Flow Conditioning of Hatchery‐Reared Razorback Sucker Increases Apparent Survival in the Wild

Abstract

Hatchery augmentation of dwindling wild populations has become a common strategy to avoid extinction of endangered fishes. While benign hatchery conditions can lead to low persistence of stocked individuals, experiments have demonstrated that flow conditioning of Razorback Sucker Xyrauchen texanus can increase swimming performance and reduce downstream movements from desired locations after stocking in the Colorado River basin, USA. However, managers have been slow to adopt its use, likely because linking experimental flow conditioning to scales that are relevant to conservation has been difficult. We reared age-2 Razorback Sucker in two raceways (control: n = 530; flow conditioning: n = 533) for 10 weeks to assess whether flow conditioning could increase apparent survival after stocking into the San Juan River, New Mexico. We used riverwide active sampling and remote PIT tag antennas to resample individuals for 3 years after stocking. Using Cormack-Jolly-Seber mark-recapture models, we assessed the effects of flow conditioning, size at stocking, relative condition (Fulton's K), and their interactions on apparent survival and downstream movement after stocking. Flow conditioning of fish doubled the mean apparent survival (at a mean size of 325 mm TL) during the first overwinter period (control fish: 0.14, 95% CI = 0.09-0.21; flow-conditioned fish: 0.28, 95% CI = 0.19-0.38), with both groups having similar mean overwinter apparent survival estimates thereafter (both > 0.75). Size at stocking and K were positively associated with first-overwinter apparent survival regardless of treatment (mean survival was <0.20 for fish <275 mm TL but was >0.65 for fish >450 mm TL). Downstream movement after stocking was negatively associated with fish size, indicating that emigration likely contributed to higher apparent mortality of smaller fish. Our results suggest that transitioning hatchery practices to include flow conditioning of Razorback Sucker (and potentially other endangered Colorado River fishes) prior to stocking could substantially increase the conservation efficiency of these augmentation programs.

Hatchery supplementation increases potential spawning stock of Rio Grande Silvery Minnow after population bottlenecks

“…For RGS Minnow, the demographic boost is only moderate, even in years when the CPUE of wild fish is very low, because the survival of hatchery fish is likely very low: 9–25% (Yackulic et al 2022). Increasing the production of RGS Minnow may not be feasible given hatchery constraints; however, increasing postrelease survival through other means, such as flow training or release of larger fish, may be possible (Franssen et al 2021; Fonken et al 2022). Evaluation of actions intended to increase postrelease survival may be difficult, as recapture rates of small fish in medium to large rivers are often very low even when large numbers of hatchery fish are used for these studies (Archdeacon and Remshardt 2012; Platania et al 2020).…”

Reared to become wild-like: addressing behavioral and cognitive deficits in cultured aquatic animals destined for stocking into natural environments—a critical review

“…While not part of the scope of this review, it is worth mentioning that other methods than the ones covered here have been applied to improve the behavior or the physiological traits facilitating certain behaviors. Physical exercise through increased flow during rearing can influence traits relevant for postrelease performance such as stamina, behavior, and cognition (see e.g., Davison 1997, Kieffer 2010, Gomez-Pinilla and Hillman 2013, Franssen et al 2021. Reduced or variable food supply can affect, for example, metabolic traits, postrelease growth, and migration willingness (e.g., Garlock et al 2014, Persson et al 2018.…”

Movement, not survival, differs between wild and hatchery‐reared imperiled desert fishes

“…Many mark-recapture studies do not distinguish between survival and movement (Muir et al 2001;Carlson and Letcher 2003;Franssen et al 2021) and only examine apparent survival (Lebreton et al 1992) or the probability that an individual is in the population at a certain time, regardless if individuals are lost to…”

“…Hatchery‐reared fish can differ in their behavior and survival when compared to wild‐spawned fish, but often these results are variable among species and systems, making it difficult to infer results to understudied organisms (Araki and Schmid 2010). A common technique used to examine the success of stocking hatchery‐reared fish is to conduct poststocking surveys to evaluate species establishment (Franssen et al 2021; Tennant et al 2022). Unfortunately, poststocking surveys that quantify metrics for establishment cannot discern if high mortality rates or high emigration delay or prevent establishment (Gilroy et al 2012).…”

“…Understanding if population establishment following stocking is driven by poststocking mortality or emigration can help refine stocking protocols for rare and endangered fish (Pennock et al 2020). For example, alternative locations within the watershed, different release strategies such as soft releases, flow training in the hatchery, or altering the season of stocking might increase survival and retention of stocked fish (Brown and Day 2002; Franssen et al 2021; Hickerson et al 2022). Additionally, stocking of native fish in formerly occupied habitats often occurs upstream of natural or constructed fish barriers that prevent the invasion of nonnative fish (Fausch et al 2006; Hickerson et al 2021).…”