Article

1999 ◽  
Vol 56 (6) ◽  
pp. 984-993 ◽  
Author(s):  
Laurent Dagorn ◽  
Pierre Fréon
Keyword(s):  
School Size ◽  
Temporal Dynamics ◽  
Fusion Rule ◽  
After School ◽  
Dynamic Approach ◽  
Free Swimming ◽  
Individual Based Models ◽  
Tropical Tuna ◽  
Floating Objects ◽  
School Cohesion

Among the different assumptions proposed to explain why tropical tuna aggregate around floating objects ("logs"), one of the most recent is that floating objects may represent meeting points for tuna. This "meeting point hypothesis" proposes that tuna can use these floating objects to form larger schools after school fission or dispersion. The influence of meeting points on tuna school sizes is explored through different individual-based models that consider a single fusion rule and a variety of fission rules based on energetic considerations, the role of school size on school cohesion, predator attacks, and dispersion during the night. Results are first analyzed using an averaging approach to study the overall mean school size in habitats having different floating object densities. Second, a dynamic approach is used to compare the temporal dynamics of associated and free-swimming school sizes. The averaging approach indicates that in all the models (except those based on energetics), floating objects increase school size, at least up to a certain object density. The dynamic approach clearly illustrates different dynamics in the school size of associated and free-swimming schools. Most of our models show that tuna associated with logs resume schooling in larger schools after fission events.

scholarly journals Quantifying the increase in fishing efficiency due to the use of drifting FADs equipped with echosounders in tropical tuna purse seine fisheries

2020 ◽  
Author(s):  
Gwenaëlle Wain ◽  
Loreleï Guéry ◽  
David Michael Kaplan ◽  
Daniel Gaertner
Keyword(s):  
New Technology ◽  
Recent Change ◽  
Purse Seine ◽  
Catch Per Unit Effort ◽  
Katsuwonus Pelamis ◽  
Thunnus Obesus ◽  
Efficiency Increase ◽  
Tropical Tuna ◽  
Floating Objects ◽  
The Impact

Abstract Numerous pelagic species are known to associate with floating objects (FOBs), including tropical tunas. Purse seiners use this behaviour to facilitate the capture of tropical tunas by deploying artificial drifting fish aggregating devices (dFADs). One major recent change has been the integration of echosounders in satellite-tracked GPS buoys attached to FOBs, allowing fishers to remotely estimate fishable biomass. Understanding the effects of this new technology on catch of the three main tuna species (yellowfin tuna, Thunnus albacares; bigeye tuna, Thunnus obesus; and skipjack tuna, Katsuwonus pelamis) is important to accurately correct for this change in catch-per-unit-effort (CPUE) indices used for stock assessments. We analysed catch data from the French purse seine fleet for the period 2010–2017 in the Indian Ocean to assess the impact of this fleet’s switch to echosounder buoys around 2012. Results indicate that echosounders do not increase the probability a set will be succesful, but they have a positive effect on catch per set, with catches on average increasing by ≈2−2.5 tonnes per set (≈10%) when made on the vessel's own dFADs equipped with an echosounder buoy. Increases were due to a decrease in sets below ≈25 tonnes and an increase in those greater than ≈25 tonnes, with a non-linear transition around this threshold. This increase explains the considerable investment of purse seiners in echosounder buoys, but also raises concerns about bias in stock size estimates based on CPUE if we do not correct for this fishing efficiency increase.

Fishing on floating objects (FOBs): how French tropical tuna purse seiners split fishing effort between GPS-monitored and unmonitored FOBs

2018 ◽  
Vol 75 (11) ◽  
pp. 1849-1858 ◽  
Author(s):  
Julia E. Snouck-Hurgronje ◽  
David M. Kaplan ◽  
Emmanuel Chassot ◽  
Alexandra Maufroy ◽  
Daniel Gaertner
Keyword(s):  
Search Time ◽  
Fishing Effort ◽  
Purse Seine ◽  
Trajectory Data ◽  
Catch Per Unit Effort ◽  
Position Information ◽  
Foreign Objects ◽  
Tropical Tuna ◽  
Floating Objects ◽  
Over Time

Fishing on floating objects (FOBs) dominates catch in tropical tuna purse seine fisheries. One frequently cited advantage of deploying GPS-monitored FOBs is that the position information can be used for directed fishing to reduce search time for tuna. However, purse seiners also fish on foreign objects for which position information is not available. It is critical to quantify the prevalence of fishing on GPS-monitored versus unmonitored FOBs to understand how they impact fishing effort and catch per unit effort. We analyzed French commercial, observer, and FOB trajectory data in the Atlantic and Indian oceans to determine how often purse seine vessels fish on GPS-monitored FOBs. Only 2.7%–20.4% of French FOB fishing sets over 2007–2013 in both oceans were made on GPS-monitored FOBs. Though increasing over time, the low percentage suggests that French vessels do not primarily use GPS-monitored FOBs to reduce search time for tuna. We hypothesize that fishery-wide FOB deployments have important collective consequences for overall fishing effort and recommend that future effort metrics should be based on fishery-wide FOB activities.

Targeting bigger schools can reduce ecosystem impacts of fisheries

2012 ◽  
Vol 69 (9) ◽  
pp. 1463-1467 ◽  
Author(s):  
Laurent Dagorn ◽  
John D. Filmalter ◽  
Fabien Forget ◽  
Monin Justin Amandè ◽  
Martin A. Hall ◽  
...  
Keyword(s):  
Total Yield ◽  
Substantial Reduction ◽  
Management Approach ◽  
Resource Exploitation ◽  
Free Swimming ◽  
Ecosystem Impacts ◽  
Set Size ◽  
Living Resource ◽  
Tropical Tuna ◽  
Fish Aggregating Devices

Sustainability of living resource exploitation relies on an ecosystem management approach. Within tropical tuna purse seine fisheries using fish aggregating devices (FADs), such an approach incorporates the reduction of bycatch, in particular vulnerable species such as elasmobranchs. The levels of total bycatch (in mass) from fishing operations using FADs is known to be five times higher than when tuna are caught in free-swimming schools. We intend to find practical solutions to reduce bycatch in FAD sets through the investigation of the relationships between the ratio of bycatch to target catch across different set size classes in all oceans. Ratios were always highest when catches were small, with the smallest class of catches responsible for the highest total portion of bycatch (23%–43%) while only contributing negligibly to the total target catch (3%–10%). Reducing the number of fishing sets (a part of the total effort) while maintaining the same total yield could contribute to a substantial reduction in the impacts of human activities.

Comparison of condition factors of skipjack tuna (Katsuwonus pelamis) associated or not with floating objects in an area known to be naturally enriched with logs

2014 ◽  
Vol 71 (3) ◽  
pp. 472-478 ◽  
Author(s):  
Marianne Robert ◽  
Laurent Dagorn ◽  
Nathalie Bodin ◽  
Fabrice Pernet ◽  
Eve-Julie Arsenault-Pernet ◽  
...  
Keyword(s):  
Skipjack Tuna ◽  
Short Term ◽  
Free Swimming ◽  
Katsuwonus Pelamis ◽  
Meeting Point ◽  
Mozambique Channel ◽  
Alternative Hypotheses ◽  
Floating Objects ◽  
The Impact ◽  
Fish Aggregating Devices

In an area that has barely been modified by fish aggregating devices (FADs) (e.g., the Mozambique Channel, known to be naturally enriched with logs, with few FADs), we found that the condition of skipjack tuna (Katsuwonus pelamis) associated with floating objects was lower than those in free-swimming schools. As this result was found in an area that mimics the environmental state prior to the use of FADs, it questions the interpretation of previous studies where such a difference has been interpreted to reflect the impact of extensive FAD deployment on tunas. It is possible that before the use of FADs, tunas associated with logs were also in poorer condition than tunas in free-swimming schools. Our results suggest that the evolutionary reason for which tunas associated with floating objects might not relate to short-term trophic benefit, and alternative hypotheses (e.g., the meeting point hypothesis) are discussed to explain this result.

scholarly journals Population assessment of tropical tuna based on their associative behavior around floating objects

2016 ◽  
Vol 6 (1) ◽  
Author(s):  
M. Capello ◽  
J. L. Deneubourg ◽  
M. Robert ◽  
K. N. Holland ◽  
K. M. Schaefer ◽  
...  
Keyword(s):  
Population Assessment ◽  
Associative Behavior ◽  
Tropical Tuna ◽  
Floating Objects

Surface habitat modification through industrial tuna fishery practices

2021 ◽  
Author(s):  
Amaël Dupaix ◽  
Manuela Capello ◽  
Christophe Lett ◽  
Marco Andrello ◽  
Nicolas Barrier ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Indian Ocean ◽  
Habitat Modification ◽  
Pelagic Species ◽  
The Indian Ocean ◽  
Tropical Tuna ◽  
Associated Species ◽  
Floating Objects ◽  
Fish Aggregating Devices ◽  
Tuna Fishery

Abstract Natural floating objects (FOBs) have always been a major component of the habitat of pelagic species. Since the 1990s, the number of FOBs in the open ocean has increased greatly as a result of the introduction of fish aggregating devices (FADs) by the industrial tropical tuna purse seine vessels. These changes, and their potential impacts on the species that associate with FOBs, remain poorly understood. Using fisheries observer data, data from satellite-linked tracking buoys attached to FOBs and Lagrangian simulations, this study quantifies the temporal changes in the density and spatial distribution of FOBs due to the use of FADs in the Indian Ocean (IO) between 2006 and 2018. From 2012 to 2018, the entire western IO is impacted, with FADs representing more than 85% of the overall FOBs, natural FOBs less than 10%, and objects originating from pollution 5%. Results also suggest that both FADs and natural FOBs densities are lower in the eastern IO, but this initial investigation highlights the need for further studies. Our study confirms that FADs have greatly modified the density and spatial distribution of FOBs, which highlights the need to investigate potential consequences on the ecology of associated species.

scholarly journals Temporal dynamics of sitting behavior at work

2020 ◽  
Vol 117 (26) ◽  
pp. 14883-14889
Author(s):  
Pam ten Broeke ◽  
Merlijn Olthof ◽  
Debby G. J. Beckers ◽  
Nicola D. Hopkins ◽  
Lee E. F. Graves ◽  
...  
Keyword(s):  
Temporal Dynamics ◽  
Exercise Behavior ◽  
Sitting Time ◽  
Event Analysis ◽  
Time To Event ◽  
Dynamic Approach ◽  
Work Time ◽  
Sit To Stand ◽  
Objectively Measured ◽  
Continuous Chain

Sitting for prolonged periods of time impairs people’s health. Prior research has mainly investigated sitting behavior on an aggregate level, for example, by analyzing total sitting time per day. By contrast, taking a dynamic approach, here we conceptualize sitting behavior as a continuous chain of sit-to-stand and stand-to-sit transitions. We use multilevel time-to-event analysis to analyze the timing of these transitions. We analyze ∼30,000 objectively measured posture transitions from 156 people during work time. Results indicate that the temporal dynamics of sit-to-stand transitions differ from stand-to-sit transitions, and that people are quicker to switch postures later in the workday, and quicker to stand up after having been more active in the recent hours. We found no evidence for associations with physical fitness. Altogether, these findings provide insights into the origins of people’s stand-up and sit-down decisions, show that sitting behavior is fundamentally different from exercise behavior, and provide pointers for the development of interventions.

Massive increase in the use of drifting Fish Aggregating Devices (dFADs) by tropical tuna purse seine fisheries in the Atlantic and Indian oceans

2016 ◽  
Vol 74 (1) ◽  
pp. 215-225 ◽  
Author(s):  
Alexandra Maufroy ◽  
David M. Kaplan ◽  
Nicolas Bez ◽  
Alicia Delgado De Molina ◽  
Hilario Murua ◽  
...  
Keyword(s):  
Relative Proportion ◽  
Major Change ◽  
Purse Seine ◽  
Fourfold Increase ◽  
Natural Objects ◽  
The Indian Ocean ◽  
Tropical Tuna ◽  
Floating Objects ◽  
Fish Aggregating Devices ◽  
Logbook Data

Since the mid-1990s, drifting Fish Aggregating Devices (dFADs), artificial floating objects designed to aggregate fish, have become an important mean by which purse seine fleets catch tropical tunas. Mass deployment of dFADs, as well as the massive use of GPS buoys to track dFADs and natural floating objects, has raised serious concerns for the state of tropical tuna stocks and ecosystem functioning. Here, we combine tracks from a large proportion of the French GPS buoys from the Indian and Atlantic oceans with data from observers aboard French and Spanish purse seiners and French logbook data to estimate the total number of dFADs and GPS buoys used within the main fishing grounds of these two oceans over the period 2007–2013. In the Atlantic Ocean, the total number of dFADs increased from 1175 dFADs active in January 2007 to 8575 dFADs in August 2013. In the Indian Ocean, this number increased from 2250 dFADs in October 2007 to 10 300 dFADs in September 2013. In both oceans, at least a fourfold increase in the number of dFADs was observed over the 7-year study period. Though the relative proportion of natural to artificial floating objects varied over space, with some areas such as the Mozambique Channel and areas adjacent to the mouths of the Niger and Congo rivers being characterized by a relatively high percentage of natural objects, in no region do dFADs represent <50% of the floating objects and the proportion of natural objects has dropped over time as dFAD deployments have increased. Globally, this increased dFAD use represents a major change to the pelagic ecosystem that needs to be closely followed in order to assess its impacts and avoid negative ecosystem consequences.

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