Abstract While oyster farms and sea otters (Enhydra lutris) coexist in some locations, sustaining these farms and growing interest in their expansion necessitate a comprehensive evaluation of potential interactions. We assessed sea otter interactions with oyster farms through behavioral observations of otters in oyster farms, adjacent non‐farm areas (controls), or bays with no farming activity (references) in southcentral Alaska in 2022–2023. Behavioral observations, conducted through scan surveys, captured sea otter activities (e.g., resting, grooming, swimming, and foraging). Targeted foraging observations tracked foraging success and prey (species and count). We hypothesized that sea otters preferentially used oyster farms for foraging and resting activities compared to non‐farm areas. Contrary to our hypothesis, sea otter activities showed no significant difference in foraging or resting behaviors between oyster farms and controls. Similarly, foraging behavior, including success and prey diversity, did not differ among areas. The dominant prey items in our study included clams (e.g., butter clam [Saxidomus gigantea]), crabs (e.g., helmet crab [Telmessus cheiragonus], red rock crab [Cancer productus]), and mussels (e.g., Pacific blue mussel [Mytilus trossulus]). Notably, there were no observations of farmed oysters being consumed by sea otters. There was strong evidence of differences in the average number of prey consumed per sea otter per dive between the control and reference areas, with the control area averaging 2.6 prey items per dive (SD = 3.6) compared to 4.8 prey items per dive (SD = 7.3) in the reference area. These differences may be attributed to variations in prey biomass and environmental conditions. Our observations indicate that there are no discernible differences in overall sea otter activity or foraging behavior in the presence of oyster farms.

Mating individuals of the helmet crab Telmessus cheiragonus were found during scuba diving in Taui Bay, Sea of Okhotsk, in September 2024. Mating occurred within depths 0.6–10 m and at a water temperature of 8–9°C. The largest crab aggregations were observed at a depth of 2.5–2.8 m in the macrophyte zone. The minimum carapace width in functionally mature males was 84 mm; in females, it was 48 mm. The ratio of females to males found during the study was 1:1.8 in general.

Evaluation of the molting stage of crustaceans is essential for studying their mating behavior because of molt-dependent changes in their behavior. For example, in species in which females mate just after molting, sexually mature premolt females are ready for courtship and postmolt females are ready for copulation. Non-invasive methods of evaluating molt stage are essential in studies of molt-dependent mating behavior so that normal behavior is not disrupted by the evaluation itself. The goal of the present study was to establish a non-invasive evaluation method for the helmet crab Telmessus cheiragonus, which is a model species for research on crustacean sex pheromones. We have identified morphological and behavioral indicators of molt stage. A morphological indicator of molt stage was a change in the color of the edge of telson and sixth abdominal segment, from a dark line to red in premolt animals to white in postmolt animals, which can be observed with the naked eye. A behavioral indicator of molt stage was that premolt females tended to fold their walking legs and chelae to adopt a precopulatory guarded position during artificial handling, whereas late postmolt stage females with developed ovaries and early premolt females in an early molting stage did not show this behavior. These non-invasive morphological and behavioral characteristics are useful indicators of the premolt stage of sexually mature female helmet crabs.

По материалам 1978–2008 гг. (975 желудков обработано количественно-весовым методом, около 2 тыс. желудков вскрыто и проанализировано в полевых условиях) рассмотрены особенности питания керчака-яока Myoxocephalus jaok в прикамчатских водах Охотского, Берингова морей и Тихого океана и предпринята попытка выяснить место этого вида рогатковых в трофической системе данного района. Показано, что керчак-яок характеризуется широким спектром питания (свыше 100 кормовых объектов), однако наибольшее значение в его рационе имеют рыбы (в среднем 64,1 % массы пищи) и десятиногие раки (32,2 %). Основу первых составляют камбалы Pleuronectidae (24,3 % массы пищи), минтай Theragra chalcogramma (14,4 %), тихоокеанская песчанка Ammodytes hexapterus (9,5 %) и рогатковые Cottidae (5,6 %); вторых ― крабы семейства Majidae (22,4 %) (главным образом краб-стригун Chionoecetes opilio (14,2 %) и краб-паук Hyas coarctatus (8,1 %)), а также крабы семейства Atelecyclidae (4,7 %) (преимущественно пятиугольный волосатый краб Telmessus cheiragonus (4,5 %)) и креветки семейства Crangonidae (3,1 %). Рассмотрены сезонные, локальные, межгодовые и возрастные изменения состава пищи керчака-яока. Установлено, что этот вид является факультативным хищником-засадчиком; ему свойственна высокая пластичность питания, дающая возможность использовать значительный набор пищевых компонентов. В трофической системе прикамчатских вод выделены звенья, формирующие биомассу керчака-яока.

N-acetylglucosamino-1,5-lactone (NAGL) is a molting biomarker in the blue crab Callinectes sapidus The concentration of this compound in urine is highest at the premolt stage. Since sexually mature premolt females release sex pheromone in their urine, NAGL is a candidate sex pheromone molecule in C. sapidus This compound has not been reported in other species. In the present study, we quantified the concentration of NAGL in the urine of the helmet crab Telmessus cheiragonus, using nuclear magnetic resonance spectroscopy, and found that the concentration increases toward the day of molting and decreases after molting. However, the total amount of NAGL collected from individual animals was greatest two to five days after molting, because the amount of urine collected was the lowest at the premolt stage, and it increased after molting. The highest median concentration of NAGL in T. cheiragonas was 29 μmol l(-1), which is 75% of the highest concentration reported in C. sapidus This is the first report of NAGL as a molting biomarker in a species other than C. sapidus We assume that NAGL is part of a pheromone bouquet in these two species.

Based on materials from plankton surveys carried out in 2004–2009, the period of occurrence, density, and distribution of larvae of three commercial species of crabs in the Peter the Great bay and adjacent areas of Sea of Japan were studied. The larvae of the horsehair crab Erimacrus isenbeckii (Brandt, 1848) occurred in the plankton from mid-March to early June, within the range of water temperature from −1 to 10.8°C. The larvae of the helmet crab Telmessus cheiragonus (Tilesius, 1812) appeared in the plankton in mid-April and occurred to the end of June within the temperature range from 2.8 to 13.0°C. The larvae of the snow crab Chionoecetes opilio (O. Fabricius, 1788) appeared in the plankton in mid-April as well, but some individuals sporadically occurred until early August. All the species of crabs produced one generation of larvae for their reproduction season. The terms of larval stay in plankton depended on water temperature and the duration of the pelagic period increased in colder years. In that area, the larvae of C. opilio were the most abundant (up to 41 ind./m3) and the zoea density of horsehair and helmet crabs was significantly lower (no more than 2 ind./m3). The larvae of C. opilio occurred over the entire area of the Peter the Great bay; the greatest aggregations of their early stages were observed in its southwestern open part. The maximum density of E. isenbeckii zoea was recorded in the south of the Amursky bay and in the Posyet bay. Individual larvae of T. cheiragonus occurred in the Posyet bay and in the southern part of the Amursky and Ussuriisky bays. The late-stage larvae of all crab species were concentrated in areas of the coastal circulation.

The analysis of the data obtained during the plankton surveys in Possyet Bay (Peter the Great Bay of the Sea of Japan) in 2000–2001 is presented. The larvae of eight crab species were registered in the plankton: the red king crab Paralithodes camtschaticus (Tilesius, 1815), the snow (opilio) crab Chionoecetes opilio (Fabricius, 1780), the Arctic lyre crab Hyas coarctatus ursinus (Leach, 1815), the kelp crab Pugettia quadridens (de Haan, 1839), the helmet crab Telmessus cheiragonus (Tilesius, 1815), the Japanese swimming crab Charybdis japonica (A. Milne-Edwards, 1861), the pea crab Pinnixa rathbuni (Sakai, 1934), and the porcelain crab Pachycheles stevensii (Stimpson, 1858). These species belonged to six families: Lithodidae, Atelecyclidae, Majidae, Portunidae, Porcellanidae, and Pinnotheridae. The role of the variability of some of the hydrological factors in the meroplankton larvae development was studied. In May, the crab larvae were found mostly in the open part of the bay. In June, they were transported by the current to the northern part of the bay. In July, they spread uniformly in all the bay areas; however, patchiness was observed. The maximal population density of the crab larvae was registered for July and varied from 6.8 to 23.3 ind. m−3. The crab larvae appeared in the plankton in 2000 and 2001 earlier than for the average season.

Larval and post-larval crab distribution was surveyed in three different habitats in Kachemak Bay, Alaska to determine temporal and spatial variability. Distribution varied temporally and spatially from June 2005 to September 2006. Nine sites of varying habitat complexity were surveyed monthly using scuba surveys and light traps to measure habitat variables and quantify crab zoeae and megalopae. A total of 10,016 crabs belonging to seven families were identified. Four species comprised the majority (97%) of the total crab assemblages and included Cancer oregonensis, Fabia subquadrata, Telmessus cheiragonus, and Pugettia gracilis. Peak abundances occurred in summer but varied on small temporal scales with species. No single bay-wide variable determined the appearance of all species. Depending on species, appearance may be influenced by seasonality of environmental variables. Spatially, highest abundances occurred in habitats with less structural complexity. Spatial differences in crab abundance may have resulted from variability on large scale physical transport mechanisms and not kelp-mediated flow alterations.

The effects of preventing female helmet crabs, Telmessus cheiragonus from mating during one breeding season on egg production and egg viability were assessed by investigating the egg clutches of the females isolated from males. A total of 38 females and 18 males were collected in April before the mating peak in 1996 and 1997 in the sublittoral zones of Usujiri, southern Hokkaido, Japan. Eighteen females were held together with 18 males (mating group) and 20 females were isolated from males (non-mating group) during about 7 months of captivity. Subsequently, 11 females of the mating group molted, copulated and produced an egg clutch, and 10 females of the non-mating group molted and spawned without mating. Egg clutch weight and egg diameter did not differ significantly between these two groups. There was also no significant difference in the percentage of viable eggs in an egg clutch between the groups. These results show that preventing female T. cheiragonous from mating during one breeding season has no effect on either clutch size or % viable eggs in a clutch. Sperm storage over one mating season in this species may be advantageous because it allows multiparous females, especially larger ones which could molt and copulate less frequently, to ensure their eggs will be fertilized.

Sexually competent females of Telmessus cheiragonus (helmet crab) release two pheromones that elicit grasping and copulation behaviors in males (Kamio et al., 2000, 2002, 2003). Our study aimed to use behavioral and electrophysiological techniques to identify the site of reception of these sex pheromones. In behavioral experiments, either the inner or the outer flagella of the antennules were ablated bilaterally from male crabs, and responses of male crabs to female odor were examined. When the inner flagella were surgically ablated, the sexual response (i.e., grasping and copulation behavior) of male crabs was not significantly changed relative to control animals that had their second antennae ablated. In contrast, the sexual response was significantly reduced when the outer flagella of the antennules were ablated, suggesting that the outer flagellum is the receptor organ that detects the sex pheromones. In electrophysiological experiments, urine, which in females contains the pheromone that elicits grasping behavior by males but does not contain the pheromone eliciting copulation, whose release site is not known, was tested. Female and male urine as well as shrimp extract evoked phasic responses of chemosensory afferents innervating aesthetasc sensilla on the outer flagellum of male crabs. The response of the afferents had significantly higher magnitude and lower threshold when female urine was applied. Thus, behavioral and electrophysiological observations suggest that in male helmet crabs, the outer flagellum of the antennule is the chemosensory organ that detects female sex pheromone.

: To clarify the annual testicular maturation cycle in the helmet crab Telmessus cheiragonus, seasonal histological changes of the testis and occurrence of grasping pairs and recently copulated females with fresh sperm plugs were investigated. The testis was composed of seminiferous ducts with many testicular lobules. Development of the lobules was divided into six stages (spermatogonia proliferation, first spermatocyte, reduction division, spermatid, spermiogenesis and free sperm stage) based on the spermatogenic phase of the germ cells in each lobule. The mean percentage of the lobules during each stage was calculated every 1–3 months. Developed lobules occurred with a high percentage throughout the year except in June when developing lobules predominated. Grasping pairs and females with fresh sperm plugs were collected during April–July with a peak in May–June. These results suggest that the males have testis with many developing lobules in June when they are active for mating. Newly formed spermatozoa may be stored in the testis and the vas deferens until the next mating season after June, as the spermatozoa may not have an opportunity to fertilize eggs until the next season and there is no sign of spermatozoa absorption in the testis.

The mating behaviour of the helmet crab, Telmessus cheiragonus, was observed in the laboratory to obtain information of its fishery management and seed production. Females always moulted before copulation and all moulting females copulated with their mates, while males performed precopulatory guarding before their mates moulted. The average duration of precopulatory guarding was 11.8±5.0 SD days. Sex ratios in experimental tanks did not influence the first guarding duration of male but diminished the female's guarded duration under female-biased treatment. Competition among males for females was observed; larger males appeared to have a competitive advantage. Males started copulation in 41.2±10.9 SD min after females moulted and the copulation lasted for 110.6±6.6 SD min. Postcopulatory guarding duration was 4.0±6.6 SD h. Small males tended not to guard and to copulate with females larger than themselves. Common features and differences in mating behaviour between T. cheiragonus and Erimacrus isenbeckii is discussed.

Animals employ multi-step mate recognition processes to mate with their proper part- ners, for a given mating season. The signals used in mate recognition in Crustacea are fairly well stud- ied, but these studies have so far focused on the signals used in precopulatory (or courtship) behavior. Signals that mediate copulation have never been experimentally demonstrated. Here, we report the presence of a copulation pheromone in the crab Telmessus cheiragonus which was previously unde- scribed in brachyuran Crustacea. This pheromone is released from postmolt females for more than 21 d after molting and evokes copulation behavior in male crabs. The postmolt female urine that con- tains precopulatory mate-guarding-inducing pheromone did not induce copulatory behavior in male crabs. Postmolt females that were prevented from releasing urine still elicited copulation behavior in males, thereby indicating that the pheromone is different from a pheromone that elicits precopulatory guarding in males. The copulation pheromone is a water-borne pheromone with a molecular weight of less than 1 kDa. T. cheiragonus employs 1 pheromone that elicits precopulatory guarding and another pheromone that elicits copulation. This strategy ensures mating between proper partners.

Annual reproductive cycle of the helmet crab Telmessus cheiragonus was investigated based on the histological observations of the ovary and the gonadosomatic indices (GSI = ovarian weight x 100 / body weight). The ovarian maturity was divided into five phases (Phase I-V). Minimum mature size of female was 36.0 mm in carapace length. The annual reproductive cycle in the adult females (more than 36.0 mm carapace length) consisted of the incubating period (October-March) and the maturing period (April-September). During the incubating period, the ovarian maturity was Phase I-II (mean GSI±SD = 3.8±4.7 %) when most of the females were ovigerous. During the maturing period, the ovarian maturity increased to Phase V (GSI ≤ 21.6 %) when the females seemed to be frequently copulating, because the soft shell adult females, which could copulate, occurred with highest frequency. The spawning of most females seemed to occur at the end of the maturing period. These results suggest that the ovarian maturation cycle requires one year, and during the incubation period ovaries are immature.

Abstract A new reliable bioassay method has been developed for detection of female sex pheromone(s) of the helmet crab Telmessus cheiragonus using artificial sponges based on the grasping behavior of male crabs. The seawater, male urine, and pre- and postmolt female urine were tested for pheromonal activity which resulted in the detection of activity only in urine from pre- and postmolt females.

Postlarval chromatophores as an adaptation to ultraviolet radiation.

Abstract Diet of sea otters (Enhydra lutris) using a haulout site on the north side of the Alaska Peninsula was determined from 50 scats. Dominant prey species were mussels (Mytilus edulis), followed by three species of clams (Siliqua spp., Spisula polynyma, and Tellina lutea), sand dollars (Echinarachnius parma), and helmet crabs (Telmessus cheiragonus). Our results support preliminary findings by Cim‐berg et al. (1984) that this sea otter population preys heavily on mussels and that the presence of low caloric value sand dollars in their diet is significant. Coupled with population estimates, our results also provide evidence that this population of sea otters may be declining due, in part, to overdepletion of food resources.