How do fish end up in isolated bodies of water when they can’t swim there themselves? For centuries, researchers have assumed that water birds transfer fish eggs into these waters — however, a systematic literature review by researchers at the University of Basel has shown that there is no evidence of this to date.
To objectively measure the lack of evidence, the Basel research team conducted a systematic literature review. The result shows that no in-depth scientific studies exist to prove that water birds disperse fish eggs.
To rule out the possibility that the unsuccessful search was due to their method, the researchers also used the same approach to look for evidence of the dispersal of aquatic invertebrates. In this case, they found numerous scientific publications supported by experiments and field studies.
For their study, the Basel researchers also reviewed online forums and surveyed around 40 experts from research, private institutions, and enviromental NGOs. Their aim was to determine the prevalence of the theory of fish dispersal by water birds both inside and outside the research community. The majority of experts that took part in the survey found the theory so plausible that they deemed the mystery to have been solved. However, none of them could draw on any empirical evidence.
“The lack of evidence does not mean that water birds are not responsible for the dispersal,” says Dr. Philipp E. Hirsch from the University of Basel. “But we simply do not yet know what roles are played by birds, humans and other processes.” Paper. (paywall) – Philipp Emanuel Hirsch, Anouk N’Guyen, Roxane Muller, Irene Adrian-Kalchhauser, Patricia Burkhardt-Holm. Colonizing Islands of water on dry land-on the passive dispersal of fish eggs by birds. Fish and Fisheries, 2018; DOI: 10.1111/faf.12270 More.
The researchers here deserve a lot of credit for just admitting that we don’t know how the fish get there. But in their field, there isn’t anything like canned Darwinblather they can just insert in order to imply that we do know. Just by admitting that we don’t know, we might find out faster. There won’t be a lot of intellectual substances like Darwinblather that must first be cleared away.
See also: Biogeography: Monkeys sailed the ocean blue?