Assessing environmental stressors on a commercial walleye fishery from a large northern ecosystem (Tathlina Lake) using water chemistry and paleolimnology

Abstract

Tathlina Lake (Northwest Territories, Canada) is a large, shallow ecosystem in the rapidly warming northern boreal forest. This lake is of considerable cultural and economic significance as it supports a commercially important walleye (Sander vitreus) fishery that has experienced large fluctuations since the 1940s, the causes of which are poorly understood. Here we used paleolimnology to describe long-term environmental changes in the lake that may have contributed to recent collapses in walleye populations. The sub-fossil remains of diatoms and chironomids were used to assess changes in turbidity, nutrients, and oxygen levels, all of which are important to walleye. Minimal changes have occurred in diatom assemblages from the early 1920s to present, suggesting that turbidity and nutrients have not changed markedly in the lake. Hypoxia-tolerant chironomid taxa were found throughout the sediment record, and our modern water chemistry showed that oxygen levels were supersaturated in the summer, but close to the lower tolerance limit of walleye in winter. An increase in sedimentary chlorophyll-a since~1940 suggests Tathlina Lake is affected by recent climate warming. Our findings indicate that walleye populations are likely regularly exposed to hypoxic winter conditions, which may increase the sensitivity of the population to other interacting stressors that occur with recent climate warming. Long-term records of environmental change in large, shallow northern lakes are rare, and paleolimnology provides a framework to reconstruct missing monitoring data, especially in lakes that are economically and culturally important to northern communities.

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

“…For example, drivers that affect Walleye growth and survival during the first spring (i.e., egg and larval production period) appear paramount to understanding eventual recruitment outcomes, largely owing to their influence on the ability of larvae to evade predators (Brooking et al 1998), consume the needed prey to make the transition to piscivory (Quist et al 2004), and accumulate sufficient length or lipids to survive the first winter of life (Pothoven et al 2014). Survival during the first winter is also related to hypoxia, though there is an additional peak during summer (Brandt et al 2011;Stewart et al 2016). This builds on prior work by Honsey et al (2020) describing the first winter as a critical time for recruitment, but provides alternative mechanisms to their emphasis on thermal conditions.…”

Fisheries Volume 48 Number 4 April 2023

“…For example, drivers that affect Walleye growth and survival during the fi rst spring (i.e., egg and larval production period) appear paramount to understanding eventual recruitment outcomes, largely owing to their infl uence on the ability of larvae to evade predators (Brooking et al 1998 ), consume the needed prey to make the transition to piscivory (Quist et al 2004 ), and accumulate suffi cient length or lipids to survive the fi rst winter of life (Pothoven et al 2014 ). Survival during the fi rst winter is also related to hypoxia, though there is an additional peak during summer (Brandt et al 2011 ;Stewart et al 2016 ). This builds on prior work by Honsey et al ( 2020 ) describing the fi rst winter as a critical time for recruitment, but provides alternative mechanisms to their emphasis on thermal conditions.…”

Intense variability of dissolved oxygen and temperature in the internal swash zone of Hamilton Harbour, Lake Ontario

“…High variability of water quality parameters, such as T and DO, could pose challenges to fishes in HH, and upwelling of hypoxic water has been found to increase mortality in some instances (as in Lake Erie; Kraus et al 2015). With a preferred thermal range of 18-22°C (Christie and Regier 1988) and preferred DO concentrations >3-5 mg L −1 (Stewart et al 2016), walleye (Sander vitreus) is an example of a species whose habitat is expected to be strongly affected by upwelling of the cold, hypoxic hypolimnion in HH. Brooks et al (2018) investigated the spatial ecology of reintroduced walleye in HH and found highest residency of this top predator was actually in regions found in the present study to have the highest DO and temperature variability (i.e., western end of the harbour).…”