Three-dimensional digital mapping of ecosystems: a new era in spatial ecology

Ecological processes occur over multiple spatial, temporal and thematic scales in three-dimensional (3D) ecosystems. Characterizing and monitoring change in 3D structure at multiple scales is challenging within the practical constraints of conventional ecological tools. Remote sensing from satellites and crewed aircraft has revolutionized broad-scale spatial ecology, but fine-scale patterns and processes operating at sub-metre resolution have remained understudied over continuous extents. We introduce two high-resolution remote sensing tools for rapid and accurate 3D mapping in ecology—terrestrial laser scanning and structure-from-motion photogrammetry. These technologies are likely to become standard sampling tools for mapping and monitoring 3D ecosystem structure across currently under-sampled scales. We present practical guidance in the use of the tools and address barriers to widespread adoption, including testing the accuracy of structure-from-motion models for ecologists. We aim to highlight a new era in spatial ecology that uses high-resolution remote sensing to interrogate 3D digital ecosystems

Vertical migrations of fish schools determine overlap with a mobile tidal stream marine renewable energy device

Large increases in the generation of electricity using marine renewable energy (MRE) are planned, and assessment of the environmental impacts of novel MRE devices, such as kites, are urgently needed. A first step in this assessment is to quantify overlap in space and time between MRE devices and prey species of top predators such as small pelagic fish. Here, we quantify how the distribution of fish schools overlaps with the operational depth (20–60 m) and tidal current speeds (≥1.2–2.4 m/s) used by tidal kites, and the physical processes driving overlap. Fish schools undertake diel vertical migrations driven by the depth of light penetration into the water column, controlled by the supply of solar radiation and water column light absorption and scattering, which in turn depends on the cross‐sectional area of suspended particulate matter (SPM). Fish schools were found shallower in the morning and evening and deeper in the middle of the day when solar radiation is greatest, with the deepest depths reached during predictable bimonthly periods of lower current speeds and lower cross‐sectional area of SPM. Potential kite operations overlap with fish schools for a mean of 5% of the time that schools are present (maximum for a day is 36%). This represents a mean of 6% of the potential kite operating time (maximum for a day is 44%). These were both highest during a new moon spring tide and transitions between neap and spring tides. Synthesis and applications. Overlap of fish school depth distribution with tidal kite operation is reasonably predictable, and so the timing of operations could be adapted to avoid potential negative interactions. If all interaction between fish schools was to be avoided, the loss of operational time for tidal kites would be 6%. This information could also be used in planning the operating depths of marine renewable energy (MRE) devices to avoid or minimize overlap with fish schools and their predators by developers, and for environmental licencing and management authorities to gauge potential ecological impacts of different MRE device designs and operating characteristics

Towards spatial management of fisheries in the Gulf: benthic diversity, habitat and fish distributions from Qatari waters

Abstract As with many other regions in the world, more complete information on the distribution of marine habitats in the Gulf is required to inform environmental policy, and spatial management of fisheries resources will require better understanding of the relationships between habitat and fish communities. Towed cameras and sediment grabs were used to investigate benthic habitats and associated epifauna, infauna and fish communities in the central Gulf, offshore from the east coast of Qatar, in water depths of between 12 and 52 m. Six different habitats were identified: (i) soft sediment habitats of mud and (ii) sand, and structured habitats of (iii) macro-algal reef, (iv) coral reef, (v) mixed reef, and (vi) oyster bed. The epibenthic community assemblage of the mud habitat was significantly different to that of sand, which in turn differed from the structured habitats of coral reef, mixed reef and oyster bed, with the macroalgal assemblage having similarities to both sand and the other structured habitats. Fish assemblages derived from video data did not differ between habitats, although certain species were only associated with particular habitats. Epibenthic diversity indices were significantly lower in mud, sand and macro-algal habitats, with no differences recorded for fish diversity. Soft sediment grab samples indicated that mud habitats had the highest benthic diversity, with Shannon-Weiner values of &amp;gt;4, and were more diverse than sand with values of 3.3. The study demonstrates high biodiversity in benthic habitats in the central and southwestern Gulf, which may in part be due to the absence of trawling activity in Qatari waters. There is a strong influence of depth on benthic habitat type, so that depth can be used to predict habitat distribution with a high level of accuracy. The presence of outcrops of hard substrata creates a mosaic of patchy shallow structured benthic habitat across extensive areas of the offshore seabed. Such heterogeneity, and the association of commercially exploited fish species with specific habitats, indicates that this region is well suited to a spatial approach to fisheries management.</jats:p

Thresher Sharks Use Tail-Slaps as a Hunting Strategy

<div><p>The hunting strategies of pelagic thresher sharks (<i>Alopias pelagicus</i>) were investigated at Pescador Island in the Philippines. It has long been suspected that thresher sharks hunt with their scythe-like tails but the kinematics associated with the behaviour in the wild are poorly understood. From 61 observations recorded by handheld underwater video camera between June and October 2010, 25 thresher shark shunting events were analysed. Thresher sharks employed tail-slaps to debilitate sardines at all times of day. Hunting events comprised preparation, strike, wind-down recovery and prey item collection phases, which occurred sequentially. Preparation phases were significantly longer than the others, presumably to enable a shark to windup a tail-slap. Tail-slaps were initiated by an adduction of the pectoral fins, a manoeuvre that changed a thresher shark's pitch promoting its posterior region to lift rapidly, and stall its approach. Tail-slaps occurred with such force that they may have caused dissolved gas to diffuse out of the water column forming bubbles. Thresher sharks were able to consume more than one sardine at a time, suggesting that tail-slapping is an effective foraging strategy for hunting schooling prey. Pelagic thresher sharks appear to pursue sardines opportunistically by day and night, which may make them vulnerable to fisheries. Alopiids possess specialist pectoral and caudal fins that are likely to have evolved, at least in part, for tail-slapping. The evidence is now clear; thresher sharks really do hunt with their tails.</p></div

Behaviour diagram of prey item collection phase, as observed from events that were recorded in the sagittal plane.

<p>A motion animation (top) represents 3.16 s⁻¹ of an event that was recorded by handheld underwater video camera 19 August 2010. Inserts show a thresher shark circling and collecting three sardines that were stunned during the strike phase of a successful hunting event.</p

Behaviour diagram of a thresher shark's overhead tail-slap, with preparation (1–2), strike (3–14) and wind-down recovery (15–27) phases, as observed from events, which occurred in the sagittal plane.

<p>A motion animation (top) represents 1.08 s⁻¹ of an event which was recorded by handheld underwater video camera on 17 June, 2010. Center inserts profile the key characteristics of the behaviour, while inserts shown in the transvers plane (bottom), were interpreted from other video sequences.</p

Comparative analysis of the trajectory arc that formed the path of a thresher shark's overhead tail-slap as observed from six hunting events recorded in the sagittal plane.

<p>The relative distances (cm) the tip of the tail was from the posterior base of the pectoral fin (x/y intercept  = <i>0</i>) were plotted at intercepts that were standardised for precaudal length. The motion of the trajectory is left to right.</p

Diagram showing the method used for analysing the kinematics of a thresher shark's tail-slap from a sequence of video still images.

<p>For sagittal plane events, three key anatomical parts (a) the tip of the tail, (b) the midpoint of the caudal peduncle, and (c) the tip of the snout were tracked in two dimensions using the posterior base of the pectoral fin as a fixed reference point (x/y intercept  = <i>0</i>). The arc length of a thresher shark's tail-slap is shown in dashed line.</p

The kinematics of an overhead tail-slap, as observed from six thresher shark hunting events that were recorded in the sagittal plane.

<p>A) The movements of the tip of the tail (solid), the caudal peduncle (dotted) and the snout (dashed) were tracked in relation to their relative distances (cm) from the posterior base of the pectoral fin (x/y intercept  = <i>0</i>) at the time they were plotted. B) The biphasic acceleration of the tip of a thresher shark's tail reached its peak at the apex of its trajectory arc. C) The maximum trajectory speeds of a thresher shark's tail were tracked in relation to their relative distances (cm) from the posterior base of the pectoral fin (x/y intercept  = <i>0</i>) at the time they were plotted. The variability in the separation points of preparation (blue); strike (red); and wind-down recovery (green) phases among the six analysed events is shown in grey shading.</p