The Gulf sturgeon population in the Pearl River was monitored from 1992 through 1996 and compared to historical data sets from the 1960s and 1980s. The estimated population sire iii 1996 was approximately 300 fish with adults comprising about 3 percent of the population. Annual mortality rates in the late 1960s were about 9 percent; these rates increased to almost 40 percent in 1985 and decreased to about 26 percent during 1992 through 1996. Population modeling was used to evaluate the sturgeon's status and recovery potential. Results of models suggest that this population can only withstand mortality rates in the range of 13 to 18 percent, depending upon recruitment assumptions. Population models indicated that catch and fishing effort data specified in the Gulf Sturgeon Recovery Plan may not detect a declining population. Population models can be used to simulate annual variation in population sire under different rates of mortality. Recovery goals can address a specific source of mortality simulated in the model and monitoring can determine the success of recovery efforts. Population modeling does not require considerably more effort or expertise over that already required to conduct monitoring studies.

The tension between wildlife protection under the Endangered Species Act and water management in the Platte River Basin has existed for more than 25 years. The Platte River provides important habitat for migratory and breeding birds, including three endangered or threatened species: the whooping crane, the northern Great Plains population of the piping plover, and the interior least tern. The leading factors attributed to the decline of the cranes are historical overhunting and widespread habitat destruction and, for the plovers and terns, human interference during nesting and the loss of riverine nesting sites in open sandy areas that have been replaced with woodlands, sand and gravel mines, housing, and roadways. Extensive damming has disrupted passage of the endangered pallid sturgeon and resulted in less suitable habitat conditions such as cooler stream flows, less turbid waters, and inconsistent flow regimes. Commercial harvesting, now illegal, also contributed to the decline of the sturgeon. Endangered and Threatened Species of the Platte River addresses the habitat requirements for these federally protected species. The book further examines the scientific aspects of the U.S. Fish and Wildlife Service's instream-flow recommendations and habitat suitability guidelines and assesses the science concerning the connections among the physical systems of the river as they relate to species' habitats.