Search

Four oceanographic moorings were deployed across the South China Sea continental slope near 21.85∘ N, 117.71∘ E, from 30 May to 18 July 2014​​​​​​​ for the purpose of observing high-frequency nonlinear internal waves (NLIWs) as they shoaled across a rough, gently sloping bottom. Individual waves required just 2 h to traverse the array and could thus easily be tracked from mooring to mooring. In general, the amplitude of the incoming NLIWs tracked the fortnightly tidal envelope in the Luzon Strait; they lagged by 48.5 h and were smaller than the waves previously observed to the southwest near the Dongsha Plateau. Two types of waves, a waves and b waves,​​​​​​​ were observed, with the b waves always leading the a waves by 6–8 h. Most of the NLIWs were remotely generated, but a few of the b waves formed locally via convergence and breaking at the leading edge of the upslope-propagating internal tide. Waves incident upon the moored array with amplitude less than 50 m and energy less than 100 MJ m−1 propagated adiabatically upslope with little change of form. Larger waves formed packets via wave dispersion. For the larger waves, the kinetic energy flux decreased sharply upslope between 342 and 266 m, while the potential energy flux increased slightly, causing an increasing ratio of potential-to-kinetic energy as the waves shoaled. None of the waves met the criteria for convective breaking. The results are in rough agreement with recent theory and numerical simulations of shoaling waves.

The propagation of waves in shallow waters is affected by the bottom topography unlike deep water waves of the coastal environment. Due to the interaction of the wave with bed topography, the wave transformation processes occur. Refraction, diffraction, shoaling, and breaking are the wave transformation processes that occur in the coastal environment. The significant wave height over rugged topography is a standardized statistics to denote the characteristic height of the random waves in a sea state. Therefore, the objective of the present study is to predict the significant wave height over rugged topography. The SWAN standalone and SWAN DHH platform are used to predict significant wave height over rugged topography in Mehamn harbour, Norway. The SWAN model results are almost similar to the lab data of Vold and Lothe (2009) for all the 22 scenarios at all the output locations. Further, the four cases reported by Taehun (2011) and lab data from Vold and Lothe (2009) for that four cases are compared with the SWAN model results. It is observed that the SWAN model results are much closer to the lab data of Vold and Lothe (2009).

We report an experimental study addressing the characteristic hydrodynamic transformations of unstable wave groups as well as JONSWAP wave fields propagating from deep-water towards shallow regions. Long zones of linearly rising floor levels have been installed to mimic a simplified coastal morphology. The breather surface elevation evolution data show a very good agreement with the depth-adapted nonlinear Schrodinger-type model. Our results suggest that the residual effects of four-wave resonance interactions in the shallower regions is relevant for the nonlinear group propagation over steep bottom topography slopes. When considering broadband JONSWAP processes, the model fails in predicting the evolution of kurtosis, independently of the values of significant wave height adopted. Nonetheless, consistency with the data is achieved when narrowing the spectrum of the JONSWAP wave field. Our study emphasizes the strong potential of weakly nonlinear frameworks in modeling complex wave shoaling problems and wave transformations in coastal zones.

Shoaling behaviour is commonly displayed by fishes and is thought to reduce predation and increase foraging efficiency. Shoaling relies on coordination between individuals, with higher cohesion and alignment among individuals within a shoal providing greater net benefits of this behaviour. Whilst single species often shoal together in conspecific groups, mixed-species shoaling is frequently observed and has been identified as an important determinant of individual fitness for the multiple species involved. Despite their prevalence, the structure of mixed-species shoals and the mechanisms by which individuals gain protection from predators and enhance their foraging efficiency are not as well understood as for single-species shoals. In fact, mixed-species shoals may be less coordinated than single-species shoals, raising the intriguing question of why fishes form mixed-species shoals when this behaviour could be less beneficial than single-species shoaling. Here we used in situ stereo-video techniques to compare within and between shoal differences in cohesion and alignment, for mixed- and single-species shoals containing the tropical vagrant Indo pacific sergeant major damselfish, Abudefduf vaigiensis, in temperate waters. As expected, mixed-species shoals were less aligned than single-species shoals. However, within mixed-species shoals conspecifics were more cohesive and aligned than were heterospecifics, suggesting coordinated single-species subgroups formed within larger mixed-species shoals. The formation of subgroups may mitigate costs associated with differences between species, therefore enhancing benefits of mixed-species shoaling. As such, multiple levels of social structure may exist within mixed-species shoals that could facilitate growth and survival for vagrant A. vaigiensis in temperate regions. More broadly, this research highlights the importance of considering detailed internal structures of mixed-species shoals when trying to understand cost–benefit trade-offs experienced by individuals.

4 pages, figures, 1 box, We outline key mechanisms by which fishing can change the shoaling tendency and collective behaviour of exploited species – an issue that is rarely considered and poorly understood. We highlight potential consequences for fish populations and food webs, and discuss possible repercussions for fisheries and conservation strategies, We acknowledge financial support from the Spanish Ministry of Science and Innovation (Juan de la Cierva Incorporación Research Fellowship to V.S. #IJC2018-035389-I), the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation to ICM-CSIC (#CEX2019-000928-S), the Zukunfstkolleg, Institute for Advanced Study at the University of Konstanz (Postdoctoral Fellowship to J.W.J), the European Union’s Horizon 2020 research and innovation programme (grant to M.C. #869300, FutureMares), the PELWEB project (grant of the Spanish Government to M.C. #ES-PN-2017-CTM, #2017-88939-R), and the marEEshift program of the German Ministry of Education and Research (grant to R.A. #01LC1826D)

Shoaling internal solitary waves near the Dongsha Atoll in the South China Sea dissipate their energy and enhance diapycnal mixing, which have an important impact on the oceanic environment and primary productivity. The enhanced diapycnal mixing is patchy and instantaneous. Evaluating its spatiotemporal distribution requires comprehensive observation data. Fortunately, seismic oceanography meets the requirements, thanks to its high spatial resolution and large spatial coverage. In this paper, we studied three internal solitary waves in reversing polarity near the Dongsha Atoll and calculated their spatial distribution of diapycnal diffusivity. Our results show that the average diffusivities along three survey lines are 2 orders of magnitude larger than the open-ocean value. The average diffusivity in internal solitary waves with reversing polarity is 3 times that of the non-polarity reversal region. The diapycnal diffusivity is higher at the front of one internal solitary wave and gradually decreases from shallow to deep water in the vertical direction. Our results also indicate that (1) the enhanced diapycnal diffusivity is related to reflection seismic events, (2) convective instability and shear instability may both contribute to the enhanced diapycnal mixing in the polarity-reversing process, and (3) the difference between our results and Richardson-number-dependent turbulence parameterizations is about 2–3 orders of magnitude, but its vertical distribution is almost the same.

Animal groups are known to exhibit collective behaviours that allow for effective responses to predators and environmental factors. Habitats with high levels of structural complexity have been shown to influence the collective tendencies of these animal aggregations. However, the effect of anthropogenically induced habitat complexity on collective tendency is still unknown. We examined the effect of a water control structure (WCS), located in an estuarine salt marsh system, on the collective behaviours of free ranging juvenile Gulf menhaden (Brevoortia patronus), a schooling forage fish. Using an acoustic imaging sonar, behavioural observations prior to and during predator attacks were collected in an open marsh canal as well as in the vicinity of the WCS. We found that fish in schools responded to the WCS by swimming in a less aligned and cohesive manner, while maintaining an increased ability to transfer social information. Our results demonstrate that collective tendency in schooling fish is affected by the presence of anthropogenically introduced habitat complexity, prior to and during predator attack. Our study, thus, strengthens the idea that the complex environmental conditions induced by the presence of man-made structures may play a large role in structuring collective behaviour and trophic interactions in aquatic environments.

The main objective of this paper is to examine the influences of both the principal wave direction and the directional spreading parameter of the wave energy on the wave height evolution of multidirectional irregular waves over an impermeable sloping bottom and to propose an improved wave height distribution model based on an existing classical formula. The numerical model FUNWAVE 2.0, based on a fully nonlinear Boussinesq equation, is employed to simulate the propagation of multidirectional irregular waves over the sloping bottom. Comparisons of wave heights derived from wave trains with various principal wave directions and different directional spreading parameters are conducted. Results show that both the principal wave direction and the wave directional spread have significant influences on the wave height evolution on a varying coastal topography. The shoaling effect for the wave height is obviously weakened with the increase of the principal wave direction and with the decrease of the directional spreading parameter. With the simulated data, the classical Klopman wave height distribution model is improved by considering the influences of both factors. It is found that the improved model performs better in describing the wave height distribution for the multidirectional irregular waves in shallow water.

Understanding how fish associate with habitats across marine landscapes is crucial to developing effective marine spatial planning (MSP) in an expanding and diversifying ocean economy. Globally, anthropogenic pressures impact the barely understood temperate mesophotic ecosystems and South Africa’s remote Amathole shelf is no exception. The Kei and East London region encompass three coastal marine protected areas (MPAs), two of which were recently extended to the shelf-edge. The strong Agulhas current (exceeding 3 m/s), which runs along the narrow shelf exacerbates sampling challenges. For the first time, a remotely operated vehicle (ROV) surveyed fish and their associated habitats across the shelf. Results indicated fish assemblages differed between the two principle sampling areas, and across the shelf. The number of distinct fish assemblages was higher inshore and on the shelf-edge, relative to the mid-shelf. However, the mid-shelf had the highest species richness. Unique visuals of rare Rhinobatos ocellatus (Speckled guitarfish) and shoaling Polyprion americanus (wreckfish) were collected. Visual evidence of rhodolith beds, deep-water lace corals and critically endangered endemic seabreams were ecologically important observations. The ROV enabled in situ sampling without damaging sensitive habitats or extracting fish. This study provided information that supported the Amathole MPA expansions, which extended protection from the coast to beyond the shelf-edge and will guide their management. The data gathered provides baseline information for future benthopelagic fish and habitat monitoring in these new MPAs.

Lofer cyclothems of the Alpine Upper Triassic have many features in common with Holocene sediments of Florida Bay. The modal ‘complete' Lofer cycle is essentially symmetrical, having a deepening and shoaling phase, as does the cycle-in-progress in Florida Bay. Lateral discontinuity and thickness variations within members of the Lofer cyclothems indicate syn-depositional relief, possibly in the form of mud banks, the signature feature of Florida Bay sedimentation. Spatial and temporal dimensions, although poorly constrained, appear comparable. Analogous depositional textures, biota and sedimentary structures, while not unique to either environment, strengthen the inferences that can be made about the Triassic depositional environment and regarding future evolution of the modern environment. The striking similarities between the Holocene icehouse sediments and the Late Triassic greenhouse deposits suggest that sedimentation patterns at the scale of individual cycles or parasequences may be largely independent of the global climate regime.

Whale sharks are known to feed primarily on zooplankton all over the world; however, recent findings suggest that they also prey on fish using behaviors that have not been fully described. Here, we provide detailed evidence of whale sharks interacting with schools of anchovy on four occasions in Bahia de Los Angeles, Baja California, Mexico. Three of these were predatory interactions in multi-species feeding frenzies, and one was a non-predatory interaction. In predatory interactions, whale sharks exhibited two types of feeding behaviors: (1) stationary suction-feeding, a previously described behavior for whale sharks, and (2) lunge-feeding, which has not been previously described in whale sharks, but has been observed among other large filter feeders, such as rorqual whales. The whale sharks moved simultaneously around the school of anchovy, lunging simultaneously or one after another into the school, with 66% (N = 17) of these lunges occurring in the same direction. In the non-predatory interaction, whale sharks exhibited “sit-and-wait" behavior. The evidence presented here, along with previous observations, suggests that whale sharks may change their feeding strategy from suction to lunge-feeding when other predators corner schooling fish.

For predators, cooperation can decrease the cost of hunting and potentially augment the benefits. It can also make prey accessible that a single predator could not catch. The degree of cooperation varies substantially and may range from common attraction to a productive food source to true cooperation involving communication and complementary action by the individuals involved. We here describe cooperative hunting of Galapagos sea lions (Zalophus wollebaeki) for Amberstripe scad (Decapterus muroadsi), a schooling, fast swimming semipelagic fish. A group of 6–10 sea lions, usually females only, drove scad over at least 600–800 m from open water into a cove where, in successful hunts, they drove them ashore. Frequently, these “core hunters” were joined toward the final stages of the hunt by another set of opportunistic sea lions from a local colony at that beach. The “core hunters” did not belong to that colony and apparently were together coming toward the area specifically for the scad hunt. Based on the observation of 40 such hunts from 2016 to 2020, it became evident that the females performed complementary actions in driving the scad toward the cove. No specialization of roles in the hunt was observed. All “core hunters” and also opportunistically joining sea lions from the cove shared the scad by randomly picking up a few of the 25–300 (mean 100) stranded fish as did scrounging brown pelicans. In one of these hunts, four individual sea lions were observed to consume 7–8 fish each in 25 s. We conclude that the core hunters must communicate about a goal that is not present to achieve joint hunting but presently cannot say how they do so. This is a surprising achievement for a species that usually hunts singly and in which joint hunting plays no known role in the evolution of its sociality., We describe cooperative hunting of groups of Galapagos sea lions (Zalophus wollebaeki) for Amberstripe scad (Decapterus muroadsi), a schooling, fast swimming fish which they drive ashore by complimentary actions. The “core hunters” were together coming to the area specifically for the scad hunt. We conclude that the core hunters must communicate about a goal that is not present to coordinate joint hunting which is a surprising achievement for a species that usually hunts singly and in which joint hunting plays no role in the evolution of its sociality.

An internal gravity wave model was employed to simulate the generation of internal solitary waves (ISWs) over a sill by tidal flows. A westward shoaling pycnocline parameterization scheme derived from a three-parameter model was adopted, and then 14 numerical experiments were designed to investigate the influence of the pycnocline thickness, density difference across the pycnocline, westward shoaling isopycnal slope angle and pycnocline depth on the ISWs. When the pycnocline thickness on both sides of the sill increases, the total barotropic kinetic energy, total baroclinic energy and ratio of baroclinic kinetic energy (KE) to available potential energy (APE) decrease, whilst the depth of isopycnal undergoing maximum displacement and ratio of baroclinic energy to barotropic energy increase. When the density difference on both sides of the sill decreases synchronously, the total barotropic kinetic energy, ratio of baroclinic energy to barotropic energy and total baroclinic energy decrease, whilst the depth of isopycnal undergoing maximum displacement increases. When the westward shoaling isopycnal slope angle increases, the total baroclinic energy increases whilst the depth of turning point almost remains unchanged. When the depth of westward shoaling pycnocline on both sides of the sill reduces, the ratio of baroclinic energy to barotropic energy and total baroclinic energy decrease, whilst the total barotropic kinetic energy and ratio of KE to APE increase. When one of the above four different influencing factors was increased by 10% while the other factors keep unchanged, the amplitude of the leading soliton in ISW Packet A was decreased by 2.80%, 7.47%, 3.21% and 6.42% respectively. The density difference across the pycnocline and the pycnocline depth are the two most important factors in affecting the characteristics and energetics of ISWs.

Semi-submersibles for offshore oil exploration and exploitation often suffer from severe wave impacts in extreme ocean environments. Owing to the complex wave interactions among structural components of semi-submersibles, in-depth analyses on the characteristics of wave impact events are of significance for both industry and academia. An experimental study was carried out to investigate the local wave impact loads on a semi-submersible, with focus on understanding the wave impacts by identifying typical impact modes. Quantitative criteria are proposed to classify major wave impacts on the semi-submersible into six modes and two types. The results show that the classification is reasonable and provides valuable information for studying wave impacts on semi-submersibles. The incident wave characteristics at the fore column of the semi-submersible have important influence on the wave impact mode. The fore-column dominating wave impacts exert the most intense loads on the fore column and feature well-developed breaking waves or slightly breaking waves at the fore column. However, the aft-column dominating wave impacts exert the most intense loads on the aft column or the deck bottom and feature non-breaking waves at the fore column. Energy loss during the fore-column impact weakens the impact severity on the aft column in the fore-column dominating wave impacts. The shoaling effect of the submerged pontoon and different motion configurations of the platform result in higher occurrence rate of the aft-column dominating wave impacts. Different impact modes are also distinguished by different spatial distributions of wave impact loads.

Group behaviours in fish are widespread, and are increasingly used to develop new optimisation algorithms for solving complex tasks. However, how external factors regulate individual spatial location in a fish school represents an overlooked aspect that is fundamental to understand collective dynamics. Herein, the neon tetra Paracheirodon innesi, a highly social fish species, has been used to analyse the effect of different ecological contexts, including food availability and predation risk, on the place preference of individual agents in the group. A robotic school of fish has been developed to establish a biohybrid interaction enabling accurate isolation of the individual choice of living fish without disturbance from other conspecifics. Results show that the individual optimal position in the group is context dependent, as individual fish continuously modify their location in the school according to different external scenarios. Individual fish stayed as close to food as possible to better compete with conspecifics. In the presence of a robotic predator, fish preferred to locate in the middle of the aggregation to favour dilution effects. When no stimuli were provided, fish preferred to stay at the back of the school, probably to exploit the increased likelihood of predator detection by conspecifics swimming ahead. This study provides new basic knowledge on how swarm intelligence and self-organisation processes of fish are affected by the individual agent. Furthermore, these findings can inspire innovative task optimisation approaches potentially applicable in engineering contexts.

The social niche hypothesis theorizes that repeated social interactions between group members is an important mechanism for generating consistent individual differences in behaviour. However, such frequent interactions also have the potential to mask or suppress behavioural differences if individuals conform towards a group behavioural norm (i.e. the social conformity hypothesis) by either synchronizing their behaviour or shifting their behaviour towards that of influential group members. Both of these predictions hinge on the notion that social feedback among group members plays a key role in modulating consistent behavioural variation; thus, in the absence of such feedback, it could be expected that such consistent variation will be reduced. Here, we investigated how a 1-month housing with a stable social group, as opposed to being socially isolated, affected consistent individual differences in the shoaling tendencies of threespine stickleback, Gasterosteus aceluteus. Specifically, we repeatedly tested the tendency of individual sticklebacks to shoal with conspecifics before and after their social experience. In support of the social conformity hypothesis, we observed a four-fold increase in among-group differences, but no change in among-individual differences, in the shoaling tendencies of sticklebacks housed in groups. A post hoc analysis revealed that the increase in among-group differences may have been driven by the most ‘social’ pretreatment group member. Conversely, fish that were housed in isolation, expressed a notable, albeit nonsignificant, decrease in individual shoaling variation and repeatability. This decrease in shoaling variation corresponded with an increase in the average shoaling tendencies of solitary fish post-treatment, suggesting that solitary fish converged towards a similarly high level of shoaling tendencies post-treatment. For both treatment groups, however, we found among-individual positive correlations in pre- and post-treatment shoaling tendencies, suggesting that individuals may inherently differ in their shoaling tendencies, but that the social environment plays an important role in mediating the expression of these differences.

Multispecies schools of small planktivorous fishes are important constituents of reefs and coastal infrastructure; however, determining the extent and distribution of these schools is challenging. Here, we describe a novel use of a low-cost portable multibeam echosounder from a small vessel, which can concurrently measure detailed bathymetry and the distribution of mid-water targets with high spatial accuracy, regardless of light availability or water clarity. Fish abundance and biomass are not easily quantified by multibeam echosounders, so we developed a new metric for delineating the gridded horizontal distribution of school thickness, and assessed the metric's efficacy by examining its correlation with mean volume backscattering strength derived from a calibrated 38 kHz split-beam echosounder (R = 0.67). We measured the distribution of fish school thickness around clusters of large concrete modules of an artificial reef using a multibeam echosounder, complemented with underwater video to aid species identification. The mean distribution of school thickness was mapped around the reef field with generalized additive mixed models. Model spatial predictions indicated schools aggregated around module clusters, rather than individual modules. Dynamic schools of fish in relatively shallow coastal waters (~ 30 m) can be surveyed over 400,000 m at 3 m s in just 60 min. Portable multibeam echosounders are an accessible and valuable addition to quantifying the dynamic distributions of coastal fishes around features with high vertical relief.

This study explores the counterpart of marine heatwave, known as the cold blob, in the Northeast Pacific (NEP) by selecting the long-lived events with the normalized sea surface temperature (SST) anomalies averaged over the blob area (160°–135° W, 40°–50° N) smaller than − 0.75 for at least 5 months. There are 10 summer-peak events with a stronger intensity and 7 winter-peak events. The summer-peak cold blob events are mostly attributed to the vertical entrainment when the mixed layer depth is shoaling. For the winter-peak group, the greater heat loss at surface is the principal factor to stimulate the cold blob, associated with the intense westerly anomalies around the blob area. However, the vertical entrainment generally hinders the amplification of winter-peak cold blobs. Moreover, the advection of colder-than-normal water to the blob area contributes much less for both two groups. We conjecture that the NEP cold blob and tropical La Nina-like state are potentially linked. The summer-peak cold blob event is often followed by a La Nina event in the ensuing winter. On the other hand, the equatorial La Nina-like SST cooling in late summer and autumn in turn enhances the winter-peak cold blobs. We find the subtropical region, particularly near the Baja California, may act as the oceanic bridge to connect the NEP cold blob and equatorial La Nina.

Visual observations performed by members of the International Public Organization Association of Underwater Activities of Crimea and Sevastopol have allowed for obtaining the abundance characteristics of brown meagre (Sciaena umbra Linnaeus, 1758) in the Crimean Black Sea waters. There have been 290 observations completed with an average duration of 4 h each and 64 fish specimens examined with a length (SL) of 31.4 ± 0.9 cm and weight of 830 ± 65 g in adult fish and SL 13.5 ± 0.2 cm and weight of 78 ± 4 g in juveniles. The state of the species has not been evaluated as threatened. The distribution density is 2000–3100 ind./ km2. Adult fish up to 4 years old and ≤1000 g in weight account for 70% of the shoaling stock; individuals more than 1500 g in weight are few in numbers. Juveniles commonly form separate aggregations.

Present work studied the lesion mechanism of coastal clam and its vulnerability assessment subject to the hydrodynamic disturbance of extreme storm events. A clam habitat at the northeast coast of China was chosen for the demonstration study. Relocation failure after passive transport due to excessive substrate erosion or suffocation in anoxic burial under overburdening sedimentation was identified the major cause of negative biomass responses during the storm. Based on the biological propensity and physiological sensitivity of the clam, a tunable loss probability function correlating the mortality with the shell length and the seabed change was proposed. A hydrodynamic model was then adopted to compute the sediment transport and net changes in the seafloor in response to the comprehensive process of storm waves and surge. The spatial distribution of the damage states was evaluated based on the numerical results incorporating the loss probability function. The estimated damage was mainly concentrated along the wave shoaling and breaking belts parallel to the shoreline. High surge levels pushed the “damage belt” shoreward, in which case large waves were able to propagate close to the shoreline before breaking. The scientific findings are helpful to better understand the vulnerability of the clam habitat to the storm disturbance. The study result as well provides a practical methodology of the storm risk assessment for benthic communities in broader ecological and geophysical scopes. The methodology are expected to be further validated and improved by more widespread sampling on coastal ecosystem or mariculture that will withstand future storms.

This article focuses on improving the understanding of the electromagnetic (EM) scattering from water waves modulated by shoaling effect arising from different upslope submarine topography in the nearshore zone. Simulation of EM bistatic scattering from water waves in the nearshore zone where the water depth becomes gradually shallower is presented. The shallow water waves with periodic sinusoidal type are simulated by the model that is based on Boussinesq approximation theory, which can accurately construct the detailed wave structure in the nearshore zone, and the analytical model-the second-order small slope approximation is applied to modeling the EM bistatic scattering from the shallow water waves. Comparisons of the bistatic scattering coefficient (BSC) between water waves corresponding to different submarine plane-upslope topography in the nearshore zone have shown that the angular position of harmonics of BSC will change as upslope varies: higher-order harmonics for plane-upslope cases would be far away from the specular peaks for flat topography case. Moreover, the wave height of the shallow water waves and nonlinear effect will greatly impact changing trend of the BSC. Simulations for TMA spectrum-based water waves also support the fact that the transfer of wave energy from low frequency to higher frequency wave components would be intensified in the shallow water zone with the upslope submarine topography. The results in this article indicate that shallow water waves would reflect some interesting scattering features that traditional deep-sea waves did not show, which will be helpful to the further quantitative investigation of scattering characteristics of nearshore waves.

In the Northwestern Pacific Ocean, in recent years, there has been an increase in the populations of eastern mackerel (Scomber japonicus) and Far Eastern sardine (Sardinops sagax). In the Far East, large-tonnage fishing trawlers capable of successfully harvesting (catching) mackerel and Far Eastern sardines are engaged in fishing for pollock and other traditional objects of fishing. The purpose of this article is to show how underutilized stocks of mackerel and Far Eastern sardine can be developed by medium tonnage vessels using twin fishing techniques. For the biotechnological substantiation of the parameters of the twin trawl system according to the degree of influence on the object of production (catch), it was divided into 7 zones, in each of which the object of production (catch) has one or another behavioral reaction. The article substantiates the necessary (optimal) vertical opening of the mouth of the trawl for complete vertical fishing of schools of fish based on echometric diagrams of the vertical distribution of schools of mackerel and Far Eastern sardine and the accepted response distances of fishing objects to elements of the trawl system. The biotechnical substantiation of the parameters of the twin trawl system for the extraction (catch) of Pacific mackerel and Far Eastern sardine has been carried out. The length of the twin trawl, the angle of attack of the upper, lateral and lower layers of the trawl shell, the length of the wings of the trawl are determined, the necessary ratio of the shaded area of the shell of the trawl to its fictitious area for mediumtonnage vessels with different traction characteristics is determined. Based on the speed parameters of fish in different zones of the trawl system, the distance between twin vessels, the length of the cords and the length of the cables are determined.

Shoaling decisions in the wild are determined by a combination of innate preferences of the individual along with the interplay of multiple ecological factors. In their natural habitat as well as in the laboratory, zebrafish is a shoaling fish. Here, we investigate the role of group size and associated vegetation in shaping shoaling preferences of wild male zebrafish. We studied the association preference of males to groups of female shoals in a multi-choice test design. We found that males made greater proportion of visits to an 8-female group compared to 2 and 4-female groups. However, males spent similar proportions of time across the three female-containing groups. When artificial vegetation was incorporated along with female number as an additional factor, we found that males prefer high and moderately vegetated patches compared to low or no-vegetation groups, irrespective of the number of females in these patches. Based on experiments using a novel multi-choice design, our results show that preference for group size can change due to interaction of two separate factors. This work is a first attempt to understand the role of aquatic flora in determining shoaling preferences in zebrafish, using an experimental paradigm consisting of a gradation in female and vegetation densities.

Animal behaviour has been broadly studied for its social or functional aspects but less often for understanding the interactions between organisms and their ambient conditions. A pilot observational study was performed by means of underwater camera to investigate the correlation between environmental factors and the density of fish in the epipelagic habitat of a European temperate reservoir. Explored factors confirmed a positive correlation between water temperature and all observed categories: non-predatory, predatory, single non-predatory and schooling fish, as well as freshwater bream and roach. On the other hand, de-trended solar irradiance was found to be negatively correlated with density of non-predatory fish, freshwater bream and European perch. Sunshine duration was negatively correlated with the density of predatory fish. Precipitation a showed positive relationship with single non-predatory fish and European perch, whereas wind strength had a negative relationship with density of schooling fish. Furthermore, density of predatory fish was positively correlated with density of single non-predatory fish and counts of observed clusters. Altogether, findings indicate that fish density is correlated with abiotic factors and the occurrence of predators. This suggests that more ecologically complex studies should be encouraged for better understanding of ecological interactions that drive the structure of aquatic ecosystems.

Spur-and-groove (SAG) morphology characterizes the fore reef of many coral reefs worldwide. Although the existence and geometrical properties of SAG have been well documented, an understanding of the hydrodynamics over them is limited. Here, the three-dimensional flow patterns over SAG formations, and a sensitivity of those patterns to waves, currents, and SAG geometry were characterized using the physics-based Delft3D-FLOW and SWAN models. Shore-normal shoaling waves over SAG formations were shown to drive two circulation cells: a cell on the lower fore reef with offshore flow over the spurs and onshore flow over the grooves, except near the seabed where velocities were always onshore, and a cell on the upper fore reef with offshore surface velocities and onshore bottom currents, which result in depth-averaged onshore and offshore flow over the spurs and grooves, respectively. The mechanism driving this flow results from the net of the radiation stress gradients and pressure gradient, which is balanced by the Reynolds stress gradients and bottom friction that differ over the spur and over the groove. Waves were the primary driver of variations in modelled flow over SAG, with the flow strength increasing for increasing wave heights and periods. Spur height, SAG wavelength, and the water depth at peak spur height were the dominant influences on the hydrodynamics, with spur heights directly proportional to the strength of SAG circulation cells. SAG formations with shorter SAG wavelengths only presented one circulation cell on the shallower portion of the reef, as opposed to the two circulation cells for longer SAG wavelengths. SAG formations with peak spur heights occurring in shallower water had stronger circulation than those with peak spur heights occurring in deeper water. These hydrodynamic patterns also likely affect coral and reef development through sediment and nutrient fluxes.

The variability of the Atlantic Meridional Overturning Circulation (AMOC) and the Meridional Freshwater Transport (Mov) at 24°N, 11°S, and 30°S, simulated with the GFDL-CM3 model under the historical (1860–2005) and RCP 4.5 and 8.5 scenarios (2006–2100) are examined. The results are compared with the climatology and observations in the search for salinity biases that would compromise the accuracy of the state of the future climate predicted by this model. The AMOC wavelet analysis shows a predominant decadal variability at 24°N, whereas the annual signal is more prominent in the South Atlantic. The Mov magnitude varies considerably among the latitudes: increasing at 24°N, rather stable at 11°S and decreasing at 30°S. Such a pattern is followed by an AMOC weakening regardless of the latitude until the end of the 21st century, indicating that a reduction in Mov in the southern South Atlantic and an increase in the North Atlantic are potential drivers of the AMOC destabilization. Both model and observations agree on the stability of the circulation, even though the model projects a stronger AMOC than the latter. Besides the AMOC weakening, a shoaling of its upper limb is also observed. Salinity biases were found mostly in the South Atlantic in the upper 1000 m of the water column, with the model results significantly deviating from the observations and climatology in the mid-Atlantic, especially at 30°S. Possible causes for the abovementioned results, including potential drivers for salinity biases are discussed.

Collective movement is critical to the survival of some animals. Despite substantial progress in understanding animal collectives such as fish shoals and bird flocks, it is unknown how collective behaviour is affected by changes in multiple environmental conditions that can interact as stressors. Using a fully factorial repeated-measures design, we tested the independent and combined effects of darkness and acoustic noise on the collective motion of three-spined sticklebacks, Gasterosteus aculeatus, quantified using high-resolution tracking data from video. Corresponding to the importance of vision in shoaling behaviour, darkness increased nearest-neighbour distances and reduced coordination, measured as speed correlations and differences in directional heading between nearest neighbours. Although individual swimming speeds were not impacted by darkness, the group's centre of mass was slower, an emergent effect of reduced polarisation (i.e. greater group disorder) in darkness. While additional acoustic noise had no detectable effect on these variables, it altered group structure, with fish being more likely to be found side by side one another. Fish were also further from the arena wall (i.e. showed reduced wall following) when there was additional acoustic noise. There was only weak evidence for additive or interactive effects of the two stressors. Across the different environmental contexts, there were consistent, repeatable differences between groups (i.e. group personality variation) in the speed, turning angle and distance from the arena wall of individuals, but the only collective behaviour that was repeatable was group polarization. Our study demonstrates that multiple stressors can have independent effects that impact different aspects of behaviour and highlights the need for empirical studies on multiple stressors as their effects can be unpredictable.

The landings of Indian oil sardine (Sardinella longiceps, Clupeidae) along the southeastern Arabian Sea are about 43.8% of total Indian oil sardine production. The annual landings of this species exhibit large-scale variability with prolonged years of surplus or deficit landings without identified reason. Evaluating Indian oil sardine landings along the Kerala coast during 1961–2017 in relation to environmental variations, we have elucidated a putative link between variability in landings versus environmental parameters and climate indices. The variables examined in this study, such as salinity and temperature along with physical indices such as upwelling and mixed layer depth (MLD) of the ocean help to propose a mechanism to temporal variability in the landings of Indian oil sardine. Colder temperature and timely intense upwelling lead to nutrient enrichment in the surface water, which promotes the growth of phytoplankton (chl-a) and thereby food availability to Indian oil sardine are found during years with surplus catch. Less saline surface waters and shoaling of MLD at these times could lead to the aggregation of fish at particular depths and thereby a good catches. The reverse mechanism, such as more surface saline water, warm temperature, downwelling or weak upwelling, and less nutrient enrichment, leads to deficit landings. Further, it was noticed that the Pacific decadal oscillation and Atlantic multidecadal oscillation have a more pronounced impact on Indian oil sardine landings over the coast of south-eastern Arabian Sea than previously reported ENSO associated impacts. All these point towards climate change implications for the Indian oil sardine fishery.

Projected sea-level rise will raise coastal water tables, resulting in groundwater hazards that threaten shallow infrastructure and coastal ecosystem resilience. Here we model a range of sea-level rise scenarios to assess the responses of water tables across the diverse topography and climates of the California coast. With 1 m of sea-level rise, areas flooded from below are predicted to expand ~50–130 m inland, and low-lying coastal communities such as those around San Francisco Bay are most at risk. Coastal topography is a controlling factor; long-term rising water tables will intercept low-elevation drainage features, allowing for groundwater discharge that damps the extent of shoaling in ~70% (68.9–82.2%) of California’s coastal water tables. Ignoring these topography-limited responses increases flooded-area forecasts by ~20% and substantially underestimates saltwater intrusion. All scenarios estimate that areas with shallow coastal water tables will shrink as they are inundated by overland flooding or are topographically limited from rising inland. Sea-level rise raises water tables, causing flooding from below and saltwater intrusion. A modelling study predicts that coastal California groundwater flooding will expand 50–130 m inland with 1 m of sea-level rise, with areal flooding extent strongly dependent on topography and drainage capacity.

Equilibrium beach profiles are explained in the context of a thermodynamic theory in which energy dissipation rate due to shoaling waves is extremized through a variational principle. The issue of whether this extremum corresponds to a maximum or a minimum of the action integral under the assumptions made is answered by computing the second variation of the integral around the equilibrium profile: it turns out to be a minimum.

Pattern formation and collective behaviour in animal aggregations is highly complex and occurs across many scales, over a wide range of environmental conditions. The patterns found in collective behaviour may be modulated by the environmental habitat in which a group is located. Here, we consider whether habitat context influences the collective behaviour of fish schools under threat of predation in a dynamic salt marsh system. By comparing collective responses of wild forage fish prior to and during predator attack across three environmental contexts, we examine whether schooling state is influenced by the habitat that fish schools reside in. Our results indicate that habitat context had a much stronger effect on collective state relative to predation. The habitats studied (both a marsh edge habitat and a higher complexity habitat) induced changes in the behavioural state of fish schools compared to a free-field context, which demonstrates an alteration of the collective behaviours performed by the school. This suggests that other ecological factors, such as the local environment, plays a larger role than predation risk in structuring the spatial and temporal group level patterns found in collective behaviour.

We present in situ and remote observations of a Mississippi plume front in the Louisiana Bight. The plume propagated freely across the bight, rather than as a coastal current. The observed cross-front circulation pattern is typical of density currents, as are the small width (≈100 m) of the plume front and the presence of surface frontal convergence. A comparison of observations with stratified density current theory is conducted. Additionally, subcritical to supercritical transitions of frontal propagation speed relative to internal gravity wave (IGW) speed are demonstrated to occur. That is in part due to IGW speed reduction with decrease in seabed depth during the frontal propagation toward the shore. Theoretical steady-state density current propagation speed is in good agreement with the observations in the critical and supercritical regimes but not in the inherently unsteady subcritical regime. The latter may be due to interaction of IGW with the front, an effect previously demonstrated only in laboratory and numerical experiments. In the critical regime, finite-amplitude IGWs form and remain locked to the front. A critical to supercritical transition eventually occurs as the ambient conditions change during frontal propagation, after which IGWs are not supported at the front. The subcritical (critical) to critical (supercritical) transition is related to Froude number ahead (under) the front, consistently with theory. Finally, we find that the front-locked IGW (critical) regime is itself dependent on significant nonlinear speed enhancement of the IGW by their growth to finite amplitude at the front.

Group size is an important criterion in social decisions. Accordingly, assessing quantities is common in many animals. In fishes, studies on numerical abilities focus on a limited range of species. Arguably, cichlids show the greatest variability of social patterns among vertebrates. Nevertheless, knowledge about their quantitative abilities is scarce. Here we use the Lake Tanganyika cichlid Lamprologus callipterus to scrutinize the quantitative abilities of fish in the context of shoaling. Females chose between different numbers of conspecifics, varying in absolute and relative number differences. In half of the trials both shoals were composed of familiar sisters, while all fish were unfamiliar non-kin in the other half. Test fish consistently preferred the larger of two shoals, irrespective of the ratios. Their activity differed significantly between familiarity/relatedness treatments, indicating recognition of this parameter. L. callipterus therefore has fine-tuned discrimination skills, adding to the evidence that quantitative abilities are widespread in fishes.

The formation of a recirculating subsurface core in an internal solitary wave (ISW) of depression, shoaling over realistic bathymetry, is explored through fully nonlinear and nonhydrostatic two-dimensional simulations. The computational approach is based on a high-resolution/accuracy deformed spectral multidomain penalty-method flow solver, which employs the recorded bathymetry, background current, and stratification profile in the South China Sea. The flow solver is initialized using a solution of the fully nonlinear Dubreil–Jacotin–Long equation. During shoaling, convective breaking precedes core formation as the rear steepens and the trough decelerates, allowing heavier fluid to plunge forward, forming a trapped core. This core-formation mechanism is attributed to a stretching of a near-surface background vorticity layer. Since the sign of the vorticity is opposite to that generated by the propagating wave, only subsurface recirculating cores can form. The onset of convective breaking is visualized, and the sensitivity of the core properties to changes in the initial wave, near-surface background shear, and bottom slope is quantified. The magnitude of the near-surface vorticity determines the size of the convective-breaking region, and the rapid increase of local bathymetric slope accelerates core formation. If the amplitude of the initial wave is increased, the subsequent convective-breaking region increases in size. The simulations are guided by field data and capture the development of the recirculating subsurface core. The analyzed parameter space constitutes a baseline for future three-dimensional simulations focused on characterizing the turbulent flow engulfed within the convectively unstable ISW.

Mini purse seine has a major contribution in increasing production of small pelagic catches in Pelabuhan Perikanan Pantai (PPP) Muncar, because it has high productivity and the construction made according to catch schooling fish. This research aims to compare the catches composition and catch rate of mini one-boat and two-boat purse seine in Bali Strait, Indonesia. This research was conducted in Mei 2018 in Muncar, East Java, Indonesia. The method used in this research is survey. The primary data are total catch composition, fork length, individual weight of total catch and operation time of both fishing gears. Data were analysed by main catch and bycatch proportion, legal size proportion and catch rate. The results showed that the mini two-boat purse seine had a greater catch volume compared to the mini one-boat purse seine. The bycatch composition dominates in both fishing gear. The proportion of legal-size catching is 67% of the total. The fork length is not significantly different and for the total catches is significantly different. The catching rate of the mini purse seine one boat catch rate is lower at 4,048.67 kg/hour, compared to the mini two-boat purse seine which is 9,189.18 kg/hour.

Pro-social effects of oxytocin and its homologues are well-documented in birds and mammals. However, in fishes, the effect of isotocin, the homologue of oxytocin, on social behaviour is less clear. Studies in fishes have generally shown no effect of isotocin on social behaviours or even an anti-social effect. In our study, we measured association preference for conspecifics in 92 adult guppies (46 females and 46 males), half of which were injected with isotocin and the other half with an isotocin antagonist. We found that individuals injected with isotocin spent 29% more time associating with conspecifics than individuals injected with an isotocin antagonist. The effect of isotocin on association time did not differ between males and females. Our study provides some of the first evidence of a pro-social effects of isotocin in a fish and suggests that in fishes, isotocin may have a homologous role to oxytocin, at least in promoting shoaling behaviour.

In coastal engineering, as shoaling waves break in shallow water, most wave-breaking research has been focused on depth-induced wave breaking. However, violent wave breaking under storm conditions ...

—Bottom sediment cores from the Langtibeito (Yamal Peninsula) and Gol’tsovoe (Gydan Peninsula) background arctic lakes are studied. The sedimentation rate estimated from 210Pb and 137Cs accounted for 0.17 and 0.20 cm/y, respectively. The element composition, grain-size composition, and loss on ignition were determined layer-by-layer in both cores. The element concentrations in the bottom sediments of both lakes throughout the entire core length are at the background level. The mercury content in the subsurface layers of sediments in both lakes, unlike other elements, was much higher than its local background contents. This is likely related to its atmospheric influx through transboundary transport. The comparison of diatom and grain-size data revealed the rebuilding of lake ecosystems in response to lake shoaling. The bioindication methods are promising for reconstructing the recent climatic changes in arctic regions.

Social cohesion and prey location in seabirds are largely enabled through visual and olfactory signals, but these behavioural aspects could potentially also be enhanced through acoustic transfer of information. Should this be the case, calling behaviour could be influenced by different social–ecological stimuli. African Penguins Spheniscus demersus were equipped with animal‐borne video recorders to determine whether the frequency and types of calls emitted at sea were dependent on behavioural modes (commuting, sedentary and dive bout) and social status (solitary vs. group). For foraging dive bouts we assessed whether the timing and frequency of calls were significantly different in the presence of schooling prey vs. single fish. The probability of call events was significantly more likely for birds commuting early and late in the day (for solitary birds) and during dive bouts (for groups). During foraging dive bouts the frequency of calls was significantly greater for birds diving in the presence of schooling fish and birds called sooner after a catch in these foraging scenarios compared with when only single fish were encountered. Three call types were recorded, 'flat', 'modulated' and 'two‐voice' calls, but there was no significant relationship detected with these call types and behavioural modes for solitary birds and birds in groups. The results of this study show that acoustic signalling by African Penguins at sea is used in a variety of behavioural contexts and that increased calling activity in the presence of more profitable prey could be of crucial importance to seabirds that benefit from group foraging.

Many coastal engineering designs utilize empirical formulas containing the Equivalent Deep-water Wave Height (EDWH), which is normally given a priori. However, no studies have explicitly discussed a method for determining the EDWH and the resulting design wave heights (DEWH) under irregular wave conditions. Unfortunately, it has been the case in many design practices that the EDWH is incorrectly estimated by dividing the Shallow-water Wave Height (SWH) at the structural position with its corresponding shoaling coefficient of regular wave. The present study reexamines the relationship between the Shallow-water Wave Height (SWH) at the structural position and its corresponding EDWH. Then, a new procedure is proposed to facilitate the correct estimation of EDWH. In this procedure, the EDWH and DEWH are determined differently according to the wave propagation model used to estimate the SWH. For this, Goda's original method for nonlinear irregular wave deformation is extended to produce values for linear shoaling. Finally, exemplary calculations are performed to assess the possible errors caused by a misuse of the wave height calculation procedure. The relative errors with respect to the correct values could exceed 20%, potentially leading to a significant under-design of coastal or harbor structures in some cases.

The purposed of this research is to analyze the performance of purse seine fishing gear operated on FADs and purse seines that hunt schools of fish (without FADs) based on four aspects of performance (biological, technical, social, economic) . This research method is a survey method, taking 10 samples of each of the FAD purse seines and without FADs and analyzed using the scoring method through the biological, technical, socio-cultural and economic performance approaches. The results obtained by performed the FAD purse seine and non-FAD purse seine were in good enough criteria, namely ≥ 50 - 75%. In general, the performance of the two fishing gear units did not have a significant difference, because there were similarities and differences that did not greatly differ from each aspect of the performance review. Based on the biological aspects, the performance of purse seine without FADs is better than that of the purse seine using FADs because catch fish with a suitable size and uniform species. whereas based on the economic and technical aspects, the performance of purse seine using FADs is better than purse seine without FADs. This is due to higher catch production and income. Based on the social aspect, the performance of both of them has no difference.

We present observations of shoaling nonlinear internal bores off the coast of central California. The dataset includes 15 moorings deployed during September–October 2017 and cross-shore shipboard surveys. We describe the cross-shore structure and evolution of large-amplitude internal bores as they transit from 9 km (100-m depth) to 1 km offshore (10 m). We observe that two bores arrive each semidiurnal period, both propagating from the southwest; of the total, 72% are tracked to the 10-m isobath. The bore speeds are subtidally modulated, but there is additional bore-to-bore speed variability that is unexplained by the upstream stratification. We quantify temporal and cross-shore variability of the waveguide (the background conditions through which bores propagate) by calculating the linear longwave nonrotating phase speed co and using the nonlinearity coefficient of the Korteweg–de Vries equation α as a metric for stratification. Bore fronts are generally steeper when α is positive and are more rarefied when α is negative, and we observe the bore’s leading edge to rarefy from a steep front when α is positive offshore and negative inshore. High-frequency α fluctuations, such as those nearshore driven by wind relaxations, contribute to bore-to-bore variability of the cross-shore evolution during similar subtidal waveguide conditions. We compare observed bore speeds with co and the rotating group velocities cg, concluding that observed speeds are always faster than cg and are slower than co at depths greater than 32 m and faster than co at depths of less than 32 m. The bores maintain a steady speed while transiting into shallower water, contrary to linear estimates that predict bores to slow.

Seabed fluid escape is active in the Makran subduction zone, Arabian Sea. Based on the new high-resolution 2D seismic data, acoustic blanking zones and seafloor mounds are identified. Acoustic blanking zones include three kinds of geometries: Bell-shaped, vertically columnar and tilted zones. The bell-shaped blanking zone is characterized by weak and discontinuous reflections in the interior and up-bending reflections on the top, interpreted as gas chimneys. Vertically columnar blanking zone is interpreted as side-imaged gas chimneys associated with focused fluid flow and topped by a seafloor anomaly expressed as a localized reflection discontinuity, which may together serve as a vent structure. Tilted acoustic blanking zone could be induced by accretionary thrust activity and rapid sedimentation surrounding slope. Seafloor mounds occur at the sites of bell-shaped acoustic blanking zone and may be associated with the material intrusion. Bottom simulating refectors (BSRs) are widely distributed and exhibit a series of characteristics including diminished amplitude, low continuity as well as local shoaling overlapping with these acoustic blanking zones. The large amount of gases dissociated from the gas hydrates migrated upwards and then arrived at the near-seafloor sediments, followed by the formation of the gas hydrates and hence the seafloor mound.

The Peruvian upwelling system hosts a marine ecosystem with extremely high productivity. Observations show that the Peruvian upwelling system is the only eastern boundary upwelling system (EBUS) with an out-of-phase relationship between seasonal surface chlorophyll concentrations and upwelling intensity. This “seasonal paradox” triggers the following questions: (1) what are the unique characteristics of the Peruvian upwelling system, compared with other EBUSs, that lead to the out-of-phase relationship, and (2) how does the seasonal paradox influence ecosystem functioning? Using observational climatologies for four EBUSs, we diagnose that the Peruvian upwelling system is the only one to reveal that intense upwelling coincides with deep mixed layers. We then apply a coupled regional ocean circulation biogeochemical model (CROCO–BioEBUS) to assess how the interplay between mixed layers and upwelling regulates the seasonality of surface chlorophyll in the Peruvian upwelling system. Our model reproduces the “seasonal paradox” within 200 km off the Peruvian coast. We confirm previous findings regarding the main contribution of mixed layer depth to the seasonality of chlorophyll, relative to upwelling. Deep mixed layers in austral winter cause vertical dilution of phytoplankton and strong light limitation, impacting growth. The effect of advection, though second-order, is consistent with previous findings for the Peruvian system and other EBUSs, with enhanced offshore export opposing the coastal build-up of biomass. In addition, we find that the relatively colder temperatures of upwelled waters slightly dampen phytoplankton productivity and further slow the build-up of phytoplankton biomass. This impact from the combination of deep mixed layers and upwelling propagates through the ecosystem, from primary production to export and export efficiency. Our findings emphasize the crucial role of the interplay between mixed layer depth and upwelling and suggest that surface chlorophyll may increase, along with a weakened seasonal paradox, in response to shoaling mixed layers under climate change.

Retreat of marine outlet glaciers often initiates depletion of inland ice through dynamic adjustments of the upstream glacier. The local topography of a fjord may promote or inhibit such retreat, and therefore fjord geometry constitutes a critical control on ice sheet mass balance. To quantify the processes of ice–topography interactions and enhance the understanding of the dynamics involved, we analyze a multitude of topographic fjord settings and scenarios using the Ice-sheet and Sea-level System Model (ISSM). We systematically study glacier retreat through a variety of artificial fjord geometries and quantify the modeled dynamics directly in relation to topographic features. We find that retreat in an upstream-widening or upstream-deepening fjord does not necessarily promote retreat, as suggested by previous studies. Conversely, it may stabilize a glacier because converging ice flow towards a constriction enhances lateral and basal shear stress gradients. An upstream-narrowing or upstream-shoaling fjord, in turn, may promote retreat since fjord walls or bed provide little stability to the glacier where ice flow diverges. Furthermore, we identify distinct quantitative relationships directly linking grounding line discharge and retreat rate to fjord topography and transfer these results to a long-term study of the retreat of Jakobshavn Isbræ. These findings offer new perspectives on ice–topography interactions and give guidance to an ad hoc assessment of future topographically induced ice loss based on knowledge of the upstream fjord geometry.