DNR about-face on gill nets cannot be supported by its own science

The Michigan Department of Natural Resources Fisheries Division has a proud, well-deserved legacy of leadership in restoring balanced fish communities to the Great Lakes.  A central element of this legacy was the Department’s recognition that lake trout restoration was all but impossible so long as tens of millions of feet of non-selective, lethal gill nets were fished annually.  Michigan led the Great Lakes states in conversion of gill nets to the more selective trap nets, zonal management that included recreational and rehabilitation zones, and limited entry to the commercial fishery (Tanner and Tody, 2002: https://fisheries.org/docs/books/x55039xm/7.pdf ). Here we offer a review of the science and assessment work conducted or led by the Fisheries Division that informed the DNR’s long-standing position that gill nets are incompatible with restoration of a balanced predator-prey fish community, lake trout restoration in particular.  A vast quantity of research is conducted elsewhere and by others on bycatch management and gill nets in particular (Johnson et al. 2004a: https://www2.dnr.state.mi.us/Publications/pdfs/ifr/ifrlibra/Research/reports/2070rr.pdf ) but here we confine our evidence to work undertaken or led by the DNR’s Fisheries Division.

Lessons From the Past About Gill Nets Can’t Be Ignored

During the mid-20th century hundreds of millions of feet of commercial gill net were fished annually. Fish stocks were already seriously declining from overfishing when invasive sea lampreys, alewives, and rainbow smelt further disrupted Great Lakes fish communities. The combined effect of overfishing and invasive species was more than the fish community could sustain and the near or total extinction of lake trout and certain species of ciscos in the Great Lakes followed. Absent predators to control their numbers, alewives exploded, creating a crisis of dead and dying alewives awash on Great Lakes beaches.

This catastrophe set the stage for introducing top predators to convert alewife biomass into an economically and ecologically valuable salmonid community and restore the native lake trout.  But the Fishery Division worried that, even after sea lamprey numbers had been dramatically reduced, lake trout could not be restored to the Great Lakes unless gillnet effort was converted to a less lethal, more selective gear type (Tody and Tanner, 2002: https://fisheries.org/docs/books/x55039xm/7.pdf ).  These fears were confirmed when in 1968 onboard monitoring of Lake Michigan gillnetters produced an estimate that 71,000 mostly juvenile lake trout were caught incidentally in the whitefish and chub gillnet fisheries (Rybicki and Schneeberger, 1990; https://quod.lib.umich.edu/f/fishery?view=toc;iel=1;c=fishery;idno=aag2862.1960.001).

This finding was not surprising: DNR researcher Robert Haas (http://protectmiresources.com/wp-content/uploads/2023/02/1978-Robert-Haas-Overveiw-of-the-Great-Lakes-Commercial-Fishery-with-Special-Emphasis-on-the-use-of-gill-nets-and-impoundment-gear.pdf, in a review of literature, reported that from 1929-1954 about 15 million very small lake trout were killed in small-mesh gill nets set for chubs and that number of small lake trout nearly equaled the number of older trout caught in large mesh. Also, many lake trout caught in small-mesh gill nets were larger, subadult-sized, approximately 21 inches in length, caught by their teeth.  Haas concluded that gillnet effort in the Great Lakes had to be drastically reduced to sustain both commercial and recreational fisheries and foster natural reproduction. In a court-ordered study comparing bycatch of gill nets and trap nets, it was determined that a gillnet fishery in northern Lake Huron with a whitefish quota of 240,000 pounds would kill as bycatch the entire harvestable surplus of lake trout in that management unit – gill nets could not be fished selectively where lake trout rehabilitation was a priority (Johnson et al. 2004b; (https://www2.dnr.state.mi.us/PUBLICATIONS/PDFS/ifr/ifrlibra/Research/reports/2071rr.pdf).

Turning to the agreements with five tribes with fishing rights under the Treaty of 1836, as a central element of the 2000 Consent Decree, and with strong DNR support, $14,000,000 was invested in conversion of about 50% of tribal gillnets to trap nets which reduced lake trout mortality rates to targeted levels (Johnson et al. 2004a:  (https://www2.dnr.state.mi.us/Publications/pdfs/ifr/ifrlibra/Research/reports/2070rr.pdf Johnson et al. 2004a:                          ( https://www2.dnr.state.mi.us/Publications/pdfs/ifr/ifrlibra/Research/reports/2070rr.pdf).  (For a description of gill nets and trap nets, see: https://www.michiganseagrant.org/topics/coastal-hazards-and-safety/commercial-fishing-net-safety/.)

Gill Nets Catch and Kill, Decimating Even Non-Target Species

As the name implies, most fish in gill nets are entangled by the gills. Fish caught by the gills may suffocate or sustain irreversible damage to the gill arches, including bleeding from the gills (Johnson et al. 2004a (https://www2.dnr.state.mi.us/PUBLICATIONS/PDFS/ifr/ifrlibra/Research/reports/2071rr.pdf ). During the period 1972-1974, 70% to 83% of 7,670 lake trout caught incidentally in gill nets during three years of study were classed as dead or moribund by Lake Superior fishermen who had agreed to record the condition of their lake trout catch as the nets were lifted (Haas, R. C.; http://protectmiresources.com/wp-content/uploads/2023/02/1978-Robert-Haas-Overveiw-of-the-Great-Lakes-Commercial-Fishery-with-Special-Emphasis-on-the-use-of-gill-nets-and-impoundment-gear.pdf). Haas, furthermore, reports many released lake trout died later from injuries.  This mortality rate estimate was similar to that measured by others (Johnson et al. 2004a:  https://www2.dnr.state.mi.us/Publications/pdfs/ifr/ifrlibra/Research/reports/2070rr.pdf ). Haas also reports that a significant portion of gillnet catch escapes or falls out of the mesh after capture and that the mortality of these fish could approach 40%; however, this loss (waste) of fish from gill nets is not clearly known and is almost never reported.

DNR Reverses Gillnet Position, Throwing Science and Previous Investments Out the Door

Paradoxically, and in a complete about-face, the Fisheries Division’s Tribal Unit has now agreed to a reversal of the DNR’s previous gillnet positions, has abandoned the $14,000,000 gill net-to-trap net conversion project, and has embraced a vast expansion of gillnet “opportunities” for tribal fishers in the 1836 Treaty Waters of Michigan’s Great Lakes. This new position on gill nets is supported by neither science nor the DNR’s legacy of successful reduction of fish killed as commercial bycatch – the mortality of incidentally caught, not-targeted species such as lake sturgeon and lake trout, principally in gill nets. The Tribal Unit of the DNR gives no science-based or other credible evidence in defense of this new expansionist gillnet policy.

In conclusion, we could not find any evidence to support the Tribal Unit’s recent reversal of the Fisheries Division’s long-standing and well-founded policy of minimizing the use of gill nets in the Great Lakes. Thus, we conclude gill nets are incompatible with basic tenants of resource stewardship, particularly the rehabilitation of lake trout, lake sturgeon, ciscoes, and other species. We draw this conclusion based exclusively upon the scientific work of the DNR’s own fisheries biologists.