Research into pāua movement and their genetics supports Kaikoura’s fisheries

Image taken by Giulia Trauzzi.

Moana Project genetics and ocean circulation research is helping to piece together what has happened to the pāua populations in Kaikoura following the 2016 earthquake which greatly disrupted their habitat. 

In November 2016 the Kaikoura region experienced a series of significant earthquakes that caused large coastal uplift of up to six meters along 110 kilometers of coastline. This uplift led to extensive habitat modification and mortality of a wide range of species in the intertidal and subtidal zones. 

Pāua were particularly affected with very high mortality rates and the loss of a sizable number of their historically critical habitats. 

To protect the surviving pāua populations and associated habitats, a fishing closure was introduced in November 2016; this was lifted early last December for a three-month period for recreational and commercial fishers. On Monday the fishery closed again as officials look to assess the effects of the reopened fishery.  
 
The Moana Project is helping this effort, by examining the genetic connectivity of larval pāua in the area. Seafood Innovations PhD student Giulia Trauzzi is trying to identify source and sink populations. Source populations are habitats where numbers grow large enough to supply individuals to other areas, and sink populations are populations of pāua whose larvae settle there but have come from other locations (no self-recruitment). Sink populations may be large in numbers as well as the sources, however they only receive larvae, and they are maintained by other sites. 
 
Giulia explains “The ability of pāua to survive and adapt to a changing environment is strongly tied to the reproductive success of the offspring of those populations and how these are connected both physically and genetically. 

Losing a population of pāua at a site that is connected to another population further away would have less of an impact if the second population is the one that provides larvae to the first one, acting as a source.” says Giulia.  

“However, if a drastic change in the environmental conditions and/or spread of disease causes the loss of a source population, then there would be no more larval exchange between the two and the overall loss of individuals and correlated genetic variation will be significant. Less genetic variation means less ability to adapt to different environments.”  
 
Understanding how natural populations are connected genetically is key to learning how these populations can survive natural events, even catastrophic events such as the Kaikoura earthquake. This knowledge alongside a better understanding of oceanic processes such as circulation, can also help to reveal both the short - and long- term effects that these events have on the populations, especially in a fisheries management context.  

To complement this work, Moana Project PhD student Phellipe Couto is developing a wave-hydrodynamic model to better understand the coastal circulation offshore Kaikoura and the surrounding area.  

The model will characterise the patterns of coastal circulation over the past five years. This will help us understand how circulation controls the transport of material along the coast and from coast to the deeper ocean, taking into consideration changes in the seabed following the earthquake.   

Phellipe says, “the inclusion of post-earthquake bathymetric data (a 3D map of the seabed) and wave forcing into the hydrodynamic model provides a better representation of water circulation over areas associated with pāua habitats, especially since changes in the seabed impact shallow water circulation.” 

His research will also define the main drivers (oceanic and atmospheric processes) of the circulation, which is key for predicting water movement into the future. Phellipe explains: “the combined effects of the large-scale ocean circulation (water movement that takes place in deeper waters near the Kaikoura Canyon) with those closer to the coast, like tides and breaking waves, need to be well understood to accurately predict pathways of pāua larvae transport. 

By providing this background knowledge of the coastal ocean circulation we can support Giulia’s research by better understanding the effects of dispersion (the distribution of material over a wide area),” notes Phellipe, “and in turn inform pāua recovery strategies.”