Date of Award


Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)


Wildlife Ecology and Wildlife Conservation


Joseph Zydlewski

Second Committee Member

Stephen Coghlan Jr.

Third Committee Member

Michael Kinnison


The State of Maine issues an unlimited number of commercial permits for the harvest of White Suckers Catostomus commersonii in Maine’s inland waters. The fishery provides a necessary source of fresh lobster Homarus americanus bait to coastal communities at a time when other bait sources are scarce. The impacts of the increasing number of permits and subsequent numbers of fishermen on the white sucker population is unknown. The Maine Department on Inland Fisheries and Wildlife (MDIFW) has closed a number of waters due to concerns that overfishing and incidental catch of other fish species may occur.

In Chapter 1, we investigated demographic differences of White Suckers from lakes open to and closed to harvest. Each harvested lake was paired to a lake closed to harvest (reference lake) of similar size. Fish were captured from each lake and biological information was collected for each individual (i.e. sex, mass, gonadosomatic index, fecundity, and age). Distributions of each demographic were compared in a series of paired lake by sex analysis. Fish from harvested lakes were younger, smaller, and had lower fecundity than fish from reference lakes. Estimated mortality rates for harvested lakes were also two fold higher than reference lakes. There were some detectable differences in growth parameters from the von Bertalanffy growth function ( and K) between lake pairs as might occur under selective pressure. White Suckers are long-lived and the few differences found in growth may also reflect the infancy of the fishery (established in 1991). These data do suggest that current levels of exploitation are resulting in age truncation of white sucker populations.

In Chapter 2, we built a deterministic population model of White Suckers using parameters from literature and field studies to investigate the theoretical effects of harvest mortality on age-structure and fecundity. We compared the age-structure of White Suckers from our reference lakes to a baseline model and observed and simulated distributions were similar. When harvesting mortality increased in the model there was an expected truncation in age-classes. The average mortality from harvested lakes was used to run the harvest model and the age structure was compared to the aggregate of harvested lakes. A similar age truncation pattern occurred, however distributions were different. This could be due to the variation in the additive mortality estimated for each harvested lake. The results of harvest pressure were evaluated under the assumptions of –both a Beverton-Holt and Ricker recruitment curves.

In Chapter 3, we determined the spatial scale of harvesting effort in Maine using commercial sucker permits issued from 2006 to 2016. Of the 7-biological regions managed by MDIFW, Region B had the highest number of permitted waters and Region G had the lowest. A list was also compiled for each biological region for waterbodies with 8 permits (issued in the last 5-years) to provide managers an idea of where to focus efforts for monitoring in future harvest seasons. Possible areas for improvement to aid in management might include the use of a central database for harvesting information, as well as requiring more harvest information from commercial harvesters. It would be advantageous for managers if future commercial sucker report logs were site-specific to inform managers of areas that harvesters repeatedly target.

In aggregate, this study provided an important first-look at harvest impacts on white sucker populations in Maine. We now have a better understanding of how White Suckers respond to additive mortality through both field work and deterministic models. The permit analysis also provides managers with specific locations where monitoring efforts could be focused for the next harvest season. Additional data on the number of traps used, where traps are set, effort, and catch total per harvester will be important for future fishery management. Monitoring the age structure of harvested lakes could help assess the viability, productivity, and resilience of white sucker populations. An important next step in the commercial sucker fishery is identifying critical levels of white sucker mortality that cause declines in resilience and productivity, ultimately leading to population collapse.