A Multitracer Approach to Quantifying Resource Utilization Strategies in Lake Trout Populations in Lake Huron

Abstract

Lake ecosystems are threatened by an array of stressors. An understanding of how food webs and bioaccumulation dynamics respond to these challenges requires the quantification of energy flow. We present a combined, multitracer approach using both polychlorinated biphenyls (PCBs) and stable isotopes to trace energy flow, and to quantify how lake trout feeding strategies have adapted to changes in food web structure in 3 basins of Lake Huron (ON, Canada). This combined tracer approach allows the quantification of dietary proportions (using stable isotopes), which are then integrated using a novel PCB tracer approach that employs knowledge of PCB bioaccumulation pathways, to estimate consumption and quantify energy flow between age cohorts of individual fish across Lake Huron. We observed basin‐specific differences in ultimate energy sources for lake trout, with Georgian Bay lake trout deriving almost 70% of their energy from benthic resources compared with 16 and 33% for Main Basin and North Channel lake trout, respectively. These differences in resource utilization are further magnified when they are contrasted with age. The dependency on pelagic energy sources in the Main Basin and North Channel suggests that these populations will be the most negatively affected by the ongoing trophic collapse in Lake Huron. Our study demonstrates the utility of a multitracer approach to quantify the consequences of food web adaptations to changes in aquatic ecosystems. Environ Toxicol Chem 2019;38:1245–1255. © 2019 SETAC

Basin‐Specific Pollutant Bioaccumulation Patterns Define Lake Huron Forage Fish

“…For example, should prey communities, abundances, and food-web structures be similar across multiple compartments of the same ecosystem, this would be expected to manifest in similar magnitudes and patterns of congener bioaccumulation among individuals of the same species. That basin-specific PCB profiles have now been demonstrated for top predator (Paterson et al 2016) and secondary consumer forage fish species collected from across Lake Huron confirms conclusions regarding the importance of lower trophic level processes in regulating pollutant and energy transfer within the Lake Huron food webs (Bunnell et al 2014;Paterson et al 2014;McLeod et al 2019). Bunnell et al (2014) concluded that bottom-up control mechanisms predominate in terms of nutrient and energy availability and flow in Lake Huron.…”

“…Note differences in axis scales for (C). in gut contents (McLeod et al 2019). In addition, Mida (2010) noted a general absence of mysids in North Channel bloater and rainbow smelt diets.…”

“…For rainbow smelt and bloater, ΣPCB concentrations for zooplankton from the respective basins represented the prey source and, for round goby, dreissenid mussel ΣPCB concentrations were the prey source in BMF calculations. These prey generally represent the predominant diet preferences for these fish throughout Lake Huron (McLeod et al 2019).…”

“…For example, McLeod et al (2019) used a multitracer approach to demonstrate contrasting contributions of benthic and pelagic prey resources for Lake Huron lake trout depending on basin residency. Specifically, fish occupying the Main Basin or North Channel were predicted to be more reliant on pelagic resources relative to fish collected from Georgian Bay, which derive the majority of dietary energy through benthic pathways (McLeod et al 2019). Such differences in foraging behaviors potentially reflect the rewiring of food-web predator-prey interactions that can occur following stressor events that can function to alter energy flow through previously established but minimally exploited linkages (Bartley et al 2019).…”

“…For example, increasingly chlorinated and superhydrophobic PCB congeners tend to sorb to particulate organic matter, with sediments generally representing the predominant sink of these pollutants (Lopes et al 2011). These congeners are also those that exhibit the greatest extent of food-web biomagnification, are poorly biotransformed with significant environmental half-lives, and can therefore likely act as surrogates of benthic-pelagic coupling (McLeod et al 2019). In comparison, the less hydrophobic and chlorinated tri-, tetra-, and pentachlorobiphenyl congeners are increasingly water soluble relative to such superhydrophobic congeners and are less likely to exhibit the phenomenon of food-web biomagnification (Drouillard et al 2009).…”