361 
Interdecadal change in growth of 
sablefish ( Anoplopoma fimbria ) 
in the northeast Pacific Ocean 
Michael F. Sigler' 
Email address for contact author katy.echave@noaa.gov 
1 Auke Bay Laboratories 
Alaska Fisheries Science Center, National Marine Fisheries Service, NOAA 
Ted Stevens Marine Research Institute 
17109 Pt Lena Loop Rd 
Juneau, Alaska 99801 
2 University of Alaska Fairbanks 
School of Fisheries and Ocean Sciences 
235 O'Neill 
Fairbanks, Alaska 99445 
Abstract — Errors in growth estimates 
can affect drastically the spawner-per- 
recruit threshold used to recommend 
quotas for commercial fish catches. 
Growth parameters for sablefish (Ano- 
plopoma fimbria ) in Alaska have not 
been updated for stock assessment pur- 
poses for more than 20 years, although 
aging of sablefish has continued. In this 
study, length-stratified data (1981-93 
data from the annual longline survey 
conducted cooperatively by the Fisheries 
Agency of Japan and the Alaska Fish- 
eries Science Center of the National 
Marine Fisheries Service) were updated 
and corrected for discovered sampling 
bias. In addition, more recent, randomly 
collected samples (1996-2004 data from 
the annual longline survey conducted 
by the Alaska Fisheries Science Center) 
were analyzed and new length-at-age 
and weight-at-age parameters were esti- 
mated. Results were similar between 
this analysis with length-at-age data 
from 1981 to 2004 and analysis with 
updated longline survey data through 
2010; therefore, we used our initial 
results from analysis done with data 
through 2004. We found that, because 
of a stratified sampling scheme, growth 
estimates of sablefish were overesti- 
mated with the older data (1981-93), 
and growth parameters used in the 
Alaskan sablefish assessment model 
were, thus, too large. In addition, a com- 
parison of the bias-corrected 1981-93 
data and the 1996-2004 data showed 
that, in more recent years, sablefish 
grew larger and growth differed among 
regions. The updated growth informa- 
tion improves the fit of the data to the 
sablefish stock assessment model with 
biologically reasonable results. These 
findings indicate that when the updated 
growth data (1996-2004) are used in 
the existing sablefish assessment model, 
estimates of fishing mortality increase 
slightly and estimates of female spawn- 
ing biomass decrease slightly. This study 
provides evidence of the importance of 
periodically revisiting biological param- 
eter estimates, especially as data accu- 
mulate, because the addition of more 
recent data often will be more biologi- 
cally realistic. In addition, it exempli- 
fies the importance of correcting biases 
from sampling that may contribute to 
erroneous parameter estimates. 
Manuscript submitted 4 January 2012. 
Manuscript accepted 31 May 2012. 
Fish. Bull. 210:361-374 (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. 
Katy B. Echave (contact author) 1 
Dana H. Hanselman' 
Milo D. Adkison 2 
Sablefish ( Anoplopoma fimbria) are 
a long lived, commercially impor- 
tant finfish abundant along the 
upper continental slope in the North 
Pacific, with catches ranging from 
10,000 to 35,000 metric tons (t) in 
Alaskan waters during the last 2 
decades (Hanselman et al., 2010). 
Using data provided by the NOAA 
National Marine Fisheries Service 
(NMFS) annual domestic longline 
survey, we modeled the sablefish 
population with statistical catch-at- 
age split by sex (Hanselman et ah, 
2006). To estimate fish abundance 
accurately, age-structured models 
require several biological param- 
eters, such as growth, maturity, 
natural and fishing mortality, and 
annual age or length data, as well 
as annual abundance estimates and 
catches (Quinn and Deriso, 1999). 
Errors in growth estimates can dras- 
tically affect the spawner-per-recruit 
threshold used to recommend quotas 
for commercial fish catches. Overesti- 
mation of growth rates may result in 
overestimation of biomass and, there- 
fore, recommendation of harvest rates 
that are too high (Quinn and Deriso, 
1999). Conversely, underestimation of 
fish growth can lead to underutiliza- 
tion of a resource and lost economic 
yield. Growth parameters for Alas- 
kan sablefish have not been updated 
for stock assessment purposes since 
Sasaki’s published research (1985). 
When age-length conversion matrices 
were first added to the Alaskan sable- 
fish stock assessment in 1995, they 
were constructed from data (1981-93) 
that were collected under a length- 
stratified sampling scheme. These 
data were randomized according to 
the method of Kimura and Chikuni 
(1987), but they were collected in lim- 
ited areas and over just a few years 
and were aggregated in a way that 
put too much weight on large fish 
( > 66 cm FL). For these reasons, we 
speculated that size estimates used 
in the assessment of the sablefish 
population of Alaska have been too 
large. Meanwhile, many more sable- 
fish have been aged over a larger 
geographic area. Additionally, since 
the last update on sablefish growth 
rates, significant changes in length- 
at-age have been discovered for other 
demersal species, such as Pacific 
halibut ( Hippoglossus stenolepis) and 
other flatfish species in the northeast 
Pacific Ocean. These changes have 
caused substantial changes in stock 
assessment results (Walters and 
Wilderbuer, 2000; Clark and Hare, 
2002). Because both sablefish and 
Pacific halibut have similar fisheries 
and are such commercially valuable 
fishes, a change in the assessment 
