Life history and temporal variability of escape events interactively determine the fitness consequences of aquaculture escapees on wild populations

• Published in: Theoretical population biology 2019-10, Vol.129, p.93-102
• Main Authors: Yang, Luojun, Waples, Robin S., Baskett, Marissa L.
• Format: Article
• Language: English
• Subjects: Age structure; Animals; Aquaculture; Fisheries; Fishes - genetics; Gadus morhua; Gene Flow; Life history; Life History Traits; Models, Statistical; Salmo salar
• ISSN: 0040-5809; 1096-0325
• DOI: 10.1016/j.tpb.2018.12.006

Domesticated individuals are likely to be maladaptive in the wild due to adaptation to captivity. Escaped aquaculture fish can cause unintended fitness and demographic consequences for their wild conspecifics through interbreeding and competition. Escape events from different sources exhibit great heterogeneity in their frequencies and magnitudes, ranging from rare but large spillover during a storm, to continuous low-level leakage caused by operational errors. The timescale of escape events determines the distribution of gene flow from aquaculture to the wild. The evolutionary consequences of this variation in timescale will depend on the degree of generation overlap and the focal species’ life history attributes, especially those under selection in aquaculture (e.g., growth rate, which can influence additional demographically important traits such as age at maturity). To evaluate the effects of variable escape both within and across generations, we construct an age-structured model of coupled genetic and demographic dynamics and parameterize it for species with contrasting life history characteristics (Salmo salar and Gadus morhua). Our results are consistent with earlier discrete-generation models that constant, low-level spillover can have a greater impact than rare, large pulses of leakage, even after accounting for the averaging effects of overlapping generations. The age-structured model also allows detailed evaluation of the role of different life history traits, which reveals that species with longer generation times might experience greater fitness consequences of aquaculture spillover but are less sensitive to variability in spillover. Additionally, environment-induced earlier maturity of escapees can increase the fitness effects on wild fish, especially those with shorter generation times. Our results suggest that effective management to minimize the unintended fitness consequences of aquaculture releases might require extensive monitoring efforts on constant, low-level spillover and assessment of the focal species’ life history characteristics. •Constant low-level escapees can have greater fitness effects than large spikes.•The relative effects of constant vs. variable spillover are robust to age structure.•Species with longer generation time experience greater fitness effects of escapees.•Early maturity in captivity causes greater fitness effects on shorter-lived species.