The 2016 Kaikōura earthquake was an unprecedented disturbance causing severe, long-lasting impacts to the coastal ecosystem along the northeast region of New Zealand’s South Island. The resulting coastal uplift ranged from 0.1 – 6.4 meters, with extensive die-off of intertidal and shallow subtidal communities and destruction of biogenic habitat across 140 km of productive coastline. Over subsequent years, earthquake-related stressors such as the erosion of uplifted reef platforms and inundation by mobile gravel and sediment caused further disturbances to recovering habitats and communities. The earthquake and ongoing stressors were particularly devastating to the endemic New Zealand blackfoot abalone (Haliotis iris), or pāua, a species of great cultural and commercial importance.

Pāua are large marine gastropods that inhabit inshore rocky reefs throughout New Zealand, and comprise valued cultural, recreational and commercial fisheries. Adult pāua aggregate on wave-exposed subtidal rocky reefs while juveniles settle from plankton and recruit into cryptic habitat in the low intertidal and shallow subtidal zones. The shallow nature of juvenile pāua and their habitats made them vulnerable to coastal uplift, which caused widespread mortality of juveniles and adults, and habitat destruction. This prompted an emergency closure of the pāua fishery along the Kaikōura coastline, which had been a productive and lucrative part of New Zealand’s wild capture fishery. The closure created a need from managers, fishers and mana whenua for scientific information on the affected populations and their recovery dynamics through time.

This research was initially designed to quantify earthquake effects on juvenile pāua populations and their habitats, but grew to include surveys of commercial enhancement efforts during the fishery closure, and effects of the re-opening of the fishery, particularly the shore-based recreational fishery, after 5 years of closure. Pāua abundances and sizes were assayed at 26 coastal sites over 7 years. This data set includes c. 5,000 quadrat samples and 26,500 pāua shell measurements, providing long-term demographic information from which population assessments are derived.

The absence of fishing pressure post-earthquake led to a rapid increase in juvenile pāua abundance across all sites where appropriate rocky habitat was present. The mean density of juvenile pāua across all of the sampled shallow habitats increased from 1.61 to 6.34 pāua m-2 in the first three years, indicating there was good post-earthquake reproduction in the remaining adult stock. Significant shifts in population structure occurred over time and after 4 years 60% of the shallow pāua achieved the average size of maturity at c. 85 mm shell length. Over that time period, the abundance of legal-sized pāua (125 mm shell length) more than doubled; these were so abundant that nearshore populations resembled an historical unfished population. The surprisingly fast rebuilding of inshore populations was due not only to having no fishing pressure, but also having a productive spawning biomass, good recruitment over several years, and quick replacement of abundant juvenile habitat after the coastal upheaval. These results indicated good recovery and contributed to the ministerial decision to reopen the Kaikōura coastline to commercial and recreational fishing in 2021.

One initiative in response to the earthquake disturbance was the 2018 release of 167,000 hatchery-reared juvenile “seed” pāua by commercial pāua divers into natural habitats to enhance recovery. Surveys of the abundance and growth of the seed pāua showed the average annual growth after 3 years was c. 28 mm yr-1, and that many seed had reached mature sizes, although growth was poorer at sites densely populated with natural recruits. Seed pāua comprised ca. 12% of sampled populations after three years, suggesting there was a reasonable return on seeding them out. Alternative pāua enhancement methods of outplanting larvae were also trialled. In 2019 the experimental release of 200,000 swimming larvae into natural settlement habitat in the field did not significantly increase the abundance of recruit pāua after 5 months, and survival was very poor at 0.02%. However, outplanting small rocks containing recently settled post-larvae resulted in a significant increase in pāua abundance compared to controls. Survival of outplants using this method was much better at 9% after 4 months. This is one of the few long-term assessments of commercial-scale enhancement and larval outplanting in New Zealand, and comprised a report to industry to guide future population enhancement efforts

The final component in this research gauged recreational fishing effects from the 2021 re-opening of Kaikōura pāua fishery, during which the recreational catch allocation was 5 tonnes but actual harvest was an estimated 42 tonnes. Subtidal surveys of fished and unfished sites before and after the fishing season showed significant negative effects from shore-based fishing, with a 72% reduction of legal size pāua biomass at fished sites, and no significant changes at unfished controls. At one easily accessible reef next to the highway, an estimated 92% of the legally sized pāua (>125 mm) were harvested. Intertidal surveys at 26 sites before and after the fishing season showed a 66% reduction of the legal size pāua that accumulated over the five-year closure. A stage-based matrix model parameterised with data from this thesis estimated a population decline of 14% during the 3-month recreational fishing season. If the recreational harvest had been held to the 5 t allocation limit, the model estimated positive population growth of 4%, highlighting the importance of constraining the harvest to the set allocation. The results highlight the vulnerability of this abalone fishery to acute, short-term fishing pressure without adequate protective controls, and are relevant to global management of abalone fisheries, most of which are under intense fishing pressure.

Altogether, this research depicts the recovery, restoration, and subsequent recreational overfishing of an iconic abalone population. The work will help improve management initiatives and future enhancement efforts of the fishery by providing long-term demographic data sets, informative analyses and models, and recommendations based on detailed, long-term field research. The findings are relevant internationally, with many countries experiencing collapses to their abalone fisheries and seeking sustainable solutions. Drawing from the insights gained from this research, I offer recommendations to improve the sustainability of New Zealand’s abalone populations. These include consideration of key aspects of their life history and habitat requirements, and modern approaches to abalone fishery management.