Geology topics

D.L. Yule

Publications and source records attributed to D.L. Yule.

8 recordsLinked to original sources

USGS2012

Habitat use by fishes of Lake Superior. I. Diel patterns of habitat use in nearshore and offshore waters of the Apostle Islands region

Diel patterns of distribution of fishes in nearshore (15–80 m depth) and offshore (>80 m) waters of the Apostle Islands region of Lake Superior were described using bottom trawls, mid-water trawls, and acoustic gear during day and night sampling. These data revealed three types of diel migration: diel vertical migration (DVM), diel bank migration (DBM), and no migration. DVM was expressed by fishes migrating from benthopelagic to pelagic strata and DBM was expressed by fishes migrating horizontally from deeper waters in the day to shallower waters at night while remaining within the benthopelagic stratum. Most fishes that did not exhibit diel migration showed increased nighttime densities as a result of increased activity and movement from benthic to benthopelagic strata. Rainbow Smelt ( Osmerus mordax), Cisco ( Coregonus artedi ), Bloater ( C. hoyi ), Kiyi ( C. kiyi ), juvenile Trout-Perch (Percopsis omiscomaycus ), and adult siscowet ( Salvelinus namaycush siscowet ) exhibited DVM. Lake Whitefish ( C. clupeaformis ), lean Lake Trout ( Salvelinus namaycush namaycush ), and juvenile siscowet exhibited DBM. Adult Trout-Perch and adult Pygmy Whitefish ( Prosopium coulteri ) exhibited a mixture of DBM and DVM. Burbot ( Lota lota ), Slimy Sculpin ( Cottus cognatus ), Spoonhead Sculpin ( C. ricei ), and Deepwater Sculpin ( Myoxocephalus thompsonii ) did not exhibit diel migration, but showed evidence of increased nocturnal activity. Ninespine Stickleback ( Pungitius pungitius ) exhibited a mixture of DVM and non-migration. Juvenile Pygmy Whitefish did not show a diel change in density or depth distribution. Species showing ontogenetic shifts in depth distribution with larger, adult life stages occupying deeper waters included, Rainbow Smelt, lean and siscowet Lake Trout, Lake Whitefish, Pygmy Whitefish, Ninespine Stickleback and Trout-Perch. Of these species, siscowet also showed an ontogenetic shift from primarily DBM as juveniles to primarily DVM as adults. Across all depths, fishes expressing DVM accounted for 73% of the total estimated community areal biomass (kg ha −1 ) while those expressing DBM accounted for 25% and non-migratory species represented 2% of the biomass. The proportion of total community biomass exhibiting DVM increased with depth, from 59% to 95% across ≤30 m to >90 m depth zones. Along the same depth gradient, the proportion of total community biomass exhibiting DBM declined from 40% to 1%, while non-migrators increased from 1% to 4%. These results indicate that DVM and DBM behaviors are pervasive in the Lake Superior fish community and potentially provide strong linkages that effect coupling of benthic and pelagic and nearshore and offshore habitats.

Aquatic Ecosystem Health & Management↗

USGS2011

Evaluation of methods to estimate lake herring spawner abundance in Lake Superior

Historically, commercial fishers harvested Lake Superior lake herring Coregonus artedi for their flesh, but recently operators have targeted lake herring for roe. Because no surveys have estimated spawning female abundance, direct estimates of fishing mortality are lacking. The primary objective of this study was to determine the feasibility of using acoustic techniques in combination with midwater trawling to estimate spawning female lake herring densities in a Lake Superior statistical grid (i.e., a 10′ latitude × 10′ longitude area over which annual commercial harvest statistics are compiled). Midwater trawling showed that mature female lake herring were largely pelagic during the night in late November, accounting for 94.5% of all fish caught exceeding 250 mm total length. When calculating acoustic estimates of mature female lake herring, we excluded backscattering from smaller pelagic fishes like immature lake herring and rainbow smelt Osmerus mordax by applying an empirically derived threshold of −35.6 dB. We estimated the average density of mature females in statistical grid 1409 at 13.3 fish/ha and the total number of spawning females at 227,600 (95% confidence interval = 172,500–282,700). Using information on mature female densities, size structure, and fecundity, we estimate that females deposited 3.027 billion (10 9 ) eggs in grid 1409 (95% confidence interval = 2.356–3.778 billion). The relative estimation error of the mature female density estimate derived using a geostatistical model—based approach was low (12.3%), suggesting that the employed method was robust. Fishing mortality rates of all mature females and their eggs were estimated at 2.3% and 3.8%, respectively. The techniques described for enumerating spawning female lake herring could be used to develop a more accurate stock–recruitment model for Lake Superior lake herring.

Transactions of the American Fisheries Society↗

USGS2010

Empirical evaluation of predator-driven diel vertical migration in Lake Superior

Recent studies on Lake Superior suggest that diel vertical migration (DVM) of prey (generalized Coregonus spp.) may be influenced by the density of predatory siscowet (Salvelinus namaycush). We empirically evaluated this hypothesis using data from acoustic, midwater trawl, and bottom trawl sampling at eight Lake Superior sites during three seasons in 2005 and a subset of sites in 2006. We expected the larger-bodied cisco (Coregonus artedi) to exhibit a shallower DVM compared with the smaller-bodied kiyi (Coregonus kiyi). Although DVM of kiyi and cisco were consistent with expectations of DVM as a size-dependent, predator-mediated process, we found no relationship between siscowet density and the magnitude of DVM of either coregonid. Cisco appear to have a size refuge from siscowet predation. Kiyi and siscowet co-occur in demersal habitat > 150 m during the day, where visual predation is unlikely, suggesting predator avoidance is not a factor in the daytime distribution of kiyi. Seasonal patterns of kiyi DVM were consistent with reported DVM of their primary prey Mysis relicta. Our results suggest that consideration of nonvisual foraging, rather than lightbased foraging theory (i.e., the antipredation window), is necessary to understand the processes driving DVM in deepwater systems.

Canadian Journal of Fisheries and Aquatic Sciences↗

USGS2009

Can pelagic forage fish and spawning cisco (Coregonus artedi) biomass in the western arm of Lake Superior be assessed with a single summer survey?

Management efforts to rehabilitate lake trout Salvelinus namaycush in Lake Superior have been successful and the recent increase in their numbers has led to interest in measuring biomass of pelagic prey fish species important to these predators. Lake Superior cisco Coregonus artedi currently support roe fisheries and determining the sustainability of these fisheries is an important management issue. We conducted acoustic and midwater trawl surveys of the western arm of Lake Superior during three periods: summer (July-August), October, and November 2006 to determine if a single survey can be timed to estimate biomass of both prey fish and spawning cisco. We evaluated our methods by comparing observed trawl catches of small (<250 mm total length) and large fish to expected trawl catches based on acoustic densities in the trawl path. We found the relationship between observed and expected catches approached unity over a wide range of densities, suggesting that our acoustic method provided reasonable estimates of fish density, and that midwater trawling methods were free of species- and size-selectivity issues. Rainbow smelt Osmerus mordax was by number the most common species captured in the nearshore (<80 m bathymetric depth) stratum during all three surveys, while kiyi Coregonus kiyi was predominant offshore except during November. Total biomass estimates of rainbow smelt in the western arm were similar during all three surveys, while total biomass of kiyi was similar between summer and October, but was lower in November. Total biomass of large cisco increased substantially in November, while small bloater Coregonus hoyi biomass was lower. We compared our summer 2006 estimates of total fish biomass to the results of a summer survey in 1997 and obtained similar results. We conclude that the temporal window for obtaining biomass estimates of pelagic prey species in the western arm of Lake Superior is wide (July through October), but estimating spawning cisco abundance is best done with a November survey.

Fisheries Research↗

USGS2008

Factors affecting bottom trawl catches: Implications for monitoring the fishes of Lake Superior

An annual daytime bottom trawl survey of the Lake Superior fish community designed in 1978 does not adequately assess the entire community. Whereas recent studies have recommended that pelagic species be surveyed with a combination of acoustic and midwater trawling methods (AC-MT), we used bottom trawling to study the effects of depth, diel period, and season on biomass estimates and the sizes of bottom-oriented species. Day and night bottom trawl samples were collected within 48 h at three depths (30, 60, and 120 m) at a Lake Superior site during eight sampling periods that included two seasons each year (early summer and late summer to early fall) for 2 years (2004 and 2005). Depth significantly affected the biomass of seven of the eight species analyzed, while diel period affected the biomass of six species. For most species, average biomass levels were higher at night. The effect of season on biomass was comparatively low (three species were significantly affected). Depth significantly affected the sizes of six bottom-oriented species, as the average length of most species increased with depth. The effects of diel period (three species) and season (one species) on average length were comparatively small. By adding night bottom trawl samples to night AC-MT collections, the entire fish community of Lake Superior can be monitored with a single lakewide survey employing multiple gears. The establishment of offshore sampling (i.e., where depths exceed 80 m) will provide estimates of deepwater species that have been largely undersampled by the 1978-designed survey. We recommend that the present fish community survey be maintained, albeit at a reduced level, until a nighttime survey time series is well established (in 3-5 years).

North American Journal of Fisheries Management↗

USGS2007

Vertical distribution of fish biomass in Lake Superior: Implications for day bottom trawl surveys

Evaluation of the biases in sampling methodology is essential for understanding the limitations of abundance and biomass estimates of fish populations. Estimates from surveys that rely solely on bottom trawls may be particularly vulnerable to bias if pelagic fish are numerous. We evaluated the variability in the vertical distribution of fish biomass during the U.S. Geological Survey's annual spring bottom trawl survey of Lake Superior using concurrent hydroacoustic observations to (1) test the assumption that fish are generally demersal during the day and (2) evaluate the potential for predictive models to improve bottom trawl–determined biomass estimates. Our results indicate that the assumption that fish exhibit demersal behavior during the annual spring bottom trawl survey in Lake Superior is unfounded. Bottom trawl biomass (B BT ) estimates (mean ± SE) for species known to exhibit pelagic behavior (cisco Coregonus artedi, bloater C. hoyi, kiyi C. kiyi, and rainbow smelt Osmerus mordax; 3.01 ± 0.73 kg/ha) were not significantly greater than mean acoustic pelagic zone biomass (B APZ ) estimates (6.39 ± 2.03 kg/ha). Mean B APZ estimates were 1.6- to 4.8-fold greater than mean B BT estimates over 4 years of sampling. The relationship between concurrent B APZ and B BT estimates was marginally significant and highly variable. Predicted B APZ estimates using cross-validation models were sensitive to adjustments for back-transforming from the logarithmic to the linear scale and poorly corresponded to observed B APZ estimates. We conclude that statistical models to predict B APZ from day B BT cannot be developed. We propose that night sampling with multiple gears will be necessary to generate better biomass estimates for management needs.

North American Journal of Fisheries Management↗

USGS2007

Using multiple gears to assess acoustic detectability and biomass of fish species in lake superior

Recent predator demand and prey supply studies suggest that an annual daytime bottom trawl survey of Lake Superior underestimates prey fish biomass. A multiple-gear (acoustics, bottom trawl, and midwater trawl) nighttime survey has been recommended, but before abandoning a long-term daytime survey the effectiveness of night sampling of important prey species must be verified. We sampled three bottom depths (30, 60, and 120 m) at a Lake Superior site where the fish community included all commercially and ecologically important species. Day and night samples were collected within 48 h at all depths during eight different periods (one new and one full moon period during both early summer and late summer to early fall over 2 years). Biomass of demersal and benthic species was higher in night bottom trawl samples than in day bottom trawl samples. Night acoustic collections showed that pelagic fish typically occupied water cooler than 15°C and light levels less than 0.001 lx. Using biomass in night bottom trawls and acoustic biomass above the bottom trawl path, we calculated an index of acoustic detectability for each species. Ciscoes Coregonus artedi , kiyis C. kiyi , and rainbow smelt Osmerus mordax left the bottom at night, whereas bloaters C. hoyi stayed nearer the bottom. We compared the biomass of important prey species estimated with two survey types: day bottom trawls and night estimates of the entire water column (bottom trawl biomass plus acoustic biomass). The biomass of large ciscoes (>200 mm) was significantly greater when measured at night than when measured during daylight, but the differences for other sizes of important species did not vary significantly by survey type. Nighttime of late summer is a period when conditions for biomass estimation are largely invariant, and all important prey species can be sampled using a multiple-gear approach.

North American Journal of Fisheries Management↗

USGS2006

Hydroacoustic estimation of zooplankton biomass at two shoal complexes in the Apostle Islands Region of Lake Superior

Hydroacoustics can be used to assess zooplankton populations, however, backscatter must be scaled to be biologically meaningful. In this study, we used a general model to correlate site-specific hydroacoustic backscatter with zooplankton dry weight biomass estimated from net tows. The relationship between zooplankton dry weight and backscatter was significant (p < 0.001) and explained 76% of the variability in the dry weight data. We applied this regression to hydroacoustic data collected monthly in 2003 and 2004 at two shoals in the Apostle Island Region of Lake Superior. After applying the regression model to convert hydroacoustic backscatter to zooplankton dry weight biomass, we used geostatistics to analyze the mean and variance, and ordinary kriging to create spatial zooplankton distribution maps. The mean zooplankton dry weight biomass estimates from plankton net tows and hydroacoustics were not significantly different (p = 0.19) but the hydroacoustic data had a significantly lower coefficient of variation (p < 0.001). The maps of zooplankton distribution illustrated spatial trends in zooplankton dry weight biomass that were not discernable from the overall means.

Journal of Great Lakes Research↗