Below the Surface: Important Considerations while Diving

Hang around a group of divers long enough and the conversation will inevitably turn to dive conditions. Winds, waves, and currents play a significant role in our ability to safely enjoy the ocean and select a quality dive site. But what you see from the surface is only a small piece of the puzzle. Particularly when it comes to spearfishing, the factors at play beneath the surface will have a much larger impact on your potential for success.

Visibility

It should come as no surprise that seawater is not the still, crystal-clear liquid you get from your tap at home. First, and most obviously, things live in it. From the large to the small, these organisms all contribute cells and poop and little bits of detritus to water they inhabit. Second, the ocean is always in motion. When those organic particles and sand get suspended in the water column, they contribute to something called turbidity.

Technically speaking, turbidity is a measure of the degree to which the water loses its transparency due to the presence of suspended particulates. For our purposes, it is basically a measure of how stirred up the water column is. The more wind and wave action you have, the more particulate matter (e.g. poop and sand) is going to slosh around. And like smoke in the air, the more particulate matter sloshes around the water column, the harder it becomes to see.

Because turbidity results from the suspension of sediment and other particles, you can often improve visibility by moving away from the coast (a key source of sediment) and into deeper water (surface wave action has less of an effect the deeper you go).

Phytoplankton also play a key role in visibility. These microscopic photosynthetic organisms are always present in the ocean, but their populations are constrained by the availability of sunlight and other nutrients. When a flood of nutrients enters the ecosystem—for example, from urban/agricultural runoff or a particularly sunny day—phytoplankton populations can bloom (otherwise known as an algal bloom), turning otherwise blue waters a deep, murky green.

Because light does not penetrate water well, algal blooms are often limited to the top of the water column. It is usually possible to dive below an algal bloom where visibility is better. In the summer in Central California, it is common for visibility to resemble pea soup on the surface but open up around 30 to 40 feet deep. Of course, if you have a ceiling of algae above you, it will be dark on the bottom—be sure to bring a flashlight.

Finally, it is important to keep in mind that what qualifies as “good” visibility varies from place to place. In the tropics or on the open ocean, it is not uncommon to have visibility of 100 feet or more. In the cold waters of Monterey Bay, by contrast, it is typical to hunt in 10-15 feet of visibility. Different species can be easier or harder to hunt depending on the visibility, so figure out what works for your target fish and plan accordingly.

Finding Fish

The first step in any successful hunt is to figure out where your prey is likely to be. Fortunately for us, fish are relatively predictable. If you can find good structure and a consistent source of food, there’s a pretty good chance you’ll be able to connect with game fish.

What constitutes good structure varies depending on the species you are hunting. In Central California, for example, rockfish, lingcod, and other groundfish inhabit networks of holes and caves in rocky reefs (read about “hole hunting” here). Kelp is a good indicator that a reef is below, as kelp must attach to a hard structure on the bottom. Another trick is to look at the land next to your dive site. Typically, the features you see on land will continue for some distance into the water (a sand beach will be next to a sand-bottomed dive site, a rocky beach next to a rocky dive site, steep bluffs next to a steep dive site, etc.). Wrecks mimic reefs, and can be a fantastic place to find reef species in otherwise sandy environments.

Other species, such as halibut and flounder, will more often be found over a sandy bottom. In these cases, it helps to hunt the interface between reefs and sand patches.

Even when hunting blue water, structure can be a critical tool for finding fish. Fish aggregation devices (“FADs”), loose pieces of kelp (kelp paddies), or even pieces of garbage attract small fish in search of camouflage and protection. And where there are small fish, there are often larger fish looking to eat them. Just be sure to pick up any garbage you find after you’ve inspected it for fish.

If you’ve found what should be good structure but still can’t seem to find the fish, take a deep breath and pay close attention to what is going on around you. Diving seabirds are a telltale sign that bait is nearby, and where there is bait, there is likely to be game fish. A large aggregation of sea lions, on the other hand, might spook fish to a reef further away.

At the end of the day, if you pay attention to how the ecosystem is working and use the conditions to your advantage, you’ll maximize your chances of getting on your target fish and putting dinner on the table.