No benefits from steelhead net pen experiment

Grand Rapids, Mich. — A 3-year experiment to determine if steelhead survival improves when hatchery-born yearlings are allowed to acclimate in a pen before being released to open water showed no benefit, according to state officials who add the approach may even be detrimental. 

“We were a little surprised (by the findings),” said Jan VanAmberg, manager of Marquette and Thompson state fish hatcheries, referring to the 2011-2013 experiment at three Lake Huron ports – Harrisville, Harbor Beach, and Van Etten Creek on the AuSable River. “We hoped to see the same dramatic (positive) response we see in chinook salmon. But the bottom line of this study was net pens do not make a difference with steelhead.” 

Net pens have long been used to boost chinook salmon survival and returns to Lake Michigan ports where they are stocked. The young hatchery plants are held in pens at lower-river locations where they are fed for a couple of weeks before being released. The approach lets them imprint on the river and grow larger and more hearty before running the gauntlet of predators they may encounter in the open lake. 

VanAmberg said steelhead stocked directly into the lake survived better than penned fish at Van Etten, and much better at Harrisville, with mixed results at Harbor Beach, which has better water quality. 

All steelhead were fin-clipped so they could be identified later. A total of 205,653 were stocked during the study. Creel surveys determined that penned and direct-planted steelhead were caught by anglers.  

Their size when planted also made a difference. Larger stocked fish returned better than smaller stocked fish. One site each year received 8.2-inch steelhead while the others got 7-inch steelhead. 

“The larger fish returned twice as well as the smaller fish,” VanAmberg said. 

Why net pens boost salmon survival but do not for steelhead is still a matter of speculation. Some of it, VanAmberg says, has to do with the nature of each species and their size when stocked.