Publication Abstract

Catchability of brown shrimps (Crangon crangon) in relation to environmental variables: experimental and modelling approaches

Catchability of brown shrimps (Crangon crangon) in relation to environmental variables: experimental and modelling approaches

J. Addison, A. Lawler and M.D. Nicholson

Research surveys of the brown shrimp (Crangon crangon) have been undertaken in The Wash fishery on the east coast of England at 32 stations each month over the last five years. These surveys carry out 30-minute tows using a commercial fishing vessel, but for obvious logistical reasons stations are 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. Catchability of Crangon is influenced primarily by emergence behaviour, which is controlled by light levels and endogenous rhythms. Field experiments showed that catch rates of commercial-sized shrimps were higher at night than in daylight hours, proportionally more smaller shrimps were caught at night, and catch rates of predators of shrimps such as whiting (Merlangius merlangus) were much higher at night. A multiple regression approach using generalised linear modelling techniques to examine the influence on catch rates of 18 environmental and physical factors recorded during our surveys allowed us to convert catch rates into an index of abundance.

Reference:

J. Addison, A. Lawler and M.D. Nicholson, 2001. Catchability of brown shrimps (Crangon crangon) in relation to environmental variables: experimental and modelling approaches. ICES CM 2001/Q:01. 13pp.

J. Addison*, A. Lawler* and M.D. Nicholson*

ICES CM 2001/Q:01: 13pp