Tougher Oysters, Faster Salmon: A Hatchery Field Trip

A Morning at Marsh Creek Hatchery

1Mr. Tobiah Grunwald's eighth grade marine science class took a field trip to the Marsh Creek Shellfish Hatchery, which sits on a dock beside a muddy bay. The hatchery grows young oysters and sells them to oyster farmers. Its manager, Dr. Kofi Sandström, explained that two oyster diseases spread through the bay decades ago. Both are caused by tiny parasites, and in some years they killed most of the oysters on the farms.

2Not every oyster died. Some were more resistant, partly because of the gene versions they inherited. So the hatchery began a breeding program. Each round, it planted young oysters in cages in the bay, where the diseases are common, and waited two years. Then it spawned only the oysters that survived and grew well, and their young became the next generation. Each round took about two years. The hatchery also kept an unselected line: each round, its parents were wild oysters picked at random from the bay. Both lines were planted in the same cages at the same time. Student Yesenia Marlowe copied the results in Table 1.

3Dr. Sandström said breeding changes which gene versions are common in a line, so the bred oysters' DNA now differs, on average, from that of wild oysters. He added one worry: the hatchery uses only about 50 parents in each round, and using few parents for many rounds can leave less genetic variation in the line.