Fernando R. Elorriaga-Verplancken

Population and individual foraging patterns of two hammerhead sharks using carbon and nitrogen stable isotopes

RATIONALE Individual foraging behavior is an important variable of predators commonly studied at the population level. Some hammerhead shark species play a significant role in the marine ecosystem as top consumers. In this context, stable isotope analysis allows us to infer some ecological metrics and patterns that cannot usually be obtained using traditional methods. METHODS We determined the isotopic composition (δ(13)C and δ(15)N values) of dorsal muscle and vertebrae of Sphyrna lewini and Sphyrna zygaena using a continuous-flow system consisting of an elemental analyzer combined with a Delta Plus XL mass spectrometer. Foraging variability by sex and by individual was inferred from the isotopic values. RESULTS There were no significant differences in the isotopic values of muscle samples between sexes, but there were differences between species. The trophic niche breadth of the two species was similar and overlap was low. A low niche overlap was observed between S. lewini individual vertebrae. We found differences in the δ(15)N values of S. zygaena vertebrae, with lower values in the first group of samples. CONCLUSIONS Despite these hammerhead shark species inhabiting the same area, there was low trophic niche overlap between species and individuals, due to different individual foraging strategies, according to the carbon and nitrogen isotopic profiles obtained. The use of tissues that retain lifetime isotopic information is useful to complement studies on trophic ecology.

Climatic anomaly affects the immune competence of California sea lions

The past decades have been characterized by a growing number of climatic anomalies. As these anomalies tend to occur suddenly and unexpectedly, it is often difficult to procure empirical evidence of their effects on natural populations. We analysed how the recent sea surface temperature (SST) anomaly in the northeastern Pacific Ocean affects body condition, nutritional status, and immune competence of California sea lion pups. We found that pup body condition and blood glucose levels of the pups were lower during high SST events, although other biomarkers of malnutrition remained unchanged, suggesting that pups were experiencing early stages of starvation. Glucose-dependent immune responses were affected by the SST anomaly; specifically, pups born during high SST events had lower serum concentrations of IgG and IgA, and were unable to respond to an immune challenge. This means that not only were pups that were born during the SST anomaly less able to synthesize protective antibodies; they were also limited in their ability to respond rapidly to nonspecific immune challenges. Our study provides empirical evidence that atypical climatic conditions can limit energetic reserves and compromise physiological responses that are essential for the survival of a marine top predator.

Isotopic effects of different preservation methods on scales of olive ridley sea turtles (Lepidochelys olivacea) from the Mexican Central Pacific

RATIONALE Stable isotope analysis can be used to obtain information on olive ridley sea turtles in the Mexican Central Pacific (MCP). Tissue samples such as scale, muscle, and blood are usually not analyzed immediately and are preserved in different substances such as ethanol, formalin, sodium chloride, the ideal being liquid nitrogen. Due to logistical reasons, the latter preservation method cannot always be used. The objective of the present study was to evaluate the efficiency of dimethyl sulfoxide (DMSO) as a preservation agent for later stable isotope analysis. METHODS Forty-eight paired scale samples of olive ridley were collected in MCP waters and preserved in DMSO and liquid nitrogen. We determined their δ13 C and δ15 N values using a Carlo Erba 1108 elemental analyzer coupled to a ThermoFinnigan Delta Plus XP isotope ratio mass spectrometer (precision ±0.2‰ for each stable isotope). The mean isotopic ratios of each preservation method were compared. RESULTS Significant differences were observed between the isotopic ratios of samples in the two preservatives. Samples preserved in DMSO resulted in more negative isotopic values than those in liquid nitrogen, and a correction factor was calculated. The correction factors were 2.1‰ for δ13 C values and 0.8‰ for δ15 N values. CONCLUSIONS DMSO is not equivalent to liquid nitrogen for the preservation of olive ridley scales to be used for isotopic analysis. If DMSO has to be used for logistical reasons a replicate sample should also be collected to be able to estimate a correction factor. Copyright

Insights into the Feeding Habits of False Killer Whales (Pseudorca crassidens) in the Mexican Central Pacific

The false killer whale (Pseudorca crassidens) is a widely distributed odontocete, and some aspects of its basic biology, such as feeding patterns at different time scales, are not well known. Stable isotope values (δN and δC) from the skin of ten false killer whales belonging to two distinct groups (A and B) sampled in October 2012 in the Mexican Central Pacific (MCP) were analyzed. Isotopic analyses were also run on muscle tissue from ten potential fish and squid prey species, some of which were extracted from billfish stomachs. Isotopic results for false killer whales showed mean values of 16.3‰ (Group A) and 17.0‰ (Group B) for δN, and -14.8‰ for δC (both Groups A and B). Fish and squid isotopic values showed a trophic discrimination factor in relation to those of false killer whales of +3.3 to 4.0‰ for δN and +2.9‰ for δC. This suggests that these whales probably fed within the study area on these prey species or on other species with similar isotopic values. Through photographic data, we identified individuals of Group B in the same area 2 mo later (December 2012) when they were observed feeding on fishes. One false killer whale from Group A had a fragment of billfish beak embedded in its body, indicating an interaction between these two species. Results suggest that false killer whales may share the same type of food resource with billfish species such as the sailfish, an abundant species in the MCP area.

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

The Earth′s climate is warming, especially in the mid- and high latitudes of the Northern Hemisphere. The northern elephant seal (Mirounga angustirostris) breeds and haul-outs on islands and the mainland of Baja California, Mexico, and California, U.S.A. At the beginning of the 21st century, numbers of elephant seals in California are increasing, but the status of Baja California populations is unknown, and some data suggest they may be decreasing. We hypothesize that the elephant seal population of Baja California is experiencing a decline because the animals are not migrating as far south due to warming sea and air temperatures. Here we assessed population trends of the Baja California population, and climate change in the region. The numbers of northern elephant seals in Baja California colonies have been decreasing since the 1990s, and both the surface waters off Baja California and the local air temperatures have warmed during the last three decades. We propose that declining population sizes may be attributable to decreased migration towards the southern portions of the range in response to the observed temperature increases. Further research is needed to confirm our hypothesis; however, if true, it would imply that elephant seal colonies of Baja California and California are not demographically isolated which would pose challenges to environmental and management policies between Mexico and the United States.

Mercury concentrations in three ray species from the Pacific coast of Baja California Sur, Mexico: Variations by tissue type, sex and length

Total mercury concentrations ([THg]) were determined in muscle and liver of the bat ray (Myliobatis californica), shovelnose guitarfish (Pseudobatos productus) and banded guitarfish (Zapteryx exasperata). Generalized linear models (GLM) were used to determine the effects of size and sex in [THg] and showed that both are determinants of [THg] in these species. The [THg] in both tissues significantly increased with length especially in sexually mature organisms with a steeper slope for mature male than mature female. This may relate to elasmobranchs sexual dimorphism driven variation in growth rates. Median muscle [THg] was significantly greater than liver in each ray species but there were some individuals with higher liver [THg] than muscle. There were individuals with muscle [THg] higher than the advisory thresholds of 0.2 and 0.5mgkg-1ww (2.4 and 11% of the bat ray; 2.1 and 10% of the shovelnose guitarfish; 12.6 and 45% of the banded guitarfish, respectively).

Population status of the Guadalupe fur seal (Arctocephalus townsendi)

The Guadalupe fur seal (GFS, Arctocephalus townsendi) was distributed on the islands of Baja California, Mexico, and southern California, United States. The species was intensively hunted during the 19th century, and in the late 1920s it was thought that it was extinct, but in 1954, a few animals were located on Isla Guadalupe, Baja California. Since the current status of the GFS population is unknown, we used counts of pups collected between 1984 and 2013 from Isla Guadalupe, which is still the only place where the species reproduces, and used Bayesian inference to assess both the population trend and abundance. The GFS population increased from 1984 to 2013 at an average annual growth rate of 5.9% (range 4.1–7.7%), and for 2013 the abundance was estimated between 34,000 and 44,000 individuals. The current abundance of the GFS represents about one-fifth of the estimated historical population size, and although the population has continued to increase, the species has not expanded its breeding range, which potentially affects its recovery.

Atypical Red Blood Cells Are Prevalent in California Sea Lion Pups Born during Anomalous Sea Surface Temperature Events

To date, there is limited knowledge of the effects that abnormal sea surface temperature (SST) can have on the physiology of neonate pinnipeds. However, maternal nutritional deficiencies driven by alimentary restrictions would expectedly impact pinniped development and fitness, as an adequate supply of nutrients is essential for growth and proper functioning of all body systems, including red blood cell synthesis and clearance. Here, we investigated red blood cell morphology of California sea lion (CSL) pups from the San Benito Archipelago born during the 2014 and 2015 anomalously high SST events recorded in the northeastern Pacific Ocean. We examined whether atypical erythrocyte morphologies were more common in 2015, when the high SST event was more pronounced, and whether the stable isotope signature of pup fur, as an indicator of maternal feeding strategies, accounted for the number of atypical cells. Various atypical erythrocyte morphologies were more prevalent and more abundant than reference values. Evidence of iron deficiency was found in both years, and only pups born in 2014 showed evidence of active erythropoiesis. Microcytes and reticulocytes were more common in pups with higher isotopic δ13C and lower δ15N values, suggesting a probable relationship between maternal feeding strategies and the effect of climatic anomalies on red blood cell physiology of their pups. As developing pinnipeds require increased oxygen storage capacity for diving and foraging, the presence of atypical erythrocytes could be relevant to CSL pup fitness if the underlying cause is not reverted. This study is a first step to explore the effects that climatic alterations in the marine environment can have on the blood physiology of developing individuals.