Refined Sampling Technique Yields Fresh Data About Elusive Catfish Species In Louisiana
story by Matthew Duplessis , LDWF Biologist & Jonathan Winslow, LDWF Biologist
When you think of catfish, your first thought is probably of a plate of fried filets with hushpuppies and french fries. While delicious, that is not always the first thought for Louisiana Department of Wildlife and Fisheries (LDWF) Inland Fisheries biologists. Several different species cross their mind when hearing the word “catfish.”
There is a group of small, bottom-dwelling catfish in North America called madtoms. Madtoms are considered to be one of the most imperiled, or at-risk, group of fish on the continent. Over half of all 29 madtom species in North America are listed as threatened or endangered. These fish exhibit nocturnal behavior and often have a camouflage color pattern. There are seven different species of madtoms that occur in Louisiana.
One of these seven species is the frecklebelly madtom (Noturus munitus). Within Louisiana, it is only found in the Pearl River Basin. In comparison to the more well-known (and commercially/recreationally important) blue catfish, channel catfish and flathead catfish, madtoms are quite small. Frecklebelly madtoms rarely reach 3.5 inches long. They are light brown with dark brown saddles across the back, which gives them excellent camouflage in their preferred habitat of fast flowing stream riffles with stable gravel beds. A depth of less than two feet is desirable, and submersed vegetation and/or woody debris is lagniappe.
The frecklebelly madtom became especially interesting to LDWF in 2010 when it was petitioned for federal listing under the Endangered Species Act. A listing decision deadline was set for September 2020. It was petitioned due to a perceived decline in abundance and distribution. The combination of very specific habitat requirements, and the fact that the preferred habitat is limited, can make the frecklebelly madtom’s existence vulnerable. A lack of targeted studies involving this species only adds to the perceived decline in abundance and distribution.
In response to the petition, Inland Fisheries biologists in the Lacombe office wrote a State Wildlife Grant (SWG) proposal requesting federal and state funds to complete a two-year, targeted study of the frecklebelly madtom. Once the SWG was approved, biologists began completing the work outlined in the grant proposal. The main objective was to survey new and historical sites within the preferred habitat of the frecklebelly madtom. Note: a new site is one which has not been sampled but has all of the attributes that would lead biologists to believe the area could support a population of frecklebelly madtom; a historical site is one which has been sampled previously that produced a sighting of a frecklebelly madtom. A secondary objective was to provide fish assemblage estimates. This is just a fancy term that describes how many different species of fish were present, and how many of each species were present. A final objective was to provide catch per unit effort (CPUE) data, which basically describes how many fish were collected in a given amount of time. All objectives aimed at evaluating whether this fish should be given special protections under federal law.
Surveys were conducted in the frecklebelly madtom’s preferred habitat throughout the Pearl River Basin in Louisiana using a 10-foot x 6-foot x 3/16-inch mesh seine and a backpack electrofishing unit, simultaneously. The seine was set at the bottom end of the sample site with one person holding each side of the seine. Another person with a backpack electrofishing unit entered the site upstream of the seine and began electrofishing in a downstream direction, which allowed the seine to collect the species. This process was repeated until a minimum of 900 seconds of electrofishing was achieved.
Data collected from this survey was used to determine presence and/or absence of frecklebelly madtoms, CPUE and relative abundance estimates (which indicate how rare or common a species is relative to other species in a given location). In total, biologists collected 3,411 individual fish that represented 28 different species. Of the 3,411 fish collected, 724 were frecklebelly madtoms - ranking them second in relative abundance. Only the blacktail shiner (Cyprinella venustus) was more abundant. A comparatively large portion (39%) of frecklebelly madtoms came from the four historic locations, which made up only 21% of the overall samples. The mean CPUE of the frecklebelly madtom across all sampling locations was 100.53 captured fish per hour. Results of the combined data analyses, specifically the high relative abundance and high mean CPUE, indicates that the frecklebelly madtom likely has a stable population throughout the Pearl River Basin in Louisiana.
Why were the results of this study so vastly different than previous studies on the same species? LDWF Biologists believe that answer lies in the updated sampling technique. Instead of just backpack electrofishing or just seining, LDWF biologists learned, through communication with biologists in surrounding states, that using both techniques simultaneously was most effective. Once this new technique was initiated, the number of frecklebelly madtom observations increased, and biologists were able to define and pinpoint even more precisely where the little catfish liked to hide.
All of this data was shared with the U.S. Fish and Wildlife Services (USFWS) to assist with the Species Status Assessment (SSA). The SSA report documents the results of a comprehensive biological review of the scientific data about the status of the species that has been petitioned for listing as either threatened or endangered. After the SSA was complete, in November of 2020 the USFWS proposed a rule NOT to list the frecklebelly madtom as an endangered or a threatened species throughout all of its range. Rather, they determined that the distinct population segment in the Upper Coosa River in Georgia and Tennessee warranted only a threatened listing (not endangered).
Much of the frecklebelly madtom’s range in Louisiana is in legislated Natural and Scenic Rivers, Bogue Chitto National Wildlife Refuge, and LDWF wildlife management areas, which allows for habitat protection that will help to preserve the populations of this species and others in the Pearl River Basin. With the habitat protections and the findings of a robust population, LDWF agrees with the decision that the federal listing of the Louisiana population is not warranted at this time. This work will ultimately save these areas from being subject to unnecessary restrictions and regulations, and will allow recreational activities to continue as they have for many years.
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