The isotopic composition of baleen whales’ epidermis structural layers can give information about dietary change over time. This study investigated if epidermis layers integrated isotopic values that record physiological changes from gestation to lactation. Epidermis tissues (n = 43) were collected from free ranging lactating female gray whale and calves during the beginning of three breeding seasons. Modelling of δ 13 C and δ 15 N values show intra- and inter-individual differences based on epidermal layers, age class and year of sampling. The isotopic composition of mother-calf pairs is correlated, and the estimates of the maximum mother-to-calf isotopic difference was ~1.4‰ for δ 13 C and between 1 and 1.5‰ for δ 15 N values. Change in δ 15 N values among epidermal layers in calves was associated with the transition from fetus to consumption of maternal milk. It is here proposed when lactation influences calf epidermis, δ 15 N values decrease consistently from the outermost to the innermost layer. However, if a calf was born only few days before collection, epidermis integrates more variable δ 15 N patterns because gestation still affects the isotopic composition of the layers. The possibility of calculating mother-to-calf nitrogen isotope fractionation, and the regularity of changes between calf layer δ 15 N values, allowed results of an isotopic clock model to predict the age of each calf when sampled with its mother. This model has the potential to be a straightforward method to estimate the beginning of lactation, therefore calf birth date when direct observations are not feasible. The non-lethal remote collection of epidermis appears to be an effective tool for the study of the physiology of reproduction of baleen whales. The parallel study of the three epidermal structural layers highlighted the importance of considering the unique mother-calf pair physiological status at the time of sampling time when stable isotope results are interpreted.
Stable isotope analysis is a useful tool for studying the ecology of marine consumers, as carbon (δ 13 C) and nitrogen (δ 15 N) isotope ratios may reflect individuals' patterns of diet and habitat use. Knowledge of foraging strategies has significant implications for the conservation of endangered loggerhead turtles Caretta caretta (Linnaeus, 1758). In this study, δ 13 C and δ 15 N isotope data were used to assess resource use patterns of the Mediterranean loggerhead turtles (Aeolian Archipelago, Southern Italy). δ 13 C and δ 15 N values from carapace scutes of 54 loggerheads of different curved carapace length (CCL) and health status were compared with those of eight potential prey items (benthic, pelagic and fishery discards). MixSIAR results suggested that pelagic prey (from goose barnacles to planktivorous fish) comprised most of loggerheads' diet, with small variations (i.e. benthic prey or fishery discards) depending on size (δ 13 C and δ 15 N) and health (δ 15 N) of individuals. δ 13 C variations with turtles' size might reflect changes in dietary habitats during life stages. However, the loggerhead turtles and their main source of prey (pelagic prey) had a higher variation in values of δ 15 N compared to δ 13 C. This suggested that smaller-sized turtles might preferentially feed on pelagic prey in oceanic habitats and then, as they reach a larger size, gradually enter neritic waters, including in their diet prey sources with higher δ 13 C and δ 15 N. Some turtles foraging on longline baits/debris also displayed a marked increase in δ 15 N. These δ 15 N variations might be explained by differences in diet (trophic differences) and somatic growth rates among individuals, or dietary dilution.
Eastern gray whales’ distribution range and plasticity in feeding behavior complicates the understanding of critical life-history such as pregnancy and lactation. Our goal was to determine if females who experienced gestation, gave birth, and lactated their calves, assimilated a high proportion of benthic amphipods from the Bering Sea, which are considered the species’ main prey. We used Bayesian stable isotope mixing models to estimate the probability of contribution of food items sampled along the species’ distributional range, using isotopic data on amphipods from the Bering Sea, mysids from Vancouver Island, and amphipods and polychaetes from Ojo de Liebre Lagoon. We sampled epidermal tissue from lactating females (n = 25) and calves (n = 34) and analyzed their carbon and nitrogen isotopic composition. Model outcome indicated that benthic amphipods from the Bering Sea were not the primary food for the eastern gray whale. Each mother performed a different feeding strategy, and prey from Vancouver Island were generally as important as that from the Bering Sea. Moreover, model results indicate a constant use of Ojo de Liebre Lagoon as a feeding ground. Our results appear to agree with previous studies that report continuous feeding by females to satisfy certain physiological requirements (e.g., fatty acids omega-6) during migration and breeding time. Future investigations of the isotopic composition of all those prey items that could be assimilated by the eastern gray whale emerge as critical. Both historical and recent information, that would provide insights in the species feeding ecology under past and present environmental conditions, should be considered as equally important to establish conservation and management plans.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.