Entrainment of Endangered Sturgeon by a Large Water Diversion: Rescue, Enumeration, and Conservation Opportunities

The Bonnet Carre’ Spillway diverts water from the Mississippi River through a floodway into Lake Pontchartrain to reduce river stages at New Orleans and prevent flood damages. Pallid Sturgeon, a federally listed species under the Endangered Species Act, and Shovelnose Sturgeon, listed under the Similarity of Appearance rule, are entrained through the Spillway structure and become trapped in the Spillway canals and other waterbodies. Five openings and corresponding rescue operations occurred between 2008 and 2019 after each Spillway closure. Operational parameters spanned a range of water temperatures and seasons with magnitude and duration of discharge varying across all openings. A total of 70 days with crew number ranging from 6 to 12 were expended to rescue 57 Pallid Sturgeon and 362 Shovelnose Sturgeon after the five openings that spanned 240 total days. More sturgeon were entrained at higher water temperatures, with greater numbers of bays opened, and for longer periods of time. 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 less than 1% of the total population size in the Lower Mississippi River are entrained. However, this does not take into account those individuals entrained but not captured and the potential impacts of more frequent openings of the structure. Conservation recommendations are provided to increase catch efficiency and recovery of the endangered sturgeon.

Sampling the Central Channel Provides Additional Information on Fish Assemblages in a Large Boatable River in the U.S. Midwest

It is a challenge to adequately characterize the fish assemblages of large rivers because of their sizes and high spatial–temporal habitat heterogeneity. Multiple sampling methods are often needed, but their uses increase cost and present difficulty for data standardization. In this study, we examined how much new information central-channel electrofishing sampling could add to typical shoreline electrofishing in a large and relatively shallow river, the lower Wabash River, in the U.S. Midwest. We found that the two types of samples differed markedly in species composition, and each was strongly associated with a subset of species. Shoreline samples captured more fish individuals and species, and reached higher functional diversity, but central-channel samples often captured several large benthivore and migratory species such as Redhorse and Shovelnose Sturgeon. Central-channel electrofishing appears to be a quick and low-cost method to supplement shoreline sampling in monitoring and assessing large shallow rivers.

Timely Events in Their Interrelation to Paddlefish and Sturgeon Harvest from 1945-2010

Due to the high amounts of harvest of natural fish populations, overexploitation can occur and subsequently lead to depleted fisheries. This is especially true for commercially exploited roe-bearing species that exhibit late age at maturation and intermittent spawning. Overexploitation can create an imbalance in natural ecosystem function and in turn jeopardize the livelihood of commercial fishers. Despite the problems created by overexploitation, trends of commercial harvest on large inland river roe-bearing populations have received minimal attention. As such, we evaluated trends in commercial fishing data from 1945-2010 for two roe-bearing species (paddlefish Polyodon spathula and shovelnose sturgeon Scaphirhynchus platorynchus) from two of the largest inland rivers in North America (Mississippi River and Missouri River) adjacent to Missouri. Commercial sturgeon and paddlefish catch has varied from ∼160 to 35,150 kg over the course of the 55-year duration. Abnormally high catches corresponded to initiation of worldwide caviar markets, onset of extensive regulations on the Missouri and Mississippi rivers, and the Caspian Sea fishery collapse; respectively. Further, our results suggest that the harvest of sturgeon and paddlefish have increased since 1945 and may be influenced by local, regional, and international events. Despite the increase in harvest and the possibility of overharvest, commercial fishing regulations have not been thoroughly evaluated for effectiveness. Further evaluation of current management and regulations of these paddlefish and sturgeon fisheries is suggested, especially considering these fisheries may be influenced by local, regional, and international events. Taking potentially influential events into consideration when evaluating and implementing regulations and authorizing commercial harvest permits are vital in sustaining a long term commercial fishery and protecting the livelihood of commercial fishers.