Br. Dumbauld et al., EFFICACY OF THE PESTICIDE CARBARYL FOR THALASSINID SHRIMP CONTROL IN WASHINGTON-STATE OYSTER (CRASSOSTREA-GIGAS, THUNBERG, 1793) AQUACULTURE, Journal of shellfish research, 16(2), 1997, pp. 503-518
The pesticide carbaryl is applied to intertidal oyster beds in Washing
ton State to control burrowing thalassinid shrimp. We studied efficacy
and found a significant dose response relationship for both ghost shr
imp, Neotrypaea californiensis, and mud shrimp, Upogebia pugettensis.
A threshold response was observed, suggesting that reducing the commer
cial application rate below 5.6 kg ha(-1) would decrease efficacy and
increase variability of resulting kill, particularly for Upogebia. Exp
osure time (time between application at low tide and flood tide) signi
ficantly affected the relationship, suggesting that even lower rates (
e.g., 2.5 kg ha(-1)) could be effective when exposure lime is sufficie
ntly long (>2-3 h). Typical oyster beds are exposed from 2 to 6 h duri
ng minus spring tides. Carbaryl persisted slightly longer (40-45 days)
in muddier substrate where Upogebia is present than in the well-drain
ed sand inhabited by Neotrypaea. However, given rapid initial decline
after application (<1 ppm in 24 h), reducing application rate would no
r greatly influence persistence at levels toxic to nontarget species.
This study suggests that growers should be aware of the species of shr
imp present on individual oyster beds, because Neotrypaea causes much
higher initial oyster seed mortality than does Upogebia. No oysters su
rvived beyond 300 days on untreated or treated plots where Neotrypaea
was present. Because of seasonal recruitment of postlarvae to the estu
ary in late summer and early autumn, Neotrypaea is also able to reinfe
st treated plots immediately, suggesting that long-term control for th
is species is more problematic.