In order to better understand why swordfish concentrate their feeding habits in certain depths on any given night or why the bite is better during different times of the month requires you to better understand how the effects of moonlight influence swordfish.
Before you can understand how moonlight affects swordfish, you must understand the moon and its phases. The moon revolves around the earth in 27 days. The first phase of the moon at the beginning of its new revolution is what we call the “New Moon”. The new moon is when the moons face is in the shadow of the earth causing the moon to reflect no light and look dark to us. A week after the “new moon” the moon will be in its first quarter, meaning that one quarter of the moons total surface is reflecting light back to earth. Since we only see 50% of the moons surface, when the moon is in its first quarter it is actually referred to as a half moon by many of us since one half of the moons face is reflecting light. One week after the first quarter the moon will be full, and the whole face of the moon which is visible to us will be reflecting light. One week after the Full Moon and again the moon will appear as half since it will be in its last quarter. One week after the last quarter the moon will have completed its lunar cycle and be a “New Moon” again.
Now, if we look back to our past swordfish trips and our catch statistics we would see patterns for a few nights when all bites were at depths greater than 200′. And we would also see a pattern for a couple nights when all bites were at depths less than 100′. These changes are a direct effect from the amounts moonlight which was present during these patterns. We know swordfish are predatory species feeding on concentrations of squid and mackerel which are both diurnal species, meaning that during the bright daylight hours they stay in the deeper darker depths of the ocean and as daylight diminishes and night falls they rise to the shallower depths. Now, moonlight plays a role in where the concentrations of the bait will be congregating. For example, during a full moon, since much of the moonlight is shining through the oceans surface, the bright moonlight will cause the bait to stay deeper in the water column. Conversely, during a new moon with virtually no moonlight breaking the oceans surface the bait will congregate in shallower depths closer to the surface.
Of course, we should always have a bait in both the deeper and shallower part of the water column no matter what moon phase we are in, just in case there is swordfish wandering. Although, the brightness of the moon is an extremely good indication of what depth the majority of the swordfish bites we will be. During nights when the moon is full and bright the majority of baits should be fished deeper in the water column.