Fernando R. Elorriaga-Verplancken | Instituto Politécnico Nacional (original) (raw)
Papers by Fernando R. Elorriaga-Verplancken
The pygmy killer whale (Feresa attenuata) is one of the least studied cetacean species. It is a p... more The pygmy killer whale (Feresa attenuata) is one of the least studied cetacean species. It is a pan-tropical toothed whale not previously reported in the Gulf of California (GC). The aim of this study is to analyze the first sighting for this region in environmental and dietary terms. In October 2014, three pygmy killer whales were stranded and three others were sighted at sea in the Bay of La Paz, Baja California Sur, Mexico. We analyzed stomach contents and used skin samples from the dead individuals to evaluate stable isotopes of N and C. We found high δ 15 N (19.2 ± 0.2‰) and low δ 13 C (-16.5 ± 0.1‰) values, similar to those reported for other teuthophagous cetaceans in the GC. We also identified the remains of purpleback flying squids (Sthenoteuthis oualaniensis) in the stomach of the stranded individuals. The presence of tropical species, like the pygmy killer whale and probably the purpleback flying squid, appeared to be related to the anomalous SST in the GC in 2014, which was 1 to 1.5° C warmer than the same period during 2013. This highlights the importance of monitoring how environmental changes alter the composition and distribution of cetacean species and their prey.
RATIONALE: Stable isotope analysis can be used to obtain information on olive ridley sea turtles ... more 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 δ 13 C and δ 15 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 δ 13 C values and 0.8‰ for δ 15 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.
using fur from offspring to infer values for adult females and can be used in conjunction with ne... more using fur from offspring to infer values for adult females and can be used in conjunction with new Pinniped neonates are indirect indicators of their or existing data. The mother-neonate relationship mothers' foraging areas and the prey they con-should be considered with caution as variations sume. However, the isotopic difference between may arise from different factors, some of which neonates and their mothers is often unknown, pre-can be controlled. senting a substantial obstacle to our understanding of foraging behavior. In this study, we assessed the Key Words: Guadalupe fur seal, Arctocephalus isotopic differences between Guadalupe fur seal philippii townsendi, stable isotopes, mothers, (GFS) neonates and their mothers. Fur was samoffspring, isotopic variation pled from ten 1-mo-old GFS neonates and their adult female GFS mothers on Guadalupe Island,
The abundance of California sea lions (Zalophus californianus) (CSLs) and Guadalupe fur seals (Ar... more The abundance of California sea lions (Zalophus californianus) (CSLs) and Guadalupe fur seals (Arctocephalus philippii townsendi) (GFSs) from the San Benito Archipelago (SBA) was determined through nine monthly surveys in 2014–2015. Assessment of their foraging habits was examined based on the isotopic analysis of pups (maternal indicators) (SIAR/ SIBER-R). Environmental variability between 2014 and 2015 was also analyzed, in terms of sea surface temperature (SST) and chlorophyll (Chl-a) concentration. Both otariids reached their highest abundance in July of both years; however, relative to 2014, the 2015 survey showed a 59.7% decline in the total GFS abundance and a 42.9% decrease of GFS pups, while total CSL abundance decreased 52.0% and CSL pup presence decreased in 61.7%. All monthly surveys for both otariids showed a similar trend (>50% decrease in 2015). Compared to 2014, the 2015 GFSs isotopic niche was three times larger (2.0 in 2015, 0.6 in 2014) and the δ 13 C was significantly lower. CSLs also showed significantly lower δ 13 C and higher δ 15 N in 2015. Interannual segregation was greater for CSLs, and their pup body mass was also significantly lower during the 2015 breeding season (mean = 8.7 kg) than in the same season of 2014 (mean = 9.9 kg). The decrease in δ 13 C for both otariids reflected a more oceanic foraging; most likely associated with the decline in primary productivity in surrounding areas to the SBA, related to a higher SST caused by the 2015 ENSO, with a subsequent increase in foraging effort. These would explain the fewer observed individuals on land, especially pups, which showed diminished body condition (CSLs). This study highlights the importance of marine mammals as sentinel species that respond dynamically to changes in environment, providing valuable information on the effect of ENSO on pinnipeds in Mexican waters.
The pygmy killer whale (Feresa attenuata) is one of the least studied cetacean species. It is a p... more The pygmy killer whale (Feresa attenuata) is one
of the least studied cetacean species. It is a pantropical
toothed whale not previously reported
in the Gulf of California (GC). The aim of this
study is to analyze the first sighting for this region
in environmental and dietary terms. In October
2014, three pygmy killer whales were stranded
and three others were sighted at sea in the Bay of
La Paz, Baja California Sur, Mexico. We analyzed
stomach contents and used skin samples from the
dead individuals to evaluate stable isotopes of N
and C. We found high δ15N (19.2 ± 0.2‰) and
low δ13C (-16.5 ± 0.1‰) values, similar to those
reported for other teuthophagous cetaceans in the
GC. We also identified the remains of purpleback
flying squids (Sthenoteuthis oualaniensis) in the
stomach of the stranded individuals. The presence
of tropical species, like the pygmy killer
whale and probably the purpleback flying squid,
appeared to be related to the anomalous SST in
the GC in 2014, which was 1 to 1.5° C warmer
than the same period during 2013. This highlights
the importance of monitoring how environmental
changes alter the composition and distribution of
cetacean species and their prey.
Harbour seals (Phoca vitulina) and northern elephant seals (Mirounga angustirostris) are the only... more Harbour seals (Phoca vitulina) and northern elephant seals (Mirounga angustirostris) are the only phocid species found in
Mexico. There is evidence that harbour seals at other latitudes exhibit non-migratory behaviour; however, there is lack of
knowledge regarding this species’ movements in Mexico. In contrast, elephant seal migrations to high latitudes are documented. In order to analyse this behaviour in harbour seals, hair samples (N ¼ 19) were collected from weaned, or nearly weaned, pups on Natividad Island, Baja California (BC), during the 2013 breeding season (February). Lanugo samples (N ¼ 20) were also collected from elephant seal pups on the San Benito Archipelago (60 km north of Natividad) during the same season, providing information on maternal foraging during the last 4–5 months before sampling. Of the two species, BC harbour
seals had higher isotope values, reflecting their non-migratory behaviour. These differences may be due to the depleted
base values in the higher latitude foraging areas used by northern elephant seals relative to the areas around Natividad frequented
by harbour seals. A lower trophic position by elephant seals was considered but taken as an unlikely explanation for
this variation. Bayesian analysis confirmed the distinction, with a low overlap value (0.4) and different isotopic spaces (Phoca:
0.5, Mirounga: 1.6). Building upon previous studies of the trophic ecology of the two phocids that inhabit the region, we
provide new information by comparing the two species during the same season using the same tissue type sampled from individuals of similar age classes.
The California sea lion (CSL) and the northern elephant seal (NES) are the two most abundant pinn... more The California sea lion (CSL) and the northern elephant seal (NES) are the two most abundant pinniped species inhabiting the San
Benito Archipelago (Baja California, Mexico). This study reports the results of the first survey to gather abundance information from
continuous breeding seasons (2012–2015) and over the course of a single year (2014). Relative to the previous year, the abundance of CSLs
declined in July 2014; however, based on historical censuses, the colony at the archipelago was catalogued as “stable”. Intra-annually, the CSL
abundance was regulated by pups and adult females, which reached their peak during the breeding season (July). Moreover, we hypothesize that
subadult males from the west coast of Baja California enter the Gulf of California. The NES fluctuations were most affected by the breeding
season (February), when the number of pups and adult females peaked, and by the important presence of juveniles in May and September. The
NES colony at the archipelago was catalogued as “in decline”, based on previous countings. This high-resolution survey complements past and
future studies in the region, and adds another dimension to our understanding of these species, which is largely based on information from their
main rookeries in California.
This note constitutes the first report of the Guadalupe fur seal (Arctocephalus townsendi) for Oa... more This note constitutes the first report of the Guadalupe fur seal (Arctocephalus townsendi) for Oaxaca. This subadult male was found stranded ona beach in Cerro Hermoso, in the Lagunas de Chacahua National Park (PNLC). This record is highly relevant because the normal range for this furseal is farther north, in Guadalupe Island and a recolonization site in the San Benito Archipelago, more than 1,300 km from the stranding location.This is the southernmost report for A. townsendi and the first case for Oaxaca, increasing the number of known marine mammal species for thisarea in the Mexican South Pacific. Because of the current population growth of this otariid, we highlight the necessity of tracking these atypicalsightings over time.
AbstractRationaleIndividual foraging behavior is an important variable of predators commonly stud... more AbstractRationaleIndividual 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.MethodsWe determined the isotopic composition (δ13C and δ15N 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.ResultsThere 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 δ15N values of S. zygaena vertebrae, with lower values in the first group of samples.ConclusionsDespite 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. Copyright © 2015 John Wiley & Sons, Ltd.
Aquatic Mammals, 2014
of food resource with billfish species such as the sailfish, an abundant species in the MCP area.
Marine Biology, 2013
We assessed the foraging habits of California sea lions, Zalophus californianus, from Isla Santa ... more We assessed the foraging habits of California sea lions, Zalophus californianus, from Isla Santa Margarita, BCS, Mexico, by analyzing d 13 C and d 15 N values of dentin collagen. Since dentin is deposited annually in growth layer groups (GLGs), it can be subsampled to construct ontogenetic isotopic profiles at the individual level. We drilled 20 canine teeth and obtained 141 samples for isotopic analysis that were assigned to age-specific categories from GLG-based estimated ages. Pups' GLGs had the highest mean d 15 N values and the lowest mean d 13 C values, a pattern likely driven by the consumption of milk. Juveniles had d 15 N values between those of pups and adult females, which may reflect continued nursing into the second year or preferential consumption of coastal benthic versus pelagic prey. Significant differences were observed between the sexes of adults; adult females had lower mean d 13 C and d 15 N values than adult males. Higher isotope values in adult males relative to females may reflect a higher trophic position, but differences in foraging grounds cannot be excluded as a potential explanation because tracking data are not available at this time. Evidence of intra-specific foraging diversification may be related to a strategy to reduce competition within and among age and sex categories.
We present the first report of a neonate California sea lion near Manzanillo, Colima, Mexico, abo... more We present the first report of a neonate California sea lion near Manzanillo, Colima, Mexico, about 900 km
from the southernmost breeding colonies recognized for the species. The sighting occurred June 25th, 2011, and during
the 2 following days, in La Boquita beach. Near the site of the sighting, sea surface temperature (SST) was recorded.
SST values were some of the lowest recorded in the region (21-24° C), similar to the ones typically recorded in feeding
areas in the southern Gulf of California in winter (~20.9° C). California sea lion females give birth in summer and stay
close to their colonies where they feed their young during approximately one year. Thus, their feeding areas tend to
be confined within a radius of about 30 km from their colonies. This close relationship between breeding and feeding
make extralimital births important; the increasing knowledge regarding travel patterns of individuals may provide
better ways to analyze the species status and its future conservation
Biological Trace Element Research, 2008
The pygmy killer whale (Feresa attenuata) is one of the least studied cetacean species. It is a p... more The pygmy killer whale (Feresa attenuata) is one of the least studied cetacean species. It is a pan-tropical toothed whale not previously reported in the Gulf of California (GC). The aim of this study is to analyze the first sighting for this region in environmental and dietary terms. In October 2014, three pygmy killer whales were stranded and three others were sighted at sea in the Bay of La Paz, Baja California Sur, Mexico. We analyzed stomach contents and used skin samples from the dead individuals to evaluate stable isotopes of N and C. We found high δ 15 N (19.2 ± 0.2‰) and low δ 13 C (-16.5 ± 0.1‰) values, similar to those reported for other teuthophagous cetaceans in the GC. We also identified the remains of purpleback flying squids (Sthenoteuthis oualaniensis) in the stomach of the stranded individuals. The presence of tropical species, like the pygmy killer whale and probably the purpleback flying squid, appeared to be related to the anomalous SST in the GC in 2014, which was 1 to 1.5° C warmer than the same period during 2013. This highlights the importance of monitoring how environmental changes alter the composition and distribution of cetacean species and their prey.
RATIONALE: Stable isotope analysis can be used to obtain information on olive ridley sea turtles ... more 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 δ 13 C and δ 15 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 δ 13 C values and 0.8‰ for δ 15 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.
using fur from offspring to infer values for adult females and can be used in conjunction with ne... more using fur from offspring to infer values for adult females and can be used in conjunction with new Pinniped neonates are indirect indicators of their or existing data. The mother-neonate relationship mothers' foraging areas and the prey they con-should be considered with caution as variations sume. However, the isotopic difference between may arise from different factors, some of which neonates and their mothers is often unknown, pre-can be controlled. senting a substantial obstacle to our understanding of foraging behavior. In this study, we assessed the Key Words: Guadalupe fur seal, Arctocephalus isotopic differences between Guadalupe fur seal philippii townsendi, stable isotopes, mothers, (GFS) neonates and their mothers. Fur was samoffspring, isotopic variation pled from ten 1-mo-old GFS neonates and their adult female GFS mothers on Guadalupe Island,
The abundance of California sea lions (Zalophus californianus) (CSLs) and Guadalupe fur seals (Ar... more The abundance of California sea lions (Zalophus californianus) (CSLs) and Guadalupe fur seals (Arctocephalus philippii townsendi) (GFSs) from the San Benito Archipelago (SBA) was determined through nine monthly surveys in 2014–2015. Assessment of their foraging habits was examined based on the isotopic analysis of pups (maternal indicators) (SIAR/ SIBER-R). Environmental variability between 2014 and 2015 was also analyzed, in terms of sea surface temperature (SST) and chlorophyll (Chl-a) concentration. Both otariids reached their highest abundance in July of both years; however, relative to 2014, the 2015 survey showed a 59.7% decline in the total GFS abundance and a 42.9% decrease of GFS pups, while total CSL abundance decreased 52.0% and CSL pup presence decreased in 61.7%. All monthly surveys for both otariids showed a similar trend (>50% decrease in 2015). Compared to 2014, the 2015 GFSs isotopic niche was three times larger (2.0 in 2015, 0.6 in 2014) and the δ 13 C was significantly lower. CSLs also showed significantly lower δ 13 C and higher δ 15 N in 2015. Interannual segregation was greater for CSLs, and their pup body mass was also significantly lower during the 2015 breeding season (mean = 8.7 kg) than in the same season of 2014 (mean = 9.9 kg). The decrease in δ 13 C for both otariids reflected a more oceanic foraging; most likely associated with the decline in primary productivity in surrounding areas to the SBA, related to a higher SST caused by the 2015 ENSO, with a subsequent increase in foraging effort. These would explain the fewer observed individuals on land, especially pups, which showed diminished body condition (CSLs). This study highlights the importance of marine mammals as sentinel species that respond dynamically to changes in environment, providing valuable information on the effect of ENSO on pinnipeds in Mexican waters.
The pygmy killer whale (Feresa attenuata) is one of the least studied cetacean species. It is a p... more The pygmy killer whale (Feresa attenuata) is one
of the least studied cetacean species. It is a pantropical
toothed whale not previously reported
in the Gulf of California (GC). The aim of this
study is to analyze the first sighting for this region
in environmental and dietary terms. In October
2014, three pygmy killer whales were stranded
and three others were sighted at sea in the Bay of
La Paz, Baja California Sur, Mexico. We analyzed
stomach contents and used skin samples from the
dead individuals to evaluate stable isotopes of N
and C. We found high δ15N (19.2 ± 0.2‰) and
low δ13C (-16.5 ± 0.1‰) values, similar to those
reported for other teuthophagous cetaceans in the
GC. We also identified the remains of purpleback
flying squids (Sthenoteuthis oualaniensis) in the
stomach of the stranded individuals. The presence
of tropical species, like the pygmy killer
whale and probably the purpleback flying squid,
appeared to be related to the anomalous SST in
the GC in 2014, which was 1 to 1.5° C warmer
than the same period during 2013. This highlights
the importance of monitoring how environmental
changes alter the composition and distribution of
cetacean species and their prey.
Harbour seals (Phoca vitulina) and northern elephant seals (Mirounga angustirostris) are the only... more Harbour seals (Phoca vitulina) and northern elephant seals (Mirounga angustirostris) are the only phocid species found in
Mexico. There is evidence that harbour seals at other latitudes exhibit non-migratory behaviour; however, there is lack of
knowledge regarding this species’ movements in Mexico. In contrast, elephant seal migrations to high latitudes are documented. In order to analyse this behaviour in harbour seals, hair samples (N ¼ 19) were collected from weaned, or nearly weaned, pups on Natividad Island, Baja California (BC), during the 2013 breeding season (February). Lanugo samples (N ¼ 20) were also collected from elephant seal pups on the San Benito Archipelago (60 km north of Natividad) during the same season, providing information on maternal foraging during the last 4–5 months before sampling. Of the two species, BC harbour
seals had higher isotope values, reflecting their non-migratory behaviour. These differences may be due to the depleted
base values in the higher latitude foraging areas used by northern elephant seals relative to the areas around Natividad frequented
by harbour seals. A lower trophic position by elephant seals was considered but taken as an unlikely explanation for
this variation. Bayesian analysis confirmed the distinction, with a low overlap value (0.4) and different isotopic spaces (Phoca:
0.5, Mirounga: 1.6). Building upon previous studies of the trophic ecology of the two phocids that inhabit the region, we
provide new information by comparing the two species during the same season using the same tissue type sampled from individuals of similar age classes.
The California sea lion (CSL) and the northern elephant seal (NES) are the two most abundant pinn... more The California sea lion (CSL) and the northern elephant seal (NES) are the two most abundant pinniped species inhabiting the San
Benito Archipelago (Baja California, Mexico). This study reports the results of the first survey to gather abundance information from
continuous breeding seasons (2012–2015) and over the course of a single year (2014). Relative to the previous year, the abundance of CSLs
declined in July 2014; however, based on historical censuses, the colony at the archipelago was catalogued as “stable”. Intra-annually, the CSL
abundance was regulated by pups and adult females, which reached their peak during the breeding season (July). Moreover, we hypothesize that
subadult males from the west coast of Baja California enter the Gulf of California. The NES fluctuations were most affected by the breeding
season (February), when the number of pups and adult females peaked, and by the important presence of juveniles in May and September. The
NES colony at the archipelago was catalogued as “in decline”, based on previous countings. This high-resolution survey complements past and
future studies in the region, and adds another dimension to our understanding of these species, which is largely based on information from their
main rookeries in California.
This note constitutes the first report of the Guadalupe fur seal (Arctocephalus townsendi) for Oa... more This note constitutes the first report of the Guadalupe fur seal (Arctocephalus townsendi) for Oaxaca. This subadult male was found stranded ona beach in Cerro Hermoso, in the Lagunas de Chacahua National Park (PNLC). This record is highly relevant because the normal range for this furseal is farther north, in Guadalupe Island and a recolonization site in the San Benito Archipelago, more than 1,300 km from the stranding location.This is the southernmost report for A. townsendi and the first case for Oaxaca, increasing the number of known marine mammal species for thisarea in the Mexican South Pacific. Because of the current population growth of this otariid, we highlight the necessity of tracking these atypicalsightings over time.
AbstractRationaleIndividual foraging behavior is an important variable of predators commonly stud... more AbstractRationaleIndividual 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.MethodsWe determined the isotopic composition (δ13C and δ15N 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.ResultsThere 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 δ15N values of S. zygaena vertebrae, with lower values in the first group of samples.ConclusionsDespite 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. Copyright © 2015 John Wiley & Sons, Ltd.
Aquatic Mammals, 2014
of food resource with billfish species such as the sailfish, an abundant species in the MCP area.
Marine Biology, 2013
We assessed the foraging habits of California sea lions, Zalophus californianus, from Isla Santa ... more We assessed the foraging habits of California sea lions, Zalophus californianus, from Isla Santa Margarita, BCS, Mexico, by analyzing d 13 C and d 15 N values of dentin collagen. Since dentin is deposited annually in growth layer groups (GLGs), it can be subsampled to construct ontogenetic isotopic profiles at the individual level. We drilled 20 canine teeth and obtained 141 samples for isotopic analysis that were assigned to age-specific categories from GLG-based estimated ages. Pups' GLGs had the highest mean d 15 N values and the lowest mean d 13 C values, a pattern likely driven by the consumption of milk. Juveniles had d 15 N values between those of pups and adult females, which may reflect continued nursing into the second year or preferential consumption of coastal benthic versus pelagic prey. Significant differences were observed between the sexes of adults; adult females had lower mean d 13 C and d 15 N values than adult males. Higher isotope values in adult males relative to females may reflect a higher trophic position, but differences in foraging grounds cannot be excluded as a potential explanation because tracking data are not available at this time. Evidence of intra-specific foraging diversification may be related to a strategy to reduce competition within and among age and sex categories.
We present the first report of a neonate California sea lion near Manzanillo, Colima, Mexico, abo... more We present the first report of a neonate California sea lion near Manzanillo, Colima, Mexico, about 900 km
from the southernmost breeding colonies recognized for the species. The sighting occurred June 25th, 2011, and during
the 2 following days, in La Boquita beach. Near the site of the sighting, sea surface temperature (SST) was recorded.
SST values were some of the lowest recorded in the region (21-24° C), similar to the ones typically recorded in feeding
areas in the southern Gulf of California in winter (~20.9° C). California sea lion females give birth in summer and stay
close to their colonies where they feed their young during approximately one year. Thus, their feeding areas tend to
be confined within a radius of about 30 km from their colonies. This close relationship between breeding and feeding
make extralimital births important; the increasing knowledge regarding travel patterns of individuals may provide
better ways to analyze the species status and its future conservation
Biological Trace Element Research, 2008