Shawn Gerrity1, David Schiel1, Spencer Virgin1
1University of Canterbury, New Zealand
The 2016 Kaikōura earthquake in southern New Zealand was a large-scale disturbance with complex ecological effects. Coastal uplift affected inshore rocky reef communities, including populations of blackfoot abalone (pāua, Haliotis iris), a species of high cultural and commercial value. Mortality of pāua, damage to obligate habitats, and concerns over recruitment failure necessitated a fishery closure to facilitate recovery.
Pāua and habitats were surveyed at 26 sites for 7 years to assess earthquake effects and population recovery. Results showed high spatiotemporal variability in pāua abundance and population structure. Juvenile pāua density quadrupled in 3 years due to prolific post-earthquake reproduction, and populations shifted to larger sizes in the absence of harvest. After 3 years juveniles emerged from intertidal habitats and moved into subtidal adult aggregations likely at the onset of maturity. A widespread increase in recruitment and adult biomass enabled the reopening of substantial commercial and recreational fisheries after 5 years of closure. Generalised linear models tested for effects of time, site, degree of coastal uplift, and habitat on pāua abundance. These indicated lasting negative earthquake effects, especially at the most damaged sites where gravel inundation inhibited recovery.
Relative to international examples of poor recovery of abalone populations from disturbance and overfishing, the rebuilding of Kaikōura’s pāua fishery was exceptional. Sufficient survival of spawning biomass, recovery or replacement of habitats, an intact life cycle, and a fishery closure all aided recovery. However, excessive recreational harvest of pāua since the re-opening may reduce the population’s spawning potential and resilience to future disturbances.
Biography
Shawn is a post-doctoral research associate specializing in long-term field studies of temperate rocky reefs. His PhD focused on the recovery, restoration and fishing effects of endemic abalone populations affected by the cataclysmic 2016 Kaikoura Earthquake. Shawn uses a range of intertidal and subtidal surveys to assess spatiotemporal trends in algal and invertebrate communities, with the ultimate goal of informing coastal fishery management, and (ultimately) improving his fishing success.