| Summary: | Progress Code: onGoing Statement: Two different methodologies have been employed to collect these data. From 1988 to 2004 a full census of all colonies on the island were conducted each year between the 13th and 17th of October - details of which are presented below. From 2005 onwards, owing to diminishing resources, a decision was made to only census a representative sample of the southern elephant seal colonies on the island. 5 colonies were selected as being representative of the whole island. Further information about this 'partial' census can be found in a word document available for download from the URL given below. In the data graphs displayed below, the 'Full Census' graph present data collected between 1988 and 2004 using the full census method. The 'Partial Census' graph present data from 1988 onwards using the partial census method - for the period 1988-2004, the figures for the 5 colonies used in the partial census have been obtained from the full census data. Full Census Method: Female Elephant seals haul-out to pup on island beaches according to a very regular pattern (Gaussian or Normal distribution) and timetable (peak haul-out between 13 and 17 October). They group together in 'harems' with a few associated dominant males and are readily counted due to their obvious locations on open beaches and their lack of movement once ashore and having pupped. Thus counts of females can be made accurately to within +/- 5%. The counts of the adult females (cows), fully weaned pups and dead pups are summed daily, and separately, through October for the west and east isthmus beaches. These totals represent the time distribution of numbers of cows ashore for each of these beaches. Corrections to the census totals are made in two stages: Firstly, Gaussian curves are fitted to these distributions by least-squares calculations. From the equation to the curve for the west isthmus, the day of maximum numbers is determined as the calculated mean day. If the day of maximum numbers is not October 15, then the total ...
|
|---|