Article

Keeping track of fish life in Langebaan Lagoon

Nomtha Myoli and Dr Paul Cowley

Sun-warmed, sheltered waters harbour abundant fish stocks in South Africa's only lagoon, Langebaan, situated in the West Coast National Park. Fishing enthusiasts catch a range of species including the white stumpnose, but the concern is that the catch rates are too high and that this fish may become rare as in other coastal areas. This leads to question the role played by the National Park's no fishing area in sustaining the precious fish life of Langebaan.

Langebaan is an eco-attraction which presents a unique environment for marine life along the west coast. The lagoon is rich in produce supporting important fisheries businesses, the largest seafood farming projects in SA and not forgetting fun coastal activities like fishing, windsurfing, kitesurfing and boardsailing. As a result the towns of Langebaan and nearby Saldanha Bay are growing at a high rate. Sea-front properties in this area are in demand and buyers are attracted by the prospects of fishing; it has been estimated that one in four households owns a boat. Many of the fish species which occur in Langebaan are not typical west coast species, but are more commonly found along the warmer south coast. Some of these fish have possibly become isolated from their south coast populations. Although some of the fish are known to migrate (move for favourable conditions), it is uncertain whether the Langebaan populations do move to other coastal areas considering that they are probably isolated and continuously present in the lagoon waters. Scientists have not yet studied the links and migrations between Langabaan populations and those of the south coast.

What is known is that fish stocks in Langebaan are exploited. Because of this the resources of Langebaan Lagoon and the close-by Saldanha Bay may be endangered therefore the effective fishery management measures in protecting these resources need to be tested. Fortunately, the lagoon was zoned as a protected area in 1976 and was later declared as a National Park and Marine Protected Area (MPA). MPAs are declared by law to safeguard the ocean's diverse marine life. The lagoon was divided into three sections where fishing is allowed in zone A only, power boats are excluded from zones B and C and all boats are excluded from zone C (see map). Although the original motivation for these designations was the protection of migrant birds, it is now clear that the refuge (protected) areas that exclude fishing may play an important role in conserving stocks of white stumpnose, steenjie, white steenbras, kob and elf. The effect of this zoning on the fishery is not understood, yet there is a strong possibility that the protected area sustains fish catches by protecting some of the fish for at least part of the year.

Four agencies have undertaken a collaborative effort to study the fish stocks of Langebaan and investigate the management role of the MPA. These partners are: Marine and Coastal Management (MCM), the Norwegian Institute for Nature Research, the South African Institute for Aquatic Biodiversity (SAIAB) and the South African National Parks. The project will be the basis of a long-term monitoring programme and create links between protected area managers, fishery managers and scientists. The first phase is over five years (2005-2009), during which fish monitoring, biology, catch rates, mortality rates and movements will be researched. Environmental awareness, post-graduate student training (capacity building) and research collaboration will be emphasized. This project is funded by the Norwegian government through the NORSA programme.

According to Dr Paul Cowley, Senior Aquatic Biologist at SAIAB, the first objective was to investigate the movement patterns of white stumpnose in the lagoon. A trial study using sound (acoustic) telemetry technique was carried out in November 2004. The technology of underwater telemetry involves the wireless transfer of information from an attached or implanted fish tag (transmitter) to data-logging receivers; this makes it possible for fish researchers to describe fish movement patterns.

Sound tags can be implanted into the white stumpnose without rejection.

To begin with, a laboratory experiment carried out on 24 white stumpnose at MCM's Sea Point Aquarium revealed that sound (acoustic) tags can be implanted into white stumpnose without rejection or any apparent effects on survival or growth. Thereafter, four fish were caught and tagged in the no fishing zone B and were manually tracked using a small boat kitted with a hand-held receiver over a short term period (four days). The fish moved up to 15km along deep channels from where they were caught in the no-fishing zone occasionally straying into the fishing zone. Therefore protection is not guaranteed in the fishing zone. These results suggested that a broader study should be done with acoustic listening posts stationed along channels.

The project's team of research scientists recently launched the broader study in which 30 tagged white stumpnose will be monitored using 20 data-logging listening stations anchored throughout the lagoon in the protected and unprotected areas. Information will be collected by the listening stations and will be downloaded monthly for the duration of the project while the hand-held receivers will be used now and again to confirm the information. Similar experiments on the other important fish species will be conducted in the near future.

The perceptions relating to the use of MPAs as a conservation tool remain insufficiently tested, due to a lack of no fishing MPAs world-wide. Therefore, the finding of this work could be useful beyond our borders. Although the status of coastal fish stocks are difficult to evaluate it is important to remember that there is no price 'tag' when it comes to saving our marine biodiversity.

More information:

www.saiab.ru.ac.za 

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