Tab D, No. 3
Gallaway, B.J., J.G. Cole, R. Meyer, and P. Roscigno. 1999. Delineation of essential
habitat for juvenile red snapper in the northwestern Gulf of Mexico. Transactions
of the American Fisheries Society. Vol. 128:713-726.
Abstract: Seasonal habitat suitability index models were developed for juvenile red
snapper Lutjanus campechanus in the western Gulf of Mexico. Habitat factors
considered in the analysis included water temperature, salinity, and dissolved
oxygen at the bottom; depth and density of offshore petroleum platforms; and
low-relief bottom structures. High-value habitat for juvenile red snapper is
characterized by depths between 18 and 64 m, water temperatures of 24–26°C,
salinities around 35%, and dissolved oxygen levels of at least 5 mg/L. Density of
low-relief structures was not a significant habitat element, and an inverse
association was found between juvenile red snapper abundance and the density of
offshore platforms. Results of the model analysis suggest that the step-like
expansion of the hypoxic area (dissolved oxygen 2 mg/L) offshore of the mouth
of the Mississippi River and west to the Louisiana–Texas border, which first
occurred in 1993, has reduced habitat carrying capacity for juvenile red snapper in
this region by up to 25%, averaging 19%. This environmental change may limit
the level to which overfished Gulf red snapper stocks can be rebuilt to historical
levels.
Rooker, J.R., A.M. Landry, Jr., B.W. Geary, and J.A. Harper. 2004. Assessment of a
shell bank and associated substrates as nursery habitat of postsettlement red
snapper. Estuarine, Coastal and Shelf Science. Vol. 59:653-661.
Abstract: Trawl surveys were conducted in 2000 and 2001 to examine patterns of
distribution and abundance of postsettlement red snapper (Lutjanus campechanus)
on a shell bank, Freeport Rocks Bathymetric High (FRBH), in the northwestern
Gulf of Mexico. In addition, otolith-based methods were used to determine age,
hatch-date, growth and mortality of new recruits associated with FRBH. Date and
region were significant factors affecting density of red snapper in 2000. Peak
densities of red snapper were observed in July and August, and mean density
among habitat types (shell bank, inshore mud, offshore mud) was similar (range:
50-52 ind per hectare) in 2000. Alternatively, a habitat effect was detected during
a limited survey conducted in 2001, with density higher on the shell bank than
inshore or offshore mud habitat. Postsettlement red snapper were first detected at
approximately 16 mm standard length, and individuals less than 20 mm were
present in all habitats. Estimated ages of red snapper ranged from 26 to 121 d,
with new settlers (< 20 mm) typically less than 28 d. Predicted hatch dates ranged
from early April to mid August with a single peak occurring from late May to
early June. Growth rate for the April-May cohort (0.817 mm per day) was similar
to the June-July cohort (0.830 mm per day). Habitat-specific differences in
growth were observed, and rates were highest for individuals from the inshore
habitat (0.881 mm per day). Mortality rates (Z) during the early post-settlement
period were approximated using catch curves, and early life mortality of red
snapper was 12.1% per day (Z = 0:129). While the difference in mortality
between cohorts was negligible, a habitat-specific difference in mortality was
observed. Mortality rate of red snapper inhabiting the inshore mud habitat (Z =
0:045, 4.4% per day) was lower than rates observed for individuals on the shell
bank (Z = 0:120, 11.9% per day) or offshore (Z = 0:099, 9.3% per day) habitat.
Individuals residing in the inshore habitat had significantly higher growth rates
and significantly lower mortality rates, suggesting that recruitment potential was
higher for these individuals.
Rooker, J.R., A. Landry, and T. Dellapenna. 2005. Assessment of bathymetric highs as
nursery habitat of newly settled red snapper. Unpublished Final MARFIN
Report. Grant Number: NA17FF2872. 19 p.
Abstract: Four bathymetric highs on the inner continental shelf in the Northwest (NW)
Gulf of Mexico (Freeport Rocks, Sabine Bank, Heald Bank, Rio Grande Bank)
were characterized using digital side scan sonar and multibeam bathymetry data.
Acoustic data were used to create habitat maps (i.e. delineate habitat boundaries)
of potential red snapper nursery habitats, which were used to direct trawling
activities. Trawl surveys were conducted in 2003 and 2004 during the annual
settlement period of red snapper (May to September). Date, bank, and habitat
were identified as factors affecting red snapper density and peak recruitment
occurred from July-August on Sabine Bank, Heald Bank, and Freeport Rocks; Rio
Grande Bank was only surveyed during peak recruitment and thus temporal
variability was not evaluated. Densities of red snapper during the primary
recruitment period were markedly higher on Freeport Rocks than all three other
banks. Settlement patterns of a congener, lane snapper were also assessed and
densities of this species were highest on Sabine Bank. Red snapper densities were
higher on the offshore mud habitat at both Sabine Bank and Heald Bank than shell
ridge or inshore mud habitats. Still, a significant habitat effect was observed only
at Heald Bank. At Freeport Rocks, the ridge system was not continuous and thus
the “shell ridge” designation was further divided into two habitats: shell ridge and
sand ridge (no shell). Densities of red snapper varied among the four habitats at
Freeport Rocks, with peak numbers on the inshore habitat; however, no habitat
effect was observed. Also, densities of red snapper on sand ridge (no shell) and
shell ridge habitats were similar. Results suggest that temporal variability in the
settlement season of red snapper in the NW Gulf of Mexico is relatively low,
while regional variability in recruitment to natural banks is high. In addition,
results showed that newly settled red snapper and lane snapper settle successfully
to a variety of substrates, including both structured (shell hash) and unstructured
(mud bottom) habitats.
Szedlmayer, S.T. and J. Conti. 1998. Nursery habitats, growth rates, and seasonality of
age-0 red snapper, Lutjanus campechanus, in the northeast Gulf of Mexico.
Fishery Bulletin. Vol. 97:626-635.
Abstract: We sampled inner shelf habitat in the northeast Gulf of Mexico, for age-0 red
snapper, Lutjanus campechanus, to estimate growth rates and seasonality, as well
as to identify nursery habitats. We collected 7507 age-0 red snapper in 1994 and
1995, from 536 10-min trawl tows. Red snapper first settled to benthic habitat in
June after reaching 17.4 mm standard length (age=26 d). In both years, catch per
unit of effort (CPUE=number/10-min tow) peaked July through September, then
declined in the fall as fish were leaving the habitat before winter. Most fish (80–
81%) were caught at one location, 13 km south of Mobile Bay, Alabama. At this
location in 1995, the August CPUE ±SE (712 ±243) far exceeded all previous
estimates. Based on otolith microincrements, hatching-date frequencies showed
distinct cohorts in June and July 1994 and May and June 1995. Growth rates for
the June (0.77 mm/d) and July (0.71 mm/d) cohorts in 1994 were significantly
faster compared with growth rates for May (0.51 mm/d) and June (0.67 mm/d)
cohorts in 1995. Density-dependent mechanisms may be operating with faster
growth rates and lower CPUEs in 1994, compared with slower growth rates and
higher CPUEs in 1995. However, environmental constraints may also be
operating, as indicated by the slow growth rate of the May 1995 cohort that
probably resulted from colder temperatures. Newly settled red snapper were
aggregated on the inner shelf, at a particular location and time period. These
concentrations indicated an important nursery habitat just south of Mobile Bay,
Alabama, from July through September.
Szedlmayer, S.T. and J.C. Howe. 1997. Substrate preference in age-0 red snapper,
Lutjanus campechanus. Environmental Biology of Fishes. Vol. 50(2):203-207.
Abstract: We tested age-0 red snapper, Lutjanus campechanus, for sand or shell
substrate preference in a circular tank (1.5 m diameter × 0.6 m deep). The test
tank was divided into two equal areas of whole oyster shell or sand substrates. All
trials were video taped for 20 to 25 min. Tapes were viewed on a monitor and
locations of all fish recorded and timed with respect to substrate. Mean ± SE time
on shell was 11.6 ± 0.5 sec (4 fish trial–1) and 13.8 ± 1.1 sec (1 fish trial–1).
Mean ± SE time on sand was 9.7 ± 0.4 sec (4 fish trial–1) and 8.9 ± 0.5 sec (1 fish
trial–1). Fish spent significantly more time on shell compared to sand substrate in
four-fish trials (paired t-test, p < 0.10) and also in single-fish trials (paired t-test, p
< 0.05). Shell substrate may offer increased food and shelter for age-0 red snapper
compared to sand substrate. However, a preference for shell substrate in the
natural habitat may occur only during the nursery period, because as fish grow (>
100 mm TL) in the late fall they probably outgrow the shell habitat.
Workman, I.K., and D.G. Foster. 1994. Occurrence and behavior of juvenile red
snapper, Lutjanus campechanus, on commercial shrimp fishing grounds in the
northeastern Gulf of Mexico. Marine Fisheries Review. Vol. 56(2):9-11.
Abstract: Red snapper, Lutjanus campechanus, is subject to significant overfishing in
U.S. Gulf of Mexico waters, and regulations are being implemented to reduce
fishing mortality and restore them to a 20% spawning potential ratio by the year
2009. One source of mortality that must be reduced to achieve this goal is the
incidental capture of juvenile red snappers in shrimp, Penaeus spp., trawls.
NOAA's National Marine Fisheries Service is conducting research to develop
shrimp trawl modifications to reduce the snapper bycatch. An important part of
this research is the study of juvenile red snapper behavior on commercial shrimp
grounds and in relation to trawling gear. An area of high juvenile red snapper
abundance was identified off the coast of' Mississippi. Most snappers were
observed around structures or objects on the bottom which they appeared to use
for refuge or orientation. Those ranging over barren bottom had no apparent point
of orientation. When encountered by shrimp trawls, most juvenile snappers rose
above the trawl footrope and fell back into the trawl. These observations have
directed research toward modifying shrimp trawls to release juvenile red snappers
after entry, rather than preventing them from entering a shrimp trawl.
Workman, I., Shah, A., Foster, D., and Hataway, B. 2002. Habitat preferences and site
fidelity of juvenile red snapper (Lutjanus campechanus). ICES Journal of Marine
Science. Vol. 59:S43–S50.
Abstract: Ten small reefs constructed of either oyster shell or polyethylene webbing and
ten randomly selected open-bottom sites within a distance of 3.7 km of the reefs
were used to determine juvenile red snapper [Lutjanus campechanus (Poey,
1860)] habitat preferences. The reefs were deployed at 40, 50, 70, and 90 m from
a flare stack located in a gas field off the coast of Mississippi. Juvenile red
snapper were observed at one of the open-bottom sites when it was first surveyed,
but none during a second survey conducted 45 days later. Age-0 and age-1 fish
showed a preference for the more complex study reefs, but presence of age-1
appeared to limit recruitment of age-0 to a reef. As age-1 fish started to leave the
reefs, increased numbers of age-0 were observed moving onto them. However,
age-0 were never observed at the 40-m reef occupied by older fish throughout the
study. Distance from the flare stack also appeared to have an effect on recruitment
to the reefs. Age-0 were first observed at the 50-m reefs. They appeared at the 70m reefs a week later and at the 90-m reefs almost a month later. Age-1 fish
showed a preference for the reefs located closest to the flare stack. Juvenile red
snapper site fidelity was determined using fish that either were tagged and
released on site or were removed from the capture site before release. Fish from
the on-site release were repeatedly sighted at the capture reef over about a 2month period. Displaced fish, as determined with tracking equipment, were able
to find their way back to the capture reef from as far away as 0.43 km in about 25
min. We conclude that juvenile red snapper are not only faithful to structures, but
also have homing capabilities.