Reconstructing the past: design and function of Granton otter trawl gear at the turn of the twentieth century, as used in South Africa’s first trawl surveys (1897–1904)

Abstract

Long-term change in marine environments is frequently investigated by comparison of historical and contemporary trawl catches. Such investigations are challenged by unquantified biases due to advances in gear technology and a lack of knowledge on the fishing power of historical trawl designs. To address this problem, historical surveys can be repeated by imitating historical trawl gear and methods. With that goal in mind, we investigated the trawl gear used in 1897–1904 surveys by South Africa’s first research vessel, the SS Pieter Faure. Trawl gear materials and dimensions were captured from historical reports, literature and photographs, providing a detailed plan for reconstruction of a trawl net with replicated functionality. The gear consisted of an early ‘Granton’ otter trawl net made of tarred Manila hemp. The otter doors were flat wooden boards in a steel frame, connected directly to the net headline and ground-rope. The towing speed was estimated to be 1.35 m·s−1 (2.62 knots). The development of this otter trawling equipment and its fishing performance relative to earlier, later and modern technology is discussed. The results provide a case study of trawling technology used during the first two decades of commercial and scientific otter trawling in South Africa and the UK, and other regions, such as Europe, USA and Australia. This example provides an internationally relevant foundation for studies of historical trawl records, their associated technology and fishing power from the late 19th and early twentieth century.