Charles E. O'Clair

Seasonal Migration and Distribution of Female Red King Crabs in a Southeast Alaskan Estuary

ABSTRACT Seasonal movements and distribution of primiparous and multiparous red king crabs (Paralithodes camtschaticus) were monitored with ultrasonic biotelemetry approximately weekly for 1 year in Auke Bay, Alaska. Migration was associated with life-history events and may have occurred in response to spatial and temporal variations in environmental conditions and resources. All crabs displayed distinct shifts in depth and habitat use and followed a general pattern of seasonal movement as follows: (1) gradual movement to deep water in spring after mating and egg extrusion, and residence there through early November; (2) abrupt, synchronous movement into shallow-water areas in November, and residence there through late February or early March; and (3) gradual, synchronous movement to intermediate depths followed by movement into shallow water to molt and mate between late March and late May. The behavior of primiparous crabs was more variable than that of multiparous crabs. The differences in behavior may result from ontogenetic shifts in movements, and habitat selection. The annual range of primiparous crabs (x = 11.9 km2) exceeded that of multiparous crabs x( = 3.6 km2). Mean depth was directly correlated with photoperiod, and the sudden, synchronous movement of crabs between habitats coincided with thermohaline mixing. Females displayed a highly aggregated distribution, especially during winter in shallow water, where podding behavior of adult crabs was documented for the first time.

DUNGENESS CRAB, CANCER MAGISTER, DO NOT EXTRUDE EGGS ANNUALLY IN SOUTHEASTERN ALASKA: AN IN SITU STUDY

Abstract The reproductive biology of female Dungeness crabs was studied with crab-pot and dive-transect sampling in five bays within or near Glacier Bay National Park and Preserve, southeastern Alaska, in April and September yearly from 1992 to 1998. A large percentage of nonovigerous, mature females was found in April, a time when females were expected to be brooding eggs that hatch in May and June. Our study examined differences between ovigerous and nonovigerous females collected in April and September samples to corroborate our previous laboratory study in which we found nonannual egg extrusion among Dungeness crabs. Seasonal differences in the catches of ovigerous and nonovigerous females, crab sizes, shell condition, and appendage injury were examined. Additionally, all crabs collected from two bays were tagged beginning in the fall of 1995; tagging was conducted twice annually. Our pot and dive data indicate that females, particularly larger ones, do not extrude eggs annually. Larger females have lower molting probabilities, which limits mating potential and increases reliance on stored sperm. The tagging study confirmed that at least some females do not extrude eggs in one year and then extrude eggs at a later time without molting, thus skipping at least one reproductive season. A reproductive cycle of Dungeness crabs in Alaska is introduced which includes earlier egg extrusion by larger females and nonannual egg extrusion.

A preliminary study of idiopathic lesions in the Dungeness crab, Cancer magister, from Rowan Bay, Alaska

Seventeen Dungeness crab, Cancer magister, from a Log Transfer Facility (LTF) in Rowan Bay, Alaska, were examined in a histopathological study because of what appeared to be high prevalences of shell disease that typically involved periopod, arthrodial membranes. Dungeness crab (N = 9) from a reference site in Rowan Bay were later examined. The severity and prevalence of the most frequently observed idiopathic lesions, melanized nodules and granulomas, in both groups were statistically tested. This paper reports the findings of this preliminary study.

Reproductive condition of Dungeness crabs, Cancer magister, at or near log transfer facilities in southeastern Alaska

Abstract To determine if the reproductive condition of female Cancer magister is altered by exposure to decomposing bark and wood waste at log transfer facilities (LTFs) five reproductive variables in crabs resident at or near LTFs in six bays in southeastern Alaska were compared with those in crabs at nearby control sites. Crabs were collected at all sites in spring 1982 and at one bay (Rowan Bay) in November 1982 and April 1983. Crabs were in contact with bark deposits only at the Rowan Bay LTF which, throughout the study, harbored a smaller percentage of ovigerous crabs ( x = 33%, P ) with lower fecundity ( y = 3·9 × 10 5 eggs , P ) than did the control site ( x = 76%, y = 9·6 × 10 5 eggs ). The percentage of ovigerous crabs and crab fecundity at the other bays averaged 81% and 8·9 × 105 eggs, respectively. Concentrations of hydrogen sulfide and ammonia were elevated in the pore water of bark deposits, but only the former reached concentrations acutely toxic to some Crustacea. The level of fouling and mortality in Cancer magister eggs was directly correlated with the abundance of the nemertean egg predator Carcinemertes errans in the crabs brood. Crabs at the LTF suffered greater egg mortality and harbored more C. errans than did control crabs in April 1983 but not May 1982. The level of egg fouling in crabs at the Rowan Bay LTF was similar to that at the control site.

Reduced survival and condition of the bivalves Protothaca staminea and Mytilus edulis buried by decomposing bark

Abstract The bivalves Protothaca staminea and Mytilus edulis were exposed to five depths of decomposing bark from an active log transfer facility for 13–96 days in a field experiment at Auke Bay, Alaska. Survival and condition of both species was inversely related to depth and duration of bark coverage. As little as 6 cm of bark reduced survival; survival declined most rapidly between 10 and 15 cm of bark. The depths of bark under which half the animals died after 96 days of exposure were 12·8 ± 1·6 cm for P. staminea and 10·9 ± 1·5 cm for M. edulis . Interstitial water in the bark deposits had low concentrations of dissolved O 2 (2·5–5·3 mg/liter) and elevated concentrations of hydrogen sulfide (1·0–8·1 mg/liter total sulfide) and ammonia (46–131 μg-at N/liter) compared to the surface water from the control treatment. Survival of P. staminea and M. edulis was inversely related to concentrations of hydrogen sulfide and ammonia and directly related to dissolved O 2 concentrations.