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.

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.

scholarly journals Precision in bycatch estimates: the case of tuna purse-seine fisheries in the Indian Ocean

2012 ◽  
Vol 69 (8) ◽  
pp. 1501-1510 ◽  
Author(s):  
Monin J. Amandè ◽  
Emmanuel Chassot ◽  
Pierre Chavance ◽  
Hilario Murua ◽  
Alicia Delgado de Molina ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Linear Models ◽  
Purse Seine ◽  
Reliable Estimate ◽  
Routine Practice ◽  
Marine Animals ◽  
Trade Offs ◽  
The Indian Ocean ◽  
Current Sampling ◽  
Tropical Tuna

Abstract Amandè, M. J., Chassot, E., Chavance, P., Murua, H., Delgado de Molina, A., and Bez, N. 2012. Precision in bycatch estimates: the case of tuna purse-seine fisheries in the Indian Ocean. – ICES Journal of Marine Science, 69: . Estimating bycatch, i.e. the incidental catch of non-target marine animals and undersized individuals of target species, by raising observer data to the whole fishery is routine practice. The annual bycatch of the European tropical tuna purse-seine fishery over the period 2003–2009 was estimated at 11 590 t [95% confidence interval: (8165–15 818 t)], corresponding to 4.7% of the tuna landings. An analysis of the variability in the precision of this estimate, based on generalized linear models and Monte Carlo simulations, showed that the current sampling coverage of the tropical tuna fishery observer programme, which is 4.6% of the fishing trips, resulted in large uncertainties in bycatch estimates by species, i.e. none of the estimates have a relative root mean square error smaller than 50%. Although the overall magnitude of bycatch of the fishery appeared to be small, the current sampling coverage was insufficient to give any reliable estimate for low-occurring species, such as marine turtles, some oceanic pelagic sharks, and some billfishes. Increasing the sampling coverage would likely improve bycatch estimates. Simulation outputs were produced to help define (i) trade-offs between the priority species to be monitored, (ii) the estimation precision, (iii) expected accuracy, and (iv) the associated sampling costs.

scholarly journals The past, present and future use of drifting fish aggregating devices (FADs) in the Indian Ocean

Marine Policy ◽  
2014 ◽  
Vol 45 ◽  
pp. 163-170 ◽  
Author(s):  
Tim K. Davies ◽  
Chris C. Mees ◽  
E.J. Milner-Gulland
Keyword(s):  
Indian Ocean ◽  
The Past ◽  
The Indian Ocean ◽  
Fish Aggregating Devices

scholarly journals The lichen flora of the Chagos Archipelago, including a comparison with other island and coastal tropical floras

2000 ◽  
Vol 18 (1) ◽  
pp. 185-198
Author(s):  
Mark R.D. Seaward ◽  
André Aptroot
Keyword(s):  
Indian Ocean ◽  
Cocos Nucifera ◽  
Island Size ◽  
Specific Level ◽  
Surface Areas ◽  
Tropical Areas ◽  
The Indian Ocean ◽  
Associated Species ◽  
Chagos Archipelago ◽  
Lichen Flora

The 1996 Chagos Expedition provided the first opportunity to study the archipelago’s lichen flora. Seventeen of the 55 islands were ecologically investigated, some in more detail than others, and lists and representative collections of lichens have been assembled for many of them. In all, 67 taxa have been recorded, 52 to specific level. Although the islands have a low biodiversity for cryptogamic plants, as would be expected in terms of their relatively young age, remoteness and small terrestrial surface areas, those taxa that are present are often found in abundance and play significant ecological roles. There is a good correlation between total lichen biodiversity and island size, despite the fact that Cocos nucifera is such an important substratum for cryptogamic plants and its presence on all islands studied provides a consistently high associated species count. Comparisons of lichen floras for ten island and coastal tropical areas show good correlations (based on the Sörensen Coefficient) within the Indian Ocean as would be expected, but poorer correlations exist within and between Pacific Ocean and neotropical floras. Ranked correlations between Chagos and other floras are in the sequence Maldives > Laing Island > Aldabra > Tuamotu > Pitcairn > N.Mariana & Belize > Guadeloupe > Cook. When coefficients are calculated using only the Physciaceae, different correlations and sequences are derived, but the affinities of the Indian Ocean islands remain strong. However, although the lichen flora of Chagos is characteristic for an Indian Ocean, it is dominated by pantropical species.

scholarly journals Model designs of Indonesian tuna fishery management in the Indian Ocean (FMA 573) using soft system methodology approach

2018 ◽  
Vol 44 (2) ◽  
pp. 139-144 ◽  
Author(s):  
Tri W. Nurani ◽  
Prihatin I. Wahyuningrum ◽  
Sugeng H. Wisudo ◽  
Soraya Gigentika ◽  
Risti E. Arhatin
Keyword(s):  
Indian Ocean ◽  
Fishery Management ◽  
Soft System Methodology ◽  
The Indian Ocean ◽  
System Methodology ◽  
Tuna Fishery

scholarly journals Indian Ocean subtropical mode water: its water characteristics and spatial distribution

2009 ◽  
Vol 6 (1) ◽  
pp. 723-739
Author(s):  
T. Tsubouchi ◽  
T. Suga ◽  
K. Hanawa
Keyword(s):  
Spatial Distribution ◽  
Indian Ocean ◽  
Three Dimensional ◽  
Careful Examination ◽  
Distribution Area ◽  
Vertical Temperature ◽  
Mode Water ◽  
Subtropical Mode Water ◽  
Water Characteristics ◽  
The Indian Ocean

Abstract. We examined Indian Ocean Subtropical Mode Water (IOSTMW) and described its characteristics using an isopycnally averaged three-dimensional hydrographic dataset. Through careful examination of the spatial distribution and water characteristics of the core in the layer of minimum vertical temperature gradient, we concluded that the IOSTMW exists as a robust structure in the western part of the Indian Ocean subtropical gyre in summer. The averaged IOSTMW properties during approximately 1960–2004 were 16.54±0.49°C, 35.51±0.04 psu, and 26.0±0.1 σθ. The IOSTMW distribution area was 27–38° S, 25–50° E.

scholarly journals Fish behaviour from fishers’ knowledge: the case study of tropical tuna around drifting fish aggregating devices (DFADs)

2007 ◽  
Vol 64 (11) ◽  
pp. 1517-1528 ◽  
Author(s):  
Gala Moreno ◽  
Laurent Dagorn ◽  
Gorka Sancho ◽  
David Itano
Keyword(s):  
Indian Ocean ◽  
Local Ecological Knowledge ◽  
Western Indian Ocean ◽  
Future Research ◽  
Ecological Knowledge ◽  
Fish Behaviour ◽  
Planning And Design ◽  
Tropical Tuna ◽  
Fish Aggregating Devices

Purse-seining for tropical tuna is one of the most technologically advanced fisheries in the world. The purpose of this study was to apply local ecological knowledge (LEK) to assist in the planning of future in situ studies of fish behaviour around drifting fish aggregating devices (DFADs) by prioritizing research topics, thereby reducing the number of potential hypotheses to explore. Interviews of fishing masters of the purse-seine fleets working in the western Indian Ocean provided an alternate, independent, and previously unexplored source of behavioural information, specifically on the attraction, retention, and departure behaviours of tuna schools in relation to DFADs. Most fishing masters agreed that the maximum attraction distance of a DFAD is approximately 10 km and generally agreed to the following statements. Tuna form distinct schools under FADs, commonly segregated by species and size. The main reasons for the departure of tuna aggregations from FADs are changes in currents or FAD movements and location in relation to physical or oceanographic features. The number of actively monitored DFADs at sea in the western Indian Ocean was estimated at approximately 2100. Incorporating fishers into the planning and design stages of future research projects will facilitate collaborative and integrated approaches.

scholarly journals Forecasted consequences of simulated FAD moratoria in the Atlantic and Indian Oceans on catches and bycatches

2016 ◽  
Vol 74 (3) ◽  
pp. 780-792 ◽  
Author(s):  
Lauriane Escalle ◽  
Daniel Gaertner ◽  
Pierre Chavance ◽  
Alicia Delgado de Molina ◽  
Javier Ariz ◽  
...  
Keyword(s):  
Monte Carlo ◽  
Indian Ocean ◽  
Atlantic Ocean ◽  
Fishing Effort ◽  
Bony Fishes ◽  
Whale Sharks ◽  
The Indian Ocean ◽  
Fish Aggregation ◽  
Fishing Fleets ◽  
Tropical Tuna

Given the increasingly extensive use of drifting fish aggregation devices (FADs) by the purse-seine fisheries targeting tropical tunas, fishing effort restrictions have been introduced to manage tropical tuna stocks. However, these measures are focused on the protection of juvenile tunas and do not take account of the potential impact on bycatch or associated megafauna (whales and whale sharks). An iterative “fishing-day” Monte Carlo simulation model was developed to investigate the consequences on tropical tunas and bycatch of introducing extensive area 6-month moratoria on FAD activities. The model allowed for variability in a range of plausible values of the parameters characterizing the fishing operations conducted by European purse-seiners in the eastern tropical Atlantic and western Indian Oceans for the period 2005–2014. Monte Carlo simulations, using probabilities based on these fishery data, were carried out for the French and Spanish fishing fleets separately to account for differences in fishing strategies. The models predicted a decrease in FAD sets and an increase in free school sets. As a consequence, the catch of small tuna (<10 kg) decreased while the catch of large tuna (≥10 kg) increased, leading to an overall increase in tuna catch of 100–200 tons/year/vessel in the Atlantic Ocean, and a decrease of 400–1500 tons/year/vessel in the Indian Ocean. The bycatch decreased in the Indian Ocean, while in the Atlantic Ocean billfishes, turtles and chondrichthyans bycatch increased slightly and other bony fishes decreased. Because fishing practices were modified, whale and whale shark associated sets increased slightly in the Indian Ocean.

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