Trade-offs between bycatch and target catches in static versus dynamic fishery closures.

While there have been recent improvements in reducing bycatch in many fisheries, bycatch remains a threat for numerous species around the globe. Static spatial and temporal closures are used in many places as a tool to reduce bycatch. However, their effectiveness in achieving this goal is uncertain, particularly for highly mobile species. We evaluated evidence for the effects of temporal, static, and dynamic area closures on the bycatch and target catch of 15 fisheries around the world. Assuming perfect knowledge of where the catch and bycatch occurs and a closure of 30% of the fishing area, we found that dynamic area closures could reduce bycatch by an average of 57% without sacrificing catch of target species, compared to 16% reductions in bycatch achievable by static closures. The degree of bycatch reduction achievable for a certain quantity of target catch was related to the correlation in space and time between target and bycatch species. If the correlation was high, it was harder to find an area to reduce bycatch without sacrificing catch of target species. If the goal of spatial closures is to reduce bycatch, our results suggest that dynamic management provides substantially better outcomes than classic static marine area closures. The use of dynamic ocean management might be difficult to implement and enforce in many regions. Nevertheless, dynamic approaches will be increasingly valuable as climate change drives species and fisheries into new habitats or extended ranges, altering species-fishery interactions and underscoring the need for more responsive and flexible regulatory mechanisms.

Assessing the population-level conservation effects of marine protected areas.

Marine protected areas (MPAs) cover 3-7% of the world's ocean, and international organizations call for 30% coverage by 2030. Although numerous studies show that MPAs produce conservation benefits inside their borders, many MPAs are also justified on the grounds that they confer conservation benefits to the connected populations that span beyond their borders. A network of MPAs covering roughly 20% of the Channel Islands National Marine Sanctuary was established in 2003, with a goal of providing regional conservation and fishery benefits. We used a spatially explicit bioeconomic simulation model and a Bayesian difference-in-difference regression to examine the conditions under which MPAs can provide population-level conservation benefits inside and outside their borders and to assess evidence of those benefits in the Channel Islands. As of 2017, we estimated that biomass densities of targeted fin-fish had a median value 81% higher (90% credible interval: 23-148) inside the Channel Island MPAs than outside. However, we found no clear effect of these MPAs on mean total biomass densities at the population level: estimated median effect was -7% (90% credible interval: -31 to 23) from 2015 to 2017. Our simulation model showed that effect sizes of MPAs of <30% were likely to be difficult to detect (even when they were present); smaller effect sizes (which are likely to be common) were even harder to detect. Clearly, communicating expectations and uncertainties around MPAs is critical to ensuring that MPAs are effective. We provide a novel assessment of the population-level effects of a large MPA network across many different species of targeted fin-fish, and our results offer guidance for communities charged with monitoring and adapting MPAs.

Las áreas marinas protegidas (AMPs) cubren entre 3-7% de los océanos del planeta y las organizaciones internacionales piden una cobertura del 30% para el 2030. Aunque numerosos estudios muestran que las AMPs producen beneficios de conservación dentro de sus límites, muchas de estas áreas también están justificadas por otorgarles beneficios de conservación a las poblaciones conectadas que abarcan más allá de sus fronteras. Una red de AMPs que cubre aproximadamente el 20% del Santuario Marino Nacional de las Islas del Canal fue establecida en 2003 con el objetivo de proporcionar beneficios para la conservación y las pesquerías regionales. Usamos un modelo de simulación bioeconómica espacialmente explícito y una regresión bayesiana de diferencia-en-diferencia para examinar las condiciones bajo las que las AMPs pueden proporcionar beneficios de conservación a nivel poblacional dentro y fuera de sus límites y para evaluar las evidencias de esos beneficios en las Islas del Canal. Hasta el 2017, estimamos que la densidad de la biomasa de los peces focalizados tuvo un valor medio de 81% (90% intervalo creíble 23-148) dentro de las AMPs de las Islas del Canal que fuera de ellas. Sin embargo, no encontramos un efecto claro de estas AMPs sobre la densidad de biomasa total promedio a nivel poblacional; el efecto medio estimado fue de -7% (90% intervalo creíble -31 - 23) entre 2015 y 2017. Nuestro modelo de simulación mostró que los tamaños del efecto de las AMPs menores al 30% tenían mayor probabilidad de ser difíciles de detectar (incluso cuando estaban presentes); los tamaños de efecto más pequeños (que es probable que sean comunes) fueron incluso más difíciles de detectar. Claramente, es muy importante comunicar las expectativas e incertidumbres en torno a las AMPs para asegurar que éstas sean efectivas. Proporcionamos una evaluación novedosa de los efectos a nivel poblacional de una red extensa de AMPs para muchas especies de peces focalizados y nuestros resultados ofrecen una guía para las comunidades encargadas de monitorear y adaptar las AMPs.

Improved fisheries management could offset many negative effects of climate change.

The world's oceans supply food and livelihood to billions of people, yet species' shifting geographic ranges and changes in productivity arising from climate change are expected to profoundly affect these benefits. We ask how improvements in fishery management can offset the negative consequences of climate change; we find that the answer hinges on the current status of stocks. The poor current status of many stocks combined with potentially maladaptive responses to range shifts could reduce future global fisheries yields and profits even more severely than previous estimates have suggested. However, reforming fisheries in ways that jointly fix current inefficiencies, adapt to fisheries productivity changes, and proactively create effective transboundary institutions could lead to a future with higher profits and yields compared to what is produced today.

Protecting marine mammals, turtles, and birds by rebuilding global fisheries.

Reductions in global fishing pressure are needed to end overfishing of target species and maximize the value of fisheries. We ask whether such reductions would also be sufficient to protect non-target species threatened as bycatch. We compare changes in fishing pressure needed to maximize profits from 4713 target fish stocks-accounting for >75% of global catch-to changes in fishing pressure needed to reverse ongoing declines of 20 marine mammal, sea turtle, and seabird populations threatened as bycatch. We project that maximizing fishery profits would halt or reverse declines of approximately half of these threatened populations. Recovering the other populations would require substantially greater effort reductions or targeting improvements. Improving commercial fishery management could thus yield important collateral benefits for threatened bycatch species globally.

Global fishery prospects under contrasting management regimes.

Data from 4,713 fisheries worldwide, representing 78% of global reported fish catch, are analyzed to estimate the status, trends, and benefits of alternative approaches to recovering depleted fisheries. For each fishery, we estimate current biological status and forecast the impacts of contrasting management regimes on catch, profit, and biomass of fish in the sea. We estimate unique recovery targets and trajectories for each fishery, calculate the year-by-year effects of alternative recovery approaches, and model how alternative institutional reforms affect recovery outcomes. Current status is highly heterogeneous-the median fishery is in poor health (overfished, with further overfishing occurring), although 32% of fisheries are in good biological, although not necessarily economic, condition. Our business-as-usual scenario projects further divergence and continued collapse for many of the world's fisheries. Applying sound management reforms to global fisheries in our dataset could generate annual increases exceeding 16 million metric tons (MMT) in catch, $53 billion in profit, and 619 MMT in biomass relative to business as usual. We also find that, with appropriate reforms, recovery can happen quickly, with the median fishery taking under 10 y to reach recovery targets. Our results show that commonsense reforms to fishery management would dramatically improve overall fish abundance while increasing food security and profits.

Status and solutions for the world's unassessed fisheries.

Recent reports suggest that many well-assessed fisheries in developed countries are moving toward sustainability. We examined whether the same conclusion holds for fisheries lacking formal assessment, which comprise >80% of global catch. We developed a method using species' life-history, catch, and fishery development data to estimate the status of thousands of unassessed fisheries worldwide. We found that small unassessed fisheries are in substantially worse condition than assessed fisheries, but that large unassessed fisheries may be performing nearly as well as their assessed counterparts. Both small and large stocks, however, continue to decline; 64% of unassessed stocks could provide increased sustainable harvest if rebuilt. Our results suggest that global fishery recovery would simultaneously create increases in abundance (56%) and fishery yields (8 to 40%).