Daniel Gaertner

Institute of Research for Development | IRD · UMR 248 MARBEC

The creation of Exclusive Economic Zones (EEZs) in 1982 gave coastal countries sovereignty over their local tuna resources, whereas the migratory nature of tuna calls for regional management. However, as regional tuna management by Regional Fisheries Management Organisations (RFMOs) does not always facilitate optimal management of local resources b...

To fulfil fisheries management objectives that often include implementing the precautionary and ecosystem‐based approaches, multispecies fisheries data need to be analysed. Amongst the different methods dealing with these multidimensional data, self‐organizing maps (SOMs) remain rarely used, although they are highly flexible in data input and offer...

Targeting tunas associated with drifting Fish Aggregating Devices (dFADs) raises questions on the sustainability of tropical tuna fisheries. To limit catches of juvenile tunas, multiple time-area dFADs-fishing moratoria have been implemented by ICCAT since 1998. In this study we assessed the effectiveness of two different dFADs time-area closures i...

It is useful to complement more sophisticated stock status estimations based on stock assessment models with simpler approaches based on analyses of raw catch-effort data to maximize the probability of detecting overexploitation and hyperstability as early as possible. Here we develop a series of annual indices for the spatial distribution of catch...

Several studies have shown that the school type at release can significantly influence the amplitude of the movements of a tagged fish. In particular, it has been shown that seamounts can have a retention effect on tuna, suggesting that their migration patterns may differ significantly depending on the school type at release. However, many tuna rel...

An objective of the Atlantic Ocean Tropical tuna Tagging Programme (AOTTP) was to estimate Type-I (immediate) and Type-II (long-term) tag-shedding rates for tropical Atlantic tunas from double-tagging experiments. Historical information on tuna tag-shedding studies conducted in different parts of the world was incorporated as prior distributions us...

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 attach...

The use of echosounder buoys deployed in conjunction with Drifting Fish Aggregating Devices (DFADs) has progressively increased in the tropical tuna purse seine fishery since 2010 as a means of improving fishing efficiency. Given the broad distribution of DFADs, the acoustic data provided by echosounder buoys can provide an alternative to the conve...

This study addresses novel questions on the dynamics of tuna aggregations around floating objects, using echosounder buoys data collected throughout the drifts of newly deployed Drifting Fish Aggregating Devices (DFADs) in the Atlantic Ocean (AO) and Indian Ocean (IO). Time series of presence/absence of tunas were obtained by supervised classificat...

The time series of EU purse seine fleet catches per unit effort (CPUE) of yellowfin tuna (YFT) from the Indian Ocean were standardized using an extension of the Delta-lognormal GLMM to three components. The aim was to depict the trend in abundance for adult YFT observed in free schools (FSC). The originality of this work relied on the inclusion of...

A major concern for tropical tunas, is the worldwide increasing use of drifting floating objects or FOBs by purse seiners. The main concerns over FOB-related fishing are common for the different t-RFMOs as is the reduction in yield per recruit of some target species (i.e. yellowfin and bigeye tuna), the increased by-catch, generation of marine debr...

In an ecosystem approach to fisheries management (EAFM) framework of the tuna purse-seine fishery, the assessment of target species, but also that of bycatch species, is essential. In the Atlantic and Indian oceans, purse-seine nets are sometimes set around tuna schools associated with whale sharks and baleen whales, although less frequently than a...

Comment, depuis plusieurs décennies, la recherche scientifique contribue-t-elle au développement des pays du Sud ? À travers plus de 100 succès emblématiques de la recherche en partenariat, cet ouvrage nous plonge au coeur des grandes questions de développement : oeuvrer pour des sociétés plus justes, lutter contre les maladies, faire face aux risq...

In response to the increasing use of FADs in the purse seiner tropical tuna fishing, legal binding measures have been implemented by RFMOs to limit the number of FADs used by vessel. Broad terminology referred to buoys and FADs use is included in different management measures which should be standardized among RFMOs and precisely defined to avoid s...

The EU purse seine fleet catches of yellowfin tuna (Thunnus albacares) from the Indian Ocean were standardized using the framework described in Katara et al. (2016, 2017) with a Delta-lognormal generalised linear mixed model developed specifically for the standardisation of tropical tuna catch per unit effort (CPUE) time series. With the aim to dep...

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 availabl...

In the tropical eastern Atlantic Ocean, whale sharks are sometimes encircled by nets of tropical tuna purse-seiners. In order to estimate the post-release survival of encircled individuals, a post release survival experiment, using pop-up satellite tags, was conducted in this ocean in 2014. This study presents updated results from this experiment....

Le présent document a calculé plusieurs indicateurs des pêcheries en rapport avec l'effort de pêche et diverses CPUE des senneurs communautaires opérant dans l'océan Atlantique pendant la période 1991-2015. Ce travail a été réalisé parce que ces indicateurs fondamentaux des pêcheries demeurent très utiles pour mieux comprendre de nombreux changemen...

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...

En 2015, la flottille de senneurs français était composée de neuf senneurs d'une capacité de stockage > 700 t et d'une longueur hors tout > 60 m et d'un navire de support de 40 m de longueur hors tout. La capacité de la flottille et l'effort nominal global sont restés stables ces dernières années, avec un nombre total annuel d'environ 2.000 opérati...

We revised the existing framework for tuna CPUE standardisation in light of the increasing literature that advocates the use of mixed effects models to account for the characteristics of logbook data. We apply the framework on yellowfin tuna (YFT) from the Indian Ocean, caught by the purse seine EU fleet (Spain and France) from 1984 to 2015. We use...

The European Research project " Catch, Effort, and eCOsystem impacts of FAD-fishing " (CECOFAD) set out to improve our understanding of the use of drifting fish-aggregating devices (DFADs) in tropical purse seine tuna fisheries in open ocean ecosystems. Data from unofficial technology information related to FAD-fishing were retrieved and the change...

Time–area regulations have been introduced to manage stocks of tropical tuna, given the increased use of drifting fish aggregation devices (FADs). However, the consequences in terms of changes in fishing strategies and effort reallocation may not always be as expected. For instance, in the eastern Pacific Ocean, previous studies have highlighted th...

Tropical tuna purse-seine fisheries spatially co-occur with various megafauna species, such as whale sharks, dolphins and baleen whales in all oceans of the world. Here, we analyzed a 10-year (2002–2011) dataset from logbooks of European tropical tuna purse-seine vessels operating in the tropical Eastern Atlantic and Western Indian Oceans, with the...

The failure to achieve fisheries management objectives has been broadly discussed in international meetings. Measuring the effects of fishery regulations is difficult due to the lack of detailed information. The yellowfin tuna fishery in the eastern Pacific Ocean offers an opportunity to evaluate the fishers’ responses to temporal regulations. We u...

1. Whale shark, the world's largest fish, is believed to be particularly vulnerable owing to its biological characteristics (slow growth, late maturation, great longevity) and is listed as Vulnerable by IUCN and included in Appendix II of CITES. 2. Whale sharks are occasionally encircled in tropical tuna purse‐seine nets, throughout this global fis...

The French purse seine fleet was composed in 2014 of 9 purse seiners of storage capacity >700 t and >60 m length overall, and 1 support vessel of 40 m length overall. The fleet capacity and overall nominal effort have remained stable in the recent years with a total annual number of about 2,000 fishing sets made in 2014, among which 55% on free-swi...

The drifting Fish Aggregating Device (dFAD) purse seine fishery is complex and fishing effort depends on a multitude of factors. Traditional indices of fishing effort such as searching time are meaningless for this fishery. We composed a comprehensive list of 28 candidate variables that describe the dFAD fishery and used them as predictors of fishi...

A key objective of the Regional Tuna Tagging Project—Indian Ocean was to estimate tag-shedding rates, Type-I (immediate tag shedding) and Type-II (long-term tag shedding). To assess this, a series of double-tagging experiments (26,899 double tags released with 4555 recoveries) were conducted as part of the broader tagging program. After omitting da...

Fisheries bycatch is considered to be one of the most significant causes of mortality for many marine species, including vulnerable megafauna. In the open ocean, tuna purse seiners are known to use several cetacean species to detect tuna schools. It exposes them to encirclement which can lead to incidental injury or death. While interactions betwee...

Fisheries bycatch is considered to be one of the most significant causes of mortality for many marine species, including vulnerable megafauna. In the open ocean, tuna purse seiners are known to use several cetacean species to detect tuna schools. This exposes the cetaceans to encirclement which can lead to incidental injury or death. While interact...

Fisheries bycatch is considered to be one of the most significant causes of mortality for many marine species, including vulnerable megafauna. In the open ocean, tuna purse seiners are known to use several cetacean species to detect tuna schools. This exposes the cetaceans to encirclement which can lead to incidental injury or death. While interact...

1 This paper makes an analysis and a discussion of the numbers of drifting fish aggregating devices (DFADs) active in the eastern Atlantic Ocean and of the potential interest to manage purse seine fisheries based on a limitation of FADs numbers. Potential risks linked with a massive use of FADs are first discussed. Based on new information on the n...

Productivity and Susceptibility Analysis (PSA) is a methodology for evaluating the vulnerability of a stock based on its biological productivity and susceptibility to fishing. In this study, we evaluated the vulnerability of 60 stocks of tuna, billfishes and other teleosts caught by the tuna longline fleets operating in the South Atlantic and India...

A key objective of the Regional Tuna Tagging Project Indian Ocean was to estimate tag-shedding rates, Type-I (immediate tag shedding) and Type-II (long-term tag shedding). To assess this, a series of double-tagging experiments (26,899 double tags released with 4555 recoveries) were conducted as part of the broader tagging program. After omitting da...

Indices of CPUE are presented for skipjack tuna (Katsuwonus pelamis) for the Indian Ocean over the period 1980-2013. The analysis was initiated under the framework of the E.U. research project CECOFAD, whose objectives are to enhance our understanding of fishing effort units and improve the accuracy of purse-seine CPUE estimates. Skipjack stock ass...

Within the Ecosystem-based fisheries management framework, we evaluated the changes over time in bycatch species of the European tuna purse-seine fishery operating in the eastern Atlantic Ocean. Bycatch data was collected during two scientific observer programs conducted in the late 1990s and in the late 2000s. Over these two time periods, we compa...

Recent resolutions of the Indian Ocean Tuna Commission (IOTC) have been implemented to improve scientific knowledge on the effects of drifting fish aggregating devices (DFADs) through increased data collection and reporting. Here, we report information on DFADs collected from three distinct data sources to describe the use of DFADs and buoys by the...

This study presents indirect estimates of Atlantic skipjack natural mortality rates (M) based on life history parameters. M is estimated in one hand for the entire population and on the other hand by length size classes, using 7 and 4 different estimators, respectively. For all the M-estimators a Monte Carlo resampling is used to account for uncert...

The objective of the European Research project " Catch, Effort, and eCOsystem impacts of FAD-fishing " (CECOFAD) is to improve our understanding of the use of fish-aggregating devices (FAD) in tropical purse seine tuna fisheries on open-sea ecosystems. Due to the relevance of accurate indices of abundance derived from catch per unit of effort, the...

The intrinsic population growth rate (r) of the surplus production function used in the biomass dynamic model and the steepness (h) of the stock-recruitment relationship used in age-structured population dynamics models are two key parameters in fish stock assessment. There is generally insufficient information in the data to estimate these paramet...

In the lack of fishery-independent information, catch per unit of effort (CPUE) is the conventional abundance index. In the case of the tropical tuna purse seine fisheries, a critical difficulty lies in the definition of an effective fishing effort, because fishermen use two different fishing modes (free swimming schools versus schools under fish a...

Standardized skipjack catch rate of the European purse seine fleets in the Indian ocean from 1990 to 2010 using generalized linear models (delta-lognormal model) is presented. An index based on logbooks data for the skipjack FAD catch has been standardized and calculated from the product of the annual effect of the LSMeans of the lognormal and bino...

Time-area closures have become a frequently used tool to control fishing effort and protect feeding and spawning areas. However, because time-area closure strata are mainly based on biological and ecological considerations, and do not accounts for fishermen’s behavior-at-sea, this type of regulation tool may not entirely achieve its objectives. Wit...

The influence of Venezuelan skippers' behaviour on the catchability of surface tuna schools was modelled using logistic regressions. Data obtained from observers onboard purse seiners indicated that fishers' fine-scale decisions, such as chasing and setting a school, were influenced by (i) the skipper's skill, (ii) the fishing equipment used (e.g.,...

Ecological risk assessment is a useful methodology for assisting the management of fisheries from an ecosystem perspective. Atlantic tuna fisheries, managed by the International Commission for the Conservation of Atlantic Tunas (ICCAT), are economically important and interact with several bycatch species. In spite of these interactions, no comprehe...

In order to assess the growth of the Indian Ocean skipjack (Katsuwonus pelamis), recaptures of conventional tagging data released during the Regional Tuna Tagging Project of the Indian Ocean (RTTP-IO) between May 2005 and August 2007 were reanalyzed using the von Bertalanffy-Fabens growth model. Our results (ie, K = 0.282 and L ∞ = 76.876 cm) are c...