CURRENT RESEARCH PROJECTS
Isotopes in Fish Ecology
Movement patterns and annual migrations of animals are vital components of their ecology but have not been thoroughly studied due to fundamental limitations in using physical tags. Isotope measurements of animal tissues represent natural markers that can provide information on spatial origins without the need for extensive tagging of individuals in a population. Otoliths are structures in the inner ears of fishes that grow on a daily cycle by the alternation of calcium carbonate and protein accretion which form concentric layers. Elements (e.g., Sr isotopes) in the surrounding waters substitute for Ca in the otolith's carbonate matrix and can be recovered from discrete increments throughout a fish's life using high resolution mass spectrometry. Since otoliths are metabolically inert, their isotopic composition can provide a permanent chronology of different water masses (geochronology) of habitats occupied by fish, and they are ideal structures for reconstructing movement patterns.
Ecology of Pacific Salmon
The extent to which salmon from different watersheds mix in their foraging grounds in the ocean is important for assessing the effects of ocean conditions and fishing mortality on breeding population abundances and for predicting whether the demographic consequences will be concentrated or diffuse. Integrating historical coded-wire tag recoveries with natural tags (i.e., genetic and otolith chemistry/microstructure) is a promising approach to actualizing ecosystem models, understanding the spatial ecology of salmon in the ocean, and monitoring restoration efforts in freshwater habitats. I initiated a project with Drs. Paul Koch, Earth Sciences (UCSC), Carlos Garza and Brian Wells (NOAA Fisheries Santa Cruz Laboratory) to link freshwater sources of California Chinook salmon to their ocean distributions using physical and natural isotopic and molecular tags of origin. The ability to identify the natal origins of individuals, their abundance and distribution in the ocean is key to minimizing mortality on protected stocks and harvesting healthy populations.
Role of Aquaculture in Salmon Population Dynamics
Quantifying the contribution of wild (naturally spawned) and hatchery Chinook salmon to the mixed-stock ocean fishery is critical to understanding their relative importance to the persistence of salmon stocks. The inability to distinguish hatchery and wild salmon has inhibited the detection of declines or recoveries for many wild populations. My previous work using otolith microstructure (daily growth patterns) determined that nine-out-of ten adults caught off the Central California coast originated in a hatchery. I have a project exploring the contribution of hatchery fish to the in-river spawning population on the Mokelumne River watershed with Dr. Peter Weber (Lawrence Livermore National Laboratories), J.D. Wikert (US Fish and Wildlife Service), Michelle Workman (East Bay Municipal Utilities District), and Dr. Bruce MacFarlane (NOAA Fisheries Santa Cruz Laboratory) funded by the USFWS. The Central Valley fall-run is currently listed as a "species of concern" largely due to a lack of information on the status of wild populations. Results from this research will provide an estimate of hatchery vs. wild fish contributing to natural fall-run populations, data which will be critical for the ESA status update for the fall-run scheduled for 2010. A change in this listing could have large socio-economic impacts.
Maintenance of Life-history Diversity
Steelhead - The population dynamics of rainbow trout (O. mykiss) depend on the relative abundance of the anadromous (steelhead) and non-anadromous (resident) life history forms, the rates of reproductive exchange between forms, and level of connectivity among populations in other rivers. However, these data have been difficult to acquire using traditional approaches. I have a project to determine the migratory history, maternal origin, and population connectivity of rainbow trout in the Mokelumne River watershed using otolith microchemistry with Drs. Christopher Donohoe (Institute of Marine Science, UCSC), Peter Weber (LLNL), Jonathan Moore (Ecology & Evolutionary Biology Department, UCSC), and Michelle Workman (EBMUD). This project is funded by EBMUD. Photo courtesy of Morgan Bond
Isotopic Otolith Networks for Salmonids (IONS)
The generation and analysis of continuous maps of isotope ratios (isoscapes) are growing tools to track animal migrations across the landscape. These maps focus on regional variation in light isotopes (e.g., oxygen, carbon, and nitrogen) generated by processes resulting in spatial differences in foodwebs. Thus, animals are linked through foodwebs to underlying isoscapes. This realization has led to a renaissance of interest in describing and predicting isoscapes from local to continental scales as a means to track animal migration. The development of a strontium (Sr) isoscape, which is predicated on variations in watershed lithology, is in its infancy relative to light-isotope mapping and has not been developed or used in fish ecology until now. The success of using molecular tools and 87Sr/86Sr as natal markers in the California Central Valley to further knowledge of salmon ecology, prompted interest in its use in other systems. Colleagues at the NOAA Fisheries Northwest Fisheries Science Center, Dr. Edmundo Casillas, David Teel, Matthew Jones (University of Montana) and I initiated a feasibility project to develop a Sr isoscape for the upper Columbia River watershed. This project funded by NOAA's NWFSC aims to better understand the geologic mechanisms driving Sr isotopic variation in watersheds for use with molecular tools in identifying critical habitats necessary for the growth, survivorship, and reproductive success of salmonids.
Quantification of Larval Dispersal in Marine Systems
The spatial structure and dynamics of coastal marine fish populations is strongly influenced by the transport and recruitment of larvae among local populations. Nonetheless, determining the scale and patterns of larval exchange among adult populations (i.e., connectivity) is by far the most difficult demographic parameter to quantify in marine systems due to the inability to tag and track the movement of small larvae. In particular, the extent of local retention of larvae versus regional dispersal to other populations is currently debated in the field of marine ecology and has profound implications for the design and effectiveness of Marine Protected Areas (MPAs) for marine conservation and fisheries management. I am exploring the use of artificial manipulation of otolith chemistry to track the movement of larvae of fully marine fishes. This study quantifies population connectivity for kelp rockfish (Sebastes atrovirens), an open-coast species, in the central California region by artificially marking and recovering larval otoliths and characterizing water circulation patterns. This project is a collaboration among Drs. Mark Carr (EEB UCSC), Peter Raimondi (EEB UCSC), and Margaret McManus (University of Hawaii). Photo courtesy of Jarred Figurski.