Written by: Stuart Caird, Master of Science (Environmental Science) student
As the ever-present and passionate voice of Dr Mike Joy once uttered, “Our waterways are in dire straits”[i]. Unfortunately for us, Dr Joy is not referring to the 70’s/80’s rock band……….
A recent Ministry for the Environment report on the health of New Zealand’s water systems does not make for pretty reading, specifically for lakes. Of allmonitored lakes, 44% are currently eutrophic (or worse); stretching to 84% for lowland lakes[ii]. These values are deeply disturbing.
Lake systems are a pivotal, natural, freshwater resource that hold significant cultural and social importance for many. Lakes are poorly understood and analysed ecosystems in the field of environmental science and ecology, more so in regard to their native fish species, particularly in New Zealand. This is frankly quite disconcerting.
Native species of fish act as natural regulators for freshwater lake systems. As vulnerable, delicate and fragile components of a lake ecosystem, their health and abundance can be used as an inference for overall lake health. Fluctuations in native fish populations can have severe implications for wider ecosystem response[iii] [iv]. Understanding the resilience mechanisms of native fish, particularly to natural and anthropogenically-induced changes, is thus of paramount importance to scientists and freshwater decision makers.
Resilience, what is that?
In an ecological sense, resilience refers to the capacity of an ecosystem to react to disturbance and maintain the same major structure and function[v] [vi]. See below for an illustration of the key concept that underpins resilience.
Why is this important?
The ecological resilience of lake systems, determines how intensely and rapidly organisms (as part of their wider lake ecosystem), respond to natural perturbations. Historically, these changes were driven by natural events or variations such as climate patterns, however, increasingly today, anthropogenic changes act as the key perturbators.
Where do native fish fit in?
Native fish typically have a narrow window of environmental tolerance; they cannot “handle the jandal” when it comes to (environmental) stress. Based on this assumption, understanding of their resilience to change should be straightforward, right?
Much has been made about the ability of native fish to cope with the introduction of foreign species, case and point in New Zealand, with the introduction of rainbow and brown trout and the impact on galaxiid species[viii] (as captured on camera below).
Despite their inherent lack of ability to adapt to environmental change, native species of fish often offer varying degrees of response to different, widespread environmental perturbations [x] ,3, 4.
Does this mean native fish are particularly stubborn to certain specific environmental stresses, but, are particularly inept at dealing with others?
Well, it would appear this way, at least based on the current pool of freshwater, science knowledge. Reviewing the current day understanding of native fish response to natural and more crucially, anthropogenic, changes, will bring into question their resilience; opening up a whole new can of “scientific worms”.
Watch this space. In the coming years, understanding of lake systems, resilience and native fish will prove truly fascinating. Of this I have little doubt.
Hopefully, this greater degree of knowledge will help to pave
the way forward for environmental policy makers in the not-so distant future!
[ii] Ministry for Environment. (2019). Environment Aotearoa 2019: New Zealand’s Environmental Reporting Series. Wellington, New Zealand.
[iii] Clapcott, J., Schallenberg, M., Kelly, D., Death, R., MacNeil, C., Young, R., … & Scarsbrook, M. (2011). Approaches to assessing ecological integrity of New Zealand freshwaters. Science for Conservation, 307, 84.
[iv] Schallenberg, Marc, Mary D. de Winton, Piet Verburg, David J. Kelly, Keith D. Hamill, and David P. Hamilton. “Ecosystem services of lakes.” Ecosystem services in New Zealand: conditions and trends. Manaaki Whenua Press, Lincoln (2013): 203-225.
[v] Holling, C. S. (1973). Resilience and stability of ecological systems. Annual review of ecology and systematics, 4(1), 1-23.
[vi] Folke, C., Carpenter, S., Walker, B., Scheffer, M., Elmqvist, T., Gunderson, L., & Holling, C. S. (2004). Regime shifts, resilience, and biodiversity in ecosystem management. Annu. Rev. Ecol. Evol. Syst., 35, 557-581.
[vii] Scheffer, M., Carpenter, S. R., Lenton, T. M., Bascompte, J., Brock, W., Dakos, V., … & Pascual, M. (2012). Anticipating critical transitions. science, 338(6105), 344-348.
[viii] McIntosh, A. R., McHugh, P. A., Dunn, N. R., Goodman, J. M., Howard, S. W., Jellyman, P. G., … & Woodford, D. J. (2010). The impact of trout on galaxiid fishes in New Zealand.
[ix] Harvie, W (2018). Beloved brown trout damage native fish, insects and waterways. Retrieved October 14th from https://www.stuff.co.nz/the-press/news/100983463/beloved-brown-trout-damage-native-fish-insects-and-waterways
[x] Naigaga, I., Kaiser, H., Muller, W. J., Ojok, L., Mbabazi, D., Magezi, G., & Muhumuza, E. (2011). Fish as bioindicators in aquatic environmental pollution assessment: a case study in Lake Victoria wetlands, Uganda. Physics and Chemistry of the Earth, parts A/B/C, 36(14-15), 918-928.