Research assessment for the management of the industrial shallow-watermulti-species shrimp fishery in Sofala Bank in Mozambique

摘要

The industrial shallow-water shrimp fishery at Sofala Bank whose annual average catch of 8600 t is valued at about US$ 80 million, is one of the main industries in Mozambique. The shrimps are also fished by an artisanal and semi- industrial fishery. The industrial fleet is managed by a combination of limiting the number of vessels, catch quota and seasonal closures. The main species caught are Penaeus indicus and Metapenaeus monoceros with average catches of 4600 and 2500 t, respectively. The other species (P. japonicus, P. latisulcatus and P. monodon) have increased from 10% of the catch in the 1980s to 20% since 1992 due to increased night fishing. Standardized catch rates for all species showed a high level of variation between vessels, 200-650 kg/day, that are related to vessel length (r = 0.78). The fishing power increased linearly for vessels from 14 to 30 m with little increase from 30 to 40 m. The mean weight of P. indicus increased from March to August and then declined as new recruits enter the fishery. While the mean weight of capture by December was similar to that at the start of the fishery in March, the relative numbers caught were about 20 times greater in March compared to December. The spatial distribution of the mean shrimp weight at the time of recruitment in March shows that smaller shrimps occur inshore in shallow water 5-15 m. The annual variation in the P. indicus and M. monoceros catch can be explained by a pre-season recruitment survey catch rate and fishing effort (r = 0.81, n = 8, p = 0.07) and monthly run-off of the Zambeze River in the previous wet season (r = 0.64, n = 19, p - 0.01), respectively. This study provides a basis for improved stock assessment and management by: (a) standardization of fishing effort; (b) greater effective effort control through control of increases in fishing power by vessel size or controls on trawl net sizes; (c) extension of seasonal closures to include March based on the recruitment pattern of the main species; (d) use of the prediction of catches in the management of the fishery; (e) temporary (March-April) or permanent spatial closures of the inshore shallow waters based on the introduction of the vessel monitoring system to protect juvenile shrimps.