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The influence of surface currents on the dispersal of coho salmon (Oncorhynchus kisutch) from the Strait of Georgia

University of British Columbia

The dispersal pattern of coho salmon (Oncorhynchus kisutch) was studied to explore the extent to which coho distribution can be explained by random movement and advection by surface currents. A computer simulation model was constructed to simulate the dispersal of tagged coho salmon after 13 months of ocean residence. The simulation model is spatially organized into 310 habitat boxes representing the waters surrounding Vancouver Island. Simulated fish represented by number of particles were released and subject to pure random walk and biased random walk procedures. The biases in particle movements were proportional to the strength and direction of the surface currents. The behaviour of the fish also included a weak shore seeking tendency. The general pattern of surface currents of the waters around Vancouver Island was estimated using the results of oceanographic studies available from that area. Best estimates of surface current was based on the seasonal pattern in each major water bodies. Catch-effort analysis was performed to determine the nature of troll fisheries which are used to compare the results of the model. The troll fisheries are found to be more intensive in the outside region (in the west coast of Vancouver Island) than in the Strait of Georgia region. The distribution of tag recoveries was analyzed by using the abundance index of tag per unit effort (TPUE) from each recovery regions. From the TPUE distribution of Big Qualicum fish, it is significant that there are more fish in the inside area, especially in the Strait of Georgia region compared to the outside area. The simulation results show that the model is sensitive to current as compared to random movement. The general pattern of simulated fish distribution is found to be abundant in the Strait of Georgia region, followed by the Central troll region in the northern part of Vancouver Island, and the southwest and northwest regions, respectively. Trapping event by the surface current is speculated to cause the high proportion of fish in the Strait of Georgia compared to other regions. The comparison between the distribution resulted from the simulation models and the observed distribution from the tag return data shows a qualitative similarity which suggests that the influence of surface currents on fish dispersal is apparent. From this study it is apparent that the influence of surface currents alone is not enough to account for interannual variability in the distribution of tag recoveries. Several factors, such as directed migration of the fish, availability of food and oceanographic conditions, including anomalous flushing events, wind and sea surface temperature, were speculated to become the potential factors that might cause the interannual variations.

Thesis/Dissertation

application/pdf

2009-01-16

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http://hdl.handle.net/2429/3733

Oceanography

University of British Columbia

UBCV

DSpace