IMBeR IPO, IMR, Norway
Institute of Oceanography, National Taiwan University, Taiwan
Empirical dynamical modeling toward ecosystem-based fisheries managements
Mechanistic understanding is important for effective policy and management recommendations on fisheries, particularly in the ecosystem context. Two classic approaches have been commonly used for this purpose: correlation analysis and parametric models using a set of assumed equations. For approach 1, we face the long-lasting problem that correlation does not imply causation. For approach 2, we encounter the difficulty that we do not know the exact set of equations and ecosystems are complex. Here, we show that the objective is better addressed using an alternative equation-free approach based on nonlinear state space reconstruction using time series data, known as Empirical Dynamic Modeling. This approach can distinguish causality from correlation and provide better forecasting skills for fish abundance in the complex environmental context, thus leading to mechanistic understanding. We demonstrate the methodology using Pacific sardines, Fraser River sockeye salmons, and Maizuru Bay fish community.
Monterey Bay Aquarium Research Institute, USA
Disentangling a web of feeding interactions connecting surface adn deep-sea ecosystem
Collectively, marine ecosystems are fueled by the networks of feeding interactions, or food webs, that bridge primary and secondary producers up through top predators. Parameterizing predator-prey interactions across a diversity of consumers (e.g., fishes, cephalopods, crustaceans, gelatinous animals), and tracing the subsequent flow(s) of energy through an ecosystem is a longstanding, formidable challenge for marine ecologists. However, large-scale ecosystem management (or, of individual species or resources within an ecosystem) amidst the backdrop of climate change and increasing anthropogenic pressures, depends on robust understanding of the composition and flexibility of trophic links that bind and fuel an ecosystem. By merging a targeted combination of traditional empirical tools (stomach content analysis and in situ observations) alongside integrative biochemical tracers (bulk and compound-specific isotopes, trace metals), we have yielded surprising new trophic insights about how pelagic animals feed, and subsequently connect surface communities with those found at mesopelagic and bathypelagic depths. This talk presents vignettes of open ocean and deep-sea food web studies across the central North Pacific and the California Current, including new efforts to coordinate and scale-up toward global food web understanding across diverse biogeochemical provinces.
CLS Collecte Localisation Satellites, France
Developing Predictive Models to Estimate the Impact of Climate and Fisheries on Tuna Stocks.
Today about two-thirds of tuna and billfish catch world-wide is made of skipjack, yellowfin, bigeye and albacore tuna; besides 70% of these tunas are withdrawn from the tropical areas of Indian and the western and central Pacific oceans. High fishing pressure coincides with rapidly growing atmospheric CO2 concentrations that follow the trend of the worst RCP8.5 scenario assumed by IPCC in 2011. It is evident that sustainable ecosystem management requires the use of a comprehensive approach that involves tools incorporating the impact of both climate and fisheries on the fish stocks. The Spatial Ecosystem And Population Dynamics Model (SEAPODYM) is one of such tools describing spatial and temporal population dynamics while integrating relationships between the dynamical processes and the environmental variables. The model predictive skills are gained from the use of a robust estimation approach of population dynamics and fisheries parameters. Several types of data can be included in the Maximum Likelihood Estimation approach: catch, fishing effort and size frequencies of catch, tagging data, acoustic biomass estimates, eggs and larvae densities. The resulting model with data assimilation can be used for various management applications that are based either on historical reconstruction of stock dynamics, operational real-time modelling, or long-term projections. A recent study relying on SEAPODYM applications for four tuna species provided projections over the 21st Century under the environmental forcings from five different Earth System models with RCP8.5 scenario. The new envelope of projections confirms previous results and shows an eastward shift of skipjack and yellowfin biomass over time, with a large uncertainty for the second half of the century. The negative impact is weaker for bigeye tuna and albacore due to geographic extension of favorable spawning habitats. The historical fishing pressure is estimated to have reduced the adult stocks of these tuna species by 30-55 % by the end of 2010, depending on species and region. This is much more than a decrease attributed to climate change only. With current levels of fishing effort the fishing will likely remain the dominant driver of tuna populations decrease until mid-century; however the fish abundance redistribution associated with climate change could have strong implications regionally, particularly for the Asian and Pacific countries and the management of the resource at basin scale.