Survival under the Gravel: the Effects of Egg Size and Parental Identity on the In Situ Hatching Success of Chinook Salmon

Abstract

Early‐life mortality in salmon is influenced by both extrinsic (i.e., environmental) and intrinsic (i.e., parental) factors; however, the intrinsic factors have rarely been studied in the wild and relatively little is known about how egg mass and parental effects mediate in situ survival. Thus, we addressed four research objectives related to intrinsic factors and the early‐life survival of Chinook Salmon Oncorhynchus tshawytscha: (1) assess the effect of egg mass and parental effects on in situ hatching success, (2) assess the effect of redd gravel composition and its interaction with egg mass on in situ hatching success, (3) determine whether in situ egg mass–survival relationships have population‐level consequences, and (4) determine whether results from hatchery studies translate to the wild. Embryos from three Chinook Salmon populations located in the Laurentian Great Lakes were reared from fertilization to 15 d posthatch, both in the hatchery and in the wild. We found that egg mass influenced in situ hatching success in the Credit (concave down) and Sydenham rivers (positive‐linear), whereas there was no relationship between the two variables in the Pine River. Maternal identity explained a significant amount of the variation in hatching success for the Pine (20%) and Sydenham (12%) rivers. Within populations, no interaction was found between egg mass and gravel composition; however, hatching success was negatively related to the sand content of a redd when the data were pooled among the populations. Importantly, egg mass and quantitative genetic parameter estimates were different between samples from the hatchery and those from the wild, indicating that hatchery‐based observations cannot be transferred to the wild. Finally, we used both the in situ survival data and previously published data in a simulation analysis, which showed that both linear and nonlinear egg mass–survival relationships can greatly influence the number of alevins produced by a population, depending on where the population egg mass distribution falls along an egg mass selection gradient.

Early survival in Atlantic salmon is associated with parental genotypes at loci linked to timing of maturation

“…A plausible mechanism explaining our results is that that variation in six6 alters early life survival via changes in egg composition. In oviparous species, the composition of eggs, such as hormone levels, albumin and fat content, may mediate the phenotype and behaviour of the offspring, and subsequently their fitness (Williams 1994; Thorn and Morbey 2019; Widowski et al 2022). In Chinook salmon, carotenoid composition in the eggs has been shown to be associated with early life survival (Tyndale et al 2008).…”

Elevated incubation temperature improves later‐life swimming endurance in juvenile Chinook salmon, Oncorhynchus tshawytscha

“…In the wild, early incubation and rearing temperatures should affect swimming performance primarily through effects on L F or other body size traits at key developmental milestones. A salmon reared in warm water is expected to hatch and emerge with a smaller body size, both in general (Beacham & Murray, 1985, 1990 and in the focal population of the current study (Thorn & Morbey, 2019), and smaller fish generally have poorer swimming performance. In turn, poorer…”

Gastrulation and hatch as critical thermal windows for salmonid embryo development

“…It is also important to note that, although the theory presented here is robust, the temperature regimes used are not suitable to apply to real world situations. This is because embryo survival in laboratory conditions is typically greater than in the field (Thorn & Morbey, 2019), and the sensitivity of different species to the same environmental conditions varies substantially. Furthermore, as demonstrated by differences in survival between studies A and B, within species variation in response to similar thermal stress is observed.…”