A matrix model and elasticity analysis for New Zealand's blackfoot pāua Haliotis iris

- A matrix population model for blackfoot pāua was developed and parameterised.
- Survival of largest adults was highly influential for population growth.
- Survival of smaller animals was more important in faster growing populations.
- Conservation and fishery management may benefit from focusing efforts on adult survival.

Whether used for conservation or fisheries planning, matrix population models can help clarify how to allocate conservation effort across a species life history. In this research we develop and analyse a matrix population model for the New Zealand blackfoot pāua (abalone) Haliotis iris. Preliminary calculations for one population of H. iris yielded a population growth rate (PGR) of 16%. However due to uncertain parameter values we trialled larval settlement rates that resulted in population growth rates (PGRs) from 0 to 17%. The results showed that specific knowledge about settlement rate and juvenile survival was unimportant for the relative influence of these life-history parameters on this deterministic matrix model. Survival of the larger adults consistently had the highest sensitivity and elasticity, however in a rapidly growing population survival of the smaller animals gained importance. Also, the somewhat arbitrary placement of the shell length division between the two classes of adults created changes, with larger classes having higher elasticities. In addition elasticity, (indicating effect on the population growth rate) was concentrated in the older adults. However sensitivity, (with its greater emphasis on evolutionary change) placed more emphasis on slightly younger adults. These findings suggest that survival of larger adult paua, which is the stage typically targeted for harvest, is a key factor in fishery productivity, restoration, and conservation of the species.