Stable isotope analysis (SIA) has emerged as a common tool in ecology and has proven especially useful in the study of animal diet, habitat use, movement, and physiology. SIA has been vigorously applied to the study of marine mammals, because most species live in habitats or undergo large migrations/movements that make them difficult to observe. Our review supplies a complete list of published SIA contributions to marine mammal science and highlights informative case examples in four general research areas: (1) physiology and fractionation, (2) foraging ecology and habitat use, (3) ecotoxicology, and (4) historic ecology and paleoecology. We also provide a condensed background of isotopic nomenclature, highlight several physiological considerations important for accurate interpretation of isotopic data, and identify research areas ripe for future growth. Because it is impossible to conduct controlled laboratory experiments on most marine mammal species, future studies in marine mammal ecology must draw on isotopic data collected from other organisms and be cognizant of key assumptions often made in the application of SIA to the study of animal ecology. The review is designed to be accessible to all audiences, from students unfamiliar with SIA to those who have utilized it in published studies.

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Using stable isotope biogeochemistry to study marine mammal ecology

The stable isotope composition of animal tissues can provide intrinsic tags to study the foraging and migratory ecology of predators in the open ocean. Chapter 13 (this volume) demonstrated that by comparing the isotope values of an animal and its local prey or environment, the animal’s movements can be estimated, given that isotopic variation exists between habitats. The utility of using geographical variations in stable isotopes values, or isoscapes to study the movements of marine predators has been limited because of our lack of knowledge on the spatial variation of the carbon, nitrogen, and oxygen isotope values in the open ocean.

Using Isoscapes to Trace the Movements and Foraging Behavior of Top Predators in Oceanic Ecosystems

Sea ice in the Arctic is one of the most rapidly changing components of the global climate system. Over the past few decades, summer areal extent has declined over 30, and all months show statistically significant declining trends. New satellite missions and techniques have greatly expanded information on sea ice thickness, but many uncertainties remain in the satellite data and long-term records are sparse. However, thickness observations and other satellite-derived data indicate a 40 decline in thickness, due in large part to the loss of thicker, older ice cover. The changes in sea ice are happening faster than models have projected. With continued increasing temperatures, summer ice-free conditions are likely sometime in the coming decades, though there are substantial uncertainties in the exact timing and high interannual variability will remain as sea ice decreases. The changes in Arctic sea ice are already having an impact on flora and fauna in the Arctic. Some species will face increasing challenges in the future, while new habitat will open up for other species. The changes are also affecting peoples living and working in the Arctic. Native communities are facing challenges to their traditional ways of life, while new opportunities open for shipping, fishing, and natural resource extraction.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2013RG000431

Arctic sea ice in transformation: A review of recent observed changes and impacts on biology and human activity

Isotope ratios of actively cycled elements vary as a function of the biogeochemical processes in which they participate and the conditions under which those processes occur. The resultant spatiotemporal distribution of isotopes in environmental materials can be predicted using models of isotopefractionating processes and data describing environmental conditions across space and time, and it has been termed an isoscape, or isotopic landscape. Analysis of isoscapes and comparison of isoscape predictions with observational data have been used to test biogeochemical models, calculate aerially integrated biogeochemical fluxes based on isotope mass balance, and determine spatial connectivity in biogeochemical, ecological, and anthropological systems. Isoscape models of varying quality are available for stable H, C, N, and O isotopes in a range of Earth surface systems, but significant opportunities exist to refine our understanding of biogeochemical cycles and our ability to predict isoscapes through the development of more mechanistic and more comprehensive isoscape models.

/pdf/isoscapes-spatial-pattern-in-isotopic-biogeochemistry-46clgamlkz.pdf

Isoscapes: Spatial Pattern in Isotopic Biogeochemistry

Arctic marine mammals (AMMs) are icons of climate change, largely because of their close association with sea ice However, neither a circumpolar assessment of AMM status nor a standardized metric of sea ice habitat change is available We summarized available data on abundance and trend for each AMM species and recognized subpopulation We also examined species diversity, the extent of human use, and temporal trends in sea ice habitat for 12 regions of the Arctic by calculating the dates of spring sea ice retreat and fall sea ice advance from satellite data (1979–2013) Estimates of AMM abundance varied greatly in quality, and few studies were long enough for trend analysis Of the AMM subpopulations, 78% (61 of 78) are legally harvested for subsistence purposes Changes in sea ice phenology have been profound In all regions except the Bering Sea, the duration of the summer (ie, reduced ice) period increased by 5–10 weeks and by >20 weeks in the Barents Sea between 1979 and 2013 In light of generally poor data, the importance of human use, and forecasted environmental changes in the 21st century, we recommend the following for effective AMM conservation: maintain and improve comanagement by local, federal, and international partners; recognize spatial and temporal variability in AMM subpopulation response to climate change; implement monitoring programs with clear goals; mitigate cumulative impacts of increased human activity; and recognize the limits of current protected species legislation

https://onlinelibrary.wiley.com/doi/pdf/10.1111/cobi.12474

Arctic marine mammal population status, sea ice habitat loss, and conservation recommendations for the 21st century.

The 2008 IUCN (International Union for Conservation of Nature) review of the status of the world’s mammals identified marine mammals (IUCN 2008) as disproportionally threatened and data poor compared to their terrestrial counterparts, and their status was noted as a particular concern (IUCN 2008, Mace et al. 2008, Schipper et al. 2008). The threats faced by marine mammals were identified as being different, with accidental mortality and pollution being dominant threats that superseded habitat loss, which was identified as the principal concern for land mammals. It was suggested that harvesting remained a major threat for half of the marine mammal species in the world. The distribution of marine mammals was described as being concentrated in tropical and temperate coastal platforms and associated with high levels of primary productivity. Threat levels were highest for marine mammals living in the North Atlantic, North Pacific and Southeast Asia. Range size was described as generally declining toward both poles. Although these generalities are of course correct for all marine mammals, it must be recognized that the larger number of species of cetaceans compared to other marine mammal groups (85 cetaceans, the polar bear Ursus maritimus, 4 extant sirenians and 36 pinniped species) biases the conclusions in the assessment for marine mammals to such a degree that a separate summary for the pinnipeds of the world is warranted. Additionally, a species-level assessment masks some important conservation concerns for pinnipeds with species classified as Least Concern actually containing threatened subspecies ( e.g., ringed seals). Finally, and perhaps most importantly, climate change issues were not specifically addressed in the vast majority of marine mammal assessments done for the 2008 IUCN review (IUCN 2008). We present here a complete assessment of the status and threats facing pinnipeds at the subspecies level, integrating the expected impacts of changing patterns of threat due to global climate change.

https://repositoriodigital.ipn.mx/bitstream/123456789/12836/1/kovacs_kit_m._2012_marine_mammal_science_3750.pdf

Global threats to pinnipeds

Female northern elephant seals, Mirounga angustirostris, from Ano Nuevo (AN) in central California feed offshore in mid-latitude waters (40°–55°N). Migratory patterns and foraging locations of seals from Mexico are unknown. Rookeries on San Benitos (SB) islands in Baja California Sur, Mexico, are ∼1,170 km south of AN. Although the colonies are similar in size, seals from SB begin breeding earlier and have an earlier breeding birthing peak than seals from AN. To determine if the foraging location of seals from Mexico was similar to that of seals from California, we measured δ13C and δ15N values in the hair of 48 suckling pups at SB and 37 from AN, assuming that their isotopic signatures reflected those of mothers' milk, their exclusive diet. The mean δ13C and δ15N values for SB pups (−16.1‰± 0.9‰ and 17.7‰± 0.9‰, respectively) were significantly higher than those for AN pups (−17.6‰± 0.4‰ and 15.6‰± 1.0‰, respectively). From data on environmental isotope gradients and known behavior of SB and AN populations, we hypothesize that the isotope differences are due to females in the SB colony foraging ∼8° south of seals from AN. This hypothesis can be tested by deployment of satellite tags on adult females from the SB colony.

Differences in foraging location of mexican and california elephant seals: evidence from stable isotopes in pups

Before, during, and after El Nino (EN) 1982–83, several aspects of California sea lion biology were being studied in the Gulf of California (Sea of Cortez) and the Pacific coast of Baja California, Mexico, as part of a long-term program initiated by representatives of Centro de Investigaciones Biologicas in 1978 (Aurioles et al. 1983; Le Boeuf et al. 1983; Aurioles and Sinsel 1988). The program involved monitoring the population distribution and abundance, estimating annual pup mortality rates, and estimating winter immigration rates of subadult males at major rookeries and resting sites. During winter, a large number of subadult males move into rookeries and resting sites on both coasts of the southern Baja California peninsula (Aurioles et al. 1983). These movements may be analogous to the northward movements of sea lions inhabiting southern California waters (Fry 1939; Mate 1975) which are associated with fluctuations in the distribution of Pacific hake (Merluccius productus; Ainley et al. 1982). Subadult males from the central Gulf may follow the southward fall-winter migration of the Monterey sardine (Sardinops sagax), the threadfin herrings (Ophistonema libertate, O. bulleri, and O. medirastre) and the mackerel (Scomber japonicus) which are the basis for sardine fishery in the Gulf (Aurioles, in press).

David Aurioles

Papers

Using Isoscapes to Trace the Movements and Foraging Behavior of Top Predators in Oceanic Ecosystems

Global threats to pinnipeds

Differences in foraging location of mexican and california elephant seals: evidence from stable isotopes in pups

Effects of the El Niño 1982–83 on California Sea Lions in Mexico