Comparing in situ and satellite temperature data on the Agulhas Bank to understand changes in anchovy (Engroulis encrasicolus) distribution

Master Thesis


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University of Cape Town

Satellite data have high spatial/ temporal resolution, extensive coverage and are easily accessible, making them a common part of many studies on the oceans. One such important study to use satellite data found a relationship between the cross-shelf SST difference on the Agulhas Bank and the relative distribution of anchovy (Engraulis encrasicolus) spawner biomass east of Cape Agulhas. However, other studies have shown that nearshore satellite data may not be as accurate as originally believed. Using the relationship observed in the aforementioned study as a test, I compared time series' from two types of in situ temperature data to satellite SST data. A combined CTD/CalVET (PISCTD) data set was used for in situ data on the coastal and offshore regions of the Agulhas bank whereas a data set with two UTRs was used for inshore in situ data. None of the data sets correlated significantly with each other, save the two UTRs. Both in situ data sets showed a negative relationship between the size of the cross-shelf temperature difference on the Agulhas bank and the increase in anchovy biomass there, whereas the satellite data showed a positive relationship. This was largely due to the pattern of decadal warming observed in the in situ data whereas the satellite data showed decadal cooling. Even though it was found that the difference in sampling methodology between the satellite and in situ data sets prevented them from being accurately compared, the difference in the annual and decadal patterns between these two types of data do support other findings showing discrepancies between remotely-sensed and in situ data for nearshore environments.

Includes bibliographical references.