Synthesizing Professional Opinion and Published Science to Build a Conceptual Model of Walleye Recruitment

Abstract

Understanding and predicting recruitment, longstanding goals in fisheries science and ecology, are complicated by variation in the importance of environmental drivers coupled with the dynamic nature of individual ecosystems. Developing an understanding of recruitment from well‐monitored stocks offers an opportunity to overcome these complexities. We used a systematic literature review, a survey, and a workshop attended by professionals with expertise in recruitment of Walleye Sander vitreus to identify common environmental drivers of Walleye recruitment and additional sources of variation (i.e., context dependencies) among populations. The importance of individual environmental drivers, as well as the direction of their influence, differed as a function of geographic region, lake surface area, and Walleye life stage. The literature suggested abiotic conditions (e.g., temperature) during the first year of life were influential in determining recruitment. Professional opinion noted the importance of biotic factors, with prey availability and predation risk having the most consistent relationships with recruitment. We synthesized this information to propose a conceptual model that illustrates the suite of characteristics that shape Walleye recruitment over large spatial and temporal scales. Our findings emphasize the importance of first‐year growth and system‐specific contextual factors, which can alter the relative importance of the environmental drivers of recruitment.

Factors affecting walleye and sauger recruitment in Lewis and Clark Lake, South Dakota, 2001–2022

“…We found abiotic factors (mainly mean monthly outflow) were more strongly correlated to variation in age-0 walleye CPUE than biotic factors, but that both biotic and abiotic factors were significantly correlated to variation in age-0 sauger CPUE. Our findings add needed information to river-reservoir management of walleye and sauger because the role of outflow in regulating age-0 walleye abundance has been rarely considered (Krabbenhoft et al, 2023) and investigations into factors driving sauger recruitment are rare.…”

“…Direct management of entrainment through construction of barriers or deterrents may be more effective for bolstering reservoir native (see Jesus et al., 2021 for review) and sport fish populations in situations where entrainment is known to be a large source of individual loss (Fish Guidance Systems Ltd and Hydro Energy Developments Limited, 1996; Weber & Flammang, 2019). For walleye, a paucity of research on the impact of reservoir outflow on walleye recruitment (Krabbenhoft et al., 2023) may result in knowledge gaps and could be why effects of outflow are not directly managed. Consideration of reservoir outflow as a factor affecting fish recruitment is prudent for reservoir managers in that alternative courses of action to more common management strategies (i.e., stocking) may be elucidated where appropriate.…”

An evaluation of the relative size, body condition, and survival of triploid Walleye in the wild

“…Although catch rates of age‐0 fish were lower in 2020 (i.e., only natural‐origin fish) than in the other study years (i.e., stocked fish and possibly natural‐origin fish), natural recruitment of Walleye can be variable and could make contributions in some years (Krabbenhoft et al. 2023). Thus, if natural reproduction occurred during the other study years, our estimates of relative survival for age‐0 triploids would be biased low and therefore represent a worst case scenario for the relative survival of triploid Walleye.…”

Simulated effects of imperfect sterile sport fish stocking on persistence of fertile fish in new exploited populations

“…In this scenario, we would anticipate “flashy” dynamics with periods of relatively high densities of natural‐origin fish followed by periods of low densities, particularly if recruitment or population productivity is autocorrelated and driven by broader temporally dynamic environmental or ecological processes or regime shifts (Essington 2021). Given the paucity of information on the recruitment dynamics of nonnative Walleye and potential region‐specific biotic and abiotic drivers (Krabbenhoft et al 2023), we did not consider autocorrelated recruitment. Instead, we identified year‐by‐year probabilities of success derived by Hansen et al (2015) and then let σ govern the random generation of strong, average, or weak year‐classes within a successful year.…”

“…Thus, developing and sustaining a new triploid fishery would require stocking fish with IRs <100%, which carries the risk of starting a new feral population if the stocked diploid fraction survives to maturity and becomes self‐sustaining. However, because a host of biotic and abiotic factors influence Walleye recruitment (Raabe et al 2020; Krabbenhoft et al 2023) and diploids would be greatly outnumbered from the onset of stocking, it is unknown how stocking a small number of diploid fish would affect the likelihood of creating a self‐sustaining population. Under these conditions, moderate levels of reproductive interference by triploid males could limit expansion of diploids above baseline stocking levels.…”