Theodore V. Willis

Combining genetic and demographic information to prioritize conservation efforts for anadromous alewife and blueback herring

A major challenge in conservation biology is the need to broadly prioritize conservation efforts when demographic data are limited. One method to address this challenge is to use population genetic data to define groups of populations linked by migration and then use demographic information from monitored populations to draw inferences about the status of unmonitored populations within those groups. We applied this method to anadromous alewife (Alosa pseudoharengus) and blueback herring (Alosa aestivalis), species for which long‐term demographic data are limited. Recent decades have seen dramatic declines in these species, which are an important ecological component of coastal ecosystems and once represented an important fishery resource. Results show that most populations comprise genetically distinguishable units, which are nested geographically within genetically distinct clusters or stocks. We identified three distinct stocks in alewife and four stocks in blueback herring. Analysis of available time series data for spawning adult abundance and body size indicate declines across the US ranges of both species, with the most severe declines having occurred for populations belonging to the Southern New England and the Mid‐Atlantic Stocks. While all alewife and blueback herring populations deserve conservation attention, those belonging to these genetic stocks warrant the highest conservation prioritization.

Influence of stocking history on the population genetic structure of anadromous alewife (Alosa pseudoharengus) in Maine rivers

Abstract Stocking programs have been used extensively to mitigate declines in anadromous fishes, but these programs can have long-term unintended genetic consequences. Stocking can homogenize population structure, impede local adaptation, and hinder the use of genetic stock identification as a fishery management tool. Using 12 microsatellite loci, we evaluate the spatiotemporal genetic structure of 16 anadromous alewife (Alosa pseudoharengus) populations in Maine, USA, to determine whether inter-basin stocking practices have influenced population structure and the genetic diversity of the species in this region. Although, no pre-supplementation samples exist, comparative analyses of stocked and non-stocked populations show that stock transfers have influenced alewife population genetic structure. Genetic isolation by distance (IBD) was non-significant among stocked populations, but significant among non-stocked populations. However, two populations, Dresden Mills and Sewell Pond, appear to have resisted genetic homogenization despite stocking. Non-significant genic and genetic differentiations were broadly distributed among alewife populations. Hierarchical AMOVA indicated highly significant differentiation among temporal replicates within populations, and Bayesian clustering analysis revealed weak population structure. A significant correlation was observed between stocking (time and events) and pairwise

A long-term rusty crayfish (Orconectes rusticus) invasion: dispersal patterns and community change in a north temperate lake

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Patterns in fish species composition across the interface between streams and lakes

FST′ among alewife collections, and an analysis of IBD residuals showed a significant decline in the amount of genetic differentiation among populations as the extent of stocking activity increased. These findings call for an increased awareness of evolutionary processes and genetic consequences of restoration activities such as inter-basin stock transfers by fisheries management and conservation practitioners.

Genetic diversity and structure of two hybridizing anadromous fishes (Alosa pseudoharengus, Alosa aestivalis) across the northern portion of their ranges

Two hundred years ago, the volcano Tambora caused an extreme climate event that altered fisheries halfway around the world. Global warming has increased the frequency of extreme climate events, yet responses of biological and human communities are poorly understood, particularly for aquatic ecosystems and fisheries. Retrospective analysis of known outcomes may provide insights into the nature of adaptations and trajectory of subsequent conditions. We consider the 1815 eruption of the Indonesian volcano Tambora and its impact on Gulf of Maine (GoM) coastal and riparian fisheries in 1816. Applying complex adaptive systems theory with historical methods, we analyzed fish export data and contemporary climate records to disclose human and piscine responses to Tambora’s extreme weather at different spatial and temporal scales while also considering sociopolitical influences. Results identified a tipping point in GoM fisheries induced by concatenating social and biological responses to extreme weather. Abnormal daily temperatures selectively affected targeted fish species—alewives, shad, herring, and mackerel—according to their migration and spawning phenologies and temperature tolerances. First to arrive, alewives suffered the worst. Crop failure and incipient famine intensified fishing pressure, especially in heavily settled regions where dams already compromised watersheds. Insufficient alewife runs led fishers to target mackerel, the next species appearing in abundance along the coast; thus, 1816 became the “mackerel year.” Critically, the shift from riparian to marine fisheries persisted and expanded after temperatures moderated and alewives recovered. We conclude that contingent human adaptations to extraordinary weather permanently altered this complex system. Understanding how adaptive responses to extreme events can trigger unintended consequences may advance long-term planning for resilience in an uncertain future.