Cornelius’ Corner: “Fish Are Friends, Not Food!”

Silt plumes in the Lower Pond

Greetings friends,

It been a busy few weeks in the park, so heads’ up – this blog is a long one! As many of you know already, my coworkers have been working very hard to repair damage caused by heavy siltation coming from upstream in Concord Creek. In 2016, PennDOT started a major project to widen and realign that roadway where it runs through the headwaters of Concord Creek. The project involved a lot of earth-moving and had very poor silt controls, so a lot of fine soil particles ended up entering the creek and moving downstream into the park. Once they hit the mill dam, the silt plumes moved down the millrace and from there entered the Frog Pond and Trout Ponds, where they smothered the gravel substrate, aquatic vegetation, and all of the food and shelter resources that our aquatic wildlife rely on.

Staff and volunteers recover wildlife as the Frog Pond drains

Obviously, the silt had a major impact on the park – the Frog Pond got very shallow and went from a leafy bottom to a muddy bottom. It was such a drastic difference that my coworkers saw a complete change in the dragonfly species laying their eggs in the pond! The Trout Ponds also got silted in, which unfortunately meant that they became too shallow and warm to stock trout in anymore. This had the effect of closing down the trout fishing program that had been in operation since the 1960s, and made my coworkers and the surrounding community very sad. On the history side of things, the millrace got so full of silt that we couldn’t get enough water into the Mill to power the water wheel!

To help fix all the damage, my coworkers worked with many different experts over several years to build a plan that would not only restore the millrace, Frog Pond, and Trout Ponds to their pre-siltation conditions, but to make them even better! As part of that process, the Frog Pond had to be drained in order to get the silt dry enough to be scooped out by heavy equipment. Don’t worry though – park staff and volunteers spent a whole day recovering pond animals as the water went down! In total, they collected over 400 tadpoles, over 250 sunfish of multiple species, numerous minnows, an American eel, and several bass, as well as uncounted numbers of dragonfly nymphs, crayfish, isopods, and other aquatic invertebrates. The adult frogs and turtles pretty much took care of themselves and relocated as the water receded.

Large shiner during recovery

The animals that were collected were all moved to other locations elsewhere in the park, where they are spending the few weeks in safe habitats before the pond can be refilled again. Once the refilled pond has settled and stabilized, the animals will be moved back to the pond so you can visit them again on a future trip!

The one exception to the animals returning to the pond are a few fish and other species, which have been moved to the new fish tank in the front room of the Visitor Center. As my new neighbors, their job is to show off what underwater life is like in the park and to introduce visitors to species they may not otherwise get to meet. So now that we’ve gotten through the details, let me introduce you to my new neighbors!

First up are the tessellated darters. These little fish are slender, with flat bellies and two prominent dorsal fins. They spend most of their time exploring the bottom of the tank, so their speckled brown-green-tan coloration is perfect for blending in with the rocks and gravel. They get the name “darter” from their rapid darting movements while they are hunting for food like small crustaceans, snails, and insect larvae. My coworkers love them because they help keep the mosquito population under control by eating all the mosquito larvae!

Sunfish and chub in the new Visitor Center tank

Also in the tank is a golden shiner. My coworkers were very excited to find this fish because they had never been seen in the park before, even with two formal fish species surveys and countless pond and stream-based programs. They must be very fast swimmers to avoid all of those nets over the years! The shiner is in the minnow family, but has a flatter body than many minnow species in addition to the gorgeous shimmery scales that give them their name. They prefer clear water with lots of aquatic vegetation, so it is no wonder that they like the frog pond the best. They are omnivores that eat algae and insects, but only very small ones because of how small their mouths are. Golden shiners are frequently used as bait by fishermen looking for larger catches, so my coworkers wonder if the shiners in the park are somebody’s escaped bait.

Next, we have the creek chub. They may be little now, but these are one of the biggest minnow species in our area. The males can reach up to 12 inches long! While there are many pale brown minnows with dark stripes on their sides, the chub are best identified by the black spot in front of their dorsal fin and the one by their tail. This species is common throughout the eastern United States pretty much anywhere east of the Rocky Mountains. They have a very important ecological role, in that they are a favorite food for many larger predators. Here in the park, they are hunted by trout, bass, kingfishers, and snapping turtles among others. They nest in little dug-out gravel pits that they make by shoving larger gravel out of the way. Once they have the nest build, other species of fish (like the shiners) will use the gravel pits to lay their eggs too!

Mussel and darter in the new Visitor Center tank

We also have a juvenile redbreast sunfish, which is the most common species of sunfish we see in the park! This species grows very slowly compared to other sunfish like bluegill and pumpkinseeds, but they can reach about 6 inches in 2-3 years. They have the most varied diet of all the park’s sunfish, as they forage for bottom-dwelling insects, larvae, snails, crayfish and other small organisms. They like pools with woody debris, so my coworkers designed the tank to include branches for them to hang out in.

Last but not least are the invertebrates! We have one Eastern elliptio freshwater mussel in the tank whose job it is to keep the water clean. Because it is a filter feeder, it sucks up water and filters out algae, microorganisms, and nutrients like fish poop. It can filter up to 10 gallons of water per day, which means that our fish friends will have a lovely clean home. (You can read more about our freshwater mussels in my blog from August 2022!) The other invertebrates living in the tank are freshwater snails. They love to eat algae, so they help keep the glass clear for visitors to see through. Luckily, the darters love to eat snail eggs, so we won’t get overrun!

Cornelius watches the fish in their new home

Thanks for sticking with me through such a long post, and be sure to stop by the front room of the Visitor Center to welcome my new friends to the neighborhood. Of course, when you do, make sure you say hi to your friendly neighborhood corn snake! (I’ll be the one in the log, staring across the room at all of the aquatic entertainment!)

Happy fall!

– Cornelius