Assessing the quality and value of Parapercis colias nurseries in the Marlborough Sounds, New Zealand

Coastal nursery habitats are critical for maintaining the populations of many of New Zealand’s most important fisheries species. Changes in the availability and quality of nursery habitats in response to anthropogenic activities may be affecting the number of fish that successfully recruit into adult populations. It is therefore important to identify which habitats are the most important nurseries, what qualities make them valuable, and how we can protect and restore them to support fish stocks. Parapercis colias are an important commercial and recreational fishery species found mostly around the South Island of New Zealand. Juveniles and adults spend most of their lives on the seafloor, where they depend on biogenic habitats for food and shelter. The Marlborough Sounds has been a popular fishing ground for P. colias since the 1900s, but has also been exposed to destructive fishing activities such as commercial shellfish dredging, which have caused damage to biogenic habitats. Although previous studies have observed interactions between adult P. colias and their habitats, juvenile habitat associations have been rarely explored. Additionally, no studies have explored the qualities of valuable P. colias nurseries. In this thesis, I quantified the growth and diet of juvenile P. colias collected from a set of nursery habitats in the Marlborough Sounds, New Zealand, including bryozoan fields, dog cockle beds, horse mussel beds, biogenic clumps, and reef edges. I used juvenile lengths, weights, and ages to investigate differences in growth among habitats. I also used juvenile stomach contents to investigate differences in diet among habitats, specifically focusing on the diversity, abundance, and biomass of prey taxa found. My results show that not all nursery habitats are equal in value. In particular, reef edges appear to support significantly faster juvenile growth than other habitats. Juveniles diets differed in the diversity, abundance, and biomass of prey taxa among habitats. In particular, juveniles from reef edges consumed more prey items compared to juveniles from other habitats. Diets were primarily dominated by crustaceans in all habitats, with gammarids and mysids being particularly important prey items in both abundance and biomass. Knowledge of the qualities of valuable nursery habitats is critical to the conservation of biogenic habitats and the management of coastal fisheries. My data will provide important information for the modelling and management of P. colias stocks in New Zealand, and will help to further our understanding of how they might respond to changes in the marine environment.