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So long and thanks for the fish

Professor Tony Booth of the Ichthyology and Fisheries Science Department gave his Inaugural Lecture entitled “So long, and thanks for all the fish” this week. In his lecture he pointed out that our fisheries resources are under siege and scientists, fishermen and consumers all have a role to play in ensuring that fisheries remain sustainable using the best scientific advice possible.

Professor Booth’s lecture investigated stock assessment (i.e. how scientists assess a resource) and what data they need to back their recommendations up. He said, “When the different fish stocks are individually assessed, sobering statistics emerged.

“A total of 70% of the world’s known stocks are over-exploited and there is little scope for expansion. There has been a peak in wild fish catches 20 years ago.

“So, in 20 years I predict that only the rich will be able to afford wild-caught fish and that due to class issues and population growth, there will be more conflict over the utilisation of these resources. Management is clearly needed and management needs a long, long-term perspective that spans multiple generations.”

As Prof Booth wrapped up his lecture, he illustrated two stock assessment examples. The two examples chosen were from resources that he has assisted in assessing and represent two very different species with different life histories and different sources of data.

The one species was the red roman, a popular recreational and commercial linefish species that is frequently sold in supermarkets and restaurants. It is lives for 18 years in shallow reef habitats and is a protogynous hermaphrodite. Prof Booth pointed out that, “Very little fisheries data are available and the best data are that relating to its movements and biology.”

The second example of species he looked at was the sablefish from the Gulf of Alaska. He noted that, “This is a deep-dwelling fish that lives for over 90 years with fish of 40 years of age common in catches. It supports a valuable fishery and is assessed annually. Red roman is an example of a data poor stock, while sablefish is data rich.”

The poor data available for red roman is mainly biological. The most recent data collected is already reasonably old as red roman live to 18 years of age. Catch-rates extend a reasonable period but are fragmented and quite poor in quality.

This means that despite catch-rates that are unstandardised, catch rates have dropped to between 5 and 17% of historic levels. Assuming doubling of fishing power over this 100 year period, would then suggest that catch-rates are at most 9% of historical levels. Prof Booth concluded by confirming the concerning truth that, “This is not good.”

The data available to assess sablefish is good. There are catches from two gears – a trawl fishery and a long-line fishery. The trawl fishery targets small fish and the longline fishery large fish. There are six abundance indices – four from commercial vessels and two from research biomass surveys.

During the past 50 years since data was collected fish have been aged annually and validated annually. Over almost 50 years there has been male and female length frequency data collected.

Professor Booth made a final plea to the audience, “To the fishermen in the audience. Please stick to the rules and regulations. They are there for a purpose – the primary purpose being that your grandchildren’s grandchildren can also catch a fish when they go fishing some day.

“For the fish eaters in the audience. If you wish to take the high road, I also suggest that you buy fish that has been sustainably harvested. The Marine Stewardship Council certifies those fisheries that it considers, after quite rigorous peer review, to be sustainable. The sablefish resource in Alaska is one of 69 global fisheries with such a certification. You will also be pleasantly surprised to know that South African hake is also MSC certified.”

Inaugural lecture introduction

Pic: From left - right: Professor Tony Booth and Vice-Chancellor, Dr Saleem Badat.