Home > Biology Projects
Buoys as Autonomous Observatories of Pelagic Ecosystems
Investigation of Aggregation Behavior
of FAD-Associated Small Yellowfin Tuna and Size Dependant Vertical Stratification
Progress reports (PDF): FY
2009, FY 2008,
FY 2007, FY
2006, FY 2005,
Associative behavior is a major component of the life of pelagic fishes.
Tropical tunas and other fish species are frequently found in association
with a variety of floating objects and with topographic features such
as seamounts. Increasingly, fishermen exploit these associations to
expand their catches and each year, modern industrial tuna fisheries
release thousands of floating fish aggregating devices (FADs) throughout
the world's oceans. Although structure-associated aggregations are typically
comprised of tunas, there are also sharks, rays, billfish, dolphinfish,
sea turtles, and other species caught at FADs. These species, together
with the high numbers of sub-adult tunas, are usually not retained but
discarded at sea by industrial fisheries. With the increase in catch
rates occurring at FADs, including from increased purse seine activity,
the standard methods for fishery stock assessment and management have
been significantly impacted. Fisheries exploiting these FADs can no
longer be managed species by species and the need exists for an ecosystem-based
approach to fishery management. These changes require the development
of new techniques for stock assessment and fishery management that take
into account these structure associated aggregations and their importance
to the fishery.
researchers believe that appropriate observations and understanding
of the aggregation/association phenomenon of fish at FADs will enable
fishery researchers in developing fishery-independent indices of local
abundance. Earlier fish tracking studies indicate that tunas are usually
not located immediately beneath FADs but rather 'orbit' around FADs
at varying distances. Hence, researchers propose that an accurate underwater
observatory must be able to collect scientific data by "sweeping"
the entire circumference of the FAD in order to estimate the size of
the aggregation and to eventually distinguish different species and
size classes of fish. With the rapid evolution in electronic tag design
and capability, project researchers will study the feasibility of developing
a tag capable of using acoustic information to determine the 'ecological'
circumstance surrounding the tagged fish. Such as whether the fish is
participating in collective (schooling) behavior or whether the fish
is associated with a floating object. If new sensors on schooling or
association can be developed they could be coupled with a recent telemetry
innovation - CHAT tags (Communicating History Acoustic Transmitters).
These devices remotely transfer archived data from the fish to the listening
stations deployed on the seabed or on buoys. Data transfer from the
fish to the buoy is achieved by "sonic modem" technology.
This would represent a major advance because 'ecological' tags with
CHAT capabilities could provide insight into the behavioral and physiological
history of many fish species without requiring research ship time.
The main objective of the project is to develop prototypes and methods
for creating observatories of pelagic ecosystems. This will be achieved
through specific objectives:
of autonomous 'smart FADs. To be equipped with:
sonar to observe the collective components of aggregations
a listening station to observe the individual components of the
an appropriate power system for an autonomous operation of these
uplinks to download stored data to land-based stations
the observatories will also accommodate other oceanographic sensors
such as doppler current meters, temperature sensors, as well as down-looking
sonar systems designed to observe scattering layer organisms (corresponding
to some components of the diet of large pelagic fishes).
Identification of specifications for ecological sensors and transmitters
This would help determine the types of marine acoustic signatures that
could be used to design an 'ecology tag' that would indicate whether
a fish was in a school of conspecifics or in the vicinity of a floating
object. CHAT versions of this tag could eventually be used in conjunction
with the smart FADs.
Co-occurence of large pelagic species at FADs
To use coded transmitters to document the individual behavior of non-tuna
species in networks of FADs. Fish carrying the individually coded tags
will be detected by data collectors ("listening stations")
mounted on FADs in the Hawaiian waters. This will constitute the first
network of instrumented buoys for studying residence times, patterns
of visitation to the FADs, spatial dynamics, and species interactions.
The research activities of the project are distributed into four main
Organization of an international workshop on the concepts of pelagic
Scientists studying small pelagic fish and those working on large pelagic
fishes do not use the same tools and methods to observe their animals.
A main objective of this workshop is to gather specialists from each
of these groups, as well as scientists and engineers involved in acoustic
and electronic tags, to exchange ideas and develop tools to advance
the concept of observatories of pelagic ecosystems. This workshop was
convened in October 2002, see project page "Workshop
on How to Improve Studies on the Collective Behavior of Pelagic Fish".
Development, testing and validation of the hardware and software components
required to produce an autonomous 360° sonar
Design and development of sonar hardware and software will be headed
by Dr. Jules Jaffe of Scripps Institution of Oceanography. Dr. Jaffe
is a marine biophysicist specializing in underwater bioacoustics research.
He will oversee the selection of hardware sonar components including
the transducer, power supply, 360° 'sweep' mechanism, and buoy design.
ship-borne acoustic surveys will be conducted to document school distributions
around FADs and to calibrate synchronous data recorded by the side-scan
system being evaluated for the FAD-based prototype. Prior to incorporation
of the side-scan system into a buoy with 360° capabilities, the
side-scan system will be deployed from a vessel moored adjacent to a
FAD. Side-scan surveys of associated tuna schools will be conducted
simultaneously with the use of a SIMRAD sonar system deployed on a separate
vessel. In this way validation and interpretive software can be developed
prior to the incorporation of the sonar into an autonomous platform.
Synchronous experimental fishing at the FAD will also be conducted to
cross-validate the split-beam and FAD sonar data. Data storage and transmission
capabilities will be addressed by Wildlife
Computers, Inc. of Seattle, Washington.
Development of criteria for designing 'ecology tags'. Acquisition of
specifications for the development of new electronic tags with 'ecological'
of new 'ecological' sensors, identifying the types of sounds produced
by schools and floating objects is necessary. This task will consist
of identifying underwater sounds produced by schools of tuna and FADs
and will be under the direction of Mr. Miguel Pol (New Caledonia) who
is an expert in the collection and analysis of underwater sounds. Precise
recordings of groups of tunas and a single fish swimming in a tank will
be recorded to allow design of a hydrophone and filtering system that
will exclude sounds produced by fish carrying the tag but that will
be sensitive to sounds generated by a large school. School signatures
will be obtained from the field by recording sounds produced by tuna
schools associated with coastal FADs. Estimates of sizes and composition
of the schools will be made using appropriate sonar systems. Similarly,
recording of sounds produced by FADs will be done to identify the characteristics
that should be detected by the future integrated hydrophone.
Electronic tagging of non-tuna species associated with Hawaiian FADs
Throughout the duration of the project an intensive study of the dynamics
of pelagic species in networks of FADs will be conducted. More than
a dozen of the Hawaii FADs have been equipped with listening stations
and tropical tunas are currently being equipped with ID electronic tags.
Project researchers plan to install listening stations at other FADs
around O'ahu Island and the neighbor islands as well as tagging other
species such as sharks, marlins and mahimahi. This large network of
listening stations will expedite optimal future deployment of the smart
FADs and will also provide very useful novel data on species interactions,
e.g., timing of associations.
funding for this 2-year project to be available mid 2003.