The first Article I wrote in this series, “Tuna resources increasing?” was supported by the recent decision made by the Commission for the Conservation of Southern Bluefin Tuna (CCSBT) to increase its total allowable catch (TAC). This decision was made based on the scientists’ advice that southern bluefin stock level had shown some recovery. It appeared that the recruitment for this stock was at a minimal level almost ten years ago, and hence the spawning biomass had been reduced until very recently with some time lag after the initial recruitment. However some recoveries in the recruitment level have been made since then,and stock abundance has increased. It is not known whether this recovery was due to an improvement in the natural environment, favorable for the stock, or it was due to the positive effect of the regulatory measures taken for the fisheries. However, even if it is due to the natural environment, without strict compliance with the regulations, this improvement would not be achieved. Up to now, the fishers observed catch quota with care, whilst also providing all the fishery data to the governments and the Commission, only to be rewarded by even more strict regulations. With this continuing negative chain, the fishers have become weary. Therefore this reversal of such a tendency is a very important milestone and is encouraging news for the fishers.
The excessive catch over the quota or TAC naturally has a reverse effect on the stock. However, the real importance is that such a violation of the regulations has a very strong impact on the analyses of stock status, as the basic data on which the analyses are made become very uncertain. Let us take the case of Atlantic bluefin tuna. The Atlantic Tuna Commission (ICCAT) reported that the purse seine catches of Atlantic bluefin tuna in the Mediterranean Sea have been significantly underreported in the mid-2000s. However, it is generally easy to estimate the accurate amount of associated fishing effort (e.g. number of sets, number of fishing days). Catch-per-unit-effort, which is considered indicative of stock abundance, is calculated by reported catches divided by the total amount of effort. As the underreported catch is divided by real effort, the value of abundance index would be less than real, by the magnitude of unreported catches. Therefore, the results of the stock analyses will give us a false impression, where the stock status would appear worse than the actuality. That would lead the managers to take even stricter regulatory measures. By not complying, the fishers are jeopardizing their own livelihood.
The fishers can now counter-attack such unnecessary and excessive regulations with simply good behavior, as shown in the case with southern bluefin tuna.