In Southern California the inherent tension between conservation and fisheries is evident in the trade-off between the need to protect endangered sea turtles from getting caught in fishing nets and the importance of commercial swordfish as a source of income and livelihood for California fishers.
This month the National Oceanic and Atmospheric Administration once again used a novel management approach to mitigate the trade-off — dynamic ocean management. The approach uses boundaries that are flexible in space and time to manage mobile species and dynamic human activities such as fishing.
The approach is especially needed off the coast of Southern California, where drift gill nets target swordfish using milelong sheets of mesh that hang vertically in the ocean. But the nets can also accidentally snare bycatch species, including sharks, dolphins, whales, sea turtles and sea lions. Of these, the bycatch of loggerhead turtles is an acute problem because not that many are left.
Over the last half-century the North Pacific population of loggerheads has declined an estimated 50% to 90%.
Over the last half-century the North Pacific population of loggerheads has declined an estimated 50% to 90%, although more recently the population appears to be stable or increasing. To protect the remaining population, the turtles are listed under the Endangered Species Act. Catching protected species threatens the sustainability of the fishery and the livelihoods of the fishermen.
However, avoiding the bycatch of highly mobile species like loggerheads is not straightforward.
Loggerheads from the North Pacific population are remarkable ocean wanderers. Born in Japan, young loggerheads leave the beach of their birth for the open ocean of the Pacific. The turtles must brave ocean predators, starvation and crippling cold before reaching California’s productive waters. Decades later, adult loggerheads journey back to the beach where they were born to reproduce.
Conventionally, fisheries bycatch is dealt with by using permanent or seasonal closures. Permanent closures effectively protect species that are fixed in one place, such as deep-sea corals. Seasonal closures are used when bycatch occurs during the same period each year, such as when a migratory species interacts with a fishery.
But loggerheads are neither fixed in one place nor inadvertently caught during a specific season. They are highly mobile and only rarely and sporadically interact with the fishery, meaning that permanent or seasonal closures would have no effect on bycatch reduction most of the time. Such conventional closures offer few benefits to the turtles while incurring substantial opportunity costs to fishers.
Dynamic ocean management is a novel solution for reducing loggerhead bycatch. Dynamic strategies use real-time data on ocean conditions such as temperature, currents and wind, to forecast where marine species are likely to be. These forecasts allow closures to be enacted where and when they can most benefit biodiversity. And just as important, dynamic ocean management ends closures when species aren’t present, which helps the fishers avoid unnecessary opportunity costs.
By analyzing historical data on bycatch events, scientists have learned that the loggerheads are most likely to interact with California’s drift gill net fishery when ocean temperatures are warmer than normal. NOAA uses this relationship between turtles and temperature to guide the timing of the Loggerhead Conservation Area off the coast of Southern California.
When an El Niño weather pattern is occurring or forecast to occur, or when local ocean temperatures are warmer than normal, the Loggerhead Conservation Area is activated to prevent loggerhead bycatch by prohibiting fishing within its boundaries. This was the equation when the NOAA reviewed data last month and called for the conservation area to go into effect from June 1 to Aug. 31, unless changing ocean conditions indicate bycatch is no longer likely.
Since the Loggerhead Conservation Area was mandated in 2003, it has been closed three times for a grand total of seven months. This is the fourth closure. And since 2003, only one loggerhead has been reported caught in the fishery and was released alive.
The Loggerhead Conservation Area has been able to maximize benefits to turtles while minimizing the negative impacts to fishers caused by missed fishing opportunities.
Although only a few applied examples of dynamic ocean management exist, it’s gaining traction. Locations as diverse as Hawaii, Alaska and Australia use dynamic ocean management to prevent bycatch in their fisheries. In our climatically uncertain future, dynamic ocean management may be increasingly necessary.
Increasing global temperatures and marine heat waves have already begun to alter ocean conditions, leading marine species to travel beyond their normal ranges and to have new interactions with fisheries. By design, dynamic strategies are able to prevent these new bycatch threats by responding to the changing environment. It’s an approach tailor-made for our times.
Heather Welch is a research associate with the National Oceanic and Atmospheric Administration and UC Santa Cruz.