This exciting new research addresses the issue of juvenile fish habitats as 'bottlenecks' to increasing coastal fishery production for juvenile snapper in the Hauraki Gulf and East Northland, and juvenile blue cod and tarakihi in the greater Marlborough Sounds.
It is thought that loss or reduced areas of biogenic habitats (living habitats such as seagrass meadows, horse mussel beds, and sponge gardens) limit juvenile fish numbers.
In March-May of 2017, researchers undertook surveys in both regions to determine where newly settled juvenile fish occurred and what habitats they were found in. We sampled over 400 sites in depths of 3-30 m, using a small beam trawl (targets small-sized fishes) fitted with Go-Pros to sample soft-sediment habitats or a small but very high-definition towed underwater video-camera system in sensitive and rocky habitats.
Data are still being processed, but preliminary findings show that juvenile blue cod were never the dominant component of the catch around the top of the south, but nursery areas were present around the northern half of D'Urville island and the outer sounds (eastern and western sides of Trio and Chetwode Islands); while the video survey identified additional nursery grounds in the outer Pelorus and outer Queen Charlotte Sounds.
Go-Pro footage identified living habitats, such as horse mussel beds, sponges and bryozoans were present in areas with juvenile blue cod; while in the towed-video surveys juvenile blue cod were mostly found within a narrow zone of low-lying boulder-cobble and/or biogenic debris directly off reef edges
Next, we will examine which juvenile fish get the best real estate, their links to adult populations, and what threats and stressors affect them; and then run real-life 'what-if' model-scenarios using different management strategies to identify the best way to reduce/remove bottlenecks to significantly increase fishery yields (by Tara Anderson, Mark Morrison and Ian Tuck).