Type of Document Dissertation Author DeVries, Douglas Alan Author's Email Address firstname.lastname@example.org URN etd-04062006-141323 Title The Life History, Reproductive Ecology, and Demography of the Red Porgy, Pagrus Pagrus, in the Northeastern Gulf Of Mexico Degree Doctor of Philosophy Department Biological Science, Department of Advisory Committee
Advisor Name Title Christopher C. Koenig Committee Co-Chair Joseph Travis Committee Co-Chair Churchill B. Grimes Committee Member Don R. Levitan Committee Member Duane Meeter Committee Member John S. Elam Committee Member Keywords
- Reef Fish
- Spatial Variability
- Captive Red Porgy
- Spawning Behavior
- Sexual Dichromatism
- Sensitivity To Exploitation
- Site Fidelity
- Source Sink
Date of Defense 2005-12-05 Availability unrestricted AbstractThis study examined the reproductive ecology of the red porgy Pagrus pagrus (Sparidae) in the NE Gulf of Mexico and the temporal, bathymetric, and small scale spatial variability of its life history traits and demographics. Almost 4000 specimens were collected using standardized hook and line gear year-round, Mar 1998-Sep 2001, in the NE Gulf - most (n=2,586) at 9 sites off NW Florida in 30-68 m.
Spawning grounds were widespread, spawning occurred primarily Dec – Feb, and 50% of females matured at 211 mm and <2 yr. Fish changing sex were found Mar-Nov at all 9 primary sampling sites, and were 206 - 417 mm TL and ages 2 - 9 yr, strong evidence the process is socially controlled. Red porgy are permanently sexually dichromatic, pair spawners, and do not form large, predictable spawning aggregations. Neither protogyny nor their reproductive ecology appears to make them more sensitive than gonochorists to exploitation - they are probably less so in some cases. Traits such as widespread spawning grounds, no tendency to form spawning aggregations, absence of behaviorally-related size or sex selectivity, socially controlled sex change, co-occurrence of sexes year-round, and an extended period of transition, should stabilize or enable rapid compensation of sex ratios in red porgy (preventing sperm limitation or disruption of mating).
Size and age composition, size at age, survival rates, transition rates, sizes and ages at transition, and sex ratios all differed significantly at a scale of only 10’s of km. Environmental heterogeneity and site fidelity probably explain most of those differences, which likely reflect phenotypic, not genetic, effects. Habitat patches likely have variable hydrological, geological, biological, exploitation, and ecological characteristics. Once recruited to a patch, philopatric adults are exposed to a unique suite of factors which could affect growth, mortality, and reproduction. Such small spatial scale differences in many traits suggests a complex structure of local subpopulations; these resemble Crowder et al.’s (2000) sources and sinks or the broadly - defined metapopulation of Kritzer and Sale (2004). Pooled data from such a complex population structure could introduce excessive variability to parameter estimates and bias stock assessments.
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