WAMSI Study to Protect Fish During Dredging

A global study has assessed the potential risk from dredging to coastal fish and fisheries and identified guidelines that could protect 95 per cent of fishes from dredging‐induced mortality.

Dredging operations worldwide are forecast to intensify in the future to meet the demands of an increasing rate of coastal development and shipping activities and up to 20 per cent of fish species are likely to experience lethal and sub-lethal impacts as a result, according to results published in Conservation Letters.

The Western Australian Marine Science Institution Dredging Science Node brought together a team of researchers from universities and management agencies in Australia, led by Dr. Amelia Wenger at the University of Queensland, to develop evidence-based management guidelines to protect fish and fisheries from impacts associated with dredging.

The study found that more than 2,000 ports worldwide are within the range of at least one threatened species, while 97 ports are located within the range of five or more threatened species.

It also determined that globally, between 2010 and 2014, 40.9 million tons of global commercial fisheries catch and 9.3 million tons of small-scale fisheries catch were extracted within five kilometers of a port, including many species known to be sensitive to sediment.

Dr Wenger said that fish larvae were most likely to be affected by dredging sediment but that there were measures that could be taken to markedly increase the survival rate.

“While adult fish are unlikely to experience lethal impacts during dredging activities, we found that fish during early life history stages are at risk to lethal and sublethal impacts at suspended sediment concentrations and exposure durations regularly occurring during dredging operations,” she said.

“We found that maintaining suspended sediment concentrations below 44 mg/L  and for less than 24 hours would protect 95% of fishes from dredging‐induced mortality. Seasonal restrictions during peak periods of reproduction and recruitment could also protect species from dredging impacts,” Dr Wenger explained.

The thresholds developed in the study are considered to be a starting point for an adaptive management framework, to be used in conjunction with a monitoring program that evaluates the effectiveness of different management strategies at mitigating impacts to fish and fisheries.