Dec 27 2015

Dr. Ray Hilborn Responds to NPR: Not All Global Fish Stocks in Decline

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 December 22, 2015 — In a commentary published by CFOOD, Dr. Ray Hilborn, Professor at the School of Aquatic and Fishery Sciences at the University of Washington and author of the book Overfishing: What Everyone Needs to Know,addresses claims made by a recent NPR story that global fish stocks are in decline. According to Dr. Hilborn,the opposite is true for many important global fisheries: stocks in Europe, the United States, Russia, and Japan are actually increasing, while stocks in Australia and parts of Canada remain stable.
 
Fish Stocks Are Declining Worldwide, And Climate Change Is On The Hook.

 
This is the title of a recent NPR posting — again perpetuating a myth that most fish stocks are declining.

 

Let’s look at the basic question: are fish stocks declining? We know a lot about the status of fish stocks in some parts of the world, and very little about the trends in others. We have good data for most developed countries and the major high seas tuna fisheries. These data are assembled and compiled in the RAM Legacy Stock Assessment database, available to the public at www.ramlegacy.org. This database contains trends in abundance for fish stocks comprising about 40% of the global fish catch and includes the majority of stocks from Europe, North America, Japan, Russia, Peru, Chile, Argentina, Australia, New Zealand and South Africa. Major fisheries of the world that are not in the data base are primarily in S. and SE Asia.
The figure below shows the trend in abundance of fish stocks in these different regions.
Clearly not all fish stocks are declining; they are increasing in the Atlantic Ocean (tuna fisheries), European fisheries, both EU (recent increases), and non-EU (Iceland and Norway), Russia and Japan, and US East Coast, Southeast and Gulf, and US West coast.

 

Fish stocks in recent years are stable in Australia, Canadian East Coast, South Africa, and Alaska.
We do see long term declines in Canada’s West Coast, the Indian Ocean (tuna fisheries), New Zealand, Pacific Ocean (tuna fisheries) and South America. A characteristic of each of these regions is that they are late developing fisheries, the Pacific and Indian oceans didn’t see wide scale industrial fishing until much later than the Atlantic Ocean and the decline seen is part of the process of developing new fisheries and is planned. The fish stocks in these regions are healthy as very few of these fish stocks are overfished.

 

For the places we don’t have good data (Africa and Asia), what we do know suggests those areas are seeing significant declines in abundance.

 

So clearly not all fish stocks are in decline-the pattern depends on the region. We can see from the above graph that with good fisheries management, stocks can recover. The NPR story got the big picture wrong, it isn’t climate change that is on the hook, it is the presence of effective fisheries management that determines the trend in abundance of fish stocks.

 

The scientific paper on which the NPR story was produced was much more subtle and did not say that fish stocks were decline – that was invented by the authors of the NPR story. The paper estimated that the recruitment potential of the fisheries was declining, specifically that the number of 1 year old fish per adult fish showed a decline in many regions of the world. Interestingly, the paper identified the N. Atlantic as the region of most concern, but when we look at abundance data, the N. Atlantic is the place we see the most stock rebuilding.

 

The number of 1 year old produced is known as recruitment, and the original paper used the data in the RAM Legacy Stock Assessment database to estimate these trends. The statistics used in the original paper are complex, but we can look quite simply at the trends in recruitment – not the recruitment per spawning adult as done in the paper.
This graph shows the recruitment trend for all stocks in the RAM Legacy Stock Assessment database, with blue the trend if all stocks given the same weight, and red with large stocks giving much more weight. The size of the dots or squares shows the relative number of stocks for which we have data in each year. We do see a clear trend in recruitment decline, with perhaps 10 or 15% decline over the 40 years of available data.

 

Is this decline in recruitment due to climate change? That is one possibility, but it is also possibly due to stocks being fished to lower abundance over that time as seen in the first graph. However, regardless of the reason, this decline is small and fish stocks can easily rebuild if good fisheries management is put in place.

 

Read the commentary from Dr. Hilborn at CFOOD

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