Regular pinniped censuses at Año Nuevo Island, California, were initiated by our research group in 1967 to support studies of reproductive behavior of male elephant seals, Mirounga angustirostris.

Research on elephant seals at the colony has continued since, expanding to cover female behavior, reproductive success, physiology and energetics, migrations and foraging, and more. The other species of pinnipeds, Steller sea lion (Eumetopias jubata), California sea lion (Zalophus californianus), and harbor seal (Phoca vitulina), have been the focus of additional studies.

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Censuses were collected to support the wide range of research, but population size of has been an important topic as the elephant seal population expanded. We described the initial expansion to the mainland in 1975, and in 2011 described details of long-term growth and then stabilization of the breeding elephant seal population over the entire colony.

Año Nuevo has also been central to understanding the entire northern elephant seal population, which has recovered from a remnant population in Mexico after overhunting and continues to grow.

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The field notebooks in which censuses were recorded from 1967-2005 were saved. They are now archived at the University of California Santa Cruz library:

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UCSC Elephant Seal and other Pinniped Research records. UA 132. Special Collections and Archives, University Library, University of California, Santa Cruz.

Field counts of pinnipeds from high ground near the colony. Data were originally written into small notebooks, one census per day. These were transcribed into digital format and organized into a MySQL database over 2004-2006. After 2005, data were entered directly into this database via a web interface, and any paper notes used by observers were not stored. The data archived here was extracted from the MySQL database after the census of 25 May 2017.

Archive of all pinniped census results, Año Nuevo, California, 1967-2017

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Introduction

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Regular pinniped censuses at Año Nuevo Island, California, were initiated by our (BJL) research group in 1967 to support studies of reproductive behavior of male elephant seals, Mirounga angustirostris. The research expanded to include he other species of pinnipeds, Steller sea lion (Eumetopias jubata), California sea lion (Zalophus californianus), and harbor seal (Phoca vitulina), by the mid-1970s, and censuses included all the species from the beginning. When elephant seals colonized the mainland adjacent to Año Nuevo Island in 1975, research and accompanying censuses began on the Año Nuevo mainland.

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Daily censuses were carried out site-by-site, counting animals in groups on individual beaches, dunes, or rock outcrops. Besides counting the species separately, animals were also divided into various age and sex categories that could be distinguished visually. The island and two sections of the mainland (called the main point and the north point) were counted separately; sometimes one observer would cover both mainland sections in a day, but the island was always counted separately because crossing the channel by boat is time-consuming. This means that island censuses and mainland censuses were not routinely done on the same day, but in many cases they were.

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In the original census data, a single entry consists of one location, one category, a date, and a single count. Those original data include 352,702 of these individual records, on 3331 different days. This full table is provided here as Table 5.

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A more useful format of the data, involves summing animals by species and age-sex category over all locations on day: these are daily censuses, always however separated into the three main regions (island and two mainland sections). In these tables, a single row has summed counts of one species on one day in one of the three regions, with several columns separating age-sex categories. Those data are included here as tables 1a-1c and 2-4.

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Two more supporting tables and two supporting files are included in the archive. One table has abbreviations for individual locations (Table 6) and the other has abbreviations for age-sex categories (Table 7). There is a file with descriptions of the tables and all columns, and a pdf having more references, maps, and information about the original notebooks that held hand-written census data. The latter are now archived in the University of California, Santa Cruz, library. All files are listed below.

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MaFemalePupCensusArchive.tab Table 1a. Total daily counts of elephant seal females and pups.

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MaMaleCensusArchive.tab Table 1b. Total daily counts of elephant seal adult and subadult males.

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MaJuvCensusArchive.tab Table 1c. Total daily counts of elephant seal juveniles.

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EjCensusArchive.tabTable 2. Total daily counts of Steller sea lions.

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PvCensusArchive.tab Table 3. Total daily counts of harbor seals.

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ZcCensusArchive.tab Table 4. Total daily counts of California sea lions.

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FullCensusArchive.tab Table 5. Every individual count of one age-sex category at a single location on one day.

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CensusLocationArchive.tab Table 6. Table of location abbreviations, with coordinates of each.

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CensusAgeArchive.tab Table 7. Table of abbreviations for age-sex categories.

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Table Descriptions.txt. Descriptions of every table column.

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CensusArchiveTables.pdf. A pdf describing original notebooks, with maps of the Año Nuevo colony included.

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