Thomas C. Pratt

Research to Guide Use of Barriers, Traps, and Fishways to Control Sea Lamprey

ABSTRACT This paper provides a rigorous and directed research framework for fostering innovations in the design, implementation, and operation of barriers, traps, and fishways used to control the sea lamprey (Petromyzon marinus) in the Laurentian Great Lakes. It was developed to support the Great Lakes Fishery Commissions milestone pledging to decrease reliance on chemical lampricides and achieve 50% of sea lamprey suppression through alternative control technologies, including barriers and traps. The paper first substantiates the need to develop a long-term research plan for barriers, traps, and fishways by summarizing (i) current management challenges, (ii) the barrier, trap, and fishway options being used to meet these challenges, and (iii) the key uncertainties in our knowledge regarding these options. The paper then proposes a long-term research strategy that envisions a transition from barriers designed to block the upstream spawning migrations of sea lamprey, to barrier and trap combinations that facilitate physical removal of sea lamprey and, in some cases, passage of non-target fishes, to barrier and trap designs that are specific to sea lamprey, transparent to non-target fishes, and safer for operators. Thirteen research needs are identified to support this strategy along with a general work plan on how they can be achieved. The research needs and work plan highlight the exceptional opportunity to develop the Great Lakes basin as a leading, international research center for fish migration and passage, and the development of environmentally friendly barriers.

Balancing Aquatic Habitat Fragmentation and Control of Invasive Species: Enhancing Selective Fish Passage at Sea Lamprey Control Barriers

Abstract Barriers to prevent spawning migrations of sea lampreys Petromyzon marinus remain an important component of an integrated sea lamprey management program in the Laurentian Great Lakes. Concerns about effects on nontarget fishes have led to the construction of specially designed vertical-slot trap-and-sort fishways to mitigate potential barrier effects. To improve passage at these fishways, we used passive integrated transponder technology to assess the performance of two fishways located on low-head sea lamprey barriers. Fishways on the Big Carp River (which flows into Lake Superior) and Cobourg Brook (which flows into Lake Ontario) were assessed for attraction efficiency, trap attraction and retention, and passage efficiency. Based on the results of these assessments, fishways were modified by increasing the trap volume and altering the funnel characteristics to reduce escapement from the trap and then reassessed. Attraction efficiency for all tagged fish was high (≥80%) at both sites in all year...

Effect of Fin Clipping on Overwinter Growth and Survival of Age-0 Walleyes

Abstract We tested whether a pelvic fin clip influenced the overwinter survival and growth rate of age-0 walleyes Stizostedion vitreum reared in the presence or absence of predators (adult walleyes or burbot Lota lota) in 0.3-ha artificial ponds located in eastern Ontario. Survival and growth differed significantly between the two years of the study, and growth was reduced in the presence of predators in one year, but neither survival nor growth differed significantly between clipped and unclipped fish. Our results indicate that, unless detrimental effects occur after the first year of life, fin clipping is a safe and valuable tool for the identification of hatchery-reared walleye fingerlings.

Preliminary Evaluation of a Large-Scale American Eel Conservation Stocking Experiment

Abstract Significant declines in the recruitment of American eels Anguilla rostrata to formerly productive habitats in the upper St. Lawrence River and Lake Ontario resulted in the implementation of an experimental conservation stocking program. Nearly 3.8 million American eels (glass eel and elver stages) were stocked during 2006–2009. Our study objectives were to (1) assess the adequacy of sampling procedures for following temporal changes in stocked eel abundance, (2) examine captured eels for evidence of spinal trauma, (3) qualitatively evaluate whether stocked eels would disperse outside of stocking locations, and (4) provide initial data on biological variables describing young stocked yellow eels. Boat electrofishing was successful at capturing all four stocked year-classes, and the densities of stocked eels in the main stocking locations ranged from 25 to 275 eels/ha. Estimated sampling precision ranged from 0.15 to 0.28, and the estimated sample sizes required to detect a 50% change in stocked ee...

Use of Underwater Visual Distance Sampling for Estimating Habitat-Specific Population Density

Abstract We contrasted fish abundance estimates generated from mark–recapture and underwater visual distance sampling to determine whether the latter method is a potentially valuable fisheries assessment tool. We further examined whether altering the detection function or habitat stratification and including lake characteristics such as Secchi depth, temperature, and fish density affected distance sampling estimates. Distance sampling produced estimates that were comparable to those of mark–recapture techniques (r 2 = 0.60), and the relationship improved considerably when two species that were difficult to sample visually were removed from the analysis (r 2 = 0.88). The precision of mark–recapture estimates was significantly better than that of distance sampling. Distance sampling estimates were more similar to mark–recapture estimates when stratified by habitat than when pooled across habitats. The addition of Secchi depth, temperature, fish density, or a combination thereof to a regression equation that...

Development and experimental assessment of an underwater video technique for assessing fish-habitat relationships

Developing tools that aquatic managers can use to understand the impact of human development on fish habitat is important in an era where our aquatic resources are under increasing pressure. To this end, we examined whether an underwater video camera was useful for quantifying fish habitat use in inland lakes by 1) examining patterns in fish habitat use, residency time and feeding behaviour among habitat types, 2) determining the precision and statistical power of the aforementioned estimates, and 3) assessing whether our habitat-specific camera estimates were reflective of whole-system estimates. Lastly, we used our protocol in an experimental situation to test site-specific fish habitat use at sites where habitats were manipulated (removed or added). We demonstrated that our underwater video protocol could successfully capture site-level habitat use that corresponded with whole-system abundance estimates, addressing the concern that habitat-based surrogates of fish productivity be validated on a whole-system scale. Unfortunately, our underwater video technique was unable to discriminate fish habitat use patterns among simple habitat types and unable to consistently separate differences in among-habitat fish feeding and residency behaviours. Our ability to detect a difference was low in all among-habitat comparisons. In the aquatic systems where habitat was added, we documented a significant shift in fish habitat use towards the addition sites and away from control sites, but no corresponding increase in system-wide fish biomass or production; no changes were apparent in the habitat removal lakes. A combination of longer filming duration, more filming sites or changing to a mobile transect method would likely address the data deficiencies that limited our ability to make site-level inferences about fish habitat use.

Morphological and genetic variation in Cisco ( Coregonus artedi ) and Shortjaw Cisco ( C. zenithicus ): multiple origins of Shortjaw Cisco in inland lakes require a lake-specific conservation approach

The study of cisco diversity in inland lakes of North America has been plagued by taxonomic uncertainty linked to high phenotypic plasticity and an ongoing reliance on morphology to differentiate species. More recently, this uncertainty has hindered the development of conservation plans and status assessments of ciscoes. This study presents the first range-wide comparison of morphological and genetic variation between Cisco (Coregonus artedi) and Shortjaw Cisco (C. zenithicus). Using morphological and genetic data from 17 lakes, three sets of analyses were undertaken to evaluate alternate hypotheses explaining the pattern of cisco phenotypic diversity in inland lakes. Morphotypes (MTs) representing the two taxa were phenotypically distinct (largely reflective of differences in gill raker number and jaw morphology) within lakes but highly variable across lakes. Shortjaw Cisco was only recognizable when compared to sympatric Cisco and some populations were morphologically similar to Cisco from other lakes. Analysis of AFLP data revealed two genetic clusters that conformed to differences in geography (eastern and western groups), rather than hypothesized taxonomic boundaries. Genetic variation strongly suggests that each of these unique sympatric pairs of MTs originated recently and locally, in parallel, from the ancestral Cisco. Phenotypic and genetic distinctiveness between MTs were not related. MTs were sometimes clearly recognizable despite a lack of genetic differentiation, suggesting that the canalization of phenotypic plasticity is unevenly completed across lakes. These results provide evidence that the taxon-based approach is clearly inadequate for the protection of Shortjaw Cisco. In Canada, status assessment should aim to identify lake-specific designatable units (DU). Given the idiosyncratic nature of each instance of Shortjaw Cisco, it is expected that the strength of morphological, biological, ecological and genetic evidence for individual DUs will vary among lakes.

Ontogenetic shifts in morphology and resource use of cisco Coregonus artedi

Two previously described lacustrine cisco Coregonus spp. morphs [i.e. a small (<300 mm fork length, L(F)), low-gillraker (≤44) morph and a large (≥300 mm L(F) ), high-gillraker (≥45) morph] from Great Slave Lake, NT, Canada, were found to be synonymous with cisco Coregonus artedi. Geometric body shape did not differ between the two size classes nor could they be differentiated by 24 size-corrected linear measurements, indicating that the two groups had similar phenotypes. Strong, positive correlations between all linear characters and geometric centroid size (a composite variable of fish body length, mass and age) suggested that body morphology changed with age as fish grew. Total gillraker number (N(GR)) increased with L(F) according to: N(GR) = 36.3 + 0.034L(F). Differences in gillraker number and phenotype with age and size were explained by shifts in habitat and trophic resource use. Relative abundance within 0-30, 30-60, 60-90 and >90 m depth strata differed between size classes suggesting that morphology changed when fish shifted their habitat as they grew older. Large C. artedi had lower δ(13)C and slightly higher δ(15)N, indicating greater reliance on pelagic prey resources (i.e. more or larger zooplankton, such as Mysis spp.), compared to small C. artedi, which relied slightly more on benthic prey. Gillraker shape and number have always been used as key diagnostic characters in coregonine taxonomy; based on the findings presented here, ontogenetic shifts should be accounted for in resulting classifications.

Contribution and Relative Survival of Age-0 Walleyes Stocked at Two Sizes in Six Eastern Ontario Lakes

Abstract Size at stocking is believed to be a critical factor in determining the success of stocking events for many species. We examined the relative performance of summer (reared extensively, planted in June, average weight < 1 g) and fall (reared intensively, planted in September, average weight ∼ 10 g) walleye Stizostedion vitreum fingerlings stocked at a 5:1 summer-to-fall fingerling ratio into six small lakes in Eastern Ontario. One lake was stocked concurrently during 1990-1993, and three lakes were given paired plants in 1992 and 1993; stocking assessments occurred at age 1 and as adults in 1997. Two additional lakes were stocked in 1998; in one the stocking failed, and in the other the stocking was assessed at age 1. Walleyes planted as summer fingerlings were significantly larger at first annulus formation than those planted as fall fingerlings, but these size differences disappeared in the adult fish recovered 4-7 years after the paired plants. By the time the fish were adults, summer fingerlin...

Morphometric variation among spawning cisco aggregations in the Laurentian Great Lakes: are historic forms still present?

Cisco (Coregonus artedi Leseur, formerly lake herring Leucichthys artedi Leseur) populations in each of the Laurentian Great Lakes collapsed between the late 1920s and early 1960s following a multitude of stressors, and never recovered in Lakes Michigan, Erie and Ontario. Prior to their collapse, Koelz (1929) studied Leucichthys spp. in the Great Lakes basin and provided a description of their diversity. Three cisco morphotypes were described; a ‘slim terete’ morphotype (L. artedi artedi), a ‘deep compressed’ morphotype (L. artedi albus), and a deep-bodied form resembling tullibee in western Canadian lakes (L. artedi manitoulinus). Based on body measurements of 159 individuals (Koelz 1929), we used discriminant function analysis (DFA) to discriminate historic morphotypes. Shapes of historic morphotypes were found to vary signifi cantly (Pillai’s trace = 1.16, P < 0.0001). The fi nal DFA model used nine body measurements and correctly classifi ed 90% of the historic cisco. Important discriminating measurements included body depth, eye diameter, and dorsal fi n base and height. Between OctoberNovember of 2007-2011, we sampled cisco from 16 Great Lakes sites collecting digital photographs of over 1,700 individuals. We applied the DFA model to their body measurements and classifi ed each individual to a morphotype. Contemporary cisco from Lakes Superior, Ontario and Michigan were predominantly classifi ed as artedi, while the most common classifi cations from northern Lake Huron were albus and manitoulinus. Finding historic morphotypes is encouraging because it suggests that the morphological variation present prior to their collapse still exists. We conclude that contemporary cisco having shapes matching the missing historic morphotypes in the lower lakes warrant special consideration as potential donor populations in reestablishment efforts.