Decline in New Zealand's freshwater fish fauna: effect of land use

Abstract

The number of New Zealand’s freshwater fish listed as threatened has increased since 1992 when the first New Zealand threat classification system list was compiled. In this study, temporal and land cover-related trends were analysed for data on freshwater fish distribution, comprising more than 20000 records for the 47 years from January 1970 to January 2017 from the New Zealand Freshwater Fish Database. The analysis included individual species abundance and distribution trends, as well as an index of fish community integrity, namely the Index of Biotic Integrity (IBI). Of the 25 fish species that met the requirements for analysis to determine changes in the proportion of sites they occupied over time, 76% had negative trends (indicating declining occurrence). Of the 20 native species analysed for the proportion of sites occupied over time, 75% had negative trends; 65% of these were significant declines and more species were in decline at pasture sites than natural cover sites. The average IBI score also declined over the time period and, when analysed separately, the major land cover types revealed that the IBI declined at pasture catchment sites but not at sites with natural vegetation catchments.

Threshold responses of riverine fish communities to land use conversion across regions of the world

“…One exception to this association was New Zealand, where fish community composition shifted rapidly to much lower threshold levels of agricultural (>1.5 times) compared to urban land use. Agricultural intensification is a well‐recognized cause of substantial loss of freshwater fish diversity in New Zealand (Joy, Foote, McNie, & Piria, 2019). This is driven, in part, by the fact that the native fish fauna is unique from other regions/countries in lacking both planktivorous and herbivorous species, and thus is particularly prone to agricultural‐induced alteration to habitat quality and primary productivity.…”

The influence of nutrient enrichment on riverine food web function and stability

“…New Zealand, like many developed countries, has experienced considerable decline in ecological health over the last 25 years—largely from eutrophication in lowland, agriculture‐dominated catchments (Foote et al., 2015; Joy et al., 2019; Julian et al., 2017; Larned et al., 2016). Exacerbations of existing nutrient enrichment and natural floods are two of the most common disturbances facing rivers.…”

“…High weighted averages would indicate a community with keystone species that are also sensitive to the given disturbance, which may mean that community is less stable to the disturbance than a community with a lower weighted-average. New Zealand, like many developed countries, has experienced considerable decline in ecological health over the last 25 yearslargely from eutrophication in lowland, agriculture-dominated catchments (Foote et al, 2015;Joy et al, 2019;Julian et al, 2017;Larned et al, 2016). Exacerbations of existing nutrient enrichment and natural floods are two of the most common disturbances facing rivers.…”

Trade-Offs Underwater: Physiological Plasticity of Rainbow Trout (Oncorhynchus mykiss) Confronted by Multiple Stressors

“…However, fish are not only exposed to predictable stress situations such as seasonal changes, but also to unpredictable stressors such as pathogens and man-made toxicants. A further reason to select fish for the present study on environmentally-induced resource trade-offs is because fish are particularly under pressure by global environmental change, and as a consequence, both their diversity and abundance are declining [37][38][39][40]. The environmental stressors that were applied to manipulate the resource status of the trout included: (1) limited food availability, as it occurs in a predictable seasonal way in temperate aquatic habitats, (2) a pathogen infection, as a booster of resource demand, both for the nutrition of the parasite and for the host immune response [41], and (3) exposure to a man-made contaminant.…”