Monk Seal Ecosystem Model Data: A Comparison of Ecosystem Structure and Energy Flows of Monk Seal Populations from Laysan Island and French Frigate Shoals in the Northwestern Hawaiian Islands

To understand various ecosystem dynamics that could explain observed changes and differences in monk seal biomass at French Frigate Shoals (FFS) and Laysan (LAY), Ecopath with Ecosim (EwE) version 6.4.4 modeling software was used to conduct two types of simulations, sensitivity (to understand the system) and hindcast (to evaluate drivers of monk seal population dynamics). EwE models for LAY and FFS were developed and model output was compared between the 2 models. The model output data included in the data sets represent the most important conclusions as reported in the publication from this study. These are (1) the mean of the last 5 years of each perturbation for sensitivity assessment; and (2) hindcast simulations. The first data set was used to understand the main drivers of the trophic structure and energy flow in the ecosystems. Four perturbation scenarios were simulated for a time span of 40 years (2010 through 2049): (a) baseline (compare static structural ecosystem composition between FFS and LAY), (b) altered predator abundance (30% decrease in biomass of main predators in the ecosystem), (c) altered monk seal prey abundance (30% decrease in biomass of main monk seal prey groups, with and without bottomfish to test how much bottomfish accounts for changes, and (d) altered primary productivity (change productivity annually by 10% for both phytoplankton and benthic algae through an annual forcing factor of 0.9 and 1.1 on both groups). The hindcast simulations were performed to evaluate the importance of historical stressors to monk seal population dynamics by selecting the best-fit model for the monk seal biomass time series (1998-2015). Stressors included were (a) fishing with time series based on commercial fishery data, (b) environment with time series of the monthly PDO index as a multiplier for primary productivity, (c) additional mortality simulated with a constant removal of monk seals of varied intensities, and (4) combinations of these 3 stressors (2a and 2c being the most important with regard to the observed trend in monk seal population). Time series observation data of monk seal biomass and benthic bottomfish biomass, as well as catch time series of bank sharks (only for FFS), benthic and demersal bottomfish, bank jacks, and macroheterotrophs (lobsters) were loaded into Ecosim for model fitting. Refer to Weijerman et al (2017) for complete details.

The main objective of this study was to understand the difference in ecosystem dynamics that could explain the observed decrease in monk seal biomass at French Frigate Shoals and the more stable biomass at Laysan. Specifically we investigated the relative influence of potential drivers---including primary productivity, prey population, and predation---on the monk seal populations in 40-year simulations and the external drivers of climate and fishing with an additional mortality on monk seals in hindcast simulations. Understanding the drivers and predictability of population trends will illuminate areas of focus for Hawaiian monk seal recovery efforts.

Weijerman M, Robinson S, Parrish F, Polovina J, Littnan C (2017) Comparative application of trophic ecosystem models to evaluate drivers of endangered Hawaiian monk seal populations. Mar Ecol Prog Ser 582:215-229. https://doi.org/10.3354/meps12320

The output datasets include (1) Forecast simulations with monthly output for the last 5 years of a 40-year simulation run (year 2044 through 2049). Monthly output includes biomass of a variety of marine organisms, such as seabirds, sharks, fish, turtles, plankton, and algae; (2) Hindcast simulations from 1998 through 2015 include simulated monk seal and bottomfish biomass factoring a few key external drivers.

While every effort has been made to ensure that these data are accurate and reliable within the limits of the current state of the art, NOAA cannot assume liability for any damages caused by errors or omissions in the data, nor as a result of the failure of the data to function on a particular system. NOAA makes no warranty, expressed or implied, nor does the fact of distribution constitute such warranty.

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NOAA Coral Reef Ecosystem Program (CREP) Data Sharing Recommendations, version 9.0 updated August 12, 2015:

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Example citation:

"This publication makes use of data products provided by the Ecosystem Sciences Division (ESD), Pacific Islands Fisheries Science Center (PIFSC), National Marine Fisheries Service (NMFS), National Oceanic and Atmospheric Administration (NOAA), with funding support from the NOAA Pacific Islands Fisheries Science Center (PIFSC). The analysis and interpretations presented here are solely that of the current authors.”

Data can be accessed online via the NOAA National Centers for Environmental Information (NCEI) Ocean Archive.

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Please cite PIFSC Ecosystem Sciences Division (ESD) when using the data.

Suggested citation:

Pacific Islands Fisheries Science Center, 2019: Monk Seal Ecosystem Model Data: A Comparison of Ecosystem Structure and Energy Flows of Monk Seal Populations from Laysan Island and French Frigate Shoals in the Northwestern Hawaiian Islands from 1998 through 2015, https://www.fisheries.noaa.gov/inport/item/35796.

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Model outputs (Excel/csv files) were generated using Ecopath with Ecosim version 6.4.3.

Model output data (i.e., predictions) provide a range of potential answers based on the available data and should not be used for tactical management.

Monk seal biomass data comes from beach counts. Bottomfish biomass data was model derived based on stock assessments of the bottomfish fishery. All generated data is model derived and has some uncertainty associated with it.

Best-fit of model-simulated output data and observational data was based on the least square fitting criterion and summed the squared deviations. Additionally, the Akaike's information criterion (AIC) was calculated taking into account the small sample size.

All available biological data for the areas of interest were used. Fishery data was limited to 2010 as NOAA discontinued stock assessments once the fishery was closed.

Data sets are model output data.

Model dynamics were validated with a hindcast simulation (1998-2015). Time series data of monk seal biomass and bottomfish biomass were loaded into Ecosim for validation and to fine-tune the model by adjusting vulnerability values and so minimize the residuals between predicted and observed time series of monk seal and bottomfish biomass using a least-square fitting criterion. We manually adjusted vulnerability values of interest based on the results from the perturbation scenarios and restricted them to ecological meaningful values (i.e., preferably between 1 and 3 with 10 as maximum value).

Model data is stored on an external hard drive and backed up to a server at PIFSC weekly by the data steward. Data on the PIFSC server are managed by NOAA IRC and NOAA Fisheries ITS.

Input data was collected for the Ecopath with Ecosim model (EwE) from Parrish et al 2011; PIFSC Ecosystem Sciences Division data, monk seal data, bottomfish stock asessment data, and other sources defined in Weijerman et al 2017 MEPS. The model output data is generated with the EwE model. See Weijerman et al 2017 MEPS for details.