Certification of toothfish fishery in doubt

A New Zealand-led survey of young toothfish in Antarctica has found high densities of the highly-prized fish in the southern Ross Sea.

Spearheaded by the National Institute of Water and Atmospheric Research of New Zealand (NIWA), the survey is a first in a series of surveys that will monitor numbers of young Antarctic toothfish in the Ross Sea region. Information to monitor the abundance of adult toothfish is currently collected, but this is the first survey that collects the same information for young fish.

The main objective of the survey is to establish feasibility of developing a time-series of surveys to monitor young toothfish in the southern Ross Sea using standardized commercial longline fishing gear. Using the survey results, scientists will be able to model and forecast the future fish population.

Fifty-nine random locations were surveyed using longlines, each comprising 4,600 hooks, set for up to 24 hours, within a survey area of 30,000 square kilometers. Fishermen caught mainly 70- to 100-cetermeter toothfish (at times over 100 individuals per line), in depths from 300 to 900 meters. The fish caught were then measured and sexed, with biological samples taken for further analysis back in New Zealand.

The survey also demonstrated the feasibility of collecting samples for wider ecosystem monitoring. A large number of samples of muscle tissue and stomachs were collected from Antarctic toothfish and several other fish species, and will be analyzed to understand feeding habits and relationships with other organisms in the food chain.

“To monitor fish abundance properly, it is necessary that the surveys be conducted in a controlled and rigorous way. For example, this means using the same fishing gear and the same bait, at the same time and location every year. It is also important that the survey is carefully designed so that it samples the main area in which the target population is found,” said Stuart Hanchet, NIWA marine scientist. “This survey will be an important monitoring tool to make sure the level of fishing remains sustainable.”

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