Striped bass exploitation in tailwater habitats of east-central Oklahoma

Striped Bass (Morone saxatilis) is naturally anadromous, but a few land-locked populations have been documented that are self-sustaining, including fish in the Arkansas River, Oklahoma. This rare population is the source of brood stock for the Oklahoma Department of Wildlife Conservation hatcheries and is an important sportfish stock. Striped Bass often congregate in tailwater habitats, where anecdotal observations indicate anglers can harvest numerous fish daily. This suggests the need to evaluate the sustainability of harvest in these locations. It is unknown what portion of fish from the Arkansas River population use tailwater habitats or the timing and duration of use. The objectives of this study were to: 1) determine size structure , abundance, and total mortality rate of Striped Bass in the tailwaters of Tenkiller Lake and Lake Eufaula; 2) determine the extent and timing of immigration and emigration of Striped Bass in tailwater habitats to determine the potential for overharvest when they congregate in tailwater areas; 3) estimate delayed hooking mortality of Striped Bass in spring and summer; and 4) using the above data and modeling simulations, determine the potential for growth overfishing of Striped Bass in the tailwater reaches. We sampled 2,730 Striped Bass using boat electrofishing and tagged with passive integrated transponder (PIT) tags to estimate demographic data using a capture-recapture model. A subset of these Striped Bass was tagged with angler reward tags (internal anchor tags, n = 681) and dual technology acoustic-radio telemetry tags (n = 111) to estimate exploitation and track movements, respectively. Anglers returned 116 tags from 2020 to 2022; and our angler reporting rate was estimated to be 14.3%. Annual harvest mortality is minimally 7% (unadjusted for reporting rate) but could be as high as 42% (i.e., adjusting for compliance; but this exceeds the measured total mortality rate (34.3%) so true exploitation is probably 7–34.3%). Our abundance estimates for Striped Bass varied seasonally (ranging from 782 to 38,597 seasonally) and had a high level of uncertainty likely due to relatively low recapture rates. Additionally, our results indicated that Striped Bass exhibited a strong fidelity to their respective habitats within seasons, with fidelity probabilities ranging from 0.98 to 1.00. Movement among segments was common among seasons, indicating these localized populations mix with a larger population annually. Striped Bass were primarily in tailwater habitats during summer. Delayed hooking mortality data were collected in summer 2022. Due to habitat conditions that year, angling catch rates were low. Twenty-nine Striped Bass were tagged, and only eight Striped Bass remained tagged long enough to be tracked at least one day. The total time tracked for these eight fish was between one and three days. There were no confirmed mortalities, treatment, or control. Because of the low sample size, literature values for delayed hooking mortality were also used to supplement field data in the models. The yield-per-recruit model indicated exploitation at 30% or higher leads to recruitment overfishing. A 600 mm minimum TL regulation and 25–30% exploitation rate achieve maximum yield (954 kg/1,000 recruits). Maximum yield related to an average size at harvest of 718-mm TL; thus, growth overfishing occurs for any regulation where average size of harvest is smaller than 718 mm (which the model predicted would occur for any minimum length < 600, and for minimum length = 600 if exploitation was > 30%, it never occurred with minimum length requirements > 650). Increasing the minimum length regulation improves size structure, but a maximum length regulation had minimal effect unless it was implemented at a sufficiently small size (i.e., < 700 mm). Although catch-and-release mortality can be relatively high at times in the literature, according to our model, it appears to have a small effect on size structure, except when exploitation rates are > 50% and a restrictive maximum size regulation (< 800 mm) is used.  The current population appears sustainable, especially considering the annual mixing dynamics and apparently large population (though we see a lot of uncertainty in the population estimates). However, modeling indicates that if enhancing size structure is an agency priority, then implementing more restrictive regulations could be advantageous.