Large basket fish traps, with a hexagonal shape and one inverted end, are typically used in Zanzibar and are called ‘Dema’ in Swahili. These fish traps, which have a large mesh size, were initially made from palm leaves and mangrove wood saplings. Nowadays, chicken wire is also used to build these traps, and the mesh sizes of the sidewalls are getting reduced.
Description of these traps
Dema basket fish traps consist of two parts. The hexagonal holding basket and the entry basket. Behind Michamvi Beach, I measured eight different Dema traps, and the sizes of the holding baskets averaged 1.3 x 1.3 x 0.59 m.
Hexagonal holding basket
Shaved stripes of palm leaves were used for weaving the mesh, held in place by dried-out wood saplings of various wood species. The mesh openings were about 5 cm or 2’’.
The trap is built so that, first, three base saplings are laid out. On top of these three saplings, two will be laid crosswise over the basis.
Thereafter, the outside frame of the lower base will be added, which results in a hexagonal shape with an inverted end on one side. The entry cone will be plugged into this inverted end. However, mesh weaving will start parallel to both X-laid saplings before adding the entry cone.
Entry cone
The entry cone is open on the bottom so that crabs or lobsters can enter without obstacles into the entry cone ramp. Viewing the entry cone from the side, the upper side is parallel to the trap deck, but the lower side is conically reduced towards its end. When fitted into the holding basket, this lower side will act as a ramp, leading into the trap.
However, the design of this entry cone is still more ingenious. The opening of the entry cone is closed by a unique basket weaving, and the animal has to use the exit window (marked red in the pictures) on top of the ramp and turn towards one side. Therefore, it is improbable that it will ever find the entry/exit port of the trap when inside.
Chicken wire mesh traps
Some newly built Dema fish traps have bottoms and sidewalls covered with chicken wire mesh. However, the top deck and entry funnel are still traditionally woven with palm leaf splines.
Which kind of bait is used in Dema fish traps?
Bait for trapping fish: Green seaweed with brittle stars inside will be put into the trap.
These brittle stars will stay within the weed to hide. To catch brittle stars, they are either directly collected in the lagoon and kept in a PET bottle until used or caught in such a bottle. For this purpose, fish innards are put into an empty bottle, which will be sunk and weighted with a stone into the water during low tide. The following day, the bottle will be filled with brittle stars. A bait is, so to speak, baited.
Brown seaweed will be put into the fish trap as bait for lobsters.
Unspecific baits are:
- Sea urchins (Urumba in Swahili)
- Green sea salad (Ulva spp.)
- Polychaete worms (Daa in Swahili)
- Grated coconuts
- Papaya leaves and raw fruits
- Dead octopus or small fish
Operation of the traps
In the late afternoon, the Dema fish traps will be baited and brought by boat to 5 – 10 m deep waters at seagrass/seaweed beds or coral reefs. There, connected by a nylon rope, they will be lowered to the seafloor and weighted down with stones or pieces of dead corals. Often, these stones were already strapped to the traps before lowering them to the seafloor. The position of the trap will be marked with a 1.5 l PET bottle as a buoy at the end of the rope. They are left overnight and retrieved the following day. After harvesting, the traps are rebaited and redeployed as long as there is a satisfactory catch.
Catch rates
According to (Jiddawi, 2012), the average daily catch rate for Dema fish basket traps is high. In 2009, the following average catch rates were measured as follows:
- Gill net: 38 kg/trip
- Surrounding net: 25 kg/trip
- Dema basket trap: 8.3 kg/trip
- Hook and line: 5.4 kg/trip
- Octopus spear: 6.2 kg/trip
Therefore, Dema basket traps are an essential fishing tool in Zanzibar. For example, 52% of fishermen at Chakwa Bay use these traps, and only 26.6% hand lines. Spears, nets, and fish fence traps makeup 21.4% of all catches. Figures were taken from (Jiddawi, 2012); link see above. After deducting all costs, De La Torre-Castro et al. (2014), determined that fishers using basket traps harvested the largest catches and revenues in their whole study, which were obtained mainly from seagrasses and coral habitats at Chakwa Bay. With the Dema basket traps, fishermen earned a mean income of 1,545 – 6,149 TZS (1.4 – 5.5 USD) daily.
Other uses of Dema basket fish traps
These fish traps have a unique design and are also used as decorative elements, e.g., for ceiling lighting. Due to their hexagonal shapes, six small trap elements can be combined into one bigger, star-shaped structure.
Lessons learned about Dema fish traps:
- Hexagonal fish traps with one inverted end are unique to Zanzibar.
- Baiting is done with easily collectible seaweeds, endoderms, and others.
- There is a high catch rate, and no specific skills or time efforts are necessary.
- These traps are also used as design elements in reduced sizes.
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