Merluccius

Abstract: The mean trophic level (TL) of fish landed in fisheries on the east and west coasts of Canada is declining by 0.03–0.10·decade–1, similar to global trends. This finding is based on data from United Nations Food and Agriculture Organization and the Canadian Department of Fisheries and Oceans and other Canadian sources for the period 1873–1997. Significant rates of decline in mean TL were obtained even when key species — Atlantic cod (Gadus morhua) on the east coast and Pacific herring (Clupea pallasi) and Pacific hake (Merluccius productus) on the west coast — were omitted from the analysis. Fish taken in inland water fisheries did not exhibit a decline in mean TL. Two models were developed, based on length and age, respectively, for correcting TL estimates of individual species for the effects of changes in body size due to changes in fishing mortality. Both produced corrections that were small relative to changes in mean TL that resulted from changes in species composition of the catch over time. Overall...

Abstract: The advection of Merluccius productus larvae offshore appears to be a significant factor in establishing recruitment levels. Pacific hake spawn mostly in January and February over the continental slope in the area of study. The offshore distribution of larvae is positively correlated to offshore Ekman transport, while year class strength and offshore Ekman transport a t the time of spawning are negatively correlated. Since the juvenile nursery is inshore over the continental shelf, larvae advected seaward of the continental shelf probably have poor survival as juveniles. Larval survival also appears to be poor in cold years of strong offshore transport. A multiple regression model accounts for 72 % of the variance in an index of year class strength.