Gill-Net Saturation by Lake Trout in Michigan Waters of Lake Superior

Hansen, Michael J.; Schorfhaar, Richard G.; Selgeby, James H.

doi:10.1577/1548-8675(1998)018<0847:gnsblt>2.0.co;2

Cited by 25 publications

(25 citation statements)

References 10 publications

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“…The primary benefi t of a delta-GAM is that the effects of soak time and fi sh accumulation can be understood after accounting for variation in total fi sh catch that might be due to all the other predictor variables in a model (Li et al, 2011). By accounting for soak time, fi sh accumulation, and other predictor variables, we found an improvement over previous (primarily gill net) studies that focused on only those predictor variables that were directly related to the gear saturation process itself (e.g., Minns and Hurley, 1988;Hansen et al, 1998;Akiyama et al, 2007). A secondary benefi t of delta-GAMs is that they can account for zero-infl ation.…”

Section: Figurementioning

confidence: 80%

Influence of soak time and fish accumulation on catches of reef fishes in a multispecies trap survey

Bacheler¹,

Bartolino²,

Reichert³

2013

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Abstract-Catch rates from fisheryindependent surveys often are assumed to vary in proportion to the actual abundance of a population, but this approach assumes that the catchability coefficient (q) is constant. When fish accumulate in a gear, the rate at which the gear catches fish can decline, and, as a result, catch asymptotes and q declines with longer fishing times. We used data from long-term trap surveys in the southeastern U.S. Atlantic to determine whether traps saturated for 8 reef fish species because of the amount of time traps soaked or the level of fish accumulation (the total number of individuals of all fish species caught in a trap). We used a deltageneralized-additive model to relate the catch of each species to a variety of predictor variables to determine how catch was influenced by soak time and fish accumulation after accounting for variability in catch due to the other predictor variables in the model. We found evidence of trap saturation for all 8 reef fish species examined. Traps became saturated for most species across the range of soak times examined, but trap saturation occurred for 3 fish species because of fish accumulation levels in the trap. Our results indicate that, to infer relative abundance levels from catch data, future studies should standardize catch or catch rates with nonlinear regression models that incorporate soak time, fish accumulation, and any other predictor variable that may ultimately influence catch. Determination of the exact mechanisms that cause trap saturation is a critical need for accurate stock assessment, and our results indicate that these mechanisms may vary considerably among species.

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Section: Figurementioning

confidence: 80%

Influence of soak time and fish accumulation on catches of reef fishes in a multispecies trap survey

Bacheler¹,

Bartolino²,

Reichert³

2013

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“…The management areas were designed to be similar in size to the range of lake trout movement in Lake Superior, based on studies that showed 90% of marked lake trout were recaptured within 80 km of release sites, regardless of their size at release or length of time at large (Eschmeyer et al 1953;Buettner 1961;Pycha et al 1965;Rahrer 1968;Swanson 1973;Ebener 1990;Peck and Schorfhaar 1991). Contracted commercial fisherman, Michigan Department of Natural Resources (MIDNR), and Chippewa-Ottawa Resource Authority (CORA) conducted the surveys using standard nets (114-mm stretched measure mesh, 210/2 multifilament nylon twine, 18 meshes deep, hung on the ½ basis) fished from late April through early June during 1970-1998. Nets were not all of the same length, so catch per effort (CPE) was defined as the number of fish caught per kilometer of net.…”

Section: Methodsmentioning

confidence: 99%

“…Nets were not all of the same length, so catch per effort (CPE) was defined as the number of fish caught per kilometer of net. Nets were fished for varying numbers of nights, so CPE was standardized to one net-night using conversions developed from gill-net saturation studies in 1995 (Hansen et al 1998). The individual lift CPE of wild and stocked lake trout was transformed to natural logarithms, adding 1 to each CPE to adjust for zero catches: log e (CPE ϩ 1).…”

Section: Methodsmentioning

confidence: 99%

“…Our first objective was to quantify the contribution of wild and stocked lake trout to catches of age-7 wild lake trout (hereafter, recruitment) in areas of Michigan waters of Lake Superior during 1970-1998. Previously, Hansen et al (1997a showed that stocked lake trout were largely responsible for recruitment in Michigan waters where wild lake trout stocks recovered after 1970.…”

Section: Please Scroll Down For Articlementioning

confidence: 99%

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Recruitment Dynamics of the 1971–1991 Year‐Classes of Lake Trout in Michigan Waters of Lake Superior

Richards

Hansen

Bronte

et al. 2004

N American J Fish Manag

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In the 1950s, populations of lake trout Salvelinus namaycush in Lake Superior collapsed because of excessive exploitation and predation by sea lampreys Petromyzon marinus. Restoration began in the 1950s with the stocking of juvenile, hatchery‐reared lake trout and controls on fisheries and sea lampreys. Partial restoration was declared in 1996 because wild fish made up most of the populations in many areas, especially in Michigan waters, so stocking was dramatically curtailed in most areas. We evaluated the production of age‐7 lake trout (recruits) by age‐8 and older wild and stocked parental lake trout (spawners). Using Ricker stock–recruitment models, we also evaluated the effects of large‐mesh (114‐mm stretch measure) gill‐net effort on wild lake trout recruitment in Michigan waters of Lake Superior during 1970–1998. In general, the density of wild lake trout spawners increased, whereas that of stocked lake trout spawners decreased in all management areas investigated. The density of recruits was best described by the combined density of wild and stocked parents, which suggested similar reproductive contributions for both. Recruitment rates declined significantly with increasing spawner density in four of the five management areas and suggested that carrying capacities were reached and exceeded, which may serve as an indicator of population restoration. We conclude that both wild and stocked lake trout have contributed to the recruitment of lake trout in Michigan waters of Lake Superior. Large‐mesh gill‐net fishing effort varied in all Michigan management areas but did not account for the significant variation in wild lake trout recruitment. We conclude that levels of large‐mesh gill‐net fishing effort during 1970–1998 were not having an appreciable effect on wild lake trout recruitment in Michigan waters of Lake Superior.

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“…By use of the estimated catchability per 2 h of fishing, an ordinary gillnetting with the permitted mesh size of 52 mm performed in much the same way as in this study, but with an effort of 6 h per gillnet toward the end of August, the annual quota set at 40 charr for Linnévatn would have been exceeded by a total effort of five gillnets. Although this calculation may overestimate the catch because of gear saturation (Hansen et al, 1998;Borgstrøm & Qvenild, 2000;Olin et al, 2004), in addition to the fact that a larger effort may yield a lower catch per effort (Angelsen & Olsen, 1987), the high estimated catchability indicates that the total catch would have been substantial after a few days of gillnetting even with a very low fishing effort. The anecdotally high catches from Svalbard's lakes may therefore not be an indication of high densities of large fish, but is more likely an effect of an exceptionally high catchability rate.…”

Section: Discussionmentioning

confidence: 99%

High lacustrine gillnet catchability of anadromous Arctic charr

2010

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Arctic charr is the only freshwater fish in most of the High Arctic, with both resident, anadromous, and landlocked populations present. The anadromous Arctic charr is particularly highly sought-after, and has been an important food source for people living in Arctic regions. A recent decline in harvest in many areas has been related to overexploitation by extensive gillnetting. Very few studies, if any, have estimated the gillnet efficiency for harvesting anadromous Arctic charr. In this study, all anadromous Arctic charr ascending the lake, Linnévatn, in western Spitsbergen, Svalbard, were marked over a period of 5 weeks, in July-August 2008. Recaptures in the lake were obtained by gillnetting with three mesh sizes (39, 45, and 52 mm measured knot-to-knot) during three periods. The total number of anadromous charr in the lake was estimated by both Schnabel and Petersen mark-recapture methods. The catchability increased significantly with fish size. Anadromous charr in the length-class 40.0-56.9 cm captured by the legal mesh size in Svalbard lakes (52 mm) had a mean catchability of 0.0023 per gillnet per 2 h fishing effort, and the catch quota which is set at 40 charr for Linnévatn by the Governor of Svalbard, would have been filled by less than five gillnets, each used for 6 h. Although this short fishing time may give an overestimation of catchability due to the avoidance of gear saturation, the high catchability values still indicate that anadromous Arctic charr populations may be extremely vulnerable to gillnetting. Hence, in addition to catch quotas set for each population, a restriction on the number of gillnets allowed per harvester should also be considered.

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Gill-Net Saturation by Lake Trout in Michigan Waters of Lake Superior

Cited by 25 publications

References 10 publications

Influence of soak time and fish accumulation on catches of reef fishes in a multispecies trap survey

Influence of soak time and fish accumulation on catches of reef fishes in a multispecies trap survey

Recruitment Dynamics of the 1971–1991 Year‐Classes of Lake Trout in Michigan Waters of Lake Superior

High lacustrine gillnet catchability of anadromous Arctic charr

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