Big Rivers Flathead Catfish Final Report

Flathead catfish (Pylodictis olivaris) are native to the Missouri and Mississippi rivers, and support
extremely important fisheries on these big rivers. The Missouri River supports a recreational fishery, and
the Mississippi River supports both recreational and commercial fisheries. Missouri’s big river, flathead
catfish populations have not been intensively managed in the past, and information needed to inform
management and regulatory decisions is limiting. Flathead catfish were sampled in the Mississippi and
Missouri rivers using low-frequency electrofishing, and these data, along with tag return information,
were used to estimate exploitation and other population demographics (e.g., size structure, age and
growth, and total annual mortality). Management and regulatory recommendations focus on increasing
yield available to fishers and ensuring sustainability of big river, flathead catfish populations.
A total of 8,395 flathead catfish ranging in size from 2-50 inches (51-1,270 mm) total length (TL) was
collected from eight study sites. Pectoral spines were aged from 2,114 flathead catfish; ages ranged
from 1-24 years on the Missouri and Mississippi rivers. In the Missouri River, flathead catfish reached 14
inches by age 4 (1 pound), 18 inches by age 5 (2 pounds), 24 inches by age 7 (5 pounds), 30 inches by
age 10 (10 pounds), and 36 inches by age 17 (20 pounds). Mississippi River flathead catfish were
estimated to take the same number of years to reach 14 and 18 inches as Missouri River fish but took an
additional year to reach 24 inches, two additional years to reach 30 inches, and four additional years to
reach 36 inches. To estimate exploitation, we tagged 836 flathead catfish in the Mississippi River and
850 in the Missouri River, with approximately 70 percent of tags having a standard reward value ($25)
and the remainder having a high reward value ($150). As of 1 January 2020, 281 flathead catfish tags
were reported by fishers. Reporting rates differed between sites and rivers; reporting rates on the
Mississippi River ranged from 43-88 percent and from 46-78 percent on the Missouri River. Total annual
exploitation was 10 percent (7 percent for recreational harvest and 3 percent for commercial harvest)
on the Mississippi River and 12 percent (all recreational harvest) on the Missouri River. On the
Mississippi River local exploitation ranged from approximately 9 percent at sites 2 and 4 to 12 percent at
site 1. Local exploitation on the Missouri River ranged from 9 percent at sites 5 and 7 to 16 percent at
site 6.
Growth or recruitment overfishing was not evident in our simulations. If fishing effort remains steady,
our models predict that a minimum length limit (MLL) would offer a slight improvement in yield and
trophy fishing potential. Furthermore, recreational anglers are thought to be more supportive of a MLL
to improve chances of catching a trophy-sized flathead catfish as opposed to other regulations including
gear restrictions or reduced daily bag limits. Commercial fishers may also support a MLL given the
predicted increase in yield. Therefore, fisheries managers aiming to increase yield on the Mississippi and
Missouri rivers should consider a MLL (e.g., 18 or 21 inches TL). In our simulations a protected slot limit
of 26-34 inches, like the blue catfish regulation at Lake of the Ozarks and Harry S. Truman Lake,
improved the trophy fishing potential more than predicted with a MLL, but decreased yield by 16-36
percent. If public opinion favors trophy fishing potential and fishers are willing to accept a minimal
decline in yield, then restricting the number of fish over 30 inches per day should be considered, as well. 2
This option would be most appropriate on the Missouri River where maintaining or improving yield is
not currently a management objective.
Recommendations:
- In coordination with Outreach & Education Division, staff develop a communication plan during
FY2021. Inform stakeholders about the outcomes of this research and determine constituent
attitudes and opinions concerning catfish harvest regulations and management objectives.
o Survey recreational and commercial catfish fishers during FY2021, to determine
attitudes and preferences associated with catfish management, angling, and harvest.
o During FY2021 inform and coordinate with neighboring state agencies (IL, KS, KY, NE,
and TN) responsible for managing border water fisheries.
o Conduct public meetings during FY2021.
- Based on the results of this study (blue catfish final report (MDC 2019) and this report), public
input (catfish harvest survey and public meetings), and discussions with neighboring state
agencies:
o If public sentiment is similar to existing human dimensions data (i.e., fishers are in large
part harvest oriented):
▪ Coordinate communication, planning, and development of regulation change
proposals (if necessary at all) for blue catfish and flathead catfish concurrently
during FY2021.
▪ If minimum length limits are proposed for blue catfish and it is desirable to have
similar regulations for both blue catfish and flathead catfish:
• Propose a minimum length limit on recreationally harvested flathead
catfish from the Missouri and Mississippi rivers during FY2021
• Propose a minimum length limit on commercially harvested flathead
catfish from the Mississippi River and possibly the St. Francis River
during FY2021
• Recreational and commercial minimum length limits should be set at
the same level on the Mississippi River and possibly the St Francis River.
o If public sentiment is different than existing human dimensions data (e.g., anglers are
willing to sacrifice yield to improve trophy fishing potential):
▪ Develop appropriate regulation change proposals (if necessary at all) for blue
catfish and flathead catfish concurrently during FY2021.
▪ If necessary, propose regulation changes on recreationally harvested flathead
catfish from the Missouri and Mississippi rivers during FY2021.
▪ If necessary, propose regulation changes on commercially harvested flathead
catfish from the Mississippi River and possibly the St. Francis River.
▪ Recreational and commercial length limits should be set at the same level on
the Mississippi River and possibly the St. Francis River.
- Update Missouri’s catfish management plan and objectives by FY2023. Consideration should be
given to drafting more quantitative management objectives (e.g., catch per unit effort, size 3
structure, or growth rates), and objectives that outline recommendations for reevaluation of
these fisheries.