There are hundreds of thousands of fisheries-related mortalities of seabirds each year. Population trends for these species are highly influenced by changes in adult survival, their maximum growth rates are low, and little additional mortality can have a large impact on the population. As a result, many albatrosses and petrels are at risk of extinction, but limited demographic data makes it difficult to quantify the risk for many species. The goal of this research is to use population modelling tools to assess potential impacts with minimal data. In particular, the question of how much additional mortality a population can sustain is addressed when there is only knowledge of the adult survival rate, age at first breeding, and the number of breeding pairs.
In this thesis, a simple decision rule designed for marine mammals is applied to albatrosses and petrels. In order to use this rule, adult survival, age at first breeding, a minimum estimate of the population size, and the maximum growth rate of the population are needed. While estimation of adult survival is well developed, work was required to calculate the other values from available data. A simple population model was developed to extrapolate from the number of breeding pairs to the total population size (given survival and age at first breeding); the effect of variable fecundity rates on the calculation of generation time and the maximum growth rate of a population was examined, relative to an estimate that only requires survival and age at first breeding; and a method for estimating the age at first breeding using capture-recapture data was suggested that accounts for study duration and emigration, in addition to capture probability.
This work can help managers make better informed decisions when little is known about a population. For example, around 5,800 pairs of Gibson's albatrosses (Diomedea gibsoni) breed each year. Based on the work presented in this thesis, they may be able to sustain 1,000 - 1,200 additional mortalities per year. However, given concern about their conservation status, a mortality level below 100 - 120 is desired, and any mortality beyond that level suggests a need for more intensive management.
| Identifer | oai:union.ndltd.org:ADTP/243346 |
| Date | January 2009 |
| Creators | Dillingham, Peter W, n/a |
| Publisher | University of Otago. Department of Mathematics & Statistics |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://policy01.otago.ac.nz/policies/FMPro?-db=policies.fm&-format=viewpolicy.html&-lay=viewpolicy&-sortfield=Title&Type=Academic&-recid=33025&-find), Copyright Peter W Dillingham |
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