17 November 2014

Disappearing river monsters

The Protect Africa’s Sawfishes project continues to collect baseline data describing where remaining sawfish populations occur. Ultimately, this information will be used to direct conservation efforts for sawfishes to where they are most needed. In 2014, interviews with fishermen, fish traders and fisheries observers were carried out in three African countries: The Gambia and Liberia in West Africa, and Mozambique in east Africa.

Female largetooth sawfish (total length 5.1 m) landed at
Kartong on 21st June 1975.
Two species of sawfishes, the largetooth sawfish (Pristis pristis) and the smalltooth sawfish (Pristis pectinata), formerly inhabited the east Atlantic, including much of the West African coast. Sawfishes were probably once a common sight in West Africa. Cambridge biologist Budgett (1899), on an expedition to The Gambia colony, wrote:
 ‘…frequently in the morning, when the trammel-net was examined, a Crocodile (Crocodilus cataphractus) or a Sawfish (Pristis perotteti) had to be slain’. 
Likewise, a Swedish study carried out in the 1930s suggested that sawfishes were plentiful in Gambian waters: 
This sawfish is common in the river at all seasons. . . . [I]t was [also] caught in remarkably great numbers, just at the mouths of creeks.  It is known by the natives in all parts of the river in the Gambia’. 
Forty years later, Nigel Downing, then a PhD student at Cambridge University, encountered many largetooth sawfish in the Gambia River. Fishermen working several hundred kilometres upriver in freshwater often caught sawfish, particularly juveniles. At the coast, Nigel also encountered fishermen hauling a 5-metre female largetooth sawfish, pregnant with 15 pups, onto the beach. Sawfish were a common sight for fishermen then, but were not targeted catch; rather, they were seen as a nuisance as they easily became entangled in fishing nets and were difficult, and dangerous, to release. Between 1974 and 1975, Nigel collected data from 65 sawfish. Most of these were juveniles and were caught in the months just after the rainy season. Interestingly, despite the supposed presence of both smalltooth and largetooth sawfishes in West African waters, he only documented largetooth sawfish in the Gambia River.

Female largetooth sawfish (5.64 m) caught in the
Gambia River on 19 June 1975.
Interviews conducted with fishermen in The Gambia in March 2014 suggested that sawfish are no longer a common sight; some fishermen did not even recognise the image of a sawfish. Others said they had last seen a sawfish 20 years ago or more. Most interviewees clearly perceived that sawfish had declined in Gambian waters and suggested that the widespread use of fishing nets and the presence of industrial fishing trawlers off the coast as potential causes for this decline. In contrast to other parts of West Africa such as Guinea-Bissau, few respondents in The Gambia mentioned any cultural importance of sawfishes, which were seen simply as a source of food. Only one respondent specifically mentioned removing the fins of sawfish to sell them, suggesting that this practice may not have been widespread in The Gambia.

Combining the findings from these two studies, an all-too-familiar story unfolds: largetooth sawfish were formerly abundant in the Gambia River but in the space of forty years, may have become locally extinct. It is difficult to pinpoint the drivers for this decline, but the transition from traditional fishing techniques to the use of modern gears such as longlines and monofilament nets may have contributed. Commercial demersal trawl fisheries, which have contributed to the decline of sawfishes in other regions, operate in the Gambia estuary, and fishing using drift nets and gill nets occurs throughout the river. The development of shark fisheries in The Gambia in the 1960s and 1970s, by Ghanaians, likely also had a considerable impact on sawfish. The race is on to identify any remaining sawfish populations in African waters, before they meet a similar fate. 

R.Leeney’s fieldwork in The Gambia was funded by the Mohammed Bin Zayed Species Conservation Fund. This study is now published as:
Leeney, RH & Downing, N. Sawfishes in The Gambia and Senegal – shifting baselines over forty years. Aquatic Conservation: Marine and Freshwater Ecosystems. 
The paper is available here.

The Cambridge University Museum’s blog also featured a story on sawfish in The Gambia – take a look here

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