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as much as 100 m with then rewly-h.tch€d young into the low()red rcservoir. Due to lhe lack of
cover however, it is unlikcly that many of these young suwived. Unfavourable conditions for
nestitrg and habilat conditions thal have undoubtedly resulted in low survival of juveniles, have
probably been the most imporlant impacts of the resewoir drawdown upon its resident alligator
INTRODUCTION
M.n'n.de impoundmenls are b€coming an increasingly abundant form of welland
habitat as natural lotic systems are allered for purposes of buman industrial, recrentionalrnd/or
irrigational needs. Crocodilian populations inhabiting such wctlands musl eithCr adapt to living
in these nerv resewoir habitats, move elsewhere or perish. Although some populations are
su iving in such impoundmerts (Alcila ^nd DyJ-iacco 1989), little intormalion is rv l?Lble
concerning these animals' population biolo$/ and produclivity in these h^t'itats. Particularly
hcking is any information concerning the responses of such animAls to thc pcriodic lowcring of
water levcls which is oommonly required in multipurpose reservoirs.
Among the beslstudied crocodili^ns utilizing . man-made reservoir arc the American
allie tors (Anigator mksissippiell'r') inhabiling the ll30 ha Par Pond reactor cooling reservon on
the U.S. Departmcnt of Energ/s Savannah River Sire (SRS) near Aikcn, South Carolina, in the
southeastern Unjtcd States (Murphy 1977, l98l; Brisbin 1982; Brnndt 1989, l99l). Throughout
the over 20 years that the Par Pond nlligalof potulalion hzrs been studicd, this reseruoir wffi
never subjected 1() clr^wdown rctivities, and the resultanl slabiliry of its waler levcls albw€d the
development of extensive beds ot submerged/emcrgcnt aquatic vcgctltion, pnrticularly in those
portions of thc lake \{,ilhin lhe 5 6m depth contour (l'arker st dl 1973; Snilh e/ da 19:i6).
Between cxrly July and mid-Seplember 1991, howcvcr, thc watcr level of I'rr l'ond wns lowcred
by approximately 6m 10 allow Ior repair work 10 the reservoir's relaining dam. lhis drawdown
reduced the surf^ce arm of rhe reservoir by approximalely 507, and exposed nearly all of the
submergent/emcrgent vegetrlion along the lake's margins. 'l}le reservoir has remained at this
lowered lcvel throughout thjs sludy (July l99l through July 1992), leaving n bare shorcUnu,
surrounded by approximrtely 526 h. of cxposed mudflats which, during the spring of 1992,
beg:rn to undergo terrestrial plant suct(iss in mnny arcas.
Previous studies of thc Par Pond rlligrtors havc revealed thnt the number of residcnt
animals hns more th^n doubled Irom An estimatcd 110 lC) 266 individuals frorn 1972-197810
1986-1988 (Muryhy 1977, 1981; Brnrdl 1989, l99l). Tbese same sludies hrve showr thal hilc
the sex rntio hns not changed during thrs period the populalion's age slruclure shifted slrikingly
from a high proportion (64%) of l:rrgc adults in the 19705 to a high propo ion (81%) of
iuveniles in the 1980s. As indicared by Brnndt (1989, 1991), these ch:rnges have been
accompanied by an incrersc in the reproduclive oulpul from an average of 2.310 ,t.0 nesls per
year during the samc pcriod, all being ind'cativc of n healthy and growing population which at
that time, had nol yet reached its cnrrying capacity. lllerc is now conccrn, however, that
chang€s created by the reservoir drawdown of 1991 night reduce ihe reservoir' suitability for
alligators, particularly juveniles as a resulr of cxposurc and des.ruclion of subnergent/emergent
vegeiation along the lake's margins.