Environmental determinants of fecundity and pup growth in fur seals

Brief description

This indicator is no longer maintained, and is considered OBSOLETE.

INDICATOR DEFINITION
The fecundity (pupping rates) of female fur seals and the growth rates of their pups relative to changes in sea surface temperatures (local primary production) in the vicinity of Macquarie Island.

TYPE OF INDICATOR
There are three types of indicators used in this report:
1.Describes the CONDITION of important elements of a system;
2.Show the extent of the major PRESSURES exerted on a system;
3.Determine RESPONSES to either condition or changes in the condition of a system.

This indicator is one of: CONDITION

RATIONALE FOR INDICATOR SELECTION
A highly negative correlation has been detected between sea surface temperatures in the vicinity of Macquarie Island and fur seal fecundity and pup growth. A dataset of over ten years has shown that autumn sea-surface temperatures are highly negatively correlated with female fecundity in the following breeding season.

Rather than the reproductive success in terms of fecundity and pup growth being seen simply as a correlate of SST and presumably ocean productivity, the measure is much more than this. What the dataset from the Macquarie Island fur seal populations is rather more unique, in that they indicate how environmental variability effects the reproductive success of animals at annual and lifetime scales. This is especially important as we can now show what impacts environmental/climatic phenomena such as the Antarctic Circumpolar Wave, and global warming will have on fur seals, and how changes in the environment may impact on the viability of populations. In this situation, the data clearly suggest that warmer ocean temperatures significantly effect the reproductive success of fur seals. Sustained warmer temperatures would therefore impose demographic constraints on populations.

DESIGN AND STRATEGY FOR INDICATOR MONITORING PROGRAM
Spatial scale: SST data are obtained from a 1 degree square just north of the island that represents the region in which most females obtain food throughout their lactation period.

Frequency: Data on the reproductive success of fur seals is to be collected annually.

Measurement technique: Each breeding season (November-January), the reproductive success of tagged females is monitored, including their pupping success, and the growth rates of their pups.

RESEARCH ISSUES

LINKS TO OTHER INDICATORS

Lineage

Progress Code: completed

Statement: This indicator is now OBSOLETE. These data are no longer archived in this location, and are therefore not up-to-date.

The Macquarie Island fur seal population consists of a marked, and largely known-aged population of fur seals. Each breeding season (November-January), the reproductive success of tagged females is monitored, including their pupping success, and the growth rates of their pups.

Data from surface chlorophyll A concentration indicates that cooler sea-surface temperatures are associated with great local production in the vicinity of Macquarie Island. Cooler SSTs therefore are likely to be indicative of greater primary production and food availability for seal populations. Autumn months (March-May) are a period when female fur seals begin their active phase of placental gestation (after 4 months delayed implantation), it is also a period when the energy demand of suckling pups are greatest (end of lactation for Antarctic fur seals). As a period of nutritional stress, environmental variability in food abundance is most significant at this time. SST appears to provide a simple and reliable indicator of the state of the environment at this time, and in fact can be used as a window to predict pupping success 6-7 months in advance of the breeding season.

Analysis of reproductive success and SST data over a number of years enables correlations between changes in regional oceanography and seal reproductive success to be assessed.