Life History, Diet, And Reproductive Dynamics Of The Sheepshead (Archosargus probatocephalus) In The Northeastern Gulf Of Mexico

摘要

Sheepshead (Archosargus probatocephalus) are a popular recreational fisheries species in the Gulf of Mexico. Unfortunately, the highest reported catch of this species occurs primarily during their reproductive period. As a result, fishers have expressed their concerns to management about a potential overharvest. This research attempts to fill in the biological gaps for Sheepshead in order to provide management with information that will ensure future successful management practices. The specific goals of this research are to: (1) examine the life history of Sheepshead in the northeastern Gulf of Mexico (NE GOM), (2) understand the prey composition and feeding habits during their reproductive period, (3) determine the distribution of spawning adults, and (4) assess the spatial and temporal changes in abundance and population demographics on offshore sites.;Sheepshead were captured from three unique habitats (nearshore estuaries, Sikes Cut, and offshore reefs) from January 2016- April 2017 in the NE GOM. Sheepshead were sampled exclusively during their reproductive period, which is from January through May, using a variety of different fishing methods.;Otoliths were removed, sectioned and aged for 224 individuals. Von Bertalanffy growth equations were fit to the length-at-age data from this region. Growth was found to be variable across their geographic range. Maximum asymptotic length (441mm) and growth rate (0.24) were consistent with previous studies in Florida. Average age of Sheepshead was much higher than in other regions of Florida, potentially due to habitat degradation and development in the regions like Tampa Bay compared to the lack of development along the NE GOM's "Forgotten Coast".;Stomach and intestinal contents were removed, identified to the highest taxonomic level, and the volumes were enumerated to assess for fullness. Contents and stomach fullness were compared across habitats. Multidimensional scaling plots with presence absence transformation of Sheepshead stomach content data were created using a Bray--Curtis similarity matrix. A one-way ANOSIM showed no significant (p=0.79) difference in Sheepshead diet by habitat type. This suggested feeding habits overlapped across habitat type. This could be a result of (1) similar prey items across habitats, (2) movement between habitats, or (3) different digestion rates of hard-bodied organisms. Sheepshead exhibited proportionally more empty stomachs and lower fullness scores offshore. Feeding was less frequent on offshore reefs, which could be due to less prey, energy reserves from past feeding events, or more focus on spawning.;Gonads were removed, weighed, and either macroscopically staged (males), or histologically staged (females). Gonadosomatic indices, spawning activity, and histological stage were compared across three habitat sites. A higher proportion of active and imminent spawning individuals were found on offshore reefs and at Sikes Cut. Nearshore habitats exhibited a low proportion of spawning activity. This suggested nearshore habitats were not preferred spawning habitats, possibly due to lower salinities which cause declines in fertilization success. Abundance was assessed monthly using submersible rotating video devices on the three offshore sites only.;Abundance was found to significantly (p < 0.001) increased during Sheepshead spawning season. Abundance was also significantly different (p < 0.001) across reef site. This suggested formation of spawning aggregations that differed across a spatial scale.;Population demographics were measured by using laser photogrammetry during early, middle, and late spawning season on the three offshore sites. Sheepshead demographics were found to change across spatial and temporal scales. Average size was significantly less (p = 0.01) on Two Dog Reefballs, suggesting spawning populations are different across a local region. Sheepshead were significantly larger (p = 0.04) during the middle of their spawning season. This could be an evolutionary adaption to maximize fertilization success during peak spawning season.;Sheepshead stocks have remained stable over the past few decades in the SE US. However, with increased fishing pressure during their reproductive period, both fishers and management recognize the potential for future declines. Results and findings from this study will be used when making future regulation decisions for Sheepshead.