Last week, I posted that hooded mergansers, annual visitors from the north, have arrived in our wetlands for the season. They’re busily forming pair-bonds as I write. Over the years I’ve counted as many as 41 mergs at one time floating on our wetland’s water here at the museum. Early in the season it’s not unusual to see larger numbers until the fish-eating diving birds disperse, pairs and small groups choosing their favorite ponds and lakes at which to rest, fish, and display. On a typical fall or winter day there may be from one to perhaps ten mergansers present. Some will stay with us, others will move on.
Besides crustaceans, molluscs, aquatic insects and crayfish, hooded mergansers, smallest of the three North American mergansers, eat fish. Our population of golden shiners, the only fish I’d ever recorded in our wetlands, has disappeared, the only fish species I’d recorded until this summer, that is.
In years past, the raspy rattle of a kingfisher was never far away. I would see or hear a kingfisher daily. Over the past several years our local kingfisher has stopped paying daily visits to the wetlands. No fish, no kingfishers. Like the mergansers, kingfishers will, and do, eat other aquatic life but fish are their main source of protein. They secure these fish by diving head first into the water from a perch or hover.
But don’t fret, I’m once again hearing the kingfisher’s rattle over the wetlands with increased frequency. What’s brought this “punk-haired” bird back? Maybe it’s that other species of fish I’ve been seeing in the wetlands.
Yes, another species of fish has found its way into our wetlands, Gambusia or mosquitofish. Where did they come from? Ellerbe Creek runs through the museum property. But although the wetlands eventually empties into Ellerbe Creek via a culvert pipe several feet above a tributary of the creek, there is no direct connection to our wetlands. There’s no way for a fish to simply swim into the wetlands.
Golden shiners are oviparous, egg laying fish. They could easily hitch a ride into the wetlands via ducks, geese, heron, or even a kingfisher. The sticky eggs, having been deposited in another pond or lake find themselves attached to the legs, feet or feathers of one of those birds and delivered to our wetlands when that bird pays a visit here. Once here, the eggs hatch and voila, there are fish in the wetlands.
Mosquito fish are viviparous, they bare live young. It would be very difficult for a live fish to hitch a ride into the wetlands, they just wouldn’t survive the flight.
Enter, the museum’s summer camp program. This past summer, campers spent an hour or so twice a week in Ellerbe Creek which as I’ve mentioned runs through the museum property. The campers were equipped with nets and buckets, so any frogs, tadpoles, fish or any other living thing in Ellerbe Creek was subject to capture by the campers.
The campers transported their captives back to the “lab” to study. They were then released into the wetlands (Everything but crayfish, that is. I asked them not to release crayfish into the wetlands). Mosquito fish breed throughout the summer. Gestation is about 24 days. There are now many, many mosquitofish in the wetlands.
Golden shiners can reach ten inches. Most specimens found in a typical pond or lake are about 3 – 4 inches. That’s a good size for a heron, merganser or kingfisher to make a meal of.
Mosquitofish are much smaller. The females are about two inches or so, the males barely reaching half that size. Much smaller fare for the birds. It’ll be interesting over the next few months to see if it’s worth the birds’ effort to catch such small prey.
Mosquitofish are native to this area but there are two species. I don’t know if the species we have in our wetland is the native eastern mosquitofish (Gambusia holbrooki) of the southeastern states or the western mosquitofish (Gambusia affinis) of the south-central states. Mosquitofish have been introduced across the country as a mosquito control weapon, they eat mosquito larvae. Records of those introductions are not reliable so it’s difficult in some places to determine what species was originally in a particular water drainage. It probably doesn’t matter which species we have. They’re very similar and were once considered sub-species of Gambusia affinis.
Whether or not mosquitofish are better at controlling the mosquito population than any other species of fish is questionable. They’re now considered invasive in many areas, ostensibly controlling the mosquito population at the expense of the local native fish numbers. Of course, in our wetland, there are no other fish species, that I’m aware of.
When I spotted the first arrivals of the season on October 20, I quickly snapped a photo to document the occasion. Looking at the photo, I notice something in the background. A raccoon walking along the shore had spotted the mergansers and was eyeing them from the bank, no doubt licking its chops.
Never a dull moment.
You may be wondering what happened to the golden shiners that used to occupy the wetlands. Red swamp crayfish would be my reply. Read about them here.