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Parasite avoidance is increasingly considered to be a potential driving factor in animal migrations. In many marine and freshwater benthic fish, migration into a pelagic environment by developing larvae is a common life history trait that could reduce exposure to parasites during a critical window of developmental susceptibility. We tested this hypothesis on congeneric fish (family Galaxiidae, genus Galaxias) belonging to a closely related species complex sampled from coastal streams in southeastern New Zealand. Migratory Galaxias have larvae that migrate to pelagic marine environments, whereas the larvae of non-migratory species rear close to adult habitats with no pelagic larval phase. Both migratory and non-migratory fish are hosts to two species of skin-penetrating trematodes that cause spinal malformations and high mortality in young fish. Using generalized linear models within an Akaike information criterion and model averaging framework, we compared infection levels between migratory and non-migratory fish while taking into account body size and several other local factors likely to influence infection levels. For one trematode species, we found a significant effect of migration: for any given body length, migratory fish harboured fewer parasites than non-migratory fish. Also, no parasites of any kind were found in juvenile migratory fish sampled in spring shortly after their return to stream habitats. Our results demonstrate that migration spares juvenile fish from the debilitating parasites to which they would be exposed in adult stream habitats. Therefore, either the historical adoption of a migratory strategy in some Galaxias was an adaptation against parasitism, or it evolved for other reasons and now provides protection from infection as a coincidental side-effect.

Berm breaching of intermittently closed estuaries, either naturally or due to management practices, results in a physicochemical disturbance due to the flushing of water, material and biota into the ocean and the subsequent tidal influx. In 2007 and 2008 comparative and controlled studies were employed in three New Zealand estuaries: Sawmill Creek (46°04′S 170°12′E), Otokia Creek (45°57′S 179°20′E) and Kaikorai Lagoon (45°56′S 170°23′E), to investigate the impact of berm breaching on the hyperbenthic macroinvertebrate community in intermittently closed estuaries. Significant changes in community structure occurred in both the weekly comparative and the controlled studies (ANOSIM P<0.01). Furthermore, the catch per unit effort of both total and key invertebrate taxa significantly increased after breaching (ANOVA P<0.01). However, substantial numbers of individuals were expelled into the ocean (5,800 individuals, 20-min sample) while new taxa immigrated into the estuaries. Along with migration-related changes to community structure, berm breaches also resulted in the loss of ∼80% of inundated habitat and the concentration of existing populations. Consequently, the management of intermittent estuary connections to the ocean has implications for the ecology of individual, managed estuaries and also for regional coastal populations of epibenthic invertebrates.

Objective: To review the available evidence that examines the association between climatic and agricultural land use factors and the risks of enteric zoonoses in humans and consider information needs and possible pathways of intervention. Methods:The electronic databases PubMed, Web of Science and Embase and government websites were searched systematically for published literature that investigated the association of climatic and/or agricultural exposures with the incidence of the four most common enteric zoonotic diseases in New Zealand (campylobacteriosis, salmonellosis, cryptosporidiosis and giardiasis). ResultsThe 16 studies in the review demonstrated significant associations between climate, agricultural land use and enteric disease occurrence. The evidence suggests that enteric disease risk from environmental reservoirs is pathogen specific. In some rural regions, environmental pathogen load is considerable, with multiple opportunities for zoonotic transmission.Conclusions: Enteric disease occurrence in NZ is associated with climate variability and agricultural land use. However, these relationships interact with demographic factors to influence disease patterns.Implications: Improved understanding of how environmental and social factors interact can inform effective public health interventions under scenarios of projected environmental change.

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