouper were highest from late April to mid-May with peak ingress around new moons. Juvenile gag were caught from June through September with highest catch-per-unit-effort (CPUE) in July and August. Time of year, percent seagrass coverage, seagrass species, and sound influenced CPUE of juvenile gag grouper. Growth rates of juveniles were rapid (~1.6 mm/d) during summer months and did not differ between years. The mean PLD was ~ 43 d and did not differ among collection months suggesting no effect of PLD on survival. An annual index of post-larval abundance (adjusted for lunar effects) was developed. The spawning stock biomass (SSB) from the most recent gag grouper assessment was positively correlated with this index; thus, the post-larval index could be used as a fishery-independent index of SSB.
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    Foraging ecology of the early life stages of four shark species (Rhizoprionodon terraenovae, Carcharhinus limbatus, Carcharhinus isodon, and Carcharhinus brevipinna) in Apalachicola Bay, Florida.
    (2003-04-30) Bethea, Dana Michelle; Dr. Jeffrey Buckel, Committee Chair; Dr. Peter Rand, Committee Member; Dr. Jason Osborne, Committee Member; Dr. John Carlson, Committee Member
    As top predators, sharks have an important role in marine ecosystems in relation to populations of fish and invertebrates at lower trophic levels. Fishery management plans stress the need for an ecosystem approach, but few quantitative data on the foraging ecology of sharks have been published. Results from a literature review found that shark species close in taxonomic relation have high diet overlap. Stomach contents and catch data of early life stages of Atlantic sharpnose (Rhizoprionodon terraenovae), blacktip (Carcharhinus limbatus), finetooth (Carcharhinus isodon), and spinner sharks (Carcharhinus brevipinna) taken from fishery independent surveys in Apalachicola Bay, Florida, April-October 1999-2002 were examined to test for resource competition. All species are capable of taking teleost prey from birth, though Atlantic sharpnose and blacktip sharks show an ontogenetic shift in diet. Young-of-the-year Atlantic Sharpnose sharks feed mainly on shrimp, juveniles on sciaenids, and adults on clupeids. Young-of-the-year blacktip sharks feed mainly on sciaenids, whereas juveniles feed on clupeids. The primary prey of young-of-the-year and juvenile finetooth and spinner sharks is menhaden. Seven of ten size-selectivity tests showed neutral selection. Atlantic sharpnose and finetooth sharks consume relatively small-sized prey (over 60% <20% of their length) compared to teleost piscivores while blacktip sharks consume relatively larger prey (58% >20% of their length). Regardless of maturity state and species, diet overlap is high for species-life stage combinations that are similar in size; however, species-life stages did not show significant overlap in habitat use. One possible interpretation is that prey categories shared by similar-sized species are not limiting, but competition may exist for available habitat resources. More intensive monitoring is needed to fully understand temporal and spatial habitat use patterns among these early life stages. Quantifying the links among these sharks and the links between these sharks and resource species are critical for ecosystem modeling and a key step to a broader approach in fisheries management.