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Member
Posts: 2680
Location: Essexville, MI./Saginaw Bay. | I e-mailed my DNR bud this morning asking if he ever got the results from the Michigan State Student that was assigned to take Bi-Catch data from the commercial netters Boats on Saginaw Bay last year. This data was a real eye opener for me. It reinforced for me some things I kinda of knew and assumed. Yet was surprised by some other data. With last years summer sport catch being down to 160,000 walleyes, I was surprised what the commercial bi-catch kill rates were. His written results are printed below.
QUANTIFYING THE BYCATCH OF SAGINAW BAY, LAKE HURON’S COMMERCIAL TRAP NET FISHERY.
Saginaw Bay, Lake Huron’s commercial fisheries have experienced tremendous change through the years. The bay currently supports commercial trap net fisheries for several target species including lake whitefish (Coregonus clupeaformis) in the deep water outer bay and yellow perch (Perca flavescens) in the shallow water inner bay. Catch rates of non-target species in these fisheries (bycatch) is currently unknown.
Throughout the 2010 fishing season, I quantified bycatch in trap nets by observing onboard commercial fishing vessels. Though all non-target species incidentally caught by the commercial trap net fishery were evaluated, I emphasized capture of walleye (Sander vitreus) and lake trout (Salvelinus namaycush) because these species are important foci of Great Lakes management. Specifically, I related the number of individuals of each species caught to varying environmental conditions and fishing practices. In addition, I counted the number of discarded floating walleye and lake trout to obtain a baseline mortality estimate.
Overall, significantly more walleye were caught per trap net lift in the inner bay as opposed to the outer bay. Alternatively, significantly more lake trout were caught per trap net lift in the outer bay as opposed to the inner bay. Walleye bycatch was highest in May (µ = 280.9/lift) and decreased each month to a low in August (µ = 8.3/lift). Similarly, walleye mortality was also highest in May (µ = 130.9/lift). Lake trout bycatch was highest in August (µ = 72/lift) and lowest in June (µ = 3.1/lift). Lake trout mortality was highest in August (µ = 20.8/lift).
I analyzed the data to determine how covariates such as air and water temperature, target species catch rate, and soak time influence bycatch and bycatch mortality rates. Catch of non-target species was most influenced by time of year and soak time with longer soak times resulting in higher catches. Walleye bycatch mortality was most influenced by trap net depth and magnitude of target catch. Increased trap net depth and larger target catches resulted in increased mortality.
Lake trout mortality was most influenced by surface water temperature and target catch. Lake trout mortality increased with target catch and surface water temperature. Total estimated walleye bycatch mortality for the 2010 inner bay trap net fishery was 101,872 individuals. Total estimated lake trout bycatch mortality for the 2010 outer bay trap net fishery was 2,979 individuals. | |
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Member
Posts: 2300
Location: Berlin | Stupid question but what happens to these fish? | |
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| Seagulls have to eat too!! Same thing happens on the bay of green bay prob. not as high due to less nets, I would think. Could be wrong just what ive heard from some locals up there. | |
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Member
Posts: 174
| On Green Bay the incidental catch is sold as cat food. | |
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Member
Posts: 2680
Location: Essexville, MI./Saginaw Bay. | IMEO, if commercial fishermen were allowed to keep and profit (in any form) from any of their (Non target specie) Bi-Catch, I believe you'd soon see new trap net area placings that would boost Bi-Catch walleyes from 100,000 to 200,000. All non target fish species not included and described in their legal license (by law) have to be thrown back into the water as soon as caught.
Edited by walleye express 5/25/2011 11:17 AM
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Saginaw Bay 2010 Commercial Bi-Catch/kill rates/data.