The Importance of Environmental Exposure History in Forecasting Dungeness Crab Megalopae Occurrence Using J-SCOPE, a High-Resolution Model for the US Pacific Northwest

Emily L Norton1, Samantha Siedlecki2, Isaac Kaplan3, Albert J Hermann1, Jennifer L. Fisher4, Cheryl Morgan5, Suzanna Officer6, Casey Saenger7, Simone R Alin8, Dr. Jan A Newton, PhD9, Nina Bednarsek10 and Richard A Feely11,12, (1)University of Washington, Cooperative Institute for Climate, Ocean, and Ecosystem Studies, Seattle, United States, (2)University of Connecticut, Department of Marine Sciences, Groton, United States, (3)NOAA NWFSC, Seattle, WA, United States, (4)Oregon State University, Cooperative Institute of Marine Resources Studies, Newport, OR, United States, (5)Vancouver, BC, Canada, (6)Whitman College, Walla Walla, WA, United States, (7)University of Washington, Joint Institute for the Study of the Atmosphere and Ocean, Seattle, WA, United States, (8)NOAA Pacific Marine Environmental Laboratory, Seattle, United States, (9)University of Washington, Applied Physics Laboratory, Seattle, United States, (10)Southern California Coastal Water Research Project, Biogeochemistry, Costa Mesa, United States, (11)NOAA Pacific Marine Environmental Laboratory, Ocean Climate Research Division, Seattle, WA, United States, (12)NOAA Pacific Marine Environmental Laboratory, Seattle, WA, United States
Abstract:
The Dungeness crab (Metacarcinus magister) fishery is one of the highest value fisheries in the US Pacific Northwest, but its catch size fluctuates widely across years. Although the underlying causes of this variability are not well understood, the abundance of M. magister megalopae has been linked to recruitment into the adult fishery four years later. These pelagic megalopae are exposed to a range of ocean conditions during their dispersal period, which may drive their occurrence patterns. Environmental exposure history has been found to be important for some pelagic organisms, so we hypothesized that inclusion of environmental exposure history would improve our ability to predict M. magister megalopae occurrence patterns compared to using 'in situ' conditions alone. We combined local observations of M. magister megalopae and regional simulations of ocean conditions to model megalopae occurrence using a generalized linear model (GLM) framework. The modeled ocean conditions were extracted from J-SCOPE, a high-resolution coupled physical-biogeochemical model. The analysis included variables from J-SCOPE identified in the literature as important for larval crab occurrence: temperature, salinity, dissolved oxygen concentration, nitrate concentration, phytoplankton concentration, aragonite and calcite saturation state, and pH. GLMs were developed with either in situ ocean conditions or environmental exposure histories generated using particle tracking experiments. We found that inclusion of exposure history improved the ability of the GLMs to predict megalopae occurrence. Of the five swimming behaviors used to simulate megalopae dispersal, several behaviors generated GLMs with superior fits to the observations, so a biological ensemble of these models was constructed. Our results highlight the importance of including exposure history in larval occurrence modeling and help provide a method for predicting pelagic megalopae occurrence. This work is a step towards developing a forecast product to support management of the fishery.
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