Economic repercussions of fisheries-induced evolution

Fish stocks experiencing high fishing mortality show a tendency to mature earlier and at a smaller size, which may have a genetic component and therefore long-lasting economic and biological effects. To date, the economic effects of such ecoevolutionary dynamics have not been empirically investigated. Using 70 y of data, we develop a bioeconomic model for Northeast Arctic cod to compare the economic yield in a model in which life-history traits can vary only through phenotypic plasticity with a model in which, in addition, genetic changes can occur. We find that evolutionary changes toward faster growth and earlier maturation occur consistently even if a stock is optimally managed. However, if a stock is managed optimally, the evolutionary changes actually increase economic yield because faster growth and earlier maturation raise the stock's productivity. The optimal fishing mortality is almost identical for the evolutionary and nonevolutionary model and substantially lower than what it has been historically. Therefore, the costs of ignoring evolution under optimal management regimes are negligible. However, if fishing mortality is as high as it has been historically, evolutionary changes may result in economic losses, but only if the fishery is selecting for medium-sized individuals. Because evolution facilitates growth, the fish are younger and still immature when they are susceptible to getting caught, which outweighs the increase in productivity due to fish spawning at an earlier age

Roles of density-dependent growth and life history evolution in accounting for fisheries-induced trait changes

The relative roles of density dependence and life history evolution in contributing to rapid fisheries-induced trait changes remain debated. In the 1930s, northeast Arctic cod (Gadus morhua), currently the world’s largest cod stock, experienced a shift from a traditional spawning-ground fishery to an industrial trawl fishery with elevated exploitation in the stock’s feeding grounds. Since then, age and length at maturation have declined dramatically, a trend paralleled in other exploited stocks worldwide. These trends can be explained by demographic truncation of the population’s age structure, phenotypic plasticity in maturation arising through density-dependent growth, fisheries-induced evolution favoring faster-growing or earlier-maturing fish, or a combination of these processes. Here, we use a multitrait eco-evolutionary model to assess the capacity of these processes to reproduce 74 y of historical data on age and length at maturation in northeast Arctic cod, while mimicking the stock’s historical harvesting regime. Our results show that model predictions critically depend on the assumed density dependence of growth: when this is weak, life history evolution might be necessary to prevent stock collapse, whereas when a stronger density dependence estimated from recent data is used, the role of evolution in explaining fisheries-induced trait changes is diminished. Our integrative analysis of density-dependent growth, multitrait evolution, and stock-specific time series data underscores the importance of jointly considering evolutionary and ecological processes, enabling a more comprehensive perspective on empirically observed stock dynamics than previous studies could provide

Resilience of the trophic cascades in the Black Sea and Baltic Sea regime shifts

The Black Sea and the Baltic Sea are two European lake-like marine systems where regime shifts have occurred. Both ecosystems show similar features and hold comparable long-term records for the main food web components and external pressures. Here we analyse Black Sea and Baltic Sea multi-trophic time series applying the same statistical tool, which allowed us to characterize tipping points and quantify the main dynamics ruling each regime phase. In both systems a trophic cascade, consequence of overfishing, drove a shift between regimes. This work focuses on the robustness of this ecological mechanism. By simulating environmental scenarios we tested whether enhanced bottom-up effects could counteract the development of the trophic cascades once these have been triggered. We found that under certain environmental settings the trophic cascade signals blur at different levels suggesting that the observed changes resulted from a combination of heavy fishing and unfavourable conditions. Through the outlook of one single methodology applied to two different but comparable systems we discuss the obstacles we may find if we are to promote a more desirable state and management measures considering synergistic effects of fishing and future climate change

A shift in hake (Merluccius merluccius) population of the NW Mediterranean induced by a combined effect of climate and fishery harvesting

Climate and fisheries are often interacting with each other and producing complex synergic effects on the population dynamics of marine species. The drastic change in the climatic conditions in the North Atlantic (NA) in the early eighties triggered changes in local weather and hydrographical conditions in the Mediterranean Sea. In the other hand, the long term fishery harvesting on the stock of European hake (Merluccius merluccius) off the Balearic Islands (BA, NW Mediterranean) changed the properties of the population and its structure in the early eighties, which could have triggered a different response to the environmental variability. Using time series analysis (on the environmental and hake CPUE time series) and a population simulation model, we examine the hypothesis that these processes are linked and, in turn, a combined effect of fishery harvesting and environmental changes in the NA induced an ecological shift in the hake population off BA. The results points out that the changes in the variance and modes of hake CPUE were consistent with changes in the hydroclimatic variability in the NW Mediterranean induced by the North Atlantic climate. Population simulations show that age-structured populations act like a filter of the environmental fluctuations and can intrinsically generate cycles (‘cohort-resonance effect’) consistent with the 12 yr mode observed in the CPUE before the eighties. Size selective fishing mortality could erode the age structure and change the population filter properties. The population would have changed from internally-generated fluctuations to an externally-forced fluctuations mode after the eighties, increasing its dependency on the recruitment variability. This fits with the observations which show the high dependency of the CPUE on the recruitment variability and the winter condition modes predominating after eighties. Our results emphasize the importance of the interaction between fisheries, environment and internal dynamics that can cause transitory shifts in the behaviour of a populatio

Drivers of change in China’s energy-related CO₂ emissions

CO2 emissions are of global concern because of climate change. China has become the largest CO2 emitter in the world and presently accounts for 30% of global emissions. Here, we analyze the major drivers of energy-related CO2 emissions in China from 1978 when the reform and opening-up policy was launched. We find that 1) there has been a 6-fold increase in energy-related CO2 emissions, which was driven primarily (176%) by economic growth followed by population growth (16%), while the effects of energy intensity (−79%) and carbon intensity (−13%) slowed the growth of carbon emissions over most of this period; 2) energy-related CO2 emissions are positively related to per capita gross domestic product (GDP), population growth rate, carbon intensity, and energy intensity; and 3) a portfolio of command-and-control policies affecting the drivers has altered the total emission trend. However, given the major role of China in global climate change mitigation, significant future reductions in China’s CO2 emissions will require transformation toward low-carbon energy systems

What is blue growth? The semantics of “Sustainable Development” of marine environments

This Special Issue is intended to help readers gain a better understanding of the various definitions of blue growth, as well as to give a heightened awareness of the constraints of, and possibilities within, the important concept. Increased communication among those working together on these topics is of utmost importance, especially considering the diversity of the backgrounds of those who have a role to play in blue growth and sustainable development. Scientists, policy makers, business people, and the larger society need to become more precise and transparent in their language and meanings in order to effectively work together, and hopefully one day succeed in our joint goal to secure blue growth

Spatial variation in biodiversity loss across China under multiple environmental stressors

Biodiversity is essential for the maintenance of ecosystem health and delivery of the Sustainable Development Goals. However, the drivers of biodiversity loss and the spatial variation in their impacts are poorly understood. Here, we explore the spatial-temporal distributions of threatened and declining ("biodiversity-loss") species and find that these species are affected by multiple stressors, with climate and human activities being the fundamental shaping forces. There has been large spatial variation in the distribution of threatened species over China's provinces, with the biodiversity of Gansu, Guangdong, Hainan, and Shaanxi provinces severely reduced. With increasing urbanization and industrialization, the expansion of construction and worsening pollution has led to habitat retreat or degradation, and high proportions of amphibians, mammals, and reptiles are threatened. Because distributions of species and stressors vary widely across different climate zones and geographical areas, specific policies and measures are needed for preventing biodiversity loss in different regions