Growth and Population Size of Grass Carp Incrementally Stocked for Hydrilla Control

Abstract

In weed control plans that use Grass Carp Ctenopharyngodon idella for intermediate control of hydrilla Hydrilla verticillata, the knowledge of population dynamics improves efficacy of management. Our objective was to characterize growth, mortality, and associated population metrics of long‐lived (up to 16 years) triploid Grass Carp that were incrementally stocked into Lake Gaston, Virginia–North Carolina, starting in 1995. Grass Carp (ages 1–16) were collected by bowfishers during 2006–2010. Growth of Grass Carp was described by the von Bertalanffy growth model as Lt = 1,297[1 − e −0.1352(t +1.52)], where Lt is TL at age t. We used three methods to estimate Grass Carp mortality, and annual abundance and biomass of Grass Carp were estimated from each mortality estimate. Estimated annual mortality ranged from 0.20 to 0.25 depending on the method used. The use of constant mortality rates versus age‐specific mortality rates produced divergent models of Grass Carp biomass and represented a different approach for tracking the progress of weed control. Grass Carp biomass (but not abundance) was related to hydrilla coverage in Lake Gaston based on several scenarios that described time lags between Grass Carp stocking in year i and decreases in hydrilla coverage (in years i, i + 1, …, i + 5). Regardless of the mortality estimate used to derive Grass Carp biomass, the strongest biomass–hydrilla coverage relationship was observed for a time lag of 4 years. Fish older than age 10 constituted nearly 50% of the total Grass Carp biomass in Lake Gaston during some years, and the relationship between Grass Carp biomass and hydrilla coverage was strongest when fish up to age 16 were included in models. These results indicate that Grass Carp up to at least age 16 are important for weed control, thus highlighting the need for stocking models and bioenergetics models that include contributions of older fish when assessing long‐lived Grass Carp populations.Received January 23, 2012; accepted October 3, 2012

A Comparison of Grass Carp Population Characteristics Upstream and Downstream of Lock and Dam 19 of the Upper Mississippi River

“…Grass Carp population characteristics described herein varied from those reported for both stocked populations in lakes and naturalized populations in other Mississippi River tributaries. Grass Carp captured both downstream and upstream of LD19 were smaller compared with populations captured using similar gears from the Missouri River (mean TL 6 SE ¼ 803 mm 6 6.8; Wanner and Klumb 2009a) and age structure was younger and represented a more restricted age structure than populations in a Virginia lake (Stich et al 2013). Additionally, the mean length-at-age and von Bertalanffy parameter estimates for Grass Carp captured both upstream and downstream of LD19 suggests that Grass Carp are smaller, reach the asymptotic length quicker, and reach a smaller maximum size compared with Grass Carp captured in South Carolina, USA (Morrow et al 1997), Florida, USA (Shireman et al 1980), and Virginia, USA (Stich et al 2013).…”

“…Difficulties related to capture and low Grass Carp densities offer limited opportunities to formally evaluate populations unless substantial effort is allocated toward the collection of Grass Carp (Sullivan et al 2019). Assessments of adult Grass Carp populations have often focused on stocked or introduced populations in the southeastern or eastern United States (Shireman et al 1980;Morrow et al 1997;Stich et al 2013) with few assessments conducted within the Mississippi River watershed (but see Wanner and Klumb 2009a). Lock and Dam 19, a key focal point for naturalized Grass Carp management because limited upstream migration occurs, creates a semipermanent barrier between Grass Carp populations that exhibited different population characteristics throughout our study.…”

“…Little information is available documenting Grass Carp capture rates throughout their native or introduced range. Methods such as bow fishing (Morrow et al 1997;Stich et al 2013) and commercial harvests (Pflieger 1978) have been used to obtain individuals but cannot be used to infer patterns in relative abundance estimates. Within the Missouri River basin, standardized sampling surveys (e.g., trammel, gill, mini-fyke, and hoop nets) have been used to estimate Grass Carp relative abundance.…”

Persistent fibrosis and decreased cardiac function following cardiac injury in theCtenopharyngodon idella(grass carp)

“…1B). These fish are capable of exceeding 25 kg in mass and 1 meter in length in aquaculture conditions, thus their size is several orders-of-magnitude greater than the previously studied species (Stich et al, 2013). As an invasive species to the United States, early efforts to sterilize these fish by removal of the gonads were ineffective due to their ability to regenerate reproductive organs within months of removal (Underwood et al, 1986).…”

Influence of river discharge on grass carp occupancy dynamics in south‐eastern Iowa rivers

“…For example, fish communities in Mississippi River Pools 8, 13, and 26 are routinely monitored employing pulsed‐DC electrofishing, but only 260 grass carp have been captured from 1990 to 2017 (<0.001% of catch; http://www.umesc.usgs.gov/ltrmp.html). Therefore, existing grass carp population assessments are largely limited to stocked populations in lakes (Clemens, Spangler, Robertson, et al, ; Stich, Dicenzo, Frimpong, Jiao, & Murphy, ), and limited information exists on naturalized grass carp populations in North American rivers.…”