Update on North Branch Trout Population

Although there have not been any definite conclusions to the cause of the reported trout population decline, this foundation and some other dedicated groups have been diligently investigating it. Monitors for chemical pollution were installed and initial reading showed no significant chemicals of concern. The recorders have been sent to U.S. Fish and Wildlife scientists for additional evaluation.

Insect surveys conducted later in 2018 also showed no measurable decline in the number or health of the insects that are the primary food source for North Branch trout.

The Michigan DNR fish biologists also conducted a survey in September to determine if disease pathogens were adversely impacting the trout population. No significant pathogens were detected and a copy of the email sent by them is shown below:

As part of the investigation into the cause for the decline in trout populations in the North Branch Au Sable last year, we collected 62 brook trout and had them tested for diseases at the MSU laboratory. I recently received the results, and have included a summary from Gary Whelan below. "On 9/17/2018, a total of 62 Brook Trout were collected from the North Branch of the Au Sable River and delivered alive to the Michigan State University Aquatic Animal Health Laboratory. The goal of this collection was to examine if fish pathogens could have been involved in the trout population changes seen in 2018 on this stream. MSU examined all fish and an expected number of external parasites were found at low intensities in 10-15% of the fish. None of the key bacterial pathogens were found other than 3/62 fish being documented as having bacterial kidney disease at low levels which is about the expected background level. Viral analyses showed no changes in cell culture and all fish were negative for IPNv, VHSv, and IHNv along with a host of other viruses that the cell lines used would detect. A total of 6/62 were infected with Myxobolus cerebralis, the causative agent of Whirling Disease, which is consistent with previous results for this pathogen in this stream. Overall based on these results, it does not appear that pathogens were key factor in the changes in trout populations in the North Branch of the Au Sable River."

The Anglers of the Au Sable also published two articles on this topic in their Fall 2018 issue of Riverwatch. Starting on page 5 there are two very good articles by Betsy Henning & Neil Wallace and by Josh Greenberg. Click on the picture of the cover to read a digital copy.

We will continue to keep you updated as any new information becomes available and we thank you for your support as we continue to work on this and other issues to preserve and protect the North Branch..