Ontogenetic selection on hatchery salmon in the wild: natural selection on artificial phenotypes

Sea-weeding enhances early coral survival on seeding devices, but benefits of seeding diminish after one year

Borrowing from principles of aerial seeding in terrestrial reforestation, coral seeding utilises "devices" designed to increase coral spat survival. However, device-assisted coral survival has not been compared to natural survivorship, nor have devices been trialled in environments with strong competitors such as macroalgae. Herein, we deployed seeded devices alongside terracotta tiles, a proxy for natural coral recruitment dynamics. Tiles and devices were deployed to plots examining ongoing macroalgae removal ("sea-weeding"), and survival was monitored over two years. First-year coral survival was enhanced on devices compared to natural survival, and devices conferred the greatest survival benefit when deployed in areas where "sea-weeding" was undertaken. However, over the second year, the benefits of sea-weeding for device-assisted survival were lost, with no significant difference in survival on devices in control versus weeded plots. On average, devices retained 1.3 surviving colonies at two years, which was lower than naturally-occurring juvenile density in removal plots, but higher than control plots. Several factors influenced survival, including the starting spat density, orientation of deployment surface, and site. After two years, 50 % of devices yielded one live coral, but site-based survival varied between 37 % and 93 %. The estimated cost per surviving coral varied when accounting for site-based survival (high survival: $334 coral-1; low survival: $577 coral-1), which could be reduced via future efficiencies. The results of this study inform the potential outcomes of coral seeding on macroalgae dominated reefs, and highlight that assessing survival up to one year is not sufficient to measure long-term restoration goals.

Salmon hatchery strays can demographically boost wild populations at the cost of diversity: quantitative genetic modelling of Alaska pink salmon

Hatcheries are vital to many salmon fisheries, with inherent risks and rewards. While hatcheries can increase the returns of adult fish, the demographic and evolutionary consequences for natural populations interacting with hatchery fish on spawning grounds remain unclear. This study examined the impacts of stray hatchery-origin pink salmon on natural population productivity and resilience. We explored temporal assortative mating dynamics using a quantitative genetic model that assumed the only difference between hatchery- and natural-origin adults was their return timing to natural spawning grounds. This model was parameterized with empirical data from an intensive multi-generational study of hatchery-wild interactions in the world's largest pink salmon fisheries enhancement program located in Prince William Sound, Alaska. Across scenarios of increasing hatchery fish presence on spawning grounds, our findings underscore a trade-off between demographic enhancement and preservation of natural population diversity. While enhancement bolstered natural population sizes towards local carrying capacities, hatchery introgression reduced variation in adult return timing by up to 20%. Results indicated that hatchery-origin alleles can rapidly assimilate into natural populations, despite the reduced fitness of hatchery fish attributable to phenotypic mismatches. These findings elucidate the potential for long-term demographic and evolutionary consequences arising from specific hatchery-wild interactions, emphasizing the need for management strategies that balance demographic enhancement with the conservation of natural diversity.

Captive-bred Atlantic salmon released into the wild have fewer offspring than wild-bred fish and decrease population productivity

The release of captive-bred animals into the wild is commonly practised to restore or supplement wild populations but comes with a suite of ecological and genetic consequences. Vast numbers of hatchery-reared fish are released annually, ostensibly to restore/enhance wild populations or provide greater angling returns. While previous studies have shown that captive-bred fish perform poorly in the wild relative to wild-bred conspecifics, few have measured individual lifetime reproductive success (LRS) and how this affects population productivity. Here, we analyse data on Atlantic salmon from an intensely studied catchment into which varying numbers of captive-bred fish have escaped/been released and potentially bred over several decades. Using a molecular pedigree, we demonstrate that, on average, the LRS of captive-bred individuals was only 36% that of wild-bred individuals. A significant LRS difference remained after excluding individuals that left no surviving offspring, some of which might have simply failed to spawn, consistent with transgenerational effects on offspring survival. The annual productivity of the mixed population (wild-bred plus captive-bred) was lower in years where captive-bred fish comprised a greater fraction of potential spawners. These results bolster previous empirical and theoretical findings that intentional stocking, or non-intentional escapees, threaten, rather than enhance, recipient natural populations.

Prescriptive Evolution to Conserve and Manage Biodiversity

We are witnessing a global, but unplanned, evolutionary experiment with the biodiversity of the planet. Anthropogenic disturbances such as habitat degradation and climate change result in evolutionary mismatch between the environments to which species are adapted and those in which they now exist. The impacts of unmanaged evolution are pervasive, but approaches to address them have received little attention. We review the evolutionary challenges of managing populations in the Anthropocene and introduce the concept of prescriptive evolution, which considers how evolutionary processes may be leveraged to proactively promote wise management. We advocate the planned management of evolutionary processes and explore the advantages of evolutionary interventions to preserve and sustain biodiversity. We show how an evolutionary perspective to conserving biodiversity is fundamental to effective management. Finally, we advocate building frameworks for decision-making, monitoring, and implementation at the boundary between management and evolutionary science to enhance conservation outcomes.