Pup Growth of the Guadalupe fur seal, Arctocephalus townsendi.

THERYA, Abril, 2010 Vol.1(1): 75-90 DOI: 10.12933/therya-10-8 PUP GROWTH OF THE GUADALUPE FUR SEAL, Arctocephalus townsendi. Juan-Pablo Gallo-Reynoso1*, Ana-Luisa Figueroa-Carranza2 Abstract Pups of the Guadalupe fur seal were captured, marked with hair bleach, measured and weighed between two and four times during their first year of life, during three consecutive years (1991, 1992 and 1993) conforming a sample of 132 pups of both sexes. The following parameters were measured: standard length, body mass, and axilar girth, these were measured in the first hours to days of birth when the pup still had attached a soft umbilical cord, and at 40, 145 and 220 days after birth. Mean birth body mass was 4.9 ± 0.5 kg, n = 17 (males: 4.9 ± 0.4 kg, n = 7; females: 4.9 ± 0.5 kg, n = 10), mean length was 64.4 ± 4.3 cm, n = 17 (males: 67.2 ± 3.5 cm, n = 7; females: 62.5 ± 3.7 cm, n = 10). Growth was exponential to 145 days and stabilized to 220 days at weaning age (weaning takes place between February and March at 9-10 months of age), mean weaner’s body mass was 14 ± 2.8 kg, n = 13 (males: 13.7 ± 3.6 kg, n = 5; females: 14.3 ± 2.0 kg, n = 8) with a mean length of 89.4 ± 8 cm, n = 13 (males: 91.3 ± 8.5 cm, n = 5; females: 86.4 ± 6 cm, n = 8). Body mass was not significantly different between the sexes for the fur seal pups, although lengths were significantly different at birth and at several other stages. The curves of body mass-length relationship showed high variability, but nevertheless showed a high correlation, the body mass and length regression was significant (r2 = 0.7024, P < 0.001). Much of this variability is caused by the long foraging trips of the females. This leads to drastic changes in pup body mass due to rapid milk intake during a mean of 5.03 days of female attendance and major body mass loss during female absence of a mean of 11.5 days. Key words: Guadalupe fur seal, Arctocephalus townsendi, Isla Guadalupe, pup growth. Resumen Crías del lobo fino de Guadalupe fueron capturadas, marcadas con decolorante de pelo, medidas y pesadas de dos a cuatro veces durante su primer año de vida, en tres años consecutivos (1991, 1992 y 1993) conformando una muestra de 132 crías de ambos sexos. Se midieron los siguientes parámetros: longitud estándar, peso corporal y circunferencia axilar, estas fueron tomadas en los primeros días del nacimiento, cuando la cría aún tenía el cordón umbilical suave. Estas crías se midieron y pesaron a los 40, Centro de Investigación en Alimentación y Desarrollo. Unidad Guaymas. Carretera a Varadero Nacional km 6.6, Col. Las Playitas. Guaymas, Sonora 85480, México. E-mail: , autor corresponsal 2 Área de Protección de Flora y Fauna Islas del Golfo de California, Comisión Nacional de Áreas Naturales Protegidas. Isla Peruano, esquina Isla de la Rasa. Col. Lomas de Miramar, Guaymas, Sonora 85450, México 1 PUP GROWTH OF THE GUADALUPE FUR SEAL, Arctocephalus townsendi. 145 y 220 días después de nacidas. El peso promedio al nacimiento fue de 4.9 ± 0.5 kg, n = 17 (machos: 4.9 ± 0.4 kg, n = 7; hembras: 4.9 ± 0.5 kg, n = 10), la longitud promedio fue de 64.4 ± 4.3 cm, n = 17 (machos: 67.2 ± 3.5 cm, n = 7; hembras: 62.5 ± 3.7 cm, n = 10). El crecimiento fue exponencial hasta los 145 días en que se estabiliza hasta los 220 días, edad del destete (el destete sucede entre Febrero y Marzo a los 9-10 meses de edad). El peso promedio al destete para ambos sexos fue de 14 ± 2.8 kg, n = 13 (machos: 13.7 ± 3.6 kg, n = 5; hembras: 14.3 ± 2.0 kg, n = 8) con una longitud promedio de 89.4 ± 8 cm, n = 13 (machos: 91.3 ± 8.5 cm, n = 5; hembras: 86.4 ± 6 cm, n = 8). Los pesos para ambos sexos no fueron significativamente diferente para las crías. Sin embargo, las longitudes fueron significativamente diferentes al nacimiento y en otras etapas del crecimiento, por lo tanto, la curva de crecimiento de la relación peso-longitud mostró una gran variabilidad para las crías de ambos sexos a cualquier edad, a pesar de que no se encontró una alta correlación, la regresión del peso y la longitud fue significativa (r2 = 0.7024, P < 0.001). Esta gran variabilidad en el peso y la longitud se debe a los largos periodos de ausencia de las hembras durante su alimentación en el mar. Esto produce cambios drásticos en el peso de las crías debido a la rápida ingesta de leche durante un promedio de 5.03 días de atención por la hembra y una gran perdida de peso durante la ausencia de la madre que dura un promedio de 11.5 días. Palabras clave: Lobo fino de Guadalupe, Arctocephalus townsendi, Isla Guadalupe, crecimiento de las crías. Introduction Quantitative data on the growth rates of Arctocephalus townsendi pups are nonexistent, and there are few data available on pup and juvenile sizes from the stranding records (Roletto 1984; Webber and Roletto 1987; Hanni et al. 1997). There are several measurements of adult individuals in the field (Fleischer 1978; Gallo-Reynoso and Figueroa-Carranza 1996), but no one of this information relates to the increase of size and body mass until weaning in the wild. Studies of maternal strategies in Guadalupe fur seals (Figueroa-Carranza 1994; Gallo-Reynoso et al. 2008), Juan Fernández (Francis et al. 1998) and Sub Antarctic fur seals (Georges et al. 2001) show that pups of these three species are exposed to the longest periods of fasting of any otariid while the mother is feeding at sea. Mean duration of feeding trips of Guadalupe fur seal females was found to be 9.0 – 13.5 days (1992 and 1993 respectively with a maximum of 24 days), very long compared to other otariids previously reported (Gallo-Reynoso et al. 2008). The attendance period lasted 5.1 – 6.5 days (1992 and 1993 respectively). The 43.2% fat rich milk of Guadalupe fur seal females (Figueroa-Carranza 1994), is higher in energy density than that reported for other temperate species, and similar to that of the Sub Antarctic fur seal (Arctocephalus tropicalis) with a mean of 42.8%, (Georges et al. 2001) and the Juan Fernández fur seal with 41% (Francis et al. 1998; Georges et al. 2001). In general maternal strategies in fur seals are well known for the sub polar and tropical species, but not much is known about the maternal strategies of temperate fur seals (Schultz and Bowen 2004). Therefore it is interesting to inquire how the attendance pattern and milk energy content affects the growth and weaning size of Guadalupe fur seal pups living in an area of moderate 76 THERYA Vol.1(1): 75-90 Juan-Pablo Gallo-Reynoso, Ana-Luisa Figueroa-Carranza primary productivity in a temperate zone. The aim of this study is to describe male and female growth from birth to 220 days, weaning age, of pups born during three consecutive years (1991, 1992 and 1993). Methods Study area.- Isla Guadalupe (29°00’N, 118°15’30”W) is located 240 km west of Baja California, México. The island lies within the California Current, the average sea surface temperature is 18°C (range: 16°C spring, 20°C summer; Lynn and Simpson (...truncated)