Keeping Kelp Healthy: Why Trophy Fishing Should Stop

A study of the massive and beautiful Californian sheephead fish has revealed some startling consequences of fishing, where removing the largest of these creatures from the kelp forests they call home can actually harm the region itself, with the kelp suffering from a decline seemingly born of grief for their captured friends.

Of course, the kelp forests aren't actually grieving the loss of these fish. However, in the absence of overfished sheepheads, kelp forests become increasingly vulnerable to native sea urchins, whose grazing habits can wreak havoc on the sea plants.

The Californian sheephead "is a really iconic species in our local kelp forests and it's fascinating because it's big, it's beautiful and it changes sex," research biologists Jenn Caselle said in a recent statement. "There's a lot going on with this species, and its effect on the kelp forest food web is essential."

Caselle conducted a study of these fish with lead researcher Scott Hamilton, a member of Moss Landing Marine Laboratories, that looked at how changes to a Californian sheephead population can ripple across an ecosystem, impacting the predator-prey relationship of other species.

The results were recently published in the journal Proceedings of the Royal Society B.

According to the study, the fish act a lot like caretakers for the kelp forests that characterize southern California waters. They are primary predators of local sea urchins, eating young ones to ensure kelp grazing stays at a manageable level.

However, this control policy is at least in part reliant on the largest and older of sheepheads to eat the larger urchins. (Scroll to read on...)

Unfortunately, as these fish grow, they can surpass the minimum size limit for a fishery, becoming prime targets for commercial and trophy fishing.

"The main point of our work is not necessarily about fishing reducing abundance; it's about how fishing reduces size structure," Caselle explained. "If you have a species whose predation rate depends on that size, you can have strong trophic effects without even thinking about abundance changes."

The researchers propose that marine reserves raise the minimum size limit to help alleviate overgrazing in kelp forests, allowing the ecosystems to recover.

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