Straight from the biologist's mouth: Monitoring Commercial Harvest in Saginaw Bay

By: Tom Goniea
Senior Fish Biologist, DNR

I wanted to provide a little insight into some of things we do in regards to fisheries management on the Great Lakes. Throughout the year, DNR staff monitor state-licensed commercial fishing activity and collect a variety of data on species harvested as well as from fish that are released back into the lake. In May 2015, I was out on Saginaw Bay collecting such data.

Fisheries biologist holding a large catfish caught on a commercial fishing vesselDays spent riding and monitoring the fishery are usually long. I left Lansing at 5:30 am to meet the commercial fisher at his dock in Pinconning at 8 am. Today I lucked out. The weather was fairly nice for early May, a little breezy but the temperatures were decent. Over the next seven hours, eight traps nets were lifted and cleared of fish. The combined commercial harvest from all nets included roughly 6,000 pounds of whitefish, 500 pounds of catfish, and 71 yellow perch. Additionally, thousands of walleye, sheepshead, suckers, and other species were released alive back to the bay.

While I was there to observe, the main purpose of the trip was to collect age and growth data from the yellow perch harvest. Collecting perch data from Saginaw Bay is something that the DNR tries to do in the spring and fall of the year. The day's goal had been to collect a 100 fish sample, so the fact that only 71 perch were in the nets was a little disappointing. Still I made the best of it and took what data I could from the perch on board.

Fisheries biologist measuring a yellow perch caught on a commercial fishing vesselThe first item collected was total length of every perch to the nearest millimeter. Today the perch ranged from 217 mm (8.5 inches) to 343 mm (13.5 inches). NOTE: 8.5 inches is the commercial minimum size limit for yellow perch on Saginaw Bay.

Second, I removed the first three dorsal spines from each fish with a pair of wire cutters for aging.

Fish can be aged in various ways depending on species, for some fish we look at their scales. For others we use a bone in the head called an otilith (a fish's inner ear). Yellow perch are aged by examining the spines that make up the dorsal fin on the fish's back. Like the rings in a tree, every year fish will lay a growth ring in the spine. After collection, the spine can be sectioned just like a tree trunk and the rings counted. Of course unlike the tree, fish spines are quite small and the rings can only be counted with the aid of a microscope. When the age of a fish has been determined, it is then paired with the total length of that fish. Biologists then use these two pieces of information together to determine growth rate for a single fish. When age and length is collected from many fish, the combined data can be used to estimate the growth rate of the entire population.

The data collected on this trip will be paired with commercial harvest data which will be collected in October and analyzed over the coming winter. It will then be added to other information the DNR collects in its traditional fish surveys as well as recreational angler catch data provided by the creel program and charter boat program. Together all these pieces help Fisheries Division manage and make informed recommendations regarding the fishery.

I hope you enjoyed this write up. Check back for descriptions of future monitoring trips I make around the Great Lakes. Cheers and have a great summer!

Fisheries biologist collecting yellow perch spines while on a commercial fishing vessel