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We developed two weight-length models from 231 populations of larval sea lampreys (Petromyzon marinus) collected from tributaries of the Great Lakes: Lake Ontario (21), Lake Erie (6), Lake Huron (67), Lake Michigan (76), and Lake Superior (61). Both models were mixed models, which used population as a random effect and additional environmental factors as fixed effects. We resampled weights and lengths 1,000 times from data collected in each of 14 other populations not used to develop the models, obtaining a weight and length distribution from reach resampling. To test model performance, we applied the two weight-length models to the resampled length distributions and calculated the predicted mean weights. We also calculated the observed mean weight for each resampling and for each of the original 14 data sets. When the average of predicted means was compared to means from the original data in each stream, inclusion of environmental factors did not consistently improve the performance of the weight-length model. We estimated the variance associated with measures of abundance and mean weight for each of the 14 selected populations and determined that a conservative estimate of the proportional contribution to variance associated with estimating abundance accounted for 32% to 95% of the variance (mean = 66%). Variability in the biomass estimate appears more affected by variability in estimating abundance than in converting length to weight. Hence, efforts to improve the precision of biomass estimates would be aided most by reducing the variability associated with estimating abundance. [ABSTRACT FROM AUTHOR]

The implementation of a sterile-male-release technique from 1991 through 1999 and evaluation of its effectiveness in the Great Lakes sea lamprey (Petromyzon matins) management program is reviewed. Male sea lampreys were injected with the chemosterilant bisazir (P,P-bis(1-aziridinyl)-N-methylphosphinothioic amide) using a robotic device. Quality assurance testing indicated the device delivered a consistent and effective dose of bisazir. Viability of embryos in an untreated control group was 64% compared to 1% in a treatment group. A task force developed nine hypotheses to guide implementation and evaluation of the technique. An annual average of 26,000 male sea lampreys was harvested from as many as 17 Great Lakes tributaries for use in the technique. An annual average of 16,100 sterilized males was released into 33 tributaries of Lake Superior to achieve a theoretical 59% reduction in larval production during 1991 to 1996. The average number of sterile males released in the St. Mart's River increased from 4,000 during 1991 to 1996 to 20,100 during 1997 to 1999. The theoretical reduction in reproduction when combined with trapping was 57% during 1991 to 1996 and 86% during 1997 to 1999. Evaluation studies demonstrated that sterilized males were competitive and reduced production of larvae in streams. Field studies and simulation models suggest reductions in reproduction will result in fewer recruits, but there is risk of periodic high recruitment events independent of sterile-male release. Strategies to reduce reproduction will be most reliable when low densities of reproducing females are achieved. Expansion of the technique is limited by access to additional males for sterilization. Sterile-male release and other alternative controls are important in delivering integrated pest management and in reducing reliance on pesticides. [ABSTRACT FROM AUTHOR]

Seasonally operated barriers in rivers are used by the Great Lakes Fishery Commission to block adult sea lamprey (Petromyzon marinus) migrations, yet pass other fish during some part of the year. Knowledge of the overlap of spawning migrations of sea lampreys and other fish species are vital for the efficient operation of the Commission's barrier program. The migration of sea lamprey spawners was compared with the migration of four other fish species using trap captures at electric barriers on eight Lake Superior tributaries during 1954 to 1979. The passage of rainbow trout (Oncorhynchus mykiss), rainbow smelt (Osmerus mordax), longnose suckers (Catostomus catostomus), and white suckers (Catostomus commersoni) prior to the capture of sea lampreys was quantified as the proportion of the annual catch of each species. Average passage over all streams and years was smallest (5%) for longnose sucker and largest (21%) for rainbow smelt. Passage prior to first sea lamprey catch was significantly different among rivers for all four species and significantly different among years for rainbow trout. Much of the variability in annual passage was unexplained by river or year effects. It is suggested that stream-specific information on run times of sea lampreys and other fishes be used to define timing of seasonal barrier operations. If barrier operations are timed to block the entire sea lamprey spawning run, then fish passage devices are needed to pass rainbow trout, rainbow smelt, longnose suckers, and white suckers. [ABSTRACT FROM AUTHOR]

Low-head barriers are used to block adult sea lamprey (Petromyzon marinus) from upstream spawning habitat. However, these barriers may impact stream fish communities through restriction of fish movement and habitat alteration. During the summer of 1996, the fish community and habitat conditions in twenty-four stream pairs were sampled across the Great Lakes basin. Seven of these stream pairs were re-sampled in 1997. Each pair consisted of a barrier stream with a low-head barrier and a reference stream without a low-head barrier. On average, barrier streams were significantly deeper (df = 179, P = 0.0018) and wider (df = 179, p = 0.0236) than reference streams, but temperature and substrate were similar (df = 183, p = 0.9027; df = 179, P = 0.999). Barrier streams contained approximately four more fish species on average than reference streams. However, streams with low-head barriers showed a greater upstream decline in species richness compared to reference streams with a net loss of 2.4 species. Barrier streams also showed a peak in richness directly downstream of the barriers, indicating that these barriers block fish movement upstream. Using Sørenson similarity index (based on presence/absence), a comparison of fish community assemblages above and below low-head barriers was not significantly different than upstream and downstream sites on reference streams (n=96, P > 0.05), implying they have relatively little effect on overall fish assemblage composition. Differences in the frequency of occurrence and abundance between barrier and reference streams was apparent for some species, suggesting their sensitivity to barriers. [ABSTRACT FROM AUTHOR]

Four sampling designs for quantifying the effect of low-head sea lamprey (Petromyzon marinus) barriers on fish communities were evaluated, and the contribution of process-oriented research to the overall confidence of results obtained was discussed. The designs include: (1) sample barrier streams post-construction; (2) sample harrier and reference streams post-construction; (3) sample barrier streams pre- and post-construction; and (4) sample barrier and reference streams pre- and post-construction. In the statistical literature, the principal basis for comparison of sampling designs is generally the precision achieved by each design. In addition to precision, designs should be compared based on the interpretability of results and on the scale to which the results apply. Using data collected in a broad survey of streams with and without sea lamprey barriers, some of the tradeoffs that occur among precision, scale, and interpretability are illustrated. Although circumstances such as funding and availability of pre-construction data may limit which design can be implemented, a pre/post-construction design including barrier and reference streams provides the most meaningful information for use in barrier management decisions. Where it is not feasible to obtain pre-construction data, a design including reference streams is important to maintain the interpretability of results. Regardless of the design used, process-oriented research provides a framework for interpreting results obtained in broad surveys. As such, information from both extensive surveys and intensive process-oriented research provides the best basis for fishery management actions, and gives researchers and managers the most confidence in the conclusions reached regarding the effects of sea lamprey barriers. [ABSTRACT FROM AUTHOR]

The Great Lakes Fishery Commission (GLFC) continues to seek additional methods of sea lamprey (Petromyzon marinus) control to reduce reliance on chemical lampricides (pesticides) and increase the efficiency of the program. Barriers to migrating sea lampreys in tributaries can significantly reduce the spawning potential of sea lamprey in the Great Lakes. These barriers can be any natural or man-made structure that restricts the access of migrating sea lampreys to spawning habitat in streams. During the past four decades, the GLFC recognized a greater need to maintain current barriers to sea lamprey spawning migration and develop new, less intrusive devices to enhance the integrated sea lamprey control program. The "standard" sea lamprey barrier uses a fixed-crest height and overhanging lip to maintain a vertical drop of about 30 cm from headwater to tailwater over the period of lamprey migration. Although most sea lamprey barriers are of fixed-crest design, alternative designs (i.e., electrical, adjustable-crest, velocity, and combined fixed-crest and electrical barriers) have been built and are being tested. Between 1958 and 1999, 61 barriers of various design have been modified or installed in Great Lakes streams. The GLFC plans to add to the 61 current barriers by building additional barriers on 90 candidate streams (Lake Superior, 10; Lake Michigan, 24; Lake Huron, 23; Lake Erie, 3; Lake Ontario, 24). As we seek to expand the role of barriers in sea lamprey management, we must remain vigilant to the hundreds of existing dams known to limit stream habitat available to sea lampreys. The current movement toward dam removal and fishway construction without regard to sea lampreys could result in additional habitat becoming available to sea lampreys. The loss of one or two large dams could easily overshadow the gains made through all the purpose-built sea lamprey barriers to date. [ABSTRACT FROM AUTHOR]

When 171 sea lampreys Petromyzon marinus were each offered a onetime choice of one large and two small lake trout Salvelinus namaycush, the ratio of their attacks (49.1%:27.5%: 23.4%) was similar to the ratio of host surface areas (51.4%:26.3%:22.3%) in laboratory tests conducted over 9 months in 1988-1989. When the smallest offered host was 560 mm total length (TL) or shorter, sea lampreys attacked the smallest host less often and the largest host more often than expected ( N = 39) under assumptions that attacks would be either equal among the hosts (numbers-dependent hypothesis) or proportional to the hosts' surface areas (area-dependent hypothesis). When the smallest host was 615 mm TL or longer, observed attacks ( N = 132) did not differ significantly from the number of attacks expected by either the numbers-dependent or the area-dependent hypothesis; however, the largest lake trout was almost always attacked more often than either of the smaller fish. These results are similar to field observations that sea lampreys kill few lake trout smaller than about 600 mm TL when larger fish are available as hosts, and that they attack larger fish (673-775+ mm TL) at a progressively greater rate as host size increases. Sea lamprey host-size selection was less pronounced in this study than in previous laboratory studies, which used smaller host fish than those now available in the Great Lakes. [ABSTRACT FROM AUTHOR]