The inevitable and the preventable in managed fisheries: where to start?

June 5, 2017 11:48 am Leave your thoughts

One might ask “Since when have we had to manage our marine fisheries?” We are not feeding them, cultivating them or protecting them from predators or adverse weather conditions. They were in existence a long time before we came and seemed to do pretty well by themselves without our help. With hindsight, we know that this is a very naive argument, but not long ago this very question was the subject of a serious scientific debate. The famous naturalist Thomas Huxley (London Fisheries Exposition, 1883) suggested that marine resources were inexhaustible, and that all we should be concerned with is the development of the most efficient method of fishing.

What has happened to change the perceptions of Huxley and his followers? Essentially, experience around the world, which has proved him wrong, often disastrously so. Numerous fish resources around the world are badly depleted and provide fishers with dismal economic returns. The reason is that while predictions about the ability of humans to develop successful harvesting techniques were gross underestimates, predictions about the inexhaustibility of the oceans living resources have proven to be gross overestimates.

In fact, the harvesting power of marine fisheries presently overrides any other natural factors and forces which shape and control fish populations. Fishing (commercial and recreational), if not controlled, has the potential to drastically reduce the size of the exploitable biomass and radically alter the marine ecosystem (we will deal with both terms “marine ecosystem” and “exploitable biomass” in future chapters).

More than 100 years after Thomas Huxley made his first predictions, the poor state of many of the world’s fish resources has brought about a new appreciation of the limitations and potential of marine fisheries. Today the conservation and sustainable utilisation of living marine resources is the basis of fisheries management policy and philosophy. However, this philosophy should not be allowed to override the basic idea that living marine resources should be exploited for our benefit. On the contrary, if done in the proper way, fishing is probably the most ecologically-sound and environmentally-safe way of producing food, certainly in comparison to agriculture and aquaculture, which results in the degradation of the environment by the overuse of land, destruction of natural terrestrial habitat, pollution and the genetic degradation of wild fish stocks.

Two sentiments are often expressed in any public discussion regarding fish resources. The most common one is normally preceded by a sad sigh “I still remember not long ago when fish (we use the term fish for lobsters, fish, molluscs and any other living marine resources) were large and look how small they are today”. The other sentiment is similar but refers to the number of fish rather than to their body size (body size is often termed somatic size in order not to confuse it with the size of the population which refers to the number of fish in the sea). Well, the reality is that, just as in other aspects of life, one cannot eat one’s cake and keep it. It is simply not possible to exploit a pristine resource and simultaneously maintain the original catch rates and fish sizes. As will become clear from future chapters it also makes little economic sense to try to maintain an exploited resource near to its original state.

In the first year of fishing, the resource is regarded as being pristine, and under pristine conditions it is expected to be at or very close to the size that it has been at for the previous thousand years. The first fishers of a new fishery are testing new economic ground, since the profitability of the fishing venture still has to be proven. Fishing progresses, markets develop, and if profits are realised, an incentive for new entrants or more boats and manpower in the fishery is created. This incentive exists for as long as the fishery is profitable, and as a result more and more fishers enter the fishery. The manpower and number of vessels involved in fishing and in processing and marketing the landed catch increases. Consequently, the amount of fish landed each year increases, at least in the beginning.

With experience, we know that the development path of new fisheries described above is never sustained indefinitely and with the passage of time, fisheries experience a number of logistical, biological and economic changes. These are described below (Figure 1):

Catch rate reduction: Catch rate in a fishery is the amount of fish caught per unit of time fishing per unit of fishing gear, and is often referred to as CPUE (Catch Per Unit Effort). Examples of fishing gear are: a rod and line, a fish trap, a throw net, a trawling vessel, a purse seine vessel.

The first sign that commercial fishing is having an impact on the natural population is that the catch rate starts to decline. Trawlers that were previously catching 20 tons of fish per day, start coming in with 17 or 15 tons per day. This makes it more expensive to maintain catches at their original levels.

Size reduction: the next indication of the effect of fishing on a fish population is that the average size of fish caught starts to decline. This is because fishing normally concentrates on larger fish, and because fish have less chance of reaching a large size and old age. This has important economic implications, because smaller fish may not be suitable for the same end products and markets as large fish. These two factors start to have an effect on the profitability of the fishery – in most cases they cause a decline in profitability.

The process we have described here is an unavoidable outcome of any new fishing operation. The question is not how to prevent it from happening but rather how far the process should be allowed to continue before the fishery becomes economically unproductive and/or the resource is under biological risk. Fisheries management is not about how to keep fish resources in their original state but rather about how far one should allow the resource to be depleted and what techniques and criteria should be applied to maintain it at an appropriate level. In many cases, however, we have not been given the opportunity to stop resource depletion at a “desirable” level since many fish resources have already been depleted well below this point. In these cases the task is one of rebuilding fish stocks to a desirable target level, perhaps more daunting than the problem of stopping depletion at an appropriate point.

Figure 1: Typical trends in fishing effort, catch, catch rate and mean body size in a fishery, showing a development phase which culminates in a maximum catch, followed by a collapse and then stabilisation at a lower level of catch

In order to be able to contemplate management in this way one needs to have a level of understanding of fish population dynamics, fish biology, how fishing affects natural processes and the extent to which one can change resource dynamics by managing the fishery. One has to accept that fish inhabit a complex and dynamic ecosystem, that one cannot go back in time to learn more about the size of the pristine population, that one cannot directly count the fish in the sea, observe them growing, reproducing and dying, or monitor their movements and record their behaviour. The task of fisheries managers and scientists is a difficult one and it will be the topic of most of the following chapters.

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