Antarctic krill (Euphausia superba) are an essential source of food for whale, seal, several fish, squid and seabird species in the Southern Ocean. Krill also play a major role in biogeochemical cycling and are the target of a growing commercial fishery. Krill can be detected and quantified with echosounders, particularly in swarms, and monitoring krill abundance and distribution is integral to assessing the status of regional populations and managing fisheries. We used echosounders to investigate the hemispherical distribution and behaviour of krill swarms during the Antarctic Circumnavigation Expedition (ACE), a multidisciplinary exercise that included measurements of atmospheric chemistry. Krill swarms were grouped using hierarchical clustering into four principal types: small swarms (on average 2 m high, 25 m long); large swarms (13 m high and 341 m long); deep swarms, which were also densely packed (average depth of 52 m); and shallower swarms, which had lower densities (average depth of 28 m). We found a weak negative relationship between the concentration of atmospheric methane close to the sea surface and the presence of krill. High densities of krill were found in the Amundsen Sea, an area purported to be of increasing importance for krill as the climate changes.

Quantifying interactions between fisheries and marine predators is fundamental to effective ecosystem‐based fisheries management. However, methods to study fine scale overlap between pelagic fisheries and predator foraging behaviour were limited by spatial resolution until the mid‐2010s when Automatic Identification Systems (AIS) started to become commonplace, enabling fishing activity to be monitored at finer resolutions. We assess fine scale overlap between the foraging grounds of Critically Endangered African penguins Spheniscus demersus rearing chicks at two colonies in South Africa and the adjacent purse‐seine fishery. Competition with the fishery is thought to be an important contributor to the penguin population decline (~78% over in the last 30 years). During a fishery‐closure experiment, we established the spatial overlap between fishing events and GPS‐tracked penguins at a population level. We also introduce a novel metric, overlap intensity, to quantify the number of individuals impacted by fishery overlap. Both spatial overlap and overlap intensity varied between years, with 2016—the year of lowest recorded anchovy Engraulis capensis recruit biomass—having the highest degree of overlap (population level spatial overlap: 4%—equivalent to 4% of cells used by penguins overlapping with a vessel—and overlap intensity: 74%—equivalent to ~20% of penguin locations occurring in the same cells as fishing events). While spatial overlap between penguins and the fishery over the 4 years was generally low (<5% at a population level), the intensity of this overlap was consistently quite high (~50%–70% in 3 of the 4 years). Synthesis and applications . While spatial overlap is commonly used to quantify interactions, it may underestimate the true degree of competition between foraging predators and fishing vessels. Our alternative population‐level measure of ‘overlap intensity’ accounts for the number of individuals involved in the areas of overlap, and may provide a more comprehensive understanding of fisheries impacts. By incorporating measures of overlap intensity into fishery management strategies, more effective and better targeted protected areas could be designated, minimising both losses to fisheries and impacts on predator populations.

In areas of high infection prevalence, effective control of schistosomiasis - one of the most important Neglected Tropical Diseases - requires supplementing medical treatment with interventions targeted at the environmental reservoir of disease. In addition to provision of clean water, reliable sanitation, and molluscicide use to control the obligate intermediate host snail, top-down biological control of parasite-competent snails has recently gained increasing interest in the scientific community. However, evidence that natural predators can effectively reduce snail abundance and, ultimately, transmission risk to vulnerable human populations remains limited. In this study, we used a Before-After-Control-Intervention (BACI) design implemented in seven lakeside areas, including three intervention areas and four control areas, on the southern shores of Lake Victoria (Tanzania) in 2019-2023. We tested whether the restoration of African catfish, Clarias gariepinus, a native species of commercial value, could reduce both the abundance of Biomphalaria snails (intermediate hosts of Schistosoma mansoni) and infection intensity in school age children (SAC). Where catfish were restored, mean site-level snail counts declined by 57% (95% CI: 29.4%, 74.3%). At primary schools located within each area, SAC infection intensity (mean parasite egg count in stool samples) also decreased significantly by 55% (95% CI: 26%, 73%). This study shows that natural predators of host snails have the potential for schistosomiasis control. Scaling up to a lake-wide approach will require systemic intervention, with snail host control contributing to a broader framework for schistosomiasis management.

Bowhead whales (Balaena mysticetus) are an iconic Arctic species with a critical ecological role as a top predator. Bowheads can reach up to 80 tonnes and 20 m, yet feed on zooplankton four orders of magnitude smaller. Arctic zooplankton community composition and distribution are changing, which may have direct impacts on bowhead foraging. Data on the threshold prey density for successful bowhead feeding are needed to predict these impacts. However, zooplankton densities are patchy temporally and spatially, influenced by oceanographic conditions that alter the location of energetically profitable patches. We assessed spatio-temporal patterns in zooplankton abundance and distribution using a multi-frequency echosounder following a systematic and opportunistic survey near feeding whales in Iqalujjuaq Fjord, Cumberland Sound, Nunavut (65.66 degrees N, 65.20 degrees W) during August 2023. Zooplankton net samples were used to validate the acoustic data. There was a strong link between copepod distribution and environmental variables (e.g. water depth and tidal cycle) (generalized additive models, P < .001). Copepods were present in 49.8% of the fjord, with a median density of 3240 copepods m(-3 )and 0.26 g Cm-3. Based on published prey density requirements, this site provides feeding opportunities for juveniles but is insufficient for the needs of adults (>0.44 g C m(-3)).

Background Understanding the relationship between resident microbiota and disease in cultured fish represents an important and emerging area of study. Marine gill disorders in particular are considered an important challenge to Atlantic salmon (Salmo salar) aquaculture, however relatively little is known regarding the role resident gill microbiota might play in providing protection from or potentiating different gill diseases. Here, 16S rRNA sequencing was used to examine the gill microbiome alongside fish health screening in farmed Atlantic salmon. Results were used to explore the relationship between microbial communities and gill disease. Results Microbial community restructuring was observed throughout the sampling period and linked to varied drivers of change, including environmental conditions and severity of gill pathology. Taxa with significantly greater relative abundance on healthier gills included isolates within genus Shewanella, and taxa within family Procabacteriaceae. In contrast, altered abundance of Candidatus Branchiomonas and Rubritalea spp. were associated with damaged gills. Interestingly, more general changes in community richness and diversity were not associated with altered gill health, and thus not apparently deleterious to fish. Gross and histological gill scoring demonstrated seasonal shifts in gill pathology, with increased severity of gill damage in autumn. Specific infectious causes that contributed to observed pathology within the population included the gill disorder amoebic gill disease (AGD), however due to the uncontrolled nature of this study and likely mixed contribution of various causes of gill disease to observed pathology results do not strongly support an association between the microbial community and specific infectious or non-infectious drivers of gill pathology. Conclusions Results suggest that the microbial community of farmed Atlantic salmon gills undergo continual restructuring in the marine environment, with mixed influences upon this change including environmental, host, and pathogenic factors. A significant association of specific taxa with different gill health states suggests these taxa might make meaningful indicators of gill health. Further research with more frequent sampling and deliberate manipulation of gills would provide important advancement of knowledge in this area. Overall, although much is still to be learnt regarding what constitutes a healthy or maladapted gill microbial community, the results of this study provide clear advancement of the field, providing new insight into the microbial community structure of gills during an annual production cycle of marine-stage farmed Atlantic salmon.

Background Measuring coastal-pelagic prey fields at scales relevant to the movements of marine predators is challenging due to the dynamic and ephemeral nature of these environments. Whale sharks ( Rhincodon typus ) are thought to aggregate in nearshore tropical waters due to seasonally enhanced foraging opportunities. This implies that the three-dimensional movements of these animals may be associated with bio-physical properties that enhance prey availability. To date, few studies have tested this hypothesis. Methods Here, we conducted ship-based acoustic surveys, net tows and water column profiling (salinity, temperature, chlorophyll fluorescence) to determine the volumetric density, distribution and community composition of mesozooplankton (predominantly euphausiids and copepods) and oceanographic properties of the water column in the vicinity of whale sharks that were tracked simultaneously using satellite-linked tags at Ningaloo Reef, Western Australia. Generalised linear mixed effect models were used to explore relationships between the 3-dimensional movement behaviours of tracked sharks and surrounding prey fields at a spatial scale of ~ 1 km. Results We identified prey density as a significant driver of horizontal space use, with sharks occupying areas along the reef edge where densities were highest. These areas were characterised by complex bathymetry such as reef gutters and pinnacles. Temperature and salinity profiles revealed a well-mixed water column above the height of the bathymetry (top 40 m of the water column). Regions of stronger stratification were associated with reef gutters and pinnacles that concentrated prey near the seabed, and entrained productivity at local scales (~ 1 km). We found no quantitative relationship between the depth use of sharks and vertical distributions of horizontally averaged prey density. Whale sharks repeatedly dove to depths where spatially averaged prey concentration was highest but did not extend the time spent at these depth layers. Conclusions Our work reveals previously unrecognized complexity in interactions between whale sharks and their zooplankton prey.

Technological advances have enabled the observation of foraging behaviour in wild marine animals. We can observe where they go, how deep they dive, how much energy they expend, and with the use of animal-borne cameras we can capture specific foraging behaviours. Here we describe a newly observed foraging behaviour in African Penguins Spheniscus demersus in which they target fish located in jellyfish tentacles. As animal-borne cameras have only been deployed on African Penguins since 2015 it is unclear whether this behaviour is novel or previously unobserved. The behaviour appears to be opportunistic and beneficial to the African Penguins as it enables them to catch stationary prey. As the availability of the African Penguin’s traditional schooling fish prey changes in the southern Benguela Current ecosystem due to climate change and overfishing, opportunistic foraging strategies like this could enable African Penguins to supplement foraging success at a low energetic cost.

Offshore pelagic ecosystems are composed of vertically and functionally distinct epipelagic, migrant and resident mesopelagic communities. While this vertical structure plays a key role in carbon sequestration and in supporting important fisheries, there is still no consensus on the respective contribution of the environmental factors (light, oxygen) and processes controlling it at both global and regional scale. Here we combine mechanistic modelling and acoustic observations from the worldwide Malaspina scientific campaign to show that, while underwater light intensity is the primary factor controlling the vertical distribution and migration of pelagic organisms globally, oxygen plays a critical role in limiting the depth of migratory communities and the abundance of mesopelagic communities in Oxygen Minimum Zones. Furthermore, we show that a faithful reproduction of acoustic observations in some regions of the global ocean (southern Indian Ocean, western Pacific) cannot be achieved without separating migratory and resident mesopelagic communities into deep and shallow groups. By proposing a unified mechanistic model and an archetypical ecosystem structure constrained by comprehensive acoustic observations, this study provides a consistent understanding of the vertical structure and function of global pelagic ecosystems and paves the way for more reliable estimates of their climate-induced variability and change. ### Competing Interest Statement The authors have declared no competing interest.

Lake Victoria is the second-largest freshwater lake in the world, and fish from the lake are a vital food resource for millions of people living around it. The silver cyprinid (Rastrineobola argentea), a small schooling pelagic species known in Tanzania as "dagaa" contributes ca. 55% to the total annual catch (ca. 0.51 million tonnes (MT) in 2014). The acoustic target strength (TS, dB re 1 m2) of dagaa, a key factor for biomass estimation, is however not well described, and is a major source of uncertainty in biomass estimation. In this study, we developed a Kirchhoff-ray mode (KRM) model to predict the TS of dagaa at standard fisheries survey frequencies. The model was based on the morphology of the body and the dual-chambered swimbladder, as obtained from X-ray images of fish ranging in total length (TL) between 2.8 and 5.4 cm. The results suggested that the swimbladder (which comprises 2.6 to 8.2% of body volume) accounts for ca. 65 to 90% of the total backscattering at 120 kHz. The predicted TS was highly dependent on tilt angle, varying by 14.0 dB at 120 kHz across the tilt range 65-115 (where 0 is head up and 180 is tail up), and TS variability with tilt generally increased with increasing frequency. The tilt angle of acoustically tracked individual fish indicated a distribution of tilt angles with a mean and s.d. of 93.5 and 15.1 & DEG;. Our model suggested a new tilt-averaged TS-TL relationship for dagaa [$T{S}_{120\ kHz} = 19.49\log ( {TL} ) - 70.3$], which leads to a TS 1.5 dB higher than the value in the relationship presently used to estimate stock biomass. The new relationship will lead to a substantial reduction (by ca. 30%) in estimated biomass. The discrepancies between the mean relative frequency response of the in situ measurements of backscatter from dagaa and the KRM model predictions were in the range of -2.9-3.1 dB at frequencies from 45 to 250 kHz. The KRM modelling and in situ broadband measurements of dagaa will be beneficial for acoustic identification and behavioural studies of dagaa, and will enable improved biomass assessment, thereby underpinning sustainable long-term management.

Raw acoustic data were collected in East Antarctica from the RSV Aurora Australis during two surveys: the Krill Availability, Community Trophodynamics and AMISOR Surveys (KACTAS) and the Krill Acoustics and Oceanography Survey (KAOS) in the East Antarctic (centre coordinate 66.5° S, 63° E). The KACTAS survey was conducted between 14th to 21st January and 2001, and the KAOS survey was conducted between 16 January and 1 February 2003. We examine the Antarctic krill (Euphausia superba ) component of these surveys and provide scientific echosounder (EK500 and EK60) data collected at 38, 120 and 200 kHz, cold water (−1 °C) echosounder calibration parameters and accompanying krill length frequency distributions obtained from trawl data. We processed the acoustic data to apply calibration values and remove noise. The processed data were used to isolate echoes arising from swarms of krill and to estimate metrics for each krill swarm, including internal density and individual swarm biomass. The krill swarm data provide insights to a predators’ views of krill distribution and density.

The daily vertical migrations of fish and other metazoans actively transport organic carbon from the ocean surface to depth, contributing to the biological carbon pump. We use an oxygen-constrained, game-theoretic food-web model to simulate diel vertical migrations and estimate global carbon fluxes and sequestration by fish and zooplankton due to respiration, fecal pellets, and deadfalls. Our model provides estimates of the carbon export and sequestration potential for a range of pelagic functional groups, despite uncertain biomass estimates of some functional groups. While the export production of metazoans and fish is modest (~20% of global total), we estimate that their contribution to carbon sequestered by the biological pump (~ 800 PgC) is conservatively more than 50% of the estimated global total (~1300 PgC) and have a significantly longer sequestration time scale (~250 years) than previously reported for other components of the biological pump. Fish and multicellular zooplankton contribute about equally to this sequestered carbon pool. This essential ecosystem service could be at risk from both unregulated fishing on the high seas and ocean deoxygenation due to climate change.

Most small-scale inland fisheries in the Global South prohibit fishing gear with smaller meshes than is legally permitted. Nonetheless, in most instances, this is not strictly enforced. But starting in 2017, Uganda and Tanzania ramped up enforcement on Lake Victoria. We used time series hydro-acoustic data to determine whether the strict enforcement achieved the management goal of increased biomass (t) of commercial species and an increase in the biomass of big Nile perch (>50 cm). The biomass for 2018- 2021 (under strict enforcement) was expected to be greater than in 2007-2017 (prior to strict enforce-ment). The biomass of key species fluctuated annually, but no spatial or temporal differences in biomass associated with strict enforcement were evident. Similarly, the biomass of big Nile perch did not increase. Our findings suggest that mesh sizes may have limited influence on fish biomass dynamics in Lake Victoria, and that high primary productivity of the lake, high turnover rates of fish species, and limited compliance by fishers likely counteract the effects of high fishing effort on biomass and size structure of fish. Therefore, the high cost of strict top-down enforcement and the societal cost of lost lives, jobs, and livelihoods may not be justified. (c) 2023 International Association for Great Lakes Research. Published by Elsevier B.V. All rights reserved.

Classification of zooplankton to species with broadband echosounder data could increase the taxonomic resolution of acoustic surveys and reduce the dependence on net and trawl samples for 'ground truthing'. Supervised classification with broadband echosounder data is limited by the acquisition of validated data required to train machine learning algorithms ('classifiers'). We tested the hypothesis that acoustic scattering models could be used to train classifiers for remote classification of zooplankton. Three classifiers were trained with data from scattering models of four Arctic zooplankton groups (copepods, euphausiids, chaetognaths, and hydrozoans). We evaluated classifier predictions against observations of a mixed zooplankton community in a submerged purpose-built mesocosm (12 m3) insonified with broadband transmissions (185-255 kHz). The mesocosm was deployed from a wharf in Ny-angstrom lesund, Svalbard, during the Arctic polar night in January 2022. We detected 7722 tracked single targets, which were used to evaluate the classifier predictions of measured zooplankton targets. The classifiers could differentiate copepods from the other groups reasonably well, but they could not differentiate euphausiids, chaetognaths, and hydrozoans reliably due to the similarities in their modelled target spectra. We recommend that model-informed classification of zooplankton from broadband acoustic signals be used with caution until a better understanding of in situ target spectra variability is gained.

The relationship between low frequency military sonar use and some whale stranding events has attracted negative attention towards the use of active sonar in the marine environment.As a consequence, there has been only limited use of active acoustic techniques by marine mammal researchers.Instead more attention has been given to the development and use of passive acoustic methods for the detection of cetaceans.Nevertheless there is great potential for the use of active acoustic systems in ecological studies, and studies aimed at improving conservation of whales and dolphins in their natural environment: active acoustic techniques can be used for the good of cetaceans, and should not just be considered a source of disturbance.We evaluated the capability of various acoustic systems -systems that are used commonly in fisheries research -to detect and track cetaceans underwater.We collected data initially with standard scientific echosounders (SIMRAD EK500) from moving vessels and from fixed moorings (EK60) at 38 and 120 kHz.Scientific echosounders have narrow beams and therefore enable sampling from only fixed and limited volumes.To overcome these limitations we progressed to use high frequency omnidirectional sonar (SIMRAD SH80) operating at 110 kHz.During Norwegian Sea ecosystem surveys (2006)(2007)(2008) we recorded the backscatter energy from three species of large whales: Fin whale (Balaenoptera physalus), Minke whale (Balaenoptera acutorostrata) and Humpback whale (Megaptera novaeanglie).During the observations no avoidance reactions by cetaceans were observed, even when the vessel's entire suite of active acoustic instruments were running (frequency range from 18 kHz to 200 kHz, maximum source level 210 dB re 1 µPa (at 20 and 110 kHz).Here we present a small sample of data from two Fin whales that show the animals backscatter response at broadside.In addition, we give an overview of the present status and possible future development of the use of standard active acoustic methods for cetacean studies.Omnidirectional sonar shows great potential as a tool for marine mammal detection, and could be developed to produce an automatic cetacean detector.Such a detector would be a highly valuable aid for seismic mitigation and ship strike prevention, and in addition could contribute to behavioural studies with its high definition time scale.Much work is required to understand relationships between cetacean body shape, physiology, kinematics and acoustic reflectivity, before a detector can be realized.

Projecting the consequences of warming and sea-ice loss for Arctic marine food web and fisheries is challenging due to the intricate relationships between biology and ice. We used StrathE2EPolar, an end-to-end (microbes-to-megafauna) food web model incorporating ice-dependencies to simulate climate-fisheries interactions in the Barents Sea. The model was driven by output from the NEMO-MEDUSA earth system model, assuming RCP 8.5 atmospheric forcing. The Barents Sea was projected to be > 95% ice-free all year-round by the 2040s compared to > 50% in the 2010s, and approximately 2 °C warmer. Fisheries management reference points (FMSY and BMSY) for demersal fish (cod, haddock) were projected to increase by around 6%, indicating higher productivity. However, planktivorous fish (capelin, herring) reference points were projected to decrease by 15%, and upper trophic levels (birds, mammals) were strongly sensitive to planktivorous fish harvesting. The results indicate difficult trade-offs ahead, between harvesting and conservation of ecosystem structure and function.

Coastal pelagic ecosystems are highly variable in space and time, with environmental conditions and the distribution of biomass being driven by complex processes operating at multiple scales. The emergent properties of these processes and their interactive effects result in complex and dynamic environmental mosaics referred to as “seascapes”. Mechanisms that link large-scale oceanographic processes and ecological variability in coastal environments remain poorly understood, despite their importance for predicting how ecosystems will respond to climate change. Here we assessed seascape variability along the path of the rapidly intensifying East Australian Current (EAC) Southern Extension in southeast Australia, a hotspot of ocean warming and ecosystem tropicalisation. Using satellite and in situ measures of temperature, salinity and current velocity coupled with contemporaneous measurements of pelagic biomass distribution from nine boat-based active acoustic surveys in five consecutive years, we investigated relationships between the physical environment and the distribution of pelagic biomass (zooplankton and fish) at multiple timescales. Survey periods were characterised by high variability in oceanographic conditions, with variation in coastal conditions influenced by meso-to-large scale processes occurring offshore, including the position and strength of eddies. Intra-annual variability was often of a similar or greater magnitude to inter-annual variability, suggesting highly dynamic conditions with important variation occurring at scales of days to weeks. Two seascape categories were identified being characterised by (A) warmer, less saline water and (B) cooler, more saline water, with the former indicating greater influence of the EAC on coastal processes. Warmer waters were also associated with fewer, deeper and less dense biological aggregations. As the EAC continues to warm and penetrate further south, it is likely that this will have substantial effects on biological activity in coastal pelagic ecosystems, including a potential reduction in the accessibility of prey aggregations to surface-feeding predators and to fisheries. These results highlight the import role of offshore oceanographic processes in driving coastal seascape variability and biological activity in a region undergoing rapid oceanic warming and ecological change.

Abstract The development of water management infrastructures, such as dams and canals, are important components of society’s response to feed a growing human population and to fight climate change. Yet, these changes in land use can also increase the transmission risk for waterborne diseases. Transmission risk associated with artificial reservoirs has been extensively documented for schistosomiasis, a parasitic disease of poverty that infects more than 240 million people worldwide. Over 90% of these cases are in sub-Saharan Africa, a region that is being steadily reshaped by climate change. Controlling the parasite’s obligate intermediate host snail is key to reducing transmission of this disease. Using commercial aquaculture to farm marketable species which predate upon these snails in vulnerable regions can have multiple positive effects, including the improved socioeconomic and nutritional health of surrounding communities. Here the authors assessed the viability of using the aquaculture of snail predators to simultaneously control schistosomiasis infection rates while alleviating economic and/or nutritional poverty in endemic regions of sub-Saharan Africa. A PRISMA-based 6-step systematic methodology was used to explore the primary literature using the case study of Côte d’Ivoire and two native species of snail predator to make evidence-based conclusions on the viability of this method for controlling schistosomiasis. This detailed thematic examination of the literature concluded that using specific approaches and species, aquaculture could be effective in reducing economic poverty and chronic malnourishment along with high levels of schistosomiasis infection. More current species-specific aquaculture data and consumer survey data are, however, needed to determine the economic and logistical effectiveness of farming native snail predators in-country. These and other opportunities for future research are highlighted.

Silver cyprinids (Rastrineobola argentea) are small pelagic fish endemic to Lake Victoria.High-quality dried fish are an important protein-rich human food.This study was carried out to determine if it would be practical to use renewable energy to dry silver cyprinid.Drying is presently achieved by laying fish out in the sun on the ground or on racks.In the wet seasons, however, drying is compromised and much of the catch becomes fit only for animal consumption, or spoils.Lake Victoria's surface waters are c.25°C year-round.Its enormous volume of tropical water offers a source of thermal energy that could be used to dry fish.As a proof of concept, we used solar-generated electricity to drive a heat pump to harvest heat energy from water in a 10,000-L rainwater tank beside Lake Victoria, used the energy to heat air, and blew the air over fish in a tent-like enclosure.Fish in the enclosure dried in about 4 h versus about 7 h outside, were free from insects, and not at risk of theft by or defecation upon by birds.The drying processes inside and outside the enclosure were modelled.The model correctly reproduced observed drying times, and enabled exploration of options to improve drying performance.Up-scaling the prototype could provide year-round sustainable fish-drying capability, reduce waste, boost food security, and add value to the catch.

Understanding how marine predators encounter prey across patchy landscapes remains challenging due to difficulties in measuring the three-dimensional structure of pelagic prey fields at scales relevant to animal movement. We measured at-sea behaviour of a central-place forager, the little penguin (Eudyptula minor), over 5 years (2015-2019) using GPS and dive loggers. We made contemporaneous measurements of the prey field within the penguins' foraging range via boat-based acoustic surveys. We developed a prey encounter index by comparing estimates of acoustic prey density encountered along actual penguin tracks to those encountered along simulated penguin tracks with the same characteristics as real tracks but that moved randomly through the prey field. In most years, penguin tracks encountered prey better than simulated random movements greater than 99% of the time, and penguin dive depths matched peaks in the vertical distribution of prey. However, when prey was unusually sparse and/or deep, penguins had worse than random prey encounter indices, exhibited dives that mismatched depth of maximum prey density, and females had abnormally low body mass (5.3% lower than average). Reductions in prey encounters owing to decreases in the density or accessibility of prey may ultimately lead to reduced fitness and population declines in central-place foraging marine predators.