Geology topics

Timothy P. O’Brien

Publications and source records attributed to Timothy P. O’Brien.

42 records · Page 3Linked to original sources

USGS2012

Relationship between mid-water trawling effort and catch composition uncertainty in two large lakes (Huron and Michigan) dominated by alosines, osmerids, and coregonines

Because it is not possible to identify species with echosounders alone, trawling is widely used as a method for collecting species and size composition data for allocating acoustic fish density estimates to species or size groups. In the Laurentian Great Lakes, data from midwater trawls are commonly used for such allocations. However, there are no rules for how much midwater trawling effort is required to adequately describe species and size composition of the pelagic fish communities in these lakes, so the balance between acoustic sampling effort and trawling effort has been unguided. We used midwater trawl data collected between 1986 and 2008 in lakes Michigan and Huron and a variety of analytical techniques to develop guidance for appropriate levels of trawl effort. We used multivariate regression trees and re-sampling techniques to i. identify factors that influence species and size composition of the pelagic fish communities in these lakes, ii. identify stratification schemes for the two lakes, iii. determine if there was a relationship between uncertainty in catch composition and the number of tows made, and iv. predict the number of tows required to reach desired uncertainty targets. We found that depth occupied by fish below the surface was the most influential explanatory variable. Catch composition varied between lakes at depths <38.5 m below the surface, but not at depths ≥38.5 m below the surface. Year, latitude, and bottom depth influenced catch composition in the near-surface waters of Lake Michigan, while only year was important for Lake Huron surface waters. There was an inverse relationship between RSE [relative standard error = 100 × (SE/mean)] and the number of tows made for the proportions of the different size and species groups. We found for the fifth (Lake Huron) and sixth (Lake Michigan) largest lakes in the world, 15–35 tows were adequate to achieve target RSEs (15% and 30%) for ubiquitous species, but rarer species required much higher, and at times, impractical effort levels to reach these targets.

Fisheries Research↗

USGS2012

Influence of water temperature on rainbow smelt spawning and early life history dynamics in St. Martin Bay, Lake Huron

Rainbow smelt are an important prey species for native and introduced salmonines in the Great Lakes. In Lake Huron, rainbow smelt populations are characterized by variable recruitment and year-class strength. To understand the influence of water temperature on reproduction, growth, and survival during larval-fish stages, we sampled spawning tributaries and larval-fish habitats during 2008 and 2009 in St. Martin Bay, Lake Huron. Spawning by rainbow smelt occurred primarily when stream temperatures were between 3 and 10 °C, which resulted in a 7–10-day spawning period during 2008, and a 15–20-day spawning period during 2009. Regardless of these differences in spawning temperatures and duration, peak larval-fish densities during 2008 were double those observed during 2009. Length–frequency analysis of larval-fish populations during both years revealed stream-hatched fish during May and a later emergence of larval rainbow smelt during summer, presumably originating from lake spawning. Warmer bay water temperatures led to earlier emergence of lake-spawned rainbow smelt larvae during 2009. Stream-hatched fish larvae experienced large-scale mortality during May 2008 resulting in a bay population consisting primarily of lake-spawned rainbow smelt larvae, but during 2009 both stream- and lake-hatched cohorts experienced higher survival concomitant with significantly higher mean population growth rates. Higher larval-fish growth rates during 2009 appeared to be density-dependent and facilitated by warmer water temperatures during late June and cooler water temperatures during July. Temperature-mediated differences in annual growth rates and irregular contributions from stream- and lake-hatched fish larvae are important factors affecting survival and abundance of young-of-the-year rainbow smelt in Lake Huron.

Michigan↗

USGS2012

Status of pelagic prey fishes in Lake Michigan, 2012

Acoustic surveys were conducted in late summer/early fall during the years 1992-1996 and 2001-2012 to estimate pelagic prey fish biomass in Lake Michigan. Midwater trawling during the surveys as well as target strength provided a measure of species and size composition of the fish community for use in scaling acoustic data and providing species-specific abundance estimates. The 2012 survey consisted of 26 acoustic transects (576 km total) and 31 midwater tows. Mean total prey fish biomass was 6.4 kg/ha (relative standard error, RSE = 15%) or 31 kilotonnes (kt = 1,000 metric tons), which was 1.5 times the estimate for 2011 and 22% of the long-term mean. The increase from 2011 resulted from increased biomass of age-0 alewife, age-1 or older alewife, and large bloater. The abundance of the 2012 alewife year class was similar to the average, and this year-class contributed 35% of total alewife biomass (4.9 kg/ha, RSE = 17%), while the 2010 alewife year-class contributed 58%. The 2010 year class made up 89% of age-1 or older alewife biomass. In 2012, alewife comprised 77% of total prey fish biomass, while rainbow smelt and bloater were 4 and 19% of total biomass, respectively. Rainbow smelt biomass in 2012 (0.25 kg/ha, RSE = 17%) was 40% of the rainbow smelt biomass in 2011 and 5% of the long term mean. Bloater biomass was much lower (1.2 kg/ha, RSE = 12%) than in the 1990s, and mean density of small bloater in 2012 (191 fish/ha, RSE = 24%) was lower than peak values observed in 2007-2009. In 2012, pelagic prey fish biomass in Lake Michigan was similar to Lake Superior and Lake Huron. Prey fish biomass remained well below the Fish Community Objectives target of 500-800 kt, and key native species remain absent or rare.

Lake Michigan↗

USGS2012

Status and trends of pelagic prey fishes in Lake Huron, 2012

The USGS Great Lakes Science Center (GLSC) conducted acoustic/midwater trawl surveys of Lake Huron during 1997 and annually during 2004-2012. The 2012 survey was conducted during September and October, and included transects in Lake Huron’s Main Basin, Georgian Bay, and North Channel. Pelagic fish density (638 fish/ha) was lower in 2012 compared to 2011, with density in 2012 only 34% of 2011. Total biomass in 2012 was 74% of the 2011 value. Alewife Alosa pseudoharengus remained nearly absent, and only one cisco Coregonus artedi was captured. Rainbow smelt Osmerus mordax density was only 31% of the 2011 density. Bloater Coregonus hoyi density was less than half the 2011 density, mostly as a result of lower density of small bloater. Density and biomass of large bloater in 2012 were similar to 2011 levels. During 2012 we observed significantly higher fish biomass in North Channel than in the Main Basin or Georgian Bay. Prey availability during 2013 will likely be similar to 2012. Lake Huron now has pelagic fish biomass similar to that observed in recent lakewide acoustic surveys of Lake Michigan and Lake Superior, but species composition differs in the three lakes. There is an increasing diversity and prevalence of native species gradient from Lake Michigan to Lake Superior, with Lake Huron being intermediate in the prevalence of native fish species like coregonines and emerald shiner Notropis atherinoides.

Report↗

USGS2009

Status and trends of the Lake Huron deepwater demersal fish ommunity, 2008

The U.S.Geological Survey Great Lakes Science Center has conducted trawl surveys to assess annual changes in the deepwater demersal fish community of Lake Huron since 1973. Since 1992, surveys have been carried out using a 21 m wing trawl towed on-contour at depths ranging from 9 to 110 m on fixed transects. Sample sites include five ports in U.S. waters with less frequent sampling near Goderich, Ontario. The 2008 fall bottom trawl survey was carried out between October 24 and November 20, 2008 and sampled only the three northern U.S. ports at DeTour, Hammond Bay, and Alpena due to mechanical problems with the research vessel and prolonged periods of bad weather. Therefore, all data presented for 2008 are based on samples collected from these ports. Compared to previous years, alewife populations in Lake Huron remain at low levels after collapsing in 2004. Age-0 alewife density and biomass appears to have increased slightly but overall levels remain near the nadir observed in 2004. Density and biomass of adult and juvenile rainbow smelt showed a decrease from 2007 despite record-high abundance of juveniles observed in 2005, suggesting recruitment was low. Numbers of adult and juvenile bloater were low despite recent high year-classes. Abundances for most other prey species were similar to the low levels observed in 2005 - 2007. We captured one wild juvenile lake trout in 2008 representing the fifth consecutive year that wild lake trout were captured in the survey. Based on pairwise graphical comparisons and nonparametric correlation analyses, dynamics of prey abundance at the three northern ports followed lakewide trends since 1992. Density of benthic macroinvertebrates was at an all-time low in 2008 since sampling began in 2001. The decline in abundance was due to decreases in all taxonomic groups and a large reduction in recruitment of quagga mussels. Density of Diporeia at northern ports in 2008 was the lowest observed. Diporeia were found only at 73-m sites of three ports sampled in northern Lake Huron. While no lakewide estimate of prey biomass was calculated due to the limited spatial scope of the 2008 survey, existing data suggest prey biomass remains depressed. Prey available to salmonids during 2009 will likely be small alewives, small rainbow smelt and small bloaters. Predators in Lake Huron will continue to face potential prey shortages.

Lake Huron↗

USGS2008

Resurgence of emerald shiners Notropis atherinoides in Lake Huron's main basin

Emerald shiners Notropis atherinoides were formerly common in Lakes Huron and Michigan, but declined during the 1960s as the exotic alewife Alosa pseudoharengus proliferated. The Lake Huron emerald shiner population was chronically depressed through 2004; however, we detected resurgence in emerald shiner density and biomass in Lake Huron during acoustic and midwater trawl surveys conducted during 2004–2006. Emerald shiners were not found during 2004, but by 2006 main basin density exceeded 500 fish/ha, biomass estimates exceeded 0.5 kg/ha, and emerald shiners contributed more to pelagic biomass than alewives or rainbow smelt Osmerus mordax . Length frequency distributions suggested that increased density was the result of two consecutive strong year classes in 2005 and 2006. Emerald shiner distributions also expanded from a focus in western Lake Huron in 2005 to a lakewide distribution in 2006. Emerald shiners occurred offshore, but were nearly always associated with epilimnetic surface waters warmer than 19°C. Resurgence of emerald shiners was likely a consequence of reduced alewife abundance, as they declined concurrently with alewife proliferation during the early 1960s. Return of this species may benefit native nearshore piscivores; however, benefits to Pacific salmonids Oncorhynchus spp. are uncertain because emerald shiners are smaller and still less abundant than historically important prey species, and they may be thermally segregated from salmonines.

Journal of Great Lakes Research↗