We can’t tell you how saddened we are to report that the impoundment is again gasping for breath this morning. The pump was removed last week, and evidently the dissolved oxygen levels have been declining. Birds began to gather at “the corner,” and small menhaden began to float on the surface. Today we woke to a cacophony of bird sounds and the smell of rotting fish. The damage seems unavoidable and systemic– the mullet are swimming with their heads out of the water, flounder float belly up in multiple locations, high tide isn’t for hours, and even the crabs have decided to get as far out of the water as possible.
Observers on the dock are disheartened– as one said, “the only dead flounder I ever want to see is one on ice in my cooler.” We agree wholeheartedly, and wish there were something we could do the stave off a major event. A short slideshow is below.
When the island staff arrived on the island this morning, the water surface looked like it was being pelted by raindrops. The fish were mouthing the water, trying to get some oxygen. Some fish had already started dying.
The staff set out on an action plan to try to avert a major fish kill:
Setup the island’s 3 inch pump at the crabbing dock. Pull water out of the impoundment and pump it right back in. The pumping action oxygenates the water.
Use the island fire truck to circulate water from the impoundment at the dry fire hydrant closest to the Landings Building. The fire department found that the dry fire hydrant is clogged. So they’re pulling water with a siphon hose.
Rent a 6 inch diesel pump for a week to circulate water. The diesel pump is scheduled to arrive this afternoon.
These actions seem to have halted the fish kill, at least for this morning. The fish have stopped mouthing the air.
In the long run, the island may find it cheaper to come up with alternative solutions for preventing fish kills. In recent years, the rice truck has failed many times due to rot. Rebuilding the rice truck with concrete under the waterline (or some material that won’t rot) so the Environmental Director can manage the impoundment would help. The rebuilt rice truck could look just like it does today above the waterline.
The island might also want to consider more bubblers, perminant pumps, and other methods of maintaining the oxygen level in the impoundment during very hot weather. Several committees and engineers have examined the problem over the years.
Several other barrier island are reporting fish kills in their impoundments this year. It’s a common problem. But one that we should try to solve.
The short answer is that there are menhaden dying, and only time will tell if the current fish kill will be major or minor. While it can be amazing for birdwatching, it isn’t the most optimal situation for the impoundment or the fish in it. We talked with Lori Sheridan Wilson, Dewees Ecologist, to see what is happening and why.
Why fish kills happen: The dissolved oxygen decreases to the point that fish can no longer survive. Menhaden are the canaries in the coal mine; they are the first to go when the O2 drops. As the water heats up, it can only support so much dissolved ogygen, which decreases as the temperature rises. In addition, the hot, dry summer has increased the salinity as well. Once the menhaden die, the decomposition process also uses oxygen, which decreases the available O2 for everyone. In tidal waters, the inflow and outflow of tides allows the fish to find water they are comfortable in. But an impounded wetland is an inexact science. Many impounded wetlands in South Carolina are experiencing fish kills this summer.
Does rain help? Sometimes. Monday night we had a sudden storm which dumped a lot of cold water into the impoundment. Theoretically this should help all the variables– dissolved O2, temperature, and salinity. But when it is a sudden downpour, things may go awry. In this case, there were layers of basically dead water in the impoundment. The water, devoid of usable oxygen, was isolated into dead zones, usually at the bottom of the impoundment. When the sudden downpour resulted in an influx of cold water, it sank to the bottom, mixing the oxygenated water with the dead water, decreasing the average dissolved oxygen in the water. A slow steady rain (like we had last night) is better for gently raising the O2 levels and lowering both temperature and salinity.
How do we try to fix the problem? Last year, when we know the dissolved O2 had reached critical levels, we basically drained the impoundment and the incoming tide flushed fresh water in. (For more on last year’s episode, click the links at the end of this post) This year, the rice trunk has had a problem keeping the water in. (Despite last week’s repairs, a new leak has resulted from a new rotten board. Lori has engaged divers to check it out and possibly fix the problem.) While we could let more water out, the future tides for the next few days won’t be high enough to flood the impoundment with lots of water, so we could exacerbate the problem even further. So the current strategy is to keep trying to get fresh water in, keep monitoring dissolved O2 levels, and try to remove the already dead fish, so they don’t consume oxygen as they decompose.
So yesterday, we watched/helped Lori and intern Lisa as they scooped buckets of dead menhaden out of the impoundment.
Menhaden make great crabbing bait– we bagged a bunch of relatively fresh ones and stored them for bait in the intern’s freezer. In addition, there is a pump at the drab dock again to improve circulation there.
We know that last year, at this point, there were lots of dying mullet, swimming on their sides to catch some air, breathing with distress. Larger flounders and red drum were gasping at the edges of the impoundment. This year, we haven’t seen distress in the larger fish yet, and the rain/cooler temps/ oxygenation should help the situation. We’ll update with more information when we have it.
Mark your calendars. Judy Fairchild just spotted a pair of roseate spoonbills in the Dewees Impoundment in front of lot 74. I said, “no way, it’s too early.” But then verified the sighting with my own eyes (and a good set of binoculars).
During the POA Annual Meeting, Lori Sheridan Wilson, the Environmental Program Director, presented a number of interesting facts and updates. We plan to make several blog posts reiterating the data for anyone who wasn’t able to attend the meeting. Our posts won’t cover everything Lori said, but they will hit some of the highlights.
“The Fish Kill of 2009” seems to be over. The water levels are low, but within the normal range. The water level should rise with the higher tides that are expected. There is the odor of rotting fish, but it’s not intense. People are fishing, crabbing and shrimping from the crabbing dock again.
3 or 4 Thousand menhaden, a few flounder, and a few other large fish died in the fish kill. Nick, the environmental intern, pulled 5 tubs of dead fish, almost entirely menhaden, out of the impoundment. The staff then buried the fish.
The number of birds in the impoundment is higher and more diverse than usual. A couple black vultures are having a grand time. They’ve taken up a post in the live oaks between lot 128 and The Landings Building. There are many more gulls in the impoundment than typical. Together with the woodstorks, egrets, spoonbills, bitterns, terns, and alligators, the vultures and gulls are efficiently cleaning up the dead fish that Nick couldn’t reach.
Many thanks to the staff for all their efforts to contain and minimize the fish kill this year.