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Silver carp, Hypophthalmichthys molitrix, escaped into the Lower Mississippi River (LMR) over 50 years ago, established reproductive populations, and spread across much of the Mississippi River Basin. Demographic rates of silver carp are needed to inform decisions on control and management of this invasive species, but have not been published for the LMR. The purpose of this paper is to report silver carp age and growth estimates from fish collected in riverine (mainstem) and backwater (lake) habitats in the LMR during the period 2011-2019, to compare our results with populations from other geographic areas in the Upper Mississippi River drainage, and to evaluate latitudinal and habitat differences in demographic parameters. Silver carp gained weight with increasing length similarly throughout the lower and upper basin. However, annual growth rates were higher in the LMR compared to northern rivers including the Illinois, Wabash, Missouri, and Middle Mississippi rivers. In the LMR, regression analyses demonstrated that females were heavier in lakes than males or females in the mainstem and that females in lakes had the lowest instantaneous mortality (-0.186). Maximum age was 8 and 10 years for females and males, respectively. The largest male weighed 13.8 kg with a total length of 1022 mm, and was 7 years old. The largest female weighed 16.0 kg with a total length of 1034 mm TL, and was 7 years old. Rapid growth rates, larger sizes, and lower mortality in the LMR, in combination with limited commercial fishing, extensive river-floodplain connectivity, and vast amounts of spawning areas, ensure that LMR silver carp will continue to act as a source of fast-growing invasive individuals for other reaches and other rivers throughout the Mississippi River Basin. [ABSTRACT FROM AUTHOR]

The Bonnet Carre' Spillway diverts water from the Mississippi River through a floodway into brackish Lake Pontchartrain to reduce river stages at New Orleans and prevent flood damage. Pallid Sturgeon Scaphirhynchus albus, a federally listed species under the Endangered Species Act, and Shovelnose Sturgeon Scaphirhynchus platorynchus, listed under the Similarity of Appearance rule, are entrained through the spillway structure and become trapped in the canals and shallow lakes. The two species of sturgeon were identified according to a suite of morphomeristic characters, not genetically, and were therefore noted as either Shovelnose Sturgeon or presumed Pallid Sturgeon. Rescue efforts were undertaken to return the entrained sturgeon back into the Mississippi River. This article describes the environmental and operational conditions that influence entrainment risk, catch, and potential impacts on the population. Five openings and corresponding rescue operations occurred between 2008 and 2019 after each spillway closure. A total of 70 days with a crew number ranging from 6 to 12 were expended to collect 57 Pallid Sturgeon, four of which were dead, and 362 Shovelnose Sturgeon, 83 of which were dead, after the five openings that spanned 240 total days. More sturgeon were entrained at higher water temperatures, with a greater number of bays opened for longer durations. Recovery of sturgeon is initially high but over time declines as sturgeon are depleted from the floodway, stranded in isolated waterbodies in the floodway, and/or displaced further downstream into Lake Pontchartrain during longer openings. Sturgeon that cannot find their way back to the floodway are unlikely to be rescued. Recent population studies indicate that only a small proportion of the Lower Mississippi River total population is entrained. However, this does not take into account those individuals entrained but not captured and the potential impacts if more frequent openings of the structure were to continue in the future. Conservation recommendations are provided to increase catch efficiency and recovery of the endangered sturgeon. [ABSTRACT FROM AUTHOR]

Two Hypophthalmichthys molitrix (silver carp) were collected in the Pearl River on 6 September 2012 during a natural fish kill in the decommissioned lock chamber of Lock-and-Dam No. 1 located at river kilometer (RKM) 47.5 in St. Tammany Parish, 9.4 km NW of the city of Pearl River, LA. Fish were a male 987 mm TL, 10.9 kg, and a female 1042 mm TL, 12.2 kg. Both fish were age 5. Eight additional silver carp (930-1054 mm TL, 9.1-14.1 kg) and one bighead carp (H. nobilis) (1065 mm TL, 15.9 kg) were collected in the West Middle Pearl River 29 September - 1 October 2015 (RKM 18.9-20.8), 10.5 km E of Slidell, LA (St. Tammany Parish). All specimens were male and ranged 6-9 years in age. A silver carp (age = 7) was collected by a recreational fisher 19 November 2015 in the Pearl River below the Ross Barnett Reservoir (RKM 480) near Jackson, MS. These three collections are believed to represent nonindigenous silver and bighead carp dispersal from the Mississippi River Basin during floods. [ABSTRACT FROM AUTHOR]