David V. Buchanan

A mycosis caused by Lagenidium sp. in laboratory-reared larvae of the Dungeness crab, Cancer magister, and possible chemical treatments☆

Abstract A mycosis in larvae of the Dungeness crab, Cancer magister, was observed about 48 hr after they had molted to second-stage zoeae in the laboratory during a chronic bioassay. The fungus was of the genus Lagenidium and caused about 40% mortality of larvae before the test was terminated. Hyphal development and subsequent sporulation of the fungus was observed over a range of 0–32‰ salinity, with an optimum around 16‰. Bioassays of eight fungicides and the herbicide trifluralin, using the larvae and fungus in separate tests, were performed to explore means of chemical treatment. Trifluralin was the most satisfactory of the chemicals screened, with captan, Cu2+, and benomyl also giving good results for certain treatment intervals of up to 96 hr. Malachite green was toxic to larvae at concentrations inhibiting the fungus.

Toxicity of the insecticide methoxychlor to the Dungeness crab Cancer magister

The toxicity of methoxychlor, determined in acute and chronic studies using larval, juvenile, and adult stages of the Dungeness crab, Cancer magister Dana, was inversely related to the age of the crabs after hatching and increased with the length of exposure. The 96-h LC50s for zoeae, juveniles, and adults were 0.42, 5.10, and 130 μg/l, respectively. Levels causing decreased survival of these same stages during exposures of more than 60 days were 0.05, 0.40, and 4.0 μg/l, respectively. Hatching of eggs was not adversely affected by methoxychlor concentrations up to 10 μg/l, and molting from prezoeae to zoeae was reduced only 30% from controls at the latter exposure concentration. Methoxychlor concentrations of 0.05 and 4.0 μg/l delayed motting of larval and juvenile crabs, respectively, and this delay was as much as 10 days for the juveniles. Sensitivity of adult and juvenile crabs to methoxychlor increased during ecdysis. In uptake experiments, juvenile crabs concentrated methoxychlor more rapidly than did adults. Juveniles exposed to 2.0 μg/l of methoxychlor and adults exposed to 1.8 and 7.5 μg/l had whole body methoxychlor concentrations after 12 days of 0.88, 0.10, and 0.51 mg/kg, respectively. Loss of the pesticide from adult crabs was rapid, and was 95% complete after 15 days of depuration. Concentrations of methoxychlor in individual tissues were found to be highest in the exoskeleton, gill, and hepatopancreas, in declining order, with less than a two-fold difference among these tissues. About 81% of the methoxychlor measured in whole body samples was associated with the exoskeleton, but it is not known whether or not the pesticide was transported through the culticle to internal tissues.

Status of Oregon's Bull Trout.

Limited historical references indicate that bull trout Salvelinus confluentus in Oregon were once widely spread throughout at least 12 basins in the Klamath River and Columbia River systems. No bull trout have been observed in Oregons coastal systems. A total of 69 bull trout populations in 12 basins are currently identified in Oregon. A comparison of the 1991 bull trout status (Ratliff and Howell 1992) to the revised 1996 status found that 7 populations were newly discovered and 1 population showed a positive or upgraded status while 22 populations showed a negative or downgraded status. The general downgrading of 32% of Oregons bull trout populations appears largely due to increased survey efforts and increased survey accuracy rather than reduced numbers or distribution. However, three populations in the upper Klamath Basin, two in the Walla Walla Basin, and one in the Willamette Basin showed decreases in estimated population abundance or distribution.

THE PREZOEAL STAGE OF THE DUNGENESS CRAB, CANCER MAGISTER DANA

1. Ninety-four per cent of eggs of the Dungeness crab, Cancer magister, held in sea water at 10.5 or 17.5° C and at salinities of 10 to 32% hatched into prezoeae during a 36-hour observation period. The highest and lowest numbers of eggs hatched at salinities of 15 and 10‰, respectively. At a salinity of 32‰, the mean percentages of eggs that hatched at 10.5 and 17.5° C were 30 and 73%, respectively.2. With increase of salinity, the percentages of prezoeae that molted to first-stage zoeae increased from 0% at 10‰ to 100% at 30 and 32‰.3. With increase of salinity from 15 to 32‰, the mean duration of the prezoeal stage decreased from more than 60 minutes to 11 minutes.4. The experimental results show that the occurrence of a free prezoeal stage of short duration is normal in the life history of C. magister. The possibility that this is true for other Brachyura is discussed.

Downstream Movements and Catches of Two Strains of Stocked Trout

Downstream movements and angler catches of 2 strains of planted yearling rainbow trout (Salmo gairdneri) were monitored for 2 years in a small Oregon stream, Mill Creek. The Roaring River strain showed a tendency for rapid downstream movement, while the Cape Cod strain tended to remain in the planted area for a longer period and were also caught in higher numbers. As many as 37.2 percent of the Roaring River trout moved out of the stream, compared to a maximum of 18.2 percent of the Cape Cod trout. J. WILDL. MANAGE. 42(2):329-333 Downstream movements of rainbow trout following stocking, have been reported widely in the literature. Migration tendencies have been attributed to condition of fish, streamflow, water temperature, physical features of streams, and available food. Although comparative studies relating to genetic differences in stocks have been undertaken (Butler and Borgeson 1965, Ratledge and Cornell 1953, Hansen and Stauffer 1971), only limited studies (e.g., Cordone and Nicola 1970) have indicated downstream movements were due to genetic characteristics of hatchery stocks. But, Needham and Behnke (1962) speculated that many modern hatchery brood stocks were primarily derived from a mixing of resident rainbow x resident cutthroat, together with anadromous steelhead trout. Behnke now believes (pers. comm., 14 March 1977) that the original McCloud River hatchery rainbow trout brood stock was derived from crossing native redband rainbow trout with anadromous steelhead trout. Due to steelhead outbreeding, a downstream movement tendency may be inherent in a portion of long established hatchery brood fish. A primary objective of stocking catchable trout is to provide recreational fishing in heavily used areas, where natural production cannot meet demand. Fish that move out of these areas soon after planting can be considered to be an economic loss to this objective. Preliminary data by the Oregon Department of Fish and Wildlife, in 1974, led to the testing of the hypothesis that there were behavioral differences between 2 strains of hatchery-reared rainbow trout, Roaring River (widely used in Oregon) and Cape Cod (widely used in Washington). The general hypotheses tested in 1975 and 1976 were: H1--that downstream movements of Roaring River trout were significantly different from Cape Cod trout following stocking; and H2-that angler catches of Roaring River trout were significantly different from Cape Cod trout in the planted area. We wish to acknowledge the cooperation of William Wingfield and his assistants at Roaring River Hatchery, Oregon Department of Fish and Wildlife. Partial funding of this research came from Federal Aid in Fish Restoration Act (DingellJohnson) funds through the U.S. Fish and Wildlife Service, Project F-94-R. We thank Dr. R. Behnke for historical information and theories on rainbow trout brood stocks. Thanks are due K. A. Moring J. Wildl. Manage. 42(2):1978 329 This content downloaded from 207.46.13.149 on Mon, 03 Oct 2016 05:45:10 UTC All use subject to http://about.jstor.org/terms 330 DOWNSTREAM MOVEMENT OF STOCKED TROUT *Moring and Buchanan and J. Ehmke for editorial assistance, and Drs. H. H. Wagner and J. Watson for critically reviewing the manuscript.

Toxicity of the herbicides 2,4-D, DEF, propanil and trifluralin to the Dungeness crab, Cancer magister.

Lethal and sublethal responses to the herbicides 2,4-D, DEF®, propanil, and trifluralin of various life history stages of the Dungeness crab,Cancer magister, were examined to estimate maximum acceptable toxicant concentrations (MATC) of each compound for this species. Zoeae were found, in long term tests, to be the most sensitive stage. Based on the experiments with this stage, MATCs were concluded to be >0.95, <6.9μg for DEF, ≥26, <220μg/L for trifluralin, ≥80, < 1,700μg/L for propanil, and < 1,000μg/L for the free acid form of 2,4-D.

Toxicity of the fungicide captan to the Dungeness crab Cancer magister

Captan did not affect the survival of Dungeness crab (Cancer magister Dana) zoea exposed to 30 μg l-1 during a chronic toxicity test lasting 69 days, but larvae were quickly killed (mean survival time = 9 days) in the same test by exposure to 450 μg l-1 of the fungicide. Delay of molting occurred, however, for later stages at 30 μg l-1. Survival of juvenile crabs was not reduced by exposure to captan for 36 days at 510 μg l-1 or, in a second test, for 80 days at 290 μg l-1. No deaths of adults exposed for 75 days to 340 μg l-1 of captan were observed. Captan appeared to accelerate hatching of eggs at all concentrations tested from 100 to 10,000 μg l-1. The development from prezoeae during a 24-h period was not inhibited by the fungicide, but at 3,300 and 10,00 μg l-1, the two highest concentrations tested, developing zoeae exhibited a morphological deformity and were largely inactive. Under the prevailing conditions in the toxicity tests, the half-life of captan was estimated to be from 23 to 54 h. Because of the relatively low toxicity of captan to crab stages and its high rate of degradation in sewater, it is suggested that the agricultural application of captan near marine waters is not likely to affect natural crab populations or crabs in laboratory culture. Further-more, the prophylactic use of captan as a fungicidal treatment for Lagenidium sp. in larval crab cultures is considered safe when used at recommended dosages.