Date of Award

6-1950

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Wildlife Ecology and Wildlife Conservation

Abstract

Anatomical studies of Placopecten magellanicus agreed with previous investigations, except that a crystalline style was found, but only in fresh specimens. Ring mesh size of the dredge controlled relative frequency of size classes in commercial dredging, which yielded 97.7 per cent commercial sizes. Growth was most rapid during the first five years and slowest after the seventh. The minimum size for commercial utilization was about 80 millimeters, attained at about four years. The commercial catch was 60-8 per cent composed of ages up through seven years and 38.8 per cent composed of ages up through five. Maximum age was over 19 years. In 1948, spawning occurred during August and early September and gametogenesis began immediately afterward. Three year old, 60 millimeter scallops were the youngest and smallest found with well-developed gonads but most matured at about 60 millimeters. The latter were taken commercially after one spawning. The sex ratio was 0.9 females per males. Recoveries of 5.2 per cent of 250 tagged and released scallops indicated only movement from shallow into deeper water, harmful organisms were: the boring sponge, Cliona celata; the artic rock borer, Saxicava arctica; and the starfish, Asterias vulgaris. The commercial catch per unit of effort on four beds ranged from 0.22 to O.ljO gallons per 10,000 cubic feet dredged per hour and gave an approximation of relative abundance. This relationship was influenced by the type of gear, type of bottom, experience of and time of the season. On six beds, average area dredged to obtain a single commercial sized scallop ranged from 182.4 364.8 square feet. It was recommended that: 1. A four inch minimum law, enforced by regulation of dredge ring mesh size, be seriously considered. 2. The present open season be continued. 3. Scallopers be urged to destroy all starfish dredged. 4. An intensive study of one bed be made over a full year period. 5. Further studies be made to include catch per unit of effort, age and growth, migration, early developmental stages, mortality and hydrographic characteristics of scallop beds.

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