Guts to Glory

Examining a Fish’s Stomach Contents Tells a Story

Capt. Mike Genoun September 2, 2015

Offshore anglers are outdoorsmen to the truest sense of the word. We’re not afraid to battle the elements or get our hands dirty, and we’re certainly not afraid of a little blood and guts. That said, on a personal level I might be taking things to the extreme and I’m afraid I may need professional help…I’ll let you decide.

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Photo: Scott Kerrigan

During my younger years employed as a deckhand and then captain of a large partyboat, followed by an exciting stint behind the helm of a canyon-equipped Hatteras, at the conclusion of each trip I always took the initiative to butcher the day’s bounty. Filleting and gutting fish was not a rigorous task that I felt like I had to do, rather it was a task I enjoyed doing.

When I had the time to dig deep and inspect the fish’s stomach contents, most were empty, likely explaining why the hungry predator fell victim to the lure or bait in the first place. This comes as no surprise, because fast moving game fish burn a tremendous amount of energy. Pelagic predators have super fast metabolic rates and powerful stomach enzymes that help to digest prey as efficiently as possible. It’s all about gaining maximum energy for minimal effort so the fish can keep on feeding and keep on moving. In spite of that, there were still plenty of occasions where I found partially digested remains of a recently consumed meal.

Over the years and literally tens of thousands of fish later, taking the time to study the unfortunate carcasses and imagine how the predator/prey interaction unfolded continues to fascinate me. And while the practice obviously has no place in catch and release fisheries, for game fish destined for the fillet table it’s a habit that I refuse to break.

From my point of view, I find it extremely beneficial to my angling exploits to study a particular species’ preferred habitat and feeding characteristics, and also to know exactly what type of forage it prefers to consume, as well as what type of forage it is willing to consume when preferred forage may not be readily available. While most meals make perfect sense, like dozens of intact squid in the stomach of a broadbill swordfish, or nearly a hundred tiny baitfish stuffed in the belly of a gluttonous blackfin tuna, there are always surprises that pique my interest and curiosity even further. Learning to use these findings to help make us more successful anglers is where the real benefit of fish gut inspection lies.

Perhaps the most fascinating blue water game fish with the most varied of all diets are dolphin. Dorado…mahi mahi…whatever you call these opportunistic neon green eating-machines, fast growing dolphin will chase down and consume almost anything they can catch and fit in their mouths. Most of us have seen it with our own eyes during frenzies; green and blue streaks racing just below the surface competing with one another to pick off anything that moves.

Not only have I discovered the usual assortment of finfish ranging in size from one inch silversides to foot-long ballyhoo in the belly of dolphin, and often at the same time, but I have also found various crab and shrimp species, seahorses, pufferfish and triggerfish that have evolved to perfectly mimic the sargassum weed they rely so heavily on for survival. Perhaps the most surprising revelation is that along with eating their own kind, dolphin also consume juvenile sea turtles. These fish clearly chase down fast moving prey in open water environments and will also hunt deep inside a well formed weedline, actually hitting and disturbing the grass to dislodge tasty morsels. A dolphin’s diversified menu leads me to believe that nothing is off limits to a famished ‘phin, not even its own offspring. By the way, cobia are also notorious turtle eaters and hardly ever pass up the opportunity to feed.

I have learned valuable lessons from these autopsies, which you may or may not already know. One is that orange, gold-flake and root beer color soft plastics work extremely well when casting to schoolies, as the lures perfectly match the hatch of many of the fish’s primary food sources. D.O.A. TerrorEyz and LIVETARGET Shrimp are both excellent choices to throw on fast action spinning outfits when casting to famished fish along weedlines and around floating debris.

Another lesson is that there is almost no such thing as too big of a meal. A healthy gaffer can easily capture and swallow a whole bonito, or a three-pound peanut. This explains why you’ll rarely see me without at least one monster lure creating commotion in the spread.

Reef dwelling snapper and grouper are also extremely fascinating predators. With demersal species, which directly relate to structure, I have taken my post-mortem examinations to a new level. Before exploring the fish’s stomach contents, I carefully study the inside of the fish’s mouth and throat, going as far as removing the fish’s head and inspecting it from every angle. By doing the research, it’s easy to see which particular species are true crab crushers and which enjoy a primary diet of finfish. An upper and lower set of distinct crushing pads set in the back of the fish’s throat is a dead giveaway that this particular fish relies on crabs, clams and other shellfish. On the other hand, bottom fish with canine teeth supported by needle-sharp dentures define the sea creature as a flesh-eating beast. Many bottom dwellers have both.

Among other findings, my amateur studies of reef and wreck fish have taught me that large jolthead porgy and their close cousin the margate specialize in hunting shellfish directly on the substrate. So if you want to catch porgy, your bait needs to be directly on the bottom. You can picture these fish roaming just inches off the seafloor as they make their way from one exposed coral head to the next in their ongoing search for another meal. Unsuspecting crabs or exposed shellfish stand little chance when these tenacious bottom feeders are on the move.

The aforementioned species rarely venture more than a few feet off the bottom and never hunt the entire water column. Whereas mutton snapper, dog snapper and red snapper, also highly specialized predators relating to reefs and wrecks, prefer a diet of fish and squid, but won’t hesitate venturing deep under overhanging ledges to sniff out the occasional spiny lobster. Hungry bottom fish also enjoy octopus and sea cucumbers.

Some of the other exciting discoveries include finding partially digested Spanish mackerel in the belly of big king mackerel. Any predator capable of catching a speedy Spanish mackerel must be both fast and stealthy. The find speaks volumes of the king mackerel’s exceptional hunting abilities.

Unless you are curious like me, you probably don’t know that tilefish—a prized deep drop target inhabiting muddy plateaus across depths statewide—regularly gorge on deep-water eels. The spotted sea serpents are vicious in their own right and must put up a valiant effort against a predator known more for sucking down squid than snake-like creatures.

Examining the contents of a fish’s stomach may not be for everyone, but there are volumes of information for us to learn by simply studying our target species forage and eating habits. By doing so you may just stumble across something completely unexpected that will leave you saying, “Wow, I never knew they ate that.”

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