Study shows that fish shrink after being iced for hours

Sandusky, Ohio — In the interest of fish conservation and management of the resource, minimum lengths are often established. 

These regulations delay premature harvest long enough to allow the fish to reproduce at least once, while also allowing more fish to survive to provide higher quality fishing later. 

However, when a large number of a year class reaches the minimum size at once, it can become a chore to properly measure each questionable fish‘s total length before either icing it down, if it is found to be legal, or tossing it overboard if it measures “short.”

When 2-year-old walleyes are being caught, this might have to be done several times per trip, but multiply this thousands-fold when borderline-size yellow perch or white bass come from commercial trap nets or shore seines.

To properly measure the total length of a freshwater fish, the fish in question is laid flat on a rigid measuring board, mouth closed, and firmly pressed (but not mashed) against a fixed fish board end stop. Then, the tail is pinched and the total length is considered to be from the tip of the nose or lower jaw to the end of the longest tail lobe, which could be the top or bottom.

A few studies performed in other states and Ontario have shown that there is a degree of fish shrinkage after being iced for hours in a cooler. 

Walleye study 

In 2003, researchers with the South Dakota Game and Fish Department had a study published in the North American Journal of Fisheries Management, titled “Postharvest Length Changes of Angler-Caught Walleyes.”

They measured walleyes caught in South Dakota coming from five different water temperatures, then re-measured their lengths 5, 10, and 20 hours after being confined to livewells or stored in ice.

Walleye shrinkage occurred after being caught at all water temperatures when stored in ice. However, all walleyes gained a little length in the livewell, except when coming out of 20 C (68 F) water. The study suggested that “Enforcement personnel should take water temperature and condition of fish into account when deciding whether to write a citation, but in general a 6 millimeter leeway should suffice in most situations.”

No leeway needs to be given on livewell fish, because if anything, they likely gained a little length. 

That 6mm translates into 0.236 (0.24) inches, which equates to ¼-inch that they recommend should be considered the “line in the sand” when enforcing a minimum walleye length limit from a cooler of ice. However, they were working with 13-19-inch walleyes, not the 15-inch minimum lengths that are the subject of this discussion. 

The Ohio Revised Code states that “it shall be unlawful to take or possess a walleye that is less than 15 inches in length.” But, if a properly measured 15-inch walleye is legal to keep at the time of capture, it puts everyone in an awkward position if iced fish are measured at the dock and found to be less than 15 inches.

Who should be flexible in this situation – the angler who had no intent to break the law when the fish was caught, measured, and kept, or the professional law enforcement officer who has become educated to the realities of fish shrinkage?

Commercial fish

A less generous, but commonly reported 1 percent shrinkage rate changes a commercially legal iced 8½-inch perch to 83⁄16 inches (8.41 inches) and an 11-inch white bass to 107⁄8 inches (10.89 inches). A 1 percent shrinkage rate on a 15-inch walleye is a less generous 1⁄8-inch (14.85 inches) amount compared to the study’s ¼-inch recommendation.

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