Title
Fishing with Explosives in Tanzania: Spatial Distribution and Hotspots
Author(s)
Gill Braulik; Anja Wittich; Jamie Macaulay; Magreth Kasuga; Jonathan Gordon; Douglas Gillespie; Tim R. B. Davenport
Published
2015
Abstract
Coral reefs are of enormous social and economic importance to millions of people, including some of the world’s poorest communities. Reefs occur along the vast majority of the Tanzanian coast, and provide food for coastal communities and valuable tourist income, however, they have become increasingly degraded, due to several factors including the long-term use of explosives to catch fish. Blast fishing in Tanzania is a widespread and pervasive problem, but until now no studies have documented its occurrence at a national scale. In March and April 2015, a large-scale vessel-based survey to evaluate the whales and dolphins of Tanzania was conducted using visual observations, and acoustic recordings, to identify vocalising marine mammals. Simultaneously and inadvertently, in far greater numbers than identified cetaceans, the acoustic equipment also recorded underwater explosions from blast fishing. Acoustic data were collected for a total of 231 hours over 2692 km of the Tanzanian coast on 31 days in March and early April 2015. A total of 318 blasts were confirmed using a combination of manual and supervised semi-autonomous detection. Blasts were detected along the entire length of the Tanzanian coast, but by far the highest intensity area for blasting was in the vicinity of Dar es Salaam. Almost 39% of detected blasts were within 50km, and almost 62% within 80 km of the city. Blast frequency reached almost 10 blasts/hour near Dar on two consecutive days, which is between 3 and 10 times the frequency recorded at all other locations in the country. Other hotspots were Lindi, Tanga, and the Songo Songo area. 70% of blasts occurred in the morning, between 09:00 to 13:00. Given the scale of blast fishing in Tanzania the environmental impact on the sustainability of fisheries and health of coral reefs is likely to be substantial. In addition, considering the general sensitivity of cetaceans to anthropogenic sound, and the intensity of sound generated by explosions, it is almost certain that they, and possibly other endangered marine megafauna, are impacted negatively by blast fishing. Of particular concern is the region’s most endangered cetacean, the Indian Ocean humpback dolphin (Sousa plumbea) and the Indo-pacific bottlenose dolphin (Tursiops aduncus) both of which are restricted to shallow, near-shore waters which is exactly the habitat where blast fishing is most intense. This study is the first to provide a spatial assessment of the intensity of blast fishing along the entire coast of Tanzania. The results clearly depict the vast scale of the problem, the wide geographical distribution of blasting activity and highlight important hotspots where environmental impacts are likely to be greatest and where enforcement should be focused for maximum impact.
Keywords
blast fishing; explosives; fishing; Tanzania; spatial distribution

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