Harvest was a function of the number of yearling brown trout stocked the year before from the early 1970s to 1984.  From 1985 to 1991, however, harvest fluctuated and declined to near zero in some years, despite consistent stocking rates that averaged near 90,000 yearlings per year.

The leading hypothesis for the decline was that predation rates had increased on the stocked trout.  Predation increases were caused by recovery of walleyes and other piscine predators and fish eating birds.

We chose to evaluate three strains of brown trout to determine whether there were differences in post-stocking performance of these strains.  Later in the study we compared shoreline stocking with offshore stocking.  During the course of the study, we learned that alewife abundance was lowest in early spring and increased to peak levels as adult spawners entered Thunder Bay in June.  Thus, the timing of stocking during spring could effect subsequent survival.  For the study period, we stocked all yearling brown trout during the June peak in alewife spawner abundance. Pictured are mature Seeforellen (top) and Plymouth Rock (bottom) strain brown trout at age 2.

Seeforellen strain was significantly heavier at age than Wild Rose at ages 3 and 4, but not at age 2.  Plymouth Rock  strain reached lower average weights at age 2 than the other strains, but sample sizes of age 3+ Plymouth Rock strain were too small to compare with the other strains.

94% of all observed returns were ages 1-3.  Age 4 and older fish made up only 0.9% of the observed catch.  No Plymouth Rock strain older than age 3 were observed.

The comparison of boat and shore stocking methods was done when alewife numbers were low.  Returns from both test groups were low.  There were no significant differences between test groups.

The more successful strains (Wild Rose and Seeforellen) were used in the Boat vs.. Shore study.

Remember, the stocking window was established to capitalize on seasonal abundance of spawning alewives.

Annual abundance of adult alewives was indexed in most years using 1.5 and 2” mesh gillnets.  The catch rate rose from 1990 to 1994, remained relatively high to 1995, but had declined to below the 1990 level by 1998. This trend in alewife abundance parallels annual harvest of brown trout in Thunder Bay, with peak in harvest from 1993-1995, following years of high alewife catch rates.

Great Lakes fish communities have changed since the 1960s when alewives were overabundant and surplus production wind rowed on the beaches.  Now surplus production is pretty well tapped by a variety of predators.

Although population estimates and consumption rates of predators were not measured, incidence of brown trout in fish stomachs was highest in years when alewife numbers were low.  The chief predator fish of stocked brown trout were walleyes, but brown trout were observed in stomachs of several fish species.

As a “last gasp” effort, the MDNR will evaluate the utility of stocking smaller numbers of larger yearlings in the fall by comparing their performance with that of spring yearlings. If this does not work, perhaps it will be time to think of an alternative name for Alpena’s Brown Trout Festival.