Seasonal Habitat Use, Capture Efficiency, Population Dynamics, and Physiology of Mudpuppies (Necturus maculosus) in an Urban Lake

Author

Jared Bilak, Southern Illinois University CarbondaleFollow

Date of Award

12-1-2024

Degree Name

Doctor of Philosophy

Department

Zoology

First Advisor

Boyles, Justin

Abstract

Freshwater habitats are among the most vulnerable environments on earth, with extinction rates higher than both terrestrial and marine habitats. Common mudpuppies (Necturus maculosus) are fully aquatic North American salamanders that have experienced population declines. Despite their large size and wide geographic distribution, much of their basic natural history and ecology is understudied. Utilizing modified minnow traps, I set 3988 traps baited with fathead minnows over 58 total trapping nights in Wolf Lake, Chicago, Illinois. I captured 129 individuals using traps and observed a significant decline in capture success above 14oC (0.003 mudpuppies/trap/night above 14oC and 0.05 mudpuppies/trap/night below 14oC) with a maximum temperature of capture of 20.5oC. In addition, during ice-free periods, I collected 72 mudpuppies by rock flipping during 31 rock flipping events and 140 person hours. Comparable to our trapping data, I found a significant decline in captures above 14oC (0.34 mudpuppies/person/hour above 14oC and 1.28 mudpuppies/person/hour below 14oC) with a maximum temperature of capture of 28.9oC. There was a significant difference in total length of mudpuppies caught in traps (mean TL= 24.1±0.8cm) and rock flipping (mean TL= 15.6±0.5cm). This finding indicates the need for multiple capture methods to describe population dynamics and presence of recruitment. I found that larger individuals were found rock flipping at a greater water depth (R=0.39, p=0.0016) but not necessarily a greater distance from shore (R=0.28, p=0.025), which is indicative of the anthropogenically disturbed habitat at Wolf Lake. I used non-lethal gastric lavage method to acquire and compare stomach contents across size classes. I used Non-metric multidimensional scaling (NMDS) to visually compare diet differences and Analysis of Similarities (ANOSIM) to determine diet similarities for abundance and volume of prey items. Size classes were divided by total length into: small (0-10cm), medium (10.5-20cm), and large (>20.5cm). For abundance, 51% of the similarity was driven by amphipods and insects between small and medium mudpuppies, 59% was driven by amphipods and fish between small and large mudpuppies, and 59% was driven by fish and insect between medium and large mudpuppies. For volume, 57% of the similarity was driven by fish and crayfish between small and medium mudpuppies, 86% was driven by fish between small and large mudpuppies, and 56% was driven by fish between medium and large mudpuppies. Abundance and volume were driven by total length (p=0.001) with prey items all significantly different for abundance, and all prey items except isopods significantly different for volume. I also found amphibians in stomach contents with frogs (n=4) and a cannibalistic event were a 25.5cm individual consumed a 14cm individual. My findings suggest that mudpuppies are gape-limited, opportunistic feeders that consume a variety of prey items regardless of size. We implanted radio transmitters in twenty sub-adult to adult mudpuppies in March, 2017 and in seven sub-adult to adult mudpuppies in December, 2017 to analyze seasonal movement. Individuals were located every 16.3±0.3 days and median distance moved between tracking events was 3.7m. Further, 97% of all movements were less than 10m and all movements >10m occurred between October-May (with the exception of two events). There was no significant difference between male and female movements (p=0.26) and sedentary behavior was observed following large movements. My findings were similar to movements observed in terrestrial salamanders where individuals remain in familiar territory or within home ranges (Stebbins and Cohen 1995). The largest movements were seasonal and near-shore habitats were utilized (greatest depth 4.3m). I used hormone analysis and acute metabolic response due to temperature to analyze what is driving seasonal movements. Female hormone concentration (estradiol) did not vary across seasons (spring, summer, and winter) and males were only caught in the spring. This may be due to nest guarding behavior in females and males vacating the breeding grounds after breeding. Mass-specific oxygen consumption (mgO2/kg/hour) was highly variable with a 10.3% increase from 12.7oC to 24.3oC, a 31.9% increase from 12.7oC to 15oC, and a 16.4% decrease from 15oC to 24.3oC. I calculated a Q10 temperature coefficient of 1.4 across my study temperatures. This pattern shows limited response to acute temperature changes and can be explained by the wide latitudinal distribution of mudpuppies and the large seasonal difference in water temperature at Wolf Lake (~3oC-30oC). My study conveys the importance of extensive sampling periods for mudpuppies to accurately predict their population status due to seasonal activity patterns, difficulty of capture, and overall cryptic appearance and behavior. My findings show the need for near-shore habitat protection in conservation efforts for mudpuppy prey habitat and breeding locations.