Managing the trade-off between food production and biodiversity is a major part of conservation and sustainability—crops and pasture have long replaced wilderness as the dominant landscape on Earth—managers need to find solutions that feed everyone while minimizing environmental impact. Fisheries are no different. Scientists and managers need to find the right balance between seafood harvest and biodiversity impacts like bycatch.
A paper out this month entitled, The trade-off between biodiversity and sustainable fish harvest with area-based management (open access), shows how regulating fishing effort by area and gear can produce a win-win solution for food production and biodiversity.
The authors used two case studies to see how closing specific areas to particular kinds of fishing changed harvest and biodiversity. They calculated the equilibrium abundance of the targeted fish and non-target species of concern (birds, mammals, corals & sponges, etc.), then adjusted fishing effort by gear type and area to find the most beneficial results.
They found that the trade-off between fishery production and biodiversity is not linear, but convex, meaning win-win compromises exist in the middle. For example, biodiversity is maximized when no fishing is allowed, but a significant amount of fishing can result in only a small biodiversity loss (with the right area management in place).
Area and gear management in Alaska
The researchers used species data from Alaska to build their model. They examined how fishing for pollock, cod, sole, halibut, and crabs impacted the bycatch of corals, sponges, and albatross in different areas of Alaska.
Their results show how the biodiversity/food production trade-off changes under different fishing regulations. When fishing effort is set to maximize sustainable yield of target species corals, sponges, and albatross are severely depleted. When just a small weight is placed on biodiversity, trawling is closed in the Aleutian islands to protect the corals and sponges. Moving the biodiversity weight to 10% closes longlining in the Aleutian islands, which has some impact on corals and sponges, but not as much as bottom trawling. Closing trawling and longlining in the Aleutian islands protects two-thirds of the benthic corals and sponges in Alaska (the rest are in the Bering Sea). Moving biodiversity to 30% closes longlining in the Bering Sea to protect albatross. The next big jump occurs when trawling in the Bearing Sea is closed so coral and sponge biodiversity increases. No-take MPAs that ban all fishing start to appear when biodiversity is weighted over 90%.
Maximizing biodiversity and fishing revenue
Using well-designed area based management that ban certain types of fishing, e.g. bottom trawling where there are corals and longlining where there are albatross, the model’s win-win keeps 87% of fishing profit while protecting 77% of biodiversity.
Researchers also reported a model of California fishing that showed a similar convex relationship. In California, banning most bottom trawling and closing fishing in areas where sea birds nest moves biodiversity from 20% to 75% with almost no loss of fishing revenue.
Ray Hilborn, one of the lead authors on the study (and founder of this website), said: “Our paper shows that it is possible, or even quite easy, to maintain high levels of biodiversity without sacrificing much food production or fishing profit. The key is stopping fishing practices that impact biodiversity in areas of high biodiversity importance, for example, bottom trawling where there are high densities of corals and sponges.”
The paper goes on to critique the global effort to ban fishing in 30% of the ocean saying that a more nuanced approach, using well-designed, science-based gear restrictions would be a more effective approach: