April 02, 2012
Need a reason to plan a trip to The Bahamas? Mitchell Roffer, of Roffer's Ocean Fishing Forecasting Service (ROFFS), predicts 2012 to be a banner year in The Bahamas.
Since 2003 we have been developing an objective method for forecasting the overall fishing action at all of the Bahamas Billfish Championship (BBC) tournaments. The hypothesis for forecasting the seasonal marlin fishing action stems from the location and geographic extent of the bluer and often warmer water that occurs from the Cat Island – San Salvador Island area where it is presumed that the marlin concentrate before and during spawning. We have been referring to this water as “Bahamas blue marlin water.” We assume that the marlin are associated with this water and the more white and blue marlin water that exists in the Abaco Islands and Eleuthera Island areas, the greater the marlin relative apparent abundance will be in these areas.
Based on our observations of the fishing action in the Bahamas over the last 20 plus years it appears that excellent fishing action overall occurs within the BBC tournament area when there is a substantial volume of the blue marlin water pushing over the 100 fathom ledges along the eastern side of Eleuthera and Abaco. Relatively good fishing seasons occur when this water occurs over the 1000 fathom curves, but not the 100 fathom curve of both areas. Mediocre years occur when there is a lack of this water over these areas. Good fishing action is also linked to favorable currents and when the water mass boundaries of these currents are stable, i.e. persistent convergence, for three to five consecutive days over good bottom topography to concentrate the fish's forage. For the BBC tournament areas, the dissolved oxygen concentration does not appear to be a major factor compared with the temperature, color and clarity of the water. In other more southern Bahamas waters, the dissolved oxygen is a major controlling factor on fish distribution as low oxygen levels at depth force the fish away from the low oxygen zones and often closer to the surface. We look forward to the years when we have more dissolved oxygen measurements in the northern Bahamas and other areas around the United States.
During the last several years, the conditions were favorable as early as January and February in terms of the presence of blue marlin water off Abaco and Eleuthera. However, due to the currents generated by relatively large eddy features located 60-90 miles northeast of Eleuthera, the blue marlin water was pulled away from the BBC tournament area. In those years there have been several day periods when a relative small amount of this water moved into the tournament area and catch rates increased. Unfortunately, these favorable conditions were not persistent throughout the entire tournament season. For example in 2011 (see Figure 1 and 2) there was blue marlin water throughout the BBC area in February. However, the blue marlin water was pulled offshore of Long Island (south of Cat Island) by a relatively large clockwise eddy that is centered approximately 45 miles east of San Salvador. This eddy pulled the water northeastward and a significant amount of this water was pulled farther offshore from Cat Island and Eleuthera by a counter-clockwise eddy that is centered approximately 60 miles east of Eleuthera. Both eddy features moved away from the BBC zone. Last year we stated that “this is not favorable for good blue marlin action over the ledges off Cat Island and Eleuthera. These conditions would normally suggest that the oceanographic conditions over the BBC tournament areas were unfavorable for a highly productive blue marlin season.”
Figure 1 and Figure 2 represent the ocean conditions at the end of February, 2011. Figure 1 is a false color enhanced thermal infrared image for sea surface temperature (sst) composed of satellite data observed on February 20th and 22nd. Figure 2 is a false color enhanced ocean color image for the same period (February 20th and 22nd) derived from the NASA Aqua satellite.
Unfortunately, our analyses were accurate and the 2011 BBC season was characterized oceanographically by being dominated by Gulf Stream water and a mixture of mostly Gulf Stream and Bahamas blue marlin water. There were no extended periods when the Bahamas blue marlin water was pushing into the 100 fathom ledges for any tournament. This resulted in a mediocre BBC season, although there was a Bahamas blue marlin record of 1119 lbs. landed by fishing vessel Double Dog.
2012 Seasonal Forecast
We have been asked to forecast the BBC in March. One of the challenges of producing such an early forecast of the oceanographic conditions for the BBC is that these fishing events extend over a relatively long time frame; from the last week in April through the third week of June, 2012. And that conditions are likely to change dramatically from one event to the next. In addition, there are no reliable numerical oceanographic models or even atmospheric models to use to make high resolution local oceanographic forecasts.
The global models provide some guidance, but for the needed spatial and temporal resolution of the ocean conditions, we are forced to rely on our qualitative experience as we have been monitoring the conditions over the Bahamas for over 20 years. This experience is based on the satellite observations of the ocean conditions derived by Roffer's Ocean Fishing Forecasting Service on a near hourly basis. The satellite data (infrared for sea surface temperature and ocean color for indices of phytoplankton, clarity, and colorized dissolved organic material) are received from a variety of sources including, but not limited to NASA, NOAA, and the European Space Agency (ESA). We also use data derived from drifting buoys and from satellite altimeters. The altimeters provide a very course spatial resolution and the time delay (10 days to produce usable circulation models), limits the data's utility. While the ocean changes significantly over 10 days, the altimeter data can be used for an overall, albeit 10 day average view of the surface (above the thermocline) circulation. In addition, we use the climate data, analyses, and forecasts provided by Columbia University's International Research Institute (IRI) for Climate and Society, and NOAA's climate prediction website, as well as, the Florida State University Center for Ocean-Atmospheric Prediction Studies program. We use catch data from a variety of public and private sources.
Each year we are asked about the El Niño – La Niña situation in the Pacific Ocean although there are no obvious direct effects on the ocean conditions during the BBC tournament season, other than perhaps sea surface temperature patterns. Maybe by next year we will be more knowledgeable and enhance our use of other climate indices like the North Atlantic Oscillation (NAO) index or the Atlantic Multi-decadal index (AMO) which may be more closely related to the overall wind driven ocean circulation in the North Atlantic Ocean. In the meantime we will discuss the more popular El Niño – La Niña conditions. Presently there is a La Niña condition in the eastern tropical Pacific Ocean that is weakening. According to IRI's global models the precipitation from March through May, 2012 will be below normal and becoming normal in June. Air temperature March through June is likely to be below normal in the Bahamas, becoming normal in July. The forecasts for sea surface temperature (SST) are mixed depending on whether the global model or tropical models are used. One model (Tropical) predicts normal SST, while the Global model forecasts cooler SST of 0.9°F – 1.8°F for March through May with only 0.9°F below normal for June. It is our opinion that when the models deviate like this that not much guidance is provided, especially when the NAO index is strongly positive which suggests warmer air temperatures implying warmer SST for the U.S. east coast and northern Bahamas.
At ROFFS we have always liked to view the future in terms of present conditions along with persistence. In other words, what we have now is likely to continue into the short-term future unless we can see reasons that the conditions would dramatically change. We have derived a few indices ourselves. The ROFFS 10 year (2003-2012) mean sea surface water temperature (SST) for the core of the Gulf Stream off Miami was 78.3°F during our standard March 05-06 measurement period. The range has been as low as 74.8°F (2009) to a high of 80.5°F (2007). This year the SST was 79.1°F. While have not been recording the SST off Cat Island during this same period, the five year mean (2008 – 2012) SST for the Cat Island area is 76.0°F and this year the SST was a substantially warmer 77.4°F. While we are unsure of the significance of the higher sst in the Gulf Stream, the warmer blue marlin water off Cat Island is favorable for bringing blue marlin into the BBC area earlier than normal assuming that the water continues to warm seasonally and their migration is primarily mediated by their temperature habitat preference.
As discussed earlier the critical aspect for having a good blue marlin season is the presence of the blue marlin water pushing over the 100 fathom curve creating persistent convergence zones for food to concentrate. Figures 3 and 4 show the present distribution of the blue marlin water. Figure 3 was derived over the March 03-06, 2012 period using a variety of infrared satellite data from NOAA, NASA, and ESA data that shows the water masses based on their signature sst. Figure 4 is an ocean color image that was derived from NASA and ESA satellites over March 01-03, 2012 that show the water masses based on their signature ocean color. Clouds prevented us from providing an exact match in time due to the clouds associated with the strong cold front that stalled over the Bahamas. But using a variety of computer techniques ROFFS™ was able to remove many of the interfering clouds to allow a one day overlap of the imagery which provides a better comparison.
The conditions in 2012 are dramatically different than the conditions seen in 2011 (see Figures 1 and 2). Of note is the clockwise rotating eddy located northeast of Abaco (centered near 76°15W & 27°15'N) that has pulled a substantial pool of blue marlin water from the Cat Island – Long Island area. While some of the blue marlin water east of the Cat Island – Long Island area is being pulled northeastward by another clockwise rotating eddy northeast of Eleuthera, the eddy northeast of Abaco has been pulling the bluer marlin water westward since the first week in February and the favorable conditions already exist over the 100 fathom curve from the “Pocket” east of Cherokee Sound, over the Little Abaco Canyon to the Great Abaco Canyon. As this eddy moves northwestward it is expected to continue to pull the bluer water northwestward and maintain the conditions we have been monitoring.
As the eddy, now (first week of March, 2012) northeast of Abaco moves northwestward over the next few weeks, it is likely to be replaced by the other eddy which is presently located northeast of Eleuthera. This suggests that the blue marlin water will continue to be pulled over the BBC tournament area bringing a steady stream of marlin. Figure 5 was derived from altimeter data from NOAA/AOML/CoastWatch (10 days to produce one day of model output) ending March 05, 2012 and modified by ROFFS. It shows three (A, B, and C) clockwise eddy circulation features of many others in this region. These eddy features typically move in a northwestward direction. While the movement of eddy “B” and “C” remain to be seen it is likely and we are hopeful that they will continue their northwest motion bringing more Bahamas blue marlin water into the BBC zone.
Based on the information we have analyzed, the conclusion, i.e. our forecast, is that the BBC will have a relatively high abundance of blue marlin this season. These conditions are the most favorable that we have seen for a long time. Not incidentally, blue marlin fishing action, along with unusually early high catch rates of mahi mahi and yellowfin tuna, have been experienced from the Andros Island – Chub Cay area to Treasure Cay since January. Not only does this support our oceanographic analyses, this is also a very positive indicator for the tuna, mahi and marlin season from Jacksonville, FL to Cape Hatteras, NC this spring and early summer as the fish move northwest with the Bahamas water until it mixes with the eastern side of the Gulf Stream.
While it appears that there will be an abundance of these fish from the Bahamas to North Carolina, good fishing action on a daily basis is strongly linked to local currents. When the water mass boundaries of these currents are favorable, i.e., over good bottom topography to concentrate the bait fish, then the real fun action happens. This is controlled by sub-daily and daily, small scale movements of the currents. Stay tuned for these daily forecasts as subtle changes in the currents and convergences have dramatic impacts on the distribution of feeding concentrations of fish. Get ready the good fishing is about to happen! This is likely to be the year when fishing action in the BBC gets very good. Not the year to be sitting and watching the action on the internet.