St. Marys River

Fishing

Brook Trout

Brook trout are very hardy fish, having the ability to survive floods, drought, and even acidic environmental conditions. Brook trout are also fall spawners and their eggs undergo long winters in the nest. A strong brook trout year class is usually determined by the severity of local climatic conditions during any given winter. Hence, warm, dry winters are beneficial to hatching success and survival of the fry. Strong year classes were documented in the late 1980’s and early 1990’s, and have again shown up in recent years.

Fisheries biologists have been sampling St. Marys with electrofishing gear on an annual basis since 1998 (prior to that, sampling took place every other year). Six permanent stations were established in 1976, and the very same areas are revisited every time St. Marys is sampled. A backpack electrofisher is used to stun fish, where they are immediately netted, placed in water, identified, measured, weighed, and released. Long-term electrofishing data sets create a good picture of fish abundance, health, and distribution in the watershed. Although trout are the target species, non-game fish such as blacknose dace, mottled sculpin, and fantail darter also help scientists evaluate the stream’s overall environmental health.

Brook trout are currently thriving in St. Marys River. Successive strong year classes of brook trout since 1997 made a positive impact on the fishery prior to liming. The lime was introduced at a time when several solid brook trout spawns were being “recruited” into the fishery, hence making environmental conditions more favorable for the growing population. Brook trout in St. Marys River exceeded 1,000 fish per mile in 1999 for the first time in our investigations. Brook trout density soared to over 1,600 fish per mile in 2000 and has dropped to 1,200 per mile in 2001. What kind of size will you find? In 2001, over a quarter of the brookies collected were young-of-the-year (under 4 inches), close to 56% were between 4 and 6 inches, and the remaining 18% were 7 inches and up. Brook trout growth was good, with fish reaching 7 inches in 2.5 years. Most of the brook trout in St. Marys live only 3.5 to 4 years of age. A few brookies will reach 10 inches in this stream, but the majority of quality size fish will be 8 – 9 inches long.

Rainbow Trout

Rainbow trout were last seen in St. Marys River in 1992, when only a few specimens were collected. Wild rainbow trout once provided some great “fast water” angling in the middle reaches of the stream, but have been victimized by poor water quality.

Other Fish Species

Blacknose dace, a common mountain stream minnow, is an important food source for trout, as well as an environmental barometer in St. Marys River. Blacknose dace once thrived in St. Marys River, but their numbers have declined since the 1970’s. They are much less tolerant of low pH water than brook trout, so they make an excellent biological indicator of how well the stream is doing. Blacknose dace densities improved dramatically between 2000 and 2001, and they have expanded their range in the watershed. These are good signs for both the dace and other fish species such as sculpins and darters.

Macroinvertebrates

Macroinvertebrates are simply those creatures that have no backbone and can be seen with the naked eye. In aquatic ecosystems they include insects, mussels, snails, clams, worms, leeches and crayfish. These animals are important players at the lower levels of the food web in aquatic environments. Active sampling or monitoring a stream reach for macroinvertebrates can tell you how healthy your waterway is.

Because of St. Marys River’s low pH, it would make sense that only acid-tolerant macroinvertebrates would thrive in its waters. Data from as far back as the 1930’s show that as many as 32 types of macroinvertebrates inhabited St. Marys River, and many of them were sensitive mayfly species. When macroinvertebrate sampling resumed in earnest in the 1980’s, the number of taxa was reduced by half. Water chemistry, subtly altered over time by changes in air quality, was largely responsible for the decline in macroinvertebrate life.

Taxa richness is one way to look at the big picture. The more families and genera found usually means a healthier environment with diverse habitats. In 2001, St. Marys River averaged 29 taxa throughout the watershed. This has steadily improved through the 1990’s, partially due to a change in sampling techniques and partially as a response to liming. Mayflies, stoneflies, and most caddisflies are sensitive to poor water quality. A measure called the EPT Index examines the diversity of these three groups of insects. Beginning in 1998, the EPT Index began to improve, and, in the post-liming years, it has improved to a record high of 18 (from a low of 7 in 1990).

At the individual level, an acid sensitive mayfly, Epeorus sp., was not found in samples for 2 decades. After liming, Epeorus reappeared in significant numbers. Other mayfly species have also fared well in recent years. The acid tolerate stonefly, Leuctra sp., has also benefited from better pH levels in St. Marys River.

Biologist Reports