Keller et al : Variations in eastern North Pacific demersal fish biomass, 2003-10 
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Discussion 
The Pacific Coast groundfish fishery is exceed- 
ingly complex to manage because a wide range of 
species (90+), including a number of overfished 
and rebuilding stocks, are caught with the same 
trawl gear. Beginning in 2000, the PFMC ini- 
tiated a series of measures designed to reduce 
catch along the west coast, including fleet reduc- 
tions, closed areas, and catch restrictions. These 
measures were initiated in direct response to 
nine stocks being declared overfished from 1999 
to 2002. Landed catch from 1980 through 2010 
shows that groundfish harvests off Washington, 
Oregon, and California were significantly lower 
(rockfishes, flatfishes, sablefish) or relatively con- 
stant (Pacific hake, thornyheads) in recent years 
relative to historical rates (Fig. 8). This period of 
decreased catch corresponds to the implementa- 
tion of the PFMC’s management plan. And yet, 
despite much reduced fishing effort (and landings), 
overall survey indices of groundfish biomass off 
the western United States declined from 2003 through 
2010. The PFMC’s management directives also coincided 
with the period following expansion of the NWFSC’s 
West Coast Goundfish Bottom Trawl Survey to annu- 
ally include both the shelf region, as well as the upper 
continental slope waters along the entire coast (U.S.- 
Canada to U.S.-Mexico). We used data from this fishery- 
independent survey combined with information from 24 
stock assessments since 2005 to attempt to unravel the 
causes for the decline in biomass indices despite strict 
adherence to fishery management plans. 
Our results indicated that from 2003 through 2010 
individual groundfish stocks along the U.S. west coast 
responded in varying ways to the newly imposed man- 
agement measures, with many of the overfished spe- 
cies of concern exhibiting increases in spawning stock 
biomass (PFMC, 2008a). However, despite improve- 
ments in individual stocks there has been a gradual 
decline in overall groundfish biomass, measured as the 
sum of the biomass indices for 60 abundant groundfish 
and two benthic invertebrate species, as well as in 
major groundfish groups (e.g., sharks, flatfishes, and 
rockfishes). Twenty of the 62 species described here 
significantly decreased in observed biomass from 2003 
through 2010, whereas 6 species significantly increased. 
Of the remaining 36 species, 20 exhibited decreas- 
ing trends and 16 exhibited increasing trends. These 
changes indicate that the decline in biomass is not 
attributable to just a few species. Similar declines in 
Northwest Atlantic fish stocks have previously been 
attributed to a variety of factors including overfish- 
ing and environmental effects (Haedrich and Barnes, 
1997). Hilborn et al. (in press) noted that the dramatic 
decline in catch can be interpreted in two ways: as an 
indication of collapsing stocks caused by overfishing, 
or as a demonstration that management has effectively 
reduced catch to prevent overfishing of sensitive species. 
However, the continued decline in overall observed bio- 
03 
13 
C 
C 
03 
O 
Q 
CL 
1 5 
1 0 
0 5 
0 0 
-0 5 
-1 0 
-1 5 
1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 
Figure 5 
Annual variation in the Pacific Decadal Oscillation index (PDO) 
from January 1999 through December 2010 as it fluctuated 
between cool negative and warm positive phases. Annual 
values are the mean of the 12 months beginning in November 
of the year preceding the start of each annual survey and 
ending in October with the completion of the annual survey. 
mass along the west coast suggests that reduced catch 
in itself may not be sufficient to prevent biomass from 
further decreasing when environmental conditions are 
poor. Hsieh et al. (2008) further concluded that fishing 
pressure reduces the resilience of exploited populations 
facing negative climatic effects. 
By chance our study occurred during a period after 
the emergence of a particularly strong 1999 year class 
for many groundfish species inhabiting the California 
Current system (Haltuch and Hicks, 2009) and a pe- 
riod of changing environmental conditions as indicated 
by variability in the annual PDO index. The observed 
declining survey trends are consistent with natural 
and fishing-induced mortality estimated for the 1999 
cohort in many stock assessments, especially flatfishes, 
sablefish, and Pacific hake (Schirripa, 2007; Haltuch 
and Hicks, 2009; Stewart et al., 2011). However, the 
prevalence of this large year class among many west 
coast groundfish and its gradual depletion over the sur- 
vey period (2003-10) may not be entirely responsible for 
the dramatic decline in overall biomass estimated with 
data from our west coast fishery-independent survey. 
The decline in biomass may additionally be tied to 
environmental conditions. The annual PDO index, a 
measure of climate variability, declined from a high 
value at the start of our standardized survey (2003) 
to low and negative values near the end of the series 
examined (2007-10). Numerous studies correlate shifts 
in the abundance and distribution of marine fish to 
oscillations in ocean conditions (Francis et al., 1998; 
Beamish et ah, 1999; Hare et ah, 1999). Within the 
northern California Current system, changes in salmon 
production (Mantua et ah, 1997), landed sardine catch 
(Smith and Moser, 2003; Norton et al., 2008), and Pa- 
cific hake distribution (Benson et al., 2002) are linked 
to decadal-scale fluctuations in climate. Hollowed et al. 
(2001) further reported that production of commercial 
fish stocks (32 pelagic fish and groundfish species) in 
