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Tom Bech Letessier

Tom Bech Letessier
Zoological Society of London · Institute of Zoology

Ph.D

About

60
Publications
19,624
Reads
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918
Citations
Additional affiliations
July 2019 - present
Zoological Society of London
Position
  • Research Associate
September 2014 - June 2019
Zoological Society of London
Position
  • PostDoc Position
September 2011 - August 2015
University of Western Australia
Position
  • Research Assistant
Education
June 2007 - June 2011
University of St Andrews
Field of study
  • Marine Biology

Publications

Publications (60)
Article
Full-text available
Since the 1950s, industrial fisheries have expanded globally, as fishing vessels are required to travel further afield for fishing opportunities. Technological advancements and fishery subsidies have granted ever-increasing access to populations of sharks, tunas, billfishes, and other predators. Wilderness refuges, defined here as areas beyond the...
Article
Full-text available
Managing the footprint of highly mobile fishing fleets is increasingly important due to continuing declines in fish populations. However, social‐ecological drivers for fisher behaviour remain poorly understood for many fleets globally. Using the Sri Lankan fleet as a case study, we explored the role of social, environmental and policy drivers of ef...
Article
Full-text available
The pelagic ecosystem is the ocean's largest by volume and of major importance for food provision and carbon cycling. The high fish species diversity common in the tropics presents a major challenge for biomass estimation using fisheries acoustics, the traditional approach for evaluating mid-water bio-mass. Converting echo intensities to biomass de...
Article
The link between biodiversity and ecosystem functioning has been the topic of considerable research, but it remains unclear how biodiversity decline is compromising ecosystem functionality, particularly in the pelagic realm. Here, we explore how pelagic fish species diversity relates to functional diversity by sampling two locations, which, on the...
Article
Full-text available
Mobile predators serve important ecological functions, including acting as nutrient vectors between different ecosystems. In coral reefs, pelagic nutrient subsidies are believed to play an increasingly important role under ongoing and projected environmental changes. Here, we combine visual sightings with passive acoustic monitoring to report habit...
Article
Full-text available
Seamounts are important marine habitats that are hotspots of species diversity. Relatively shallow peaks, increased productivity and offshore locations make seamounts vulnerable to human impact and difficult to protect. Present estimates of seamount numbers vary from anywhere between 10,000 to more than 60,000. Seamount locations can be estimated b...
Preprint
Seamounts are important marine habitats that are hotspots of species diversity. Relatively shallow peaks, increased productivity and offshore locations make seamounts vulnerable to human impact and difficult to protect. Present estimates of seamount numbers vary from anywhere between 10,000 to more than 60,000. Seamount locations can be estimated b...
Article
Full-text available
Quantifying fish species diversity in rich tropical marine environments remains challenging. Environmental DNA (eDNA) metabarcoding is a promising tool to face this challenge through the filtering, amplification, and sequencing of DNA traces from water samples. However, because eDNA concentration is low in marine environments, the reliability of eD...
Article
Full-text available
Ocean health is fundamental to human prosperity. However, fisheries exploitation, industrialization and climate change imperil our oceans. Marine protected areas (MPAs) have been established in coastal habitats since the 1970s and the ongoing monitoring of these MPAs has shown their general ecological and economic value. Demonstrable benefits can i...
Article
Assessing the impact of global changes and protection effectiveness is a key step in monitoring marine fishes. Most traditional census methods are demanding or destructive. Nondisturbing and nonlethal approaches based on video and environmental DNA are alternatives to underwater visual census or fishing. However, their ability to detect multiple bi...
Preprint
Full-text available
Quantifying the diversity of species in rich tropical marine environments remains challenging. Environmental DNA (eDNA) metabarcoding is a promising tool to face this challenge through the filtering, amplification, and sequencing of DNA traces from water samples. However, the reliability of biodiversity detection from eDNA samples can be low in mar...
Article
Full-text available
The Pitcairn Islands, located in the central South Pacific, contain near-pristine marine ecosystems which support unique fish assemblages, together with both endemic and threatened species. Pitcairn itself is the only inhabited island in the group and, before this study, the environmental impact of local fisheries was unclear, with little data to i...
Article
Full-text available
Area coverage of large-scale marine protected areas (MPAs) (LSMPAs, > 100,000 km2) is rapidly increasing globally. Their effectiveness largely depends on successful detection and management of non-compliance. However, for LSMPAs this can be difficult due to their large size, often remote locations and a lack of understanding of the social drivers o...
Preprint
Full-text available
The link between biodiversity and ecosystem functioning has been the topic of considerable research, but it remains unclear how biodiversity decline is compromising ecosystem functionality, particularly in the pelagic realm. Here, we explore how pelagic fish species diversity relates to functional diversity by sampling two locations, which, on the...
Preprint
Full-text available
Seamounts are important marine habitats that are hotpots of species diversity. Relatively shallow peaks, increased productivity and offshore locations make seamounts vulnerable to human impact and difficult to protect. Present estimates of seamount numbers vary from anywhere between 10000 to more than 60000. Seamount locations can be estimated by e...
Article
Full-text available
• Monitoring large marine mammals is challenging due to their low abundances in general, an ability to move over large distances and wide geographical range sizes. • The distribution of the pygmy (Kogia breviceps) and dwarf (Kogia sima) sperm whales is informed by relatively rare sightings, which does not permit accurate estimates of their distribu...
Article
Full-text available
Given the recent trend towards establishing very large marine protected areas (MPAs) and the high potential of these to contribute to global conservation targets, we review outcomes of the last decade of marine conservation research in the British Indian Ocean Territory (BIOT), one of the largest MPAs in the world. The BIOT MPA consists of the atol...
Article
Species-specific bans are increasingly being implemented to stem loss of vulnerable marine species, but there is a paucity of evaluative research into resulting socioeconomic and ecological consequences. In 2012, a blanket ban on landing Alopiidae (thresher) sharks was introduced in Sri Lanka. We used fisher perceptions, shown to influence support...
Article
Full-text available
Spatial and temporal distribution of seabird transiting and foraging at sea is an important consideration for marine conservation planning. Using at‐sea observations of seabirds (n = 317), collected during the breeding season from 2012 to 2016, we built boosted regression tree (BRT) models to identify relationships between numerically dominant seab...
Article
Full-text available
The conservation of marine biodiversity is firmly embedded in national and international policy frameworks. However, the difficulties associated with conducting broad-scale surveys of oceanic environments restrict the evidence base available for applied management in pelagic waters. For example, the Oceanic Shoals Australian Marine Park (AMP) was e...
Preprint
Full-text available
Seamounts are important marine habitats that are hotpots of species diversity. Relatively shallow peaks, increasedproductivity and offshore locations make seamounts vulnerable to human impact and difficult to protect. Present estimates ofseamount numbers vary from barely 10000 to more than 60000), because locating and identifying them remotely can...
Article
Full-text available
Unmanned aerial vehicles (UAVs) are cost‐effective remote sensing tools useful for generating very high‐resolution (VHR) aerial imagery. Habitat maps generated from UAV imagery are a fundamental component of marine spatial planning, essential for the designation and governance of marine protected areas (MPAs). We investigated whether UAV survey alt...
Technical Report
Full-text available
A multi-criteria trial aiming to explore the use of a novel fixed-wing Unmanned Aerial Vehicle (UAV) as an enforcement and monitoring tool in the Turneffe Marine Atoll (Belize), was conducted in partnership between the Turneffe Atoll Sustainability Association (TASA), the Zoological Society of London (ZSL) and the Marine Management Organisation (MM...
Article
Full-text available
Reef sharks are vulnerable predators experiencing severe population declines mainly due to overexploitation. However, beyond direct exploitation, human activities can produce indirect or sublethal effects such as behavioral alterations. Such alterations are well known for terrestrial fauna but poorly documented for marine species. Using an extensiv...
Poster
Full-text available
We chose to trial a prototype water-landing fixed-wing UAV in The British Indian Overseas Territories (BIOT) marine reserve (640,000km2). We trialled the UAV in the BIOT reserve for megafauna surveys and illegal unreported and unregulated (IUU) fishery enforcement.
Chapter
Full-text available
With over 70 contributors from 30 agencies, the NESP Marine Biodiversity Hub has developed a suite of field manuals to describe a nationally consistent and defensible approach to marine data acquisition. This manual relates to pelagic (mid-water) BRUVS, i.e. gear designed to acquire digital video imagery of macro-organisms living in the ocean’s w...
Book
Full-text available
Australia has one of the world’s largest marine estates that includes many vulnerable habitats and a high biodiversity, with many endemic species crossing a wide latitudinal range. The marine estate is used by a variety of industries including fishing, oil & gas, and shipping, in addition to traditional, cultural, scientific and recreational uses....
Article
Tuna, billfish, and oceanic sharks [hereafter referred to as 'mobile oceanic fishes and sharks' (MOFS)] are characterised by conservative life-history strategies and highly migratory behaviour across large, transnational ranges. Intense exploitation over the past 65 years by a rapidly expanding high-seas fishing fleet has left many populations depl...
Presentation
Full-text available
The distribution of large pelagic predators can be highly heterogeneous. Investigating pelagic predator-prey interactions around localised geo-physical features (reefs, seamounts) helps elucidate and predict potential foraging mechanisms that support relatively persistent levels of elevated biomass. The Chagos Archipelago (British Indian Ocean Terr...
Article
Full-text available
Reef sharks are declining world-wide under ever-increasing fishing pressure, with potential consequences on ecosystem functioning. Marine protected areas (MPAs) are currently one of the management tools used to counteract the pervasive impacts of fishing. However, MPAs in which reef sharks are abundant tend to be located in remote and underexploite...
Article
Full-text available
Aim: Protected areas have become pivotal to the modern conservation planning toolbox, but a limited understanding of marine macroecology is hampering their efficient design and implementation in pelagic environments. We explored the respective contributions of environmental factors and human impacts in capturing the distribution of an assemblage of...
Article
A baited videographic survey at Pitcairn Island has significantly extended the known range for two reef-fish species: blue-lined triggerfish Xanthichthys caeruleolineatus and greater amberjack Seriola dumerili, with an additional minor extension noted for giant trevally Caranx ignobilis. This highlights the importance of further research in this re...
Article
We investigated drivers of reef shark demography across a large and isolated marine protected area, the British Indian Ocean Territory Marine Reserve, using stereo baited remote underwater video systems. We modelled shark abundance against biotic and abiotic variables at 35 sites across the reserve and found that the biomass of low trophic order fi...
Article
The seamounts of the southern Indian Ocean remain some of the most poorly studied globally and yet have been subject to deep-sea fishing for decades and may face new exploitation through mining of seabed massive sulphides in the future. As an attempt to redress the knowledge deficit on deep-sea benthic and pelagic communities associated mainly with...
Article
Understanding the processes driving the distribution of mid-water prey such as euphausiids and lanternfish is important for effective management and conservation. In the vicinity of abrupt topographic features such as banks, seamounts and shelf-breaks, mid-water faunal biomass is often elevated, making these sites candidates for special protection....
Article
A total of 68 cephalopod species belonging to 26 families (10–11% of the total known cephalopod diversity) were collected onboard R/V Fridtjof Nansen during a research survey on Southwest Indian Ocean Ridge in November–December 2009. This relatively small area extends from the Tropical front to the Subantarctic front with four distinctive cephalopo...
Article
Krill (Euphausia superba) are fundamentally important in the Southern Ocean ecosystem, forming a critical food web link between primary producers and top predators. Krill abundance fluctuates with oceanographic conditions, most notably variation in winter sea ice, and is susceptible to environmental change. Although links between local krill availa...
Article
Full-text available
Despite being identified as a driver of mobile predator aggregations (hotspots) in both marine and terrestrial environments, topographic complexity has long remained a challenging concept for scientists to visualise and a difficult parameter to estimate. It is only with the advent of high-speed computers and the recent popularisation of geographica...
Article
In the open ocean, the movements and habitat use of large mobile predators are driven by dynamic interactions between biological and physical variables and complex predator–prey relationships. Understanding the spatial and temporal distributions of pelagic fishes and sharks is a critical component of conservation and fisheries management. Here, we...
Article
Full-text available
In situ characterization of krill morphometry, behaviour and orientation is not yet routinely feasible, yet is critical to understanding swarm characteristics. A first step is to measure individual and aggregation behaviour. We report on successful use of a robust, low-cost underwater stereo video camera system to observe live Antarctic krill (Euph...
Article
Full-text available
In contrast to generally sparse biological communities in open-ocean settings, seamounts and ridges are perceived as areas of elevated productivity and biodiversity capable of supporting commercial fisheries. We investigated the origin of this apparent biological enhancement over a segment of the North Mid-Atlantic Ridge (MAR) using sonar, corers,...
Data
In contrast to generally sparse biological communities in open-ocean settings, seamounts and ridges are perceived as areas of elevated productivity and biodiversity capable of supporting commercial fisheries. We investigated the origin of this apparent biological enhancement over a segment of the North Mid-Atlantic Ridge (MAR) using sonar, corers,...
Article
Trophic relationships and vertical distribution patterns of dominant mesozooplankton (2-20 mm) and macrozooplankton (>20 mm) invertebrates (Euphausiacea, Copepoda, Decapoda, Amphipoda, Thecosomata and Lophogastrida) were investigated within the epi- and meso-pelagic zone (0-200 and 200-800 m depth), north (54 degrees N) and south (49 degrees N) of...
Article
Full-text available
New baseline information is presented on biogeography, abundance and distribution of euphausiids from discrete depth samples collected throughout the water column to 3000 m at 42 locations along the Mid-Atlantic Ridge (MAR) between Iceland and the Azores. Eighteen species were recorded, with Euphausia krohni and Thysanoessa longicaudata being most...
Article
Using a generalized additive model, we assessed the influence of a suite of physical, chemical and biological variables upon euphausiid species abundance throughout the Pacific. We found that the main drivers of species abundance, in order of decreasing importance, were sea surface temperature (explaining 29.53% of species variability), salinity (2...
Article
Mid-ocean ridges are common features of the world’s oceans but there is a lack of understanding as to how their presence affects overlying pelagic biota. The Mid-Atlantic Ridge (MAR) is a dominant feature of the Atlantic Ocean. Here, we examined data on euphausiid distribution and abundance arising from several international research programmes and...

Questions

Question (1)
Question
As part of our efforts to model shark distribution, derived from baited cameras, we have been applying a method of introducing a residual autocovariate (RAC) term in our Boosted Regression Trees (BRT, Elith et al 2008), to account for spatial autocorrelation (method of Crase 2012).
Now, we would like to make spatial predictions out-of-samples with our model. However, we do not know what value to set for the RAC.  I was wondering if anyone could recommend a robust way of dealing with this, or perhaps any further literature on the topic?
We would be very grateful for any assistance you are able to provide!!
Crase, B., Liedloff, A. C., & Wintle, B. (2012). A new method for dealing with residual spatial autocorrelation in species distribution models. Ecography, (35), 879–888. http://doi.org/10.2307/23272446
Elith, J., Leathwick, J. R., & Hastie, T. (2008). A working guide to boosted regression trees. Journal of Animal Ecology, 77(4), 802–813. http://doi.org/10.1111/j.1365-2656.2008.01390.x

Network

Cited By

Projects

Projects (7)
Project
This project aims to improve the understanding of the socio-economic context within which elasmobranch fisheries exist in Sri Lanka and India and key drivers for behavior change. It aims to identify how fisher perceptions and values interact with socio-economic and ecological changes with a view to improving the effectiveness of governance and management. The project will utilize a mixed-methods approach and a wide range of methods to build a community-based narrative of fisherfolk livelihoods.
Project
Standardised methods of survey design, data collection, analysis and reporting are essential to monitoring status and trends in Australia’s vast marine environment. In Australia, however, many different approaches have been developed by multiple agencies collecting data for various purposes. Combining these data sets is a difficult task (sometimes impossible). This project builds on the marine monitoring blueprint produced by the National Environmental Research Program (NERP) Marine Biodiversity Hub (the forerunner of the NESP) to provide the foundation for Standard Operating Procedures in the collection and analysis of monitoring data. Ultimately, the project aims to enable different agencies to collect concise, consistent, interpretable and fit-for-purpose evidence on the status and trends of environmental assets that will be comparable from one project/institution/area/time to the next. The resulting datasets will be collated into regional and national scale assessments, and will provide an improved information flow from survey through to management decision, supporting the Australian Government's management and monitoring requirements in the Commonwealth Marine Area. More information can be found here: https://www.nespmarine.edu.au/project/project-d2-analysis-methods-and-software-support-standard-operating-procedures-survey-design