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At least 433 records · Page 24Linked to original sources
USGS1975

Changes in the lake trout population of southern Lake Superior in relation to the fishery, the sea lamprey, and stocking, 1950-70

Commercial catch and effort statistics for 1929-70, samples of commercial catches in 1959-62, and records of examinations of all lake trout (Salvelinus namaycush) taken commercially in inshore waters of Michigan and Wisconsin in 1962-70 were the basis for descriptions of changes in the population in 1929-70. Abundance fluctuated cyclically and gradually downward in 1929-49, whereas fishing intensity tended to increase during the same period. In 1950-52, a change from cotton to nylon twine in gillnets raised effective fishing effort to 305% of the 1929-43 average in Michigan waters and to 228% in Wisconsin waters; production held near average. Abundance fell to 18% of average in Michigan in 1953-61 and to 25% of average in Wisconsin in 1956-61; in the same periods, production fell to 11% of average in Michigan and to 19% in Wisconsin. In 1962-70 abundance rose to 160% in Michigan and 246% in Wisconsin while production and fishing intensity were held low (3-14%) by regulation. Changes in abundance of lake trout were attributable to a sequence of developments in successive series of years; intensive fishing in the early 1950's; severe sea lamprey predation in the late 1950's; an 85% reduction in abundance of sea lampreys in mid 1961; and the combination of sea lamprey control, intensive stocking of yearling lake trout, and restrictions on fishing in 1962-70. A decline in average size of lake trout and the near elimination of spawning stocks in 1953-61 curtailed recruitment of native lake trout in the mid 1960's. Stocking of fin-clipped lake trout replaced natural reproduction in the early 1960's. In 1965-70, the lake trout population was composed mainly of hatchery-reared fish. Natural reproduction was reestablished on one major spawning shoal in Wisconsin in 1965, but in 1970 only 10% of the legal (17-inch and longer) and 17% of the undersize lake trout in Wisconsin were native fish. Reduction of sea lamprey abundance resulted in an immediate increase in survival and abundance of lake trout, especially of the larger sizes. As abundance of lake trout progressively increased in 1962-70, survival of the smaller legal-size lake trout increased, probably due to reduction of the predator-prey ratio and an increase in availability of larger lake trout preferred by sea lampreys. Abundance of spawning-size lake trout was limited by high natural mortality in 1965-70. Circumstantial evidence suggested that sea lamprey predation contributed a major part of the high natural mortality.

Technical Report↗
USGS1995

ENSO events in the northern Gulf of Alaska, and effects on selected marine fisheries

The 1991-93 El Nino-Southern Oscillation (ENSO) event first appeared in the northern Gulf of Alaska in autumn 1991 with warm sea-surface temperatures. In winter 1992, there were pulses of increased sea level and anomalous circulation. El Nino conditions persisted at least through summer 1993. The effects of this ENSO event on major groundfish species and Pacific herring in the northern Gulf of Alaska were examined and compared with the effects of previous ENSO events. There is little evidence that the 1991-93 or 1982-83 ENSO events affected landings of walleye pollock, Pacific cod, Pacific halibut, or arrowtooth flounder. Some changes in distribution of groundfish species were observed in 1993, but the effect was similar to changes observed in non-ENSO warm years. In general, warm ocean conditions have a positive effect on recruitment of northern stocks, but ENSO events appear to have an inconsistent effect on year-class strength within species and among different species. For example, strong year classes of halibut and arrowtooth flounder sometimes, but not always, coincide with ENSO events; ENSO events are associated with moderate to weak year classes of cod and pollock. However, post-ENSO warm years often are associated with strong recruitment of many groundfish species. Major changes have occurred in the Gulf of Alaska ecosystem since 1977. The influence of the 1976 ENSO event in precipitating these changes and the role of the frequency or strength of subsequent El Nino events is presently unknown. Herring and other stocks of small pelagic fishes may be more affected by ENSO events. In particular, decreased catches, recruitment, and weight-at-age of herring are sometimes associated with ENSO events. Furthermore, a variety of seabirds which feed mostly on pelagic forage fishes or the pelagic juvenile stages of groundfish suffered widespread mortalities and breeding failures in the Gulf of Alaska during the ENSO years of 1983 and 1993. These effects on seabirds were also observed over a wider geographic range, from California to the western Bering Sea.

Report↗
USGS1997

Zinc hazards to plants and animals with emphasis on fishery and wildlife resources

Ecological and toxicological aspects of zinc in the environment are reviewed with emphasis on natural resources. Subtopics include sources and uses; chemical and biochemical properties; carcinogenicity, mutagenicity, teratogenicity; background concentrations in biological and nonbiological compartments; effects of zinc deficiency; toxic and sublethal effects on terrestrial plants and invertebrates, aquatic organisms, birds, and mammals; and recommendations for the protection of sensitive resources.

Book chapter↗
USGS1998

Foods of Buller's shearwaters (Puffinus bulleri) associated with driftnet fisheries in the central North Pacific Ocean

We examined digestive tract contents and stable nitrogen isotope ratios (??15N) in breast muscles of Buller's shearwaters (Puffinus bulleri) salvaged from squid and largemesh driftnets in the central North Pacific Ocean. The epipelagic Pacific saury (Cololabis saira) was the predominant prey, making up 71% of prey mass in digestive tracts. The remainder of the diet included small numbers of crustaceans, small fishes, and squids. The high degree of specialization in the diet seems to indicate that in the North Pacific, Buller's Shearwaters usually feed at or near the water surface and rarely pursue food under water. Although these birds have been observed feeding on scraps from fishing vessels, our data suggest that offal comprises less than 10% of the diet. Stable nitrogen isotope values provided quantified information on the timing of arrival of migrants into the North Pacific.

Notornis↗
USGS2012

Predicted time from fertilization to maximum wet weight for steelhead alevins based on incubation temperature and egg size (Study site: Western Fishery Research Center, Seattle; Stock: Dworshak hatchery; Year class: 1996)

The accuracy of a model that predicts time between fertilization and maximum alevin wet weight (MAWW) from incubation temperature was tested for steelhead Oncorhynchus mykiss from Dworshak National Fish Hatchery on the Clearwater River, Idaho. MAWW corresponds to the button-up fry stage of development. Embryos were incubated at warm (mean=11.6°C) or cold (mean=7.3°C) temperatures and time between fertilization and MAWW was measured for each temperature. Model predictions of time to MAWW were within 1% of measured time to MAWW. Mean egg weight ranged from 0.101-0.136 g among females (mean = 0.116). Time to MAWW was positively related to egg size for each temperature, but the increase in time to MAWW with increasing egg size was greater for embryos reared at the warm than at the cold temperature. We developed equations accounting for the effect of egg size on time to MAWW for each temperature, and also for the mean of those temperatures (9.3°C).

Book chapter↗
USGS2013

Effects of dreissenids on monitoring and management of fisheries in western Lake Erie

Water clarity increased in nearshore areas of western Lake Erie by the early-1990s mainly as a result of the filtering activities of dreissenid mussels (Dreissena spp.), which invaded in the mid-1980s. We hypothesized that increased water clarity would result in greater trawl avoidance and thus reduced ability to capture fish in bottom trawls during daytime compared to nighttime. We examined this hypothesis by summarizing three analyses on fish data collected in western Lake Erie. First, we used a two-tiered modeling approach on the ration (R) of catch per hour (CPH) of age-0 yellow perch (Perca flavencens Mitchell) at night to CPH during daytime in 1961-2005. The best a priori and a posteriori models indicated a shift to higher CPH at night (R > 1) between 1990 and 1991, which corresponded to 3 years after the dreissenid invasion and when water clarity noticeably increased at nearshore sites. Secondly, we examined effects of nighttime sampling on estimates of abundance of age-2 and older yellow perch, which form the basis for recommended allowable harvest (RAH). When data from night sampling were included in models that predict abundance of age-2 yellow perch from indices of abundance of age-0 and age-1 yellow perch, predicted abundance was lower and model precision, as measured by r-squared, was higher compared to models that excluded data collected at night. Furthermore, the use of only CPH data collected at night typically resulted in lower estimates of abundance and more precise models compared to models that included CPH data collected during both daytime and nighttime. Thirdly, we used presence/absence data from paired bottom trawl samples to calculate an index of capture probability (or catchability) to determine if our ability to capture the four most common benthic species in western Lake Erie was affected by dreissenid-caused increased water clarity. Three species of fish(white perch, Morone americana Gmelin; yellow perch; and trout-perch, Percopsis omiscomaycus Walbaum) had lower mean daytime catchability than nighttime catchability after dreissenids became established, which supported the hypothesis of greater trawl avoidance during daytime following establishment of dreissenids. Results from freshwater drum (Aplodinotus grunniens Rafinesque) were opposite those of the other three species, which may be a result of behavioral shifts due to freshwater drum feeding on dreissenids mussels. Collectively, these three studies suggest that dreissenids indirectly affected our ability to assess fish populations, which further affects estimates of fish densities and relationships between indices of abundance and true abundance.

Lake Erie↗