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