Robert H. Chabreck

The Effects of Hurricane Camille on the Marshes of the Mississippi River Delta

The active delta of the Mississippi River was sampled in August 1968 to determine plant species composition, plant coverage, and soil and water chemistry. Hurricane Camille struck this area in August 1969, with winds in excess of 200 km/h and tides raging upward to 5.2 m above MSL. The delta was resampled 2 weeks following the hurricane to evaluate the immediate effects on vegetation, soil, and water, and again 1 year after the hurricane to determine the recovery rate of vegetation. The hurricane resulted in a drastic reduction of vegetation. Regrowth was rapid in the delta marshes and after 1 year plant coverage approached pre—hurricane levels of abudance; however, recovery was slower in ponds and lakes. The loss of vegetation was mainly a result of the sweeping action of wind and water, and plants were either uprooted or ripped apart and carried away by the current. Water salinity increased with the hurricane but declined by the following year and appeared to have only slight effect on marsh vegetation. Plant species caried in their response to the hurricane. Bacopa monnieri showed practically no effect, and Phragmites communis and Spartina alterniflora were reduced only slightly. Myriophyllum spicatum, Panicum repens, and Alternanthera philoxeroides were greatly reduced by the storm: and after 1 year, only Alternanthera philoxeroides showed significant recovery.

Growth rates of American alligators in estuarine and palustrine wetlands in Louisiana

A comparative study of American alligator (Alligator mississippiensis) growth rates was made in estuarine and palustrine wetlands in southwestern Louisiana. In the estuarine wetlands, where characteristic salinity levels were ≤5%, alligators grew faster and therefore reached sexual maturity earlier than did those in palustrine wetlands, which are characterized by shallow, freshwater marsh vegetation. Slower growth rates in palustrine wetlands appeared to be related to prey density, indicated by previous studies to be lower than in estuarine wetlands. Males grew faster than females and therefore reached sexual maturity at an earlier age in both habitats. This study revealed a major limitation in using total lengths as an index upon which population age structure can be based even when alligators are in the same geographic region.

Reproductive status and movement of adult female alligators

Home range size, movement, and denning behavior of 15 adult female American alligators (Alligator mississippiensis) of different reproductive status were compared using radio telemetry. Radio- collared adult female alligators had an annual home range of 35.8 ? 42.9 (SD) ha, and 30% of them nested in 1988. No difference was found between nesting and non-nesting adult females during the summer nesting season in home range size, daily movement, or percent of time spent at den sites. Likewise, no difference was found in any of the three variables during the fall brooding season when females with broods were compared to those without broods. Adult female alligators had larger home ranges, greater movement, and spent less time at or near their den sites during the spring breeding season than any other season of the year.

Habitat use by small mammals in coastal marshes of Southwestern Louisiana

A short-term study based on snap-trap capture rates of small mammals in the marsh and levee system in southwestern Louisiana was conducted in the winter-spring period. Marsh rice rats (Oryzomys palustris) dominated marsh habitats and rice rats and fulvous harvest mice (Reithrodontomys fulvescens) were co-dominants on levees. Least shrews (Cryptotis parva) and house mice (Mus musculus) were also taken. Although rice rat capture rate in marshes was twice that from levees, the difference was not significant (p=0.1428). When found on levees, rice rats preferred portions of levees adjacent to marshes and canals (p<0.0001). We found few differences in rice rat capture rates from marsh and levee habitats, although capture rates from fresh marsh and adjacent levees were select levee ridges over the marsh and canal edges (0.1≥p≥0.05). The abundance of harvest mice on levees adjacent to intermediate marshes exceeded all other levee habitats. For reasons as yet unexplained, intermediate marshes and adjacent levees had the highest small mammal abundance and species richness. Conversely, fresh marshes and their adjacent levees had the lowest abundance and variety of small mammals.

Effects of weir management on marsh loss, Marsh Island, Louisiana, USA

Weirs are low-level dams traditionally used in Louisianas coastal marshes to improve habitat for ducks and furbearers. Currently, some workers hope that weirs may reduce marsh loss, whereas others fear that weirs may accelerate marsh loss. Parts of Marsh Island, Louisiana, have been weir-managed since 1958 to improve duck and furbearer habitat. Using aerial photographs, marsh loss that occurred between 1957 and 1983 in a 2922-ha weir-managed area was compared to that in a 2365-ha unmanaged area. Marsh loss was 0.38%/yr in the weir-managed area, and 0.35%/yr in the unmanaged area. Because marsh loss in the two areas differed less than 0.19%/yr, it was concluded that weirs did not affect marsh loss. The increase in open water between 1957 and 1983 did not result from the expansion of lakes or bayous. Rather, solid marsh converted to broken marsh, and the amount of vegetation within previously existing broken marsh decreased. Solid marsh farthest from large lakes and bayous, and adjacent to existing broken marsh, seemed more likely to break up. Marsh Island has few canals; therefore, marsh loss resulted primarily from natural processes. Weirs may have different effects under different hydrological conditions; additional studies are needed before generalizations regarding weirs and marsh loss can be made.

MANAGEMENT OF WETLANDS FOR WILDLIFE HABITAT IMPROVEMENT

ABSTRACT Population levels of sporting and commercial wildlife species occupying wetlands are a product of the quantity and quality of habitat available. The rapid loss or modification of wetland habitat by other land-use practices has increased the need for special management to maintain or improve habitat quality. Habitat management practices should be designed to regulate the species composition, density, and distribution of plants. Major factors affecting plant growth in coastal wetlands are water levels and salinity, and the management practices applied should be those best suited to local conditions for maintaining these variables within acceptable limits. Special attention must be given to other needs of the wildlife species involved, because factors other than plants are also important components of favorable habitat. Management practices currently used in coastal wetlands are shallow water impoundments, water control structures in drainage systems, marsh ditches, and artificial potholes. Other treatments frequently applied are marsh burning, herbicidal treatment, and planting.