The effects of photoperiod, feeding frequency, and water temperature on formation of otolith daily growth increments in juvenile chinook salmon (Oncorhynchus tshawytscha) were examined. Feeding frequency influenced both increment number and width, whereas photoperiod and temperature affected only increment width. Fish fed once/24 h produced one increment every 24 h on average, while fish fed 4 times/24 h produced more than one increment every 24 h. Wider increments were produced in fish exposed to warmer water (11 °C) or 24 h of darkness. The ratio of otolith size to fish size remained constant throughout and between the photoperiod, temperature, and feeding frequency experiments, regardless of the number or width of increments produced. Although otolith growth is isometric with respect to increase in fish length under these experimental regimes, otolith microstructure will differ in fish of the same size reared under different environmental conditions. An understanding of factors affecting otolith increment production is required before increment number and width can be used to assess growth rates.Key words: otolith, daily, growth increments, chinook salmon

Stomach content data on 14,796 spiny dogfish (Squalus acanthias) from British Columbia waters are presented. The major dietary components based on occurrence were 55% teleosts, 35% crustaceans, and 5% molluscs. The principal food items were herring (22%) and euphausiids (14%). Prey was largely pelagic (80%), with fishes predominating in winter and invertebrates in summer. Fishes became more important in the diet with increasing dogfish size. Dogfish consumed twice as much food in summer as in winter. Annual consumption varied from 5 times biomass for small dogfish to 2.5 times for larger animals. Preliminary analyses suggest that dogfish consume over 5 times the current annual commercial catch of herring, but insignificant quantities of salmon. Key words: dogfish, Squalus, feeding, food, biomass, predation, metabolism, seasonality, survivorship, digestion

The cxcrction of dissolved inorganic and organic phosphorus by scvcrnl species of marinc crustaceans and a planktonic rotifer was measured under laboratory conditions. The rate of excretion decrcascd as bacterial activity and duration of cxperimcnts increasctl and was directly related to tempcraturc and salinity. Excretion rates were higher in early evening than at other times of day.The claily phosphorus r&miremcnts of the phytoplankton, calculated from 14C mcasurcd rates of production and an assunrcd C : P ratio of 40 : 1, were compared with phosphorus released by zooplankton.The rates of excretion and the abundance of zooplankton were used to calculate an average daily adclition of inorganic phosphorus to the photic zone. Jn Bras d'Or Lake, zooplankton released twice the average daily phytoplankton phosphorus requirement; in Morrison's Pond, only one-fifth was supplied by animal excretion. Microzooplankton excretion (not considered in this study) may explain the discrepancy between phytoplankton rcquiremcnts and rcgencrntion rate in Morrison's Pond. Phosphorus supplied from the hypolimnion by eddy diEfusion in Bras d'Or Lake was one-tenth that rcgenerated by the-zooplankton--

No abstract

For otolith increments to provide useful estimates of fish growth, otolith growth must covary closcly with somatic growth. We reared groups of juvenile chinook salmon (Onrorhynrhus rshayvrschu Walbaum) for 70 days, changing ration or temperature during a 20-day treatment period. Restricted rations halted somatic growth, however increment widths decreased gradually; somatic growth was overestimated from increment width. Otolith growth followed changes in water temperature more closely than changes in ration, supporting a hypothesized effect of metabolic rate on otolith growth. Increment growth was only loosely coupled to fish growth rate, and may also be affected by past growth histories. For juvenile fish, increment widths may not be sensitive indicators of short-term changes in growing conditions.