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Climate Change, Fish Reproduction, and the Shifting Seasonality of the Sea: What will the Future Hold?

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Wednesday, January 15, 2020
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12:00 pm - 1:00 pm ET


Rebecca G. Asch, Assistant Professor of Fisheries Biology, East Carolina University

NOAA's National Ocean Service (NOS); coordinator is
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Substantial interannual variability in marine fish recruitment has been hypothesized to be related in part to whether the timing of fish spawning matches that of seasonal plankton blooms. Environmental processes that control the timing of blooms,such as stratification, may differ from those that influence the timing of fish spawning, such as temperature‐linked reproductive maturation. These different controlling mechanisms could cause the timing of these events to diverge under climate change with negative consequences for fisheries. We use an earth system model to examine the impact of a high‐emissions, climate warming scenario (RCP8.5) on the future spawning time of two classes of temperate, epipelagic fishes: “geographic spawners” whose spawning grounds are defined by fixed geographic features (e.g., rivers,estuaries, reefs) and “environmental spawners” whose spawning grounds move responding to variations in environmental properties, such as temperature. By the century's end, projections of increased stratification cause spring and summer phytoplankton blooms to start 16 days earlier on average (±0.05 days SE)at latitudes >40°N. The temperature-linked phenology (i.e., seasonal timing)of geographic spawners changes at a rate twice as fast as phytoplankton, causing these fishes to spawn before the bloom starts across >85% of this region.“Extreme events,” defined here as seasonal mismatches >30 days that could lead to fish recruitment failure, increase 10‐fold for geographic spawners in many areas under the RCP8.5 scenario. Mismatches between environmental spawners and phytoplankton were smaller and less widespread, although sizable mismatches still emerged in some regions. This indicates that range shifts undertaken by environmental spawners may increase the resiliency of fishes to climate change impacts associated with phenological mismatches, potentially buffering against declines in larval fish survival, recruitment, and fisheries. Model results are supported by empirical evidence from ecosystems with multi-decadal observations of both fish and phytoplankton phenology.

Rebecca Asch is an Assistant Professor of Fisheries Biology at East Carolina University (ECU). 
She is also currently an Alfred P. Sloan Foundation Research Fellow in Ocean Sciences. Dr. Asch received a B.A. in cultural anthropology from Smith College and a M.S. and Ph.D. in biological oceanography from the University of Rhode Island and Scripps Institution of Oceanography, respectively. Prior to arriving at ECU, Dr. Asch was Postdoctoral Research Associate and Senior Nereus Fellow at Princeton University's Program in Atmospheric and Oceanic Sciences. As a fisheries oceanographer, Dr. Asch's research focuses on interactions between fish populations, plankton ecology, and climate change and climate variability.
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