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Reading Fish Behavior While Diving: Identifying What The Fish is Going to Do

Reading Fish Behavior While Diving: Identifying What The Fish is Going to Do

Reading Fish Behavior While Diving: Identifying What The Fish is Going to Do

Every fish species acts differently, and it is important to know or be able to guess how a fish will behave in any given situation. With experience, there are strategies we can learn that improve our ability to read fish behavior and get closer to all fish species. There are also broad categories for types of fish that can help determine how a given species may act. There are other factors that may impact how fish may act. For example, the frequency the fish is hunted in a given area or the time of year are both factors that can influence how a fish can be expected to act. Here, we will go over the categories of fish and how best to predict their behavior. 


Reef Fish Behavior

Reef fish are generally fish found towards the bottom of structure. Broadly, there are three types of reef fish behavior: the rocky reef fish, the roaming reef fish, and the skittish reef fish.

Rocky reef fish would include all kinds of grouper, coral trout, margate, and any other species that you would commonly find in holes or tight to the structure. These fish tend to stick to their holes, but if you find them out in the open you can expect them to do a few different things. The first is to spook. If they spook, they'll most likely look for a hole to spook into, which gives you a chance to follow them until they hide, then drop right on that hole and hole hunt them. If they spook out into the sand or get way back into a hole, you're probably better off looking for a different fish. But if they spook and hide behind a rock, a shallow hole, or a fan coral (as they often do), then your chance of success is very high if you can stay behind them and out of their line of sight during your descent, pulling the trigger as you hit the bottom. The second thing these fish tend to do is what many divers call a"flick". When you drop, the fish will square up on you, facing you with their mouths open, giving you an awkward "unicorn" shot that has a low success rate and risks running your shaft down the fillet, then "flick" broadside and head off to a different direction. Red grouper do this a lot, and it is mostly because these fish are slightly territorial and slightly curious. Once they have appraised you as something to be wary of, they then change directions and "flick". It is at this direction change that they present to you the perfect broadside shot that you can take advantage of.  

Roaming reef fish include mutton snapper, jobfish (uku), yellow jack, hogfish, and other predatory fish which tend to stay out in the sand. These fish tend to react very well to deep grunts made with the throat, which can be used to call them in from the sand. The best way to hunt them is to drop right on the edge of the reef where it meets the sand, hold onto a rock while looking out to the sand, scratch the rock with your glove, throw up a little sand and make the grunting sound. The reason that this strategy works is that these fish tend to be more curious than others, and will come in to check you out, giving you the perfect shot. 

The last kind of fish is the skittish fish, which usually is seen in large schools, but can be seen in groups as small as three or (very rarely) solo. Solo ones usually mean they're big. In the southeastern US, the best example of these fish is the mangrove snapper (called mangrove jack in Australia). When these fish tend to be smaller, and so they have a "prey mentality". They move in groups, are very reactive to movement, and will spook easily. The best way to hunt these is to dive into the reef and make your body as small and close to the reef as possible, while minimizing the amount of movement you make. After being down for a bit, the fish will get curious and move in as a school on their own without you having to do much scratching or grunting (you can do some, but don't overdo it with these kinds of fish). The bigger, smarter ones tend to stay at the edge of your range for a lot longer, and won't come in close until the end of a long dive. 

For an in depth breakdown another great method to hunt all kinds of reef fish, check out the Hunting Techniques blog post and skip to the “Cone of Death” section.


Pelagic Fish Behavior

Pelagic species can be a bit harder to read in the water. Because they are more rarely seen in a day of diving, it is easy to forget about hunting techniques and to just try and run them down. This usually results in the fish getting spooked and swimming away faster than you have any hope in catching up. The best thing to do with most blue water species, like Wahoo, is to take a calm breath and try to create an intersecting path with the fish as opposed to just approaching them directly. Body language is everything when spearfishing. You want to be a sea turtle instead of a shark. It helps if you tell yourself in your head that you don’t want to kill the fish, that you're just looking at it and taking pictures. If you believe it, it changes your body language to make the fish believe it, and that can help you close the distance.


Overlapping Species

There are some highly migratory species that tend to congregate on reefs as they move through an area. Mackerel are a common species that can be found on normal reef structure during certain times of year. These species tend to just be passing through, but they turn into targets of opportunity so you will have to take advantage of them coming through quickly. Other species may simply do large loops on structure. Cobia and yellow jack are an excellent example of fish that stick around wrecks. It is common for cobia to do large circles outside a bait ball on a shipwreck. When they do this, you can just try and make an intersecting path with them and get within range of the fish to close the deal. 


Other Factors

There are countless factors that impact how fish behave. Below is a description of a few common factors and how they can impact fish behavior and hunting technique.



As we mentioned earlier, there are several factors that can impact how a fish can behave. One of the biggest factors that can change behavior is a fish spawn. Spawns are at different times of year, are at different depths, and cause different behaviors for most species of fish. Many fish species have evolved to have mass spawns to improve the likelihood of successful breeding. That means that during certain times of years there tend to be large aggregations of a given fish species in one location and they tend to be focused on breeding rather than avoiding predation. This can afford a diver the opportunity to hunt large breeding fish of a given species where a fish may not be as focused on avoiding the diver. There is the moral issue of knowing you are taking advantage of the fish, but that comes down to the individual diver and what they are comfortable with. Other species tend to show up around spawns as well because the spawn gives opportunity for predation. Remember, life follows life!


Moon Phase

Moon phase is a common consideration for fish behavior. It often dictates when some species spawn. The moon also impacts tides and currents. Tides and currents are an under appreciated element of fish behavior. Fish tend to be more active the stronger the current and the more water that is moving. They also tend to move up current because of the nutrients that the current brings into their area. Strong currents definitely make for challenging dive conditions, but they do usually afford lots of opportunities for meeting fish.



A thermocline is a dramatic difference in water temperature that occurs at a certain depth because of a bunch of physics and environment stuff I'm not going to get into right now. You'll feel the sharp temperature change on your way down, and that's all that is important because the thermocline can impact how bait fish and other species behave. Often times, fish will sit just above or just below the thermocline. Typically the thermoclines get colder as you get deeper, so you may be able to identify if the given species prefers warmer or colder water and use the thermocline to guess where in the column they'll be. There can also be dramatic differences in visibility between two thermoclines, so watch out for a massive layer of silt or fog when you hit a thermocline.
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