Above: Bahamas/GOM ocean circulation using high resolution AVHRR SST satellite imagery taken from January/February 2015. Video courtesy: roffs.com

Since 2003 we have been developing an objective method for forecasting the overall fishing action during the April-June Bahamas Billfish Championship (BBC) tournament season. 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 and south where it is presumed that the marlin concentrate before, during, and after spawning. We have been calling this water “blue marlin water.” From satellite data it is relatively easy to identify this water based on its signature optical and surface water temperature characteristics. Our working hypothesis is that the marlin are associated with this water and the more “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. Also in recent years we have observed an association between this water and the yellowfin tuna action in the Bahamas, as well as, along the western side of the Gulf Stream between Jacksonville, Florida and Cape Hatteras, North Carolina, as well as, over the canyon areas northeast to Massachusetts. But as this article is focused on the blue marlin and the Bahamas, the discussion related to yellowfin tuna, the overfishing off west Africa, and catch rates off the United States east coast will have to wait for another article as we have time over the next few weeks. But as a teaser one should know that there are yellowfin tuna, bluefin tuna, mako sharks and swordfish being caught between Cape Hatteras, NC and the Norfolk Canyon (east of Chesapeake Bay) now.

Based on our observations of the fishing action and ocean conditions in the Bahamas, particularly from Eleuthera to the Abacos over the last 20+ 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 (600 feet, 200 meters) and shallower ledges along the eastern side of Eleuthera and the Abacos. Relatively good fishing seasons occur when this water only occurs over the 500-1000 fathom depths, but does not reach the 100 fathom and shallower depths of both areas. Mediocre years occur when there is a lack of this water over these areas. It is also important to understand that good fishing action on a daily basis is linked to the favorable direction of these currents and when the water mass boundaries of these currents are stable for three to five consecutive days over good bottom topography that normally concentrate the prey fish. For the BBC tournament areas, the dissolved oxygen concentration does not appear to be a major factor at the present time compared with the temperature and clarity of the water. In other areas south, the dissolved oxygen has a greater controlling factor on fish distribution.

The working hypothesis is based on the hourly satellite observations of the ocean conditions derived by Roffer’s Ocean Fishing Forecasting Service, Inc. – ROFFS™ (roffs.com) and catch reports provided by a variety of sources over 25+ years. The infrared (IR) satellite data are used to observe the sea surface temperature (SST) and the ocean color data are used for indices of phytoplankton (chlorophyll), water clarity, and colorized dissolved organic material are received from a variety of sources including NASA, NOAA, Suomi National Polar-orbiting Partnership (SNPP or JPSS), and the European Space Agency (ESA) satellites. ROFFS™ also uses data derived from drifting buoys, gliders, aircraft, private boats, and satellite altimeters. The altimeter data only provide a very coarse spatial and temporal resolution with a time delay (5-10 days to produce usable circulation models) that limits the data’s utility related to high resolution and real-time operational oceanography. While the ocean changes significantly over such short periods, the altimeter data can be used for an overall, albeit 5-10 day average view of the ocean’s surface circulation. It is not useful for evaluating small scale, short-term (daily and sub-daily) changes in the ocean currents or their boundaries.

During the last several years we had observed that the conditions over the BBC tournament area were particularly favorable as early as January to the first week in March in terms of the presence of “blue marlin” water off Abaco and Eleuthera as exemplified by the first week in March 2012 (Figures 1 & 2).

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As stated 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 1 and 2 show the distribution of the blue marlin water prior to the 2012 BBC season. Figure 1 was derived over the March 03-06, 2012 period using a variety of IR satellite data from NOAA, NASA, and ESA that shows the water masses based on their signature sst. Figure 2 is an ocean color image that was derived from NASA and ESA satellites over March 01-03, 2012 that shows 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 during this period. However, 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 to provide a better comparison.

During the actual 2011, 2012, 2013, and 2014 Bahamas tournament fishing seasons the “blue marlin” water was pulled away from the BBC tournament area by the ocean currents forced by various eddy features (60-120 miles in diameter) that occurred east and northeast of Abaco. Some good fishing action happened during these years due to the intermittent arrival of the “blue marlin” water and the general migration of the fish through the area. Unfortunately the favorable conditions were not persistent throughout the entire tournament season like some of the banner years in the 1990’s and early 2000’s. We do not know if this is represents a circulation regime shift in the region, but only time will tell. Our experience suggests that variability is the norm, but this is something that an longer term automated altimeter study could resolve.

Background and Some Data for 2015

In years past we had been asked by the BBC Tournament Director (now “retired King of the BBC” Al Behrendt) to forecast the entire BBC season from data available at the end of February and first week of March by the. While last year the new Tournament Director Jennifer (new “Queen of the BBC”) had allowed us to wait until later in the month to provide the update, this year we are back to the former policies. One of the challenges of producing a such an early forecast is that these exciting, entertaining, and fun fishing events extend over a relatively long time period from the end of April or first week of May through the third or fourth week of June. This year (2015) the first BBC tournament starts April 22^nd at Guana Cay. Conditions are likely to change dramatically from one fishing event to the next without any scientifically proven and field-tested methods to predict the changes over the two month period. Sorry, there still are no reliable numerical oceanographic models to use to make accurate and reliable high resolution localized oceanographic forecasts that extend for several days, never mind the entire season. ROFFS™ is working with other oceanographers to develop improved ocean and climate models, so perhaps next year our task for the seasonal forecast will be easier.

At ROFFS™, for forecasting short-term oceanographic conditions related to finding fish we generally believe that the conditions observed now are the ones likely to continue into the short-term future (days) unless we can see the mechanisms (currents) that would drive the changes. For some this is known as the persistence and climatology technique of forecasting. While we have two crystal balls in our office for forecasting, we prefer to use real data and we have learned that evaluating the preseason conditions annually provides insight into future seasonal trends. Experience is our guide as we have had moderate success in forecasting seasonal trends of fishing productivity based on the location, condition, and likely future changes of the fishes’ preferred habitat in time and space for a variety of species over many areas of the world. In the case of the BBC tournament season we derive our first indications during the first week in March in that whether or not we are observing “normal” (climatologically mean conditions) or anomalies. For this we rely on satellite data and a climate models from some of the experts in the field. One indication is sea surface temperature (SST) in the core of the Gulf Stream off Miami and the SST of the Bahamas blue marlin water east of Cat Island. Because we started our forecasting studies during the first week of March in 2003 we have continued our time series using that week.

The ROFFS™ 12 year (2003-2014) mean SST for the core of the Gulf Stream off Miami is 78.3°F during our standard March 05-06, 2013 measurement period. The SST has been as low as 74.8°F (2009) to a high of 80.5°F (2007) and we have not observed any overall trends as of yet unlike other areas such as in New England (increasing). Climate variability is not evenly distributed. This year the SST was 78.6°F in the Gulf Stream off Miami on March 05 (2015). While have not been recording the SST off Cat Island as long, the seven year mean (2008 – 2014) SST for the warmer water east of Cat Island area is 76.5°F and this year the SST was a substantially warmer 78.6°F. This is the warmest year to date for our limited data set. Early warming off Cat Island could signal an early start to good marlin action, assuming that they are on their migratory paths already. There are many factors controlling fish migrations, surface water temperature is just one of them.

The global, hemispheric and regional climate models also provide guidance into the present and future conditions. We usually use the climate data, analyses, and forecasts provided by Columbia University’s International Research Institute (IRI) for Climate and Society (http://iri.columbia.edu), NOAA’s Climate Prediction website (http://www.cpc.ncep.noaa.gov), and the National Center for Atmospheric Research (NCAR   https://climatedataguide.ucar.edu/about), as well as, sage advice from our colleagues at NOAA’s Atlantic Oceanographic and Meteorological Laboratory (AOML http://www.aoml.noaa.gov/) and the University of Miami’s Cooperative Institute for Marine and Atmospheric Studies (CIMAS http://cimas.rsmas.miami.edu/ ). We use catch data from a variety of public and private sources. Based on the 2015 IRI multi-model probability forecast, the precipitation is expected to be the climatological mean, or what many people refer to as “normal” conditions over the April-May-June period. Air temperature is likely to be normal and sea surface temperature is forecasted to be 0.0-0.9°F above the mean. This suggests that the marlin will not be delayed due to lower than normal water temperatures.

As we are learning more about air – sea interaction, climate variability and ocean-wide circulation we started considering other indices a few years ago such as the North Atlantic Oscillation (NAO) and the Atlantic Multidecadal Oscillation (AMO). Without going into great detail the NAO is the dominant mode of winter climate variability in the North Atlantic region ranging from central North America to Europe and much into Northern Asia. The NAO is a large-scale seesaw in atmospheric mass between the subtropical high and the polar low. The corresponding index varies from year to year, but also exhibits a tendency to remain in one phase for intervals lasting several years. The North Atlantic Oscillation (NAO) is a climatic phenomenon in the North Atlantic Ocean of fluctuations in the difference of atmospheric pressure at sea level between the Icelandic low and the Azores high. Through east-west oscillation motions of the Icelandic low and the Azores high, it controls the strength and direction of westerly winds, currents, and storm tracks across the North Atlantic Ocean. It is part of the Arctic oscillation, and varies over time with no particular periodicity. It appears to be one of the most important manifestations of climate fluctuations in the North Atlantic and surrounding humid climates (see Wikipedia and the previously listed web links for more details). The 2014 NAO index for January and February was positive 0.29 and 1.34 respectively. In 2013 NAO Index was positive (0.35) and February negative (-0.45), while in 2012 it was 1.17 and 0.42 respectively. The 2015 index for January and February was 1.79 and 1.32 respectively, the highest in recent years. We are uncertain what this means for current speed, direction of flow and eddy generation and movements. Research on these aspects are in their early stages.

The Atlantic Multi-decadal Oscillation (AMO) has been identified by some as a coherent mode of natural variability occurring in the North Atlantic Ocean with an estimated period of 60-80 years. It is based upon the average anomalies of sea surface temperatures (SST) in the North Atlantic basin, typically over 0°- 80°N latitude. (https://climatedataguide.ucar.edu/climate-data/atlantic-multi-decadal-oscillation-amo). The unsmoothed AMO Index for January and February 2014 was -0.039 and -0.23 respectively. In 2013 in January and February was positive 0.158 and 01.47 and in 2012 it was -0.038 and 0.031 respectively. In 2015 the January value was 0.012 but values for February were not available (http://www.esrl.noaa.gov/psd/data/timeseries/AMO/). A positive AMO is usually associated with an increase in the number of tropical storms that mature into severe hurricanes. But as the forecasted precipitation is normal for April – June it suggests that the likelihood of a major hurricane passing over the Bahamas during the BBC is low. For easy to understand answers to frequently asked questions about the AMO see  http://www.aoml.noaa.gov/phod/amo_faq.php#faq_2 .

Regarding El Niño we have yet to see or read about any direct relationship between El Niño – La Niña and the oceanographic conditions in the Bahamas. However, we continue to report the conditions. Presently we are in a weak El Niño situation. We will continue to investigate the relationship between the North Atlantic Ocean climate and the oceanographic conditions in the Bahamas in the future. But we included this information to spark your interest in climate indices.

Nowcast Analysis

Figure 3 was derived from a variety of NASA and NOAA IR satellites during March 4-5, 2015 and Figure 4 was derived from the NASA MODIS ocean and the SNPP VIIRS color imagery during March 3-4, 2015. We could not use single and same day imagery due to severe cloud interference. While these provide a visualization of the pre-season March conditions, they also provide examples of how the eddy features are pulling the “blue marlin” water away from the BBC tournament area presently. In Figure 3 and Figure 4 there is a relatively large clockwise rotating eddy centered approximately 90 miles east of Eleuthera. This eddy is pulling the dark blue (79°F) water (“Blue Marlin water) that occurs east and southeast of Cat Island in a northward direction and away from Eleuthera. To watch a video of the sea surface temperature derived circulation from January 30 to March 05, 2015 see http://youtu.be/1QYjQT3c5Tg . Northeast of Abaco another clockwise eddy is pulling the blue marlin water westward and northward, again away from the BBC tournament area.

The westward motion of the water along the northwest side of the southern eddy has resulted in a mixture (“blended”) of the blue and the blue marlin waters. This blend of different water masses has a sea surface temperature (sst) of 75°F-76°F and occurs over the Great Abaco Canyon and Little Abaco Canyon areas northeast of Abaco where the words “BLENDED BLUE MARLIN” was placed close to Abaco. Ideally the blue marlin water would be directed over these topographic features, but the presence of a blend of this water is favorable. The sst of the water now is 2°F-3°F cooler than what we usually associate with the early presence of blue marlin. But over the next 5-6 weeks we anticipate that this water will warm which is favorable for the arrival of blue marlin. However, as time continues and the water moves, the effect of the two large eddy features are expected to substantially change the flow of water. It remains to be seen how.

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Figure 3 (left hand side) was derived from a variety of infrared sensors on NASA, NOAA, ESA and SNPP satellites during March 04-05, 2015 and Figure 4 was derived from the ocean color imagery during March 03-04, 2015 from the MODIS and VIIRS sensors on the Aqua and SNPP satellites respectively.

Figure 5 (below) is an enhancement of the visualization of the currents derived from satellite altimeters by NOAA AOML’s CoastWatch program. The two major eddy features that are effecting the currents now and three additional ones are shown. The key to getting the most blue marlin water and fish to Eleuthera and Abaco is by having the center of circulation of a clockwise rotating eddy come within 30 miles of the land. This will result in a strong eddy current pulling the water over the favorable subsurface ledges and sea mounts.

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Figure 5. Altimeter based currents derived for March 5, 2015. Five eddy features are outlined. See (http://www.aoml.noaa.gov/phod/dataphod/work/trinanes/INTERFACE/) for this data.

As stated previously we do not know of any reliable oceanographic models that would allow us to make accurate and reliable forecasts of the motion of these eddy features. The path, size, shape and velocities of these features are highly dynamic and the flow is complex, non-linear with inter-acting components. Based on our experience we anticipate that these eddy features will be approaching the BBC area, but it remains to be seen if they will come close enough to bring in the bluer water and fish or continue to pull the warmer, bluer water away.

Bottom Line:

Based on what we have been observing over the last several weeks it appears that a mixture (“blend”) of Bahamas blue marlin water exists in the BBC tournament area. Water temperatures are expected to rise over the 6-8 weeks as a relatively “normal” sea surface temperature is expected. This suggests that the blue marlin’s arrival will not be delayed by water temperatures below their thermal preference. Based on continued warming and the presence of this blended blue water east of Abaco, one can anticipate the arrival of some blue marlin by the last week in April. But it is likely that sailfish, white marlin and hatchet marlin (round scale spearfish) with dominate the first tournament’s billfish catches until the warmer, bluer water arrives. Recent fishing reports suggest that an abundance of mahi occurs in this blended water, but few wahoo and billfish reside in it. More Bahamas blue marlin water is needed to provide a substantial increase in the local abundance of these highly migratory pelagic species, especially blue marlin.

There is no Bahamas blue water over the topographic “points” on the east side of Eleuthera suggesting that slow fishing is likely to continue over these favorite fishing areas. There is favorable blue water approximately 30 miles east of Palmetto Point extending to Cat Island which will substantially improve one’s chances for blue marlin and other fishing action with yellowfin tuna, wahoo, and mahi. A substantial change in the circulation is needed for the conditions close to Eleuthera to improve.

It remains to be seen what the other eddy features do regarding the later tournaments. Assuming that the rate of overfishing on these stocks has not increased, the bottom line is that the present conditions are relatively favorable for billfish and blue marlin action this BBC season especially in the waters surrounding Abaco. The fate of the fishing season will be a controlled, in part, by the inshore pull of the blue marlin water by one or more of the eddy features now located southeast of the northern Bahamas island chain.

We will continue monitoring these developments as the season progresses and will provide updates. Not only are these blue water conditions important for the fishing success in the Bahamas, but also we have learned an association of the blue marlin water and the relative apparent abundance of highly migratory fish in northeast Florida to North Carolina, as well as, over the canyon areas of the middle Atlantic states (Massachusetts to Virginia). We will write a separate forecast for these areas soon.

It is very important to note that good fishing action on a daily basis is strongly linked to local current conditions that concentrate the fish once the preferred habitat of the fish are in a particular region. When the water mass boundaries of these currents are favorable, i.e., persistently pushing over “good” bottom topography, then they concentrate the bait fish and larger fish can be found foraging. This means that the fishing action on any given day is controlled by relatively short term (hourly to daily) and relatively small scale (1-4 mile) movements of the currents and their water mass boundaries. Our experience indicates that to reliably forecast specific concentrations of fish on a daily basis one must evaluate the ocean conditions on these scales. Relatively small subtle changes in the currents and their boundaries often have dramatic effects on the distribution and concentration of fish. Stay tuned for these daily fishing forecasting analyses. Get ready for the BBC and other fishing action as the fun in the Bahamas and elsewhere is about to happen!

Safe and Successful Fishing,

Mitchell A. Roffer, Ph.D. (roffs.com)