FOR ONLINE PUBLICATION ONLY
Appendix A. Declining high-TL biomass: The Sequester Option
In the main article, we model species (or taxa specific) changes in biomass for the
high-TL species/taxa. Overall there was a decrease of approximately 40% in the biomass
of high-TL groundfishes, but this decline in abundance was not distributed evenly across
groups. Some species like Pacific hake showing almost 90% drops in biomass whereas
other species had smaller changes. Here we run a separate simulation to determine
whether modelling species specific changes was important to evaluating the impacts of
MTL and a change in the abundance of high-TL groundfishes for the structure and function
of the California Current.
We perturbed the Ecopath and Ecosim (EwE) models by reducing the biomass of all
high-TL groundfish functional groups by 40%, approximately the same decline in biomass
of high-TL groundfishes seen in the trawl survey. We applied this decrease in biomass
broadly across the groundfishes and did not match species-specific declines. The 40%
decrease in biomass was applied to the same groups as in the primary analysis. In all other
aspects, the two EwE analyses were the same.
Results of the two models were largely similar although there were some minor
differences (Table S1, Figure S1). For biomass, the same groups showed instantaneous
responses, but there were some minor differences in the dynamic response. TL
groundfishes showed a stronger instantaneous response under the species-specific
biomass modifications but no dynamic response (Table 3). Under the across the board
reduction model, this group had a weaker instantaneous response and also a weak dynamic
response.
In terms of ecosystem function, there were instantaneous increases in
zooplanktivory and macroinvertory under the general 40% reductions that were not
apparent in the species-specific model. The instantaneous decreases in consumption and
respiration seen in the species –specific model were not evident in the 40% reductions.
Both models showed similar trends in terms of dynamic responses of higher
functional groups. In both cases, competitors increased, and initial increases in
intermediate TL prey were dampened. Lower-TL prey initially decreased but then began to
recover. The ‘other’ group showed less of a response than in the main simulation.
Table S1. Change in Biomass Accumulation Rates (Instantaneous) and Mean Annual Percentage Difference
(Dynamic) Projected over 10 Years for a Subset of Non-groundfish Species, Trophic Groups, and Ecosystem
Functions Under a 40% Decline in High-TL (≥3.5) Groundfish Biomass Relative to No Decline in Predatory
Groundfishes
Standardized response
Instantaneous
Dynamic
Species group
phytoplankton
small zooplankton
carnivorous zooplankton
amphipods
krill
jellies
pandalid shrimp
crabs
squid
forage fish
salmon
low-TL groundfish
albacore
seabirds
harbour seals
whales
Na
na
++++
++++
++++
++++
++++
+++
++++
++++
+++
++
na
na
na
na
Ecosystem function
herbivory
zooplanktivory*
macroinvertivory*
piscivory*
scavenging
++++
++++
++++
na
++++












consumption
respiration
throughput
production
net primary production






+
+
+

++
+
+
+


+
+

 = no response, <10% change
+ = 10-20% increase
++ = 20-50% increase
+++ = 50-100% increase
++++ = > 100% increase
Blank cells = no response was possible with the analytical approach
*excluding high-TL groundfish
†Trophic groupings based on prey items that make up the greatest proportion of each consumer’s diet in the
Ecopath model
Figure S1. Dynamic responses of the California Current food web to a 40%, across the
board reduction in higher trophic level groundfishes (TL ≥3.5). Predicted
differences between ten-year model simulations of a 40% reduction in higher
trophic level groundfishes and baseline trajectories for intermediate and lower
trophic level prey,