CASTING THE NET BACK
100 Years of fisheries management
returned to the sea (as the regulations prescribe), the female may lose her batch of eggs. And, just as they were in 1912, size limits are an essential feature of the west coast rock lobster fishery’s management. In fact, they are a classical management measure used in lobster fisheries around the world, in spite of the fact that – in keeping with the ecosystem approach to fisheries – theoretical fisheries science may be shifting away from size limits and towards the “balanced fishery theory.” According to this theory, unselective fishing may be healthier for the ecosystem because it keeps trophic levels in balance (the trophic level of a fish is the position it occupies in the food web.)
Creating balance
Excerpt from Marine Biological Report
Groeneveld points to the south coast rock lobster fishery as an example of a “balanced fishery”. There is no size limit for this deep-sea fishery, partly because catch rates are so low and for economic reasons the fishery must retain its entire catch, and partly because the rock lobster live at great depths and there is concern about the survival rate of under-
Groeneveld points to the south coast rock lobster fishery as an example of a “balanced fishery”. There is no size limit for this deepsea fishery, partly because catch rates are so low and for economic reasons the fishery must retain its entire catch, and partly because the rock lobster live at great depths and there is concern about the survival rate of under-size animals, were they to be discarded. size animals, were they to be discarded. (Catch rates are low because the rock lobsters are distributed patchily over a large area and, unlike their west coast cousins, don’t aggregate on the seabed). However, even though fishing is not regulated by a size limit, it is considered to be sustainable. “Apart from the years in which Hout Bay Fishing was fishing the stock illegally, this is actually a very successful and sustainable fishery,” said Groeneveld. Although the basic life history of west coast rock lobster has been fairly well understood since the time when Gilchrist was penning his Marine Biological Reports, Cockcroft points out that the influence of the environment on marine species and marine fisheries is given a much higher priority by modern-day marine science.
Preservation of the Crawfish We have seen that the close season, which has been adopted with a view to the protection of the Cape Crawfish, corresponds to the months in which the males are in deep water engaged in casting their shell and in a sickly condition. They do not take the bait readily at this time and are unfit for commercial purposes. The females are at this time in shallow water, some still carrying their eggs, but most having got rid of them. This is therefore the most favourable season for the fishermen and the factories to suspend their operations, but it is doubtful if the “protection” thus afforded by such a close season is of any considerable value. The males cannot readily be got and are unfit for canning, so that fishing operations for the factories would be confined to females, but the females which have spawned in this season are just those which presumably could best be spared and the catching of which would do the least harm. As the females which have just given rise to progeny are of less value economically than those about to do so, the most effective close season would cover the months just previous to the time at which they get rid of their eggs. However suitable this close season may be therefore for the fishermen it cannot be held to be the most effective for preventing overfishing and damage to the supply. A second means adopted for the preservation of the industry was to impose a size limit of 3 inches (measured from the base of the eyestalk to the end of the carapace or shield). It was enacted that no crawfish below this size should be caught. This however protected, it is to be noted, three different classes of crawfish: first, the very small forms (males and females) such as were of commercial use as a delicacy; second, the adolescent and sexually mature males; and thirdly, the adolescent and secondly mature females. We have adduced reasons for believing that the first are particularly liable to the attacks of such natural enemies as the octopus, and nature
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MARITIME REVIEW Africa: February 2015
Heightened awareness of climate change and the impact it is having, and will have, on fishing, means that scientists and environmentalists are paying more attention to environmental variables than ever before. Gilchrist meticulously recorded information but did not have the benefit of more than 100 years of experience fishing for “Crawfish”. He used simple but wellconsidered logic in much the same way as Charles Darwin and Alfred Wallace did when thinking about evolution. The benefit these early scientist did have, however, was much higher (undisturbed) abundance levels of species such as rock lobster and hake. Today the west coast rock lobster stock is estimated to be about 3 percent of its pristine stock size. Do you think if we had responded sooner to the ideas of Gilchrist our rock lobster stocks would be in the state they are today?
has made special provision for a natural drain on these forms by their large numbers so that the damage caused by man is probably insignificant as compared with the normal mortality at this season. With regard to the second, the protection of young adolescent males, these it would appear are just the forms which can most readily be dispensed with, being the least valuable form from the point of view of the preservation of the species. An analogous case is that of seals, where the young males or “bachelors” are found to be those that can be killed off with least damage to the industry. In both cases the animal is polygamous, and there will probably always be a sufficient number of males to fertilise all the females. With regard to the third it would seem that the young female, reproducing, or about to reproduce its kind, should be the object of special care. Without doubt this protection does considerably safeguard the continuation and multiplication of the species, but it might be suggested that later stages, in which the female may be more fertile and capable of reproduction, should be the object of still more special care. A female at the zenith of its reproductive powers is the most valuable from the point of view of the preservation of the species. It would appear that as a matter of fact (though it is a point still to be investigated more fully) this period in the life of the female is between 2½ and 4 inches, so that the strict preservation of these forms would be the best means of safeguarding the industry. It could not, however, perhaps be found practicable to enforce such a regulation. The fish are caught in nets and promptly tumbled into the boat, often in the dark of early morning, when there is neither time nor opportunity for readily separating out and throwing back into the sea females between 1½ and 4 inches long. The difference between male and female are, however, as has been pointed out, well marked, and are seen by the experienced fishermen at a glance, and if any relaxation of the restrictive measures be contemplated in the future, in view of stricter protection of the females, it might quite well be in allowing the capture of young males.