Publication Abstract

Technical indicators of the temporal development of fishing power in the English demersal fisheries of the North Sea

C.M. O'Brien, J. Casey and B.D. Rackham

Fishing capacity comprises four components: (i) the number of fishing vessels, (ii) the size of each vessel, (iii) the technical efficiency of vessel operation, and (iv) the time spent fishing. Fishing power, which comprises segments (ii) and (iii), is generally not directly measurable. Both fish stock assessment and management would benefit from a better understanding of the temporal development of fishing power. Firstly, a deeper insight into the relationship between catch-per-unit-effort (CPUE) and stock abundance would enhance the accuracy of stock assessments. Secondly, refining the relationship between fishing mortality and nominal fishing effort would provide a basis to allow direct control of the fishing pressure exerted by fleets on stocks. The temporal dynamics in fishing power, however, are difficult to distinguish from stock fluctuations. The purpose of this paper is to investigate and identify such dynamics. Three independent indicators, derived using different methods are proposed. The first is an indicator of variation in catchability, derived from the relationship between fishing mortality and fishing effort. The second and the third are indicators describing variations in fishing power, based on the CPUE of a fleet of vessels, relative to the CPUE of a reference sub-fleet. The reference sub-fleet is characterised by low variation in fishing power and comprises either a set of reference vessels belonging to the fleet under examination (indicator 2) or a research vessel survey (indicator 3). The methods are illustrated using data collected from the English demersal fisheries operating in the North Sea for the time period from 1989 to 1998.

Reference:

C.M. O'Brien*, J. Casey* and B.D. Rackham* (2003) In S. Pascoe and D. Greboval (Eds) Technical indicators of the temporal development of fishing power in the English demersal fisheries of the North Sea.