摘要:

Carapace measurements of lobster larvae caught in the western part of Northumberland Strait showed that in this area the natural growth in length per moult is 34.4 per cent from stage 1 to stage 2, 31.8 per cent from stage 2 to 3, and 30.3 per cent from stage 3 to 4. The seasonal distribution of the first four larval stages was determined from plankton tows made continuously from mid-June to late September each year from 1948 to 1952. To determine natural annual growth, lobsters of 15 to 25 cm., total length, were sorted into five or six size groups and were distinctively marked by means of holes punched through the tail fan. These were liberated on six widely separated fishing grounds in the Maritime Provinces. Recoveries of these marked lobsters four to twelve months after release showed that in the southern Gulf of St. Lawrence, 15- to 20-cm. lobsters grew 8 to 9 mm. (13 to 15 per cent) in carapace length, 22 to 25 mm. (13 to 14 per cent) in total length and 80 to 95 grams (45 to 53 per cent) in weight. In southern Nova Scotia and Grand Manan 20- to 25-cm. lobsters grew 10 to 12 mm. (13 to 15 per cent) in carapace length, 27 to 34 mm. (12 to 15 per cent) in total length and 170 to 220 grams (43 to 54 per cent) in weight. From the carapace length of 4th-stage larvae and straight-line equations relating carapace length before moulting and carapace length after moulting, the average carapace lengths of lobsters in stages 5 to 20 were calculated. From observations and calculations on the growth per moult and moulting frequency, it is estimated that in the Northumberland Strait area lobsters reach a length of 14 cm. (51/2 in.) at the end of the fifth growing season (41/4 years old) and 24 cm. (91/2 in.) at the end of the ninth growing season (81/4 years).

ISSN:0706-652X    

DOI:10.1139/f53-024

出版商:NRC Research Press    

年代:1953

数据来源: NRC

摘要:

Ages were determined of 6,571 whitefish for which sizes were recorded. A length-weight relationship, the percentage of both sexes mature at each age, the sex ratio, the proportion of mature females that spawn annually and the relationship between size of fish and number of eggs were determined from smaller samples.Growth rate is difficult to assess because of net selection, but it seems to be slower than in more southerly lakes. Growth appears to be limited to the period June to September inclusive.The total annual mortality rate of 61 per cent represents the unexploited condition—four years of commercial fishing with 51/2-inch mesh gill-nets produced no obvious change. A moderate mortality rate acting at all ages will easily account for thousands of eggs being produced for every whitefish that survives to maturity—it is unnecessary to assume a low percentage of eggs fertilized or excessive mortality among fertilized eggs or among young fish.A more intensive fishery would probably increase sustained yield.

ISSN:0706-652X    

DOI:10.1139/f53-025

出版商:NRC Research Press    

年代:1953

数据来源: NRC

摘要:

not available

ISSN:0706-652X    

DOI:10.1139/f53-026

出版商:NRC Research Press    

年代:1953

数据来源: NRC