Ecological interactions and environmental stressors: assessing dietary dynamics and population stability of burbot amid non-native trout and warming winter temperatures

Abstract

Burbot Lota lota are a cold-water specialist that have a circumpolar distribution. Though historically widespread, many populations are experiencing declines, including the burbot population in the Torrey Creek drainage, Wyoming, which occurs at the southwest most extent of their native range. One hypothesis for the decline observed in burbot abundance within the drainage is the presence of non-native piscivorous predators (i.e., brown trout Salmo trutta and lake trout Salvelinus namaycush). Using diet composition, bioenergetics, and population modeling, I evaluated the effects non-native trout are having on burbot. There was little dietary overlap among all species combinations. Predation of burbot was not observed by lake trout and was minimal by brown trout, estimated at 7.9 - 37.6 kg annual for the drainage. Nevertheless, I modified a previously developed model to investigate how much predation would be necessary to negatively influence the burbot population. Both the observed and increased predation scenarios yielded positive population growth rates. However, when demographic stochasticity and parameter uncertainty were introduced, every simulation carried a risk of extirpation for burbot within a century, primarily attributed to the high uncertainty associated with the adult mortality estimate. In addition to predation effects, I investigated water temperature induced recruitment failure using a model where egg survival decreased from 86.7% at 2ºC to 47.9% at 4ºC. This critical water temperature, 4ºC, was observed to occur during the putative embryogenesis period of 2022 - 2023 for burbot in the Torrey Creek drainage. The addition of the recruitment penalty to the population models decreased the probability of persistence for all simulation and reduced mean population growth. However, the reduction in recruitment even when occurring annually resulted in higher lambda estimates than the increased predation simulation without the occurrence of a recruitment penalty, indicating that juvenile survival has a greater proportional effect on the population growth rate than the reduction in recruitment as modeled by the recruitment penalty. With the findings from the bioenergetics modeling coupled with the population modeling, direct predations and intraguild predation from brown trout and lake trout are currently not a key factor contributing to the decline of burbot within the drainage.