Filippo Galimberti 1 & Simona Sanvito 2

Transcription

1 Filippo Galimberti 1 & Simona Sanvito 2 1 Elephant Seals Research Group 2 Dept. of Biology, Memorial University of Newfoundland Research on elephant seals of the San Benitos Islands Annual Report Address for correspondence: Via Buonarroti, Milano (MI) - Italy Phone/Fax fil_esrg@tiscali.it Copyright ESRG All Rights Reserved No part of this manuscript is to be reproduced in any form without permission

2 Study area and effort Field work was carried out from 07/12/2004 to 28/02/2005 on two of the San Benitos Islands, the central (SBM) and the west islands (SBO). A single visit of the east island (SBE) was carried out around the peak of the breeding season to count the number of breeding females and to check for the presence of individuals marked on the nearby islands. At SBO the study area included the majority of the coastline used by elephant seals, and 15 out of 17 breeding groups (about 95% of the breeding females) were monitored daily. The other two groups were counted at weekly intervals, to reduce the disturbance, because they occupy areas of high sea lion density. At SBM 11 out of the 18 breeding groups (about 60% of the breeding females) were monitored daily, and the remaining at weekly intervals. Research goals Field activities were targeted to the following research goals: - Long term monitoring of the demography and dynamics of the population - Follow up of the mark/re-sight experiment for the estimation of life history parameters and breeding strategies of individuals - Study of the effects of the local demography and socionomy on the male mating tactics - Study of the effects of the environmental constraints, including topography and microclimate on the male mating tactics - Determination of the genetic paternity of males adopting different mating tactics - Vocal communication between mothers and pups Field activities The following research activities were carried out during the field work by two principal investigators, two field technicians, and up to five field helpers. 1) Mark/re-sight experiment Animals were marked with one or two numbered tags (Jumbo Rototags, Dalton Supplies) placed by surprise in the inter-digital membrane of the rear flippers. A total of 2349 tags was deployed during the whole season, 1536 at SBM and 813 at SBO. We put 1432 tags on females (1017 at SBM and 415 at SBO), 788 tags on males (428 at SBM and 360 at SBO), and 129 tags on pups (91 at SBM 1

3 and 38 at SBO). A total of 601 males (412 at SBM and 189 at SBO) and 321 females (254 at SBM and 67 at SBO) were double tagged to estimate tag loss rates. To permit fast and accurate identification of individual during behavioral observations breeding individuals were also marked with hair dye or bleach. We dye marked 521 males (253 at SBM and 268 at SBO) and 1473 females (772 at SBM and 701 at SBO). Marks were re-sighted daily in the main study area, to build a database of individual breeding histories, and weekly in the whole island. 2) Demography Censuses of the study were carried daily by 2-4 operators, for a total of 84 days at SBO and 70 days at SBM. During each census, we counted the number of breeding females in each harem, and we identified the marked animals, recording the position, status, and condition. A weekly census of the whole islands was carried out weekly. In all we collected a total of 7402 daily records for males (3811 at SBO and 3591 at SBM) and records for females (5553 at SBO and 5792 for SBM). To estimate pup mortality the coastline of the study area was scanned daily looking for dead pups, and each of the them was marked with a yellow flag and removed from the breeding beaches to avoid double counts. Dead pups were scanned for external wounds and trauma. Towards the end of the breeding the season a full count of the weaned pups was carried in the whole island, covering all of its surface, to obtain an independent estimate of productivity. 3) Topography Topographic data was collected to: - map the coastline of the island and the position of the breeding beaches, to study of the effects of position on the microclimate of the beach - map the perimeter and calculate the area of the breeding beaches, to estimate female density and harem crowding - define accurate reference points to be used in the study of the spatial structure of harems (see below) Mapping was carried out using a GIS-grade GPS system, set up with ProMark X receivers (Magellan Corporation). One receiver, fitted with a multi-path resistant aerial, was used as base station, and its geographic location was accurately determined as the weighed average about 3 millions positions collected along the season. Two receivers were used as rovers to carry out the actual mapping of points and profiles. Points were surveyed collection a minim of 500 positions. Profiles of the coastline and beaches were surveyed using the mobile option of the GPS receivers. 2

4 Topographic data collected by the rovers was then processed using the reference files of the base station to improve accuracy using MStar software(magellan Corporation). We obtained the following topographic information: - a full coastline profile of the whole SBM island and a full coastline profile of the study area of the SBO island - maps of the 13 breeding beaches of SBM, at high and low tide, with at least two replicates for each beach; maps of the 11 breeding beaches of the main study area at SBO, again with at least two replicates for each beach - at SBM a total of 64 points were surveyed to provide to geo-references for laser telemetry data and digital imagery (see below), while at SBO technical problems hampered the collection of control points; we permanently marked these points and we expect to be able to survey them the next field work season - the locations of dataloggers used to study micrclimate (see below) were determined 4) Spatial structure of the social units To study the spatial structure of the population we used two different methods: - commercial, navigation-grade, GPS receivers (GPS 12, Garmin) - a three-dimensional laser positioning system (Laser Locator, Leica Geosystems) The GPS receivers were used to collect position data of the marked males during censuses. They provide enough precision to place males in a 10x10 m square grid. In all we collected GPS 8191 positions, 3915 at SBM and 4276 at SBO. Accuracy of positions, as determined from long term runs of a GPS located at a vantage points and connected to computer with GPS monitoring software, was rather high for such commercial-grade instruments, with a circular error always < 5 meters. The laser positioning system was used to accurately map animals in 3D coordinates (accuracy +/- 0.5 m) from the distance and without any disturbance of the individuals involved. This system permits to get information on the spatial structure of the social system at the same time of behavioral data collection, although this require the joint effort of at least two operators. Laser mapping was carried out during observation periods to determine: - the position of the female mass and the profile of the harems at the beginning, half, and end of the observation - the position of each males at 5 minutes intervals Position data was collected during a total of 24 observation periods. The same system was also used to map the position of females in the various harems with standard tide conditions, to determine the mean harem crowding. At SBM this mapping was carried out on all the harems of the study area 3

5 with more than 5 females during 12 consecutive occasions, at weekly intervals. At SBM we were able to carry out the laser mapping just once, at peak breeding, on all harems of the main study area. 5) Microclimatic data To collect microclimate data we deployed 15 dataloggers located on the main breeding beaches of the study areas, 10 at SBM and 5 at SBO. The position of each datalogger was chosen to be representative of the different topography and microclimate zones of the beach, and surveyed using GPS. Five dataloggers (Hobo H8 Pro, Onset Computer Corporation) collected data on air temperature and air humidity using the integrated probes at 30 seconds interval; five more loggers (Hobo H8 Temp/Ext) collected data on air temperature and soil temperature at 30 seconds intervals; the last five loggers (Hobo H8 Industrial) were fitted with two external probes, one high-accuracy probe for air temperature and one probe for soil temperature, and collected data at 40 seconds interval. Data was downloaded to computer for checking and storage at weekly intervals. Data from dataloggers is available for a total of 70 days at SBO and 67 days at SBM. To evaluate the wind chill effect a wind speed-and-direction sensor connected to a weather station logger (Hobo Microstation) was placed in central location of the study area at SBM. To evaluate the effect of solar radiation the same weather station logger was fitted with a silicon pyranometer sensor. These sensors collected data at 40 seconds interval for a total of 66 days. 6) Behavior Observation of behavior was carried out by 1-2 observers during standard observation periods of 2- hours length, 1050 for a total of periods (397 at SBM, mean 7.2 per day, and 653 at SBO, mean 8.9 per day). Observation periods were distributed among the harems of the study area, although more periods were carried on the biggest harem at both island, that were the main target of the spatial structure study. One to four harems were observed during each period. We recorded: - all agonistic interaction between males - all mating attempts and copulations - the activity of each marked male at 5 minutes interval In all, we observed social interactions between males (7311 at SBM and 3554 at SBO, note the much higher interaction rate at SBM) and 1595 copulations (1039 at SBM and 556 at SBO). 7) Collection of skin samples Skin samples (few grams in weight) were taken from the rear flippers of elephant seals using ear notchers or from the rump using biopsy heads mounted on a 2 meters pole. In all cases sampling 4

6 was accomplished by surprise without any kind of restraint or immobilization, and resulted in a modest and short term pain for the animal. Samples were preserved in pure ethanol. We collected a total of 1232 samples. At SBM we collected 263 sample of males and 424 samples of females. At SBO we collected 305 samples of males and 240 of females During the following season (2005/2006) samples will be collected from weaned pups of the females sampled in the previous season. 8) Mother pup-communication To study mother-pup communication we recorded vocalizations using portable digital recorders (DAT recorder TCD-D7 and TCD-D100, Sony Inc.) and a dynamic cardioid microphone (Sennheiser MD 441). We recorded a total of 440 DAT segments, 390 at SBO and 50 at SBM. Conclusion and future goals The field work of the season was very productive, and the employment of a large number of field helpers permitted to study of a large proportion of the breeding individuals on both islands. The harems included in the daily monitoring spanned a wide range of sizes, from few females to more than 350. The combination of the socionomic data collected in these harems, with the information on the topography, spatial organization, and micro-climate should greatly improve our understanding of the constraints acting on male mating tactics. The collection of skin samples, which was the most complex task, was accomplished in a rather balanced way on all study harems, although collection in largest and more crowded harems was complex. Anyway, the improvement of the collection protocol and the use of the biopsy head permitted to collect samples even in the biggest harem of SBM without much disturbance to the breeding animals. Now that we have collected samples from breeding males and females we need to get the samples from the pups. This will be accomplished during the next breeding season (December 2005-February 2006). The large effort put in the tagging of breeding females should permit to recognize mothers and sample pups in a rather number of cases, letting us assess paternity success of breeding males in rather accurate way, and taking into account the harem structure of the population. 5