Begg et al.: Stock discrimination of Scomberomorus queenslandicus and S, munroi 
665 
the east coast (Begg and Sellin, 1998; Begg et al., in 
press). 
The limited movements of school mackerel indi- 
cated by tag-recapture data may also explain the 
overlap observed in the otolith composition of 2-year- 
old fish collected in Moreton Bay and Rockhampton. 
Small numbers of tagged school mackerel released 
in both these locations were recaptured in Hervey 
Bay between August and January, where they ap- 
pear to be mixing on a common feeding ground (Begg 
et al. , 1997; Begg and Hopper, 1997). 
In contrast, spotted mackerel of the same year class 
sampled in Queensland east coast waters had simi- 
lar patterns of elemental composition in their otoliths 
regardless of the region in which they were collected. 
This finding strongly supports the hypothesis of a 
single intermixing stock in the region of sampling 
derived from previous tagging, genetic, and repro- 
ductive studies, and seasonal changes in the loca- 
tion of commercial harvesting. These sources of in- 
formation suggest an annual large-scale movement 
of spotted mackerel along the Queensland east coast 
to southern feeding grounds in summer and a return 
migration in winter to northern spawning grounds 
(Begg and Hopper, 1997; Begg et al., 1997; Begg, in 
press). In addition, similar growth rates and homo- 
geneous genetic conditions of spotted mackerel 
throughout the study region support the hypothesis 
of a single east coast stock (Begg and Sellin, 1998; 
Begg et al., in press). 
The longshore East Australian Current possibly 
provides cues for the migratory cycle of spotted mack- 
erel and may facilitate larval dispersal from the 
spawning grounds and ultimately stock homogeneity 
throughout Queensland east coast waters. Proctor et 
al. (1995) proposed a similar stock structure for south- 
ern bluefin tuna on the basis of chemical composition 
of otoliths from juveniles collected along the major mi- 
gration route of the species. 
Identification of a species’ stock structure is an 
important requirement for effective fisheries man- 
agement (Rounsefell, 1975). The inability to define 
stock boundaries could unknowingly prejudice oth- 
erwise well-designed management protection efforts 
(Kutkuhn, 1981). Management of spotted mackerel 
in Queensland would be best addressed at the state 
level, because fishing effort in areas remote from one 
another may have an interaction on a single stock. 
In contrast, more localized (regional-level) manage- 
ment actions could proceed for school mackerel within 
Queensland — especially if the stock boundaries can 
be refined by further tests of the temporal persis- 
tence of the patterns described in this study. 
The use of otolith trace element analysis holds 
great potential for stock discrimination in fisheries 
for other Scom beromorus species that share common 
characteristics of migration through multiple juris- 
dictions and fishery types. However, the use of bulk 
analysis of whole otoliths allows us to infer only that 
there has been prolonged separation of fish at some 
stage in their life history. Without “life history scans” 
across otoliths, with techniques such as electron- 
probe microanalysis (Gunn et al., 1992), we cannot 
explore the possibility that mean elemental compo- 
sition is dominated by high concentrations specific 
to any particular life history stage. There is also need 
for careful selection of samples among year classes 
and time periods. Replication of sampling at inter- 
vals separated by several years and representation 
of all ontogenetic stages need to be incorporated in 
analyses to test for the consistency of spatial patterns 
in order to provide a more accurate environmental “fin- 
gerprint” for discrimination of mackerel stocks. 
Acknowledgments 
We would like to thank the commercial and recre- 
ational fishermen for cooperation and assistance in 
collection of samples; Steven Campana and four 
anonymous reviewers for critical comments and sug- 
gestions; Steve Cadrin for statistical advice; and Ian 
Brown and Hamish McCallum for reviews of this 
work. This study formed part of the Queensland De- 
partment of Primary Industries Fisheries Research and 
Development Corporation grant FRDC 92/144. 
Literature cited 
Begg, G. A. 
In press. Reproductive biology of school mackerel 
( Scomberomorus queenslandicus) and spotted mackerel (S. 
munroi) in Queensland east-coast waters. Mar. Freshwa- 
ter Res. 49. 
Begg, G. A., D. S. Cameron, and W. Sawynok. 
1997. Movements and stock structure of school mackerel 
( Scomberomorus queenslandicus) and spotted mackerel (S. 
munroi) in Australian east-coast waters. Mar. Freshwa- 
ter Res. 48:295-301. 
Begg, G. A., and G. A. Hopper. 
1997. Feeding patterns of school mackerel ( Scomberomorus 
queenslandicus ) and spotted mackerel ( S . munroi) in 
Queensland east-coast waters. Mar. Freshwater Res. 48: 
565-571. 
Begg, G. A., C. P. Keenan, and M. J. Sellin. 
In press. Genetic variation and stock structure of school 
mackerel and spotted mackerel in northern Australian 
waters. J. Fish Biol. 52. 
Begg, G. A., and M. J. Sellin. 
1998. Age and growth of school mackerel ( Scomberomorus 
queenslandicus) and spotted mackerel (S. munroi) in 
Queensland east-coast waters with implications for stock 
structure. Mar. Freshwater Res. 49:109-120. 
