The Effects of El Niño on Pinniped Populations in the Eastern Pacific

Trillmich, Fritz; Ono, Kathryn A.; Costa, D. P.; DeLong, Robert L.; Feldkamp, Steven D.; Francis, John M.; Gentry, Roger L.; Heath, C. B.; LeBoeuf, Burney J.; Majluf, Patrícia; York, Anne E.

doi:10.1007/978-3-642-76398-4_27

Cited by 59 publications

(63 citation statements)

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“…drought) and associated declines in food availability (Moss, 2001). Declines in reproductive success have been associated with decreases in food availability in a number of pinniped species Trillmich et al, 1991;Trites, 1991;Lunn, Boyd & Croxall, 1994) and have been postulated to also occur in cetacean species (Lockyer, 1986(Lockyer, , 1987. While trade-offs between maintenance and reproduction such as those that occur in elephants may occur in the life-history strategy of female sperm whales, it is unlikely that such strategies would result in the age structure observed in this study.…”

Section: Age Structurementioning

confidence: 99%

The age structure and growth of female sperm whales (Physeter macrocephalus) in southern Australian waters

Evans

Hindell

2004

Journal of Zoology

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The age of 86 individuals derived from groups of female sperm whale Physeter macrocephalus involved in three mass strandings on the north and west coasts of Tasmania in 1998 was determined from the number of dentinal growth layer groups in the teeth of individuals. Dorsal total lengths were also measured. Ages of females ranged from 0.75 to 64 years, with the majority (77%) aged between 20 and 45 years. Total lengths of female sperm whales ranged from 417-1200 cm, with 68% of females 1050-1200 cm long. Constraints associated with the age structure observed in this study and the representativeness of the age structure to that of the greater population are discussed. In an effort to assess the effects of underestimation of age estimates on age-specific demographic parameters, a model simulating changes in age structure as a result of tooth wear was developed and the resulting survival rates compared to those derived from the original age structures of the samples. Survival did not change significantly between the modelled and original age structures. Also, the survival rate calculated from Australian mature female sperm whales was compared to that calculated from sperm whales caught in whaling operations from Japanese waters. Australian mature female sperm whales demonstrated significantly higher survival rates (mean = 0.905 ± 0.046 SD range: 0.856-0.986) than mature females from Japanese waters (mean = 0.885 ± 0.034 SD; range = 0.859-0.970), possibly the reflection of higher fishing mortality on the Japanese whales. Growth equations using Gompertz and von Bertalanffy models were calculated for female Australian sperm whales and compared. Both models described growth in female sperm whales similarly. Changes in the demographic parameters of sperm whales with the cessation of whaling may be reflected in the growth rates of individuals and as such, these equations may provide a useful tool for monitoring continuing changes in the demographic parameters of this species. Without long-term mark-recapture studies on sperm whales in this region, the frequent stranding of sperm whales in south-eastern Australia provides an important opportunity to collect data on the life history and demography of this species.

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Section: Age Structurementioning

confidence: 99%

The age structure and growth of female sperm whales (Physeter macrocephalus) in southern Australian waters

Evans

Hindell

2004

Journal of Zoology

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“…For example, lactating Antarctic fur seals (Arctocephalus gazella) have been shown to adjust the lengths of their trips in response to changes in krill abundance, making longer trips and expending more energy when prey were scarce and making shorter trips and spending more time ashore when prey were abundant (Costa et al 1989;Boyd et al 1994;McCafferty et al 1998;Boyd 1999). During the 1983 El Niño when prey were scarce, female South American fur seals (Arctocephalus australis), Galápagos fur seals (Arctocephalus galapagoensis), northern fur seals (Callorhinus ursinus), and California sea lions (Zalophus californianus) also made longer feeding trips than normal (Costa et al 1985;Trillmich and Limberger 1985;Ono et al 1987;DeLong and Antonelis 1991;Heath et al 1991;Majluf 1991;Trillmich and Dellinger 1991). This is also consistent with a more recent study which showed that lactating Steller sea lions at Año Nuevo Island in California spent more time at sea during a moderate 1992 El Niño (Hood and Ono 1997).…”

Section: Introductionmentioning

confidence: 99%

Maternal attendance patterns of Steller sea lions (Eumetopias jubatus) from stable and declining populations in Alaska

Milette¹,

Trites²

2003

Can. J. Zool.

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Maternal attendance patterns of Alaskan Steller sea lions (Eumetopias jubatus) were compared during the summer breeding seasons in 1994 and 1995 at Sugarloaf Island (a declining population) and Lowrie Island (a stable population). Our goal was to determine whether there were differences in maternal attendance between the two populations that were consistent with the hypothesis that lactating Steller sea lions in the area of decline were food-limited during summer. Our a priori expectations were based on well-documented behavioural responses of otariids to reduced prey availability. We found that foraging trips were significantly shorter in the area of population decline, counter to initial predictions. The mean length of foraging trips in the declining area was 19.5 h compared with 24.9 h in the stable area. In contrast, the mean perinatal period (time between parturition and first feeding trip) was significantly longer in the area of decline (9.9 versus 7.9 days), again countering initial predictions. The mean length of shore visits for the declining population was also significantly longer (27.0 h compared with 22.6 h where the population was stable). For both populations, the mean time that mothers foraged increased as pups grew older, whereas the time that they spent on shore with their pups became shorter. Behavioural observations of maternal attendance patterns are inconsistent with the hypothesis that lactating Steller sea lions from the declining population had difficulty obtaining prey during summer.

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“…In addition, the highest number of strandings in the USA during the 1990's was recorded during 1998, and approximately 46% were California sea lions (Le Boeuf, 2000). This coincides with a high sea lion mortality in different places and during different El Niño events (Trillmich and Limberger, 1985;Trillmich et al, 1991;Huber, 1991;Morris et al, 1999 6 ).…”

Section: Strandings Of California Sea Lions By Age Classes and Sexmentioning

confidence: 68%

“…In California, during the 1982-1983 El Niño, females stranded in higher numbers than males (Seagars and Jozwiak, 1991). Changes in prey distribution, depth and distance from shore also affect juveniles because they are less capable of reaching their food (Trillmich et al, 1991;Gilmartin and Eberhardt, 1995;Geraci et al, 1999). An indirect evidence of a decrease in prey abundance for the California sea lion during El Niño 1997Niño -1998 was the low catch of anchovies (Engraulis mordax).…”

Section: Strandings Of California Sea Lions By Age Classes and Sexmentioning

confidence: 99%

Occurrence and distribution of marine mammal strandings in Todos Santos Bay, Baja California, Mexico, 1998-2001

Bravo¹,

Heckel²,

Schramm³

et al. 2005

Lat. Am. J. Aquat. Mamm.

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ABSTRACT:The occurrence and geographic distribution of marine mammal strandings along Todos Santos Bay, Baja California, Mexico, were investigated from 1998 to 2001. The study was carried out along 30km of coast, divided into rocky and sandy shores. During the study period we responded to calls from the public about dead stranded marine mammals (SMM), and from March 1999 to December 2001 the coast was also monitored (211km total effort). A total of 153 SMM (90 from notifications, 63 from beach monitoring) from nine different species were recorded: 76% (n=117) were California sea lions (Zalophus californianus), the most abundant pinniped on the western coast of the Baja California Peninsula. Adult males stranded more often than other age and sex classes (P<0.05). The highest frequency of California sea lion strandings was located on sandy beaches (P<0.05) because carcasses may be deposited and remain more easily there than on rocky beaches. The 1998 El Niño event influenced stranding frequencies; most SMM were recorded during that year. As to seasons of the year, most SMM were recorded during spring; this may indicate a higher abundance of marine mammals in the area during this part of the year. Probable human-induced injuries were observed in 17% (n=26) of all animals. Most of these were Z. californianus (n=24), probably due to their known interaction with fisheries; 70% were males. RESUMEN:Se investigó la distribución espacial y temporal de los varamientos de mamíferos marinos en la Bahía de Todos Santos, Baja California, México, de 1998 a 2001. El estudio se realizó a lo largo de 30km de costa, dividida en costa rocosa y arenosa. Durante el periodo del estudio se respondió a llamados de la población sobre mamíferos marinos varados (MMV), y desde marzo de 1999 a diciembre de 2001 se hicieron monitoreos de las playas (211km de esfuerzo total). Se registraron un total de 153 MMV (90 de avisos, 63 de monitoreos) pertenecientes a nueve especies diferentes: 76% (n=117) fueron lobos marinos de California (Zalophus californianus), el pinnípedo más abundante en la costa occidental de la península de Baja California. Los machos adultos se vararon con más frecuencia que otras clases de edad y sexo (P<0.05). La mayor frecuencia de los varamientos de lobo marino de California se ubicó en playas arenosas (P<0.05), probablemente porque los cadáveres se depositan y permanecen más fácilmente ahí que en playas rocosas. El evento de El Niño en 1998 influenció las frecuencias de los varamientos; la mayoría de los MMV se registraron durante ese año. En cuanto a estaciones del año, la mayoría de los MMV se registraron durante la primavera; esto puede indicar una mayor abundancia de mamíferos marinos en el área durante esta temporada del año. Se observaron heridas de probable origen antropogénico en 17% (n=26) de todos los animales. La mayoría fueron Z. californianus (n=24), probablemente debido a su conocida interacción con pesquerías; 70% fueron machos.

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The Effects of El Niño on Pinniped Populations in the Eastern Pacific

Cited by 59 publications

References 0 publications

The age structure and growth of female sperm whales (Physeter macrocephalus) in southern Australian waters

The age structure and growth of female sperm whales (Physeter macrocephalus) in southern Australian waters

Maternal attendance patterns of Steller sea lions (Eumetopias jubatus) from stable and declining populations in Alaska

Occurrence and distribution of marine mammal strandings in Todos Santos Bay, Baja California, Mexico, 1998-2001

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