Pascal Bach

FIG. 3. — Dermal denticles from the trunk region of Zameus squamulosus (Günther, 1877) caught in the pelagic and demersal environment: A, MNHN 2012-0188, female, 676 mm TL; B, female from demersal zone of the southeastern Indian Ocean shown on the Figure 1B. Scale bar: 1 mm.

The purpose of this specific study is to provide the Directorate-General for Maritime Affairs and Fisheries (DG MARE) with: Updated information regarding the association or occurrence of pelagic sharks and rays in different fisheries; Updated information regarding data collection and methodological approaches for the assessment of conservation status of sharks; A critical review of existing Conservation and Management Measures (CMMs) for sharks and of the current conservation status of the species concerned; and Proposals to improve and/or provide alternative options for conservation and management of sharks taking into account any recent methodological advances and new data or information. The species of interest are the main pelagic sharks caught by pelagic fisheries, including under Sustainable Fisheries Partnership Agreements (longline and purse seine fisheries). The study also considers some pelagic elasmobranchs included in Article 13 (species prohibitions) of the Council Regu...

Although the estimation of in situ swimming speed of a fish school remains seldom 25 documented, this elementary information is needed concerning gregarious fish species 26 behavioural purposes, ecological and management studies. This study analyses data collected 27 in situ for small pelagic fish schools in two shallow water lagoon channels using multibeam 28 sonar. In horizontal beaming, the high resolution sonar covers the whole cross part of the 29 channels, providing dynamic echo traces of mobile fish schools which permit the gathering of 30 information on them during their passage inside the channels. Two school swimming speed 31 indicators are distinguished: the average of a series of instantaneous speed values (ISS, based 32 on successive measurements) and the exploratory speed (ESS, based on the total observation 33 time). These swimming speeds are estimated for each observed fish school according to their 34 Euclidian position within the sonar beam and the ID ratio defined...

The predominant policy for remedying the world fishing crisis aims at maximum sustainable yield (MSY) by adjusting gear selectivity and fishing effort to maintain sustainable stock levels. The yellowfin tuna (Thunnus albacares) fishery in the Sea of Oman has experienced intense increases in removals since 1980, with particularly high levels since the 1990s. Here, we apply a statistical catch-at-age model to time-series of catches and fishery-dependent length composition data to obtain a preliminary and general understanding of the population dynamics of this stock since the start of the fishery in 1950–2019. Despite limited data, population models consistently indicate a sharp decline in population status since the beginning of the time-series across a variety of assumptions on stock productivity and life history. The gillnet fishery takes almost exclusively immature individuals, with high fishing intensity and removal rates. Both reference models indicate the population is essentia...

Fisheries can profoundly affect bycatch species with ‘slow’ life history traits. Managing bait type offers one tool to control species selectivity. Different species and sizes of marine predators have different prey, and hence bait, preferences. This preference is a function of a bait’s chemical, visual, acoustic and textural characteristics and size, and for seabirds the effect on hook sink rate is also important. We conducted a global meta-analysis of existing estimates of the relative risk of capture on different pelagic longline baits. We applied a Bayesian random effects meta-analytic regression modelling approach to estimate overall expected bait-specific catch rates. For blue shark and marine turtles, there were 34% (95% HDI: 4–59%) and 60% (95% HDI: 44–76%) significantly lower relative risks of capture on forage fish bait than squid bait, respectively. Overall estimates of bait-specific relative risk were not significantly different for seven other assessed taxa. The lack of...

Depredation in marine ecosystems is defined as the damage or removal of fish or bait from fishing gear by predators. Depredation raises concerns about the conservation of species involved, fisheries yield and profitability, and reference points based on stock assessment of depredated species. Therefore, the development of accurate indicators to assess the impact of depredation is needed. Both the Reunion Island and the Seychelles archipelago pelagic longline fisheries targeting swordfish (Xiphias gladius) and tuna (Thunnus spp.) are affected by depredation from toothed whales and pelagic sharks. In this study, we used fishery data collected between 2004 and 2015 to propose depredation indicators and to assess depredation levels in both fisheries. For both fisheries, the interaction rate (depredation occurrence) was significantly higher for shark compared to toothed whale depredation. However, when depredation occurred, toothed whale depredation impact was significantly higher than s...

Tropical oceanic fishes, such as tunas, billfishes, and sharks, live together in the same environment the pelagic open ocean. In situ experiments have been developed to observe horizontal and vertical movements of individuals of different pelagic species, but the fact that these species share the same environment has not been studied yet. In this paper we propose a minimal model in which the movement behavior of oceanic predator fishes is driven entirely by their biotic environment, without consideration of physiological constraints. Such idea is explored with computer simulations based on the Latent Energy Environments model (Menczer and Belew 1996a). The behaviors of an evolving population of artificial fishes adapt in a three-dimensional environment where spatial distributions and temporal dynamics of prey are based on data from acoustic observations of the open ocean in French Polynesia. Interactions among individuals are modeled through their shared prey resources. Simulations pro...

The identification and mitigation of adverse effects of the bycatch of tuna longline fishery have been mainly developed and implemented for seabirds, sharks and turtles and, the knowledge on teleost bycatch for this fishery, remains very poor. This paper contributes to a comprehensive assessment of life history traits and fishery attributes of target and bycatch species caught by the tuna longline fishery in the South Atlantic and Indian Oceans. Data was compiled on seven life history traits and three fishery attributes for 33 and 27 teleost stocks caught by longliners in South Atlantic and Indian Oceans, respectively. In addition, each species was assigned into four categories describing the fate of the catch: target species for commercial use, bycatch species kept for consumption, bycatch species kept for commercial use and discarded bycatch. Life history traits and fishery attributes did not differ between oceans. However, non-target but commercialized species were smaller in the Atlantic Ocean. Teleosts caught by the tuna longline fishery was segregated into three main groups: (1) the fast growing species represented mainly by dolphinfishes (Coryphaena hippurus and C. equisellis), skipjack tuna (Katsuwonus pelamis), kawakawa (Euthynnus affinis), bullet tuna (Auxis rochei), snoek (Thyrsites atun) and blackfin tuna (Thunnus atlanticus); (2) target tunas and most other bycatch species which were part of an intermediate group and (3) billfishes including swordfish representing the large and slow growing species with moderate to high market values and unknown or highly uncertain stock status. Investment in some key life history traits (such as growth coefficient) and the development of quantitative or semi-quantitative approaches (stock assessment and Ecological Risk Assessment) should be priorized as precautionary management measures for these species.

ERA Level 2 Productivity Susceptibility Analysis for EU tropical tuna purse seiner, Soviet Union tuna purse seiner, Soviet Union longline research fleet, Taiwanese longline fleet, and La Reunion longline fleet was carried out. The productivity susceptibility analysis for all fleets showed somewhat similar results. In general, the analysis identified two main risk groups. The first one consists of pelagic and coastal sharks, characterized by relatively low productivities. The other group includes teleosts (both IOTC and non-IOTC species), characterized by higher productivities but high susceptibility to purse seine gear. Considering that sharks are beginning to receive the attention of the IOTC community, the analysis suggests that sharks at higher risk may deserve more detailed and thorough scientific monitoring and management actions.

ABSTRACT A record of a healthy specimen of slender sunfish Ranzania laevis with an amputated anal fin and healed scars is described from the south-western Indian Ocean. This is the first evidence of nektonic pelagic fish survival in spite of the ablation of a major locomotory organ and the first indication of non-lethal predation on adult slender sunfish.

Depredation by false killer whales (Pseudorca crassidens) and short-finned pilot whales (Globicephala macrorhynchus) in pelagic longlining is an issue leading to negative impacts on the economics of the fishery and on odontocetes themselves. We investigated the efficacy of a new depredation mitigation device called “DEPRED” in the interaction between bottlenose dolphins (Tursiops aduncus), spinner dolphins (Stenella longirostris), and small pelagic fish (SPF) attached to branchlines to simulate caught fish. We suggest implications for DEPRED efficacy with larger toothed whales interacting with pelagic longline capture in the open ocean. The design of the device uses streamers to both deter cetaceans and protect fish from predation. In controlled experiments, we tested its efficacy by observing changes in the dolphin's behaviour brought on by the presence or absence of the device on branchlines. First, dolphin–SPF interactions were observed at the small scale using video footage ...

Depredation on pelagic longlines targeting swordfish and tuna involves short-finned pilot whales, false killer whales and some pelagic sharks. It has adverse impacts affecting conservation, fisheries economy and fishery statistics. Thereby, there is a real need for robust and accurate indicators in order to assess the extent of depredation, which still remains a misunderstood phenomenon with poorly studied impacts. In the Seychelles archipelago, where a semi-industrial pelagic longline fishery was launched in the mid-90s, a database was built for the 2004-2006 period to assess the extent of this phenomenon through analyses of the trend of five different depredation indices: depredation occurrence, gross depredation impact, depredation rate, depredation per unit effort and economic loss per unit effort. The depredation occurrence is higher for sharks than toothed whales. The gross depredation impact reached 19.5% of the catch, while the depredation rate was significantly greater for ...

ABSTRACT Un dispositif semi-automatique de comptage des microstries de l'otolithe est présenté. Un système d'analyse d'image permet l'acquisition de l'information sous forme numérique. La modélisation de celle ci au moyen d'une méthode d'analyse des séries chronologiques contribue à l'estimation du nombre de périodes (microstries) contenues dans le signal. (Résumé d'auteur)