Bottom temperature and oxygen level were measured in the northern Gulf of St. Lawrence during a ground‐fish trawl survey held in August and September 1991. Cumulative relative frequencies of temperature and oxygen level and cumulative relative frequencies of temperature x cod and oxygen X cod were computed with consideration of the random stratified sampling scheme. A total of 84‐3% of temperature x cod frequency cumulated from 2oC to 4oC, but only 25% of the frequency of temperature alone cumulated from 2oC to 4oC. At an oxygen level of 3.4 mg/1, only 2.6% of the oxygen X cod frequency had cumulated, while 24.3% of the cumulative frequency of oxygen alone was already observed at the same oxygen level. A comparison of the cumulative relative frequencies of temperature and of temperature X cod indicates that cod choose intermediate temperatures in the available range. A comparison of the cumulative relative frequencies of oxygen and of oxygen x cod indicate that cod avoid water with an oxygen level below 3.4 mg/1. This oxygen level is known to cause physiological stress in captivity. Data from the stations with oxygen levels ± 3.4 mg/1 were ignored, and the cumulative relative frequency of temperature was recomputed. As a result, the avoidance of cold water by cod was emphasized: 23% of the cumulative frequency of temperature alone was below 2oC, and 47.8% was above 4oC, in contrast to 17.2% and 57.5%, respectively, prior to removal of data from hypoxic stations.

Atlantic cod (Gadus morhua) caught along the Labrador and Newfoundland coasts and in the Strait of Belle Isle often smell strongly of sulfur, a problem locally called "blackberry feed". Early studies have shown that the sulfurous-smelling cod had fed almost exclusively on the pteropod Limacina helicina and that dimethylsufide (DMS) was responsible for the odor. In August 1991, we conducted a cruise in the northeastern Gulf of St. Lawrence and in the Strait of Belle Isle in order to confirm the algal origin of dimethylsulfoniopropionate (DMSP, the precursor of DMS) and to determine the factors responsible for its transfer in the food web. A significant correlation was found between the distribution of DMSP and the abundance of microflagellates, dinoflagellates, cryptomonads, and prymnesiophytes (mostly Chrysochromulina spp.). The concentration of DMSP in L. helicina and in particles were also linearly related, suggesting rapid accumulation of DMSP in pteropod. The weight-specific DMSP content of L. helicina was always high (1–21 mg DMSP/g) and apparently sufficient to create blackberry feed symptoms in cod. Results from bioassay experiments demontrated that L. helicina may significantly influence the DMSP–DMS dynamics in subarctic waters.

Juvenile (83-group) Atlantic mackerel were captured between 1977 and 1980, and in 1988, in the Gulf sf St. Lawrence. Daily rings were identified and validated on their sagittae over the size range 93-1 70 mm; the age of larval and juvenile mackerel was estimated over the size range 7-1 92 mm (fork length). A one-cycle Gompertz curve was fitted to length-at-age data and the parameters were: L, = 5 80.8 mm, K = 8.043, and to = 37.7 d. The maximum calculated growth rate was 2.86 mm/d. The growth rate of 0-yr mackerel from the Gulf of St. Lawrence could be faster from that reported for 0-yr mackerel from the Middle Atlantic Bight: the mean growth rateof fish from both regions was respectively 1.38 and 1 -02 mm/d in theage interval 10-20 d; 2.38 and 2.07 mm/ d in the age interval 20-383 d; and 2.79 and 2.69 mm/d in the age interval 3 0 4 0 d. this difference in somatic growth rate could provide the basis for determining the origin of adult fish if it resulted in permanent and discernible records on the otoliths, and if otolith growth is coupled with somatic growth. Des maquereaux bleus juveniles (groupe 0) ont et6 captures entre 1977 et 1980 et en 1988 dans le golfe du Saint-Laurent. Bes anneaux quotidiens ont 4t4 rep5res et valid& sur les sagittae de ces poissons (93-1 783 mm); ['Age de larves et de juveniles a 4t6 6valu6 sur des sp6cimens dans l'intervalle de taille 7-1 92 mm. Une courbe de Gompertz 2i un cycle a ete adaptee pour les donnees sur la longueur en fonction de l%ge; [es param6tres etaient 22 12Can.

We compared daily growth patterns of otoliths of juvenile Atlantic mackerel (Scomber scombrus) younger than 91 d between the two spawning groups that occur in the Northwest Atlantic using a Gompertz model to determine whether it is possible to differentiate these groups on the basis of otolith microstructure in a mixed fishery. The growth curve parameters for the northern and southern groups, respectively, were 36.2 versus 39.7 d for the inflection point (t0), 0.047 versus 0.040 for the instantaneous growth rate (k) when t = t0, and 169.1 versus 192.5 mm for the asymptotic length at the end of the first summer of growth (L∞). These growth curves do not significantly differ (likelihood ratio test, P > 0.5). It therefore appears that the otolith microstructure corresponding to the first summer would not allow identification of the group of origin.

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