Using Archaeological Freshwater Drum Otoliths to Detect Long-Term Changes in Age and Growth

1
Using Archaeological Freshwater Drum Otoliths to
Detect Long-Term Changes in Age and
Growth Shannon Davis-Foust and Ronald Bruch
Introduction
Methods
Results
Results (cont.)
Sagittal otoliths for this study were recovered
from archaeological sites surrounding the Lake
Winnebago system (Fig. 3). The lengths of 690
otoliths were measured in mm on the longest axis,
weighed to the nearest tenth of a mg, embedded in
epoxy, sectioned with a low-speed diamond bladed
saw, and examined through a dissecting scope for
age determination. Age determinations were made
by two experienced readers by counting the opaque
zones as the boundary for annual growth
increments (Casselman 1987). Precision was
evaluated by calculating the coefficient of
variation (Campana 2001).
The best fit equation for the relationship
between fish total length and otolith length for
drum otoliths lt15.5 mm long was Log10(TL)
1.0387 Log10(OL) 1.3290) r2 0. 9806, and
the equation for otoliths 15.5 mm was Log10(TL)
1.3683 Log10(OL) 0.9591, r2 0.8560 (Fig.
4).
Freshwater drum (Aplodinotus grunniens) have been
a dominant part of the aquatic community of the
shallow Lake Winnebago System for centuries.
Since European settlement in central Wisconsin
began in the early 1800s, the Lake Winnebago
system has faced an onslaught of anthropogenic
changes including loss of thousands of acres of
emergent wetlands, eutrophication, and invasions
of non-native species such as carp and zebra
mussels. In addition to these changes, millions
of pounds of the native freshwater drum
(Acipenser fulvescens), a species considered a
rough fish, were removed annually throughout most
of the later half of the 20th century in a
combined effort by commercial fishermen and
state-funded programs (Fig. 1). The rough fish
removal program was terminated in 1990 in part
because the desired impact on drum (fewer drum)
was never detected. Despite their modern
reputation as a rough fish, drum were an
important part of the diet of Native Americans
inhabiting the shore of the Winnebago lakes,
evidenced by the 1000s of drum otoliths that
have been found in middens in excavated Native
American campsites and villages in the area.
These archaeological otoliths provided an
opportunity to compare age and growth of
Winnebago System drum from pre-historic times to
that of drum from modern times, and perhaps
provide some insight as to the impact of 60 years
of intensive drum removal in the 20th Century.
Fig. 7
Using mean total length at age for archaeological
drum ages 2-64 and modern drum ages 2-41,
archaeological drum grew slower yet attained
similar lengths to modern drum (likelihood ratio
test, F(3,96)3.8886, p0.011) (Fig. 8). Similar
differences between von Bertalanffy parameters
were obtained between lotic modern and lotic
archaeological drum.
Fig. 4
The TLs of the lotic drum (M502.3, SD96.3)
were greater than lentic drum (M362.7,
SD103.2), F(1,1214)405.619, plt0.001 (Fig. 5).
However, the length distributions between the two
time periods were not significantly different,
F(1,1214)3.667, p0.056, and there was
significant interaction between habitat type and
time period, F(1,1214)66.11, plt0.001.
Fig. 8
Conclusions

• Archaeological drum from lotic habitats had
  greater longevity and slower overall growth rates
  than modern drum.
• Archaeological drum less than age 10 grew more
  quickly than modern drum, suggesting that the
  food base for small drum may have been better and
  the food base for large drum may have been poorer
  (in relation to population densities) prior to
  European settlement.
• The inflection points observed between TL and
  OL, and OL and age in both archaeological and
  modern drum corresponds to the length at which
  there is a diet shift in modern drum (unpublished
  data).
• Sixty years of intensive drum removal operations
  may have sufficiently decreased densities to
  result in a younger age composition and increased
  growth rates in the adult Lake Winnebago drum
  population.

Calibrated by quickcal2007 ver.1.5
Sagittal otoliths were obtained from modern drum
(n148 in 1986, n177 in 2003, n126 in 2004,
n107 in 2005, n184 in 2006, n351 in 2007,
n240 in 2008, and n106 in 2009) captured by
fall assessment trawling and angling at
tournaments. A random otolith length (OL) (left
or right) was used from 1016 drum to determine
the model the best described the relationship
between OL and total body length (TL). Modern
otoliths were embedded and sectioned following
the same methods as the archaeological otoliths.
TLs of archaeological drum were calculated
using the equation derived from the relationship
between OL to TL for modern drum. TL
distributions of both archaeological and randomly
sampled modern drum were examined by grouping
them into length categories proposed by
Gabelhouse (1984). Mean length at age was
compared using paired t-tests between modern and
archaeological drum. Von Bertalanffy models were
used to compare growth rates by calculating mean
length (OLs and TLs) at age. Significant
differences between growth parameters were
evaluated drum using likelihood ratio tests. To
further evaluate differences between
archaeological and modern drum, subclasses were
created by categorizing drum as lentic or lotic
(Rypel et al. 2006). Modern drum captured during
tournaments (n287) were classified as lotic
because the majority of competitors in these
tournaments target large drum in riverine
habitat. Drum captured by trawling (n1152) were
classified as lentic. Archaeological otoliths
were assumed to be lentic if they were recovered
from sites along the lakes (n110) and considered
lotic (n508) if they were from Doty Island,
which was the only site located at the opening of
a river. Differences among length and age
distributions of archaeological/lentic,
archaeological/lotic, and randomly captured
modern/lentic and modern/lotic drum were examined
using two-way ANOVA.
Fig. 5
The CV for age determinations between the two
readers for archaeological otoliths was 0.37.
Ages of lotic drum (M31.66, SD15.23) were older
than lentic drum (M16.0, SD10.65),
F(1,1251)178.01, plt0.001(Fig. 6). Ages of
archaeological drum (M34.5, SD15.82) were older
than modern drum (M17.6, SD9.98),
F(1,1251)234.98, plt0.001. There was no
significant interaction F(1,1251)3.674, p0.056
indicating that the ages of lotic drum were
greater than lentic drum during both time periods.
Fig. 1
Fig. 2
Objectives
Sagittal otoliths from drum provide accurate
estimates of age (Davis-Foust et al. 2009) (Fig.
2), and total lengths of freshwater drum have
been estimated from their otoliths with
remarkable accuracy (Witt 1960, Priegel 1963).
Age has been estimated from a small set of
archaeological otoliths (Bergquist 1996). Witt
(1960) Priegel (1963) both concluded that
archaeological drum grew larger than modern drum
collected from archaeological sites near the
Mississippi River and Lake Winnebago however, no
studies have used otoliths to evaluate changes in
age composition or growth rates. We evaluated
changes in age and growth of freshwater drum from
prior to European settlement (circa 1850) to
modern times within the Lake Winnebago system. We
compared (1) length distribution, (2) age
distribution, and (3) growth rates between
archaeological and modern drum within lotic and
lentic subclasses.
References
Bergquist, L.A. 1996. Development of an archaeometric dating technique using freshwater drum otoliths an application of biochronology. Thesis, University of Minnesota, St. Paul. 111 pp. Campana, S.E. 2001. Accuracy, precision and quality control in age determination, including a review of the use and abuse of age validation methods. Journal of Fish Biology 59 197-242. Casselman, J.M. 1987. Determination of age and growth. pp. 209242. In S. Gill (ed.) The Biology of Fish Growth, Academic Press, London. Davis-Foust, S.L., R.M. Bruch, S.E. Campana, R.P. Olynyk J. Janssen. 2009. Age validation of freshwater drum using bomb radiocarbon. Transactions of the American Fisheries Society 138 385-396. Gabelhouse Jr, D. 1984. A length-categorization system to assess fish stocks. North American Journal of Fisheries Management 4 273-285. Priegel, G.R. 1963. Use of otoliths to determine length and weight of ancient freshwater drum in the Lake Winnebago area. Wisconsin Academy of Science, Arts, and Letters 52 27-35. Rypel, A.L., D.R. Bayne J.B. Mitchell. 2006. Growth of freshwater drum from lotic and lentic habitats in Alabama. Transactions of the American Fisheries Society 135 987-997. Witt Jr, A. 1960. Length and Weight of Ancient Freshwater Drum, Aplodinotus grunniens, Calculated from Otoliths Found in Indian Middens. Copeia 1960181-185.
Fig. 6
Acknowledgements Many thanks goes to Richard
Mason and Dr. Jeffrey Behm, Department of
Anthropology, UW-Oshkosh for providing
archaeological otoliths, and to the many WDNR
fisheries technicians that have assisted with
capturing drum and otolith processing.
An inflection point was detected between modern
and archaeological mean OLs at age (Fig. 7).
Mean OLs at age for archaeological drum were
greater than modern drum from age 2-9 (one tail
paired Students t test t2.29, p0.028), and
mean OLs for modern drum were greater than
archaeological drum from ages 10-49 (one tail
paired Students t test t-6.56, plt0.001).