The California Catholic Conference has announced that the bishops of California urge California's Catholics to vote "Yes" on Proposition 34, which would end the use of the death penalty in California; Proposition 35, which increases criminal penalties for human trafficking; and Proposition 36, which revises the three strikes law to impose a life sentence only when a new felony conviction is for a violent offense. The bishops issued a "no position" on Proposition 37; however, their summary of relevant Catholic teaching sounds very much to me like they lean toward endorsement:
All of Creation is sacred and we are called to serve as faithful stewards. Creation has an integrity and inherent value beyond its usefulness to human beings. Human beings are to be responsible stewards of creation: In this activity we work in harmony with God as co-creators. The web of life is one. —National Catholic Rural Life Conference
Forcing DNA from one species into another, in a manner that would never occur in nature, and then having to use billions of pounds of pesticides and herbicides per year to make it work doesn't sound like working in "harmony" with God to me!
You can access the website of the California Catholic Conference here: CCC