Major Prey Items Research Articles

Stable isotope analysis reveals fish juveniles as a temporal main resource consumed by invasive pumpkinseed (Lepomis gibbosus)

AbstractThe pumpkinseed Lepomis gibbosus (Linnaeus, 1758) is a small centrarchid fish species from North America that has invaded most European basins, with pronounced expected impacts. Analyses of pumpkinseed diet in its invasive range using gut content analysis (GCA) show macrozoobenthos as the most common dietary item, suggesting a competitive effect on native fish communities. Our study uses a combination of GCA and stable isotope analysis (SIA) to document pumpkinseed diet at two sites in its invaded range and relates pumpkinseed diet preferences with parasitic load. SIA revealed juvenile fish as a major prey item at one of the sites (63 and 50% of the diet of small and the large fish), while GCA showed pumpkinseed preying mostly on macroinvertebrates (chironomids, gastropods, Ephemeroptera, and Zygoptera larvae) at both sites. While infrequent infection by trophically transmitted parasitic nematodes could be related to low consumption of zooplankton, substantial infection by metacercariae of Posthodiplostomum centrarchi Hoffman1958 appears to reflect relatively high consumption rates of its intermediate host, physid snails. Using SIA allowed to demonstrate that pumpkinseed feeding in its non-native range can be based on piscivory, emphasising the need for combining multiple methods when studying the impact of non-native species on food webs.

Biological and environmental covariates of juvenile sockeye salmon distribution and abundance in the southeastern Bering Sea, 2002-2018.

Climate change is altering the distribution and abundance of marine species, especially in Arctic and sub-Arctic regions. In the eastern Bering Sea, home of the world's largest run of sockeye salmon (Oncorhynchus nerka), juvenile sockeye salmon abundance has increased and their migration path shifted north with warming, 2002-2018. The reasons for these changes are poorly understood. For these sockeye salmon, we quantify environmental and biological covariate effects within spatio-temporal species distribution models. Spatio-temporally, with respect to juvenile sockeye salmon densities: (1) sea surface temperature had a nonlinear effect, (2) large copepod, Calanus, a minor prey item, had no effect, (3) age-0 pollock (Gadus chalcogrammus), a major prey item during warm years, had a positive linear effect, and (4) juvenile pink salmon (O. gorbuscha) had a positive linear effect. Temporally, annual biomass of juvenile sockeye salmon was nonlinearly related to sea temperature and positively related to age-0 pollock and juvenile pink salmon abundance. Results indicate that sockeye salmon distributed with and increased in abundance with increases in prey, and reached a threshold for optimal temperatures in the eastern Bering Sea. Changes in population dynamics and distribution of sockeye salmon in response to environmental variability have potential implications for projecting specific future food securities and management of fisheries in Arctic waters.

Feeding habits and diet composition of Octopus cyanea (Gray, 1849) in Zanzibar waters, Tanzania

The octopus fishery in Zanzibar is an essential activity of coastal communities. To assist with developing fisheries management plans, baseline information on the feeding of Octopus cyanea (Gray, 1849) was collected in relation to sex and maturity stages. The feeding habits and diet composition of 543 O. cyanea were studied over a period of 12 months at Paje, Kizimkazi, Chwaka Bay and Nungwi. Samples at each site were collected on two days per month during spring tide. Digestive tract contents revealed that O. cyanea preyed on 36 species of crustaceans, molluscs and fishes, with crabs a major prey item. The number of prey species in a single stomach ranged from one to six. O. cyanea in Zanzibar is therefore a generalist predator with a mixed diet. The octopus gonadosomatic index (GSI) indicated a peak breeding season in June to October, which correlated with low prey consumption. Mature octopuses ingested a small amount of food from mainly small sessile prey. Females consumed less food than males of similar maturity stages, suggesting that they ate less or had higher digestion rates. The information is useful for developing fisheries management plans for the octopus fishery in Zanzibar.

The influence of temperature on Pacific hake co‐occurrence with euphausiids in the California Current Ecosystem

AbstractUnderstanding the influence of ocean conditions on predator–prey relationships can provide insight for ecosystem‐based fisheries management. Pacific hake (Merluccius productus) are abundant and commercially important groundfish in the California Current Ecosystem (CCE) that consume euphausiids (krill) as a major prey item. We used data from the biennial joint U.S.‐Canada Integrated Ecosystem & Acoustic Trawl Survey for Pacific hake (2007–2019, n = 8 surveys) to quantify co‐occurrence of age 2+ hake with krill in relation to bottom depth, continental shelf break location, surface chlorophyll‐a, and 100‐m temperature. Vertical distributions of hake varied among years and were not correlated to krill depth. Hake hotspots occurred primarily off the Oregon coast and near Cape Mendocino, while most krill hotspots occurred in the northern CCE. The probability of co‐occurrence was greatest during cool ocean conditions (100‐m temperature 1°C below average), averaging 41.0% and extending throughout most of the CCE. During warm ocean conditions (100‐m temperature 1°C above average), predicted co‐occurrence averaged 17.0% and was concentrated near Cape Mendocino. These results indicate that hake‐krill co‐occurrence is a function of predator and prey spatial distributions and overall krill abundance. Furthermore, temperature influences hake‐krill co‐occurrence and may explain some of the variation in hake growth and recruitment to the fishery.

The Impact of a Southern Ocean Cyclonic Eddy on Mesopelagic Micronekton

AbstractMesoscale eddies shape the foraging ecology of predators such as marine mammals and seabirds. A growing number of animal tracking studies show that predators alter their swimming, diving, and foraging behavior within mesoscale eddies. However, little is known about how Southern Ocean eddies influence the distribution of mesopelagic micronekton (fish, squid, and crustaceans), which are major prey items of megafauna. Studies in other oceanic regions have found that eddies can influence the abundance and community composition of micronekton. Here, we analyze acoustic observations from a 14‐day survey of a cyclonic mesoscale eddy, its surrounding waters, and the Polar Frontal Zone (PFZ) waters where the eddy formed. We report and interpret spatial patterns of acoustic backscatter at 18 and 75 kHz, proxies indicating combined changes in species, size, and abundance of micronekton. We find that the vertical distribution of acoustic backscatter matched the underwater light conditions characteristic of the eddy core, periphery, and surrounding waters, at scales smaller than 10 km. The median water‐column integrated acoustic backscatter values in the eddy core were only half of those measured in the Sub‐Antarctic Zone waters surrounding the eddy, but similar to those measured in the PFZ, where the eddy originated 27 days prior. These results suggest that, as for physical and chemical tracers, the eddy maintained its biological characteristics from its source waters creating a unique habitat compared to its surroundings.

Predation of the critically endangered Fijian crested iguana (Brachylophus vitiensis) by the swamp harrier (Circus approximans)

AbstractThe Fijian crested iguana (Brachylophus vitiensis) is the largest extant lizard in Fiji, where it enjoys life in the absence of any mammalian predators. On the only island where this iguana is abundant, the only predator appears to be the swamp harrier (Circus approximans), which is non‐selective in its iguana prey, catching individuals in a similar proportion to their size availability. Here we report on the first observation of a reptile being the major prey item of the swamp harrier.

Metabarcoding analysis of trophic sources and linkages in the plankton community of the Kuroshio and neighboring waters

Trophic sources and pathways supporting early life stages are crucial for survival of forage fishes recruiting around the oligotrophic and unproductive Kuroshio. However, information is limited for the Kuroshio planktonic food web and its trophodynamics because of its high biodiversity. Here, we explore trophic sources and linkages in the Kuroshio plankton community using metabarcoding analysis of gut-content DNA for 22 mesozooplankton groups. The major prey was dinoflagellates and calanoids for omnivorous groups, and calanoids and gelatinous organisms for carnivorous groups. Larvaceans and hydrozoans were the most frequently appeared prey for both omnivores and carnivores, whereas they were minor constituents of the available prey in water samples. Although calanoids overlapped as major prey items for both omnivores and carnivores because they were the most available, contributions from phytoplankton and gelatinous prey differed among taxonomic groups. Further analysis of the metabarcoding data showed that in addition to omnivorous copepods like calanoids, gelatinous groups like larvaceans and hydrozoans were important hubs in the planktonic food web with their multiple trophic linkages to many components. These findings suggest that gelatinous organisms are important as supplementary prey and provide evidence of niche segregation on trophic sources among mesozooplankton groups in the Kuroshio.

DNA Metabarcoding Revealed Interspecific Dietary Difference and Prey Selectivity in Juvenile Horseshoe Crabs Carcinoscorpius rotundicauda and Tachypleus tridentatus From Hong Kong

Horseshoe crabs provide important ecological services including bioturbation and linking of food web in the shallow waters, but their populations are declining globally, leading to major concerns on conservation of these iconic animals. Baseline information of horseshoe crab ecology, such as their trophic role and food source, is pre-requisite for habitat protection plan and captive restocking program. Trophic ecology of Asian horseshoe crabs is relatively poorly understood and previous studies on their juveniles have suggested that they are selective feeders rather than opportunistic generalists. This study demonstrates a non-invasive approach, using DNA metabarcoding analyses of the nuclear 18S rRNA gene on fecal samples to assess the dietary compositions of Carcinoscorpius rotundicauda and Tachypleus tridentatus juveniles to (1) determine their dietary compositions and trophic roles in their ecosystem, (2) determine any prey selectivity, and (3) distinguish the interspecific dietary differences with potential implications on the habitat requirement and ecological partitioning between these two horseshoe crab species. The results based on relative read abundance (RRA) suggested that oligochaetes were the major prey items for both C. rotundicauda (41.6%) and T. tridentatus (32.4%). Bivalves and crustaceans were second major prey groups for C. rotundicauda (8.6 and 8.4%, respectively). Surprisingly, anthozoans contributed a considerable portion of T. tridentatus’s diet (22.8%), which has never been reported. Furthermore, the major prey groups identified in the fecal samples were not the dominant benthic organisms in the studied area as revealed by environmental DNA (eDNA) analyses on the sediment samples, implying that both species are selective feeders rather than dietary generalists. Significant differences observed in the dietary compositions of the two species might be partially due to the difference in habitat preference between the two species. This study provides new insights into the trophic ecology of the two Asian horseshoe crab species in the estuarine habitat and establishes a new framework for future detailed molecular dietary analyses on all developmental stages of horseshoe crabs around the world, which will allow us to evaluate the food sources needed for the survival of horseshoe crabs and facilitate future conservation strategies without killing the animals.

The Diet Composition and Ingested Plastics of Laysan and Black-Footed Albatrosses Incidentally Captured by the Pelagic Longline Fishery in the Western North Pacific

The stomach contents (food and ingested plastics) of Laysan Albatross Phoebastria immutabilis and Black-footed Albatross P. nigripes were examined by necropsy analysis of birds caught as bycatch in the pelagic longline fisheries in the Western North Pacific. The contents were classified separately for the proventriculus and gizzard. Undigested fish and cephalopods were found in the proventriculus, while hard objects such as cephalopod beaks, plastics, and pebbles were found in the gizzard. This indicates that the retention time of soft tissues in fish or cephalopods differs from that for hard objects. The main prey of both albatrosses consisted of mesopelagic cephalopods such as Cranchiidae, Gonatidae, Histioteuthidae, and Onychoteuthidae species. Laysan Albatrosses also foraged on small teleosts (Japanese Anchovy Engraulis japonicus and some Myctophidae fishes) as major prey items. The estimated dorsal mantle length of cephalopods preyed upon by the albatrosses was below 200 mm, which was smaller than the mature sizes of those cephalopods and the size class mainly preyed upon by cetaceans. This implies that the albatrosses may forage on immature cephalopods floating in the surface layer. Ingested plastics were found in 71.8% of Laysan and 31.8% of Black-footed Albatrosses and plastic fragments were the most abundant.

Predation By the Nonnative Rainbow Trout, Oncorhynchus Mykiss (Walbaum, 1792), on the Native Biota from Freshwater Environment of the Central Andes (Argentina)

Abstract This study aimed to examine the impact of the nonnative rainbow trout Oncorhynchus mykiss on the native biota that inhabits freshwater environments of the central Andes, Argentina. To assess the predation pressure on native Andean vertebrates and invertebrates, the stomach contents were taken from rainbow trout caught at three Andean sites. Results showed that the major prey items were the native torrent catfish Hatcheria macraei (100% in diet), Elmidae coleopterans (23%), and the native crab Aegla affinis (38%) in the rainbow trout stomachs collected from Cipolletti Dam (North zone), Yaucha River (Middle zone), and Vaina Stream (South zone), respectively. This preliminary study exhibits the predation pressure of the rainbow trout on native Andean species and suggests that policies are necessary to control the release of fry of this exotic salmonid in the Andes region.

Population dynamics, growth, production, and reproduction of the purple clam Amiantispurpurata

AbstractAmiantis purpurata is the dominant clam of shallow subtidal soft bottom communities in Buenos Aires province where it is a major prey item of economically important fish and gastropods as well as anemones. Despite its significant role in the benthic food web, there are few studies dealing with the population biology of this species. Growth, age, mortality, and production along with reproductive patterns and size at first maturity of A. purpurata were investigated at Mar del Plata (38 ºS) area and compared with a population at the southernmost point of distribution, the only other studied population (42 ºS). Early growth was empirically documented for the first time for this species by following a newly recruited cohort throughout the first two years of growth. This allowed for the size and age at first maturity to be accurately determined and provided early growth data for models, which are often difficult to obtain. Larger asymptotic size and quicker rates were reached at lower latitudes. Reproduction followed patterns similar to other temperate venerid bivalve populations with a more extended period of spawning observed at Mar del Plata. The studied population shows relatively high growth rates, achieves sexual maturity at approximately two years of age, and successfully recruits in this area, which was not observed in the other studied population for over 15 years. The environmental conditions in this area are likely more favorable than that of the southernmost population which shows low growth rates and no successful recruitment.

Evaluating the performance of the Bayesian mixing tool MixSIAR with fatty acid data for quantitative estimation of diet

We test the performance of the Bayesian mixing model, MixSIAR, to quantitatively predict diets of consumers based on their fatty acids (FAs). The known diets of six species, undergoing controlled-feeding experiments, were compared with dietary predictions modelled from their FAs. Test subjects included fish, birds and mammals, and represent consumers with disparate FA compositions. We show that MixSIAR with FA data accurately identifies a consumer’s diet, the contribution of major prey items, when they change their diet (diet switching) and can detect an absent prey. Results were impacted if the consumer had a low-fat diet due to physiological constraints. Incorporating prior information on the potential prey species into the model improves model performance. Dietary predictions were reasonable even when using trophic modification values (calibration coefficients, CCs) derived from different prey. Models performed well when using CCs derived from consumers fed a varied diet or when using CC values averaged across diets. We demonstrate that MixSIAR with FAs is a powerful approach to correctly estimate diet, in particular if used to complement other methods.

Feeding ecology of deep-water Arabian red shrimp, Aristeus alcocki Ramadan, 1938 (Decapoda: Penaeoidea: Aristeidae) from southwestern India (Arabian Sea)

The Arabian red shrimp, Aristeus alcocki Ramadan, 1938 constitutes a commercially important decapod in the southern coast of India with an annual average catch of greater than 2,122 tons. The diet contents in connection to the sex, maturity, season and size group of this species were investigated using an aggregate number of 634 samples collected from the south-west coast of India. The diet components of A. alcocki were deduced to consist of 71 prey categories, which belonged to smaller crustaceans (e.g. amphipods, decapods, euphausiids), foraminiferans (Rotaliida, and Miliolida), molluscs (bivalves, gastropods, and cephalopods), polychaetes, and bryozoans. Feeding pattern of the studied species was examined using Amundsen graphical method, which recognized that A. alcocki exhibited different degrees of generalization and specialization with various preys. The marginal seasonal variation related to major prey items could be attributed to the environmental fluctuations of the deep waters and other biological processes. Considering stomach fullness and food quality, the females of A. alcocki were found to be the effective predators than males. The parameters, such as population characteristics, somatic and gonadal development might be attributed to this variation. Notably, the larger-sized animal have good swimming ability, which could help in an effective selection of prey, while the smaller individuals depend on the epibenthic organisms for their food. This study comprises the first report on the feeding biology of A. alcocki in the Arabian Sea.

How a Scorpion Toxin Selectively Captures a Prey Sodium Channel: The Molecular and Evolutionary Basis Uncovered.

The growing resistance of insects to chemical pesticides is reducing the effectiveness of conventional methods for pest control and thus, the development of novel insecticidal agents is imperative. Scorpion toxins specific for insect voltage-gated sodium channels (Navs) have been considered as one of the most promising insecticide alternatives due to their host specificity, rapidly evoked toxicity, biodegradability, and the lack of resistance. However, they have not been developed for uses in agriculture and public health, mainly because of a limited understanding of their molecular and evolutionary basis controlling their phylogenetic selectivity. Here, we show that the traditionally defined insect-selective scorpion toxin LqhIT2 specifically captures a prey Nav through a conserved trapping apparatus comprising a three-residue-formed cavity and a structurally adjacent leucine. The former serves as a detector to recognize and bind a highly exposed channel residue conserved in insects and spiders, two major prey items for scorpions; and the latter subsequently seizes the "moving" voltage sensor via hydrophobic interactions to reduce activation energy for channel opening, demonstrating its action in an enzyme-like manner. Based on the established toxin-channel interaction model in combination with toxicity assay, we enlarged the toxic spectrum of LqhIT2 to spiders and certain other arthropods. Furthermore, we found that genetic background-dependent cavity shapes determine the species selectivity of LqhIT2-related toxins. We expect that the discovery of the trapping apparatus will improve our understanding of the evolution and design principle of Nav-targeted toxins from a diversity of arthropod predators and accelerate their uses in pest control.

Dietary fat concentrations influence fatty acid assimilation patterns in Atlantic pollock (Pollachius virens).

A key aspect in the use of fatty acids (FA) to estimate predator diets using quantitative FA signature analysis (QFASA) is the ability to account for FA assimilation through the use of calibration coefficients (CC). Here, we tested the assumption that CC are independent of dietary fat concentrations by feeding Atlantic pollock (Pollachius virens) three formulated diets with very similar FA proportions but different fat concentrations (5-9% of diet) for 20 weeks. CC calculated using FA profiles of diet and triacylglycerols in pollock liver were significantly different for the three diets. To test the robustness of diet estimates to these differences, we used the CC set derived from feeding the diet with the lowest fat concentration, published prey FA profiles and realistic diet estimates of pollock to construct 'pseudo-predators'. Application of QFASA to each pseudo-predator using the three sets of CC and the same prey FA profiles resulted in diet estimate biases of twofold for major prey items and approximately fivefold for minor prey items. This work illustrates the importance of incorporating diets with fat concentrations that are similar to natural prey when conducting feeding experiments to calculate CC. This article is part of the theme 'The next horizons for lipids as 'trophic biomarkers': evidence and significance of consumer modification of dietary fatty acids'.

The diet of coyotes and red foxes in Southern New York

Coyotes (Canis latrans) and red fox (Vulpes vulpes) are both generalist predators presently found in the Northeastern United States. This study aimed to identify major prey items of both species in suburban New York, investigate consumption of anthropogenic resources, and examine seasonal changes in diet. Scat samples were collected from 2017 to 2018 for coyotes, and from 2011 to 2012 for red fox. Hairs, feathers, bone fragments and other scat components were classified by comparison with reference collections. Logistic regression was used to determine whether season or location predicted the presence of various food items. The most common food items for coyotes were white-tailed deer (Odocoileus virginianus), found in 54.2% of samples, and cricetid rodents, found in 16.9% of samples. For red fox the most common food items were birds, found in 39% of samples, and cricetid rodents, found in 37.8% of samples. Anthropogenic waste appeared in 11.9% of coyote scat samples and made up 1.3% of the total weight of items recovered from samples. No anthropogenic items were found in red fox scat, nor were remains from threatened piping plovers (Charadrius melodus), known to breed in the study area. Seasonal changes in diet were not detected for either species. Overall our results show that coyotes and red fox in suburban areas of Southern New York are persisting primarily on natural prey items, and not being subsidized by anthropogenic food sources.

Spatiotemporal Patterns of Latrine-Site Use by Small-Clawed Otters in a Heterogeneous Rice Field Landscape

Tropical rice fields with asynchronous growth stages provide a good model to investigate the effects of landscape heterogeneity on the use of agricultural landscapes by wildlife. The small-clawed otter (Aonyx cinereus) uses rice fields as latrine sites in Southeast Asia. Through a 53-week survey of latrine sites, we analyzed the spatiotemporal patterns of latrine-site use by small-clawed otters in an asynchronous rice field in West Sumatra, Indonesia. Based on a generalized linear mixed model incorporating local environmental factors, otter latrine-site visitation was positively associated with the vegetative stage of rice cultivation and the biomass of a major prey item, the golden apple snail (Pomacea canaliculata). The vegetative stage of rice cultivation and golden apple snail biomass were closely associated with deep water in rice fields; therefore, water availability in rice fields is likely important in determining the spatiotemporal patterns of small-clawed otter latrine-site use in the asynchronous rice field landscape. To consistently provide latrine sites for small-clawed otters, we recommend that asynchronous rice cultivation be maintained, or zoning of synchronous and asynchronous rice cultivation areas be planned in the region.

Determination and precision of otolith growth zone estimates of Electrona antarctica in the Southern Kerguelen Plateau region in the Indian sector of the Southern Ocean

Antarctic lanternfish (Electrona antarctica) is the dominant mesopelagic fish species in the Southern Ocean. It is the most common myctophid occurring south of the Antarctic Polar Front, and an important component of Southern Ocean food webs, both as a zooplankton predator and as a major prey item for higher predators. Despite its importance, there are major gaps in current understanding of the life history of E. antarctica, with previous ageing studies having produced inconclusive results, hampering our understanding of the population structure in this species and its role in marine ecosystems. This is particularly relevant around the Kerguelen Plateau, a highly productive region in the Indian sector of the Southern Ocean, where E. antarctica is a key mid-trophic level species. The present study took advantage of mesopelagic sampling efforts in the southern Kerguelen Plateau region on the 2015–2016 Kerguelen Axis study, and enumerated growth zones in the otoliths of a sample of 100 E. antarctica collected during the voyage. Growth zones were counted using both sectioned and whole otoliths and the precision of estimates was estimated by repeat counts. The estimated number of growth zones in the sectioned otoliths of E. antarctica (standard length 53–97 mm) ranging from 2 to 9. The average coefficient of variation (CV) and average percentage error (APE) for the estimated growth zones were 6.78% and 4.51%, respectively based on counts of sectioned otoliths. The number of growth zones in sectioned otoliths is positively related to weight of otolith and standard length of fish. The results presented here can inform future work on age structure and life history of E antarctica in the Southern Ocean as understanding of the nature of growth rings improves.

Feeding strategy, dietary overlap and resource partitioning among four mesopredatory catfishes of a tropical estuary.

The feeding strategy, overlap and trophic interactions of four demersal catfishes inhabiting Cochin Estuary, Arius maculatus (n = 67), A. subrostratus (n = 63), A. arius (n = 21) and Mystus gulio (n = 69) were investigated through gut-content analyses. The indices of relative importance revealed that the prey items in their stomachs were dominated by crustaceans except in A. arius where molluscs constituted the major prey item. The highest diet and niche breadth values (3.93, 0.36 respectively) were recorded in A. subrostratus, while the lowest was recorded in A. arius (2.64, 0.23 respectively). Pianka's overlap, calculated through null models constructed by Ecosim 7.0, revealed significant niche overlap between A. maculatus and A. subrostratus (O-0.91, P < 0.001), between A. maculatus and M. gulio (O-0.72, P < 0.05) and between A. subrostratus and M.gulio (O-0.64 P < 0.05). However, no overlap was recorded between A. arius and other species. The trophic niche breadth along with prey specific abundance confirmed that these fishes are highly specific feeders. The present results on trophic level status indicate that these catfishes are mid-level carnivores that can be considered as moderate benthic mesopredators and are specialist feeders unlike most catfishes.

Climate change impact on the feeding habits of Indian mackerel observed along the Kerala coast

While most food and feeding research in fisheries emphasize the feeding habits and diet components of the fish, the aim of the present work was to assess any change in the diet composition of Indian mackerel Rastrelliger kanagurta (Cuvier, 1816) and identify the role of climate change in effecting it. Non-parametric statistical technique, the Generalized Additive Model (GAMs) was used for modeling the causal link of diet changes in relation to climate change using mgcv package of R software. Monthly Index of Relative Importance (IRI) was calculated for 36 months from January 2013 to December 2015 and major prey items in the diet were identified. Climatic variables - Sea Surface Temperature (SST), precipitation (Pr), Chlorophyll a (Chl a), salinity and Ekman transport or coastal upwelling index (CUI)) pertaining to the study area were extracted for the period. Length-wise IRI was compared to check the existing patterns in the feeding habits of the fish. The dominant prey items observed in the gut of Indian mackerel during the study period were diatoms ( Fragillaria sp., Nitzchia sp., Thalassiothrix sp., Thalassiosira sp. and Coscinodiscus sp.), dinoflagellates (Ceratium sp., Ornothocercus sp., Dinophysis sp. and Prorocentrum sp.), copepods (Calanoida, Cyclopoida and Harpacticoida), decapods (Acetes) and tintinnids (Tintinnopsis sp., Codenellopsis sp. and Flavella sp). GAM models were fitted with monthly IRI of the major prey items (copepods, diatoms, dinoflagellates, Acetes and tintinnids) in the gut and climatic variables. Model selection was done in terms of sharpening the relation between the predictors and the response variable using Akaike information criterion, R-squared and F-statistics. GAM model results revealed that occurrence of prey items in the diet of Indian mackerel were influenced by environmental variables. An increase in the relative importance of dinoflagellates, Acetes and tintintids in the diet over the historic period was observed. The study also revealed a shift in the diet composition of younger fishes. The results of the current study provide a more in-depth assessment of the nonlinear relationship between climatic variables and diet composition of Indian mackerel.