Remote Sensing of Whitings in the Bahamas

Whitings on both the Great Bahama Bank (GBB) and Little Bahama Bank (LBB) were evaluated using data collected from 2000-2010 by the Moderate Resolution Imaging Spectroradiometer (MODIS) instruments onboard the Terra and Aqua satellites. A semi-objective method was developed to classify whiting patches from other look-alike features using the recently developed Floating Algae Index (FAI) algorithm, an empirical cloud masking algorithm, and a gradient analysis from the 250-m resolution MODIS data. A total of 1,500 images with minimal cloud cover was used to calculate long-term and seasonal trends as well as an average daily coverage for both banks. Annual and monthly frequency of occurrences for whitings at every location was also calculated. Based on the results, the distribution of whitings over the GBB was restricted between 25–30\u27N and 23–45\u27N and occurred most frequently on the edge of the bank. Whitings were observed throughout the LBB and at much higher frequencies than in the GBB, especially on the east side from November to February. Results from daily whiting coverage indicate whitings cover nearly twice as much area over the LBB compared to the GBB. Whitings show a clear seasonal variation with respect to coverage on both banks. Whiting coverage over the LBB has a clear seasonal variation with peak coverage in spring (April) and fall (November) and minimum coverage during summer. Whiting coverage over the GBB peaks in spring (April), but no second peak or seasonal minimum was observed. Sea surface temperature (SST), photosynthetically available radiation (PAR) and wind were compared to the observed long-term and seasonal trends of whiting coverage. Using multi-variable analyses, the influence of SST and PAR on monthly whiting coverage over the GBB from 2000-2010 was found to be statistically significant, though the correlation between the three values was low. The results indicate that these parameters may not directly influence whiting origin and coverage but rather have an effect through influence mechanism, for example through phytoplankton blooms. It is hypothesized that whitings are directly influenced by cyanobacterial phytoplankton, which are dependent on SST and PAR. Long-term trends in whiting coverage differ between the two banks. In general, whiting coverage appeared to be decreasing from 2000-2010 over the LBB, while the opposite trend was observed over the GBB during the same time period. It is currently unclear what led to these opposite trends due to lack of long-term, in-situ measurements of the water environments in the two banks. However, this is the first study that documents the long-term trends for both banks, from which one may infer that the processes affecting whiting occurrence in the two banks vary greatly and future research is needed to understand the driving forces of whitings in order to improve the current understanding of their contributions in the global carbon cycle