ICES, stocks and the ecosystem

Wait a minute! Suddenly we are being told that models used for years to assess stock and fix total allowable catches aren't good any more. So, how could they have been good in the past? Haven't many fisheries been managed for some decades now using models that consider fish in isolation? Haven't they been used for stock assessments and fixing TACs which have served as the basis of management by individual and, even, marketable quotas?

What sparked my interest was an article I have just caught up with in the newsletter of the International Council for the Exploration of the Sea (ICES) (No. 40, September, 2003), by Mikko Heino of the Bergen Institute of Marine Research.

Entitled "Does fishing cause genetic evolution in fish stocks?", I have highlighted some extracts below in italics.

The argument

"There are three key areas where ICES is at the forefront of developing the ecosystem approach in fisheries [Hear! Hear!]. The first is by broadening the techniques used to model fish populations so that they consider not just single stocks but also their interactions with the wider ecosystem. Models that consider fish stocks in isolation from their ecosystem have clearly had their day, and fisheries science is moving on."

"The new breed of models," continues Heino, "such as multi-species Virtual Population Analysis (VPA) and the 4M family of models [4M is complex system for modelling crops] are capable of considering the populations of a number of species at the same time, along with some modelling of their natural predators."

Let us go back now more than a decade. In his 1992 lecture to the World Fisheries Congress in Athens, the late Dr. Ray Beverton said that fisheries science had been slow to appreciate the limitation of all the variants of the mathematical models of fishery dynamics. He said their tendency was to produce "dubious though superficially plausible results". VPA [develped by Beverton], said Dr. Beverton, should stand rather as an acronym for 'Very Provisional Assessment'.

Forty seven years ago, in 1957, the very same Ray Beverton published a famous work with Sidney Holt, "On the dynamics of exploited fish populations". Known also as 'yield-per-recruit analysis', their model became one of the main pillars of wisdom supporting fishery science. According to Beverton speaking in 1992, he said it had been 'enthusiastically overused'.

But let's return to Heino: "The second area where ICES is helping to develop the ecosystem approach is by continuing to improve understanding of how the marine ecosystem functions. Probably for as long as there have been scientists, there has been the recognition that part of the variability in the numbers of fish is the result of changes in their food supply. This is especially the case when fish are at the sensitive larval stage. Food supply is related in part to the physical environment in the sea.

"As recent sessions at the ICES Annual Science Conference have shown, we are getting a much better understanding of the relationships between the physical environment, the plankton and fish larval ecology. This new knowledge is allowing us in some areas to start making meaningful, operational predictions on the future levels of recruitment based on both existing stock size (the traditional approach) and knowledge of the climatic regime operating."

Heino then goes on to explain the effect that trawling may have on the marine ecosystem, and brings up genetic make-up. This is apart from the more obvious effects on the size and composition of the target and other species, including marine mammals, birds and invertebrates. One has also to take into account the effects on the rates of various ecosystem processes, (such as alterations in the food web) or changes in the nutrient cycle and habitats.

Apart from the fact that all this is coming from ICES, it is also all old news for the readers of this column. This page has spent a decade reporting, not simply from me but many others, about the drawbacks of 'conventional' stock assessment and management practices on catch quotas, especially those based on simplistic models isolated from non-fishing effects. Indeed in 2003, that dissent was seen in World Fishing in January, April, September and October with 'dissidents' speaking such as Dr. Jonas Bjarnason and Jon Kristjansson of Iceland, Dr. Gary Sharp and Prof. Russ McGoodwin of the USA. And these are just a few of the voices.

Hence, I must ask the honest question: "Is ICES reviewing, or going to review its methodology, and take into consideration the attack on the present management system by the prestigious Royal Society (RS)?" (See WF November 2003 cover story by Peter O'Neill). The RS indicated that TAC quotas (based on assessment of size of populations), "...will always be uncertain as they are naturally highly variable, driven by a multitude of factors, including the intensity of exploitation...", and they should be replaced by other management means. And the RS concluded: "It is vital that this uncertainty is explicitly incorporated into fishery management and underlying models".

Back to the USSR

I turned to Dr. Serge Garcia, for more than a decade the Director of the FAO's fishery resources division, for his opinion about these recent pronouncements. While he would not refer to any specific case, Dr. Garcia was of the opinion that, while one should always consider non-fishing influences on the size of exploited fish populations, all major systems experience the problem of inertia. That means it takes them time to change direction, even when individuals have already made up their mind that change is needed.

"Stocks do oscillate," says Garcia. "The Soviet fleets, for example, were mistakenly blamed for fishing out stocks and moving to others' fishing grounds. In fact, they knew [how] to correlate oceanographic-climatic [fluctuations] with fish stock fluctuations. Their fleets were moving among areas [around the globe] trying to concentrate on fish stocks at the neap of their long-term fluctuations, and avoid them at periods of ebb." Long-term fluctuations of several species, including herring and cod, to mention but a few, also occur in the North Atlantic. Selective fishing does affect their genetics. And stock assessments are wanting. Should we tune in for more news from ICES?