Data concerning the history of the fishery, the results of scientific investigations, trawler log-book records and published catch statistics, are all being analyzed to provide an indication of the current status of the fishery on the lake. It is understood that much of this information is incomplete, of varying precision and trustworthiness. The following initial findings are necessarily tentative and will be supported by a more precise assessment when further data have been evaluated.
Despite this proviso it is considered of value to present these initial results in order that they may be taken into account when current management and policy decisions are made.
Throughout the history of the fishery there have been a number of different and independent fishing activities, including trawling and gill netting. After 1968 the total catch refers only to the catch landed at the Fish Factory. Throughout this period there have been varying levels of illegal fishing activity resulting in additional, unrecorded yields. The trend is further distorted by the imposition, in 1987, of landing quota of 1,200 tonnes a year at the factory.
This pattern of annual yields is classical for the exploitation of a virgin fishery. The one or two year build-up in fishing activity results in the very high yields of the first few years. These high levels rapidly decrease as the virgin stock of many large, old individuals is removed. In Qinghai Hu it appears that this initial high-yielding stage was passed by about 1970. Since then the recorded catches have remained relatively constant (Figure A1/2) until the present day (noting the depression of the average due to the effect of the imposed quota).
Making an arbitrary allowance for the unrecorded catches it would appear that the fishery has supported as stable yield in the order of 3,000 tonnes a year. It is significant that Zhang and Chen in their 1980 paper (referring to the period ending in 1976) on theoretical grounds (Beverton-Holt classic dynamic pool model) provide an approximate estimate of a sustainable yield of some 4,500 tonnes a year.
An initial analysis of the log-book records returned by the trawler skippers working out of the Fish Factory, has allowed an estimate of the CPUE (expressed in kg/hour trawled) for fishing over an area adjacent to the factory site. These analyses have taken into account all available records for all months of the fishing season in the years 1980 to 1989 (with exception of 1986 for which no records have been found). All these records refer to the wooden trawlers, now replaced, working in pairs. These vessels, of 19.6 m LOA, were powered by 150 hp diesel engines. During the period of the records the gear used did not change in its specification.
The results of the analyses are summarised in Figure A1/3. It is apparent that there has been little change in the CPUE throughout the decade. This has ranged between 400 and 500 kg/hr. It can be assumed therefore that there has been little change in the biomass of fish available in this locality of the lake.
At intervals since 1964 measurements have been made on samples taken from the fish landed by the factory trawlers. These data are summarised in Figure A1/4. It is apparent from these data that there has been no significant change in the size of the fish landed over a period of 25 years.
The overall picture is that of a fishery exploited at, or near, its optimum for a sustained yield. There is no evidence of the decline in yields which is commonly stated to be the case. Although the statistics of total catch are open to some doubt due to the inability to include the illegal operations and no record being available of the legal activities other than those of the Fish Factory, the steady state of the fishery during the recent decades is evident.
Additional support for this supposition is the constancy of the CPUE as an indicator of the total size of the available fishable populations. With the indications that the caught fish remain constant in size, it is reasonable to assume that the stocks of fish are not subject to any trend in their population make-up.
This general constancy of the fishable populations and the amount of their production which is being taken in the catch suggests that there is no imbalance in the exploitation and that the level of activity, up to the imposition of the quota was about optimum to maintain these conditions. It is necessary to consider the effect of the increased effort now available in the form of the new steel trawlers fitted with 250 hp engines and increased area and mesh size of the trawls.
Zhang, Y., and Chen, Y. (1980) Preliminary analysis of population dynamics on the naked carp (Gymnocypris przewalskii przewalskii (Kessler)) in Qinghai Hu. Journal of Fisheries of China, 4 (2): 157–177