In the late 1990s, depletion of the target species Penaeus notialis (Pink Shrimp) in deeper waters (50 m) of the Nigerian coast resulted in a change of target species from P. notialis (Pink Shrimp) ...to shallower water species such as Penaeus monodon (Brown Shrimp). This study investigates the hypothesis that ecosystem impacts increased as industrial fleets increased fishing in shallower areas of the Nigerian coast by comparing the state of the ecosystem before and 20 yr after commercial shrimping commenced in Nigerian coastal waters (NCW). Two fishing scenarios were developed in Ecospace, the spatial modeling module of Ecopath with Ecosim software (Ecopath with Ecosim is a mass balanced trophic model that accounts for fishing impacts on food webs), with one having trawlers fishing everywhere beginning at the turn of the century (year 2000) and the other with no trawling in the first 5 nautical miles off the Nigerian coast through the entire period of model simulation (1985–2004). Modeling results showed increases in catch for some fisheries during the study period. In addition, estimated biomass for some functional groups increased especially for Small Pelagic fishes along with Rays, Reef fishes, Large Pelagics, and shallow water shrimps. All other exploited species in our modeling scenarios were estimated to have declining biomasses. Our expectation that redistribution of fishing effort in NCW will increase negative impacts of fishing the nearshore ecosystem was not supported by model results. This counterintuitive result may be because fishing effort on average was mostly distributed in the deeper areas of the inshore waters. Although specie such as Reef fishes appear to benefit from closure of the first 5 NM to fishing, the benefits appear to be negligible. We present the first ecosystem model developed for NCW, and our research contributes to fisheries ecology by furthering understanding of tropical coastal food webs and ecological response to fishing, especially in highly perturbed ecosystems like NCW.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
In Nigerian coastal waters (NCW), fishing has increased steadily over the last seven decades. Artisanal fisheries cover the entire 850‐km length of the coast, where over 1 million fishermen exploit ...estuarine and oceanic resources up to 40 m deep, and approximately 250 industrial trawlers target fish resources in deeper waters beyond the first 9.26 km (5 nautical miles) from shore. We investigated the hypothesis that growth in fishing effort will increase impacts on coastal fish stocks, as reflected by significant reductions in the mean trophic level (MTL) and maximum mean length of the catch and an increase in the fishing‐in‐balance index. Our analyses are based on a 60‐year time series from 1950 to 2010 (obtained from the Sea Around Us Project; www.seaaroundus.org). Results showed that the impacts of fishing in NCW are high. The sustained increases in landings from the 1970s to the 2000s have resulted in less productive coastal fisheries, a reduction in the MTL of the catch (which might mean reduced biodiversity), a reduction of average size in the fisheries, and the need to expand further into deeper waters to maintain catch levels. This research contributes to fisheries ecology by furthering our understanding of coastal fisheries and their impacts on marine biodiversity.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Objective
The Gulf of Mexico hosts some of the most productive fisheries in the United States, whereas the same region is known to experience environmental stressors, such as summer hypoxia. ...Ecosystem models have been developed for the Gulf of Mexico to determine how hypoxia affects living marine resources, but these models and their output are not always easy to access or interpret by managers, thereby decreasing their implementation in a management setting. To help alleviate the gap between ecosystem model development and management utility, the current study focuses on co‐produced, user‐friendly tools that describe the effects of nutrient and hypoxia reductions on marine living resources.
Methods
Two decisions were made prior to the ecosystem model development to facilitate the transfer of model output: (1) to engage and consult fisheries and restoration managers throughout ecosystem model development to ensure that the output would provide relevant information; and (2) to provide an accessible visualization tool for making ecosystem model output readily available to support the needs of decision makers.
Result
Results from an advisory panel survey instrument and advisory panel meetings guided ecosystem model development and launched the development of a decision support tool. The iterative process of building a decision support tool incorporating feedback from survey instrument respondents resulted in an ESRI ArcGIS Dashboard that allows end‐users to identify the effects of hypoxia and respondent‐specified nutrient and hypoxia reduction goals on the biomass and distribution of fisheries species.
Conclusion
The intent is to aid managers who are actively working to address hypoxia in the Gulf of Mexico with easy‐to‐access information on the effects of planned actions and to encourage future modelers to apply action science principles to best address the needs of decision makers.
Impact statement
In this study we worked directly and iteratively with managers, who are actively working to address hypoxia in the Gulf of Mexico, to co‐produce an easy‐to‐access tool that visualizes the effects of nutrient load reduction goals on important fisheries species in the Gulf of Mexico.
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Marine Ecosystem Models (MEMs) provide a deeper understanding of marine ecosystem dynamics. The United Nations Decade of Ocean Science for Sustainable Development has highlighted the need to deploy ...these complex mechanistic spatial-temporal models to engage policy makers and society into dialogues towards sustainably managed oceans. From our shared perspective, MEMs remain underutilized because they still lack formal validation, calibration, and uncertainty quantifications that undermines their credibility and uptake in policy arenas.
We explore why these shortcomings exist and how to enable the global modelling community to increase MEMs’ usefulness. We identify a clear gap between proposed solutions to assess model skills, uncertainty, and confidence and their actual systematic deployment. We attribute this gap to an underlying factor that the ecosystem modelling literature largely ignores: technical issues. We conclude by proposing a conceptual solution that is cost-effective, scalable and simple, because complex spatial-temporal marine ecosystem modelling is already complicated enough.
•Marine Ecosystem Models (MEMs) are rarely systematically validated and calibrated.•This can potentially undermine the credibility and uptake of model output in the policy arenas where it is so direly needed.•Suggestions to assess model skill, uncertainty, and confidence abound in the literature, but applications are mostly lacking.•We identify the main technical hurdles that prevent the MEM community from moving forward, and specify a resolving framework.•We call on the MEM community to create collaboratively such a framework to produce model results with more confidence.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The Ocean Decade aims to achieve six societal outcomes: (1) A clean ocean, through identifying and removing sources of pollution; (2) A healthy and resilient ocean, with mapped and protected marine ...ecosystems; (3) A predicted ocean, enabling society to understand current and future ocean conditions; (4) A safe ocean, protecting people from ocean hazards; (5) A sustainably harvested ocean, providing food and resources for the blue economy; and (6) A transparent ocean, giving citizens equitable access to data, information and technologies. ...current ecosystem models already address possible impacts of climate change on species' habitats and food web interactions (Spence et al., 2018; Lotze et al., 2019) and are considering evolution and acclimation (Fulton et al., 2019). ...possible impacts from storms or high temperature events on coastal ecosystems could be addressed through full end-to-end interdisciplinary models, as is already done by assemblages of models informing Louisiana's Coastal Master Plan, the restoration of the Mississippi River Delta (De Mutsert et al., 2017; Baustian et al., 2018), the Baltic Sea (Niiranen et al., 2013) and the Great Barrier Reef, making this priority achievable in the Ocean Decade. 6. The Ocean and Earth-System Observation, Research and specifically Prediction of the future state of the ocean will require ecosystem models to include a broader set of industries and human behavior, including social change, requiring social and economic data (Ryabinin et al., 2019).
The pelagic ecosystems of the Western Antarctic Peninsula are dynamic and changing rapidly in the face of sustained warming. There is already evidence that warming may be impacting the food web. ...Antarctic krill, Euphausia superba, is an ice-associated species that is both an important prey item and the target of the only commercial fishery operating in the region. The goal of this study is to develop a dynamic trophic model for the region that includes the impact of the sea-ice regime on krill and krill predators. Such a model may be helpful to fisheries managers as they develop new management strategies in the face of continued sea-ice loss. A mass balanced food-web model (Ecopath) and time dynamic simulations (Ecosim) were created. The Ecopath model includes eight currently monitored species as single species to facilitate its future development into a model that could be used for marine protected area planning in the region. The Ecosim model is calibrated for the years 1996-2012. The successful calibration represents an improvement over existing Ecopath models for the region. Simulations indicate that the role of sea ice is both central and complex. The simulations are only able to recreate observed biomass trends for the monitored species when metrics describing the sea-ice regime are used to force key predator-prey interactions, and to drive the biomasses of Antarctic krill and the fish species Gobionotothen gibberifrons. This model is ready to be used for exploring results from sea-ice scenarios or to be developed into a spatial model that informs discussions regarding the design of marine protected areas in the region.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Current methods to restore Louisiana's estuaries include the reintroduction of Mississippi River water through freshwater diversions to wetlands that are hydrologically isolated from the main ...channel. The reduced salinities associated with freshwater input are likely affecting estuarine nekton, but these effects are poorly described. Ecopath with Ecosim was used to simulate the effects of salinity changes caused by the Caernarvon freshwater diversion on species biomass distributions of estuarine nekton. A base model was first created in Ecopath from 5 years of monitoring data collected prior to the opening of the diversion (1986–1990). The effects of freshwater discharge on food web dynamics and community composition were simulated using a novel application of Ecosim that allows the input of salinity as a forcing function coupled with user-specified salinity tolerance ranges for each biomass pool. The salinity function in Ecosim not only reveals the direct effects of salinity (i.e., increases in species biomass at their optimum salinity and decreases outside the optimal range) but also the indirect effects resulting from trophic interactions. Through multivariate analyses we determined that the simulated species biomass distributions in the estuary change significantly with distance from the diversion. However, the simulations do not show a significant difference estuarywide between the modeled distributions (with pooling of the data from different distances) before and after the opening of the diversion. This indicates a redistribution of species in the estuary rather than the replacement of species within the estuarine nekton community. The salinity function is a useful addition to the Ecopath with Ecosim software for estuarine ecologists and fisheries managers.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
•Ecosystem model simulates effects of hypoxia on fish and fisheries.•New spatial–temporal environmental forcing functions in Ecospace.•Nutrients increase (rather than indirectly decrease) secondary ...production.•Species-specific responses to hypoxia vary.
The formation of an extensive hypoxic area off the Louisiana coast has been well publicized. However, determining the effects of this hypoxic zone on fish and fisheries has proven to be more difficult. The dual effect of nutrient loading on secondary production (positive effects of bottom-up fueling, and negative effects of reduced oxygen levels) impedes the quantification of hypoxia effects on fish and fisheries. The objective of this study was to develop an ecosystem model that is able to separate the two effects, and to evaluate net effects of hypoxia on fish biomass and fisheries landings. An Ecospace model was developed using Ecopath with Ecosim software with an added plug-in to include spatially and temporally dynamic Chlorophyll a (Chl a) and dissolved oxygen (DO) values derived from a coupled physical–biological hypoxia model. Effects of hypoxia were determined by simulating scenarios with DO and Chl a included separately and combined, and a scenario without fish response to Chl a or DO. Fishing fleets were included in the model as well; fleets move to cells with highest revenue following a gravitational model. Results of this model suggest that the increases in total fish biomass and fisheries landings as a result of an increase in primary production outweigh the decreases as a result of hypoxic conditions. However, the results also demonstrated that responses were species-specific, and some species such as red snapper (Lutjanus campechanus) did suffer a net loss in biomass. Scenario-analyses with this model could be used to determine the optimal nutrient load reduction from a fisheries perspective.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Since 1991, the Caernarvon Freshwater Diversion has been reintroducing Mississippi River water into a previously hydrologically isolated estuary in an effort to restore wetlands. To determine the ...effect of freshwater inflow on estuarine nekton community structure, a Before—After—Control—Impact study design was applied. As a result of the opening, salinities in the impact area decreased, and the nekton community structure in the estuary changed significantly. Species of economical or ecological importance either increased in biomass or exhibited no response to the opening of the diversion. Higher abundances of small fish were observed in the area receiving freshwater flow, which is an indication that the area serves as a refuge from large marine predators. Because a salinity gradient was established, as opposed to a uniform but lower salinity regime, aquatic habitat was available to nekton species from a wide spectrum of salinity tolerances.
River diversions are a major but controversial management approach to restoring coastal wetlands and mitigating offshore oil spills in the northern Gulf of Mexico. One of the controversies concerns ...the potential displacement of and salinity stress on commercially and recreationally important fish species in response to the widespread and prolonged freshening of habitat. We developed a coupled hydrodynamics–fish movement model and applied it to the Caernarvon diversion located in the Breton Sound estuary, Louisiana. Hydrodynamics model output was used as input to the individual‐based fish movement model. The period of model simulation was from April 1 to July 1, 2010. We simulated three diversion scenarios: baseline, pulse, and oil spill mitigation. We first used field data from Bay Anchovy Anchoa mitchilli and showed that the model predicted downestuary shifts similar to those observed in field studies under large diversions. We then defined generic low‐ and intermediate‐salinity fish species and simulated each under the three diversion scenarios. Compared with the baseline diversion scenario, more than 50% of the intermediate‐salinity individuals moved about 15 km farther downestuary under the pulse diversion scenario and moved more than 35 km under the oil spill mitigation diversion scenario. The effects of the diversions on the low‐salinity species were evidenced by individuals becoming more dispersed (i.e., spreading out downestuary) and more exposed to bursts of too high salinity. Our conclusions agreed with those from earlier field and modeling analyses that focused on average (rather than transitory) fish responses.
Received November 4, 2013; accepted November 7, 2013
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