Benthic Habitats and the Effects of Fishing

Symposium Abstract: The Spatial Extent and Nature of Mobile Bottom Fishing Methods within the New Zealand EEZ, 1989-90 to 1998-99

S. J. Baird, N. W. Bagley, B. A. Wood, A. Dunn, and M. P. Beentjes

doi: https://doi.org/10.47886/9781888569605.ch122

Temporal-spatial representation of fishing effort distribution for the main mobile bottom fishing methods used in New Zealand waters was investigated using 10 years of commercial effort data, from 1989-90 to 1998-99. Tow position data were used to map the changes in fishing patterns for fisheries using otter trawls on the bottom by collating the number of fishing operations and the area swept into 22 km2 blocks. The intensity of effort varied between fishing years: many 22 km2 blocks were trawled more than 10 times, representing a swept area of more than 10 km2. In most fishing years a median of 2 tows were made in each block (with the third quartile at 4-6 tows) and the maximum number of tows in a block was 370. Swept area values were scaled to vessel power and graphic representations of these data indicated areas trawled by heavier ground gear. Transects of selected areas for each fishing year showed large differences in the monthly spread of effort. Analyses of data for other otter trawl effort (predominantly inshore) and shellfish dredge effort are based on larger fishery areas because fine-scale position data were not collected. At this scale, spatial and temporal relationships between fisheries with different gear types were evident. Ground gear components used in the main otter trawl and dredge fisheries are described. The requirements for consistent data collection and the application of this work to a wider understanding of the impact of fishing in New Zealand waters are discussed.