More examples of the pitfalls associate with the misrecording or misreporting of fishing data

This month’s column is a continuation of our short review of case studies in which misreporting and or misinterpretation of basic data played a significant role in the management of certain fish stocks. The two following examples are from the South African west coast rock lobster fishery.

1. Size structure data supplied by the industry

In the early 1990s the catch rate of the South African West Coast rock lobster Jasus lalandii declined significantly. As part of a scientific debate which was initiated to explore the reasons for this decline and to propose remedies it was suggested that the exclusive harvest of large lobsters above the 89 mm carapace length minimum size was putting too much pressure on this relatively small component of the resource, given the reasonable assumption of a very large stock of lobsters below the minimum size.

The industry, keen to pursue this argument, volunteered to conduct a survey aimed at estimating the quantities of lobsters below the minimum size. The industry was aware of the implications of the finding of such a survey, especially the positive nature of a result indicating large numbers of lobsters just below the minimum size. For whatever reasons the survey results indicated an abnormally large frequency of lobsters on the 88 – 89 mm size range. It seems that somebody decided to record lobsters between 80 and 88 mm as 88 mm lobsters. If anything this was not much more than a white lie. No attempt was made to increase the total number of lobsters sampled, rather some inventive data massaging.

The result was that when the size data were plotted, a distinct horn was created just below 89 mm. The end result of this exercise was that:

• All the data from the industry survey were discarded
• The industry lost credibility
• The entire survey program which was initiated and, initially, designed by the industry was taken over by the South African management agency, the Sea Fisheries Institute of the Department of Environmental Affairs and Tourism.
• The scientific deliberations regarding possible changes in lobster minimum sizes was sidetracked and ultimately delayed, since the credibility of claims and information which were provided by the industry as part of the debate were now questioned as well.

2. Use of catch rate data as a biological or an economic index

Since 1995 there has been a substantial increase in the catch rate of West Coast rock lobsters, by a factor of about four. This high catch rate has been associated with a relatively low TAC in relation to the industry’s catching capacity. The high catch rate and the low TAC has transformed the entire way in which fishing companies have deployed their fishing effort. Since landing the TAC is not an issue, far greater emphasise has been placed on increasing the value of the catch and at reducing fishing costs.

In other words the industry has been transformed from one which is volume driven to one which focuses on cost savings and product quality and value. As a result, fishing vessels have started to fish closer to home in order to save fuel and working hours. This is despite the fact that much higher catch rates can be achieved further afield. The sacrifice in catch rate in this case is insignificant in comparison to the operational costs saved. Fishers have also been instructed to target preferred lobster sizes – at present smaller lobsters are preferred as they fetch better prices in the Far East.

This targeted fishing, which probably involves some selective discarding of large lobsters, also reduces the potential catch rate. Another issue associated with substantially improved catch rates are the problems caused for processing and marketing. If product comes in from the sea at a rate faster than can be processed or marketed, then skippers are instructed to restrict their daily catches. This is typically achieved by setting catch tallies which are considerably less than what could be caught if the total numbers of onboard traps are used. The problem is that skippers generally report the number of traps onboard and not the number of traps actual used, and these erroneous trap values are then used in calculating the CPUE (catch (kg) / number of traps).

A further problem in the West Coast rock lobster fishery is that the CPUE calculations have no time unit. Consequently, changes in soak time which may affect catch rate are not recorded, and presently the impact of different soaking periods on CPUE is not calculated.

The end result is the creation of contradictory perceptions about the resource, scientists versus fishers. Fishers say we never had it so good, scientists say, no, your catch rate trend is considerably less than you assume, and there is no cause for celebration. Industry people are, of course, guilty by not accurately recording information (mainly the exact number of traps used) critical to a proper calculation of catch rate. However, on the management authority’s side there seems to be a level of indifference to the collection and interpretation of factors which may be negatively biasing catch rates.

The reason is simple. There is no biological risk associated with management decisions based on the assumption that the catch rate is lower than its real value, since if anything, TAC allocations would be more conservative and resource depletion less. It seems that sometime a much keener investigative approach to possible biases in catch rate data seems to take place when the agenda is factors which may be increasing efficiency in the fishery (positive biases). We believe that similar consideration should be made when and if negatively biasing factors effecting the commercial CPUE.