Natural markers in otoliths (stable isotopes, trace elements) are being used to determine the connectivity between early life (estuarine) and adult (coastal) habitats of red drum (Sciaenops ocellatus). Young-of-the-year (YOY) red drum were sampled from several estuaries in Texas: Sabine Pass, East Bay-Galveston, West Bay-Galveston, Matagorda Bay, Copano Bay, Aransas Bay, and the Lower Laguna Madre. Stable isotopes (d¹³C, d¹⁸O) and trace elements (Mg, Ca, Mn, Sr and Ba) were quantified in the otoliths and signatures differed among estuaries. North to south gradients were observed for d¹³C, d¹⁸O, and both isotopes were enriched in otoliths of red drum from southern sites relative to northern sites. Correct assignment to a specific estuary based on stable isotopes ratios alone was greater than 80% in each year. Classification success was further improved (>90%) when trace elements were added to the model. Interannual variability in otolith chemistry was present but classification success was high when year classes were pooled into 4 regional groups (Sabine to East Bay, West Bay to Matagorda, Copano Bay to Aransas Bay, and Lower Laguna Madre). To establish the nursery origin of adult red drum, otolith cores were isolated, and stable isotope and trace element composition of cores were determined. Chemical signatures in the otolith cores (~ first year of life) of adult red drum were matched to YOY signatures to assess the connectivity between estuarine (early life) and coastal (adult) habitats.

Post-release survival of hatchery fishes is imperative to the success of any supplemental stocking program. However, evidence has shown that hatchery fishes often exhibit behavioral deficiencies, leading to higher rates of mortality versus their wild counterparts. We investigated differences in survival skills between hatchery and wild red drum (Sciaenops ocellatus) and examined if exposure to natural stimuli (e.g. habitat, predators, live prey) influenced survival skills of hatchery individuals. Laboratory trials using high-speed videography (250 frames per second) and field mesocosm experiments were used to investigate differences in prey-capture (e.g., attack distance, mean attack velocity, capture time, maximum gape, time to maximum gape, gape cycle duration, and foraging behaviors) and anti-predator performance (e.g., reaction distance, response distance, maximum velocity, time to maximum velocity, mean acceleration, and maximum acceleration) of hatchery and wild red drum.

Experimental trials indicated that anti-predator performance measures differed significantly between hatchery and wild red drum. Variability in prey-capture and anti-predator performance for hatchery and wild red drum was high (CV range: 5.6 – 76.5%), and was greatest for hatchery fish for the majority of performance variables tested. Exposure to natural habitat (Spartina alterniflora marsh) did not appear to afford any obvious survival benefits to hatchery red drum, although survival skills did vary according to ontogenetic stage. Hatchery red drum exposed to natural predators (pinfish, Lagodon rhomboides) exhibited significantly greater attack distances during feeding events, and anti-predator performance variables were 20 – 300% in these individuals versus natďve red drum. In predation experiments with free-ranging pinfish predators, mortality rates (Z) ranged from 0.047 – 0.060 h-1 • predator-1; however no significant differences in mortality were found between fish reared with and without predators. Hatchery red drum reared on live prey (Artemia franciscana, mysid shrimp) demonstrated enhanced prey-capture and foraging behaviors as well as anti-predator performance relative to fish reared on artificial (pellet) diets. Findings of this research indicate that several behavioral patterns differed between hatchery and wild red drum; however, these differences may be mediated through the use of various pre-release exposure techniques.

High speed video

Click to view high-speed video of red drum anti-predator performance

Further Reading
Beck JL, Rooker JR (2008) The Impact of Habitat Exposure and Ontogeny on the Survival Skills of Hatchery Red Drum, Sciaenops ocellatus (Linnaeus) North American Journal of Aquaculture (In press)

Beck JL, Rooker JR (2008) Prey-capture and anti-predator performance of hatchery-reared and wild red drum: are survival skills impacted by early life exposure? Transactions of the American Fisheries Society (In press)

Although much effort has been directed toward the management of red drum stocks, research on growth and survival during early life has received limited attention. As a result, several projects were initiated to examine the early life ecology of red drum in estuarine systems in Texas. Specific objectives of this research were to estimate spatial and temporal variation in the condition, growth, and mortality to estimate cohort- and site-specific mortality rates, and to determine the recruitment potential of different cohorts. A synopsis of some of the salient findings from this research is given below (see Publications for complete list of papers from this work).

Patterns of growth and mortality were examined for postsettlement red drum, Sciaenops ocellatus, inhabiting seagrass meadows in the Aransas Estuary, Texas. Age and growth rates of larvae and early juveniles were estimated by using daily increments in otoliths. Otolith-derived estimates of age indicated that individuals spend approximately 20 d in the pelagic environment before entering demersal habitats (i.e. before settlement). Instantaneous growth coefficients (g) of red drum ranged from 0.049 (4.8%/d) to 0.051 (5.0%/d). Site-specific differences in growth were also examined and a significant site effect was detected. Interannual and cohort-specific (10-d cohorts) mortality rates were estimated from declines in loge abundance (abundance-at-age plots), and results indicated that mortality during the early postsettlement period was substantial. Instantaneous mortality coefficients (Z) were similar between years (0.134 [12.5%/d] to 0.139 [13.0%/d]), and no significant interannual effect was observed. Conversely, cohort-specific mortality rates ranged widely (0.106–0.265 [10.1– 23.3%/d]) and losses were lowest for midseason cohorts. Recruitment potential (G:Z ratio) was highest for midseason cohorts (1.30–1.56) and lowest for early and late-season cohorts (<1). Although G:Z ratios varied over spatial and temporal scales, ratios were >1, suggesting that all year classes experienced favorable nursery conditions.

Further Reading
Rooker JR, Kraus R, Secor DH (2004) Dispersive behaviors of black drum and red drum: is otolith Sr:Ca a reliable indicator of salinity history? Estuaries 27: 334-441

Rooker JR, Holt GJ, Holt SA, Fuiman LA (1999) Spatial and temporal variability in growth, mortality, and recruitment potential of post-settlement red drum (Sciaenops ocellatus). Fishery Bulletin 97: 581-590

Rooker JR, Holt SA, Soto MA, Holt GJ (1998) Post-settlement patterns of habitat use by sciaenid fishes in subtropical seagrass meadows. Estuaries 21: 315-324

Rooker JR, Holt GJ, Holt SA (1998) Vulnerability of newly settled red drum (Sciaenops ocellatus) to predatory fish: is early-life survival enhanced by seagrass meadows? Marine Biology 131: 145-151

Rooker JR, Holt SA (1997) Utilization of subtropical seagrass meadows by newly settled red drum (Sciaenops ocellatus): patterns of distribution and growth. Marine Ecology Progress Series 158: 139-149

Rooker JR, Holt GJ, Holt SA (1997) Condition of larval and juvenile red drum (Sciaenops ocellatus) from estuarine nursery habitats. Marine Biology 127: 387-394

Rooker JR, Holt GJ (1996) Application of RNA:DNA ratios to evaluate the condition and growth of larval and early juvenile red drum (Sciaenops ocellatus). Marine and Freshwater Research 47: 283-290

Estuaries are vital nursery grounds for several finfish species, including southern flounder (Paralichthys lethostigma). Southern flounder are commercially important throughout the Gulf of Mexico, second only to red snapper in price/weight in Texas markets. This species is also highly sought by recreational fishers, especially during fall spawning runs when adults are especially vulnerable both to bank and boat fishermen. In this study, we examined large-scale (site-specific) and small-scale (habitat-specific) variation in settlement of southern flounder in the Galveston Bay Estuary (GBE). We also evaluated the condition and growth of newly recruited individuals in the GBE in order to determine the value of different bays and habitats. Biochemical condition (RNA:DNA) and growth (otolith microstructure analysis) were used to measure the relative fitness of individuals. These two measures were used in conjunction with density data to evaluate the relative value of areas occupied by post-settlement southern flounder.

Evidence suggested that density and condition of newly settled southern flounder may vary at the bay scale, suggesting that parts of GBE do not function equally as nurseries. In contrast, at a smaller scale (i.e. habitat-specific), differences in density, condition and growth were negligible among habitats in close proximity. Preliminary evidence suggested that physical processes (e.g. wind driven currents, tidal forcing) likely played an important role in determining settlement densities of southern flounder in GBE. Low densities of southern flounder in the GBE in both years of sampling may also indicate that they are recruitment limited. East Bay was found to be a hot-spot for settlement, however, lower density areas in the GBE may contribute a large portion to the adult population. Relative condition of individuals as measured by RNA:DNA ratios showed that that southern flounder were in good nutritional condition (range: 6.3 – 15.1), suggesting that food was not a limiting factor in any of the bays or habitats sampled. Growth was also found to be relatively similar across areas, indicating that a variety of habitats maintained favorable conditions for growth and survival of new recruits. Results of this study indicate that either nursery value of the GBE habitat was similar or newly settled southern flounder are a highly adaptive fish that can utilize a variety of habitat types in the GBE as nursery grounds.

Further Reading
Glass LA , Kraus RT, Rooker JR, Holt GJ (2008). Distribution, condition, and growth of newly settled southern flounder (Paralichthys lethostigma) in the Galveston Bay Estuary, Texas. Journal of Sea Research (In press)

Sagittal otolith of 40-day-old southern
flounder

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Dr. Jay R. Rooker · Department of Marine Biology
Texas A&M University @ Galveston
5007 Ave U, Galveston, Texas 77551
rookerj@tamug.edu · 409-740-4744
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