Most pinniped populations are monitored by surveys, by boat or aircraft, over a wide area of distribution. Such surveys are often carried out under the auspices of government departments, and may occur seasonally, annually or less often. Such surveys offer a broad picture of the population numbers, fluctuations and distribution of a species. Index site monitoring involves 'zooming in' on a particular site within an area.

This 'zooming in' or index site monitoring allows for more detailed monitoring of parameters of the seal's biology such as estimates of abundance from series of counts at the site, the social structure of seals at the site, activity budget of known or marked individuals, timing of pupping, location and habitat of birth sites, pup development and dispersal, site disturbance or other problems, etc. Index site monitoring should ideally be carried out as a continuous annual series, leading to a better understanding of how stable the use of a particular site is, how breeding at the site varies from year to year, and developing problems of conservation status. Index sites are probably chosen by virtue of their accessibility to regular observers and visibility of the animals from the shore or small boat. They may be a particular beach or set of rocks, or a cluster of sites along a small stretch of coast, or within a sea inlet. One site may not be the location for all aspects of the seals' annual cycle, e.g. a site might be used for pupping but not for moulting, or vice versa, and awareness of such limitations is important to evaluating index site data.  Nevertheless, with awarness of these caveats, index site information has immense value to understanding the natural history and local population dynamics within a larger population, and has the advantage that it may be carried out by individuals or natural history societies living locally.

Detailed monitoring of a seal site may be advisable at a particular site if local people should be concerned about local development, e.g. of a fish farm development in the vicinity of a seal haul-out or breeding area.

Any individual or group wishing to set up a local index site monitoring programme should contact the society, which is available for consultation on such a programme. The Society may be able to assist with the estalishment of the programme, identification of seals and interpretation of monitoring data. Any data forwarded to the Society will not be released on the website or shared with any 3rd party without the permisson of the data authors.