Foraging Behavior of Lactating Guadalupe Fur Seal Females
FORAGING BEHAVIOR OF LACTATING GUADALUPE FUR SEAL FEMALES
Juan Pablo Gallo-Reynoso!, Ana-Luisa Figueroa-Carranza2 and Burney J. Le Boeuf
J Centro de Investigaci6n, en Alimentaci6ny Desarrollo, A.C. Unidad Guaymas, Carretera a Varadero Nacional km 66, Col. Las Playitas, CP 85480 Guaymas, Sonora, Mexico, @ CE. jpgallo ciadmx 2 Area de Protecci6n de Flora y Fauna, Islas del Golfo de California, CONANP, Calle Isla del Peruano
la C . CP esquina Calle Isla de Rasa, ol Lomas de Miran/at: 85450 Guaymas, Sonora, Mexico, @ CE: afiguero conanp,gob.mx 3 Office for Research and Institute of Marine Sciences, 29 Clark Kerr Hall, 1156 High Street, University California, a i of Santa Cruz. C liforn a 95064 USA, CE: leboeu./@ucsc,edu
cer el comportamiento alimentario de las Resumen: El objetivo de este estudio fueel cono hembras de lobo fino de Guadalupe, Arctocephalus townsendi. Se obtuvo la localizaci6n en el mar de tres hembras adultas y el compOltamiento de buceo de una hembra adulta haciendo uso de instrumentos registradores del tiempo de buceo con localizaci6n geognifica(GLTDRs). Las hef!1bras se alimentaron en la Corriente de California al sur de la Isla de Guadalupe. La distancia media del viaje redondo fue de 2,375 ± 1,389 km. La distancia a la zona de alimentaci6n fue de 444 ± 151 km. El primer viaje de alimentaci6n fue de 10 ± 4 dfas. EI Segundo viaje de alimentaci6n fue de 19 ± 8 dias. Los viajes de alimentaci6n combinados promediaron 14.4 ± 8.3 dias, durante los cuales la velocidad del nado fu e de 1.9 ± 0.1 m/s. El tiempo de transito comprendi6 el 47.9%, el tiempo de buceo fu e de 36.2%, y el tiempo de descanso el 15.9%. El tiempo de alimentaci6n
(tiempo ocupado en la zona de alimentaci6n, que incluye tiempos de tninsito y buceo) fue el 75% de todo el tiempo pasado en el mar. La profundidad promedio alcanzada por una hem bra fue de 17 ± 10 m. La duraci6n promedio de los buceos fue de 2.6 ± 1.4 min. EI intervalo en superficieentre buceos fue de2 min. El tiempo de fondo promedio fuede 1.4 min. Los buceos estaban organizados en trenes de buceos; se registraron 23 trenes de buceos, con una duraci6n promedio por tren de buceo de 3:04 ± 2:30 h. El promedio de buceos por tren de buceo fue de 63 ± 60 buceos. La hembra buce6 durante la noche y transit6 durante el dia. Los buceos comenzaron tfpicamente alrededor de las 2030 h y terminaron alrededor de las 0530 h. EI patr6n de buceos y la distancia viajada por las hem bras lactantes para alimentarse es similar al de otras especies de lobos finos.
Palabras clave: Arctocephalus townsendi, Comportamiento de buceo, Isla Guadalupe, Lobo fr no de Guadalupe, localizaci6n en el mar, Mexico, viajes de alimentaci6n.
Abstract: The aim of this study was to elucidate the foraging behavior of female Gu adalupe fur seals, Arctocephalus townsendi. The location at sea of three adult females and the diving behavior of one adult female were obtained using geographic location time-depth recorders (GLTDRs). The fem ales fed in the California Cun'ent south of Isla de Guadalupe. Mean total
...... _ ...... Lorenzo, C., E. Espinoza y J. Ortega (eds.), 2008. Avances en el Estudio de los Aifamijerosde Mexico. Publicaciones Espeeiales, Vol. n, Asociaci6n Mexicana de Ma5tozoologfa, A, c.. Mexico, D. F. 596 Foraging of Guadalupe fur seal
distance traveled was 2,375 ± 1,389 km. Distance to feeding grounds was 444 ± 151 km. The first fe eding trip averaged 10 ± 4 days. The second fe eding trip had a mean duration of 19 ± 8 days. Feeding trips combined averaged 14.4 ± 8.3 days during which the swimming speed was 1.9 ± 0.1 m/s. Transit time accounted fo r 47.9%, diving time was 36.2%, and resting time was 15.9%. Tin1(� spent foraging (time spent in the foraging area which includes some transit and diving times) was 75% of all the time at sea. Mean dive depth of one female was 17 ± 10 m. Mean dive duration was
2.6 ± 1.4 min. Mean surface interval between dives was 2 min. Mean bottom time was 1.4 min. Dives were organized in bouts; 23 bouts were recorded with an average duration of3:04 ± 2: 30 h. Mean number of dives per bout was 63 ± 60 dives. This fe male dived during the night and tran sited during the day. Diving typically started around 2030 h and ended around 0530 h. The diving pattern and distance traveled by nursing fe males to forage is similar to that of other fur seals.
Key Words: Arctocephalus townsendi, Guadalupe fur seal, Diving behavior, foraging trips, Guadalupe Island, location at sea, Mexico.
INTRODUCTION
Until recently, migrations and fe eding areas used by pinnipeds were documented by the observa tion offree ranging individuals at sea. Sightings of stranded, marked or tagged individuals at non rookery locations (Condit and Le Boeuf, 1984) were used to describe migratory routes. Radiote lemetry was developed to locate animals and describe their distribution and movements while at sea, which provided recovery information (Loughlin et at., 1987). The development of micropro cessor based techniques has given new insight into the movements and dispersal of marine ma mmals (DeLong et aI., 1992) integrating sampling protocols on sensors to register simultaneously water temperatures, pressure and time, and storing data on electronic memory. Lately the use of satellite -micro transmitters and sensors has given new tools fo r the description of individual movements and dispersal over long distances and on water column movements. The aim of this study was to use microprocessor based techniques to describe the track, location, duration and diving behavior during foraging trips of lactating Guadalupe fu r seals Arctocephalus townsendi. The Guadalupe fur seal is an endemic and endangered species in Mexico, and is protected by
NOM-059-sEMARNAT-2001 (DOF, 200 I), the species was subject to heavy exploitation until its su pposed extinction at the beginning of the xx century, the species is making an extraordinary come back due to conservation efforts (Gallo-Reynoso, 1994). There are only two rookeries where this species breeds, the east side of Isla Guadalupe and the southeast coast oflsla San Benito del Este (Maravilla and Lowry, 1999). Single animals, however, have been observed at various islands and localities along the coast of Baja California and California (Stewart et al., 1987). Guadalupe fur seals are rarely seen at sea. Since) 967, there have been only three individuals seen and reported in the Southern California Bight (Brownell and DeLong, 1968; Bonnell et aI., 1980), fo ur at Southeastern Farallon Island (Hanni et aI., 1997) and one adult female at Point Lobos (Lander et al., 2000). Several Guadalupe fur seals have been observed in the Channel Islands (Stewartet at., 1987), including a newbornpup at San Miguellsiand (Melin and DeLong, 1999). Fur seal sightings at. 597 Gallo et
in Mexican waters include one seal in the open sea betweenIsla Guadalupe and Islas San Benito (Rice et aI. , 1 965), several fur seals on Isla Cedros and Islas San Benito (Cruz, 1986), one juvenile atIsl a Asunci6n (P. Pyle, pel's. comm., 1994), and several groups offe males over the continental shelf of Baja California, near Islas San Benito and Isla Cedros in July 2004 (J.P.G., personal observation). Some subadult males have been observed inside the Gulf of Cali fomi a at Los Islotes, Baja Califomia Sur, Islas Encantadas, Baja California (Maravilla, 1997), a fur seal stranded at Bahia Bacochibampo, Sonora (Aurioles et aI., 1993), a juvenile female that stranded alive on a beach near Zihuatanejo (Aurioles-Gamboa and Hernandez-Camacho, 1999), and a subadult male at the northernpo int of Isla San Pedro Nolasco. Sonora in May 2005 (lP.G., personal observa tion). These records show that Guadalupe fursea ls are capable of swimming long distances fr om their home rookery while fo raging at sea, but it is not clear where lactating females go to forage between nursing their pups on the rookery as well as the cost associated with nursing. Other furseals, like the northernfu r seal, Calforhinus ursinus, forage from100 km to 258 km or more from the PribilofTslands (Gentry and Kooyman, 1986; Robson et aI., 2004). Loughlin et al. (1987) reported a round trip of740 km by a nursing fe male from St. Paul Island. A distance of over 70 km has been recorded from radiotracked northern fur seal females off San Miguel Island (Antonelis et aI., 1990). Other northern fur seal females were observed at distances of 80 to 160 km fr om St. Paul Island (Goebel et aI., 1991). Australian fur seal females (A . pusillus doriferus) were observed at 100 km fromthe rookery over Bass Strait (Arnould and Hindell, 2001). Long distance movements of 2,300 to 2,740 Ianhave been reported in subantarctic fu r seals, A. gazella, in the Southern Ocean (Bester, 1989; Goldsworthy and Shaughnessy, 1989). A distance of more than 500 km from the rookery has been recorded for Juan Fernandez fu r seal fe males (Francis et al., 1998). In this paper we describe the foraging location of three Guadalupe fur seal fe males and their diving characteristics obtained with diving instruments and the implications that this has for the conservation.
METHODOLOGY
We instrumented seven lactating females with time-depth-Iocation recorders or GL.TDRS (DeLong et af., 1992; Hill, 1993). These fe males were depm1ing on their firstor second feeding trip after giving bir1h at Isla de Guadalupe in June-July 1992 and July 1993.
Female capture Females were captured early in the morning on days when the tide was low. Two people, each one carrying a hoop-net offme mesh nylon 1.5 m deep and 90- 120 cm diameter (Fuhrman Diver sified, Seabrook, Texas) crawled toward the chosen fe male keeping a low profile. One person netted the female while the other served as back up. Once captured, two other persons armed with
2.5 m white pine poles repelled attacks from territorial bulls. The female was taken outside the territory to reduce disturbance. 598 Foraging of Guadalupe fur seal
Immediately after capture the seals were weighed with a 100 kg industrial spring scale (Jogua Din, Basculas Nuevo Leon). Each animal was held on a restraining board with a detachable and neoprene-padded neck brace to prevent the animal from backing up (Gentry and Holt, 1982). Standard length (tip of nose to tip of tail) and other body measurements were taken (ASM, 1967). The general condition of the fe male was recorded as well as any scars or notches in the flippers (Gallo-Reynoso and Figueroa-Carranza, 1996).
Female condition "Pita", "Maya" and "Piri" were heavy, large and probably multiparolls fe males (mean weight
= 52.5 ± 1.8). "Cata" weighed 54 kg, and was probably a multiparous fe male but had no pup. "Lupe", "Atl" and "Rita", were small, slender and probably younger and less experienced than the other females (mean weight = 41.2 ± 1.3; Gallo-Reynoso and Figueroa-Carranza, 1996).
Instrumentation Afterclea ning a section ofthe dorsal furwit h acetone, an 8 cm wide plastic mold was placed on the dorsal midline of each female above the shoulders. The mold was filledwit h marine epoxy (Evercoat Ten-set, Fiber Glass-Evercoat Co., Cincinnati, Ohio) and the adhesive was worked under the hair, fo llowing the method of Le Boeuf et al. (1988) and Costa et al. (1989). Each female was instrumented with an Mk3e geolocation time-depth recorder (15 x 2.6 cm diameter, 136 g; Wildlife Computers, Woodinville, Washington) and a very high frequency (VHF) 150 g radio-transmitter (6 cm length x 2 cm diameter; 148-149 MHz; Advanced Telemetry Systems; Bethel, Milmesota). Approximate total weight of the instruments was 386 g. Attachment was by means of a stainless steel hose clamp glued into the marine epoxy. All subjects were marked with black dye (Nice'n Easy, Clairol, Ultra blue) or with white cream bleach (Wellite, Wella Corp., Englewood, New Jersey). While restrained, the animals were kept wet by pouring seawater over them and by keeping wet towels underneath them. Their heads were covered with a blue polyethy lene tarp to prevent injury to the eyes by the strong glare and sunlight. Time Depth Recorders sampling protocol was set at: depth every 30 seconds to obtain good descriptions of the dives, and water temperature (0C) every60 seconds. Condition: wet or dry. The mean number of geolocation readings extracted was 4,102 ± 2,135. The instrument internalclo ck was calibrated before and aftereach deployment. Softwarepr ovided by Wildlife Computers was used to download the data from the GLTDR to a lap-top computer for initial analyses.
Recovery of instruments Arrival and departure of fe males was monitored with a Te lonics Inc. (Mesa, Arizona) TR-2 scanning telemetry receiver, as well as by daily visual survey� of the rookery (Costa et at., 1989). Females were recaptured upon returnfr om feeding trips lasting 15-28 days. Animals were weighed and measured again, and the instrument and epoxy cradle removed. We applied waterproof, non fragrant, hypoallergenic baby sunblock lotion (spI" 29) to the exposed skin to prevent sunburn while the females were on land (Banana Boat, Sun Pharmaceuticals, Ltd.). New furwas observed at. 599 Gallo et
growing 8 days afterremov al. Two of the four fe males carrying GLTDRS were not relocated owing in part to the rough oceano graphic conditions prevailing during June to Augu st of 1992 an "El Nino" year. The first instru mented female never came back to her pupping site and her pup was lost by a combination of high surf and high tide on July 4. The other female was observed on the rookery nursing her pup on 8 July. We attempted unsuccessfully to recapture her. The female went to sea for a day and returned to nurse her pup for two more days then this fem ale departed on 11 July for a long second feeding trip of more than 28 days. Her pup was fo und dead on 9 August; the pup was emaciated with a weight of 4.7 kg below the mean weight of 5.2 ± 0.8 kg (n= 13) of a newborn pup. The female had not returned to the rookery when we left the island, but was observed the fo llowing breeding season (1993) with a pup. Two of the four GLTDRS were recovered but no dive data were logged due to a faulty salt switch. Nevertheless, we obtained geolocation data fr om these two GLTDRS.
During the breeding season of 1993, three fe males were instrumented with GLTDRS, only one of which was recovered. The first instrumented female did not return while we were present. Her pup was still alive and in good shape after 33 days of fa sting. The second instrumented fe male returned after 14 days at sea. This GLTDR was successfully recovered. The third instrumented fe male returned after 16 days at sea. Her behavior was erratic, coming and going from telTitory to territory,but never coming back to the ten'itoryin which she had given birth . She was last heard on the radio on 14 August to the south ofthe study area in a deep cave; we were not able to locate her.
Migratory path and travel speed Light level data provided estimates of the time of dawn and dusk from which an algorithm calculated position to within ± 1 degree in latitude and longitude (DeLong et at., 1992; Hill, 1993). Ambiguities in latitude were adjusted by matching sea surface temperatures (SST) recorded by the diving instrument to mean SST of the area compiled semi-monthly fr om satellites by the
National Meteorological Weather Service (Ashville, North Carolina; Le Boeuf el aI., 1993) . At sea locations were filtered,remo ving any unrealistic fixes of Latitude and Longitude in terms of the approximated rate of travel speed (2 m/s) for a seal of similar size and weight than a Guadalupe fur seal female. Position was plotted at daily intervals to calculate the m ean daily distance tra veled. Minimum travel speed was calculated as the distance in kilometers between two points, one at the beginning and one at the end of a segment of the track where the seal was traveling. Mini mum travel speed, mean daily distance traveled and total distance traveled by Guadalupe fur seal fe males were calculated by using marine chmts of the area (Secretaria de Marina, SM 010, Ensenada to Mazati Diving behavior Dive bout duration was defined following Gentry and Kooyman (1 986). Bouts were defined as diving sequences having no interdive intervals greater than 40 minutes and consisting offiveor 600 Foraging of Guadalupe fur seal more dives (a requisite that was necessary for calculating dives per hour). Transit times were measured from departure to the onset of the first dive bout, and from the end of the last bout to return onto the rookery (Gentry et aI., 1986a). RESULT S Location at sea During the first feeding trip, females showed a tendency to move to the northwest of Isla de Gu adalupe (Fig. 1). In the second feeding trip, females traveled to the south-southeast (Fig. 1). Mean maximum distance to feeding grounds was up to 444 ± 151 km (range: 222-589 km) from Isla Guadalupe. Mean total distance traveled was 2,375 ± 1,389 km (n = 4 of 3 females; one female made two trips, range: 704-4,092 km). Mean daily distance traveled was 171 ± 10 km/day (n = 4 of 3 females; one female made two trips, range: 157-179 km/day; Table I). This suggests that intensive feeding took place between Latitude 24°00 to 28°00, and Longitude 114°00 to 12 0°00. This corresponds to a foraging area of about 86,400 square nautical miles (160, 121 square km; Fig. 1). Sea surface temperature (SST) in these waters was in the range of 17.6°C to 22 .7°C. Feeding trip duration and nursing duration The firstfe eding trip of instrumented females had a mean duration of I 0 ± 4 days for females (n = 4, range: 4-14 days). The second feedillg trip had a mean duration of 19 ± 8 days (n = 4, range: 8-28 days). The difference in the mean values of the two trips was not statistically signifi cant (t-test, t = -1.266, d.f.= 4, P= 0.274). Larger females took shorter trips (mean = 13 ± 8 days, n = 4) than small females (mean = 28 ± 15 days, n = 4 of 3 females; Table 2). The difference in foraging trip duration of instrumented females (mean= 14.4 ± 8. 3 days, n = 7) versus non-instru mented females (mean = 11 ± 6 days, n = 46) was not statistically significant(t = 1.517, d.f.= 52, P> 0.05). There was no significant difference in the nursing duration of large females (mean = 4 ± 1 days, n = 4) and small females (mean = 4 ± 2 days, n = 4 of3 females; t = -0.166, d.f.= 7, P> 0.05). There was no statistical difference in fasting duration of pups of large instrumented fem ales (mean = 13 ± 8 days, n = 5 of 3 females) and small instrumented females (mean = 28 ± 15, n = 4 of3 females) while the mother was away (t = -1.944, d.f.= 7, P > 0.05). Similarly days spent attending pups for large instrumented females (mean= 4 ± 1, n = 5 of 3 females) and small instru mented fem ales (mean = 4 ± 2, n = 4 of3 females) was not significantly different (t = -0.166, d.f. = 7, P = 0.873). Travel Speed Mean travel or swimming speed of these females was 1.9 ± 0.1 mis, based on the mean daily distance traveled of 171 ± 10 km . al. 60] Gallo et 30 25 • MAYA <> OnJdlOleI'lhi., b(",ksi • PITA o Sympleet(}fcuthi,tlumirw,'o"a .to. PIRI o ])(J,�itJicu:;:gig(t'f 20 �------���------L------�--J 10 J25 120 1J5 110 Figure I. Location at sea of females "Pita" (solid square) , first and second foraging trip (28 June to 31 July, 1992). "Maya" (solid circle) first foraging trip (30 June to 18 July, 1992). And "Piri" (solid triangle) second foraging trip (18 July to 2 August, I 993), in relation to squid fishingareas in the Cal iforniaCurrent of Baja California. Table 1. Total distance traveled by adult Guadalupe fur seal fe males. Calculated by plotting the geolocation positions in a marine chart of the area (Secretaria de Marina, SM 010, Ensenada to Mazatlan). Female Days at sea Total distance traveled Daily distance traveled Estimated travel velocity (Ion) (Ion/day) (m/s) Pita • 4 704.2 176.1 2.0 24 4,092.0 170.5 1.97 Maya 14 2,508.6 179.2 2.1 Piri 14 2,196.5 156.9 1.8 Mean � 14 2,375.3 170.7 1.97 SD� 8.2 1,389.2 9.9 0.1 'Values of firstand second trip. 602 Foraging of Guadalupe fur seal Table 2. Trip duration and duration of attendance to pups of large and small females. Second row per female other trip duration or attendance duration while instrumented with GLTDRS. Large females Trip duration Attendance (days) Small females Trip duration Attendance (days) (days) (days) Pita 4 3 Lupe 42' 2 24 4 All 7 4 Maya 14 6 28' 3 Rita 33' 5 Piri 14 3 2 Cata 16 ., Mean = 12.8 3.5 Mean = 27.5' 3.7 SD= 7.6 1.4 SD= 14.8· 1.5 • Values as "non-present" during the length of stay on the study area . •• Value of the probable third feeding trip of this non-nursing female. Not used to estimate the averages. Diving behavior Diving behavior was recorded fo r one female ("Piri") during a foraging trip (July 19-2 Au gust, 1993). Time at sea was 347 h or approximately 14 days (Table 3). This provided a sample of 1,465 dives :::3 m, between 18 July and 2 August (Fig. 2). Mean dive depth was 17 ± 10 m (range: 3-82 m), modal dive depth was 3.1 m (Fig. 3A). Mean dive duration was 2.6 ± 1.4 min (range: 0.5- 18 min); modal dive duration was 0.6 min (Fig. 38). Dive duration tended to increase as dive depth increased showing a slight but significantcor relation (r = 0.48, d.f.= 1, P < 0.05). Shorter and shallower dives occurred at the beginning of the record as the animal traveled south to the foraging area, the frequency of dives greater than 20 m increased rapidly. The distri bution of dive depth was negatively skewed. Dives less than 20 m tended to be within the mixed Table 3. Activity patternsduring a trip to sea of a Guadalupe fur seal female in 14.5 days or 347 h (expressed in hours (h) and percentage of time), in a total of 1,465 dives. Mean Mean Total diving Total rest time Total transit Transit times dives per dives time time day per hour outbound inbound h % h % h % h % h % 101.3 4.2 125.5 36.2 55.2 15.9 166.3 47.9 98.3 59 68.3 41 n 23 11 29 14 15 al. 603 Gallo et HOllK Of' 1l1\ Y 11 U Il (t 12 (J 11 (I 12 U It (t 11 ., U • U Jl a II _'-_lInn _ ,. :g"D �t Q .. '"' 100 Figure 2. Plot of 1,465 dives made on one trip to sea by female "Piri" over a period of 14 days (18 July to 2 August). Sunrise was at -0611 and sunset at -2002. Times are local (8 h earlier than Greenwich Mean Ti me). Minimum dive depth8 plotted was 3 m. A 1 X= 16.9 6 �.C- . 0 � 0 I- !r: '" '-' 2 �"" 0 10 26 30 46 �5t) 2 llEl'Tli (.n) 0 II ADL�J.8 1 '\""r 15 �;;. -'Q <: l- e 10 I- � '" '-' '" '" .. j u J 7 �u Ill)RAT10N (mia) Figure 3. (A) dive depth frequency analysis for female "Piri" (x= 16.9 ± 10.3 m. n= 1,465 dives). Mode 3.1 m. (B) dive duration frequency (x= 2.6 ± 1.4 min, n= 1,465 dives). Mode 3.6 min. ADL= Aerobic Dive Limit. 604 Foraging of Guadalupe fur seal layer near the surface (0-30 m), whereas deeper dives broke through the mixed layer into subsur fa ce water (>30 m; Fig. 4A, 4B, 4C). The record during the foraging trip showed a strong daily cycle of diving activity, with a mean of 92 ± 49 dives per day (range: 6-168). This fe male increased the number of dives towards the end of the foraging trip (Fig. 2), reaching an average of 6 ± 3 dives per hour. Most dives occurred from dusk to dawn. Diving typically started around 2030 h and ended around 0530 h. Deep dives started abruptly, increasing in depth towards midnight. The deepest dives occurred at midnight, with dive depth declining after dawn (Fig. 4A, 4B, 4C.; Fig. 5). Mean surface interval between dives was 2 min (range: 0.5-38.5min) with a modal surface interval of 0.6 min. Surface intervals were skewed, with most of them lasting greater than 5 min. Mean bottom dive time was 1 min (range: 0-15.5 min); modal bottom time was 0.1 min. Bottom timeshowed a tendency to increase as dive depth increased (r = 0.25, d.f.= I, P < 0.05), although this relationship is non-significant. Dive was organized in bouts; 23 bouts were recorded with an average dw'ation of3:04 ± 2:30 h (range: 36'-6:26' h). Mean number of dives per bout was 63 ± 60 (range: 7- 173). The time between departure and the first dive bout was 35.05 h (10.1% of total time at sea), that is at 249 km from the island. The time between the last dive bout and return to shore was 11.18 h (3.2% of total time at sea), at 79 km (Table 4). Houn OF DAY 20 21 22 o 4 5 0 - � 23 'M llrrNNN-- --N""'·I"'-'r�W'�""�'rrv��, 22 21 20 �/- ___ ,- --�-��-l ------�� 20 40 19 A 18 60 17 20 21 22 23 o 3 "-U 0 23 � ! 22 :>: ;;> :c 20 ------21 t � w 20 '" Q "- 40 I'} I �:;: / 18 ;- 60 17 I I 0 23 22 20 21 20 4() 19 c 18 60 17 Figure 4. Exampl.es of different days on the dive record. Sunrise was at -0611 and sunset -2002 h. (A) crepuscular diving while transiting to the foraging area. (8) crepuscular and night diving at the middle of the foraging trip, the seal has reached the foraging area and starts its way back. (C) crepuscular, night and deep diving prior to the last two days foraging in a full moon night. af. 605 Gallo et N=J"(65 o 80 80 60 0 60 0 o l �<9 tg0 t 0 � 40 o� 00 0 20 o 4 8 12 16 20 24 LOC,\L TIMf, (HOUR OF DAY) Figure 5. Cumulative distribution of dives by hour of day by female "Piri" over a period of 14 days. Condi tions are similar to Figure 2. Table 4. Dive bout characteristics ora Guadalupe fur seal female in 23 dive bouts (J ,439 dives). Dives Dives per Bout Dives! h Time of bout Depth per Surface lnterbout excluded bout duration in bout underwater bout interval per interval (%) (h) (%) bout (min) (min) Mean Mean Mean Mean Mean Mean Mean (±SD) (±SD) (±SD) (±SD) (±SD) (±SD) (±SD) range range range range range range range 26 62.7 5.05 10.5 38 15 2.08 9.42 (\.8) (60.1) (4.05) (4.04) (26.9) (6.32) (4.5) (7.19) 7-173 0.6- 6.26 6-27 4-86.4 4.3-27.1 0.5-38.5 0.42-20.40 Note: includes all bouts that fit the dual criterion of including no interdive intervals >40 min, and including at least five dives. Note that bout duration does not equate with percentage of time spent diving. Effect of instrument There was no difference in the duration of the first trip (t = -0.632, df = 2, P> 0.05, n = 4) and the second trip (t = -1.185, d.f. = 7, P> 0.05, n = 9) of instrumented and non instrumented fe males. This was also the case for the second trip duration of instrumented and non instrumented females during the summer of 1993 (t = -0.241, d.f. = 14, P> 0.05, n = 16). Foraging of Guadalupe fur seal 606 ...... _ ...... _...... DISCUSSION Location at sea During the firstfe eding trip, females showed a tendency to move northwest ofIsla de Guadalupe against th e flow of the California Current (Fig. 1). In the second part of the fe eding trip, fe males traveled south-southeast (Fig. 1). They were probably taking advantage of the California Current, swimming south in a parallel direction to the Baja California Peninsula (Fig. 1), indicating a probable use of currents on their way south. Evidence of the utilization of oceanic CUlTents and gyres in A. gazellaand A. tropicalis has been reported by Rodriguez et al. (1993). The distance to fe eding grounds for this female in a straight line was approximately 444 ± 151 km from Isla de Guadalupe, greater than the distance traveled by two other furseals species: 160-200 km with a round trip of 400 km for C. ursinus (Loughlin et aI., 1987), and A. gazella that travel about 200 km to feed (Croxall et aI. , 1985), but similar to those of Juan Fernandez fu r seals of about 500 km (Francis et aI., 1998). At a certain point these females startedmo ving back, apparently taking more time and diving more often than on the way out from the island, suggesting that these females foraged against the flowof the California Current. Even though this is a single case, the return of one female was probably tTiggered by the full moon of August 2, 1993, as suggested by Trillmich and Mohren (1981), who found that Galapagos fur seals peaked with about twice as many animals on land near full moon, than near the new moon with a minimal number of seals. Comparing with a rehabilitated non-pregnant Guadalupe fur seal adult female (Lander et aI., 2000) that was instrumented with a satellite Time Depth Recorder (SLTDI�)on January 1998 (post El Nifio year), the trip of this female was irregular, the fe male swam to Bahia San Quintin, Isla de Guadalupe and further north to the Latitude of Mendocino County, a 2,890 km, longer than the mean total distance of2,375 kmof the three nursing fe males from Guadalupe. Due that this was a non-pregnant or nursing female its track during winter might give us some idea of where Guadalupe fur seals females forage in EI Nino conditions while they are not breeding. Preliminary analysis of24 scats and vomits show that Guadalupe fur seals feeds on vertically migrating squid (Onychoteuthis banksi, 0. boreal-japonica, Eucleoteuthis luminosa, Dosidicus gigas, Stenoteuthis ovalensis, Histioteuthis heteropsis, Symplecoteuthis luminosa, Pterygioteuthis giardi and Loligo opalescens), unidentified myctophid fishes found in shallow depths at night, and of epipelagic Pacific mackerel (Scomber japonicus) and frigate mackerel (Auxis thazard; Gallo-Reynoso, 1994; Gallo-Reynoso et al., 2000). These squids and fishes are all found in the CaliforniaCu rrent about Isla Guadalupe, Islas San Benitos and Isla Cedros, and the continental shelf of Baja California in the area were these fe males feed. The species found in their diet has been repOlted by oceanographic research cruises and fishing records (Young, 1972; Okutani, 1980; Allen et al. , 1995; Roper et aI., 1995). Feeding trip duration and nursing duration Feeding trips of instrumented females versus non i nstrumented females show that female trip Galloet at. 607 duration was not affected by the instrument, as was affected by the female condition in which larger females did shorter trips than smaller fe males, even though larger fe males spent the same time attending their pups as smaller females, this suggest a more efficient energy allocation by the larger females than the smaller ones. Foraging trips were similar or longer in duration than those of Juan Fernandez fur seal females described by Francis et al. (1998). The mean fo raging trip duration of Guadalupe fur seal non-instrumented females during the 1992 EI Nino was 9 ± 6.4 days (n = 55 trips of 18 females; Figueroa-CatTanza, 1994). In post EI Nino 1993, when oceanographic conditions were approaching nornlal, non-instrumented female's foraging trips were longer, mean= 13.5 ± 7 days (n = 31 trips of29 females; Figueroa-Carranza, 1994). ln other otariids El Niiioco nditions increase the duration of foraging trips (A. australis, A. galapagoensis, C. ursinus at San Miguel Island, and Zalophus californianus; Limberger et aI. , 1983; Trillmich et aI., 1986; Trillmich, 1986; Costa et aI. , 1991; DeLong and Antonelis, 1991; Feldkamp et aI., 199 1; Heath et aI., 1991; Majluf, 1991; Trillmich, 199 1). Our data shows that during EI N iiloconditions the trips were not affected during the breeding season, while in the post El Nino conditions the trips were longer. Our data might be related to the northward shifton the distribution of fo od either geographically or in the water column wh ich can explain the difference in foraging effort by these females. Travel speed The mean travel speed of 2 mls fo und in these three females is sim ilar to that reported for northern fur seals of 2.06 mls (combining outbound and inbound travel speed from Loughlin et aI., 1987) and only marginally faster than Galapagos fur seals of 0.6- 1.9 mls measured with velo city meters (Ponganis el a1., 1990). Guadalupe fur seal females travel speed is well within the minimum cost of transport(MeT ) of2.1 mls (Gentry et aI. , 1986b; Feldkatnp, 1987), for an otariid seal with a mean weight of 52.5 ± 1.8 kg. Mean travel speed of2 ml sec is not only similar to other otariids but also to phocids like elephant seals (Le Boeuf et aI., 1993). Diving behavior The diving characteristics of the fe male are broadly similar to those described fo r female Antarctic fur seals, A. gazella (Croxall et al., 1985; Kooyman and Trillmich, 1986; Boyd and Croxall, 1992), for female Galapagos fur seals, A. galapagoensis (Kooyman and Trillmich, 1986), fe male South American fur seals, A. australis during lactation (Trillmich et aI. , 1986), to seasonal diving shown by female New Zealand fur seal, A. Jorsteri (Mattlin, 1993), and female Juan Fernandez fur seals (Francis el aI., 1998). But they are different from those of northernfu r seals, C. ursinus that show individual specialization on shallow and deep dives (Gentry et aI., 1986b; Goebel el aI., 1991). Gentry et af. (l986b) calculated the aerobic dive limit (ADL) for fur seals of different body sizes and, using their prediction equation fo r the ADL based on body mass, the predicted ADL for the 53 kg female in th is study was 3.8 minutes. The predicted ADL was exceeded by this female in 15% of all dives (Fig. 3B), sug-gesting that lactic acid (LA) may accumulate during diving. One dive of 608 Foraging of Guadalupe fu r seal 18 min was recorded, which was 4.7 times the predicted ADL. It is not unusual for a certain percen tages of dive duration to exceed ADL; this has been noted in many species (Feldkamp et aI. , 1989; Pongan is et al. , 1990; Boyd and Croxal 1996; Costa et al. , 1996; Costa and Gales, 2000). Theoretically this fe male was capable of diving deeper than the deepest dive shown on the record (82 m). Assuming that she dived vertically during deep dives, swimming speed did not normally exceed 1.5 m/s. Based on this swimming speed and a theoretical ADL of3.8 min (Gentry et aI. , 1986b; Boyd and Croxall, 1992), the maximum depth for aerobic dives by Guadalupe fu r seals would be 174 m. The diving record suggests that dives occurred in bouts separated by extended periods spent at the surface, possibly in transit. This has been suggested fo r other species of the genus Arc/ocephalus (Gentry et aI. , 1986b; Boyd and Croxall, 1992). The geolocation method suggests that this particular seal, instead of spending time resting at the surface (or physiological "reco very" periods), was transiting to fo raging areas. Williams et al. (1992) hypothesized a similar strategy for the gentoo penguin, Pygoscelis papua. Transit to fo raging areas showed repeated short dives from surfa ce to one or two meters during the daily long surface intervals, suggesting that this fe male was clearing LA concentration with repeated short dives within the ADI.. Castellini et al. (1988) reported a similar result for Weddell seals in which LA declined rapidly as if th e seal were at the surface. Effect of instrument Attached instruments may affe ct the overall performance of seals. Nearly 17% reduction in swim speed of California sea lions, Z. californianus, was fo und by Feldkamp (1987), and Feldkamp et al. (1989). Foraging trip metabolic rate increased by 19% in northern fur seals harnessed with TORS (Costa and Gentry, 1986). However, these studies used TORS with twice the cross-sectional area and three times the mass of the instruments used in this study; furthernlOrethey were attached with harnesses, which increased drag. This suggests that our instruments had minimal effects on diving behavior and or distance traveled. During the summer of 1992, there was no difference between the firstan d second trip dura tion of instrumented and non instrumented fe males of similar weight. Similarly, during the sum mer of 1993, there was no diffe rence in trip duration of instrumented and non instrumented fe males during the second trip (Fig. 6). Similarly, Boyd et al. (1991) fo und no sign ificant difference in fo raging trip duration and time spent ashore between Antarctic fur seals with and without TORS. Studies in other diving species have shown none or little effect(Wilson et aI. , 1986). Croxall et al. (1988), Gales et al. (1990) and Kooyman et al. (1992) fo und no significant difference in fo raging trip duration or mass of prey brought ashore between instrumented and non-instrumented pen guins using similar or greater devices (cross sectional area and mass) to the TORS used in th is study. Results show that instrumented Guadalupe fur seals with geolocation time depth recorders can render high quality data on the diving behavior and fo raging trips at sea. The traveling dis tance, the fo raging area and its in situ characteristics give a wider view of the biogeographic implications fo r the conservation of a vulnerable and highly dispersing species, pointing to new Gallo et at. 609 Figure 6. Time Depth Recorder attached to the back of a Guadalupe fur seal fe male. The fe male is nursing her pup upon arrival fr om a fo raging trip; note the territorial male to the left. directions on the effective conservation of a species and the location and characteristics of their foraging area, which should have some level of management to protect the food and the feeding habits of Guadalupe furse als in their oceanic habitat over the California Current to warrant their survival. ACKNOWLEDGMENTS We are indebted to Direccion General de Intercambio Academico-UNAM, to Education Abroad Program, University of California,The National Geographic Society, the Institute of Marine Sci ences, University of California Santa Cruz, and uc-Mexus fo r fu nding the different expeditions. Thanks are given to P. Thorson for helping in the fieldin 1992, and to D. Costa for lending us the capture nets and a VHF radio-receiver. We are gratefulto R. Hill from Wildlife Computers for lending us 2 TORS for this study. We also thank A. Delgado, M. Peralta and A. Sanchez for their help in the field. We are gratefulto Secretaria de Marina and to fishermen of "Cooperativa de Langosteros y Abuloneros de Ensenada" which provided logistic support on the island. These field studies were conducted under permits No. 0561 ofSecretarfa de Pesca, and Nos. 2538, 4933 and 2025 of Secretaria de Desarrollo Urbano y Ecologia, (now SEMARNAT) Mexico. LITERATURE CITED Allen, G. R. et af. (and 39 other authors). 1995. Peces oseos. 1n Guia /'A()para fa identificaci6nde especies para losfines de fa pesca. Pacificocentro-oriental. 2: 800-1200. Fischer, w.,F. Krupp, W. Schneider, C. Sommer, K. E. Carpenter and V. H. Niem (eds.). 2:800-1200. 610 Foraging ofGuadalupe fur seal ...... •...... •...... _ ...... - ...... _ ...... _ ...... Antonelis, G. A., B. S. Stewart and W. F. Perryman. 1990. 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