Larval cisco and lake whitefish exhibit high distributional overlap within nursery areas

Abstract

Coregonine fishes, including lake whitefish (Coregonus clupeaformis) and cisco (C. artedi), are socioecologically important in the Laurentian Great Lakes and of conservation concern, but the processes driving recruitment variability are unclear. In Lake Ontario, cisco and lake whitefish exhibit similar spawning behaviours and early life histories, but population trajectories are diverging. One hypothesis is that sympatric cisco and lake whitefish larvae occupy distinct habitats and experience dissimilar local environmental conditions, despite co‐occurrence within nursery areas. We described the spatiotemporal distributions of larval cisco and lake whitefish among multiple Lake Ontario embayment nursery areas, characterised physical habitat features associated with their distributions, determined the degree of spatial habitat partitioning between species and evaluated how habitat niche divergence occurred along an ontogenetic progression. Both species were widely distributed across larval nursery areas, though lake whitefish were less abundant and more narrowly distributed than cisco. Within the yolk sac stage, lake whitefish occupied more nearshore, shallower and colder waters than cisco, indicating potential habitat niche partitioning between congeners. However, distributional differences were subtle and likely driven by differential hatch timing and staggered ontogenetic habitat shifts. Combined, our results illustrate similar habitat use between cisco and lake whitefish through the larval stage and demonstrate that ontogeny and species‐specific phenology influence habitat use for these species. This study provides additional evidence that the early life histories of cisco and lake whitefish are highly similar and does not support the hypothesis that larval habitat use differences are a major driver of differential recruitment success for these species.

Lakeshore areas of conservation interest: Characteristics of nursery areas of the threatened lake‐dwelling grayling, Thymallus thymallus

“…define sites where they occur as nursery areas (see Brown et al, 2023), which are expected to be essential for the life cycle, and hence conservation and persistence, of lake-dwelling populations (Brown et al, 2023;Paufve et al, 2022;Riley et al, 2019). Therefore, knowledge on the sites' characteristics can support efficient management measures.…”

“…To provide information that could support more efficient management and conservation measures for Lake Puruvesi, its grayling, and other similar lakes and populations, we investigated the characteristics of the sites in which larval and post‐larval grayling (less than a month old and below 40 mm, from hereon ‘grayling fry’), do and do not occur. We define sites where they occur as nursery areas (see Brown et al., 2023), which are expected to be essential for the life cycle, and hence conservation and persistence, of lake‐dwelling populations (Brown et al., 2023; Paufve et al., 2022; Riley et al., 2019). Therefore, knowledge on the sites' characteristics can support efficient management measures.…”