Up or Down?
Vertical Water Movement Can Have a Significant Impact on the Blue Marlin Bite
When playing for high stakes like those on the Bermuda billfish circuit, nothing is left to chance. Boats, tackle and gear are finely tuned and many teams purchase satellite imagery to pinpoint the most likely zones to find winning fish. There are many facets to satellite forecasting besides sea surface water temperature readings, however. Color changes, shifting eddies and currents, the length of time conditions have existed and the bottom geography are significant factors as well. So is altimetry data or graphs that depict vertical water movement across the highlighted region.
“Altimetry data measures the upwelling cyclones and downwelling warm core eddies that are present offshore,” explains Tom Hilton, president of Hilton’s Realtime Navigator, a sport-fishing service based in Texas. “In the northern hemisphere cyclones flow in a counter-clockwise rotation which brings nutrients up from the bottom to the surface. That plankton interacts with sunlight to start the first links of the food chain. That draws bait which attracts bigger game fish. But for every reaction there is a reaction. Warm core eddies flow downward, pulling everything with it, so there’s not much feeding going on.”
Hilton says the satellite software that measures altimetry uses the same technology as a state trooper with a radar gun clocking speeders on a highway. The satellite measures the distance to the sea surface and special formulas calculate the water pressure and flow upward or downward. Unlike some imagery, altimetry measurement can penetrate cloud cover, but the variances are subtle and spread over larger zones. On color graphs, cyclonic upwellings are depicted in shades of blue and light greens, while warm core downwellings are shown in reds and orange tints. Depressions are indicated by dotted lines below mean sea level and isobars show intensity.
Because Bermuda sits off the Gulf Stream and is isolated in the Atlantic Ocean, it’s a more difficult area to forecast hydrodynamic trends. A comparison between the last two seasons offers some interesting clues though. During the month of July 2015 there was a subtle upwelling feature south of the island, matched by a northern downwelling. The downwelling was closest and most prominent the second week before fading slightly during the last tournament timeline. Overall, the blue marlin catch rate was down noticeably while the white marlin bite was up. There was also only one yellow-fin tuna weighed during the three events.
In contrast, during July 2016 a very strong upwelling feature appeared off the main fishing grounds and the marlin bite was one of the best in years. One-hundred and sixty-one blue marlin were caught during the three tournaments, with nine boated weighing more than 500 pounds including the near-record 934 landed in the Big Game Classic. Only 20 white marlin were tallied last season.
“The upwelling was much more intense in 2016, that’s for sure,” Hilton says. “That’s not to say you can’t catch fish around downwellings. You can, if you work the edges. The middle is going to be pretty barren. But downwellings are not necessarily a bad thing because whenever water is pushed down like that it has to come back up somewhere else in the form of an upwelling. Remember that rule, for every action there is a reaction.”
Even though it’s too early to predict what conditions will develop for 2017 several months out, Hilton says teams that study altimetry images before-hand can anticipate conditions a couple days in advance. The image plot-ting is slow and the Hilton web site offers a loop video feature that depicts the vertical water movement over a seven-day time frame.
“The ocean is such a dynamic environment, you need to monitor it closely to determine patterns,” Hilton says. “You have to take what Mother Nature gives you and adjust accordingly. It’s kind of like playing poker. An ace may win a hand on rare occasions, but a pair of deuces will beat an ace. If you have a pair of aces like a strong upwelling and favorable sea surface temperatures, your odds get a lot better. And if you add a strong current near the intersection of major bottom structure, you’d better put all your chips on the table and bet that hand. The more these favorable conditions are stacked on top of each other, the odds of success greatly increase.”
So will 2017 be an “up or down” season? The next few months will tell. But you can also bet the dozens of teams in the hunt for those winning bills will be checking the altimetry charts closely, hoping to see saturated splotches of rich blue parked next to the Challenger and Argus Banks.
Bermuda Historial Altimetry 2012 - 2016
93 Blue marlin
69 White marlin
Billfish per team: 3.86
5 Blue marlin boated (768, 556, 527, 548, 619)
Altimetry conditions: Prominent downwelling
138 Blue marlin
29 White marlin
Billfish per team: 3.98
6 blue marlin boated (668, 547, 641, 856, 622, 594)
Altimetry conditions: Moderate upwelling
95 Blue marlin
56 White marlin
Billfish per team: 2.89
3 Blue marlin boated (573, 693, 598)
Altimetry conditions: Mixed; mild to strong upwelling southeast and mild downwelling southwest
90 Blue marlin
34 White marlin
Billfish per team: 2.84
3 Blue marlin boated (741, 605, 575)
Altimetry conditions: Moderate downwelling
161 Blue marlin
20 White marlin
1 Game fish
Billfish per team: 4.92
9 Blue marlin boated (625, 934, 703, 583, 538, 520, 765, 599, 562)
Altimetry conditions: Strong upwelling