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UBC Theses and Dissertations

The sunken gill-net fishery, and an analysis of the availability of the dog-fish (Squalus suckleyi Girard) and the soup-fin shark (Galeorhinus galeus Linnaeus) in British Columbia waters from 1943 to 1946 Barraclough, W. Edward

Abstract

As the requirements for vitamin “A” increased during World War II, the livers from the Pacific coast dog-fish (Squalua suckleyi) and the soup-fin shark (Galeorhinus galeua) became one of the principal sources of vitamin "A". Under the pressure of a high and increasing fishing intensity, the catch of these two sharks in British Columbia has dropped greatly during the years following 1944. Changes in the availability or relative abundance of the dog-fish and soup-fin shark caught in Hecate strait and the dog-fish caught off Barkley sound on the west coast of Vancouver island were determined from the analysis of the-individual tally slips or fish receipts of each fishermen's landing of the livers from these two sharks caught by sunken gill-nets. Methods employed in the analysis of the data to determine the availability, included the analysis of the total landings of the livers from each area under investigation; the average boat catches per month; and average boat catches per trip per month. The method of link relatives is used in the analysis and the catch per unit of effort off Barkley sound is determined. The availability or relative abundance of the dog-fish in Hecate strait was found to decline from 1943 to 1945 with a slight increase during 1946. The availability of the soup-fin shark was found to decline greatly from 1944 to 1946. In the year 1946, the soup-fin shark fishery in Hecate strait was almost a failure. The decline in the availability of the dog-fish and the drop in the average vitamin “A” per gram of liver oil is closely related to the removal or possible depletion of the older age classes from the population. On the west coast of Vancouver island, off Barkley sound the index of return per unit of effort (one sunken gill-net 75 fathoms long fishing over a period of 24 hours) indicated that the availability of the dog-fish has increased in each year since 1944. The sunken gill-nets (7 inch stretched mesh) were found to select; dog-fish greater than 76 cm. in length. Small dog-fish of no commercial value (less than 76 cm.) tend to pass through the meshes.

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