Figure 4-1 - uploaded by Thomas A Okey
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Map of Prince William Sound, Alaska, located at the northern apex of the Gulf of Alaska (north Pacific Ocean). Prince William Sound covers approximately 9,000 km 2 , and it contains both shallow and deep habitats (to almost 800 m depth).
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Keystone species play a central role in shaping at least some marine communities in the sense that system-wide phase shifts can be mediated by the presence, absence, or the relative abundance of these key interactors. Identifying keystones is considered crucial for understanding the resilience of ecosystems to exogenous forces because non-linear, o...
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“Infochemicals” (information‐conveying chemicals) dominate much of the underwater communication in biological systems. They influence the movement and behavior of organisms, the ecological interactions between and across populations, and the trophic structure of marine food webs. However, relative to their terrestrial equivalents, the wider ecologi...
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... We represent the biomasses of the other functional groups as the proportion of their biomass when bacalao was fished at the level of depletion i (B i ) compared to the biomass when bacalao was unfished (B 0 ). This impact is analgous to the interaction strength index developed by Okey (2004) presented in the original Floreana Island EwE model description . ...
... Our results indicate that when unfished, bacalao has a much greater keystone role in all three models, also reflected by greater ecosystem effects when unfished with dynamic simulations of bacalao exploitation. A low bacalao keystone value was also reported for the modern Floreana Island model using a different keystone index, adding confidence to our findings (Okey, 2004;Okey et al., 2004). Recent work indicates that bacalao are extremely size over-fished, suggesting that their modern diet could be different than historically (Usseglio et al., 2016). ...
... Understanding the impact that regular, although not always predictable, environmental events, such as El Niño have on ecosystems is extremely important for ecosystem-based fisheries management, as exploitation of marine resources does not occur in isolation-these events impact species of conservation interest and species of importance for the tourism sector (Lynham et al., 2015;Salinas-de-León et al., 2016). The cold-west upwelling region of the Galápagos is particularly sensitive to El Niño events, which result in increased water temperatures and large declines in primary production (Wolff, Ruiz & Taylor, 2012) with catastrophic effects on many marine species (Okey, Shepherd & Martínez, 2003;Okey, 2004;Edgar et al., 2010). Climate change projections for the Galápagos Islands from an ensemble of Earth system models indicate an increase in primary production under the strong mitigation of emissions scenario (RCP 2.6; Bopp et al., 2013). ...
The Galápagos Archipelago is home to a diverse range of marine bioregions due to the confluence of several cold and warm water currents, resulting in some of the most productive tropical marine ecosystems in the world. These ecosystems are strongly influenced by El Niño events which can reduce primary production by an order of magnitude, dramatically reducing energy available throughout the food web. Fisheries are an important component of the local economy, although artisanal and illegal overfishing have dramatically reduced the productivity of invertebrate and finfish resources in recent decades, resulting in reductions in catches for local fishers. The regionally-endemic sailfin grouper (Myctereoperca olfax), locally known as bacalao, was once the most important fished species in the Galápagos, but is now listed as vulnerable by the IUCN due to its limited range and dramatic declines in catch over time. It is unknown how reduction of this predatory species has affected ecosystem structure and function. In the absence of stock assessments, we used an estimate of unfished bacalao biomass from fishers' ecological knowledge along with unfished biomass estimates of other heavily exploited stocks-lobster (Panulirus penicillatus and P. gracilis) and sea cucumber (Isostichopus fuscus)-to create historical, unfished versions of existing modern day ecosystem models. We used the unfished and modern versions of the ecosystem models to test the ecosystem effects of bacalao exploitation at the Bolivar Channel, located in the cold, west upwelling bioregion of the archipelago during both El Niño and non El Niño years, and at Floreana Island, in the warmer, central bioregion. Fishers' ecological knowledge indicates that at present, the biomass of bacalao is at least seven times lower than when unfished. This reduced bacalao biomass is linked with a greatly reduced ecosystem role compared to when unfished, and ecosystem role is further reduced in El Niño years. Allowing bacalao populations to rebuild to at least half of unfished biomass would partially restore their role within these ecosystems, while also resulting in greater fisheries catches. Comparing ecosystem impacts caused by fishing and El Niño, fishing has had a greater negative impact on bacalao ecosystem role than regular El Niño events.
... For all bottom-up and top-down perturbations, changes in response sign among communities of practice (relative to single-species models) consistently propagated from changes in focal species responses due to trophic interaction among the focal species. The negative influence of arrowtooth on pollock represents predation as demonstrated in quantitative food web models, where the biomass-dominant arrowtooth exert high predation mortality on pollock in the Gulf of Alaska (Gaichas et al., 2010 and in Prince William Sound (Okey and Pauly, 1999;Okey, 2004). When perturbations created positive responses in the lower trophic components of the pelagic food web, arrowtooth increased, which caused pollock to decrease, which in turn caused halibut (predators of pollock) to decrease. ...
Marine ecosystems are complex, and there is increasing recognition that environmental, ecological, and human systems are linked inextricably in coastal regions. The purpose of this article was to integrate environmental, ecological and human dimensions information important for fisheries management into a common analytical framework. We then used the framework to examine the linkages between these traditionally separate subject areas. We focused on synthesis of linkages between the Gulf of Alaska marine ecosystem and human communities of practice, defined as different fisheries sectors. Our specific objective was to document the individual directional linkages among environmental, ecological, and human dimensions variables in conceptual models, then build qualitative network models to perform simulation analyses to test how bottom-up and top-down perturbations might propagate through these linkages. We found that it is both possible and beneficial to integrate environmental, ecological, and human dimensions information important for fisheries into a common framework. First, the conceptual models allowed us to synthesize information across a broad array of data types, representing disciplines such as ecology and economics that are more commonly investigated separately, often with distinct methods. Second, the qualitative network analysis demonstrated how ecological signals can propagate to human communities, and how fishery management measures may influence the system. Third, we found that incorporating multi-species interactions changed outcomes because the merged model reversed some of the ecological and human outcomes compared with single species analyses. Overall, we demonstrated the value of linking information from the natural and social sciences to better understand complex social–ecological systems, and the value of incorporating ecosystem-level processes into a traditionally single species management framework. We advocate for conceptual and qualitative network modelling as efficient foundational steps to inform ecosystem-based fisheries management.
... Examples of key species in Canada's Pacific areas include subtidal kelps, eelgrass, and cold water corals and sponges (biogenic habitat forming components), the purple sea star and other predators from salmon to seabirds, orcas, pinnipeds (predation pressure), forage fishes, benthic invertebrates, and plankton such as copepods and krill (prey availability). New approaches are available to rank species importance in whole ecosystems (Jordán et al. 2008; Okey 2004a) with respect to interaction strength and keystoneness, and this could allow conservation prioritization. Despite the importance and practical efficiency of focusing on key species, marine and coastal biological communities with stable, genetically diverse populations and higher biodiversity are more resistant to environmental changes and hence should be more resilient to the impacts of global warming (Duffy and Stachowicz 2006; Ehlers et al. 2008; Hughes et al. 2003; Steneck et al. 2002). ...
The marine life of Canada’s Pacific marine ecosystems, adjacent to the province of British Columbia, may be relatively responsive to rapid oceanographic and environmental change associated with global climate change due to uniquely evolved plasticities and resiliencies as well as particular sensitivities and vulnerabilities, given this dynamic and highly textured natural setting. These marine ecosystems feature complex interfaces of coastal geomorphology, climate, and oceanography, including a dynamic oceanographic and ecological transition zone formed by the divergence of the North Pacific Current into the Alaskan coastal current and the California Current, and by currents transporting warm tropical waters from the south. Despite long-term warming in the region, sea surface temperatures in Canada’s Pacific have been anomalously cool since 2007 with La Niña-type conditions prevailing as we enter a cool phase of the Pacific Decadal Oscillation, possibly masking future warming. When warmer El Niño conditions prevail, many southern species invade, strongly impacting local species and reorganizing biological communities. Acidification and deoxygenation are anomalously high in the region due to the weakening ventilation of subsurface waters resulting from increased stratification. A broad spectrum of biological responses to these changes are expected. Non-climate anthropogenic stressors affect the capacity of biota to adapt to climate changes. It will be challenging to forecast the responses of particular species, and to map climate vulnerabilities accurately enough to help prioritize and guide adaptation planning. It will be more challenging to develop forecasts that account for indirect effects within biological communities and the intricate and apparently non-deterministic behaviours of highly complex and variable marine ecosystems, such as those of Canada’s Pacific. We recommend and outline national and regional climate assessments in Canada and adaptation planning and implementation including integrated coastal management and marine spatial planning and management.
There is broad recognition that forage fish—small, short-lived and fast growing mid-trophic level species—are primary energy pathways in many marine food webs, and that they support other valuable fish stocks and many species of marine birds and mammals. Invertebrates such as squids, shrimps, and krill are also recognized as important forage species supporting fish stocks and the food web. Some policies have emerged to protect exploited forage species for these supportive reasons, and also due to concerns about bycatch in forage fisheries. Debate continues, however, over the importance of these forage species in particular settings, and how they should be managed. We approached this question for the U.S. South Atlantic Bight—a subtropical ecosystem from Cape Hatteras, NC to Biscayne Bay, FL in which the role of forage species is poorly understood. We modified and employed an existing Ecopath with Ecosim trophodynamic model to simulate the potential effects of changes in the biomasses of several forage groups on the broader biological community and on particular groups of interest. We found that forage groups, taken together, influenced most groups and thus structured and supported the overall biological community strongly. Many more groups were facilitated by the presence of forage groups, or by increases in them when manipulated all together, than were suppressed by them through competition or indirect trophic cascades, such as through predator subsidy. The simulated effects of each individual forage species/group varied considerably in the net balance of effects, in magnitude, and in the affected species. Atlantic menhaden (Brevoortia tyrannus) and squids (Illex illecebrosus, Loligo pealei), for example, exerted the largest effects on community structure amongst forage groups, but these effects were distributed differently amongst species in the ecosystem. Our results indicate that forage fishes as a whole are a critical component of the ecosystem, supporting large portions of the upper trophic level biomass and diversity in the South Atlantic Bight ecosystem. Our results support previous findings that that joint (cooperative) management of predator-prey fisheries complexes would result in higher ecological and economic values of regional fishery-ecosystems than would a continuation of separate (non-cooperative) management.
