Pelagic Forage Research Articles

Groundtruthing of pelagic forage fish detected by hydroacoustics in a whale feeding area using environmental DNA

AbstractConservation of whales, considered as umbrella species in marine environments, requires to be able to understand their relationships with ecosystem components such as prey species, including pelagic fish. However, studying such relationships in nature is a technical challenge. In this study, we used two noninvasive methods in combination, namely hydroacoustics and environmental DNA (eDNA), to detect five pelagic or semipelagic fish species in the Saguenay–St. Lawrence Marine Park (Québec, Canada): the sandlance Ammodytes sp., the Atlantic herring Clupea harengus, the capelin Mallotus villosus, the rainbow smelt Osmerus mordax, and the redfish Sebastes sp. The Marine Park is a major summer feeding ground for a wide diversity of marine wildlife species, including the endangered St. Lawrence beluga whale population. Up to now, scarce research efforts have been dedicated to the estimation of pelagic fish abundance and diversity in this area. Hydroacoustics allowed to easily discriminate the classification of echoes from fish, and with certain limitations to distinguish swim bladder fish from fish without swim bladder. We used eDNA to groundtruth acoustics data and to improve species identification. eDNA analyses especially demonstrated that the capelin was the most predominant species, while the abundance of the redfish and the sandlance was strongly variable over the 2 years of the study. Our results also suggest that there are annual fluctuations in prey availability that marine mammals encounter in this area. Although the approach we used is not without constraints that should be addressed in future studies, we hope that this study will contribute to science‐based conservation and fisheries management policies.

Seasonal and spatial variability in the vertical distribution of pelagic forage fauna in the Southwest Pacific

Acoustic data are an invaluable source of information for characterizing the distribution and abundance of mid-trophic level organisms (MTLOs) in the ocean. These organisms play a key role in the ecosystem as prey of top predators and as predators of lower trophic level organisms, as well as in carbon export from the surface into deeper waters. This study used 38 kHz-EK60 acoustic echosounder data from six cruises spanning 2011–2017 to explore the seasonal and spatial variability in the vertical distribution of MTLOs’ from 10 to 600 m in the New Caledonian (South Pacific) Exclusive Economic Zone. A total of 16715 acoustic vertical profiles of acoustic backscattering strength were clustered into homogeneous groups. Two small shallow scattering layers (SSLs) between 0 and 100 m, and one large deep scattering layer (DSL) at around 550 m depth, characterized the mean vertical distribution of MTLOs. A machine-learning model (eXtreme Gradient tree Boosting algorithm, XGBoost) was fitted to explain the acoustic profile clusters with environmental variables as predictors. Sun inclination was the most important factor in structuring the vertical profile shapes due to the diel vertical migration signal, followed by the mean oxygen value of the top 600 m. Bathymetry, euphotic depth, 0–600 m mean temperature and SST were the next most significant variables. Isotherm depth, surface chlorophyll-a, wind, and mean salinity had a lower influence on the shape of the vertical profiles. The model was then used to construct vertical echograms at the scale of the New Caledonian EEZ, showing an accuracy up to 87% in cross validation. Across the EEZ, the shape of vertical acoustic profiles were comparable, though layer echo intensities varied spatially with a marked north-south gradient that remained relatively constant seasonally. The vertically-averaged acoustic values were characterized by a maximum to the south of the EEZ in summer, mainly driven by high oxygen values as well as shallow euphotic depth. We also estimated a migrant proportion between day DSL and night SSL of about 78%. Our methodology offers a promising approach for analyzing the control of the environment on the vertical distribution of MTLOs for other oceanic provinces, while also providing a framework to investigate the corresponding trophic interactions between MTLOs and their predators feeding at different depths and times. Moreover, our findings stress the need to consolidate knowledge on species composition to optimize acoustic data interpretation.

Responses of the Northern Bering Sea and Southeastern Bering Sea Pelagic Ecosystems Following Record‐Breaking Low Winter Sea Ice

AbstractBering Sea sea ice during winter 2017–2018 was the lowest ever recorded. Ecosystem effects of low ice have been observed in the southeastern Bering Sea, but never in the northern Bering Sea. Observations in both systems included weakened water column stratification, delayed spring bloom, and low abundances of large crustacean zooplankton. Summer Cold Pool presence was extremely limited. Young walleye pollock production and condition were similar to prior warm years, though catches of other pelagic forage fishes were low. Summer seabird die‐offs were observed in the northern Bering Sea, and to lesser extent in the southeastern Bering Sea, and reproductive success was poor at monitored colonies. Selected bottom‐up responses to lack of sea ice in the north were similar to those in the south, potentially providing environmental indicators to project ecosystem effects in a lesser studied system. Results offer a potential glimpse of the broader Bering Sea pelagic ecosystem under future low‐ice projections.

Indicators of pelagic forage community shifts in the California Current Large Marine Ecosystem, 1998–2016

Forage fishes are ecologically and economically important in marine ecosystems worldwide and thus are a focal topic for ecosystem-based fisheries management. In the California Current Large Marine Ecosystem (CCLME), the community dynamics of forage populations have been studied at regional spatial scales, but not across regions. To evaluate indicators of the forage community at the ecosystem-wide scale, we examine temporal variability of forage assemblages in Northern (Oregon/Washington), Central (California; Point Reyes to Monterey Bay) and Southern (southern California) regions of the CCLME from 1998 through 2016 which include years with unprecedented climate variability. Forage communities fluctuated greatly between years within each region owing to regionally low abundances of common taxa in at least some years (e.g., rockfishes Sebastes spp. in each region). Comparison of species assemblages among regions indicate that that temporal shifts in assemblage structure were largely synchronous throughout the CCLME. However, dynamics of most individual taxa were out of phase between regions, indicating that different taxa drove the variability in each region. Within regions, taxa with similar adult ecological niches tended to co-vary, suggesting synchronous responses to environmental forcing. Major changes in forage assemblage structure are descriptively linked to large oceanographic perturbations such as the transition from El Niño to La Niña conditions in 1998, anomalous upwelling in 2005, and the onset of a large marine heatwave in fall-winter 2013–2014. Changes in forage assemblage structure are reflected in prey switching in the diet of California sea lions, Zalophus californianus, in the Southern region. The multivariate forage indices that we develop can serve as effective indicators of regional forage community composition shifts in the CCLME and provide managers with context on spatio-temporal changes in the structure of forage fish communities important to top predators in this system.

Isoscapes reveal patterns of δ13C and δ15N of pelagic forage fish and squid in the Northwest Pacific Ocean

Isoscapes of stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) in pelagic fish and squid were generated using 1967 measured values of forage fish and squid in the Northwest Pacific Ocean. We then used generalized additive models (GAMs) to assess the explanatory variables that best predicted regional fish and squid δ13C and δ15N values. A total of 522 squid and 1445 forage fish were analyzed for δ13C and δ15N. The explanatory variables/variates used in GAM analyses were geographical parameters (longitude and latitude), body mass, season, category of organism (fish or squid), and vertical habitat. The resulting isoscapes of δ13C showed higher values in the sub-tropical region and lower values in the sub-arctic region. The isoscape patterns of δ15N were more complex; higher values were found in both tropical and temperate regions, and lower values were observed in sub-tropical and sub-arctic regions. These heterogeneities in isoscapes of δ13C and δ15N in the Northwest Pacific could be caused by productivity dynamics, ocean currents and upwelling, and the degree of atmospheric fixation of carbon and nitrogen. These new isoscapes can be used in conjunction with predator δ13C and δ15N values to evaluate movements and trophic dynamics of predatory marine animals, including tunas, billfish, sharks, seabirds, and marine mammals, in the Northwestern Pacific Ocean.

Pelagic–littoral resource polymorphism in Hovsgol grayling Thymallus nigrescens from Lake Hovsgol, Mongolia

AbstractResource polymorphism is a widespread phenomenon in post‐glacial fishes where multiple morphotypes of a species occur sympatrically and exhibit distinct resource use. Availability of open niches and high levels of within and among species competition are thought to drive differences in morphology and may provide insights into early stages of speciation. Hovsgol grayling (Thymallus nigrescens) are endemic to Lake Hovsgol, a lake colonised by fish following the Pleistocene, and are threatened with habitat loss due to climate change and illegal harvest. Previous analysis of Hovsgol grayling diet inferred through C and N stable isotopes suggested the presence of littoral and pelagic foraging groups. We hypothesised that morphology of the two foraging groups would reflect predictions of functional morphology, indicating the presence of resource polymorphism. To test this hypothesis, we evaluated evidence from C and N stable isotopes, stomach contents, fish ages, capture location and morphology. Two foraging groups of Hovsgol grayling were identified through stomach content and C and N stable isotope analysis. Individuals with greater zooplankton consumption were more frequently captured in the pelagic zone, exhibited higher gill raker counts, larger orbit (eye) sizes, longer paired fins, narrower head width, larger maxilla and smaller size at age than the group with greater reliance on benthic invertebrate prey. These differences were generally consistent with those described in other fish species exhibiting littoral–pelagic resource polymorphism. Our study provides the first example of littoral–pelagic resource polymorphism in the salmonid subfamily Thymallinae and highlights the potential influence of competition on fish evolution.

Spatial variation in a top marine predator's diet at two regionally distinct sites.

In ecological studies it is often assumed that predator foraging strategies and resource use are geographically and seasonally homogeneous, resulting in relatively static trophic relationships. However, certain centrally placed foragers (e.g. seals) often have terrestrial sites for breeding, resting, and moulting that are geographically distinct, and associated with different habitat types. Therefore, accurate estimations of predator diet at relevant spatial and temporal scales are key to understanding energetic requirements, predator-prey interactions and ecosystem structure. We investigate geographic variation in the diet of grey seals (Halichoerus grypus), a relatively abundant and widely distributed central place forager, to provide insights into geographic variation in resource use. Prey composition was identified using scat samples collected over concurrent timescales and a multivariate approach was used to analyse diet from two contrasting habitats. Regional differences in prey assemblages occurred within all years (2011–2013) and all seasons (ANOSIM, all p<0.05), apart from in winter. Telemetry data were used to identify core foraging areas and habitats most likely associated with scat samples collected at the two haul-out sites. Regional differences in the diet appear to reflect regional differences in the physical habitat features, with seals foraging in deeper waters over sandy substrates showing a higher prevalence of pelagic and bentho-pelagic prey species such as blue whiting and sandeels. Conversely, seals foraging in comparatively shallow waters had a greater contribution of demersal and groundfish species such as cephalopods and flatfish in their diet. We suggest that shallower waters enable seals to spend more time foraging along the benthos while remaining within aerobic dive limits, resulting in more benthic species in the diet. In contrast, the diet of seals hauled-out in areas adjacent to deeper waters indicates that either seals engage in a more pelagic foraging strategy, or that seals can spend less time at the benthos, resulting in comparatively more pelagic prey recovered in the diet. The substantial differences in prey assemblages over a small spatial scale (<300 km) demonstrates the importance of using regionally-specific diet information in ecosystem-based models to better account for different trophic interactions.

Diet and trophic niche space and overlap of Lake Ontario salmonid species using stable isotopes and stomach contents

Abstract Lake Ontario supports a diversity of native and non-native salmonids which are managed largely through stocking practices. Ecological changes (e.g., invasive species) altering the food web structure accompanied with shifts in prey abundance, necessitate understanding the trophic niches of Lake Ontario salmonids to aid in management. The objectives of this study were to quantify salmonid (5 species) trophic niches and dietary proportions using stable isotope ratios (δ13C and δ15N) of a large sample set (adult fish (>300 mm; n = 672) and key offshore prey (5 species, n = 2037)) collected across Lake Ontario in 2013. Estimates of prey based on stable isotope ratios were similar to stomach contents. Based on stable isotope ratios, non-native prey dominated salmonid diet; in particular alewife (Alosa pseudoharengus) constituted the majority (0.31 to 0.93) of all salmonid diets, and round goby (Neogobius melanostomus) contributed 0.26 and 0.19 of brown trout (Salmo trutta) and lake trout (Salvelinus namaycush) diets, respectively. Trophic niche overlap was high between all salmonids, except lake trout. The largest trophic niche overlap occurred between Chinook (Oncorhynchus tshawytscha), coho (Oncorhynchus kisutch), and Atlantic salmon (Salmo salar), and their reliance on alewife infers a strong pelagic foraging strategy. Lake, brown and rainbow (Oncorhynchus mykiss) trout had larger and/or more distinct trophic niches indicative of a more variable diet across individuals and utilizing different foraging strategies and/or habitats. Overall, Lake Ontario salmonids maintained a high reliance on alewife, and their potential for plasticity in diet provides important information to management regarding population sustainability.

Marine protected areas show low overlap with projected distributions of seabird populations in Britain and Ireland

Marine Protected Areas (MPAs) are an important tool for the conservation of seabirds. However, mapping seabird distributions using at-sea surveys or tracking data to inform the designation of MPAs is costly and time-consuming, particularly for far-ranging pelagic species. Here we explore the potential for using predictive distribution models to examine the effectiveness of current MPAs for the conservation of seabirds, using Britain and Ireland as a case study. A distance-weighted foraging radius approach was used to project distributions at sea for an entire seabird community during the breeding season, identifying hotspots of highest density and species richness. The percentage overlap between distributions at sea and MPAs was calculated at the level of individual species, family group, foraging range group (coastal or pelagic foragers), and conservation status. On average, 32.5% of coastal populations and 13.2% of pelagic populations overlapped with MPAs indicating that pelagic species, many of which are threatened, are likely to have significantly less coverage from protected areas. We suggest that a foraging radius approach provides a pragmatic and rapid method of assessing overlap with MPA networks for central place foragers. It can also act as an initial tool to identify important areas for potential designation. This would be particularly useful for regions throughout the world with limited data on seabird distributions at sea and limited resources to collect this data. Future assessment for marine conservation management should account for the disparity between coastal and pelagic foraging species to ensure that wider-ranging seabirds are afforded adequate levels of protection.

Feeding behavior and trophic interaction of three shark species in the Galapagos Marine Reserve.

There is great concern about the future of sharks in Ecuador because of the lack of biological knowledge of most species that inhabit the region. This paper analyzes the feeding behavior of the pelagic thresher shark (Alopias pelagicus), the blue shark (Prionace glauca) and the silky shark (Carcharhinus falciformis) through the use of stable isotopes of carbon and nitrogen (δ13C and δ15N), with the aim of determining the degree of interaction between these species in the Galapagos Marine Reserve. No interspecific differences were found in use of oceanic vs. inshore feeding areas (δ13C: Kruskal–Wallis test, p = 0.09). The position in the hierarchy of the food web where A. pelagicus feeds differed from that of the other species (δ15N: Kruskal–Wallis test, p = 0.01). There were no significant differences in δ13C and δ15N values between males and females of the three species (Student’s t-test, p > 0.05), which suggests that both sexes have a similar feeding behavior. A specialist strategy was observed in P. glauca (trophic niche breadth TNB = 0.69), while the other species were found to be generalist (A. pelagicus TNB = 1.50 and C. falciformis TNB = 1.09). The estimated trophic level (TL) varied between the three species. C. falciformis occupied the highest trophic level (TL = 4.4), making it a quaternary predator in the region. The results of this study coincide with the identified behavior in these predators in other areas of the tropical Pacific (Colombia and Mexico), and suggest a pelagic foraging strategy with differential consumption of prey between the three species. These ecological aspects can provide timely information when implementing in conservation measures for these shark species in the Tropical Pacific and Galapagos Marine Reserve.

Classifying and combining herd surface activities and individual dive profiles to identify summer behaviours of beluga (Delphinapterusleucas) from the St. Lawrence Estuary, Canada

Studies of the behaviour of diving animals usually focus on either individual dives or surface group activities, but these complementary observations are seldom combined in the same study. We here study the summer (June–October) behaviour of St. Lawrence Estuary belugas (Delphinapterus leucas (Pallas, 1776)) by combining fine-scale individual diving data from 27 time–depth–speed recorder deployments (conducted in 2002–2005) with surface activity data from 1413 focal herd follows (conducted in 1991–2012). We classified 6312 dives into seven dive types based on shape and swim speed. Dives were then combined into five bout types, including three pelagic, one benthic, and one near-surface. We classified surface activities of herds into six clusters, differentiated primarily by their associated movement patterns (milling or directional) and additionally by herd structure and dispersion and occurrence of acrobatic surface events. Finally, we used herd focal follows conducted while tracking an individual beluga to relate dive and bout types to surface activities. Results indicate that milling at the surface was more frequently related to benthic dives, potentially, associated with behaviours such as benthic foraging, resting, socializing, and care of young. Directional surface movements were more frequently associated with pelagic dives likely used during pelagic foraging, exploration, and travelling.

Bottom-up and top-down control of small pelagic forage fish: factors affecting age-0 herring in the Strait of Georgia, British Columbia

Bottom-up and top-down control of small pelagic forage fish: factors affecting age-0 herring in the Strait of Georgia, British Columbia

Impacts of the Deepwater Horizon oil spill evaluated using an end-to-end ecosystem model.

We use a spatially explicit biogeochemical end-to-end ecosystem model, Atlantis, to simulate impacts from the Deepwater Horizon oil spill and subsequent recovery of fish guilds. Dose-response relationships with expected oil concentrations were utilized to estimate the impact on fish growth and mortality rates. We also examine the effects of fisheries closures and impacts on recruitment. We validate predictions of the model by comparing population trends and age structure before and after the oil spill with fisheries independent data. The model suggests that recruitment effects and fishery closures had little influence on biomass dynamics. However, at the assumed level of oil concentrations and toxicity, impacts on fish mortality and growth rates were large and commensurate with observations. Sensitivity analysis suggests the biomass of large reef fish decreased by 25% to 50% in areas most affected by the spill, and biomass of large demersal fish decreased even more, by 40% to 70%. Impacts on reef and demersal forage caused starvation mortality in predators and increased reliance on pelagic forage. Impacts on the food web translated effects of the spill far away from the oiled area. Effects on age structure suggest possible delayed impacts on fishery yields. Recovery of high-turnover populations generally is predicted to occur within 10 years, but some slower-growing populations may take 30+ years to fully recover.

Seasonal shifts in foraging distribution due to individual flexibility in a tropical pelagic forager, the Ascension frigatebird

The work on Ascension Island was partly funded by a Darwin Grant (# 19026) to Ascension Island Government and the University of Exeter (A.B. and B.G.), managed on-island by N.W. and S.W. Nigel Butcher and Andrew Asque assisted with preparation of loggers and equipment, and Elizabeth Marsden kindly provided the base station to download data.

Impacts of ocean climate variability on biodiversity of pelagic forage species in an upwelling ecosystem

Impacts of ocean climate variability on biodiversity of pelagic forage species in an upwelling ecosystem

Early feeding of round goby (Neogobius melanostomus) fry

Abstract Larval and early juvenile stages have been shown to strongly influence recruitment variability for fishes, with successful foraging during these stages improving growth and survival. This study provides the first targeted study of the early juvenile (“fry”) diet of the round goby ( Neogobius melanostomus ), a prominent Great Lakes invasive fish. We sampled diurnally in diverse benthic environments of nearshore western Lake Michigan and two coastal tributaries. Three major prey types numerically dominated the diurnal benthic diet: harpacticoid copepods, chydorid cladocerans and chironomid larvae. Pelagic prey, of the types observed in nocturnal, pelagic studies, were rare. It was typical for the local diet of round goby fry to feature a primary prey type which contributed > 50% numerically to the total diet, which may be associated with patchy distributions of benthic prey. An ontogenetic diet shift from harpacticoids to chydorids was suggested between 6–26 mm SL. The dominance of benthic meiofauna in the diet of round goby fry expands upon the prior narrative of nocturnal, pelagic foraging, and demonstrates the flexibility of this species to thrive in diverse nursery habitats.

Pelagic or benthic prey? Combining trophic analyses to infer the diet of a breeding South American seabird, the Red-legged Cormorant, Phalacrocorax gaimardi

The available information about the feeding habits and preferences of the Red-legged Cormorant (Phalacrocorax gaimardi) generally suggests that this near-threatened South American cormorant is a sedentary benthic forager that also incorporates pelagic prey in its diet. In order to describe the dietary composition and assess the importance of certain prey types (pelagic vs benthic), we studied the diet of this cormorant on the Argentine Atlantic coast during four breeding seasons, using a combined technique of conventional diet assessment (pellets) and stable isotope analysis. Our results show that the Red-legged Cormorant forages mainly on pelagic and demersal—pelagic prey. Results of both techniques showed the main prey to be the Patagonian Sprat, a small high-energy-content pelagic forage fish, and the Patagonian Squid, a low-energy-content demersal—pelagic invertebrate. We also found an overall low prey diversity and important interannual variation for the main prey types, as well as variation between the different breeding stages. This study therefore contributes new and unambiguous information about the Red-legged Cormorant's use of trophic resources and suggests that the combination of a conventional technique with stable isotope analysis provides a solid framework for this seabird diet assessment.

New diet data for &lt;I&gt;Mola mola&lt;/I&gt; and &lt;I&gt;Masturus lanceolatus&lt;/I&gt; (Tetraodontiformes: Molidae) off Florida's Atlantic coast with discussion of historical context

Reports on the gut contents of ocean sunfish, Mola mola (Linnaeus, 1758), are rare, and those for sharptail mola, Masturus lanceolatus (Lienard, 1840), are almost nonexistent. Here, we report new diet data obtained during opportune sampling of a small number of stranded specimens of both species, and discuss our data in the context of hypotheses on feeding behavior of M. mola. One specimen of only two M. mola had a gut full primarily of filamentous algae, and the guts of two specimens of M. lanceolatus collectively contained remains of small fish and various invertebrates, indicative of both benthic and pelagic foraging. Our limited data suggest that the diet of M. lanceolatus overlaps that reported for M. mola. At high taxonomic resolution, observed prey items suggest some particulars of our specimens' behavior just before death. We emphasize the importance of meticulous presentation of methods, data, and literature citations.

Dietary Evidence of Mesopelagic and Pelagic Foraging by Atlantic Bluefin Tuna (Thunnus thynnus L.) during Autumn Migrations to the Iceland Basin

Atlantic bluefin tuna (ABFT; Thunnus thynnus) is a large highly mobile predator fish species in the North Atlantic Ocean and Mediterranean Sea. Knowledge of its trophic role in marine food webs in summer feeding areas is presently based on recent (1980s-2010s) sampling in the Bay of Biscay, Gulfs of Maine and St. Lawrence, and from historical (1950s-1960s) sampling in the Norwegian-North Sea-Kattegat. No study has yet investigated the diets of ABFT in Icelandic waters, where it supported an experimental fishery during 1996-2005, nor in any region north of the Bay of Biscay since the 1960s. However north Atlantic temperatures and fish species distributions, including some ABFT prey species (e. g., mackerel) have been changing in the 2000s. New knowledge of ABFT diets in previously understudied parts of the species range will be useful for understanding factors affecting the trophic role, migration behavior and bioenergetics of ABFT. Here we report the dietary composition of ABFT during autumn migrations to the Iceland Basin south of the continental shelf of Iceland. A total of 36 prey species or higher taxa were observed in 421 stomach samples: 17 teleost fishes, 4 squid, 1 octopus, 11 crustaceans and 2 other invertebrate species. The most important prey species European flying squid (Todarodes sagittatus) (%N=16.70, %W=48.89; %FO=87.65), barracudinas (Paralepididae) (%N=14.05, %W=28.59, %FO=76.48) and gonate squid (Gonatus sp.) (%N=9.17, %W=7.85, %FO=75.06). Prey sizes were highly variable relative to ABFT sizes indicating highly opportunistic feeding on diverse sizes. The presence of a large proportion of mesopelagic species in the diet indicates feeding in the mesopelagic layer and extensive dive behavior. These results give new baseline knowledge for future comparison with anticipated oceanographic-biological changes in the region in the coming decades and can be used to help parameterize new models of ABFT migration behavior and trophic role.

Habitat-specific foraging strategies in Australasian gannets.

ABSTRACTKnowledge of top predator foraging adaptability is imperative for predicting their biological response to environmental variability. While seabirds have developed highly specialised techniques to locate prey, little is known about intraspecific variation in foraging strategies with many studies deriving information from uniform oceanic environments. Australasian gannets (Morus serrator) typically forage in continental shelf regions on small schooling prey. The present study used GPS and video data loggers to compare habitat-specific foraging strategies at two sites of contrasting oceanographic regimes (deep water near the continental shelf edge, n=23; shallow inshore embayment, n=26), in south-eastern Australia. Individuals from the continental shelf site exhibited pelagic foraging behaviours typical of gannet species, using local enhancement to locate and feed on small schooling fish; in contrast only 50% of the individuals from the inshore site foraged offshore, displaying the typical pelagic foraging strategy. The remainder adopted a strategy of searching sand banks in shallow inshore waters in the absence of conspecifics and other predators for large, single prey items. Furthermore, of the individuals foraging inshore, 93% were male, indicating that the inshore strategy may be sex-specific. Large inter-colony differences in Australasian gannets suggest strong plasticity in foraging behaviours, essential for adapting to environmental change.