Use of Size for Early Detection of Juvenile Hatchery Steelhead Destined to Be Precocious Males
J.M. Tipping, A.L. Gannam, T.D. Hillson, J.B.
Poole-2003
North American Journal of Aquaculture, 65(4):
318–323
Abstract:
At two Washington State hatcheries in August
1999–2002, juvenile steelhead Oncorhynchus
mykiss were size-graded and the largest fish (4.8–9.2% of the
population) were coded-wire-tagged and mixed with small fish to determine
whether the large fish were those that became precocious males. The results
showed that the large fish in August at Merwin Hatchery tended to become
precocious, although the mean lengths of the precocious and nonprecocious
fish were similar at their time of release in April. At Abernathy Fish
Technology Center (FTC), the large fish in August did not disproportionately
become precocious, and the nonprecocious fish were significantly larger than
the precocious fish at release. We suggest that precocious fish at Abernathy
FTC may have committed to precocity before August whereas fish at Merwin
Hatchery committed to precocity in August. Because only 0.82% of the large
fish became precocious, removing the 5–10% largest fish in August at the
Merwin Hatchery would be marginally successful in reducing the number of
precocious males.
(Washington Department of Fish and Wildlife, 600 Capitol Way North,
Olympia, Washington 98501-1091, USA)