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Oceanographic factors affecting the catchability of Pacific Ocean perch, Sebastes alutus (Gilbert)

University of British Columbia

A main concern in fisheries science has been to identify an accurate index of fish abundance. An underlying paradigm in the science has been that the amount of effort (calculated in hours and standardized for boat size) spent fishing was the best variable to be used to account for the variation in catches. The use of the ratio, catch per unit of effort (cpue), assumes that variations in fish abundance are due to human-controlled processes above the ocean's surface. It does not account for variation due to oceanographic processes that affect fish behaviour and movement patterns below the ocean's surface. This study investigated the possibility that oceanographic factors such as temperature, salinity and depth could have effects on the variations observed in the apparent abundance of a demersal rockfish, Pacific Ocean Perch (Sebastes alutus. Gilbert). Simultaneous monitoring of physical variables and fish abundance estimation was achieved by attaching oceanographic equipment to the fishing gear of commercial vessels, monitoring the acoustic equipment and sampling the fish catch. It was found that Perch prefer a temperature range from 6.7 °C, down to at least 4.8 °C and that their movement patterns are linked to the movement of these temperatures by coastal wind patterns. Perch prefer areas with steep bathymetry, characterized by frontal activity due to interactions between the local bathymetry and tidal currents. Concerns that sampling only from highly successful commercial vessels may have biased abundance estimates, prompted the analysis of historical records of fish catch and government research surveys. Analyses between different boat sizes, different areas and different seasons from the original historical data base and a corrected subset revealed that it was mainly differences between areas that was responsible for the biasing of estimates. Deeper areas predictably produced more fish for all sizes of boats, but were fished more often by the larger boats used in the study. Therefore the field abundance estimates are likely to be biased towards areas of larger perch concentrations.

Text

2010-11-08

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http://hdl.handle.net/2429/29875

Zoology

University of British Columbia

Graduate