Investigations into causes of variable survival of Chinook salmon stocked into Lake Huron.

Comparison of catch and lake trout bycatch in commercial trap nets and gill nets targeting lake whitefish in northern Lake Huron.

Comparison of catch and lake trout bycatch in commercial trap nets and gill nets targeting lake whitefish in northern Lake Huron.

The problem of bycatch management, with emphasis on lake trout bycatch in 1836 Treaty waters of the upper Great Lakes.

Investigations into recent declines in survival of brown trout stocked in Lake Charlevoix and Thunder Bay, Lake Huron.

Successes and failures of large scale ecosystem manipulation using hatchery production: the Upper Great Lakes experience.

Johnson, J. E., S. P. Dewitt, and J. A. Clevenger, Jr.. 2007. Investigations into causes of variable survival of Chinook salmon stocked into Lake Huron. Michigan Department of Natural Resources, Fisheries Research Report Number 2086. Ann Arbor, MI.

Abstract.-We investigated several cohorts of Chinook salmon in Lake Huron with emphasis on factors contributing to post-stocking survival. Stocked Chinook salmon were marked with oxytetracycline and/or coded-wire tags (CWT). Returns of CWT Chinook salmon to the recreational fishery were 2.5 times higher for fish pen-acclimated at the Au Sable River than for those stocked there conventionally. Return rates were only slightly enhanced by pen acclimation at Harbor Beach where the fish were probably stressed by excessive acclimation temperatures in most or all years of the study. Acclimation pens also appeared to better imprint fish to the Au Sable River where returns in fall spawning runs were 6.4 times higher for acclimated than conventionally-stocked fish. Transporting pen-acclimated Chinook salmon to the beach at the mouth of the Au Sable River enhanced performance of the 1995 cohort relative to acclimated fish stocked in the river, but beach stocking produced little improvement in survival in subsequent years when alewives were scarce. Returns of CWT Chinook salmon from all stocking sites generally decreased after 1995, as did alewife abundance. Survival of juvenile Chinook salmon and growth, condition, and survival of adult Chinook salmon appear to be positively correlated with adult alewife abundance. One-fourth of spawning-phase Chinook salmon in the Au Sable River were in critically low physical condition in fall 2004, suggesting a significant proportion of the adult population was succumbing to malnutrition. Age-0 Chinook salmon occupied the nearshore waters of Lake Huron for their first 6 months of lake residence. During May and June, both hatchery and wild juvenile salmon were taken by beach seining, particularly at the mouths of the Au Sable and Tawas rivers. Adult alewives were the most abundant of 46 species of fish sampled with beach seines while targeting Chinook salmon, and lake whitefish were caught in beach seines at many locations, especially in the Thunder Bay area. Age-0 Chinook salmon were found in stomachs of walleyes, lake trout, and other predators sampled near the beach seining sites, particularly when alewives were scarce. Pen acclimation appeared to minimize exposure of stocked Chinook salmon to predation in the beach zone because the acclimated fish were larger and appeared to migrate offshore more quickly than smaller conventionally stocked Chinook salmon. Juvenile Chinook salmon were sampled later in the summer with small-mesh gill nets in waters less than 20 m deep where water temperatures were frequently near 18°C. These juveniles fed on terrestrial and aquatic invertebrates until September when they began switching to fish, principally age-0 alewives. Growth rates were rapid, averaging 1.3 mm per day, probably driven by the relatively warm temperatures occupied. Adult alewives were the leading incidental catch in the small-mesh gillnets while targeting juvenile Chinook salmon. Age-0 Chinook salmon appeared to be buffered from predation in years when alewives were abundant. Conversely, their similar size and appearance and spatial association with alewives may have contributed to increased predation on age-0 Chinook salmon when alewives were scarce. Adult alewife abundance declined sharply after 2002, which renders the future of Lake Huron's Chinook salmon fishery highly uncertain.

Johnson, J. E., J. X. He, A. P. Woldt, M. P. Ebener, and L. C. Mohr. 2004. Lessons in rehabilitation stocking and management of lake trout in Lake Huron. Pages 157-171 in M.J. Nickum, P.M. Mazik, J.G. Nickum and D.D. MacKinlay, editors. Propagated fish in resource management. American Fisheries Society, Symposium 44, Bethesda, Maryland.

Abstract.-Lake trout, the native keystone predator of the upper Great Lakes, were extirpated from Lake Huron in the 1940s. From 1973 to 2002 more than 42 million yearling-equivalent lake trout were stocked in Lake Huron. We use assessment catch rates and statistical catch-at-age models to evaluate stocking methods and whether objectives of rehabilitation stocking, including restoration of natural reproduction, have been achieved in western Lake Huron. A rise in survival after 1989 was probably due to vessel distribution of hatchery fish to offshore stocking sites and an increase in average condition of lake trout stocked during the early 1990s. Until 2000, however, excessive sea lamprey- and fishing-induced mortality permitted few lake trout to survive to spawning age, thus suppressing reproduction. In contrast, a reproducing stock of lake trout has been rehabilitated in Parry Sound, eastern Lake Huron, where fishing and lamprey controls were more effective and stocking rates higher. Beginning in 2000, more effective lamprey and fishing controls were implemented in western Lake Huron. Modeled spawning-stock-per-recruit estimates suggest these measures produced conditions favorable for accumulation of lake trout spawning stocks. More effective management of mortality combined with recent improvements in stocking strategies should lead to improved prospects for reproduction in western Lake Huron.

Johnson, J. E., M. P. Ebener, K. Gebhardt, and R. A. Bergstedt. 2004. Comparison of catch and lake trout bycatch in commercial trap nets and gill nets targeting lake whitefish in northern Lake Huron. Michigan Department of Natural Resources, Fisheries Research Report 2071, Ann Arbor.

Abstract.-We compared seasonal lake whitefish catch rates, lake trout bycatch, and gear-induced lake trout mortality between commercial trapnets and gillnets in north-central Lake Huron. Onboard monitors recorded catches from 260 gillnet and 96 trapnet lifts from October 1998 through December 1999. Catch rates for lake whitefish were highest in fall for both gear types, reflecting proximity of spawning sites to the study area. Lake whitefish catch rates were also relatively high in spring but low in both gear types in summer. Lake trout were the principal bycatch species in both gears. The lake trout bycatch was lowest in both gear types in fall, highest in gillnets in spring, and highest in trapnets in summer. The ratio of lake trout to legal whitefish (the target species) was highest in summer and lowest in fall in both gear types. The high lake trout ratio in summer was due principally to low catch rates of lake whitefish. All but 3 of 186 live lake trout removed from trapnet pots survived for at least two days of observation in laboratory tanks. Therefore, we estimated that post-release survival of trapnetted lake trout that had not been entangled in the mesh was 98.4%. In addition, we accounted for stress-induced mortality for lake trout that were live at capture but entangled in the mesh of either gear type. Resulting estimates of lake trout survival were higher in trapnets (87.8%) than in gillnets (39.6%). The number of lake trout killed per lift was highest during summer in trapnets and during spring in gillnets. In trapnets, 85% of dead lake trout were observed to be entangled in the mesh of the pot or tunnels. Survival rates of lake trout in gillnets were higher in our study than reported by others, probably because our nets were hand lifted in a small boat. Our trapnet-induced mortality estimates on lake trout were higher than those reported by others because we adjusted our estimates to account for post-release mortality caused by handling and injury. Studies such as ours should prove useful to managers developing harvest allocation options that are consistent with the need to protect nontarget populations. For example, applying our seasonal lake trout-whitefish catch ratios to a hypothetical small-boat gillnet fishery, the lake trout bycatch from harvest of 100,000 kg of whitefish would equal the estimated lake trout production available for harvest in the study area for year 2002. The two trapnet fisheries may have incidentally killed half this number of lake trout annually from 1995-1999. Bycatch estimates are also important inputs to catch-at-age decision models used in developing rehabilitation and harvest strategies for target and bycatch species.

Johnson, J. E., J. Jonas, and J. P. Peck. 2004. The problem of bycatch management, with emphasis on lake trout bycatch in 1836 Treaty waters of the upper Great Lakes. Michigan Department of Natural Resources, Fisheries Research Report 2070, Ann Arbor.

Abstract.-We investigated the collective published record on the significance and management of commercial fisheries bycatch at both global and Great Lakes regional scales to: 1) to identify elements of Great Lakes ecosystems that are especially vulnerable as fisheries bycatch; and 2) identify opportunities to minimize incidental catch of sensitive species in Great Lakes commercial fishing gear. The majority of the world's harvestable fisheries are fully- or over-exploited, and approximately a third of the global catch is composed of bycatch and discards. Bycatch can be characterized as the incidental catch of organisms that were not targeted in a given fishing effort. Significant levels of bycatch can contribute to overharvest. Therefore, it is essential to characterize bycatch when assessing impacts of fishing. Bycatch is not always measured; failure to measure bycatch can result in underestimation of fishing mortality and thus, overestimation of quotas available for harvest. Responsible fishing practices are being encouraged worldwide and most of these efforts have focused on reducing or eliminating the amount of bycatch associated with harvest of targeted species. The magnitude of the bycatch problem is typically proportional to fishing effort. In many cases, effort exceeds what is necessary to harvest sustainable yields of target species; thus, reduction of effort is often the single most effective tool in reducing bycatch. Other methods of managing bycatch include: development and use of more selective gear, prohibiting retention of bycatch, and use of incentives and penalties in quota management. Great Lakes fisheries have mirrored the global pattern of overfishing. Recovery programs for collapsed fish populations have necessitated restrictive harvest controls. Lake whitefish Coregonus clupeaformis populations have recovered, but lake trout Salvelinus namaycush are far from rehabilitated in lakes Ontario, Erie, Michigan, and Huron. Lake trout are the native keystone species of the upper Great Lakes, are the subject of immense rehabilitation efforts, and have vulnerability similar to lake whitefish to leading gear types used in Great Lakes commercial fisheries. Efforts to limit commercial fishing to more selective gear types have been only partially successful. Bycatch of lake trout in large-mesh gill nets set for lake whitefish has exceeded lake trout harvest quotas in some management units. The selectivity of gill nets is difficult to manipulate, especially when target and nontarget fish are of similar size and overlap in spatial distribution, as is the case with lake trout and lake whitefish. Trap nets are effective in catching lake whitefish and are less lethal to the catch than gill nets. Commercial bycatch, combined with targeted fishing for lake trout (recreational and commercial) and depredation by sea lampreys Petromyzon marinus, has contributed to the delayed rehabilitation of self-sustaining lake trout fisheries. Thus, we conclude that the widespread use of nonselective gear types such as gill nets in Great Lakes commercial fisheries is inappropriate in an era of shared resources and ecosystem-level rehabilitation efforts.

Johnson, J. E., and G. P. Rakoczy. 2004. Investigations into recent declines in survival of brown trout stocked in Lake Charlevoix and Thunder Bay, Lake Huron. Michigan Department of Natural Resources, Fisheries Research Report 2075, Ann Arbor.

Abstract.-Sharp declines in the Thunder Bay, Lake Huron, and Lake Charlevoix brown trout fisheries prompted investigations into the causes of brown trout failures in these waters and possible solutions. Both Thunder Bay and Lake Charlevoix are located in the northern part of Michigan's Lower Peninsula. Test netting and diet studies of predators and prey in Thunder Bay during 1990 showed that piscivorous fish, particularly walleyes, consumed recently stocked brown trout, but that spawning aggregations of alewives during June appeared to buffer predation on stocked trout by offering ample alternate prey. The stocking date for brown trout, which had been early May, was therefore changed to mid June in 1992. Two strains of brown trout, Wild Rose and Seeforellen, were selected for field evaluation based on evidence of satisfactory lacustrine performance elsewhere, and programmed for testing in Thunder Bay and Lake Charlevoix. These strains were also compared with Plymouth Rock strain, which had been stocked in both systems prior to the study. Both Seeforellen and Wild Rose strains produced greater returns and faster growth than Plymouth Rock strain. Seeforellen and Wild Rose strains were similar to each other with respect to returns to creel, growth rates, and longevity in the fishery. However, there was evidence that Seeforellen strain produced slightly better results in Thunder Bay. The brown trout fishery in Thunder Bay rebounded with successful stockings in 1991-1995, but declined again as a consequence of poor survival of trout stocked after 1995. The short-term recovery was attributed to the later stocking window and deployment of the new test strains of brown trout. The brown trout failure after 1995 appeared to be caused by declining alewife abundance, which essentially "closed" the June stocking window. Predation on brown trout was probably exacerbated by a 8.4-fold increase in double-crested cormorant Phalacrocorax auritus numbers in the Thunder Bay area between 1989 and 1997. Offshore stocking had no measurable effect on survival of the 1996 and 1997 yearling cohorts; both nearshore and offshore treatments survived poorly in both years. The brown trout niche in Thunder Bay appeared to be tenuous. Zooplankton and other prey were scarce for age-1 brown trout. Diet of age-1 brown trout was chiefly terrestrial insects because the trout were too small to utilize the abundant adult alewives. Longevity of brown trout in the fishery was relatively short and few survived past age 4. Thus, once recruited at age 2 to a size sufficient to feed on alewives, brown trout contributed to the fishery only 1 or 2 more years. Two successive year class failures therefore were sufficient to cause collapse of the fishery. Unless alewives recover, predators decline, or another prey species (such as the round goby, a recent invader) alter the food web in a way that favors brown trout, the niche for put-grow-take brown trout management of Thunder Bay may have disappeared.

Whelan, G. E. and J. E. Johnson. 2004. Successes and failures of large scale ecosystem manipulation using hatchery production: the Upper Great Lakes experience. Pages 3-32 in M.J. Nickum, P.M. Mazik, J.G. Nickum and D.D. MacKinlay, editors. Propagated fish in resource management. American Fisheries Society, Symposium 44, Bethesda, Maryland.