Download AEBR 337 Cumulative effects of stressors on scallops and scallop habitats in the Marlborough Sounds: With insights from sites in Northland, Hauraki Gulf, and eastern Coromandel Peninsula

Scallop populations have declined across Aotearoa New Zealand and have failed to recover even after fisheries closures. It has been suggested that seafloor habitat health, rather than the number of larval recruits arriving to the seafloor, is the critical factor impeding scallop recovery in formerly abundant beds. The aim of this research was to identify optimal habitat characteristics for scallops and to determine why sites that once supported scallops no longer do. We reviewed models and data on stressors to understand how multiple stressors may have degraded scallop habitats in the Marlborough Sounds. We used field surveys of 230 sites across Aotearoa New Zealand (Northland, Auckland, Coromandel Peninsula, and Marlborough Sounds) to assess seafloor environmental characteristics in relation to scallop abundance. Our reviews revealed how human activities both on land (land clearance and forestry) and in adjacent coastal zones (bottom contact fishing) have likely impacted scallops in the Marlborough Sounds, although a lack of information on stressors at the times and places of scallop population declines precluded a clear demonstration of cause and effect. Our field data highlighted relationships between scallops and their environment, including sets of conditions where scallop densities were at their maximum, enabling us to better define what constitutes ‘good’ scallop habitat. Without this understanding, scallop restoration efforts may be less successful.