6 research outputs found
A NOVEL INDEX OF ABUNDANCE OF JUVENILE YELLOWFIN TUNA IN THE ATLANTIC OCEAN DERIVED FROM ECHOSOUNDER BUOYS
The collaboration with the Spanish vessel-owners associations and the buoy-providers
companies, has made it possible the recovery of the information recorded by the satellite linked
GPS tracking echosounder buoys used by the Spanish tropical tuna purse seiners and associated
fleet in the Atlantic since 2010. These instrumental buoys inform fishers remotely in real-time
about the accurate geolocation of the FAD and the presence and abundance of fish aggregations
underneath them. Apart from its unquestionable impact in the conception of a reliable CPUE
index from the tropical purse seine tuna fisheries fishing on FADs, echosounder buoys have also
the potential of being a privileged observation platform to evaluate abundances of tunas and
accompanying species using catch-independent data. Current echosounder buoys provide a
single acoustic value without discriminating species or size composition of the fish underneath
the FAD. Therefore, it has been necessary to combine the echosounder buoys data with fishery
data, species composition and average size, to obtain a specific indicator. This paper presents a
novel index of abundance of juvenile yellowfin tuna in the Atlantic Ocean derived from
echosounder buoys for the period 2010-2018
Comparing the distribution of tropical tuna associated with drifting fish aggregating devices (DFADs) resulting from catch dependent and independent data.
Species distribution models (SDMs) are used for a variety of scientific and management applications. For species associated with drifting fish aggregating devices (DFADs), such as tuna, spatial models can help tuna Regional Fisheries Management Organizations (t-RFMOs) understand their habitat characteristics and dynamics. DFADs are monitored and tracked with satellite linked echo-sounder buoys, which remotely provide fishers rough estimates of the abundance of fish underneath them. Although this type of catch-independent data has been recently used in scientific studies, SDMs using these data have never been compared with models using catch-dependent data (i.e. nominal catch data). This study investigates the results obtained with both data sources using Bayesian Hierarchical spatio-temporal models, allowing to analyze their advantages and disadvantages, as well as compare the predicted distributions. Although the two model outputs show, in general, similar areas of tuna presence under the DFADs, the most remarkable result of the comparison between the models derived from the two different data sources is the precision of the hotspots identified in the prediction maps. The maps obtained with acoustic data allow identifying areas of high probability of tuna presence under the DFADs with greater precision, whereas the maps derived from catch data do not allow observing any variation on a finer scale. The application of spatio-temporal models of tuna associated with DFADs using acoustic data provided by fishers’ echo-sounder buoys appears promising to identify the distribution dynamics of the species in a cost-effective way and may help designing integrated spatial programs for more efficient fishery management
Aggregation process of drifting fish aggregating devices (DFADs) in the Western Indian Ocean: Who arrives first, tuna or non-tuna species?
Floating objects drifting in the surface of tropical waters, also known as drifting fish aggregating devices (DFADs), attract hundreds of marine species, including tuna and non-tuna species. Industrial tropical purse seiners have been increasingly deploying artificial man-made
DFADs equipped with satellite linked echo-sounder buoys, which provide fishers with information on the accurate geo-location of the object and rough estimates of the biomass aggregated underneath, to facilitate the catch of tuna. Although several hypotheses are under
consideration to explain the aggregation and retention processes of pelagic species around
DFADs, the reasons driving this associative behavior are uncertain. This study uses information from 962 echo-sounder buoys attached to virgin (i.e. newly deployed) DFADs
deployed in the Western Indian Ocean between 2012 and 2015 by the Spanish fleet (42,322
days observations) to determine the first detection day of tuna and non-tuna species at
DFAD and to model the aggregation processes of both species group using Generalize
Additive Mixed Models. Moreover, different seasons, areas and depths of the DFAD underwater structure were considered in the analysis to account for potential spatio-temporal and
structure differences. Results show that tuna species arrive at DFADs before non-tuna species (13.5±8.4 and 21.7±15.1 days, respectively), and provide evidence of the significant
relationship between DFAD depth and detection time for tuna, suggesting faster tuna colonization in deeper objects. For non-tuna species, this relationship appeared to be not significant. The study also reveals both seasonal and spatial differences in the aggregation
patterns for different species groups, suggesting that tuna and non-tuna species may have
different aggregative behaviors depending on the spatio-temporal dynamic of DFADs. This
work will contribute to the understanding of the fine and mesoscale ecology and behavior of
target and non-target species around DFADs and will assist managers on the sustainability
of exploited resources, helping to design spatio-temporal conservation management measures for tuna and non-tuna species
Seasonal distribution of tuna and non-tuna species associated with Drifting Fish Aggregating Devices (DFADs) in the Western Indian Ocean using fishery-independent data.
Man-made floating objects in the surface of tropical oceans, also called drifting fish
aggregating devices (DFADs), attract tens of marine species, including tunas and nontuna species. In the Indian Ocean, around 80% of the sets currently made by the
EU purse-seine fleet are on DFADs. Due to the importance and value of this fishery,
understanding the habitat characteristics and dynamics of pelagic species aggregated
under DFADs is key to improve fishery management and fishing practices. This study
implements Bayesian hierarchical spatial models to investigate tuna and non-tuna
species seasonal distribution based on fisheries-independent data derived from fishers’
echo-sounder buoys, environmental information (Sea Surface Temperature, Chlorophyll,
Salinity, Eddie Kinetic Energy, Oxygen concentration, Sea Surface Height, Velocity and
Heading) and DFAD variables (DFAD identification, days at sea). Results highlighted
group-specific spatial distributions and habitat preferences, finding higher probability
of tuna presence in warmer waters, with higher sea surface height and low eddy
kinetic energy values. In contrast, highest probabilities of non-tuna species were found
in colder and productive waters. Days at sea were relevant for both groups, with
higher probabilities at objects with higher soak time. Our results also showed speciesspecific temporal distributions, suggesting that both tuna and non-tuna species may
have different habitat preferences depending on the monsoon period. The new findings
provided by this study will contribute to the understanding of the ecology and behavior
of target and non-target species and their sustainable management
Using fishers’ echo-sounder buoys to estimate biomass of fish species associated with drifting fish aggregating devices in the Indian Ocean.
The majority of the drifting fish aggregating devices (DFADs) used by the industrial tropical tuna purse
seine fishery are deployed with satellite linked echo-sounder buoys. These buoys provide information
on the accurate geo-location of the floating object and estimates of fish biomass underneath the DFAD.
However, current echo-sounder buoys do not provide information on species or size composition under the
DFADs. The aim of this study is to progress towards improved remote biomass estimates using the previous
models proposed in the field, based on existing knowledge of the vertical distribution of non-tuna and tuna
species at DFADs and mixed species target strengths (TS) and weights. Aiming to this objective, we use
287 fishing set information and their corresponding acoustic samples from echo-sounder buoys prior to the
fishing set in the Indian Ocean. Results show that manufacturer’s biomass estimates generally improve,
being this improvement more pronounced in NW Seychelles and in Mozambique Channel. However, the
improvement of the biomass estimates is not as large as expected, so it can be further improved, indicating
that the large spatio-temporal variability in the Indian Ocean is not easily considered with a single model.
Potential reasons driving echo-sounder buoy estimates variability, as well as the limitations encountered
with these devices are discussed, including the lack of consistent TS values for tropical tunas, among other