Biologists in North America have been studying the effectiveness of fish stocking programs ever since fish were artificially spawned, reared, and stocked in the late 1800s. Questions routinely posed with any stocking program include, "Do the small fish I stock survive to adulthood?" and "Do I really need to stock or can the population sustain itself on its own?"  To address these questions, the USGS Tennessee Cooperative Fishery Research Unit staff and students at Tennessee Tech University recently collaborated with Tennessee Wildlife Resources Agency (TWRA) biologists on an assessment of a fingerling muskellunge stocking program in middle Tennessee.

Many anglers (and even some biologists) are surprised to learn that muskellunge, a preeminent trophy sportfish in northern states, are native to streams in the Tennessee River and Cumberland River watersheds of Kentucky and Tennessee. In fact, biologists wrote in the mid-1950s that muskellunge were so abundant in some Cumberland Plateau streams of middle Tennessee that anglers used nets, gigs, trot lines, and even shotguns to harvest fish. Not surprisingly, muskellunge populations rapidly dwindled due to overfishing and habitat destruction linked to coal mining and industrial pollution.

To prevent the disappearance of muskellunge from the Cumberland Plateau, the TWRA began stocking muskellunge into the upper Caney Fork River system above Great Falls Dam in 1976. Muskellunge were stocked sporadically over several decades and during recent spring electrofishing surveys, adult muskellunge were captured that displayed signs of spawning activity (flowing eggs or milt; lesions on their flanks; torn fins). However, it was not known whether natural reproduction was occurring or whether recruitment of naturally-produced fish was sufficient to maintain the fishery.

There a number of ways to evaluate the effectiveness of a stocking program. The Tennessee CRU scientists combined telemetry, electrofishing and seining surveys, and a microtagging program to answer the questions posed by TWRA biologists. In the telemetry study, small radio transmitters were implanted into fingerling muskellunge raised in a North Carolina hatchery. An earlier pilot study in a hatchery confirmed that small muskellunge tagged with dummy transmitters would survive and grow.

However, in this system, survival of stocked, radio-tagged fish was dismal; researchers "listened" and documented that nearly 80 percent of the fish died within 60 days. One source of mortality was expected (great blue heron predation) but the number of tagged fish preyed upon by river otters, which were themselves reintroduced to Tennessee in the mid-1980s, was a surprise. Clearly, stocking naive, hatchery-reared muskellunge came with no guarantee they would survive and live long enough to reproduce.

But enough of the fish stocked since 1976 must have survived long enough to reproduce because field surveys in the present study captured young-of-year muskellunge in four of the five streams sampled. Researchers knew that none of those small fish were hatchery fish stocked the previous year given their small size when captured during the summer and fall. Also, all of the juvenile muskellunge stocked the previous year were tagged with a tiny piece of magnetized wire, detectable with a sophisticated sensor, so there was no doubt that a "small" muskellunge (less than 18 inches long) was a wild fish.

The findings from this small research project, published in 2014, prompted the TWRA last year to end its stocking program (thus, saving money) and let the population sustain itself (thus, earning the cachet of being a wild fishery). At the same time the TWRA also established a 50-inch minimum size limit to conserve and enhance this valuable wild muskellunge fishery.

Fish stocking programs are the bread and butter of many state fisheries agencies given their popularity with the angling public and some biologists are loathe to stop a stocking program once it commences. In the example presented herein, enough scientifically-valid information was collected by CRU scientists to make the biologist's decision an easy one.

The ONB features articles from Cooperative Fish and Wildlife Research Units across the country. Working with key cooperators, including WMI, Units are leading exciting, new fish and wildlife research projects that we believe our readers will appreciate reading about. This article was written by Phil Bettoli, Assistant Unit Leader at the Tennessee Cooperative Fishery Research Unit.