In a study that uniquely evaluates marine ecosystem responses to a changing climate by hemisphere, researchers report that the fish-eating, surface-foraging bird species of the Northern Hemisphere suffered greater breeding productivity stresses over the last half-century than their Southern Hemisphere counterparts. The findings suggest the need for ocean management at hemispheric scales and underscore the importance of long-term seabird monitoring programs - some of which are already under threat - by illustrating the critical role that seabirds play as sentinels of global marine change. To date, global understanding of ocean change has not explicitly considered differences, or asymmetries, in the responses of marine ecosystems in the Northern and Southern Hemispheres to human and climate impacts. Much of what is known is derived from observations of taxon-specific responses from disparate species, limiting the ability to evaluate and compare large-scale marine ecosystems. To address this issue of scale, William Sydeman and colleagues compiled breeding productivity records for 66 seabird species across the globe and between 1964-2018. They revealed varying patterns between Northern and Southern Hemisphere species. According to Sydeman et al., overall, Northern Hemisphere seabirds - particularly piscivorous species - show greater signs of stress and reduced breeding success over time, while southern species show less impact on reproductive success. The authors attribute these patterns to lower fish resources in the north, suggesting that fish populations have been more greatly impacted by human and climate effects in the Northern Hemisphere than in the Southern. Sydeman et al. note that these patterns indicate the need for different ocean management approaches between the hemispheres, with active recovery needed in northern waters and enhanced protection in the south. "The signals provided by seabird breeding productivity could easily be used to assess global change in marine ecosystems on an annual time frame with relatively simple coordination and data sharing of governmental monitoring programs," they write.
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