Birth control? Moving? Or hunting? Wildlife managers trying to handle California's growing tule elk population have few easy options.

More benign controls — especially contraception and relocating animals — are being questioned on biological and ethical grounds. Studies are under way to see how contraception affects the gene pool of wild animals, an important issue for recovering species such as tule elk, which have almost no genetic variety.

Marin County's Point Reyes Nation Seashore, home to about 525 tule elk, has perhaps the most visible and studied elk herd on the planet. There, a five-year experiment is under way to study an immuno-contraceptive vaccine that prevents females from breeding for a mating season.

But while the shot prevents most pregnancies, it has proven only to slow population growth, not stop it. And critics point out that at $300 per shot, the vaccine is too costly and impractical for free-ranging animals.

State relocation programs also continue, moving about 1,150 tule elk in the past 30 years. But most of the suitable habitat has disappeared or is already overcrowded with elk.

Moving elk is also expensive — it can cost upward of $3,000 per animal, with population reductions that usually last less than three years. As this program fades out, wildlife officials say, hunting remains the state's first choice.

"The public doesn't want to see a slaughter," said Susan Shideler, an endocrinologist at the University of California, Davis who works with the Point Reyes contraception project.