AOS Research Staff Profile
Postdoctoral Research Associate (Nereus Fellow)
Address: 314 Sayre Hall
Phone: (609) 258-2904
Email: rasch at princeton.edu
As a fisheries oceanographer by training, my research examines how oceanic and climatic conditions affect the temporal and spatial distribution of the early life history stages of fishes. More specifically, my recent research has focused on the reproductive phenology of fishes. Phenology refers to the study of seasonal, biological cycles and how they are influenced by weather and climate. My Ph.D. research investigated decadal changes in the phenology of 43 species of larval fishes in the southern California Current using data collected by California Cooperative Oceanic Fisheries Investigations (CalCOFI). Of these species, 26 exhibited long-term trends in their phenology, which appear to be more closely connected to secular warming than decadal climate oscillations, such as the Pacific Decadal Oscillation or the North Pacific Gyre Oscillation. During my Ph.D., I also examined interannual variability in the phenology of phytoplankton blooms across the North Pacific using a hindcast of the oceanic component of the NCAR Community Earth System Model (CESM), which was forced with atmospheric observations. This analysis indicated that, although long-term trends in phytoplankton phenology were only detected across ~20% of the North Pacific, in areas where changes in phenology were observed, these changes occurred at a rapid rate compared to those reported for terrestrial primary producers.
As a Senior Nereus Fellow, I plan to expand upon this previous work by examining the hypothesis that climate change will lead to a greater frequency of “mismatches” between the timing of fish spawning and seasonal phytoplankton blooms. Many fishes time spawning events to coincide with plankton blooms to ensure an adequate food supply for their larvae. However, different physical oceanographic processes control the timing of phytoplankton blooms and influence the reproductive physiology of fishes. As a result, year-to-year variations exist in the degree of synchrony between these events. During years when spawning occurs late or early relative to the timing of maximum plankton production, larval fish survival may be reduced, leading to poor fisheries recruitment in subsequent years. I plan to use an earth system model developed at the NOAA Geophysical Fluid Dynamics Laboratory (GFDL) to examine future changes in the timing of phytoplankton blooms, as well as changes in seasonal temperatures that affect when fishes spawn. Using these model projections, I will investigate whether climate-induced changes in phytoplankton and fish phenology are likely to occur at similar or distinct rates.
In addition to my current research on fish and phytoplankton phenology, I have previously conducted research investigating:
- The influence of oceanic variables (e.g., SSH, temperature, salinity, geostrophic currents, chlorophyll concentration, zooplankton volume) on the spawning habitat of forage fishes
- The impact of bottom fishing and fishery closures on the abundance of demersal fishes and invertebrate megafauna
- Ingestion of plastic microdebris by mesopelagic fishes in the North Pacific Subtropical Gyre
- The effect of ocean acidification on otolith development in fish larvae
Manuscripts in Preparation
Asch, R.G. and M.C. Long. In prep. Changes in phytoplankton phenology detected with the Community Earth System Model 1.0 (CESM1): Long-term trends and the influence of climate oscillations.
Asch, R.G. In prep. Climate change and decadal shifts in the phenology of larval fishes in the California Current Ecosystem.
Chen, D.C. and R.G. Asch. In prep. Assessing the school trap hypothesis: An analysis of habitat overlap of three coastal pelagic fish species in the southern California Current Ecosystem.
Asch, R.G. and D.M. Checkley, Jr. 2013. Dynamic height: A key variable for identifying the spawning habitat of small pelagic fishes. Deep-Sea Research Part I 71: 79-91.
Asch, R. 2013. Student Perspectives: Phenology in the California Current Ecosystem: CalCOFI and beyond. p. 211-213. In: Regional Fisheries Oceanography of the California Current System. The CalCOFI Program. S. McClatchie. Springer, New York, NY.
Davison, P. and R.G. Asch. 2011. Plastic ingestion by mesopelagic fishes in the North Pacific Subtropical Gyre. Marine Ecology Progress Series 432: 173-180.
Checkley, Jr., D.M., A.G. Dickson, M. Takahashi, J.A. Radich, N. Eisenkolb and R. Asch. 2009. Elevated CO2 enhances otolith growth in young fish. Science 324: 1683.
Asch, R.G. and J.S. Collie. 2008. The role of bottom fishing and ecological succession in structuring the benthic megafaunal community. Fishery Bulletin 106: 438-456.