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not adversely impacted by fishery interactions they may 
experience less competition because of reduced numbers 
of apex predator fishes and because more prey would be 
available with the increase in midtrophic level fishes. 
It should be noted that the almost threefold increase 
in the domestic fishery over the past decade is not the 
only change in the ecosystem. Over the same period, 
satellite-derived estimates of surface chlorophyll showed 
a decline in surface chlorophyll in the Hawaii-based 
longline fishing ground (Polovina et al., 2008). A change 
in productivity at the base of the food web could result 
in bottom-up control that could reduce the abundance of 
apex predators. Thus it is possible that the substantial 
changes we have observed in the pelagic ecosystem over 
the past decade are due to a combination of both bot- 
tom-up and top-down controls. 
A decline in mean trophic level that exceeds 0.15 
has been suggested as representing an ecologically sig- 
nificant fishing down of the food web (Essington et al., 
2006). According to this definition the change in the an- 
nual mean trophic level of the catch we observed — a de- 
cline by 0.19 from 3.85 to 3.66 — represents a significant 
fishing down of the food web in the central North Pacific 
subtropical gyre. However, an analysis of changes in 
biomass and trophic level for tunas and blue shark re- 
vealed a slight drop in the trophic level of the catch but 
showed no detectable change in the trophic level of the 
population (Sibert et al., 2006). A likely reason that we 
found a more substantial decline in mean trophic level 
of the catch is that our study encompassed not just the 
top predators but also midtrophic level fishes. 
The decline in the percentage of apex predators from 
70% to 40% of the catch and the increase in midtrophic 
level species from about 20% to 40% of the catch, as 
well as moderate and high P/B values illustrate the 
significant increase in the contribution of short-lived, 
fast-growing, high-fecundity species in the catch and 
presumably in the exploited population. These spe- 
cies increase their population size rapidly under favor- 
able conditions but given their short life spans, de- 
cline quickly in unfavorable conditions. As a result, the 
current ecosystem will likely exhibit greater temporal 
variation in response to climate variation. 
Acknowledgments 
We’d like to acknowledge the contributions of the Pacific 
Islands Fisheries Science Center (PIFSC) staff, J. Pappas, 
C. Tokita, and B. Miyamoto, for their work ensuring that 
the Hawaii-based longline logbook and observer data are 
accurate, current, and readily accessible. We also thank 
the scientific observers employed through the Pacific 
Islands Region for their collection of observer data 
from the longline fishery. This work has benefited from 
insightful discussions on the dynamics of pelagic ecosys- 
tems with J. Kitchell, C. Walters, and C. Boggs. Finally, 
acknowledgements to PIFSC colleagues R. Domokos and 
