Interactions Between Jellyfish and Marine Fish and Fisheries

Evidence is accumulating that gelatinous zooplankton populations have increased recently in many regions of the world and are widely considered as indicators of ecosystem health. Jellyfish are generally detrimental to fisheries because they feed on zooplankton and ichthyoplankton, thus are both predators and potential competitors of fish. Jellyfish blooms also impact commercial fisheries directly through filling or clogging trawls and fouling fixed gear and aquaculture net pens, resulting in enormous losses worldwide on an annual basis.   Possible benefits of jellyfish to marine fish include provisioning of food for some species and providing shelter for juvenile stages of several fish species.  There is also a relatively minor human benefit in that jellyfish are commercially fished, mostly in Asia.  However, the negative effects may greatly exceed any positive ones and the effects of jellyfish on ecosystems and the economies that depend on them can be profound.  Given the propensity of fisheries to fish at successively lower trophic levels as top predators are removed (fishing down the food web), there is a potential for fisheries to transition to more gelatinous target species in the future, which may be already occurring in some ecosystems.