The authors, Mark Butler, Donald Behringer, and Jason Schratwieser, speculate that these solution holes represent an ecological trap. Older lobsters that find shelter in slurry holes emit chemicals that attract younger lobsters to flock to them. But then the youth will become victims of any group that remains in the same solution hole. In other words, what is normally a signal for safety – a signal that there are plenty of lobsters present – may lure smaller lobsters into what the authors call a “predator death trap.”
Testing the hypothesis involved a lot of underwater surveys. First, the authors identified the solution hole with a resident red grouper. They then found a series of sites that had equal amounts of shelter, but lacked solution holes and the attendant grouper. (The study lacked a control with solution holes, but there were no grouper worth it.) At each site, researchers began daily surveys of the lobsters present, recording how large they were and tagging any that had not been found in any earlier surveys. This helps them keep track of lobster populations over time, as some lobsters may migrate in and out of sites.
To investigate predation, they attached lobsters (both large and small) via tethers, allowing them to occupy sheltered spots on the sea floor, but not leave a given location. And, after solving the lobster population dynamics, researchers caught some groupers and examined their stomach contents. In some cases, this revealed the presence of lobsters that had previously been tagged, allowing them to directly associate the prey with the size of the lobster.
lobster trap
So, what did they find? At sites where groups were present, the average lobster was 32 percent larger than at control sites. This is likely because more than two-thirds of the small lobsters tied at sites with grouper died within 48 hours. The mortality rate at control sites was about 40 percent. This is similar to the mortality rate for large lobsters at the same sites (44 percent) or sites with groupers (48 percent).
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