326 
National Marine 
Fisheries Service 
NOAA 
Abstract- — -Collecting age-composi- 
tion data is a critical aspect of stock 
assessment; however, there are no 
biological or statistical investiga- 
tions that support optimization 
of the distribution of sample size 
across species. Sample sizes for both 
collection and age-reading are often 
set by using ad hoc or historical val- 
ues. Investigations into quantifying 
the trade-offs when allocating sam- 
ple sizes across species are needed 
because resources for age determina- 
tion are always limited. In this study 
we performed analyses to investigate 
the distribution of sample sizes to 
determine ages across multiple spe- 
cies by using methods derived from 
sampling theory and simulation 
testing of stock assessment models. 
We found that, in terms of methods 
based on sampling theory, distribu- 
tion of sample size under 2-stage 
sampling could be significantly re- 
lated to the life-history characteris- 
tics of the species. Results from sim- 
ulation analysis illustrated that the 
influence of sample sizes required 
to determine age composition of fish 
on uncertainty in stock assessment 
models was related to uncertainty in 
a survey index and recruitment vari- 
ability of the species being assessed. 
The simulation analysis highlighted 
cases in which larger age-composi- 
tion sample size did not appreciably 
decrease uncertainty in the stock 
assessment model, in particular, 
for species with lower recruitment 
variability and larger survey index 
uncertainty. 
Manuscript submitted 6 April 2016. 
Manuscript accepted 4 April 2017. 
Fish. Bull. 115:326-342 (2017) 
Online publication date: 16 May 2017. 
doi: 10.7755/FB.115.3.4 
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. 
Fishery Bulletin 
<%• established in 1881 •<?. 
Spencer F. Baird 
First U.S. Commissioner 
of Fisheries and founder 
of Fishery Bulletin 
Investigations into the distribution of sample 
sizes for determining age composition of 
multiple species 
Peter-iohn F, Hulson (contact author) 
Dana H. Hartselman 
8. Kalei Shotwell 
Email address for contact author: pete.hulson@noaa.gov 
Auke Bay Laboratories 
Alaska Fisheries Science Center 
National Marine Fisheries Service, NOAA 
17109 Point Lena Loop Road 
Juneau, Alaska 99801 
Age-composition data sets provide 
the fundamental information nec- 
essary for application of statisti- 
cal catch-at-age assessment (SCAA) 
models used to estimate population 
dynamics and to manage commercial 
fisheries (Quinn and Deriso, 1999; 
Maunder and Punt, 2013). Age com- 
position data allow the tracking of 
year classes through time, providing 
an improved understanding of popu- 
lation dynamics compared with that 
gained from analyzing fishery catch 
per unit of effort or survey biomass 
indices alone. Although theoretically 
the uncertainty in age composition 
can be reduced by increasing sample 
size, agencies have limited age-read- 
ing capacity (because of budgetary 
constraints on the number of hours 
age-reading scientists can spend 
reading ages from otoliths, as well as 
the number of age-reading scientists 
that a science center can employ. 
A formal method for determin- 
ing the most efficient distribution of 
sample size across species would be 
useful for the allotment of limited 
time, personnel, and funding; howev- 
er, there is little to no existing guid- 
ance in the literature. The lack of sci- 
entific rigor used in choosing sample 
sizes for determining age composi- 
tion at the NOAA Alaska Fisheries 
Science Center (AFSC) was noted in 
the 2013 NOAA Office of Science and 
Technology program review (AFSC 1 ) 
of data collection and management. 
The reviewers noted that in light of 
potentially shrinking budgets, the 
current level of age-reading capabili- 
ties at AFSC may not be sustainable. 
Even though this conclusion was spe- 
cific to the AFSC review, this topic is 
applicable globally, whenever agen- 
cies are balancing age-reading pri- 
orities with other data collection or 
assessment priorities in their stock 
assessment programs. 
If a method were to be adopted 
that based age-composition sampling 
across species on a statistical or bio- 
logical basis, the distribution of sam- 
ple size would be different from that 
of the current method, and some spe- 
cies would experience an increase in 
the samples sizes used to determine 
age composition of fish [hereafter “the 
age-composition sample size”], while 
others would result in a decrease. 
A resulting important issue when 
discussing these changes in sample 
sizes for determining age composi- 
tion is the subsequent influence of 
increasing or decreasing sample size 
1 AFSC (Alaska Fisheries Science Center). 
2013. Summary report: Alaska Fisher- 
ies Science Center science data collection 
review, 40 p. [Available from website.] 
