Worldwide over 600 million people depend directly or indirectly on fisheries and aquaculture for their livelihoods. Fish provide essential nutrition for over 4 billion people and at least 50 percent of animal protein and essential minerals to 400 million people in the poorest countries. In addition to the pressure exerted by human activities, such as over-fishing, habitat degradation and pollution, both fisheries and ecosystems are exposed to threats related to climate change. It is known that climate change is part of Earth's geological history, but that is not all. In the last 150 years we have been observing a rapid warming of the atmosphere, intensified in the last decades and attributed to the increase in the emissions of greenhouse gases, mainly carbon dioxide from human activities.
Climate variability and change are already affecting aquatic systems physical, chemical, and biological processes. On the coastal zones for instance it is observed increasing levels of the sea. Climate change can also lead to a number of other impacts, such as intensification of storms, changes in freshwater precipitation and freshwater inputs, increased saltwater intrusion into the soils and coastal aquifers, ocean acidification, and profound changes in the force, direction and behavior of marine currents. Such alterations are expected to be already affecting fish life cycles, habitats, species compositions, distributions, and abundance, which can impact fisheries management, livelihoods, food security and sustainable development.
The potential effects of climate change on fisheries can be divided between those that will affect the fishing activity itself and those that will affect the biological and ecological dynamics of the fishery resources. In the first group, sea level rise and the increase in the frequency and intensity of the storms are highlighted, mainly for the artisanal fishery, because the climatic conditions are a limiting factor of the fishing activity. In the case of fishery resources, the main expected biological effects refer to changes in breeding or migration periods of the species; increased occurrence of diseases; changes in latitudinal and depth distribution patterns of species; changes in population size and community composition; and changes in inter- and intraspecific relations, such as competition and predation.
Brazilian fishermen already notice these changes. A study published in 2016 reports that in several Brazilian states (AL, SE, BA, CE, PI, RN, PA and AM) fishermen have observed increased tidal and river levels and the drying up of rivers, lagoons and reservoirs. Changing water regimes is detrimental to species cycles and causes failures in the species food chain and fish production. In the states of Piauí and Sergipe, the migration of marine species to the rivers has been identified. At the same time, the mortality of river fish is observed due to the increase in the quantity of salt water in the estuary. There has been a recurrent complaint that the winds have changed their incidence and intensity, and that more extreme events are now common. There is a higher number of registries of accidents with vessels, mainly in Ceará, Pernambuco, Pará, Espírito Santo, and Rio Grande do Norte, due to sudden changes of the winds and storms.
The expected effects of climate change on fishing will be greater than in other periods of geological history that we took part, because for the first time we will have given a hand to make it worse. The sum of these effects endangers the survival of millions of people especially in developing countries. Fisheries management should consider the potential effects of climate change because regular measures alone may not protect species and environments that are rapidly changing.
By Ludmila Damásio