Abstract
For species with individual variation in reproductive success, experience in breeding and the distribution of different breeders is important for population productivity and viability. Human impacts, such as climate change and harvesting, can alter this distribution and thus population dynamics. Here, we investigated the effect of spawning experience on population growth in a population of migratory brown troutSalmo truttasubject to stressors including migration barriers, harvesting, and climate change. We described the population dynamics with a structured integral projection model that differentiates between first-time and repeat spawners. We then took a scenario-based approach to test to which extent spawning experience has a positive effect on the population growth of brown trout by running 3 different model simulations: a baseline scenario with no changes to the reproductive output of the population, a non-selective scenario in which the reproductive output of all spawners was reduced, and a selective scenario where the reproductive output of only first-time spawners was reduced. We found that the reproductive output of repeat spawners is more important than that of first-time spawners for population growth, in line with other studies. Moreover, the contribution of first-time spawners to the population growth through their own survival is more important than their contribution to growth through reproduction. To ensure the continued existence of the study population, survival of first-time spawners and reproductive success of repeat spawners should be prioritised. More generally, including breeding experience adds more mechanistic detail, which ultimately can aid management and conservation efforts.
Highlights
Populations are made up of individuals that differ genetically, physically, and in acquired skills and knowledge
Our results indicate that for Hunder trout, the reproductive output of repeat spawners is more important for long-term population growth than that of first-time spawners
The survival of first-time spawners to become repeat spawners seems more important for the population dynamics than their reproductive contribution
Summary
Populations are made up of individuals that differ genetically, physically, and in acquired skills and knowledge. For species that reproduce more than once, i.e. iteroparous species, the distribution of individuals with different experience in breeding can influence the population dynamics. In species with indeterminate growth such as long-lived fish in colder regions, body and gonad mass is generally positively correlated, and larger females produce more eggs (Jonsson 1978, Trippel 1998). Given this relationship, it is common to estimate the annual reproductive output of a fish population based on its spawning stock biomass. The contribution of several small females might not be equal to the contribution of fewer large females, even though they have the same total body mass
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