The predator-prey relationships of Irish Sea poor-cod (Trisopterus minutus L.), pouting (Trisopterus luscus L.) and cod (Gadus morhua L.)

• Published in: ICES Journal of Marine Science
• Main Author: Armstrong, M. J.
• Format: Text
• Language: English
• Published: Oxford University Press 1982
• Subjects: Articles; Gadus morhua
• Online Access: http://icesjms.oxfordjournals.org/cgi/content/short/40/2/135; https://doi.org/10.1093/icesjms/40.2.135

The stomach contents of poor-cod ( Trisopterus minutus L.), pouting ( Trisopterus luscus L.), and cod ( Gadus morhua L.) from a Dublin-Bay prawn ( Nephrops norvegicus L.) fishery off the west coast of the Isle of Man were investigated using a modified gravimetric (wet weight) technique. Information is provided on the percentage composition of the average daily food intake during successive three-month periods of the year, and on predator-prey size relationships. Simplified food webs based on principal prey are presented to summarize the feeding relationships between gadoids and their prey. Poor-cod of less than 10 cm total length fed mainly on polychaetes, euphausiids, and other small Crustacea. The diet of larger predators consisted of epifaunal decapods and small demersal fish. Food items weighing between 0·25 and 2·5 % of predator body weight were predominant in the diet unless smaller items were highly abundant or optimum-sized items scarce. There was a gradual increase in the importance of the burrowing reptant Nephrops norvegicus in the diets of successive size classes of predator. Poor-cod tended to eat 0-group Nephrops , pouting ate 1-group prawns, and cod ate 2+ group prawns. Although large cod were capable of eating 3-or 4-year-old prawns, these were relatively scarce due to the effects of commercial trawling, and were infrequently found in the stomach contents. The daily food intake (g/day) during each three-month period of the year was proportional to predator length (cm) raised to a power of approximately 2·5 to 2·8. For a given size of predator, food intake was generally greatest during autumn when bottom temperatures in the Irish Sea were at a peak. Fish with ripe gonads during spring had on average maintained their stomachs between half-full and full, and appeared to have fed normally.