402 
Otolith morphometries and population structure 
of Pacific sardine ( Sarcfinops sagax ) 
along the west coast of North America 
Barbara Javor (contact author) 
Nancy Lo 
Russ Vetter 
Email address for contact author: barbara.javor@noaa.gov 
Southwest Fisheries Science Center 
National Marine Fisheries Service, NOAA 
8604 La Jolla Shores Drive 
La Jolla, California 92037 
Abstract — The broad distribution 
of Pacific sardine ( Sardinops sagax ) 
along the Pacific coast of North 
America makes it difficult for fish- 
eries managers to identify regional 
stocks of this dominant small pelagic 
species. An investigation of morpho- 
metric characteristics of otoliths of 
Pacific sardine across most of their 
range revealed regional differences in 
populations. In a survey of over 2000 
otoliths, all ages (with an emphasis 
on age-1 recruits) were compared. 
Principal components analysis, mul- 
tivariate analysis of variance, and a 
novel method derived from regression 
and residuals calculations, termed 
perimeter-weight profiles (PWPs), 
revealed otolith similarities and dif- 
ferences. The results of the different 
approaches to statistical comparisons 
did not always agree. Sardine otoliths 
from Mexican waters were generally 
lighter and more lobate than those 
from U.S. and Canadian populations. 
Age-1 otoliths from northern Califor- 
nia in 2006-07 tended to be heavier 
and smoother than those from other 
areas, including year-class cohorts 
from southern California. Compari- 
sons of age-groups and year-classes 
of northern California otoliths with 
the use of the PWP models indicated 
significant trends in year-to-year 
patterns. In conjunction with other 
established indices of population 
structure, otolith PWPs are a useful 
tool for identifying local and regional 
stocks of Pacific sardine and may help 
distinguish populations of other fish 
species as well. 
Manuscript submitted 23 November 2010. 
Manuscript accepted 7 July 2011. 
Fish. Bull. 109:402-415 (2011). 
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. 
The distribution of Pacific sardine 
( Sardinops sagax) along approxi- 
mately 5000 km of the Pacific coast 
of North America — an area span- 
ning waters of Mexico, U.S. A., and 
Canada — poses an international 
challenge to understanding popu- 
lation structure and managing the 
fishery (Fig. 1; southeast Alaska not 
shown). The three countries regu- 
late commercial fishing of this often 
dominant small, pelagic species under 
management plans based on annual 
stock assessments, but knowledge of 
sardine spawning, recruitment, and 
migratory habits is incomplete (Lo et 
al., 2010). After a peak in biomass of 
3.6 million metric tons (t) in 1936, the 
commercial fishery collapsed in the 
1940s and 1950s, possibly owing to 
overfishing or climatic changes in the 
California Current system (Norton 
and Mason, 2005; http://www.nmfs. 
noaa.gov/fishwatch/species/sardine. 
htm [accessed June 2011]). The popu- 
lation began to rebound in the 1970s, 
and a peak in biomass of 1.7 million t 
was recorded in 2000. The present 
existence of three North American 
stocks has been proposed (reviewed 
by Smith, 2005): 1) a stock along the 
California coast that migrates to the 
Pacific Northwest (Oregon to south- 
east Alaska; Wing et al., 2000); 2) a 
stock along the Pacific coast of Baja 
California, Mexico; and 3) a stock 
within the Gulf of California. Radov- 
ich (1982) proposed further dividing 
the California stock into northern and 
far northern races. 
Despite a variety of methods, in- 
cluding egg, larval, and adult sur- 
veys, fish morphometries, vertebral 
counts, tagging, and genetic, parasit- 
ic, and otolith studies, investigators 
have been unable to assign specific 
attributes and unique characteristics 
to identify regional stocks since the 
populations rebounded (Hedgecock et 
al., 1989; Grant and Bowen, 1998; 
Pereyra et al., 2004; Felix-Uraga 
et al., 2005; Smith, 2005; Lo et al., 
2005, 2010; Valle and Herzka, 2008; 
Baldwin, 2010; Dorval et al., 2011). 
Further clues to stock structure 
might be found in more detailed sur- 
veys of the morphometry and micro- 
chemistry of sardine otoliths. 
Since 1993 when a study of Atlantic 
cod ( Gadus morhua ) showed growth 
rates significantly correlated with 
otolith shape (Campana and Cassel- 
man, 1993), morphometric analysis 
has been used as a tool to detect 
stock structure and interannual vari- 
ability in a number of fish species, 
including Pacific sardine (Felix-Uraga 
et al., 2005) and other Clupeiformes 
(Somarakis et al., 1997; Turan, 2000; 
Torres et al., 2000; Gonzalez-Salas 
and Lenfant, 2007; Burke et al., 
2008). Linear measurements between 
landmark points (truss analysis), cal- 
culated geometries (e.g., circularity), 
and two-dimensional (Fourier series) 
shape analysis of otoliths are meth- 
ods typically employed. 
Otolith attributes are expressed 
under the control of genetic, physi- 
ological, and environmental factors. 
