Age structure of Antarctic krill (Euphausia superba) populations as determined by age-pigment analysis and by size-frequency analysis

1 Pages·1991·1 MB·

by  Stephen Nicol

MEMOIRS OF THE QUEENSLAND MUSEUM
AGE STRUCTURE OF ANTARCTIC KRILL Sfoup Wassignificantly preater than that of the year 1 group.
(EUPHAUSIA SUPERBA) POPULATIONS AS fo contrast, the mean weight of the individuals in the popu-
DETERMINED BY AGE-PIGMENT ANALYSIS lation decreased significantly over the course of the year
AND BY SIZE-FREQLUENCY ANALYSIS (Table 1), The weight and relative fluorescence dala were
Morphometric measurements and size frequency analysis pooled, simulating the normal field situation af 4 series ot
have conventionally been used to assess the age structure of frequency data from which peaks must be discerned, In this
crustacean populations. Certain crustaceans have, however, instance the number of year classes and the mean peak
not proven amenable to such analyses. For example, labora- heights were known 50 the resul!s from the frequency anu-
tory studies have shown that the Antarctic krill Fuphausna lyses could be compared to the expected (real) case. An
superba can live for 7~8 years (Ikeda and Thomas. 1987), a analysis of the weight specific relative fluorescence dala by
life-span far in excess of that predicted from morphometric the Macdonald-Pitcher method yielded a best til for two
delerminations. Furthermore, this species may decrease [n modal peaks, the means of which were nol significantly
size during periodso f low food availability (Ikeda and Dixon, different to the knawn means for the two year classes. The
1982) thus obscuring the relationship between measurements weightefrequency analysis also yielded a best fil for two
of body size and age. In tesponse lo these problems, an peaks bul in this case the correspondence between the means
age-determination technique was developed for E. superba of the predicted and known weight graups was nat so precise
which was based on the measurement of levels of ape-piz- oF accurate.
ments (FAPs) in the animals (Ettershank, 1983, 19844, b, These results show that under laboratory conditions it is
1985). possible to separate year groups of £. superba by FAP quanti-
Early work on FAPs held promise (Ettershank, 1983, fication and that the secumulation rate over a period of one year
1984a, 1985) but subsequent studies demonstrated methodo- 15 Brear enough that the vear groups can be discriminated even
logical problems (Nicol, 1987), Studies examining FAPs in when the data are pooled, We have alsn shown thal FAPs can
other organisms have yielded equivocal resulis (Hill and be used to demonstrate vear group separation and predict which
Radtke, 1988; Hirche and Anger, 1987) but the utility of this group {s older when size-frequency analysis gives the wrong
technique for aging populations of the species for which it answer,
was originally proposed 4 Euphausid superba 4 is yet to
be proven. Literature Cited
A population of juvenile &. superba was maintained wader Ettershank. G. 1983, Age structure and cyclical annual size
constant laboratory conditions. A sample of the populmion Change in the Antarctic krill, Euphausia superba Dana.
was removed al the start of the experjment and the animals Polar Biology 2(3): 189-193.
were frozen individually in liquid nitrogen. The surviving 19844, A new approach to the assessment of longevity in the
animals from the original populanon were frozen in liquid Antarctic krill Euphausia superba. Journal of Crustacean
nilrogen one year later. The two sets of samples were uni- Biology 4: (Special Issue |) 295-305.
lysed for FAPs (Ettershank, 1984b) and the mean fluores- 1984, Biomass Handbook 2, 1-14,
cence peak heights af the two groups were compared, The
1985, Population age structure in males and juveniles of the
resulls of the fluorescence technique were compared with
Antarctic krill Euphausia superba Dana. Polar Biology 4(4):
those of a more conventional weight-frequency analysis.
199-201,
The mean fluorescence (expressed as telative fluorescence
Hill, K.T. and Radike, R.L. 1988. Gerontological studies of the
or as weight specific relative fluorescence) of the year 2
Damsellish Dascyllus afbisella, Bulletin of Marine
Science 42(3); 424-434.
TABLE 1. The mean values and predicted mean values for Hirche, HJ. and Anger, K. 1987, The accumulation of age
the weight specific telative fluorescence and the dry weight pigments during larval development of the spider crab, Hyas
of the animals in each sample. arancus (Decapoda,Majidae). Comparative Blochemistry
and Physiology 88B(3); 777-782,
eefh; see S e Skeda, T. and Dixon, P. 1982. Body shrinkage as a possible
Fluorescence 133.286 213.873 ovet-winteting mechanism of the Antarctic krill,
Mean wt. specific | 10.625 (9.53) 21.10 (20.42) Euphasia superba Dana. Journal of Experimental
Marine Biology and Ecology 62(2): 143-151.
fluorescence
Mean dry weight | 13.286(19.34) 9.926 (9.65) Tkeda, T, and Thomas, P.G, 1987. Longevity of the Antarctic
number of samples | 37 23 krill (Euphausia superba Dana) based on a |aboratory
experiment. Praceedings of the National Institute of
Comparison between mean weight specific Muores-
Polar Research Symposium on Polar Biology t; 56~62.
cence in year | and year 2: t=-7.586, 58 df, p< 0.0001,
Nicol, S, 1987. Some limitations on the use of the lipofuscin
Comparison between mean dry weight in year | and ageing lechnique. Marine Biolagy 93(4): 609-614.
year 2:1 = 2.522, 58 df, p = 0,014,
Values in brackets are predicted means from Mac- Stephen Nical, Martin Stolp and Graham W. Hosie,
donald-Pitcher analyses of combined year 1 and year Antarctic Division, Channel Highway,
2 dala sets. Kingston, Tasmania 7050, Australia.