Whitefish Research Project: Factors Influencing Early Whitefish Survival

By Research Technician Dylan Whitaker

Years ago, lake whitefish were considered a popular sport fish in Maine and were readily caught in many waters across the state. Whitefish even supported a commercial fishery in northern Maine for a short time at the turn of the 20th century. However, many of Maine’s whitefish populations have experienced significant declines. Since then, whitefish lost much of its notoriety.

The decline of whitefish has been closely associated with the establishment of non-indigenous rainbow smelt. Rainbow smelt are believed to compete with and prey upon juvenile whitefish. 

Understanding the environmental and biological factors critical to early whitefish survival is an important information need for management and recovery efforts moving forward. This is the focus of the Whitefish Research Project.  

If you remember from my last post, we conducted whitefish spawning ground surveys and egg mat surveys (Fall 2018) in six Allagash waters where smelts have established. 

Our findings suggest that the availability of spawning habitat and the use of different spawning life-history strategies (tributary vs shoal spawners) may be an important piece to early whitefish survival and recruitment. For instance, whitefish populations in lakes with an abundance of spawning habitat, such as Ross Lake (where whitefish have coexisted with smelt in this lake for 70+ years) appear to be more resilient to smelt establishment compared to lakes with spawning ground limitations. 

The link between spawning ground availability and whitefish persistence is just one of several factors influencing early whitefish survival. Food availability for young whitefish and predation by adult smelt on larval whitefish are other important factors to consider.

This past spring, we conducted trawl tows (pictured below) to monitor post-hatch larval whitefish and zooplankton assemblages to better understand the impact food limitations have on the early survival of whitefish.

Zooplankton are microscopic organisms fed on by small fish like smelt and larval whitefish. The cyclopoid copepod, a microscopic crustacean, is the primary food resource for larval whitefish; its availability is critical to larval whitefish growth and survival.

Ross Lake, Clear Lake, Second Musquacook Lake, and Crescent Pond were trawled this past spring, immediately after ice off (when whitefish hatch), once a week, for four weeks to monitor zooplankton and larval whitefish. Ross Lake was our only lake in this study where whitefish were readily caught throughout the spring. Ross Lake was also the only lake with an abundance of cyclopoids. The other three lakes had nearly absent larval whitefish numbers (< 2 larval whitefish caught throughout the spring) and nearly absent cyclopoid densities (see chart below).

We suspect that limitations on this important food resource is tied to smelt interactions and may explain whitefish recruitment failure observed in these lakes.

The factors influencing whitefish declines appear to be more complex than initially thought. The availability of spawning/incubation habitat, food availability post hatch, and predation by adult smelts on larval whitefish are all important factors to consider when prioritizing and implementing sound management decisions moving forward. We plan on radio tagging whitefish in Ross Lake this fall to locate spawning grounds and learn more about whitefish spawning use and behavior in this water.

This project is funded in part by the U.S. Fish and Wildlife Service’s State Wildlife Grant Program and by the Maine Outdoor Heritage Fund, in which proceeds from the sale of a dedicated instant lottery tickets are used to support outdoor recreation and natural resource conservation. For more information about MOHF, visit maine.gov/ifw/mohf