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My research program has developed along three principal themes. The first primary direction is the demography, dispersal and reproduction of marine species, not only for the identification of self-recruiting populations as units for management and conservation, but also to investigate mechanisms of dispersal and patterns of demographic variability. The second primary theme, estimation of reproductive success by genetically identifying offspring of anadromous salmonids, has developed since my appointment at SAFS, and was mainly the result of collaborations with Tom Quinn and Ray Hilborn. The third direction is an almost inevitable interest in molecular genetic markers themselves, in particular, how mutation mechanisms, patterns of variability and statistical analyses affect the interpretation of molecular data in a biological context. In pursuing these aims, I have worked on a variety of marine and freshwater organisms in both the Old and New World, and have adopted an opportunistic approach that took advantage of appropriate model systems, the expertise of collaborators and available funding opportunities. My research is therefore not centered on a specific organism or system, but represents a more generalist approach to answering questions using the best model system available. Virtually all my projects are collaborations with colleagues at the UW or local State and Federal Agencies these collaborations and the number of fish and fisheries scientists in the Pacific Northwest makes Seattle one of the most exciting and inspiring places to work in the world.
Demography of Marine Populations
Although the oceans cover more than 70% of the world’s surface and provide most of the world’s wild-caught protein, our understanding of the ecology of marine organisms lags behind that of terrestrial or freshwater species. In part, this dearth of knowledge is due to the enormity of the habitat, the lack of clear boundaries to species and population distributions and the intractability of many species. For example, traditional ecological approaches such as mark-recapture can often not be applied because larval life-history stages cannot be tagged. These limitations are particularly prominent in marine pelagic fishes, one of my main areas of interest. Molecular genetic markers have revolutionized our understanding of marine populations and have led to several significant paradigm shifts concerning population sizes and dispersal in the past few decades. In particular, my research concentrates on the following topics:
Variability in Reproductive Success and Effective Population Size
Predicting the level of recruitment to a fishery is one of the primary aims of stock assessment, though the relationship between spawning stock and recruitment can be weak. This variability in recruitment may suggest that reproductive success of individual spawners is highly variable in space and time, resulting in small genetically effective population sizes. Using several model systems (New Zealand snapper, herring, pollock), I am interested in the ecological correlates of such variation in recruitment success.
Social Structure in Schooling Fish
The concept of effective population size is closely related to one of my long standing research interests, namely that of the temporal stability of pelagic fish schools. One of the predictions of small effective population size is that genetic diversity in offspring samples should be lower than that of the adult population, because individuals are more related than expected by chance. Schooling behavior may exacerbate that effect by keeping such related individuals together. Initially sparked during my PhD days by the detection of genetic differentiation among Limnothrissa schools collected in the same bay of Lake Tanganyika, my interest has been kept alive by reports from tagging studies claiming long-term cohesiveness of schools in tuna and herring. Currently, we are evaluating relatedness at the very first life-stage (i.e. eggs) in Puget Sound herring.
At its most basic level, investigations of the demography of marine species requires the identification of self-recruiting populations and barriers to migration an application that has clearly significant applications to fisheries management, though the definition of the unit ‘stock’ differs among user groups. Population identification for management purposes provides an important funding base for my research program (e.g. ongoing funded studies on spiny dogfish Squalus acanthias, Pacific cod Gadus macrocephalus, Pacific herring Clupea pallasi, Pacific halibut Hippoglossus stenolepis). These studies often demonstrate a surprising level of population sub-structuring, despite high potential for dispersal during pelagic life-history stages, and suggest more complicated patterns of dispersal than indicated by larval duration and oceanographic conditions.
Relationship Between Dispersal and Selection
The role of selection in determining dispersal patterns is currently unknown. Although fish larvae may drift from one location to another, selective mortality may occur en route or during settlement. In addition, reduced fecundity or growth of immigrants may reduce effective gene flow among populations. For example, it appears that the high differentiation at PanI in the north-east Atlantic cod is maintained by selective differences in growth and fecundity. Such selective effects may be particularly pertinent in a world with changing climate. In collaboration with Kevin Bailey and Mike Canino of the AFSC (Alaska Fisheries Science Center) we are currently starting a research project funded by the NPRB (North Pacific Research Board) which will pinpoint genomic regions under selection in larval cohorts of walleye pollock.
Reproductive Success in Anadromous Salmonids
Anadromous salmonids are an excellent model system for estimating individual reproductive success. Their migratory habit makes sampling relatively easy, and their precise homing abilities lead to relatively small, geographically well defined populations. I am currently involved in two main projects on such reproductive success: (i) a steelhead (Oncorhynchus mykiss) population in Forks Creek, Washington, that has been supplemented with hatchery fish and (ii) a sockeye salmon (Oncorhynchus nerka) population in Alaska. Inherently, such projects are long-term commitments, because both parents and offspring need to be sampled. Nevertheless, we have successfully used advanced Bayesian methods to identify immigrants to both creek and beach spawning sockeye populations. I am currently developing a similar approach on a marine species, as population genetics estimates of dispersal on small geographic scales are often difficult to obtain because even small levels of gene flow effectively homogenize allele frequencies and thus make populations indistinguishable. However, by identifying offspring of specific adult fish, such dispersal estimates may be more accurate and more relevant for MPA design.
Properties of Molecular Markers and Statistical Analyses Affecting their Interpretation in a Biological Context
Many of the applications of molecular markers described above are not trivial. Marine populations generally show low genetic differentiation, partly because populations are large and few migrating individuals per generation are sufficient to homogenize populations genetically. It is therefore important to evaluate the properties of molecular markers and associated analyses in the biological interpretation of results. Most population genetic analyses assume underlying mutation patterns that are currently not verified and are difficult to evaluate empirically in sexually reproducing organisms. As a by-product of many projects, I therefore use data to evaluate assumptions of population genetic analyses. For example, we recently compared different methods of population assignment by comparing results with parentage data of steelhead in Forks Creek, and showed remarkably high success of most methods, but also hitherto undescribed failure of widely applied clustering methods in the identification of hatchery and wild steelhead.