205 
Variations in eastern North Pacific demersal fish 
biomass based on the U.S. west coast 
groundfish bottom trawl survey (2003-2010) 
Email address for contact author: aimee.kellertS) noaa.gov 
National Oceanic and Atmospheric Administration 
National Marine Fisheries Service 
Northwest Fisheries Science Center 
Fishery Resource Analysis and Monitoring Division 
2725 Montlake Blvd E. 
Seattle, Washington 98112 
Abstract-— In response to declining 
biomass of Northeast Pacific ground- 
fish in the late 1990s and to improve 
the scientific basis for management 
of the fishery, the Northwest Fish- 
eries Science Center standardized 
and enhanced their annual bottom 
trawl survey in 2003. The survey was 
expanded to include the entire area 
along the U.S. west coast at depths 
of 55-1280 m. Coast-wide biomass 
and species richness significantly 
decreased during the first eight years 
(2003-10) of this fishery-independent 
survey. We observed an overall ten- 
dency toward declining biomass for 
62 dominant taxa combined (fishery 
target and nontarget species) and 
four of seven subgroups (including 
cartilaginous fish, flatfishes, shelf 
rockfishes, and other shelf species), 
despite increasing or variable biomass 
trends in individual species. These 
decreases occurred during a period of 
reduced catch for groundfish along the 
shelf and upper slope regions relative 
to historical rates. We used informa- 
tion from multiple stock assessments 
to aggregate species into three 
groups: 1) with strong recruitment, 
2) without strong recruitment in 1999, 
and 3) with unknown recruitment 
level. For each group, we evaluated 
whether declining biomass was pri- 
marily related to depletion (using year 
as a proxy) or environmental factors 
(i.e., variation in the Pacific Decadal 
Oscillation). According to Akaike’s 
information criterion, changes in 
aggregate biomass for species with 
strong recruitment were more closely 
related to year, whereas those with no 
strong recruitment were more closely 
related to climate. The significant 
decline in biomass for species with- 
out strong recruitment confirms that 
factors other than depletion of the 
exceptional 1999 year class may be 
responsible for the observed decrease 
in biomass along the U.S. west coast. 
Manuscript submitted 3 June 2011. 
Manuscript accepted 29 November 2011. 
Fish. Bull. 110:205-222 (2012). 
The views and opinions expressed 
or implied in this article are those of the 
author (or authors) and do not necessarily 
reflect the position of the National Marine 
Fisheries Service, NOAA. 
Aimee A. Keller (contact author) 
John R. Wallace 
Beth H. Horness 
Owen S. Hamel 
Ian J. Stewart 
Over the past 20 years, a number of 
changes have occurred in the North- 
east Pacific groundfish fishery with 
low abundance observed for multiple 
species (Field and Fox, 2006; Levins 
et ah, 2006). Historically catch and 
annual exploitation rates increased 
from the 1950s through the 1980s 
and then declined rapidly. Between 
1999 and 2002, nine important fish 
stocks in the eastern North Pacific 
off the U.S. west coast were declared 
overfished, at which time the Pacific 
Fishery Management Council (PFMC) 
introduced a series of regulatory mea- 
sures to reduce fishing pressure. Man- 
agement actions included reducing 
total allowable catch and fleet size, 
and closure of large areas of the upper 
continental shelf to fishing (PFMC, 
2008a). In response to manage- 
ment concerns the NOAA Northwest 
Fisheries Science Center (NWFSC) 
also expanded and standardized the 
annual west coast groundfish bottom 
trawl survey to provide enhanced 
scientific information for managers. 
Since 2003, the Northwest Fisheries 
Science Center (NWFSC) has con- 
ducted a comprehensive fishery-inde- 
pendent bottom trawl survey covering 
the entire coast from the U.S. -Canada 
to the U.S.-Mexico borders, at depths 
of 55 to 1280 m (Keller et ah, 2008). 
This groundfish survey follows 
strict sampling protocols with stan- 
dardization of vessels, fishing gear, 
deployment methods, catch sampling 
practices, and geographic extent from 
2003 onward (Stauffer, 2004). 
Here we summarize variations in 
biomass indices for species collected 
during the 2003-10 fisheries-inde- 
pendent west coast groundfish bot- 
tom trawl survey. We evaluate if an 
observed decline in biomass of demer- 
sal fish (target and nontarget species) 
from 2003 through 2010 can be at- 
tributed primarily to recruitment (i.e., 
depletion after strong recruitment 
events for multiple species in the late 
1990s) or to climate variability (i.e., 
poor environmental conditions). 
The 2003-10 survey time series 
covers a period within the Califor- 
nia Current system characterized by 
1) reduced catch and exploitation of 
groundfish species relative to histori- 
cal rates (Worm et ah, 2009; Hilborn 
et ah, in press); 2) the population ef- 
fects of a very strong 1998-99 year 
class observed for many west coast 
groundfish species (e.g.. Pacific hake 
[Merluccius productus ], English sole 
[Parophrys vetulus], http://www. 
pcouncil.org/ . accessed June 2011); 
and 3) a phase shift in the Pacific 
Decadal Oscillation (PDO), an El Ni- 
no-like pattern of Pacific climate vari- 
ability linked to productivity (Mantua 
et ah, 1997). The PDO is detected as 
warm or cool surface waters in the 
western Pacific Ocean, north of 20°N, 
that shift phases on a scale of about 
