No abstract

From 1992 through 1996, 257 Gulf sturgeon Acipenser oxyrinchus desotoi were captured in the Pearl River system of Louisiana and Mississippi, but adults (>130 cm fork length) constituted less than 2% of the catch. The summer population size in 1996, estimated by mark–recapture methods, was 292 individuals that were age 2 or older. Instantaneous total mortality rate (Z), estimated with a catch curve, was 0.41, for an annual mortality rate of 34%. Modeling the population with Z = 0.41 resulted in declining populations under two different recruitment scenarios. Mortality rates will have to be reduced to Z = 0.16–0.24 for the population to be self‐sustaining by 2023, the target year in the Gulf Sturgeon Recovery Plan. Mean fork length of Gulf sturgeon in the Pearl River system was significantly larger in 1970 than in 1985 and 1992–1996, indicating that the population may not have improved since 1985. An increase in population size should be detectable within 6 years of achieving acceptable levels of mortality. Efforts to reduce mortality should focus on commercial bycatch and improving winter habitat in the Lake Pontchartrain estuary and summer habitat in the Pearl River system. Weirs in the Pearl and Bogue Chitto rivers need further study to determine if improved fish passage would improve recruitment and survival of Gulf sturgeon.

Collection techniques were developed for monitoring populations of triploid grass carp Ctenopharyngodon idella stocked into the Santee-Cooper reservoirs, South Carolina, to control hydrilla Hydrilla verticillata. Skilled bowfishers, who were paid a bounty of US$50.(X) per fish, collected 69, 125, and 160 triploid grass carp in 1992. 1993, and 1994. respectively. Fish were fully vulnerable to bowfishing by age 2. Examination of sectioned utricularotoliths(lapilli)revealcd annual marks formed during May-June. Weight (W) increased linearly with age (/, years), for ages 1-6; W = -2,360 + 3,016f. Age-specific weights ranged from 0.39 kg to 15.68 kg for fish of ages 1-6. The weight to total length (TL, mm) relation varied little during the study and was W 0.00000425(TL) 3 185 . A von Bertalanffy growth equation was fitted to describe the relation between length and age. TL, = 1,044(1 -e 06I5 <' 0.59O)) Thc anmj al rate of mortality was 22% in 1994. We estimate that 350,000 triploid grass carp, weighing about 2.000,000 kg. were present in the system as of August 1994; this represented approximately 17 grass carp, or 97 kg, per vegetated hectare. Collection and aging techniques developed in this study may have application in places where triploid grass carp are conservatively and incrementally stocked into large systems. In this regard, population density and growth can be monitored and future stockings adjusted accordingly.

The Gulf Sturgeon Recovery/Management Plan defines a strategy for removing the threatened Gulf sturgeon Acipenser oxyrinchus desotoi (subspecies of the Atlantic sturgeon) from federal listing and invites revisions based on new information. The plan's objectives are reasonable and well‐stated, but the criteria incorporated within the objectives may be unsuitable for monitoring some Gulf sturgeon populations. We propose the following revisions based on a 5‐year study of Gulf sturgeon in the Pearl River system of Mississippi and Louisiana: (1) set specific statistical criteria for detecting population changes with emphasis on defining sufficient sampling effort to minimize type II errors; (2) use simple population models incorporating estimates of population size, mortality, and recruitment to ascertain population trends and define recovery; and (3) define a minimum number of adults within a self‐sustaining population (in this case 100). These revisions, while perhaps not universally applicable, are probably appropriate in systems with many outlets, such as the Pearl River, where Gulf sturgeon are most easily sampled in summertime habitats.