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Estuarine Research Projects:
- Red drum otolith chemistry: assessing contribution rates of estuarine nurseries
- Contrasting survival skills of hatchery and wild red drum
- Red drum early life history
- Southern flounder settlement and recruitment
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1. Red drum otolith chemistry: assessing contribution
rates of estuarine nurseries |
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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.
Further Reading
Rooker JR, Secor DH (eds.) (2005) Connectivity in the life cycles of
fishes and invertebrates that use estuaries. Estuarine, Coastal and
Shelf Science 64: 1-148
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
Secor DH, Rooker JR, Zlokovitz E, Zdanowicz VS (2001) Identification of
riverine, estuarine, and coastal contingents of Hudson River striped
bass based upon otolith elemental fingerprints. Marine Ecology Progress
Series 211: 245-253
Secor DH, Rooker JR (2000) Is otolith strontium a useful scalar of
life-cycles in estuarine fishes? Fisheries Research 1032: 1-14
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2. Contrasting survival skills of hatchery and wild red
drum |
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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.
| Variable |
Hatchery |
Wild |
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| Prey-capture
performance: |
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| Attack distance (mm) |
0.97 ± 0.13 |
0.82 ± 0.08 |
| Mean attack velocity
(mm/s) |
170.00 ± 11.73 |
52.73 ± 6.80 |
| Capture time (ms) |
11.31 ± 0.30 |
10.87 ± 0.36 |
| Gape cycle duration (ms) |
25.64 ± 0.50 |
25.91 ± 0.49 |
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| Anti-predator
performance: |
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| Reaction distance (mm) |
46.25 ± 7.41 |
22.70 ± 2.40 |
| Response distance (mm) |
25.02 ± 1.44 |
22.74 ± 1.15 |
| Mean velocity (mm/s) |
250.16 ± 14.40 |
227.44 ± 11.51 |
| Maximum velocity (mm/s) |
532.99 ± 34.67 |
516.91 ± 28.42 |
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Mean (± S.E.) of prey-capture and anti-predator performance variables for hatchery and wild red drum
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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)
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3. Red drum early life history |
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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
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4. Southern flounder settlement and recruitment |
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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
Site by Third Coast
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