Network analysis of wildlife translocations in New Zealand.
OBJECTIVE
To identify network measures with relevance to disease spread in a network of movements derived from the Department of Conservation (DOC) translocation records from 1970 to mid-2014, and to identify conservation sites that should be prioritised for surveillance activities and improvements to data collection to make the best use of network analysis techniques in the future.


METHODS
Data included the source and destination of translocated specimens, the species and the dates the translocations were expected to occur. The data were used to construct a directed, non-weighted network in which a translocation event represented a tie in the network. Network density, in-degree (movements entering a node of interest) and out-degree (movements leaving a node of interest) and reciprocity were calculated.


RESULTS
The data analysed consisted of 692 unique translocations between 307 sites, with the majority (518; 73%) being for birds. The constructed network for bird, reptile and frog translocations comprised 260 nodes, with 34/260 (13%) having two-way movements and 47/260 (18%) non-reciprocal movements. The median degree score (sum of in- and out-degree) was two (min 0, max 36) with a mean of 3.5 in a right skewed distribution. Most sites acted as receivers or senders of consignments with only a few having both high in- and high out-degree, and thus had characteristics that made them sites of interest for surveillance activities. These included the National Wildlife Centre at Mount Bruce, Tiritiri Matangi Island and Te Kakahu (Chalky Island).


CONCLUSIONS
The presence of linking sites that join larger clusters within the network creates the potential for rapid disease spread if a pathogen were to be introduced. The important sites that supply or receive specimens for translocations are already well recognised by those performing translocations in New Zealand, and this paper provides further information by quantifying their role within the network.
a Ministry for Primary Industries , Investigation & Diagnostic Centres and Response Directorate PO Box 40742, Upper Hutt 5140 , New Zealand.
M
M
Van Andel
b Department of Conservation , PO Box 10420, Wellington 6011 , New Zealand.
K
K
McInnes
a Ministry for Primary Industries , Investigation & Diagnostic Centres and Response Directorate PO Box 40742, Upper Hutt 5140 , New Zealand.
T
T
Tana
c mEpiLab, Infectious Disease Research Centre , Institute of Veterinary, Animal and Biomedical Sciences, Massey University , Palmerston North , New Zealand.
N P
NP
French
D000820:Animal Diseases / Q000453:epidemiology; D063147:Animal Distribution; D000818:Animals; D000835:Animals, Wild; D001001:Anura / Q000502:physiology*; D001717:Birds / Q000502:physiology*; D003247:Conservation of Natural Resources; D008954:Models, Biological; D009520:New Zealand; D011159:Population Surveillance; D012104:Reptiles / Q000502:physiology*
Network analysis; biosecurity; conservation; data integrity; disease transmission; translocations