Changes in prey, turbidity, and competition reduce somatic growth and cause the collapse of a fish population

Abstract

Somatic growth exerts strong control on patterns in the abundance of animal populations via effects on maturation, fecundity, and survival rates of juveniles and adults. In this paper, we quantify abiotic and biotic drivers of rainbow trout growth in the Colorado River, Arizona, USA, and the resulting impact on spatial and temporal variation in abundance. Inferences are based on ~10,000 observations of individual growth rates obtained through an intensive mark–recapture effort conducted over 5 yrs (2012–2016) in a 130‐km long study segment downstream of Glen Canyon Dam. Prey availability, turbidity‐driven feeding efficiency, and intraspecific competition were the dominant drivers of rainbow trout growth. Discharge, water temperature, and solar insulation were also evaluated but had a smaller influence. Mixed‐effect models explained 79–82% of the variability in observed growth rates, with fixed covariate effects explaining 79–87% of the total variation in growth parameters across five reaches and 18 quarterly sampling intervals. Reductions in growth owing in part to a phosphorous‐driven decline in prey availability, led to a substantive loss in mass and poor fish condition. This in turn lowered survival rates and delayed maturation, which led to a rapid decline in abundance and later recruitments. Reductions in feeding efficiency, due to episodic inputs of fine sediment from tributaries, and warmer water temperatures, contributed to reduced growth in downstream reaches, which led to more severe declines in abundance. Somatic growth rates increased following the population collapse due to reduced competition, and in the absence of substantive increases in prey availability. Our study elucidates important linkages between abiotic and biotic factors, somatic growth, and vital rates, and demonstrates how variation in somatic growth influences temporal and spatial patterns in abundance.

Factors Influencing Rainbow Trout Annual Growth in a Large Regulated River

“…Density dependence has been shown to be an important factor influencing the growth of Rainbow Trout in other systems (Post et al 1999; Korman et al 2017, and in press), and as such we were surprised that our findings neither supported nor were consistent with a density‐dependence hypothesis. The top predictor variables in our final model sets and most other predictors within the fish density category exhibited a significant positive correlation with Rainbow Trout growth.…”

Genomic prediction of growth in a commercially, recreationally, and culturally important marine resource, the Australian snapper (Chrysophrys auratus)

“…Using breeding values to predict population response has potential complications, such as failure to incorporate the complexity of factors and uncertainty involved in trait measurement ( Hadfield et al 2010 ). A wide range of factors affects growth in marine fishes, such as temperature ( Boltaña et al 2017 ; Wellenreuther et al 2019 ), nutritional state ( Escalante-Rojas et al 2020 ), and intra- and interspecies interactions ( Mallard et al 2020 ; Korman et al 2021 ). Although these factors can induce phenotypic plastic changes to growth, there are also important genetic components in response to these factors ( Wellenreuther et al 2019 ; Escalante-Rojas et al 2020 ).…”

Genomic prediction of growth in a commercially, recreationally, and culturally important marine resource, the Australian snapper (Chrysophrys auratus)

“…2019), nutritional state (Escalante-Rojas et al 2020) and intra- as well as inter-species interactions (Mallard et al . 2020; Korman et al . 2021).…”

“…Using breeding values to predict population response has potential complications, such as failure to incorporate the complexity of factors and uncertainty involved in trait measurement (Hadfield et al 2010). A wide range of factors affects growth in marine fishes, such as temperature (Boltaña et al 2017;Wellenreuther et al 2019), nutritional state (Escalante-Rojas et al 2020) and intra-as well as inter-species interactions (Mallard et al 2020;Korman et al 2021). Although these factors can induce phenotypic plastic changes to growth, there are also important genetic components in response to these factors (Wellenreuther et al 2019;Escalante-Rojas et al 2020).…”