219 
Spatial patterns in the dynamics of 
slope rockfish stocks and their 
implications for management 
Donald R. Gunderson 
School of Fisheries 357980, University of Washington 
Seattle, Washington 98195 
E-mail address.dgun@fish.washington.edu 
Abstract .—Trawl surveys con- 
ducted at index sites off the northern 
Washington coast between 1968 and 
1992 indicate that rockfish stocks re- 
spond to fishing over very small spa- 
tial scales. The abundance of Pacific 
ocean perch, rougheye rockfish, and 
total Sebastes (all species combined) 
remained roughly constant between 
1968 and 1992, whereas catch rates in 
an experimental management area 
only 28 km to the north declined 76- 
91%, depending on species. Declines in 
the abundance of Pacific ocean perch 
in the index area appear to be less dras- 
tic than those reported for the U.S. 
Vancouver-Columbia management 
area during this same time period. Sub- 
stantial differences in the abundance, 
species composition, and status of rock- 
fish stocks can exist over relatively 
small spatial scales, a characteristic 
that must be carefully considered in 
their management. Pacific ocean perch 
off northern Washington appear to have 
matured considerably earlier ( age 8 ) in 
1992 than they did during 1968-72 (age 
10), but growth rate did not change 
appreciably during the same period. 
Manuscript accepted 11 September 1996. 
Fishery Bulletin 95:219-230 (1997). 
The rockfish assemblage along the 
Vancouver Island-Oregon continen- 
tal slope is dominated by Pacific 
ocean perch (Sebastes alutus), 
rougheye rockfish ( Sebastes aleu- 
tianus ), darkblotched rockfish 
(Sebastes crameri), splitnose rock- 
fish (Sebastes diploproa), and 
shortspine thornyhead (Sebasto- 
lobus alascanus ) (Leaman and 
Stanley, 1993; Weinberg, 1994). It 
is typically assumed that these spe- 
cies undertake only limited migra- 
tions after they have recruited to 
the adult stock. Because these fish 
are difficult to tag successfully, this 
supposition is based primarily on 
observations of abundance and age 
composition over area and time. 
Parasite studies on Pacific ocean 
perch (Leaman and Kabata, 1987) 
also indicate that adult migrations 
are quite limited. 
Pacific ocean perch stocks in the 
Washington-southern Vancouver 
Island area were heavily exploited 
by Soviet and Japanese fleets dur- 
ing 1966-68, effectively removing 
the 1951-53 year classes. Catch per 
hour in the Washington trawl fleet 
declined 61% between 1966 and 
1968 (Gunderson, 1977). An experi- 
mental overfishing program was 
carried out in Canadian waters off 
Vancouver Island in 1980-84 (Lea- 
man and Stanley, 1993), resulting 
in 76-91% reductions in the catch 
rates for the species dominating the 
slope rockfish complex in the Cana- 
dian trawl survey area (Fig. 1) be- 
tween 1979 and 1985 (Table 1). That 
portion of the survey area lying im- 
mediately north of the U.S.-Canada 
line experienced particularly inten- 
sive fishing during 1980-84 (Lea- 
man 1 2 ). From 1986 to 1992, annual 
slope rockfish catches in Canadian 
waters off southwest Vancouver Is- 
land (Richards, 1994) often ex- 
ceeded those reported during the 
overfishing experiment, and it is un- 
likely that the abundance of these 
stocks increased during this period. 
Exploitation rates for slope rock- 
fish in the U.S. Fisheries Conser- 
vation Zone were much lower than 
those off Canada during 1980-92. 
Pacific Ocean perch are the domi- 
nant member of the slope rockfish 
community and have been managed 
under a stock rebuilding program 
in U.S. waters since 1981. This pro- 
gram has attempted to discourage 
directed Pacific ocean perch fishing 
and to restrict landings of Pacific 
ocean perch to levels that would al- 
low incidental catches and yet al- 
low the stock to rebuild over a 20-yr 
period. In 1994, for example, Pacific 
ocean perch landings could not ex- 
ceed 3,000 lb (1,361 kg) per vessel- 
trip, or 20% of all fish on board, 
whichever was less, in Pacific ocean 
perch landings greater than 1,000 
lb (454 kg). 
1 Leaman, B. M. 1995. Dep. Fisheries 
and Oceans, Biological Sciences Branch, 
Pacific Biological Station, Nanaimo, Brit- 
ish Columbia, Canada V9R 5K6. Per- 
sonal commun. 
2 Butler, J. L. 1995. Southwest Fisheries 
Science Center, PO. Box 271, La Jolla, CA 
92038. Personal commun. 
