Marine heatwaves are not a dominant driver of change in demersal fishes.

Marine heatwaves have been linked to negative ecological effects in recent decades1,2. If marine heatwaves regularly induce community reorganization and biomass collapses in fishes, the consequences could be catastrophic for ecosystems, fisheries and human communities3,4. However, the extent to which marine heatwaves have negative impacts on fish biomass or community composition, or even whether their effects can be distinguished from natural and sampling variability, remains unclear. We investigated the effects of 248 sea-bottom heatwaves from 1993 to 2019 on marine fishes by analysing 82,322 hauls (samples) from long-term scientific surveys of continental shelf ecosystems in North America and Europe spanning the subtropics to the Arctic. Here we show that the effects of marine heatwaves on fish biomass were often minimal and could not be distinguished from natural and sampling variability. Furthermore, marine heatwaves were not consistently associated with tropicalization (gain of warm-affiliated species) or deborealization (loss of cold-affiliated species) in these ecosystems. Although steep declines in biomass occasionally occurred after marine heatwaves, these were the exception, not the rule. Against the highly variable backdrop of ocean ecosystems, marine heatwaves have not driven biomass change or community turnover in fish communities that support many of the world's largest and most productive fisheries.

Half a century of rising extinction risk of coral reef sharks and rays.

Sharks and rays are key functional components of coral reef ecosystems, yet many populations of a few species exhibit signs of depletion and local extinctions. The question is whether these declines forewarn of a global extinction crisis. We use IUCN Red List to quantify the status, trajectory, and threats to all coral reef sharks and rays worldwide. Here, we show that nearly two-thirds (59%) of the 134 coral-reef associated shark and ray species are threatened with extinction. Alongside marine mammals, sharks and rays are among the most threatened groups found on coral reefs. Overfishing is the main cause of elevated extinction risk, compounded by climate change and habitat degradation. Risk is greatest for species that are larger-bodied (less resilient and higher trophic level), widely distributed across several national jurisdictions (subject to a patchwork of management), and in nations with greater fishing pressure and weaker governance. Population declines have occurred over more than half a century, with greatest declines prior to 2005. Immediate action through local protections, combined with broad-scale fisheries management and Marine Protected Areas, is required to avoid extinctions and the loss of critical ecosystem function condemning reefs to a loss of shark and ray biodiversity and ecosystem services, limiting livelihoods and food security.

Rebuilding fish biomass for the world's marine ecoregions under climate change.

Rebuilding overexploited marine populations is an important step to achieve the United Nations' Sustainable Development Goal 14-Life Below Water. Mitigating major human pressures is required to achieve rebuilding goals. Climate change is one such key pressure, impacting fish and invertebrate populations by changing their biomass and biogeography. Here, combining projection from a dynamic bioclimate envelope model with published estimates of status of exploited populations from a catch-based analysis, we analyze the effects of different global warming and fishing levels on biomass rebuilding for the exploited species in 226 marine ecoregions of the world. Fifty three percent (121) of the marine ecoregions have significant (at 5% level) relationship between biomass and global warming level. Without climate change and under a target fishing mortality rate relative to the level required for maximum sustainable yield of 0.75, we project biomass rebuilding of 1.7-2.7 times (interquartile range) of current (average 2014-2018) levels across marine ecoregions. When global warming level is at 1.5 and 2.6°C, respectively, such biomass rebuilding drops to 1.4-2.0 and 1.1-1.5 times of current levels, with 10% and 25% of the ecoregions showing no biomass rebuilding, respectively. Marine ecoregions where biomass rebuilding is largely impacted by climate change are in West Africa, the Indo-Pacific, the central and south Pacific, and the Eastern Tropical Pacific. Coastal communities in these ecoregions are highly dependent on fisheries for livelihoods and nutrition security. Lowering the targeted fishing level and keeping global warming below 1.5°C are projected to enable more climate-sensitive ecoregions to rebuild biomass. However, our findings also underscore the need to resolve trade-offs between climate-resilient biomass rebuilding and the high near-term demand for seafood to support the well-being of coastal communities across the tropics.

Persisting Worldwide Seabird-Fishery Competition Despite Seabird Community Decline.

Fisheries transform marine ecosystems and compete with predators [1], but temporal trends in seabird-fishery competition had never been assessed on a worldwide scale. Using catch reconstructions [2] for all fisheries targeting taxa that are also seabird prey, we demonstrated that average annual fishery catch increased from 59 to 65 million metric tons between 1970-1989 and 1990-2010. For the same periods, we estimated that global annual seabird food consumption decreased from 70 to 57 million metric tons. Despite this decrease, we found sustained global seabird-fishery food competition between 1970-1989 and 1990-2010. Enhanced competition was identified in 48% of all areas, notably the Southern Ocean, Asian shelves, Mediterranean Sea, Norwegian Sea, and Californian coast. Fisheries generate severe constraints for seabird populations on a worldwide scale, and those need to be addressed urgently. Indeed, seabirds are the most threatened bird group, with a 70% community-level population decline across 1950-2010 [3].

Far from home: Distance patterns of global fishing fleets.

Postwar growth of industrial fisheries catch to its peak in 1996 was driven by increasing fleet capacity and geographical expansion. An investigation of the latter, using spatially allocated reconstructed catch data to quantify "mean distance to fishing grounds," found global trends to be dominated by the expansion histories of a small number of distant-water fishing countries. While most countries fished largely in local waters, Taiwan, South Korea, Spain, and China rapidly increased their mean distance to fishing grounds by 2000 to 4000 km between 1950 and 2014. Others, including Japan and the former USSR, expanded in the postwar decades but then retrenched from the mid-1970s, as access to other countries' waters became increasingly restricted with the advent of exclusive economic zones formalized in the 1982 United Nations Convention on the Law of the Sea. Since 1950, heavily subsidized fleets have increased the total fished area from 60% to more than 90% of the world's oceans, doubling the average distance traveled from home ports but catching only one-third of the historical amount per kilometer traveled. Catch per unit area has declined by 22% since the mid-1990s, as fleets approach the limits of geographical expansion. Allowing these trends to continue threatens the bioeconomic sustainability of fisheries globally.

Gaining perspective on what we've lost: the reliability of encoded anecdotes in historical ecology.

Historical data are essential in fisheries management and conservation, especially for species that suffered significant population declines prior to ecological data collection. Within the field of historical marine ecology, studies have relied on anecdotal evidence, such as written accounts by explorers and interviews of different generations of resource users, to demonstrate the former abundance of certain species and the extent of their ranges. Yet, do we all agree on how these anecdotes are interpreted? This study examines the way that different people interpret anecdotes extracted from historical narratives. We outsource a survey to 50 randomly selected people using Amazon Mechanical Turk (www.mturk.com) and ask them to 'code' historical anecdotes based on their perceived abundance of species. We perform intercoder reliability tests to show that people's perceptions of historical anecdotes are generally consistent. The results speak to the reliability of using people's perceptions to acquire quantitative data, and provide novel insights into the use of anecdotal evidence to inform historical ecology.

Historical ecology of the Raja Ampat Archipelago, Papua Province, Indonesia.

This work presents a review of the status of marine resources of the Raja Ampat Archipelago, Papua Province, Indonesia, based on narratives of early European expeditions in various museums and libraries in Europe, Canada, and local archives in Papua. More than 500 pertinent documents on the study area were identified and located in various European museums and at the University of British Columbia library. About half of these were scanned (25,000 pages), which yielded the equivalent of 900 pages of text (or 4% of the total number of pages scanned) with observations on abundance and impact of the human population on the marine ecosystem within 2 degrees North and 2 degrees South between 127 degrees and 132 degrees East. In general, these observations, which spanned the period from 1810 to the present, suggest a decrease in the perceived occurrences of turtles, fish, and invertebrates; perceived abundance of turtles, fish, and algae; percieved subsistence exploitation of marine resources; and an increase in perceived commercial exploitation of marine resources. We conclude with a discussion of the problems and potential of contents analysis, and its use in the historical reconstruction of broad biodiversity trends.