© Brian KellyResidents near Little Lagoon in Gulf Shores are dealing with the effects of a large fish kill that occurred this week. Thousands of dead mullet in Gulf Shores can be seen in this photograph taken off of Minnow Lane Thursday, Jan. 11, 2018.
"This is not a new phenomenon," said Kevin Anson, a marine biologist with the ADCNR's Marine Resources Division. "In 2014 there was a small fish kill, in 2011 I think, we had another cold event, and it's been documented going back into the 1960s."
Thousands of fish -- mostly white mullet -- have gone belly-up on the surface of Little Lagoon or washed up on shore this week, leaving behind an ugly scene, a terrible smell, and a feeding frenzy for birds who don't mind dead mullet, even if they're a few days old.
The recent cold temperatures in the area are the most likely culprit, Anson said.
"This event was caused by the cold," he said. "When the cold temperatures come, they can't tolerate it.
The Marine Resources Division received reports of large numbers of dead fish in two separate waves, the first coming last week and the second early this week, he said. Anson said one group of fish appeared to be in more advanced stages of decomposition.
The first die-off likely came from the canals on the east end of Little Lagoon, where Anson said the shallow water might gotten colder faster than in deeper spots.
"Those [deeper] areas, at least on the first night where there may have been some die-offs, were warm enough for those fish to not die, but as you got further along, the water lost heat in those areas and there may have been an additional kill," he said. "That's kind of borne out in those two groups showing two different decomposition rates."
The white mullet is especially vulnerable to cold weather kills because of its size and behavior.
"Part of why it's white mullet is not only the biology relative to temperature tolerance, but it's also that they school and the effects of cold on the fish is that before it dies, it will become disoriented," Anson said. "They can't figure out what their surroundings are, and they may slow down their swimming behavior and start to rest on the bottom.
"It really starts to affect them before it actually kills them. The coldest temperatures occur at night, so they may not be able to see how to get out into deeper water, so they just kind of school, maintain the school and eventually will succumb if the temperatures go cold enough."
© Brian KellyFish kill in Gulf Shores, 1.11.18
"At nighttime in the summer the algae or phytoplankton takes out a lot of oxygen that's in the water," he said. "In wintertime, the algae is not as prevalent and also the water has a higher capacity to hold oxygen in colder temperatures."
The white mullet turning up dead in Gulf Shores are a different species than the striped mullet, which have more of a commercial value. White mullet are smaller, but do provide food for a number of more popular game fish.
"It is a forage fish for a lot of the fish that are popular recreationally
So far, no other fish kills have been reported after the most recent cold snap, Anson said, and the white mullet will likely be back strong when the weather warms up.
"I think it's more of an isolated event, it's not a coast-wide phenomenon where every backwater and tidal creek experienced a mullet kill," Anson said. "There were certainly thousands that were killed in Little Lagoon, but over the whole coastline here, that may make up a very small percentage of the population."
Source: The Birmingham News
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