36 
Abstract— Bycatch and resultant dis- 
card mortality are issues of global con- 
cern. The groundfish demersal trawl 
fishery on the west coast of the United 
States is a multispecies fishery with 
significant catch of target and non- 
target species. These catches are of 
particular concern in regard to spe- 
cies that have previously been declared 
overfished and are currently rebuild- 
ing biomass back to target levels. To 
understand these interactions better, 
we used data from the West Coast 
Groundfish Observer Program in a 
series of cluster analyses to evaluate 
3 questions: 1) Are there identifiable 
associations between species caught 
in the bottom trawl fishery; 2) Do spe- 
cies that are undergoing population 
rebuilding toward target biomass lev- 
els (“rebuilding species”) cluster with 
targeted species in a consistent way; 3) 
Are the relationships between rebuild- 
ing bycatch species and target species 
more resolved at particular spatial 
scales or are relationships spatially 
consistent across the whole data set? 
Two strong species clusters emerged — 
a deepwater slope cluster and a shelf 
cluster — neither of which included re- 
building species. The likelihood of en- 
countering rebuilding rockfish species 
is relatively low. To evaluate whether 
weak clustering of rebuilding rockfish 
was attributable to their low rate of 
occurrence, we specified null models of 
species occurrence. Results indicated 
that the ability to predict occurrence of 
rebuilding rockfish when target species 
were caught was low. Cluster analy- 
ses performed at a variety of spatial 
scales indicated that the most reliable 
clustering of rebuilding species was at 
the spatial scale of individual fishing 
ports. This finding underscores the 
value of spatially resolved data for 
fishery management. 
Manuscript submitted 19 January 2013. 
Manuscript accepted 25 November 2013. 
Fish. Bull. 112:36-48 (2014). 
doi: 10.7755/FB.112.1.3 
The views and opinions expressed or 
implied in this article are those of the 
author (or authors) and do not necesarily 
reflect the position of the National 
Marine Fisheries Service, NOAA. 
Co-occurrence of bycatch and target species 
in the groundfish demersal trawl fishery of the 
U.S. west coast; with special consideration of 
rebuilding stocks 
Eliza Heery (contact author ) 1 
Jason M. Cope 2 
Email address for contact author: eliza.heery@uw.edu 
1 Pacific States Marine Fisheries Commission 
Northwest Fisheries Science Center 
National Marine Fisheries Service, NOAA 
2725 Montlake Boulevard East 
Seattle, Washington 98122-2097 
Present address: Department of Biology 
University of Washington 
Box 351800 
Seattle, Washington 98195 
2 Fisheries Resource Analysis and Monitoring Division 
Northwest Fisheries Science Center 
National Marine Fisheries Service, NOAA 
2725 Montlake Boulevard East 
Seattle, Washington 98122-2097 
Bycatch, catch of incidental (non- 
target) species, is a major source of 
fish removals, and thus is a concern 
in fisheries around the world. Its 
impact on biodiversity and habitat 
health may be extensive (Dayton et 
al., 1995; Collie et al., 1997; Jen- 
nings and Kaiser, 1998; Thrush and 
Dayton, 2002), and, consequently, it 
has the potential to affect the long- 
term sustainability of marine fisher- 
ies and ecosystems. Several articles 
have emphasized the need for ecosys- 
tem management to address the pop- 
ulation health of both targeted and 
nontarget species (Pauly et al., 2000; 
Pikitch et al., 2004; Beddington et al. 
2007). A comprehensive understand- 
ing of the species composition and 
characteristics of bycatch could con- 
tribute to a greater knowledge of the 
effects of marine fisheries on ecosys- 
tems (Goni, 1998). 
Bycatch is particularly pertinent 
for multispecies fisheries, where 
the gear often cannot fully separate 
targeted and nontarget species. The 
groundfish fishery on the west coast 
of the United States (Fig. 1) is a 
multispecies fishery that primarily 
targets demersal fish species such 
as Sablefish ( Anoplopoma fimbria), 
Dover Sole (Microstomus pacificus), 
Shortspine Thornyhead ( Sebastolo - 
bus alascanus), Petrale Sole ( Eo - 
psetta jordani), and Pacific Hake 
( Merluccius productus). The majority 
of catch is acquired through the use 
of bottom-trawl nets, which are con- 
sidered one of the least discriminat- 
ing gear types (Alverson et al., 1994). 
The depths at which fish are caught 
and from which fish are raised to the 
ocean surface also cause mortality. 
Despite the long history of bottom- 
trawl fishing on the west coast of the 
United States, information on the 
species composition of bycatch in this 
fishery has only recently been regu- 
larly collected (Bellman and Heery, 
2013). 
A clear understanding of species 
co-occurrence in the total catch is im- 
portant for anticipating the ecologi- 
cal impacts of bycatch. Since 2002, 
bycatch data have been collected in 
the bottom trawl (non-hake) fishery 
by at-sea observers and are used 
by fishery managers in a variety of 
ways. Perhaps the most important 
