Managing fisheries in a changing climate

No need to wait for more information: industrialized fishing is already wiping out stocks

Effects of eutrophication, grazing, and algal blooms on rocky shores

Eutrophication can profoundly change rocky shore communities. These changes often cause the replacement of perennial, canopy-forming algae such as Fucus spp. with annual, bloom-forming algae such as Enteromorpha spp. Grazing, however, can counteract eutrophication by eliminating the annual algae�s susceptible recruits. We examine these generalizations across large scales. We use replicated ��bioassay�� experiments to compare the effects of eutrophication and grazing across four paired control versus eutrophied sites in the Northwest Atlantic and four eutrophied sites in the Baltic Sea in spring and summer. At each site, annual algal recruitment and grazing pressure were estimated using tiles seeded with Enteromorpha intestinalis propagules. Tiles were exposed for 3 weeks with grazers excluded or allowed access. Productivity of E. intestinalis recruits was strongly related to eutrophication (10-fold increase) and grazing (80% decrease) and was weakly related to season. While the absolute grazing rate increased in a linear fashion with algal productivity, the relative grazing rate remained surprisingly constant (;80%). Comparative field surveys showed that perennial algae decreased by 30-60%, while annual algae, filter feeders, and grazers increased across a gradient of eutrophication. As eutrophication increased from control to eutrophied to point source sites, rocky shore communities became increasingly dominated by single species of annual algae or filter feeders, and community diversity declined consistently by 24-46%. We conclude that grazers are important controllers of algal blooms but that, ultimately, they cannot override the effects of increasing eutrophication on rocky shore community structure and biodiversity

High Seas Fisheries: Troubled Waters, Tangled Governance and Recovery Prospects

Global fisheries are in a perceived state of crisis. Despite growing technological effort and an unprecedented global expansion of fisheries, total landings (85-100 million MT per year) have stagnated and probably entered a period of slow decline. This trend may destabilize ocean ecosystems and undermine world seafood supplies, which provide the major source of protein for 2.3bn people, and international cooperation to address this issue has been slow. This is particularly true for highseas fisheries that occur in international waters encompassing some 61% of the world\u27s ocean. These have been plagued by a fragmented and weak legal framework, poor enforcement of existing regulations, and the problem of illegal, unreported, and unregulated (IUU) fishing. On the positive side, individual States have introduced measures that have been successful in recovering overexploited resources. Turning the tide on the high seas requires strong government cooperation to enforce conservative harvest levels (quotas), as well as measures that protect biological diversity, such as protected areas, bycatch regulations, and the conservation of critical habitats. This article provides a short overview of the biological, institutional and legal dimensions of high-seas fisheries. It emphasizes that this is a unique time in history, where unprecedented awareness, scientific advances, and a growing willingness to collaborate internationally are setting the stage for a dynamic transformation of high-seas governance. What is missing is a visionary master plan on how to integrate fragmented efforts towards the common goal of sustainable development on the high seas

Coastal food web structure, carbon storage, and nitrogen retention regulated by consumer pressure and nutrient loading

By factorial field experiments we analyzed the relative effects of increased nutrient (N+P) loading and natural grazing pressure on species composition, carbon storage, and nitrogen retention in the Baltic Sea littoral food web, composed of macroalgae, grazers (snails, isopods, amphipods), and predators (shrimps, crabs, fish). Nitrogen was depleted relative to phosphorus throughout most of the year. Increasing nitrogen (6–200% over ambient concentrations) enhanced algal productivity and cover of fast-growing annual algae, grazer, and predator densities, suggesting a three-level bottom-up effect. With increasing nitrogen loading, annual algae increasingly blocked perennial algal recruitment (65–98% decrease) and growth. Grazers counteracted the effects of nutrient enrichment on algal species composition through selective consumption of annual algae. Grazer exclusion had equivalent negative effects on perennial recruitment as a 85% increase in nitrogen loading. Nutrient enrichment increased algal nitrogen content and decreased tissue C: N ratios in spring and summer but not in fall. Carbon storage and nitrogen retention, measured as C and N retained in plant biomass at the end of the growth season, were increased by grazers (C: 39%, N: 24%) but decreased with increasing nitrogen loading (C: -71%, N: -74%). Our results emphasize the important role of grazers in buffering moderate eutrophication effects and illustrate how food web interactions and shifts in species composition are tightly linked to coastal ecosystem functio

Consumer versus resource control in rocky shore food webs : Baltic Sea and Northwest Atlantic Ocean

Rocky shores are among the most productive ecosystems on the planet. Community biomass and primary productivity are dominated by canopy-forming perennial macroalgae, which fulfill important ecosystem functions including carbon storage, nutrient cycling and the provision of food and habitat for a diverse invertebrate and fish fauna. Recently, perennial macroalgae have severely declined in abundance in the Baltic Sea and other nutrient-rich coastal systems. In this thesis, I analyzed causes and consequences of these changes in a food-web context. Rocky shore food webs are characterized by strong interactions among macroalgae, sessile filter feeders, grazers and predators. Humans alter these webs by harvesting species at various trophic levels (e.g. fish, snails, macroalgae) and by adding plant nutrient resources through coastal eutrophication (dissolved inorganic nitrogen [DIN] and phosphorus compounds [DIP]). My goal was to understand the interactive effects of changes in consumer abundance and nutrient resources on benthic community structure, species diversity and ecosystem functioning. I addressed this through in situ nutrient enrichment and caging experiments and large-scale field surveys in the Baltic Sea and the NW Atlantic Ocean, which I used as model systems for nutrient-rich and nutrient-poor ecosystems, respectively. (orig.)SIGLEAvailable from TIB Hannover: RN 3292(316) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Evaluating Hierarchical Domain-Specific Languages for Computational Science: Applying the Sprat Approach to a Marine Ecosystem Model

In this chapter, we present a Model-Driven Software Engineering (MDSE) approach called Sprat, which adapts traditional software engineering practices in order to employ them in computational science. The approach is based on the hierarchical integration of so-called Domain-Specific Languages (DSLs) to facilitate the collaboration of scientists from different disciplines in the development of complex simulation software. We describe how multiple DSLs can be integrated to achieve a clear separation of concerns among the disciplines and how to apply Sprat during the different phases of the software life cycle. To evaluate our approach, we discuss results from a case study in which Sprat has been utilized for the implementation of a coupled marine ecosystem model for spatially-explicit fish stock prediction. We report on the DSLs developed for this case study, how scientists benefit from them, and on lessons learned. In particular, we analyze the results from expert interviews conducted with both scientists and professional DSL developers

Seasonal variability in global industrial fishing effort

Unidad de excelencia María de Maeztu MdM-2015-0552Identificadors digitals: Digital object identifier for the 'European Research Council' (http://dx.doi.org/10.13039/501100000781) Digital object identifier for 'Horizon 2020' (http://dx.doi.org/10.13039/501100007601) - BIGSEA PROJECTHuman beings are the dominant top predator in the marine ecosystem. Throughout most of the global ocean this predation is carried out by industrial fishing vessels, that can now be observed in unprecedented detail via satellite monitoring of Automatic Identification System (AIS) messages. The spatial and temporal distribution of this fishing effort emerges from the coupled interaction of ecological and socio-economic drivers and can therefore yield insights on the dynamics of both the ecosystem and fishers. Here we analyze temporal variability of industrial fishing effort from 2015-2017 as recorded by global AIS coverage, and differentiated by fishing gear type. The strongest seasonal signal is a reduction of total deployed effort during the annual fishing moratorium on the numerically-dominant Chinese fleet, which occurs during boreal summer. An additional societally-controlled reduction of effort occurs during boreal winter holidays. After accounting for these societal controls, the total deployed effort is relatively invariant throughout the year for all gear types except squid jiggers and coastal purse seiners. Despite constant deployment levels, strong seasonal variability occurs in the spatial pattern of fishing effort for gears targeting motile pelagic species, including purse seiners, squid jiggers and longliners. Trawlers and fixed gears target bottom-associated coastal prey and show very little overall seasonality, although they exhibit more seasonal variation at locations that are further from port. Our results suggest that societal controls dominate the total deployment of fishing effort, while the behavior of pelagic fish, including seasonal migration and aggregation, is likely the most prominent driver of the spatial seasonal variations in global fishing effort