Conservation: Examining Jack Crevalle Populations

The jack crevalle (Caranx hippos) is a wide-ranging, voracious predator with a party-crasher reputation among anglers. Got a bait in the water for tarpon this spring? Huge strike, lotta line off the reel, no jump? Good chance a big jack is on the run.

Jack crevalle—or crevalle jack, as some refer to them—can fool you on the strike, but at boatside, they’re easy to identify. They have a round black spot at the lower base of the pectoral fin and an elongated black spot on the operculum (gill plate), which isn’t found on other jacks. Also, they have enlarged scales or scutes that run along the base of the tail fin; those scutes are extremely sharp. As a fisheries biologist and angler, I learned the hard way to never grab a live crevalle by the tail without gloves!

Crevalle inhabit both the Atlantic and Pacific oceans. Fishing off the rocky coast of Nosara, Costa Rica last summer, a big jack slammed my topwater and gave me a drag-screeching battle and the impression I was fighting the mighty roosterfish.

The crevalle is a powerful battler. Big ones school up along the beaches of Southeast Florida in spring and early summer, where they’re rightfully regarded as sportfishing targets. In Everglades National Park, creel surveys indicate jack crevalle is the second most captured species. In the Florida Keys, some fishing guides pursue and promote jacks as prized inshore species like permit, bonefish, and tarpon. Jacks are no longer taken for granted. In fact, they’re the subject of some growing concern. Captain Andrew Tipler, President of the Lower Keys Guides Association (LKGA), recently vocalized concerns.

“I have seen the number and sizes of jack crevalle decline over the past 10 or so years, but it’s more about the catch reliability,” Tipler said. “In the past, I could hit several inshore and offshore spots and almost guarantee hooking some nice jacks, but now it’s hit or miss. This is an issue because jacks are a major part of our fishery.”

I asked Tipler if he had thoughts on any causes of the apparent population decline.

“I can’t say for sure, but it seems their seasonal or migratory behavior has changed over the years,” he replied. “Also, it doesn’t help that vessel traffic and fishing effort from private anglers continues to increase. It’s probably a combination of various issues like fishing pressure, overfishing of an important prey source, or declining water quality.”

The LKGA, Everglades Foundation, and a few other organizations funded Carissa Gervasi to pursue this topic for her Ph.D. dissertation at Florida International University. To address the potential population decline of this unregulated and data-poor species, Gervasi interviewed fishing guides from the Lower and Upper Keys, and analyzed fisheries-dependent datasets from the Florida Fish and Wildlife Conservation Commission (FWC) and National Park Service. Also, Gervasi attached acoustic tags and removed the otolith (ear bones) from jacks to examine age, migration, broad-scale movement patterns, and general ecology.

Unregulated species in Florida generally receive no money for research from the state, so this study was the first of its kind.

I contacted Gervasi to ask about her findings.

“Based on interviews,” Gervasi said, “most guides told me crevalle jack populations in the Florida Keys had not only declined between 30 and 100 percent, but they had declined more in the Lower than the Upper Keys. I also learned most guides believed the population had begun to decline around 2005. Some guides said the decline was most evident in large offshore individuals.”

Gervasi asked her sources to speculate on potential causes of the decline.

“Recreational and commercial harvest were the most common explanations, followed by poor water quality, and increased predator abundance,” Gervasi said. “What I found encouraging about the interviews was that most of their responses were supported by the available fisheries-dependent data, indicating interviews from local fishing experts can be one way to help understand fishery conservation issues when solid scientific data is unavailable.”

Migration studies were an important part of Gervasi’s research.

“We tagged 83 crevalle jack using surgically implanted acoustic tags and tracked them using arrays of receivers that exist along Florida’s east and west coasts,” she said. “Many of these tags are still attached to individuals collecting data, but preliminary results show large scale movement patterns, with some individuals tagged in South Florida being detected in Texas waters. Fish tagged in the Florida Keys, Southeast Florida, and Southwest Florida were all detected north of Tampa. However, only fish that were tagged in Southeast Florida made any northbound movements along the Atlantic coast.”

Six individuals that were tagged in Fort Lauderdale had traveled to the St. Lucie River before moving back south, Gervasi revealed, with southbound movements extending to the Florida Keys. “Coastal migrations seemed to be based on size with smaller fish remaining in South Florida year-round,” she said. “Movements may also be seasonal, as some fish appeared to move north in the spring and south in the fall.”

Gervasi is still collecting tag data, but so far, the preliminary data showed that crevalle jack travel between a quarter of a mile and 615 miles, and the average maximum dispersal distance was 139 miles from the point of tagging.

What do fishermen have to say about the status of jacks farther up the coast? I contacted Capt. Mike Holliday, who has been running charters out of Stuart for 37 years. Based on our correspondence, I learned spawning aggregations occur from Sebastian to Palm Beach between December and June with smaller jacks (10 to 15 pounds) showing up first followed by the larger individuals.

“By late March, the schools have many larger jacks, 20 to 40 pounds,” Holliday said. “Over the years, I’ve learned the bigger the school, the smaller the fish, and the smaller the school, the bigger the fish. On average, we intercept four to eight schools per day, which may consist of hundreds of individuals; we target these fish with large topwater plugs or flies.”

Holliday expressed concern about shark depredation.

“Until three years ago, the main predator of jacks was hammerhead sharks during April and May, just prior to the tarpon showing up,” he said. “These days, it’s big bull sharks that are preying on the jack schools, which occurs much earlier in the year…the bulls show up as early as February. We see bull sharks stalking almost every school; it’s very common to lose at least one hooked jack to a bull shark. It may happen one or four times in a day on one or four different schools. Once a shark takes one, we move on and don’t fish that school anymore. Overall, we are finding fewer schools of the larger jacks.”

Holliday said there is some local commercial fishing effort targeting jacks, but feels it’s not as prevalent as it was in the past.

“The commercial fishery is primarily one-man operations that only target the smaller jacks, 1 to 2 pounds, near inlets like Ft. Pierce or at the St. Lucie Power Plant outflow,” he said. “I believe they also target jacks at Palm Beach Inlet. Commercial boats usually troll for them using multiple feather rigs, which look like a giant sabiki rig; it’s entirely a hook-and-line fishery. The fishery is a winter-spring fishery that starts around December and ends in April. From my perspective, it’s not as prevalent as it was in the past.”

Reviewing commercial fishery data (2018-2022), I discovered jack crevalle landings ranged from 443,179 pounds in 2022 to 637,399 pounds in 2018 with an average of 555,998 pounds per year sold at $1 per pound. Overall, total commercial landings have declined since 2018.

Over the 5-year period, commercial landings occurred primarily in the central to the southern region of the state. Most of the landings were reported in Tampa (39 percent) followed by Fort Pierce (25 percent) and Fort Myers (12 percent). The commercial landings in Tampa (2018-2022) ranged from 177,997 pounds in 2022 to 267,663 pounds in 2021 with an average 214,126 pounds per year.

What I found interesting was the number of trips selling crevalles. Fort Pierce and West Palm Beach led (60%) the state in total trips, followed by Tampa (11.5%), indicating the fishery is not only more prevalent on the east coast, but the landings are much lower than on the west coast. In fact, commercial fishermen in Fort Pierce reported 33% more trips selling jacks than Tampa fishermen.

So, what does all this mean? To me it suggests that east coast commercial fishermen apply more fishing effort and catch fewer individuals than the west coast, which can either mean the schools or the individuals in the school are smaller. Also, the data showed the total landings and number of trips has declined since 2018, suggesting either that the jack crevalle population is declining or commercial fishermen are targeting other species.

Because the total landings and the number of trips is showing a similar slight declining trend over time, it is probably not a concern; more effort with less fish is always a problem in fisheries management, which is not the case here. However, it does appear the average number of pounds landed per trip has declined from 96.7 pounds in 2018 to 72 pounds in 2022, which suggests the jack schools are getting smaller because the fishery primarily targets smaller individuals.

The commercial fishery appears to target the seasonal schooling behavior, with most of the landings occurring during fall through winter. The catch is primarily comprised of immature individuals; female jack crevalle reach maturity at age 5 or 6 and males around age 4 or 5. Speaking with a local seafood dealer, they confirmed they only buy small crevalles (less than 5 pounds). The larger ones are harder to sell, probably because they are more challenging to cook or don’t taste as good.

When I asked how the fishermen are catching jacks, I was expecting to hear about a hook-and-line method, but instead I found out they are being caught with seine nets. In many ways, this explains why the landings are greater and the number of trips is lower on the west coast; it’s much easier to catch more smaller fish in seine than on hook-and-line. Florida law states that beach or haul seines cannot be larger than 500 square feet or be constructed of monofilament. Also, the stretch mesh cannot be larger than 2 inches and no more than 14 meshes can be tied in one linear foot.

Jack crevalle are an important recreational species and clearly have some added economic value. Fishing guides target them in South Florida and commercial fishermen sell them. Despite having some monetary and cultural value, the FWC categorizes jack crevalle as an unregulated species. Unregulated species have a two fish or 100-pound per person limit (whichever is more), but there are no size or seasonal restrictions.

Based on the data showing a steady decline, maintaining the 100-pound daily limit seems reasonable, but implementing an annual harvest limit, and a potential size limit, should be considered in future rulemaking.

The main issue with unregulated species is, Florida does not allocate research funds or time to these species.

While one could argue that FWC is already very busy managing regulated species, it’s clear that unregulated species may become more valuable and heavily fished with time. Let’s not forget that snook were once unpopular as table fare. Ultimately, it’s important to support research on species like the jack crevalle. These unregulated species can slowly decline before they are noticed. The solution is to take a proactive rather than a reactive approach in fishery management.

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• This article was featured in the April 2024 issue of Florida Sportsman magazine. Click to subscribe.

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