Models for Investigating Individual to Population Scale Spatial Dynamics
Reports (PDF): FY 2006,
FY 2005, FY
This project forms part of a series of studies that are being conducted
to facilitate the ambitious multi-national Oceanic Fisheries and Climate
Change Project (OFCCP)
of the International GLOBEC
Program – a component of the International Geosphere-Biosphere Programme
sponsored by the IOC and SCOR. The OFCCP will investigate the effect
of climate change on the productivity and distribution of oceanic tuna
stocks and fisheries in the Pacific with the goal of predicting short–to
long term changes and impacts related to climate variability. The ultimate
goal of the OFCCP project is to conduct simulation with ecosystem models
that include the main tuna species, using an input data set predicted
under a scenario of climate change induced by greenhouse warming as
defined by the Intergovernmental Panel
on Climate Change (IPCC). However, analyses of simulations based
on retrospective series of oceanographic and fishing data sets are necessary
to improve upon the predictive capacity of the ecosystem models, particularly
the inter-annual (ENSO) and the decadal (Pacific Decadal Oscillations)
Mixed Resolution Models for Investigating Individual to Population Scale
Dynamics, addresses ways improve upon two classes of models: Individual
Based Models (IBMs) and Advection Diffusion Reaction Models (ADRMs)
that would help to model from ocean basin to individual scale as identified
by the OFCCP objectives. Both these types of models have been successfully
applied to predicting tuna behaviors; IBMs at the very fine scale and
ADRMs at the population level.
classes of models can provide complimentary approaches to investigating
the problems of scale integration when going from individual to the
population level and from individual movements to advection-diffusion
patterns. However, the approach needs a unifying framework combining
large and small spatio-temporal scales i.e., the mixed resolutions in
a same model domain. Mixed resolution models use a stretched grid system
with greater resolution at one of multiple locations of the model domain.
objectives of the project are:
develop a unifying framework based on the development of mathematical
solutions for using mixed-resolution in ADRMs and combine IBM and
develop a range of IBMs for tunas (skipjack, yellowfin, bigeye, albacore)
and other species of importance for tuna fisheries management. For
instance, enhanced understanding of turtles' spatial dynamics might
lead to effective bycatch mitigation.
produce predicted field of key variables (temperature, currents, primary
and zooplankton production, forage biomass) at the scale of the Pacific
basin, with several focus areas where the resolution will be enhanced.
The predicted environment in these focus areas will serve for IBMs
select focus areas according to their interests and the existence
of data allowing validation of the simulations and (consequently)
parameterization of the models.
analyze scale effects and compare movement generated from IBMs and
ADRMs between them and with observations.
investigate impacts of seamounts, anchored or drifting FADs on individual
behavior from IBM simulations and observations, in the search for
deducing consequences at large-scale population level.
and programming developments required for improving movement spatial
population dynamics models would form two post-doctoral studies. The
first study will focus on developing fundamental equations and their
numerical solutions to be incorporated in the population dynamics models
based on tuna tagging data, or on environmental constraints (Spatial Environmental
Population Dynamics Model, SEPODYM) for using mixed resolution grids.
Further work on the fundamental PDEs and their numerical solutions is
necessary to combine movements at the scales of both populations and
individuals. The possibility of using non-Fickian formulation of the
diffusion equation will be explored. More accurate and faster solution
methods will be sought in conditions where diffusive movements are greater
than advective movements. Variable grid spacing finite differences methods
will be developed that are consistent with the individual based models.
post-doc study would be devoted to the development of IBMs that will
use the oceanic environment predicted by the ESSIC (Earth Science System Interdisciplinary Center)
coupled physical-biogeochemical model (temperature, currents, plankton)
and the SEPODYM model (forage). Behavior of tuna or other large pelagics
predicted with IBMs would be compared to observed movements of individuals
marked with electronic tags and to spatial patterns generated by ADRMs.
geographic regions of focus have been identified which will serve to
compare several observed and predicted key variables:
Transition Zone Chlorophyll Front (TZCF)
The Transition Zone Chlorophyll Front stretches across 8000 km in
the North Pacific with seasonal north-south shifts about 1000 km.
Satellite telemetry data on movement of loggerhead turtles and detailed
fisheries data for albacore tuna show that these apex predators travel
along the TZCF as they migrate across the North Pacific. The position
dynamics and the meandering in the TZCF, related to El Nino and La
Nina events, have shown to alter the spatial distributions of loggerhead
turtles and the catch rates of albacore tuna.
Proposed activities include simulations with the model SEPODYM
that will be used to investigate the movement of albacore along the
TZCF. IBM simulations will also be used to study the individual movement
of tuna and turtles along the front.
A number of tuna tagging studies have been carried out (conventional
tagging, archival tagging and acoustic telemetry) around the Hawaiian
Islands. An array of "listening stations" is currently being
deployed around the island of O'ahu to collect movement data of yellowfin
and bigeye tuna equipped with coded transmitters. There are also plans
to deploy listening stations around the other Hawaiian Islands and
tagging other pelagic species (sharks, marlins, mahimahi, etc.) with
transmitters. These meso-scale data will complement data collected
in the past on very fine-scale movements (acoustic telemetry, archival
tagging) and on larger-scale movements of tuna (conventional tagging).
The study of individual behavior between the different sites around
Hawaii Islands will be helpful to understand the mechanism of fine-scale
aggregations around the floating objects and seamounts. The framework
proposed here of combining IBMs and spatial population models will
be used to assess the consequence of extrapolating the individual
behaviors up to the population level.
Subtropical Convergence Zone (STCZ)
Studies on this geographic region will target on understanding the
spatial dynamics of tuna forage using acoustic methods. During an
upcoming research cruise, planned for mid 2003 in the STCZ area (R.V.
Tangaroa, NIWA), measurements of micronekton target strength will
be made in conjunction with target identification by opening-closing
net and cameras. These data will permit discrimination of acoustic
targets based on size and dB difference between frequencies so that
krill and shrimps can by distinguished from mesopelagic fish. Another
more recent discrimination technique will also be used to separate
the backscatter of swimbladder from non-swimbladder organism. The
combination of both methods allows the partitioning of acoustic backscatter
into three broad categories: swimbladder fish, non-swimbladder fish/squid,
and krill/shrimp. Net samples of microneckton will be collected for
identification of species and size distributions in these three categories.
The 2003 cruise data along with earlier data of 1997, 1999 and 2001
collected in cross-front transects will be analyzed to quantify the
spatio-temporal variability of micronekton (tuna forage) across the
frontal zone. The results of this analysis will be used to parameterize
the forage component in the SEPODYM model (biomass transfer) and to
validate the predicted spatial forage distribution. Other variables
(temperature, salinity, currents, chlorophyll) collected during these
cruises will also be useful for fine-scale validation of the fields
predicted by the ESSIC model. Impacts of predicted forage (micronekton)
spatial distribution on the spatial distribution of south Pacific
albacore will be investigated using IBMs and SEPODYM.
funding for this 2-year project to be awarded in early 2003.