Bits & Pieces: Global Esox Quest, Fast‑Growing Lakers, and Bass Target Invasive Carp

Piscatorial Pursuits: Esox Bucket List

In-Fisherman friend, former fishery biologist, and frequent Master Angler Award recipient Danny Kurttila wrote to us about his obsession with pikes, which has sent him around the world to catch all the known Esox species:

My family has always been a big fan of pike. I continue to carry on that tradition but I’ve added all the pike species. When I first began my obsession, the known esocids were northern pike Esox lucius, muskellunge E. masquinogy (three subspecies: ohioensis, immaculatus, and masquinogy), chain pickerel E. niger, American pickerel E. americanus (two subspecies: redfin pickerel E. americanus and grass pickerel E. vermiculatus), and the Asian, Amur pike E. reichertii.

Over the years, scientists changed some of the classifications (muskellunge are now a single species with a few strains),  and added two species, Italy’s Southern pike E. cisalpinus and France’s Aquitanian pike E. aquitanicus. The last two have been recognized as species for 10 years and 5 years, respectively.

I started out angling for northern pike and then developed a muskie addiction, catching the three forms (Great Lakes, ohioensis, immaculatus) and also adding tiger (hybrid) muskie. A move to Tennessee offered a chance for chain pickerel and grass pickerel. By then I realized I only needed a redfin pickerel to have all the North American species and subspecies. I made a trip to Florida specifically to catch a redfin and succeeded in catching a tiny 6-inch specimen. I was elated as I’d caught them all, although I dreamed about traveling to Asia to catch the muskie colored, pike-shaped Amur pike.

A few years ago I was diagnosed with bone cancer. Catching an Amur pike became a high goal on my bucket list (I was unaware of the Southern pike and Aquitaine pike at the time). Amur pike had been stocked in the late 60s to early 70s in Pennsylvania’s Glendale Lake, but they had died out by the 80s. A trip to Asia was required to access Amur pike. I traveled to Russia in 2017. We fished a tributary of the Amur and I caught several Amur pike, and I was excited to cross them off my list.

I later learned about the southern and Aquitanian pikes. Due to increasing health problems, I needed to make the trip as soon as possible while I was still able to travel and fish. Information was tough to find on where to fish and who to fish with. I lucked out and found an Italian angler on a muskie website who offered to take me fishing for southern pike and I found a French fish biologist (who found and pushed for separate species designation for the Aquitanian pike), who recommended a small river with a decent population of Aquitanians. I made a trip to Italy and France in 2019 and was able to catch an example of each.

Aquitanian pike can reach at least a meter in length and have yellowish light bars on some specimens, with a shorter snout, and are located in the Aquitaine region of southwest ern France. Southern pike, found in central and northern Italy, can reach over a meter in length and display several patterns, long horizontal markings being the most common. Amur pike, found in the the Amur River Basin of China, Mongolia, and the Russian Far East, can reach lengths of close to 50 inches and 30 pounds. They have silvery sides with numerous, small black or brown spots.

To catch all the esocids requires fishing three continents, North America, Europe, Asia, along with a minimum of four countries: U.S. or Canada, France, Italy, and Russia, China, or Mongolia. I thank these overseas anglers who without their help, I never would have achieved my goal. From Russia, Mikail Scopetts, Romain, and Demetrie. From Italy, Francesco Patti, David and Matthew. From France, Laurent Degrave Pro, Romain and Cedric Thevenet, Gael Denys, and Estelle. Thank you all.

–Danny Kurttila

Field Science: Growing Big Lakers Fast

­Lake trout are specially adapted to thriving in cold, low-productivity waters, but their slow growth and late maturation make populations vulnerable to overharvest and ecosystem fluctuations. Biologists from the University of Calgary recently looked into how lake trout grow differently along their native range.* The researchers sampled 90 populations along western Canada to study the species’ response to gradients like climate (indexed as length of growing season), exploitation, and prey-fish occurrence. They gathered data on length, age, and maturation (determined by gonad development) from almost 20,000 lake trout.

They found climate (number of growing degree-days above 41°F) positively correlated with growth rates and size at maturity. The reason for this is that more degree-days equates to a longer growing season and can enhance productivity of habitat, including prey abundance. Because the optimal thermal zone for lake trout is 46.4°F to 53.6°F, this trend diminishes at the edge of the species’ southern range, but most lakes within their range are deep enough for lakers to be able to thermoregulate year-round.

Angling pressure also affects growth rates. Heavily exploited lakes (determined by angling reports and the amount of infrastructure like roads, campgrounds, and marinas) had lake trout that grew faster and matured about three years earlier than those in unexploited populations. This implies that harvesting a certain number of individuals from a population frees up more resources for other individuals in the population and allows them to grow faster.

Exploitation, however, also seems to cause maturing lake trout to allocate energy toward reproduction earlier, as they have fewer adults to compete with for spawning privileges. As the maturing trout split their resources between reproduction and growth, their growth rate slows and the average size at maturity drops.

–Mary Ellen Klukow

*Wilson, K. L., and four co-authors. 2019. Life history variation along environmental and harvest clines of a northern freshwater fish: Plasticity and adaptation. J. Anim. Ecol. 88:717-733.

Invasive Species Research: Bass Versus Bighead

With the recent expansion in large rivers and reservoirs of the U.S. by populations of bighead and silver carp, anglers and fishery managers are considering ways to limit their numbers. Construction of barriers of various sorts have been proposed, as well as evaluations of commercial fishing for them. Researchers at the Illinois Natural History Survey wondered about a natural control in the form of predation by largemouth bass on young carp.*

To test preferences of bass for the two species and their vulnerability to predation, the team set up a series of small round observation tanks. In them, they stocked two different assemblages of preyfish, consisting of three individuals of bighead carp, bluegill, and golden shiner in one set, and bighead carp, silver carp, and gizzard shad in the other. To test foraging efficiency and predator-prey interactions, they used another set of tanks with 10 small individuals of each forage species with a bass from 8 to 10 inches long.

In both combinations of preyfish, bass favored bighead carp over other species. Preference for them was more than three times greater than for bluegills and shiners, which are common natural prey items. Bass were able to easily locate all the prey species, not surprising for such an opportunistic predator, but were least likely to eat silver carp.

Bass seemed to capture and eat bigheads with the least effort. The team noted that young bighead carp formed tighter schools than other species, perhaps increasing their vulnerability.

The researchers suggested that further research examine whether bass in natural systems are preying heavily on young invasive carp species. And a big unknown is how much predation would be required to limit population expansion by these prolific fish.

*Sanft, E. J. and four co-authors. 2018. Vulnerability of juvenile bighead and silver carps to predation by largemouth bass. Trans. Am. Fish. Soc. 147:1207-1214.

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