Oceanography in the Service of Fisheries

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INTRODUCTION

This paper first provides a short review of the chronic problems in fisheries and fisheries science. It then outlines a different approach to these problems by using examples from my own work. The paper briefly describes the large-scale work of some other fisheries oceanographers and, finally, integrates all the work of fisheries oceanographers in order to suggest how oceanography can best serve fisheries.

CURRENT PROBLEMS IN FISHERIES

The two chronic problems in fisheries are: first, the declining fish catch in the world, and second, the impact of industrial fishing on marine ecosystems. Worldwide fish catch has decreased by 10 to as much as 50 per cent in some areas. At the same time, the impact of fisheries has caused a decline in the actual size of fish, has resulted in the replacement of some commercial fish with less desirable species, and has caused some possibly irreversible changes in marine ecosystems. In addition, valuable high-quality protein is being discarded as by-catch.

While one may propose a number of possible reasons for these problems, as a scientist I take the point of view that if we do not understand how the oceans produce abundant supplies of fish in the first place, then there is essentially no hope in undertaking the management of this resource. For the past 50 years, fisheries management has essentially been based on the theory of population dynamics, which attributes changes in the number of new fish to the size of the existing parent population. Unfortunately this theory does not work, and a new basis for managing fisheries must be developed. This new approach to fisheries science must include recognition of the environmental control of fish populations. We need a revolution in the way we collect data and organize our thinking about the oceans. This includes technological improvements as well as academic appointments in fisheries oceanography, new textbooks, new journals, and a public/industry awareness of the necessity for change.

MARINE ECOSYSTEM RESEARCH

I will now describe some of my own work toward understanding the food chain that leads to the production of fish.

In the late 1950s, there were very few quantitative data on marine pelagic ecosystems. My former mentor, J.D.H. Strickland, and I started by writing a manual of methods in order to standardize measurements of nutrients and plankton, from which it would be possible to form the basis of environmental studies of the ocean (Strickland and Parsons, 1960).

My first opportunity to demonstrate that the environment (and not the parent population of fish) was important in fisheries dynamics, came from an unusual source. We were asked to see if we could enhance salmon production in a Canadian lake by adding nutrients. In salmon-producing lakes, the size of the young salmon varies enormously - the bigger the salmon when it leaves the lake, the more likely it is to return from the ocean as an adult. In Great Central Lake, on Vancouver Island, the fish were all very small. It is a large lake, 26km long and about 200m deep. We used our knowledge of nutrients to add a total of 100 tonnes of nitrates and phosphates to this lake. Since the lake was also the water supply for a town of 15,000 persons, a cautious approach to nutrient enrichment was adopted. Over the next 10 years, the number of salmon returning to Great Central Lake increased by a factor of 7. The environment was important! (Table 1)

Encouraged by these results, we moved to the much more difficult problem of understanding ocean ecosystems. For this we used two approaches:

(1) In one approach, we enclosed water columns large enough to hold a whole pelagic ecosystem in which the biology could be studied without continual exchange of organisms and nutrients by water movement. This equipment is called a mesocosm. In these water columns, we could experimentally manipulate different ecological parameters and study nutrients, phytoplankton, zooplankton and fish interactions under near natural conditions. …