Estimating historic effects from sedimentation and fishing
We are investigating how historical and contemporary changes to sedimentation and bottom contact fishing may influence fisheries in Tasman Bay.
Project leader: Sean Handley, NIWA
Duration: July 2017 – June 2019
Tasman and Golden Bays used to support productive green-lipped mussel, oyster and scallop fisheries, but these have been in severe decline for the last ten years. Our research is investigating whether sedimentation and bottom contact fishing have contributed to the decline.
We are measuring sediment structure and accumulation in Tasman Bay. Our research is using a unique study area, the Separation Point Power Fishing Exclusion Zone (SPEZ). This area has been protected from the use of synthetic nets and shellfish dredges for more than 30 years.
In this project, we have measured how much sediment has accumulated in Tasman Bay and where it has come from. We have sampled sediment cores across three depths inside and outside the SPEZ and calculated the rates of surface sediment accumulation using bomb-radioisotope signatures. We are now using a sediment ‘fingerprinting’ method developed by NIWA to determine the historic land-use the sediment came from. We are also estimating the rates of sediment accumulation before human disturbance by carbon-dating shells from the base of selected cores.
We are investigating the effects of bottom contact fishing on the sediment structure by comparing the environmental responses to undisturbed sediment (inside the SPEZ) and sediment disturbed by fishing (outside the SPEZ). To do this, we will analyse mollusc shell remains in the cores.
Latest news and updates
Stew Robertson has been a participant in research workshops for projects focused in Tasman-Golden Bay. He is involved with the Nelson Biodiversity Forum and founded the Tasman Bay Guardians in 2017.
A study of coastal food webs has revealed how ecosystem-based approaches to marine management could improve management of fish stocks and biodiversity in our changing coastal ocean.
In a workshop hosted in Wellington in early May, NIWA and Victoria University of Wellington researchers shared their latest findings on the effects of sediment on both shallow water and deep-sea species with iwi and stakeholders.