Activity, Shelter Usage, Growth and Recruitment of Juvenile Red Hake Urophycis chuss

Abstract

Juvenile red hake Urophycis chuss (Walbaum) live in symbiotic association with sea scallops Placopecten rnagellanicus, immediately following the hake's descent from the planktonic post-larval stage to the benthos Feeding behavior, actlvity rhythms, shelter preference and growth of juvenile fish were observed in the laboratory. Monthly field collections of juvenile red hake were used to study daily rhythms of shelter usage, size relationships between hake and scallops, recruitment patterns of hake from the plankton to the benthos, and growth rates. In the laboratory, hake activity, which included swimming and agonistic encounters, was predominantly nocturnal. Hake, ranging In size from 23 to 116 mm (TL), inhabited scallop shelters more often by day than by night in the field. Mean size of hake inhabiting scallops increased with larger scallops. Small scallops (< 100 mm) contained predominantly small hake (25-65 mm), but large scallops (> 120 mm) contained a wide size range of juvenile hake (26-116 mm). In shelter preference tests, juvenile hake chose non-living shelters over living scallops. Recruitment of hake from the plankton to the benthos lasted from September to December. Recruits in September ranged from 23 to 30 mm, while recruits in November were as large as 46 mm. Rates of recruitment were highest d u r ~n g October to November. Most hake emigrated from the scallop bed by February, at sizes of approximately 90 to 100 mm (TL), but a few individuals remained until May. Growth rates (length) of juvenile hake in the laboratory averaged from 0.61 % d-' to 1.00 % d-l, increasing with increasing average daily temperature. Growth (length) in the field during November to December was 0.93 % d-l. Results suggest that shelter is an important resource for juvenile red hake. Variable growth rates and a prolonged recruitment period of hake to the benthos may result in overlap in size between different year classes of red hake. The abundance of juvenile red hake may be a better predictor of future year-class strength than planktonic eggs and larvae.