When a new species appears in the Gulf of Mexico, it can cause concern and raise a lot of questions. Which habitat does it prefer? What will it eat? What will eat it?
One of these species of concern is the invasive tiger shrimp (Penaeus monodon), a very large shrimp that is native to Indo-Pacific, Asian and Australian waters. Jennifer Hill, an assistant professor at Louisiana Tech University, has been working to determine which type of habitat tiger shrimp prefer in the Gulf and how they might affect native shrimp populations. She is studying whether tiger shrimp will compete with native populations for food, if native shrimp are likely to become their prey and if existing Gulf predators will eat tiger shrimp.
“In general, tiger shrimp definitely don’t prefer saltmarsh habitats,” Hill said.
Adult tiger shrimp are unable to navigate through marsh grasses because of their large body size, so they prefer open habitats. Although Hill still has data to analyze, she said it looks like adult tiger shrimp may show some preference for seagrass habitats.
Native shrimp species tend to move to more structured habitats when tiger shrimp are present to try to avoid them.
“Tiger shrimp chase native shrimp,” she said. “They try to eat them. But, generally, what we find is they kinda suck at catching them.”
Native shrimp as prey?
In predation experiments, Hill has found that adult native shrimp survive 80-90 percent of tiger shrimp attempts to eat them.
“They don’t eat our native shrimp, which was one of the fears,” Hill said. “But they do try to eat them, and that results in shrimp just trying to avoid interacting with them. Obviously, no one wants to be chased around a tank and be dinner.”
The fact that native shrimp may go to structured habitats to avoid tiger shrimp could cause a higher rate of mortality for tiger shrimp when a predator is around. It could also mean that native shrimp may stay safer in more protected areas.
Tiger shrimp as prey
In the Mississippi-Alabama Sea Grant-funded project, Hill is also working to determine if the Gulf’s native predators will eat tiger shrimp. It’s a concern because tiger shrimp are very large and have different coloration from native shrimp.
It’s possible they won’t be perceived as a food source for some native predators.
Predators can be just like humans, Hill said. Some can’t wait to try new foods; others can be more traditional and have no interest in trying something new.
In pilot studies, she has found that red drum are willing and able to eat tiger shrimp relative to large white shrimp.
Because the tiger shrimp were so big (about 8-10 inches in this experiment), red drum (about 23-24 inches in the study) had to attack them before consuming them.
“The biggest problem for red drum is going to be size,” Hill said. “It’s going to have to be a decent-sized red drum (about 23.5 inches or larger) to eat some of those larger tiger shrimp.”
During 2014, the first year of the project, the tiger shrimp population in the Gulf was low, likely because of a very cold winter. They also didn’t show up in Dauphin Island Sea Lab educational trawls as they had before. Hill was expecting to use some tiger shrimp captured during educational programs for her experiments.
Paying a bounty for live tiger shrimp has been the most effective way to capture them for the study.
“It worked brilliantly,” Hill said. “Of course, we were offering $50 a shrimp, which was enough to get shrimpers’ attention.”
In 2015, the bounty spurred the collection of 50 tiger shrimp in less than a month. Because the past winter was mild, Hill expects tiger shrimp to be more abundant this season. She already received her first call of a tiger shrimp in June. It was the earliest call she has received.
If you catch a live tiger shrimp, call the Heck Lab at Dauphin Island Sea Lab at 251-861-2141 ext. 2179 so they can potentially pick up your tiger shrimp. Professor Kenneth Heck at the Dauphin Island Sea Lab is also working on the project.