Modeling food web effects of low sardine and anchovy abundance in the California Current
Introduction
Sardine, anchovy, and other forage species support economically valuable fisheries and are a main prey source for many valuable predator species (Pikitch et al., 2014); therefore fluctuations in abundance can have large implications for both fisheries and food webs (Smith et al., 2011). For instance, in the California Current off the West Coast of the USA, revenue from the Pacific sardine (Sardinops sagax) fishery recently peaked at over $21 million in 2012 (Pacific Fishery Management Council, 2014). Pacific sardine and northern anchovy (Engraulis mordax) are also main prey sources for economically valuable predators such as salmon (Oncorhynchus spp.) and albacore tuna (Thunnus alalunga) and threatened and endangered species such as humpback whales (Megaptera novaeangliae) (Szoboszlai et al., 2015).
Populations of sardine, anchovy, and other forage species can fluctuate to low levels due to climate variability and fishing (Lindegren et al., 2013, Essington et al., 2015). For instance, sardine in the California Current have recently drastically declined to 9% of peak 2007 abundance (Hill et al., 2015), and anchovy in Southern California had declined to ∼1% of peak abundance by 2011 (MacCall et al., 2016). This has raised concerns about the implications for dependent predators and fisheries in this region. Of particular concern is that anchovy and sardine are simultaneously at low abundance. Concurrent periods of low abundance are atypical but problematic: Lindegren et al. (2016) analyzed the 60 year time series from CalCOFI surveys and associated data and suggested that it is the asynchrony between anchovy, sardines, and other small pelagic fish that leads to community-level stability. Functional complementarity of these small fish species in the diets of generalist predators may typically support resilience in this ecosystem, as long as some of these forage species remain abundant. Recently, synchronous declines in forage fish species have been linked to reduced pup weights of California sea lion (Zalophus californianus) (McClatchie et al., 2016) and breeding failure of brown pelican (Pelecanus occidentalis) in the Southern California Bight (Henry, 2015).
The consequences of depleted forage fish functional groups in the California Current have been tested previously using two ecosystem models (Kaplan et al., 2013). Both the Atlantis model (Horne et al., 2010) and an Ecosim model (Field, 2004) were consistent in predicting that forage fish depletion would lead to declines in large flatfish and increases in euphausiids, cephalopods, myctophids, and mackerel. The Ecosim model also suggested tradeoffs between forage fish harvest and seabird abundance, with compensatory increases in some planktonic prey of forage fish, not seen in Atlantis. This difference suggested higher responsiveness of the Ecosim model to changes in forage fish biomass. Each of the models was limited in different capacities; Ecosim lacks spatial resolution (i.e. no potential for local depletion via fishing) and this application of Ecosim assumed extremely low sardine abundance, and the Atlantis model contained poor taxonomic resolution for forage fish groups and some predator groups. While this earlier analysis was able to identify some consistent results between models, discrepancies and the overall higher responsiveness of Ecosim versus Atlantis were unresolved in the analysis.
Subsequent to the analyses of Kaplan et al. (2013), US West Coast fishery managers have called for improved ecosystem modeling tools to predict impacts of depletion of sardine and other forage fish (Pacific Fishery Management Council, 2013). Additionally, fishery managers have launched initiatives to protect forage fish species that are presently not targeted by fisheries (Pacific Fishery Management Council, 2016). Here, we address calls by fishery managers to consider the role of forage fish, improving upon earlier efforts (Kaplan et al., 2013) by developing a revised spatially-explicit Atlantis ecosystem model of the California Current (Marshall et al., 2017). In this data-rich system, the Atlantis approach allows us to mechanistically model food web impacts on predators, competitors, and prey of sardine and anchovy to ask: What are the consequences of depletion of sardine on sardine yield and spatial distribution, and on fished predators and on other species in the food web? How does this vary at high versus low regimes of sardine and anchovy productivity (Chavez et al., 2003, MacCall, 2009), including periods such as the apparent present dearth of both species? Do these results vary spatially, for instance near major sardine fishing ports?
To begin to make multi-model inference and to understand how model structure drives prediction uncertainty (Pinnegar et al., 2005, Gårdmark et al., 2013), we have conducted this work within a multi-model setting, the Ocean Modeling Forum (www.oceanmodelingforum.org). We compare our model results to those predicted using a different modeling approach, the PREP equation (Predator Response to the Exploitation of Prey). This equation generalizes results from a set of Ecosim models considered by the Lenfest Forage Fish Taskforce (Pikitch et al., 2012); the task force intended PREP as a tool in data-limited ecosystems where diet information was available but food web or ecosystem models were lacking. In a companion paper we more thoroughly compare results between model types within the Ocean Modeling Forum setting.
Section snippets
Methods
We briefly describe the Atlantis framework, and the revised implementation for the California Current. We detail the scenarios tested to understand the role of sardine and anchovy in the food web, the analyses of model output, and the comparison of Atlantis predictions to those from the PREP equation.
Results
As detailed in each subsection below, we first focus on the Base Recruitment scenarios, summarizing the effects of simulated levels of sardine depletion on the sardine stock, and the food web; predators such as Dolphins and Large piscivorous flatfish decline most strongly when sardine are depleted. We then translate these results into ecosystem indicators, finding that most of these indicators respond only weakly to these scenarios. We next focus on the broader range of sardine and anchovy
Discussion
Fishery managers in the California Current recently called for improved ecosystem modeling of forage fish (Pacific Fishery Management Council 2013), and to the extent practical our effort specifically addresses this request. In particular, our model includes the full geographic range of the sardine stock, identifies separate fisheries per region, represents fisheries that target species other than forage fish, and has a simple representation of climate variability (recruitment regimes). Our
Funding
The Ocean Modeling Forum was supported by the David and Lucile Packard Foundation. Model development benefited greatly from a grant from the NOAA Ocean Acidification Program and National Centers for Coastal Ocean Science. TEE was supported by Pew Marine Conservation Fellows program.
Acknowledgements
This work was undertaken as part of the Ocean Modeling Forum and California Current Integrated Ecosystem Assessment. As part of the Ocean Modeling forum, the following provided feedback and assistance of this project: André E. Punt, Alec D. MacCall, Tessa B. Francis, Felipe Hurtado- Ferro, Kelli F. Johnson, Phillip S. Levin, Richard Parrish, and William J. Sydeman. Blake Feist provided GIS expertise to assign anchovy and sardine distributions from CalCOFI to the Atlantis polygons.
References (73)
- et al.
The role of environmental controls in determining sardine and anchovy population cycles in the California Current: analysis of an end-to-end model
Prog. Oceanogr.
(2015) Biogeochemical marine ecosystem models II: the effect of physiological detail on model performance
Ecol. Model.
(2004)- et al.
Ocean forecasting in terrain-following coordinates: formulation and skill assessment of the Regional Ocean Modeling System
J. Comput. Phys.
(2008) - et al.
A comparison of remote vs. local influence of El Niño on the coastal circulation of the northeast Pacific
Deep Sea Res. Part II Top. Stud. Oceanogr.
(2009) - et al.
From krill to convenience stores: forecasting the economic and ecological effects of fisheries management on the US West Coast
Mar. Policy
(2012) - et al.
Screening california current fishery management scenarios using the atlantis end-to-End ecosystem model
Prog. Oceanogr.
(2012) - et al.
Developing a high taxonomic resolution food web model of the california current ecosystem to assess the trophic position of forage fish and their predators
Ecol. Model.
(2016) - et al.
Dealing with uncertainty in ecosystem models: the paradox of use for living marine resource management
Prog. Oceanogr.
(2012) - et al.
Recent collapse of northern anchovy biomass off California
Fish. Res.
(2016) - et al.
New target fisheries lead to spatially variable food web effects in an ecosystem model of the California Current
Ecol. Model.
(2014)
Aggregation and removal of weak-links in food-web models: system stability and recovery from disturbance
Ecol. Model.
Exploring the implications of the harvest control rule for Pacific sardine, accounting for predator dynamics
A MICE model. Ecol. Model.
Demonstration of a fully-coupled end-to-end model for small pelagic fish using sardine and anchovy in the California, Current
Prog. Oceanogr.
Using an Atlantis model of the southern Benguela to explore the response of ecosystem indicators for fisheries management
Environ. Model. Softw.
Forage species in predator diets: synthesis of data from the California Current
Ecol. Inform.
Predictions from simple predator-prey theory about impacts of harvesting forage fishes
Ecol. Model.
Reconstruction of the history of Pacific sardine and northern anchovy populations over the past two millennia from sediments of the Santa Barbara Basin, California
CalCOFI Rep
Status of the California Sea Lion Population on the US West Coast. Admin. Rep. LJ-88-07
US Pacific Marine Mammal Stock Assessments: 2012 (NOAA Technical Memorandum NMFS-SWFSC 504)
From anchovies to sardines and back: multidecadal change in the Pacific Ocean
Science
Climate, anchovy, and sardine
Annu. Rev. Mar. Sci.
Global seabird response to forage fish depletion—one-third for the birds
Science
Small pelagics in upwelling systems: patterns of interaction and structural changes in wasp-waist ecosystems
ICES J. Mar. Sci.
Sampling selectivity in acoustic-trawl surveys of Pacific sardine (Sardinops sagax) biomass and length distribution
ICES J. Mar. Sci.
Fishing amplifies forage fish population collapses
Proc. Natl. Acad. Sci.
Application of Ecosystem-Based Fishery Management Approaches in the Northern California Current
Daily egg production, spawning biomass and recruitment for the central subpopulation of Northern anchovy 1981–2009
Calif. Coop. Ocean Fish. Invest. Rep.
Humpback whale diets respond to variance in ocean climate and ecosystem conditions in the California Current
Glob. Change Biol.
Lessons in modelling and management of marine ecosystems: the Atlantis experience
Fish
An integrated approach is needed for ecosystem based fisheries management: insights from ecosystem-level management strategy evaluation
PLoS One
Biological ensemble modeling to evaluate potential futures of living marine resources
Ecol. Appl.
Beyond the defaults: functional response parameter space and ecosystem-level fishing thresholds in dynamic food web model simulations
Can. J. Fish. Aquat. Sci.
Effects of fishing and acidification-related benthic mortality on the southeast Australian marine ecosystem
Glob. Change Biol.
Predicting interactions among fishing, ocean warming, and ocean acidification in a marine system with whole-ecosystem models
Conserv. Biol.
Agenda Item G.3. a: USFWS Report
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Projecting climate change impacts from physics to fisheries: A view from three California Current fisheries
2023, Progress in OceanographyRapid vulnerability assessment of Pacific sardine (Sardinops sagax) fisheries facing climate change in Mexico
2022, Progress in OceanographyPacific herring (Clupea pallasii) as a key forage fish in the southeastern Gulf of Alaska
2022, Deep-Sea Research Part II: Topical Studies in OceanographyCitation Excerpt :Ecosystem models of the southeastern Gulf of Alaska and California Current also agree in emphasizing the roles of food web complexity and forage fish guild redundancy in modulating the impacts of herring depletion on predators (Kaplan et al. 2013, 2017; Koehn et al. 2016, 2017). In the California Current, simulated forage fish depletion in both EwE and Atlantis positively affected some zooplankton and planktivorous fish through release from predation and competition, respectively (Kaplan et al. 2013, 2017). These releases resulted from generalist feeding by most predators and functional redundancy among forage fish (Koehn et al., 2016; Kaplan et al., 2017).
Fisheries management tools to support coastal and marine spatial planning: A case study from the Northern Gulf of California, Mexico
2020, MethodsXCitation Excerpt :The modeling platform summarizes biological components as functional groups aggregated by trophic, life history, or niche similarities. Further information on Atlantis can be found in the User's Guide [6], the Atlantis Wiki (https://research.csiro.au/atlantis/home/links/), and recently published Atlantis applications [29,49,50]. The Atlantis model for the Northern Gulf of California, which includes the Coastal Corridor, extends over 57,800 km2, represents ecosystem structure and function in 2008, current fishing effort, and provides a detailed representation of the Northern Gulf's oceanography, historical fishing patterns, migration and movement of key species, and variability in diet compositions [2,3].
A multi-predator trophic database for the California Current Large Marine Ecosystem
2023, Scientific Data