Publication Abstract

Adjusting for variable catchability of brown shrimps (Crangon crangon) in research surveys

J. T. Addison, A. R. Lawler & M. D. Nicholson

Research surveys of the brown shrimp (Crangon crangon) were undertaken in The Wash fishery on the east coast of England at 22 stations each month from November 1995 to March 2001. These surveys carried out 30 minute tows using a commercial fishing vessel, but for obvious logistical reasons stations were sampled at different times. This means that light conditions, tidal states and environmental conditions may vary across stations. Catch rates from these surveys are determined by both catchability and abundance of shrimps, and catchability of Crangon is influenced primarily by emergence behaviour which is controlled by light levels and endogenous rhythms. Previous experiments showed that catch rates of shrimps were influenced by light levels in The Wash fishery, and so general linear modelling techniques were used to examine the influence on catch rates of 18 environmental and physical factors recorded during our surveys. This allowed us to convert catch rates into an index of abundance.

Reference:

J. T. Addison, A. R. Lawler & M. D. Nicholson. 2003. Adjusting for variable catchability of brown shrimps (Crangon crangon) in research surveys. Fisheries Research, (1-3) 65; 285-294