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Ensuring the long-term sustainability of tuna, billfish, and other transboundary fisheries resources begins with data on the status of stocks, as well as information concerning who catches what fish, when, where, and how. Despite recent improvements in fisheries monitoring and surveillance, such dynamics remain poorly understood across the high seas. Here we delineate and describe pelagic longline activity in the Pacific Ocean using a framework that integrates descriptive vessel information and tracking data with species-specific catch reports. When parsed by distinct vessel behaviors and attributes, disaggregated fisheries data highlight the existence of multi-national, multi-specific (i.e., targeting multiple species) fishing fleets, many of which target waters that span more than one management area. Our findings emphasize the need for increased coordination across regional and sub-regional governance bodies and suggest that effective and equitable management of the sector may require efforts to move beyond single-species, single-area controls and operational distinctions based primarily on vessel flag and/or gear type alone.

Marine heatwaves (MHWs)—periods of exceptionally warm ocean temperature lasting weeks to years—are now widely recognized for their capacity to disrupt marine ecosystems1–3. The substantial ecological and socioeconomic impacts of these extreme events present significant challenges to marine resource managers4–7, who would benefit from forewarning of MHWs to facilitate proactive decision-making8–11. However, despite extensive research into the physical drivers of MHWs11,12, there has been no comprehensive global assessment of our ability to predict these events. Here we use a large multimodel ensemble of global climate forecasts13,14to develop and assess MHW forecasts that cover the world’s oceans with lead times of up to a year. Using 30 years of retrospective forecasts, we show that the onset, intensity and duration of MHWs are often predictable, with skilful forecasts possible from 1 to 12 months in advance depending on region, season and the state of large-scale climate modes, such as the El Niño/Southern Oscillation. We discuss considerations for setting decision thresholds based on the probability that a MHW will occur, empowering stakeholders to take appropriate actions based on their risk profile. These results highlight the potential for operational MHW forecasts, analogous to forecasts of extreme weather phenomena, to promote climate resilience in global marine ecosystems.

The episodic stranding of millions of pelagic red crabs (Pleuroncodes planipes) along California beaches is a striking and puzzling phenomenon. Pleuroncodes planipesare usually abundant off Baja California, Mexico, and their appearance in central California is thought to coincide with anomalously warm waters and northward advection related to El Niño. This anecdotal association has stimulated many hypotheses, but no hypothesis has gained clear and convincing support. Motivated by an unprecedented number of P. planipesstrandings and at‐sea observations in 2015–2019, we compiled 10 P. planipesdatasets spanning 1950–2019, tested the anomalous advection hypothesis using a transport analysis from 1981 to 2010, and explored other compelling hypotheses. We found P. planipespresence off central California was related to anomalous advection of waters from Mexico, sometimes but not always associated with El Niño events, with P. planipeslikely remaining residents of northern waters for several years without additional anomalous transport but potentially facilitated by warm waters. By identifying a mechanism behind episodic P. planipesrange expansions, we show that a source water index could provide an early indicator for anomalous events in the future.