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Journal ArticleDOI

Aerial surveys to monitor bluefin tuna abundance and track efficiency of management measures

27 Aug 2015-Marine Ecology Progress Series (Inter-research)-Vol. 534, pp 221-234
TL;DR: In this article, the authors presented an abundance index based on 62 aerial surveys conducted since 2000, using two statistical approaches to deal with the sampling strategy: line and strip transects.
Abstract: Conservation and management measures for exploited fish species rely on our ability to monitor variations in population abundance. In the case of the eastern stock of Atlantic bluefin tuna (ABFT), recent changes in management policies have strongly affected the reliability of fishery-dependent indicators due to drastic changes in fishing season/area, fisheries selectivity and strategy. However, fishery-independent indices of abundance are rare for large pelagic fish, and obtaining them is often costly and labor intensive. Here, we show that scientific aerial surveys are an appropriate tool for monitoring juvenile bluefin tuna abundance in the Mediterranean. We present an abundance index based on 62 aerial surveys conducted since 2000, using 2 statistical approaches to deal with the sampling strategy: line and strip transects. Both approaches showed a significant increase in juvenile ABFT abundance in recent years, resulting from the recovery plan established in 2007. Nonetheless, the estimates from the line transect method appear to be more robust and stable. This study provides essential information for fisheries management. Expanding the spatial coverage to other nursery grounds would further increase the reliability and representativeness of this index.
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Citations
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Journal ArticleDOI
TL;DR: Bottom-up control mediated by potential changes in the plankton community appeared to play an important role via a decrease in fish energy income and hence growth, condition and size in the Gulf of Lions around 2008.
Abstract: Around 2008, an ecosystem shift occurred in the Gulf of Lions, highlighted by considerable changes in biomass and fish mean weight of its two main small pelagic fish stocks (European anchovy, Engraulis encrasicolus; European sardine, Sardina pilchardus). Surprisingly these changes did not appear to be mediated by a decrease in fish recruitment rates (which remained high) or by a high fishing pressure (exploitation rates being extremely low). Here, we review the current knowledge on the population's dynamics and its potential causes. We used an integrative ecosystem approach exploring alternative hypotheses, ranging from bottom-up to top-down control, not forgetting epizootic diseases. First, the study of multiple population characteristics highlighted a decrease in body condition for both species as well as an important decrease in size resulting from both a slower growth and a progressive disappearance of older sardines. Interestingly, older sardines were more affected by the decrease in condition than younger ones, another sign of an unbalanced population structure. While top-down control by bluefin tuna or dolphins, emigration and disease were mostly discarded as important drivers, bottom-up control mediated by potential changes in the plankton community appeared to play an important role via a decrease in fish energy income and hence growth, condition and size. Isotopic and stomach content analyses indicated a dietary shift pre- and post-2008 and modeled mesozooplankton abundance was directly linked to fish condition. Despite low energy reserves from 2008 onwards, sardines and anchovies maintained if not increased their reproductive investment, likely altering the life-history trade-off between reproduction and survival and resulting in higher natural mortality. The current worrying situation might thus have resulted from changes in plankton availability/diversity, which remains to be thoroughly investigated together with fish phenotypic plasticity.

83 citations

Journal ArticleDOI
TL;DR: It is estimated that the annual consumption of small pelagic fish by bluefin tuna is less than 2% of the abundance of these populations, which is significantly lower than that of the wild populations.
Abstract: Recently, the abundance of young Atlantic bluefin tuna (Thunnus thynnus) tripled in the northwestern Mediterranean following effective management measures. We investigated whether its predation on sardine (Sardina pilchardus) and anchovy (Engraulis encrasicolus) could explain their concurrent size and biomass decline, which caused a fishery crisis. Combining the observed diet composition of bluefin tuna, their modelled daily energy requirements, their population size, and the abundance of prey species in the area, we calculated the proportion of the prey populations that were consumed by bluefin tuna annually over 2011–2013. To assess whether tuna could alter the size structure of the three small pelagic fish populations (anchovy, sardine, and sprat (Sprattus sprattus)), the size distributions of the consumed prey species were compared with those of the wild populations. We estimated that the annual consumption of small pelagic fish by bluefin tuna is less than 2% of the abundance of these populations. Fu...

20 citations


Cites background or methods from "Aerial surveys to monitor bluefin t..."

  • ...281 Moreover, these predation pressure estimates are based on calculations performed for the three 282 years (2011-2013) when tuna biomass was relatively high and sardine and anchovy biomass was 283 already relatively low (Van Beveren et al. 2014, Bauer et al. 2015)....

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  • ...Annual ABFT abundances (2011-2012) were 101 obtained from aerial surveys (Bauer et al. 2015)....

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  • ...…aerial surveys have been performed between June and October from 2000 to 2003 and from 2009 until present in the Gulf of Lions to construct a unique fishery-independent index of tuna density (Fromentin et al. 2003; Bonhommeau et al. 2010; Fromentin, Bonhommeau & Brisset 2013; Bauer et al. 2015)....

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  • ...Furthermore, 74 ABFT abundance in the Gulf of Lions has been much higher in recent years (Bauer et al. 2015)....

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  • ...Using the annual estimates of bluefin tuna densities given by Bauer et al. (2015), we calculated the abundance of tuna in the studied area by simply multiplying those annual densities with the surface area of the aerial survey transects....

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Journal ArticleDOI
02 Feb 2017-PLOS ONE
TL;DR: This study presents a methodology for the automated analysis of commercial medium-range sonar signals for detecting presence/absence of bluefin tuna (Tunnus thynnus) in the Bay of Biscay, and has the potential to automatically analyze high volumes of data at a low cost.
Abstract: This study presents a methodology for the automated analysis of commercial medium-range sonar signals for detecting presence/absence of bluefin tuna (Tunnus thynnus) in the Bay of Biscay. The approach uses image processing techniques to analyze sonar screenshots. For each sonar image we extracted measurable regions and analyzed their characteristics. Scientific data was used to classify each region into a class ("tuna" or "no-tuna") and build a dataset to train and evaluate classification models by using supervised learning. The methodology performed well when validated with commercial sonar screenshots, and has the potential to automatically analyze high volumes of data at a low cost. This represents a first milestone towards the development of acoustic, fishery-independent indices of abundance for bluefin tuna in the Bay of Biscay. Future research lines and additional alternatives to inform stock assessments are also discussed.

20 citations

Journal ArticleDOI
12 Oct 2015-PLOS ONE
TL;DR: Results indicate that densities, presence and core sighting locations of striped dolphins and ABFT were correlated, and highlight the feasibility to coordinate research efforts to explore the behaviour and abundance of the investigated species, as demanded by the Marine Strategy Framework Directive.
Abstract: Different dolphin and tuna species have frequently been reported to aggregate in areas of high frontal activity, sometimes developing close multi-species associations to increase feeding success. Aerial surveys are a common tool to monitor the density and abundance of marine mammals, and have recently become a focus in the search for methods to provide fisheries-independent abundance indicators for tuna stock assessment. In this study, we present first density estimates corrected for availability bias of fin whales (Balaenoptera physalus) and striped dolphins (Stenella coeruleoalba) from the Golf of Lions (GoL), compared with uncorrected estimates of Atlantic bluefin tuna (ABFT; Thunnus thynnus) densities from 8 years of line transect aerial surveys. The raw sighting data were further used to analyze patterns of spatial co-occurrence and density of these three top marine predators in this important feeding ground in the Northwestern Mediterranean Sea. These patterns were investigated regarding known species-specific feeding preferences and environmental characteristics (i. e. mesoscale activity) of the survey zone. ABFT was by far the most abundant species during the surveys in terms of schools and individuals, followed by striped dolphins and fin whales. However, when accounted for availability bias, schools of dolphins and fin whales were of equal density. Direct interactions of the species appeared to be the exception, but results indicate that densities, presence and core sighting locations of striped dolphins and ABFT were correlated. Core sighting areas of these species were located close to an area of high mesoscale activity (oceanic fronts and eddies). Fin whales did not show such a correlation. The results further highlight the feasibility to coordinate research efforts to explore the behaviour and abundance of the investigated species, as demanded by the Marine Strategy Framework Directive (MSFD).

20 citations

Journal ArticleDOI
TL;DR: A new method for estimating the abundance of tropical tuna that employs satellite, archival and acoustic tagging techniques and exploits the aggregative behavior of tuna around floating objects (FADs) is developed.
Abstract: Estimating the abundance of pelagic fish species is a challenging task, due to their vast and remote habitat. Despite the development of satellite, archival and acoustic tagging techniques that allow the tracking of marine animals in their natural environments, these technologies have so far been underutilized in developing abundance estimations. We developed a new method for estimating the abundance of tropical tuna that employs these technologies and exploits the aggregative behavior of tuna around floating objects (FADs). We provided estimates of abundance indices based on a simulated set of tagged fish and studied the sensitivity of our method to different association dynamics, FAD numbers, population sizes and heterogeneities of the FAD-array. Taking the case study of yellowfin tuna (Thunnus albacares) acoustically-tagged in Hawaii, we implemented our approach on field data and derived for the first time the ratio between the associated and the total population. With more extensive and long-term monitoring of FAD-associated tunas and good estimates of the numbers of fish at FADs, our method could provide fisheries-independent estimates of populations of tropical tuna. The same approach can be applied to obtain population assessments for any marine and terrestrial species that display associative behavior and from which behavioral data have been acquired using acoustic, archival or satellite tags.

18 citations

References
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BookDOI
01 Dec 2010
TL;DR: A guide to using S environments to perform statistical analyses providing both an introduction to the use of S and a course in modern statistical methods.
Abstract: A guide to using S environments to perform statistical analyses providing both an introduction to the use of S and a course in modern statistical methods The emphasis is on presenting practical problems and full analyses of real data sets

18,346 citations

Book
01 Nov 2001
TL;DR: In this article, the authors introduce the concepts of line transects, point tranchs, and related methods for study design and field methods, as well as illustrative examples.
Abstract: 1. Introductory concepts 2. Assumptions and modelling philosophy 3. Statistical theory 4. Line transects 5. Point transects 6. Related methods 7. Study design and field methods 8. Illustrative examples

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Journal ArticleDOI
TL;DR: This book presents a meta-modelling framework for estimating the probability of detection on the line or point in the context of tuna vessel observer data to assess trends in abundance of dolphins in the North Atlantic.
Abstract: 1 Introductory concepts.- 1.1 Introduction.- 1.2 Range of applications.- 1.3 Types of data.- 1.4 Known constants and parameters.- 1.5 Assumptions.- 1.6 Fundamental concept.- 1.7 Detection.- 1.8 History of methods.- 1.9 Program DISTANCE.- 2 Assumptions and modelling philosophy.- 2.1 Assumptions.- 2.2 Fundamental models.- 2.3 Philosophy and strategy.- 2.4 Robust models.- 2.5 Some analysis guidelines.- 3 Statistical theory.- 3.1 General formula.- 3.2 Hazard-rate modelling of the detection process.- 3.3 The key function formulation for distance data.- 3.4 Maximum likelihood methods.- 3.5 Choice of model.- 3.6 Estimation for clustered populations.- 3.7 Density, variance and interval estimation.- 3.8 Stratification and covariates.- 4 Line transects.- 4.1 Introduction.- 4.2 Example data.- 4.3 Truncation.- 4.4 Estimating the variance in sample size.- 4.5 Analysis of grouped or ungrouped data.- 4.6 Model selection.- 4.7 Estimation of density and measures of precision.- 4.8 Estimation when the objects are in clusters.- 4.9 Assumptions.- 4.10 Summary.- 5 Point transects.- 5.1 Introduction.- 5.2 Example data.- 5.3 Truncation.- 5.4 Estimating the variance in sample size.- 5.5 Analysis of grouped or ungrouped data.- 5.6 Model selection.- 5.7 Estimation of density and measures of precision.- 5.8 Estimation when the objects are in clusters.- 5.9 Assumptions.- 5.10 Summary.- 6 Extensions and related work.- 6.1 Introduction.- 6.2 Other models.- 6.3 Modelling variation in encounter rate and cluster size.- 6.4 Estimation of the probability of detection on the line or point.- 6.5 On the concept of detection search effort.- 6.6 Fixed versus random sample size.- 6.7 Efficient simulation of distance data.- 6.8 Thoughts about a full likelihood approach.- 6.9 Distance sampling in three dimensions.- 6.10 Cue counting.- 6.11 Trapping webs.- 6.12 Migration counts.- 6.13 Point-to-object and nearest neighbour methods.- 7 Study design and field methods.- 7.1 Introduction.- 7.2 Survey design.- 7.3 Searching behaviour.- 7.4 Measurements.- 7.5 Training observers.- 7.6 Field methods for mobile objects.- 7.7 Field methods when detection on the centerline is not certain.- 7.8 Field comparisons between line transects, point transects and mapping censuses.- 7.9 Summary.- 8 Illustrative examples.- 8.1 Introduction.- 8.2 Lake Huron brick data.- 8.3 Wooden stake data.- 8.4 Studies of nest density.- 8.5 Fin whale abundance in the North Atlantic.- 8.6 Use of tuna vessel observer data to assess trends in abundance of dolphins.- 8.7 House wren densities in South Platte River bottomland.- 8.8 Songbird surveys in Arapaho National Wildlife Refuge.- 8.9 Assessing the effects of habitat on density.- Appendix A List of common and scientific names cited.- Appendix B Notation and abbreviations, and their definitions.

1,629 citations


"Aerial surveys to monitor bluefin t..." refers methods in this paper

  • ...According to common practice, we discarded 5–10% of the largest distances, which correspond in the present study to a band width of 4.5 and 3.5 km (Buckland et al. 1993)....

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Book
01 Apr 1990

601 citations


"Aerial surveys to monitor bluefin t..." refers background in this paper

  • ...(4) r (r − 1) i=1 6 R. K. Bauer et al.: Aerial surveys to monitor bluefin tuna abundance 208 209 210 211 212 213 214 215 216 217 Spatial distribution of tuna schools As population size fluctuates, the habitat used by a species can also fluctuate (MacCall’s theoretical basin model; MacCall 1990)....

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