Climate change and the northern elephant seal (Mirounga angustirostris) population in Baja California, Mexico

Climate change impacts on seabirds and marine mammals: The importance of study duration, thermal tolerance and generation time

Understanding climate change impacts on top predators is fundamental to marine biodiversity conservation, due to their increasingly threatened populations and their importance in marine ecosystems. We conducted a systematic review of the effects of climate change (prolonged, directional change) and climate variability on seabirds and marine mammals. We extracted data from 484 studies (4808 published studies were reviewed), comprising 2215 observations on demography, phenology, distribution, diet, behaviour, body condition and physiology. The likelihood of concluding that climate change had an impact increased with study duration. However, the temporal thresholds for the effects of climate change to be discernibly varied from 10 to 29 years depending on the species, the biological response and the oceanic study region. Species with narrow thermal ranges and relatively long generation times were more often reported to be affected by climate change. This provides an important framework for future assessments, with guidance on response- and region-specific temporal dimensions that need to be considered when reporting effects of climate change. Finally, we found that tropical regions and non-breeding life stages were poorly covered in the literature, a concern that should be addressed to enable a better understanding of the vulnerability of marine predators to climate change.

Declines and recovery in endangered Galapagos pinnipeds during the El Niño event

Currently, the Galapagos sea lion (GSL, Zalophus wollebaeki) and Galapagos fur seal (GFS, Arctocephalus galapagoensis) are among the most important endemic species for conservation in the Galapagos Archipelago. Both are classified as "Endangered" since their populations have undergone drastic declines over the last several decades. In this study we estimated the abundance of both otariids, and their population trends based using counts conducted between 2014 and 2018 in all their rookeries, and we analyzed the influence of environmental variability on pup production. The GSL population size in 2018 in the archipelago was estimated to be between 17,000 to 24,000 individuals and has increased at an average annual rate of 1% over the last five years after applying correction factors. The highest number of GSL counted in the archipelago was in 2014 followed by a population decline of 23.8% in 2015 that was associated with the El Niño event that occurred during that year. Following this event, the population increased mainly in the northern, central and southeastern rookeries. The GSL pup abundance showed a decreasing trend with the increase in intensity of the El Niño. The GFS population in 2018 was counted in 3,093 individuals and has increased at an annual rate of 3% from 2014 to 2018. A high number of GFS counted in 2014 was followed by a population decrease of 38% in 2015, mainly in the western rookeries. There was interannual population fluctuations and different growth trends among regions of the archipelago. GSL and GFS pup abundance has a strong decreasing tendency with the increase in the subthermocline temperature (ST) and the El Niño 1 + 2 index. Our results provide evidence that both species are highly vulnerable to periodic oceanographic-atmospheric events in the Galapagos Archipelago which impact prey abundance and the flow of energy in the unique Galapagos ecosystem.

Causes of mortality in northern elephant seal pups on San Miguel Island, California

In February 2015, we conducted a field study of causes of mortality of northern elephant seal (Mirounga angustirostris) pups on San Miguel Island, California. Autopsies were performed on 18 freshly dead pups. Ages of pups ranged from stillborn to 6-8 wk. Gross and histologic lesions included trauma (9 of 18 pups), multifocal necrotizing myopathy (8 of 18), starvation with emaciation (7 of 18), congenital anomalies (3 of 18), bacterial infections (3 of 18), and perinatal mortality (stillbirths and neonates; 2 of 18). Trauma and emaciation or starvation were the most significant contributors to death. Bacterial infections included hemolytic Escherichia coli isolated from the lungs of 2 pups with pneumonia. Additionally, non-hemolytic Streptococcus sp. and hemolytic E. coli were isolated from the liver of an emaciated pup that had mild multifocal suppurative hepatitis. Other lesions, including a previously described necrotizing myopathy, congenital anomalies, and bacterial infections, were detected concurrently in cases with starvation and/or emaciation or trauma.

Male and female pups of the highly sexually dimorphic northern elephant seal (Mirounga angustirostris) differ slightly in body size

In mammals, males generally are larger than females, though such sexual-size differences have been documented primarily in adults and are relatively poorly known in early life. We studied sexual-size differences in pups of the northern elephant seal (Mirounga angustirostris (Gill, 1866)), which in adulthood is one of the most sexually dimorphic mammals. We studied body size at birth and weaning, at Islas San Benito, Mexico, at the southernmost limit of the species’ breeding range. Males were 10% heavier and 2% longer than females at birth. Sexes did not differ significantly in either measure of body size at weaning, although males were slightly heavier (4%) and longer (1%) than females. Neither growth rate nor suckling duration differed between the sexes. In previous studies in California, USA, pups at weaning were heavier than in our study, and males were heavier than females. These differences may reflect ecological, temporal, or life-history differences across populations. The modest difference in sexual-size dimorphism early in life in this species compared with the great difference in adulthood likely reflects multiple selective forces, including constraints on neonatal size set by body size of females, and the weakness of sexual selection at that stage of life.