Modelling fitness changes in wild Atlantic salmon populations faced by spawning intrusion of domesticated escapees

Genetic interaction between domesticated escapees and wild conspecifics represents a persistent challenge to an environmentally sustainable Atlantic salmon aquaculture industry. We used a recently developed eco-genetic model (IBSEM) to investigate potential changes in a wild salmon population subject to spawning intrusion from domesticated escapees. At low intrusion levels (5–10% escapees), phenotypic and demographic characteristics of the recipient wild population only displayed weak changes over 50 years, and only at high intrusion levels (30–50% escapees) were clear changes visible in this period. Our modelling also revealed that genetic changes in phenotypic and demographic characteristics were greater in situations where strayers originating from a neighboring wild population were domestication-admixed and changed in parallel with the focal wild population, as opposed to non-admixed. While recovery in the phenotypic and demographic characteristics was observed in many instances after domesticated salmon intrusion was halted, in the most extreme intrusion scenario, the population went extinct. Based upon results from these simulations, together with existing knowledge, we suggest that a combination of reduced spawning success of domesticated escapees, natural selection purging maladapted phenotypes/genotypes from the wild population, and phenotypic plasticity, buffer the rate and magnitude of change in phenotypic and demographic characteristics of wild populations subject to spawning intrusion of domesticated escapees. The results of our simulations also suggest that under specific conditions, natural straying among wild populations may buffer genetic changes in phenotypic and demographic characteristics resulting from introgression of domesticated escapees, and that variation in straying in time and space may contribute to observed differences in domestication-driven introgression among native populations

Stable and unstable equilibrium states in a fishery-aquaculture model

This is the pre-peer reviewed version of the following article: Bergland, H., Pedersen, P.A. & Wyller, J. (2018). Stable and unstable equilibrium states in a fishery-aquaculture model. Natural Resource Modeling, which has been published in final form at https://doi.org/10.1111/nrm.12200. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.We study interactions between fishery and aquaculture using a 3D generalized Lotka–Volterra model, where we assume that the aquaculture production may affect the growth rate in the fish stock and the productivity in harvesting. In addition, input demands from both marine industries may result in effort competition. We identify conditions for the coexistence of a unique equilibrium state inside the first octant of the phase space and equilibrium states on its boundary. Conditions for stability and instability of these states are also given, thus showing the possibility of having bistability. The equilibrium point inside the first octant is stable if the growth impact on fishery from sea farming is below the potential productivity in harvesting. In the complementary case, we have an unstable interior equilibrium, and we may then end up in stable equilibrium states on the boundary, where either the fishery or the aquaculture is wiped out

Measurements of condition and growth of cod larvae reared in mesocosms: Individual variability as a function of environmental condition or genetic inheritance

Size, dry weight and RNA/DNA measurements of 3876 cod larvae from 26 different families of recruit and repeat spawners reared in two mesocosms ( 2500m³ and 4400m³) under natural conditions were analysed. To be able to relate individual data to parental background, DNA microsatellite analysis was performed. The larvae from the two groups (recruit, repeat) already differed significantly in size and weight at hatching with the larvae from the recruit spawners being larger and heavier at the start of the experiment. Growth curves fitted for the larvae from the recruit spawning groups showed a trend of greater sizes at given ages. For all sampling dates offspring of recruit spawners had significantly higher sizes and dry weights than the repeat spawners. RNA/DNA ratios from recruit spawners showed a trend to higher ratios compared to the repeat spawners. The 2500m³ mesocosm was characterized by low plankton density during the transition from exogenous to endogenous feeding followed by a higher density during the metamorphosis period, while the 4400m³ mesocosm showed the opposite situation. The change in the food density occurring in the mesocosm was reflected in the growth rates. Survival was slightly higher in the mesocosm with the higher food density in the beginning, survival between recruit and repeat is assumed to be the same. Estimates of non-parametric probability distributions of the RNA/DNA ratios differed in the amount of scatter (variability) between mesocosms indicating that the higher food density lead to more better conditioned and fewer badly growing extremes of individual larvae in the first three weeks. When the feeding conditions changed the larvae from the low food environment could compensate and reach similar conditions, but were lacking some of the bad conditioned extremes. RNA/DNA analysis within each mesocosm showed that the individual fish exhibited very different growth and condition responses under the same environmental conditions. These different growth responses in both mesocosms were not related to being offspring of first or recruit spawners but seem to be caused by the environmental conditions