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Recipe for trophy channel cats.

Case History--Many of today's anglers are focused on catching trophy-size fish of many species. Yet few studies have evaluated factors for growing large numbers of unusually large fish.

One example of such a fishery is the channel catfish population of the lower Red River of the North in Manitoba, at the northern extent of the species range. After early studies found that the size distribution and age structure of the population were unique, managers in 1986 imposed a 4-fish bag limit, with only one over 27 inches. In 1992, the regulation was tightened to mandate release of all catfish over 24 inches.

Recently, a team of researchers examined the growth, mortality, and age and size structure of this population to understand why it's capable of producing so many giant fish* They collected catfish in hoop nets and by angling from below the dam at Lockport, Manitoba, and aged them with otoliths. They collected 11,500 catfish over four years and aged 349 of them, with a range of ages from 2 to 27. The growth rate of catfish in this population was not unusual, with fish reaching 3 inches at age-1 and requiring 5 years to reach a foot. But the annual mortality was low, just under 20 percent.

Given this low mortality, due in large part to restrictive regulations, notably the maximum-length limit, the age structure was much greater for this population than any other. The researchers conclude that allowing individuals to live longer, even without faster growth rates, can produce substantial numbers of trophy fish. Red River channel cats were the longest-lived individuals yet studied. In a nationwide review of channel catfish populations, only 36 had individuals over age-10 and only seven reported fish over 15.

Despite the number of large catfish, growth rates have not declined. Moreover, the team noted that an abundance of large fish increases fecundity, improves larval survival, and boosts larval growth, making the population more resilient to variable recruitment. Thus they recommend that managers further examine maximum-length limits as a tool to grow more trophy-size fish.

* Siddons, S. F., M. A. Pegg, N. P. Hogberg, and G. M. Klein. 2016. Age, growth, and mortality of a trophy channel cattish population in Manitoba, Canada. N. Am. J. Fish. Mgmt. 36:1368-1374.

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Title Annotation:Bits & Pieces: Blending Fishery Science with Everyday Fishing
Author:Quinn, Steve
Geographic Code:1CMAN
Date:Oct 1, 2017
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