More mahimahi may end up on your plate than ahi if the forecast made in a recent study holds true.

Longline fishermen are reducing the amount of bigeye tuna, marlin and other large fish in the Pacific, according to a paper by NOAA scientists Jeffrey Polovina and Phoebe Woodworth-Jefcoats.

But as those populations are declining, the number of smaller fish is rising. The amount of mahimahi, for instance, is increasing 7 percent a year as ahi numbers drop 2 percent annually.

The longliners put 30 million hooks in the water last year, three times more than they did 15 years ago. The increased fishing pressure, combined with other impacts such as climate change, is changing the face of the Pacific, according to the study.

“We’re not crying that things are going to go over the cliff,” Polovina said. “It’s more of a concern that it’s a potential and that management should look at a broad ecosystem approach.”

Polovina posed the question to the Western Pacific Regional Fishery Management Council at its most recent meeting. The council is one of eight that Congress created to prevent overfishing, minimize bycatch and protect fish stocks and habitat.

The council, which invited Polovina to present his findings June 28, didn’t make any specific recommendations at the time. But the members may consider a working group to explore the matter, according to Paul Dalzell, a senior Wespac scientist.

There are already some measures, such as quota limits, that have been in place for years to prevent overfishing of tuna and other targeted species. And the council, in 2005, started to incrementally implement a plan that takes an ecosystem approach to fisheries management in the Hawaiian archipelago.

But Polovina and other scientists continue to question whether enough is being done to ensure that current fishing levels are sustainable, not just for the economically viable species but the entire ecosystem.

In longline fishing, fishermen cast really long lines off the back of the boat, sometimes miles in length, with hundreds of baited hooks set at intervals along the lines. The lines are set at different depths to target different types of fish, but plenty of other fish and sea creatures are caught in the process.

Longliners are catching more lancetfish and other species with no commercial value, Polovina said, leading to more discarded fish. The bycatch rate rose to 40 percent in 2011, up from 30 percent in 1996.

But a lot of unknowns remain, Polovina said. The sampling is hardly comprehensive, so there could be benefits such as more squid or better recruitment for juvenile ahi.

A primary concern is whether the Pacific continues to produce the “goods and services” that people want, Polovina said. And removing pretty much everything at the top level is going to impact things further down the food web.

Dalzell said he expects the study to be discussed at upcoming meetings of the council’s scientific steering committee. But he said Wespac’s ability to address the issue is limited.

The vast majority of longline fishermen are outside Wespac’s jurisdiction. The Hawaii longliners comprise just 2 percent of longline fishing done in the Pacific, he said, with many fleets coming from Japan and other countries.

Global climate change and weather variations that impact fishing are also beyond the council’s control, Dalzell said.

Aside from that, the council is really more focused on the “charismatic megafauna,” he said. Wespac, due to lawsuits filed by environmental groups, has to reduce the number of sharks, turtles, dolphins and seabirds that fishermen accidentally kill.

“The biggest challenge to management is developing static responses to very dynamic ecological and human environments,” Dalzell said.

It takes about two years to get a management change in place, he said, and the danger is by that time the problem may have changed.

The bottom line for Dalzell is that the public can’t expect to have something for nothing.

“People fail to appreciate that fishing kills fish,” Dalzell said. “If you want fish, there’s going to be a cost. There’s always tradeoffs when you’re going to be exploiting part of the ecosystem.”

But it’s not all gloomy, he said, noting the study’s projected increase in mahimahi and other valuable species.

“Will there be more mahi in the water? Quite possibly,” Dalzell said. “Will it mean more mahi in the markets? That depends on economics.”

Read Polovina and Woodworth-Jefcoats’ study here: