A concerning phenomenon is unfolding in the depths of Lake Superior, prompting a scientific investigation into what researchers are calling 'zombie' fish. These are siscowet, a unique subspecies of lake trout found exclusively in the deep waters of the Great Lakes, exhibiting a severely emaciated condition.

The Discovery and Growing Concern

The discovery, made approximately 55 kilometers north of Munising, Michigan, has biologists increasingly worried as the proportion of these underweight fish continues to rise in recent years. Initial observations, spanning the last decade, revealed a gradual decline in the overall robustness of siscowet populations.

However, the situation has escalated in the past few years, with the percentage of emaciated fish observed in the deepest parts of Lake Superior jumping from around 10% to as high as 50% in some sampling instances. While not yet considered an alarming crisis, the trend is undeniably cause for concern, triggering a dedicated research effort this summer.

Potential Causes Under Investigation

The leading hypothesis centers around a disruption in the siscowet's food supply within the delicate deep-water ecosystem. Given the extreme conditions and limited resources at such depths, even a minor decline in prey fish populations could trigger widespread starvation. Scientists speculate that climate-related events in previous years may have impacted the abundance of these prey species.

Disease and Contaminants

However, other potential causes are also being investigated. This June, a research team will collaborate with pathologists from Michigan State University to collect additional samples using gill nets and conduct thorough disease screenings. The possibility of a contagious illness is being taken seriously.

The Great Lakes Fisheries Commission is also exploring the potential role of contaminants, such as mercury, and the impact of invasive sea lampreys on the siscowet population. Preliminary findings indicate that 'zombie' fish exhibit slightly elevated mercury levels compared to healthy individuals.

Ecological Role of Siscowet

Interestingly, scientists also recognize the potential ecological role of siscowet in mitigating the impact of sea lampreys on other commercially and recreationally important fish species like lake trout and whitefish. Their abundance in the deep waters may serve as a buffer, absorbing some of the lamprey attacks.

Current Status and Regional Impact

Currently, reports of emaciated siscowet have been limited to the south-central portion of Lake Superior, with no confirmed sightings on the Ontario side of the lake. The Ontario Ministry of Natural Resources has been contacted for comment, but has not yet responded. Authorities emphasize that recreational fishing is not currently at risk.

Researchers hope the situation represents a natural fluctuation within the ecosystem, but are prepared to address a potential disease outbreak if necessary. The ongoing research aims to unravel the complex factors contributing to this unusual phenomenon and ensure the long-term health of the Lake Superior ecosystem.