Biogeography of Whitebait spawning grounds at non-tidal rivermouths

We recently published a study of īnanga (Galaxias maculatus) spawning grounds at non-tidal rivermouths in Pacific Conservation Biology. 

Article freely available here

Non-tidal rivermouths are common on the east coast of the South island and south-east of the North Island where they are commonly associated with high energy mixed sand-gravel beaches that form perched lagoons or hāpua at the rivermouth. 

At the outset of the study the spatial pattern of spawning in these environments grounds was unknown. Some of the interesting findings were that the location of spawning was close to the rivermouth despite the lack of salt water intrusion or tidal influence, both of which are associated with spawning grounds in tidal situations. 

A downstream fish migration evidently still occurs prior to spawning events and fish movements were surprisingly rapid in response to spawning cues in many instances. Spawning events are triggered by water level changes as occurs in tidal rivermouths, but appear to be more haphazard due to their origins being rain events rather than regular tidal cycles.Geographical aspects of the spawning locations were remarkably consistent across all seven study sites in key aspects such as the position in the catchment, relationship with water changes and presence of riparian vegetation. 

This provides a solid basis for identifying and managing spawning habitat in other non-tidal rivers. Effects we recorded included spawning on flood events that resulted in spawning grounds being located some distance from the active channel. As with tidal situations this places the eggs at risk from human activities in those same zones, but potentially presents a more difficult management proposition due to these events being less predictable. Their irregular nature suggests they are less likely to be accommodated in riparian zone planning and management. Importantly, the spawning grounds are located close to the peak water levels experienced on these events, which coincides with areas that are only briefly inundated. 

Recognising and protecting these emphemeral flood-zone areas is the key to effective conservation.

Read the full article here

Risk factors for coastal conservation revealed by the Canterbury earthquakes

We're pleased to announce publication of the companion paper to ‘Coastal tectonics and habitat squeeze’ in the international journal Science of the Total Environment.

Risk factors for the conservation of saltmarsh vegetation and blue carbon revealed by earthquake-induced sea-level rise

dx.doi.org/10.1016/j.scitotenv.2020.141241

This paper investigates the resilience of coastal vegetation to the effects of relative sea-level change which is the subject of very few empirical studies due to the scarcity of sea-level change events of appreciable magnitude in modern times. The novel opportunity provided by the Canterbury earthquakes allowed us to design a robust impact assessment to quantify effects and identify anthropogenic factors that influenced the pattern of losses or gains. 

The findings illustrate opportunities for managing risks to coastal vegetation types such as saltmarsh which are threatened by sea-level rise. 

The conservation of these characteristic ecosystems is of global importance for the sequestration and storage of blue carbon alongside many other ecosystem services that include considerable habitat values for characteristic wildlife such as waders and shorebirds in the Christchurch case.

In summarising results from the study we derived four key principles for building the resilience of coastal ecosystems that will be of interest to coastal managers worldwide.

Kaikōura earthquake recovery - loss of connectivity and the necessity of a cross‐ecosystem perspective

Article just published in Aquatic Conservation: Marine and Freshwater Resources from our Kaikōura earthquake recovery work.

The Kaikōura earthquake in southern New Zealand: Loss of connectivity of marine communities and the necessity of a cross‐ecosystem perspective.
https://doi.org/10.1002/aqc.3122

Stuff article on Kaikōura whitebait

Great article by Sophie Trigger at the Marlborough Express that features our recent work investigating earthquake impacts on river mouths along the Kaikōura coast.

We were able to locate several whitebait spawning sites and made some interesting discoveries with many of them occurring on flood events. Read more about an ecological experiment to rescue eggs stranded high on the riverbank with the help of the Environment Canterbury flood management team.
https://www.stuff.co.nz/environment/112863187/kaikura-whitebait-discovery-could-have-flowon-effects

Whitebait spawning in Lyell Creek Waikōau

Nice article in the Kaikōura Star on our surpise finding of whitebait spawning sites in downstown Kaikōura.

The spawning habitat in this area has benefitted from riparian restoration work in Lyell Creek / Waikōau since the earthquakes.

Whitebait spawning surveys in Kaikōura coastal rivers

This summer we've been working

to fill a knowledge gap about whitebait in streams and rivers along the Kaikōura coast. Knowing where they are is useful for recovery planning in the same areas post-earthquake as well as for restoration projects in local waterways.

Our survey programme started with fish trapping to find out which species were living in which rivers, after which we selected waterways that were suspected to have good īnanga populations. They included seven catchments close to Kaikōura (Oaro, Kahutara, Lyell / Waikōau, Middle, Swan, Harnetts and Blue Duck) as well as other sites in Marlborough. After four months of surveying we discovered at least one spawning event in all of these streams and rivers and were able to map the spawning locations including some large sites!