Each population of Atlantic herring (Clupea harengus harengus) has its own seasonally fixed spawning period of a few weeks duration, but the mean spawning times of different populations differ substantially. The extant theory explains the population-specific timing of spawning relative to the plankton production blooms in the inferred larval distributional area. Support of this theory is evaluated, and found lacking, in the light of a recent "stock" hypothesis involving larval retention. The new hypothesis involves two constraints. First, the larvae of a discrete herring population develop within, and are thus adapted to, the specific oceanographic conditions of their larval retention area. Second, metamorphosis from the larval to juvenile form occurs primarily within a restricted period of the year (April to October). Given these two constraints, it is hypothesized that the timing of spawning of a herring population is a function of the time necessary to complete the larval phase and yet metamorphose within the acceptable seasonal envelope. Populations that have "good" larval retention areas can spawn in the spring and still metamorphose within the seasonal envelope. Populations with larval retention areas that are less "good" for larval growth have to spawn earlier to satisfy the two constraints. The implications of the hypothesis on the "match–mismatch" theory are briefly discussed.

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Vertical distribution of sea scallop larvae was studied from pump samples in mixed, stratified, and frontal areas of Georges Bank. The extent of larval aggregation was positively related to the degree of water column stratification. In mixed areas larvae were distributed evenly over the 40 to 50 m water column, while in stratified waters larvae showed subsurface peaks in concentration above the pycnocline. Where the pycnocline was well developed, differences in the larval centre of mass (ZCM) were associated with differences in the position of the pycnocline. Food for sea scallop larvae was measured as the concentration of chlorophyll a < 15 Km and particles 2.5 to 16 pm. In stratified areas food was usually greatest within the upper 10 m. Sea scallop larvae were most concentrated below 10 m and d~d not aggregate in relation to food concentration. The capacity of sea scallop larvae for depth regulation on Georges Bank appears limited, since there were no die1 differences in the ZCM, and sizedependent differences in vertical distribution were weak and inconsistent.

Ont. N1 G 2WI MeLaren, I. A., M. I. Trernblay, C. I. Corkett, and I. C. Roff. 1989. Copepod production on the Scstian Shelf based on life history analyses and laboratory rearings. Can. ). Fish. Aquat. Sci. 46: 56O-583.We estimated monthly and annual production of 10 copepod species (>99% of copepod biomass) from Emerald Bank, Seotian Shelf, by use of numerical and weight changes between samples for Calaseus spp., and by applyiwg daily growth rates based on stage durations and weight increments between stages for others. Of these others, stage durations were estimated from generation intervals inferred from samples sf Metridia Bucens, Pseudocalanus wewrnani, and Oithona sirnilis. For species without evident cohorts, notably Centrapages typicus awd Paracaianus parvus, we used published temperature-depewdewt durations. Production in dry weight was estimated as ca. 63.44 g-m-'-yr-' (39 g-m-'*yr-'), with peaks in May (largely Calanus spp.) and September (largely C. typicus, P. parvus, and other warm-water forms). All species except C . fiwmarchdcus and 0. sirnilis had annual rates 2 4 times those predicted by the Banse-Mosher allometric relationship between productionlbiomass ratios and adult body mass. This deviation is not attributable to assumptions in our analyses. Annual copepd production is broadly similar to recent estimates by others using similar methods for Georges Bank, Passarnaquddy Bay, NsB., and the North Sea. Les auteurs ont estime! les productions mensuelles et annuelles de dix es@ces de copepodes (comptant pour plus de 99 % de la biomasse de copepdes) du banc Emerald, sur le plateau Scotian, en utilisant des variations nurneriques et de p i d s entre des 4chantillons pour Cialaseus spp. et en appliquant les vitesses de croissanee journali&re dtapr&s les durees de stade et les augmentations de poids entre les stades pour les autres esp&ees. Parrni ces autres espgces, les durees des stades ont 4t4 estimees pour des intewalles de g6neration deduits 3 partir df6chantitlons de Metridia lucens, Pseudoca%anus newmani et Oithswa sirni8is. Pour des espkes ne presentant pas de cohgartes 6videntes, notamment Centropages typicus et ParacaBanus p a w s , les auteurs se sont servis de donnks publiks sur Bes dur&s dependantes des temperatures. La production a 4t4 estim& en poids see 3 environ 0,44 g.rn-".an-' (39 g-m-'.ans') avec des maximum en mai (essentiellement Calanus spp.) et en septembre bessentiellement C. typicus, P. parvus et autres formes d'eaux temper&$. Touks les especes, sauf C. finmarchicus et 0 . sirnilis, ont present6 des vitesses annuelles de 2 4 fois superieures 3 celles qui avaient 6tt5 prevues par la relation ailom4trique de Banse-Mosher entre les rapports productionlbiomasse et rnasse corporelle adulte. Cette deviation n'est pas attribuable A des hypth$ses formul6es au cours des analyses. La production annuelle de coNpodes est en gros semblable aux reeentes productions estirnks par dfautres,chercheurs 3 l'aide de m6thodes semblables pour le banc Gmrges, la baie Passamaquoddy au N.-B. et la Mer ...

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