Testing baits prepared from by‐product of the shrimp and snow crab industry in the pot fishery for Gadus morhua (Linnaeus, 1758) and Pollachius virens (Linnaeus, 1758)

In a study between October and November 2015 in northern Norway, bait prepared from the by‐product of the shrimp and snow crab industry was employed in the pot fishery to capture cod and saithe. Frozen natural herring was used as control bait. Pots with the three bait types were placed 1,000 m apart in order to eliminate the risk of interaction between the different baits. In total 11 sampling periods were conducted. There were no significant differences in catch rates between the different baits tested on cod and saithe. The manufactured bait tested in this study showed a continuous release of odours over a 14‐day period. Results show that the water content of the bait increases rapidly in the first phase of the immersion (until day 7), and the corresponding loss of bait mass (dry weight) suggest some physical disintegration (erosion) of the bait until the water content stabilizes. This study illustrates that it is possible to replace natural herring with hydrolysates from by‐products from shrimp or snow crab industry in the Norwegian pot fishery of cod and saithe.     

Impact Scenario for an Introduced Decapod on Arctic Epibenthic Communities

The intentional introduction of a species for the enhancement of stock or establishment of new fisheries, often has unforeseen effects. The red king crabs, Paralithodes camtschaticus, which was introduced into the Barents Sea by Russian scientists, has established a self-sustaining population that has expanded into Norwegian waters. As top benthic predators, the introduced red king crabs may have possible effects upon native epifaunal scallop (Chlamys islandica) communities. These benthic communities may be a source of prey species in late spring, when the red king crabs feed most intensively. Foraging rates (consumption, killing or severely damaging) of red king crab on native prey organisms were measured by factorial manipulation of crab density (0.5, 1.5 and 3 per m ²), size classes (immature, small mature, and large mature crabs), and by evaluating prey consumption after 48 h, in order to extrapolate a scenario of the likely impacts. Foraging rates of the red king crab on scallops ranged between 150 and 335 g per m² within 48 h. These rates did not change when crab density was altered, though an increased amount of crushed scallops left uneaten at the tank floor, were correlated with high density of small mature crabs. Foraging rate changed significantly with crab size. Consequently, the susceptibility of native, shallow water epibenthic communities to red king crab predation in the early life history stages, and during the post-mating/molting spring period, must be considered significant when foraging rates are contrasted with natural scallop biomass between 400 and 1200 g scallops per m².     

The Use of Artificial Benthic Collectors for Assessment of Spatial Patterns of Settlement of Megalopae of Carcinus maenas (L.) (Brachyura: Portunidae) in the Lower Mira Estuary, Portugal

Artificial benthic collectors have been widely used for the assessment of settlement rates of decapod crustaceans. However, to date no consistent works have addressed spatial patterns of settlement in different estuarine habitats, and no specific studies targeted the interaction of artificial surfaces with the surrounding natural substrate. It may be expected that the artificial surface may produce a different thigmotactic response when compared to the natural substrate, which may limit the use of this technique for assessment of natural settlement rates. In this study the settlement rates of megalopae of the estuarine crab Carcinus maenas were addressed, specifically deploying artificial benthic collectors in different habitats both intertidal and subtidal in the lower Mira estuary. A number of experiments were performed concerning stratification and temporal fluctuations of settlement. Further, the interaction of collector surface with the surrounding substrate was investigated, by comparing settlement rates in natural and artificial substrates in different habitats. Results have shown significant differences in settlement between different estuarine habitats, both in spatially replicated experiments and in a high-resolution temporal experiment. However, comparison between settlement rates in artificial and natural substrates has shown that there is a strong interference between collectors and surrounding substrate, limiting interpretation of results concerning settlement rates in artificial substrate alone.     

Predation by blue crabs, Callinectes sapidus, on rapa whelks, Rapana venosa: possible natural controls for an invasive species?

Blue crabs Callinectes sapidus are voracious predators in Chesapeake Bay and other estuarine habitats. The rapa whelk Rapana venosa is native to Asian waters but was discovered in Chesapeake Bay in 1998. This predatory gastropod grows to large terminal sizes (in excess of 150 mm shell length (SL)) and has a thick shell that may contribute to an ontogenetic predation refuge. However, juvenile rapa whelks in Chesapeake Bay may be vulnerable to predation by the blue crab given probable habitat overlap, relative lack of whelk shell architectural defenses, and the relatively large size of potential crab predators. Feeding experiments using three size classes of blue crab predators in relation to a size range of rapa whelks of two different ages (Age 1 and Age 2) were conducted. Blue crabs of all sizes tested consumed Age 1 rapa whelks; 58% of all Age 1 whelks offered were eaten. Age 2 rapa whelks were consumed by medium (67% of whelks offered were eaten) and large (70% of whelks offered were eaten) blue crabs but not by small crabs. The attack methods of medium and large crabs changed with whelk age and related shell weight. Age 1 whelks were typically crushed by blue crabs while Age 2 whelk shells were chipped or left intact by predators removing prey. Rapa whelks less than approximately 35 mm SL are vulnerable to predation by all sizes of blue crabs tested. Rapa whelk critical size may be greater than 55 mm SL in the presence of large blue crabs indicating that a size refugia from crab predation may not be achieved by rapa whelks in Chesapeake Bay until at least Age 2 or Age 3. Predation by blue crabs on young rapa whelks may offer a natural control strategy for rapa whelks in Chesapeake Bay and other estuarine habitats along the North American Atlantic coast.     

Impact scenario for the invasive red king crab <Emphasis Type="Italic">Paralithodes camtschaticus</Emphasis> (Tilesius, 1815) (Reptantia,Lithodidae) on Norwegian,native, epibenthic prey

Large invasive predators like the king crab, Paralithodes camtschaticus, deserve particular attention due to their potential for catastrophic ecological impact on recipient communities. Conspicuous, epibenthic prey species, such as the slow growing commercial scallop Chlamys islandica, are particularly exposed to the risk of local extinction. A research program integrating experiments and field monitoring is attempting to predict and track the impact of invasive king crab on scallop beds and associated fauna along the north Norwegian coast. The claw gape of the crab shows no limitations in handling the flat-bodied scallop. However, the potential impact of the crab on scallop may depend on the availability of other calcified prey associated with scallop beds, such as the sea star, sea urchin, and blue mussel, all species recorded in the diet of P. camtschaticus. To address this issue, a laboratory experiment on foraging behaviour of P. camtschaticus was conducted. The experimental results show that all size classes of red king crab prefer scallops, but small juveniles and medium sized crabs demonstrate active selection for starfish (Asterias rubens) that equals or surpasses the electivity of the large crab. The selection of sea urchin (Strongylocentrotus droebachiensis) and blue mussel (Mytilus edulis) is slightly positive or neutral for the three crab size classes. These results suggest that scallop beds with a rich associated fauna are less vulnerable to red king crabs predation and possibly more resilient than beds with few associated species. Also, crab size distribution is likely relevant for invasion impact, with increasing abundance of small and medium sized crabs being detrimental for alternative calcified prey associated with scallop beds. Successive stages of crab invasion will see an acceleration of scallop mortality rates associated with (i) decreasing availability of alternative prey, due to protracted predation pressure intensified by recruitment of juvenile crabs, and (ii) increased number of large crabs. Estimates of crab density and intake rates suggest that the accelerated loss rates will eventually endanger scallop beds persistence.     

Gear technology in <Emphasis Type="Italic">Nephrops</Emphasis> trawl fisheries

Nets with a small mesh size are required to catch Nephrops norvegicus, consequently large quantities of small whitefish are also caught, and much of this bycatch is undersized and is discarded dead. The main bycatch species are whiting (Merlangius merlangus), haddock (Melanogrammus aeglefinus) and cod (Gadus morhua). Here we summarize the known behavioural reactions of these species towards conventional trawls and review the results of using different trawl modifications to increase selectivity of Nephrops trawls. The trawl modifications are categorised as separator grids, separator and guiding panels, square-mesh panels, capture avoidance designs and codend modification. Finally, the extent to which these developments have been legislated for is discussed including the conditions under which new gear regulations have been introduced. Haddock and whiting rise during the trawling process facilitating their separation from Nephrops and escape, however the behaviour of small fish of these species is less consistent. Cod and Nephrops remain on bottom of the trawl, so to separate these species requires some physical filtering process. Overall, there is currently sufficient technical ability to improve selectivity in Nephrops trawls. The design of choice is dependent on the objectives of managers; for reducing discards but retaining marketable fish, square-mesh panels offer the most useful tool; to eliminate all bycatch and create a single-species fishery, grids and traditional Nephrops trawls show most potential. Whatever the objectives of the new measures, it is likely that a short-term economic impact will follow, and some form of incentive may be required to implement effective measures. A voluntary uptake of new measures by industry is preferable, however, to date, restrictions on fishing opportunities have been necessary to introduce innovative gear designs.     

Fishery of Lake Ladoga — past, present and future

The post-war fishery of Lake Ladoga can be divided according to its catch level into four periods. In the years 1945–1954 the total annual catch increased, and reached the level of 4000 tonnes. In this period the fish stocks that had increased during the war years were intensively exploited. However, this fishery was not in balance with the stocks during the period 1955–1963. As a consequence, the catch decreased drastically, being sometimes less than 2000 tonnes.Controlling the fishery restored the abundance of whitefish Coregonus lavaretus (L.) and zander Stizostedion lucioperca (L.). This increased the total annual catch to about 5500 tonnes in 1964–1989. However, the fishery control measures have not been sufficient to achieve the conservation of salmon Salmo solar L. m. sebago, brown trout Salmo trutta L. and the migratory lake whitefish stocks.A decrease in the total fish catch has been observed since 1990. This decrease may be related to the deterioration of the environment of Lake Ladoga, caused by anthropogenic factors. The unfavourable state of the ecosystem has led to decline of the whitefish stocks and, especially during the last few years, to drastical decline of zander.Acute problems, to be faced in the near future, are connected with the hatchery maintenance of several river-spawning stocks, e.g. salmon, brown trout and migratory whitefish, because the existing fish hatcheries are insufficient in capacity and technically outdated.     

Consumption rates and prey preference of the invasive gastropod Rapana venosa in the Northern Adriatic Sea

The alien Asian gastropod Rapana venosa (Valenciennes 1846) was first recorded in 1973 along the Italian coast of the Northern Adriatic Sea. Recently, this predator of bivalves has been spreading all around the world oceans, probably helped by ship traffic and aquaculture trade. A caging experiment in natural environment was performed during the summer of 2002 in Cesenatico (Emilia-Romagna, Italy) in order to estimate consumption rates and prey preference of R. venosa. The prey items chosen were the Mediterranean mussel Mytilus galloprovincialis (Lamarck 1819), the introduced carpet clam Tapes philippinarum (Adams and Reeve 1850), both supporting the local fisheries, and the Indo-Pacific invasive clam Anadara (Scapharca) inaequivalvis (Bruguière 1789). Results showed an average consumption of about 1 bivalve prey per day (or 1.2 g wet weight per day). Predation was species and size selective towards small specimens of A. inaequivalvis; consumption of the two commercial species was lower. These results might reduce the concern about the economical impact on the local bivalve fishery due to the presence of the predatory gastropod. On the other hand, selective predation might probably alter local community structure, influencing competition amongst filter feeder/suspension feeder bivalve species and causing long-term ecological impact. The large availability of food resource and the habitat characteristics of the Emilia-Romagna littoral makes this area an important breeding ground for R. venosa in the Mediterranean Sea, thus worthy of consideration in order to understand the bioinvasion ecology of this species and to control its likely further dispersal.     

Mercury accumulation in five species of freshwater fish in Lake Tyrifjorden,south-east Norway,with emphasis on their suitability as test organisms

Synopsis Mercury concentration in axial muscle of brown trout, Salmo trutta, whitefish, Coregonus lavaretus, Arctic charr, Salvelinus alpinus, smelt, Osmerus eperlanus and pike, Esox lucius, were studied in Lake Tyrifjorden during 1978–1982. Our data demonstrate that older and bigger fish on an average have higher mercury concentration than smaller and younger. Further, complex life histories as in brown trout influence the pattern of mercury accumulation. During young stages accumulation in brown trout is moderate, while accumulation in older stages is highly correlated to lake residency time. Based on our data we suggest the following requirements for a test organism and the collecting procedure; (1) life history should be simple with small sexual differences, (2) ageing should be easy and reliable, and (3) large representative samples should be easily obtained during (4) a fixed biological period i.e. the spawning period. We consider smelt as an appropriate test organism based on these criteria.     

The relationship between Trichocerca pusilla (Jennings), Aulacoseira spp. and water temperature in Loch Leven,Scotland, U.K.

Loch Leven is a shallow, eutrophic lake in the Scottish lowlands that is famous for its brown trout (Salmo trutta L.) fishery. Studies of planktonic rotifer populations began here in January 1977. Since then, samples have been collected and analysed at more or less weekly intervals. Additional information on the composition and abundance of phytoplankton and crustacean zooplankton species, and on a variety of physical and chemical determinants, has been recorded on each sampling occasion.Long-term datasets, such as that described above, are invaluable for identifying interactions between components of the plankton that only appear for short periods each year, as these interactions would probably be overlooked in data spanning a shorter period of time. This study uses the long-term data from Loch Leven to examine the food and temperature requirements of the summer rotifer species Trichocerca pusilla (Lauterborn). The results suggest that T. pusilla prefers water temperatures above 12 °C and that it feeds, primarily, on the filamentous diatom Aulacoseira spp. During the summer months, its abundance was closely related to the availability of this diatom. When filaments of Aulacoseira spp. were abundant, rotifer densities reached 1000–3000 ind. l^–1 and when they were scarce (e.g. 1980, 1997 and 1998) T. pusilla densities also remained low (i.e. less than 100 ind. l^–1). The reason for the success or failure of Aulacoseira during the summer months each year is unclear but, in general, its abundance was related to the availability of dissolved silica in the water.     

The Association between Medusa Lychnorhiza lucerna (Scyphomedusae, Rhizostomeae) and Decapod Libinia spinosa (Brachyura, Majidae) Recorded for the First Time in Neritic Waters of Argentina

The paper discusses the first record of the association between the medusa Lychnoriza lucerna Haeckel, 1880 and the decapod Libinia spinosa Milne-Edwards, 1934 in neritic waters of Argentina. Our results allow us to conclude that the symbiotic relation between these two species is a common phenomenon. The crab L. spinosa is located in the subgenital pockets of L. lucerna such that one-half of its cephalothorax is exposed to the outside. The crabs feed at the expense of the medusa, ingesting some portion of its food. A few specimens of the crab have been found, mostly females; the only male was of a somewhat larger size.     

Responses of the saucer scallop Amusium balloti to potential predators

A high natural mortality rate has been documented for the saucer scallop Amusium balloti, an Australian scallop found on sediment bottoms at 30–60 m deep, but little is known about the causes of mortality. We studied escape responses of A. balloti to five consumers common in the bycatch of the scallop fishery as a means of identifying potential predators. The scallop showed a negligible to weak response when touched with the sea star Pentaceraster regulus and the red portunid crab Portunus rubromarginatus. The response was similar to that observed when the scallop was touched with a plastic object. In contrast, A. balloti showed a consistent and vigorous swimming response to contact with the slipper lobster Thenus orientalis, the blue swimmer crab Portunus pelagicus and the coral crab Charybdis cruciata. This was not a generalized response to crustaceans, given the scallop's weak response to the red portunid crab. This is the first report of a scallop that has a strong swimming escape response to contact with decapod crustacean predators.     

Identification and characterization of microsatellite loci in the spiny spider crab <Emphasis Type="Italic">Maja brachydactyla</Emphasis>

The spiny spider crab Maja brachydactyla in an important fishery resource throughout its distribution range (Northeast Atlantic). Here we describe the isolation of nine microsatellite loci for this species. These new markers were tested in 20 crabs from NW Spain. The number of alleles ranged from 3 to 20 and expected heterozigosity from 0.57 to 0.95. All loci followed Hardy–Weinberg expectations except mMb33 and mMb307, which could be affected by null alleles. Some of these loci seem to be better fitted by a multi-step substitution process.     

Environmental effects of introducing whitefish,Coregonus lavaretus (L.), in Lake Ring

The impact of whitefish (Coregonus lavaretus (L.)) on the trophic structure of eutrophic lakes was studied in Lake Ring, a small eutrophic Danish lake (22.5 ha, mean depth 2.9 m) in which the natural fish fauna is dominated by pike (Esox lucius L.), perch (Perca fluviatilis L.), and eel (Anguilla anguilla (L.)), roach (Rutilus rutilus (L.)) and burbot (Lota lota (L.)) being the only other fish species present. A total of 10993 0+ whitefish were stocked in the lake from October 1989 to July 1990 and the structure of the fish, zooplankton and benthic invertebrate communities studied during the period 1989–1991. Stomach contents analysis revealed that the whitefish mainly ate Daphnia and copepods in 1990–1991, the proportion of copepods decreasing with increasing size of the fish and Daphnia being the overall most important food source. The density of Daphnia in the lake decreased from 72 ind. 1^-1 in 1989 to 9 ind. 1^-1 in 1991; concomitantly the large species Daphnia magna and D. pulex almost disappeared and the density of cyclopoid copepods increased from 72 to 101 ind. 1^-1, presumably because of improved food conditions, while that of calanoid copepods remained virtually unchanged. As a result chl-a increased from 19 to 47 µg 1^-1 and Secchi depth decreased from 2.4 m to 1.7 m, despite there being no change in total P and total N (0.6 mg P 1^-1 and 1.3 mg N 1^-1, respectively). Changes were also observed in the benthic invertebrates; Chaoborus, oligochaetes, and chironomids all decreased, whereas Pisidium increased. It is concluded that the stocking of whitefish in eutrophic lakes for commercial purposes may delay their recovery, or even lead to enhanced eutrophication.     

Class-specific epitopes detected by polyclonal antibodies against the secretory products of the subcommissural organ of the dogfish Scyliorhinus canicula

We have raised antisera against extracts of the subcommissural organ (SCO) of the dogfish, Scyliorhinus canicula L. Brains of 2900 specimens were collected in acetone, and the region containing the SCO and posterior commissure was removed and extracted in three different media. Antisera against these crude extracts were raised in rats and rabbits. Sequential absorptions of the antisera with extracts from different regions of the dogfish brain were performed to eliminate unwanted antibodies. When used to immunostain sections of the whole central nervous system of the dogfish, these purified antisera reacted selectively with the SCO-Reissner's fiber complex. An antiserum against bovine Reissner's fiber was also used. The antisera against the dogfish SCO and bovine Reissner's fiber showed the same staining pattern in the SCO and the Reissner's fiber of the dogfish. For comparative purposes, the brains of 15 vertebrate species from all vertebrate classes were immunostained with both antisera. The anti-dogfish SCO serum reacted with the SCO of the dogfish and that of other phylogenetically related elasmobranch species. Neither the SCO of a primitive elasmobranch species, Heptranchias perlo, nor the SCO of the other classes of vertebrates reacted with the anti-dogfish SCO serum. However, the antiserum against bovine Reissner's fiber reacted with the SCO of all the investigated species. It is concluded that some epitopes (or compounds) in the secretory material of the SCO are class-specific, whereas others are conserved and are synthesized by the SCO in most vertebrate species.     

The invasive green crab and Japanese shore crab: behavioral interactions with a native crab species,the blue crab

Blue crabs, Callinectes sapidus (Rathbun), are an ecologically and commercially important species along the East coast of North America. Over the past century and a half, blue crabs have been exposed to an expanding set of exotic species, a few of which are potential competitors. To test for interactions with invasive crabs, juvenile C. sapidus males were placed in competition experiments for a food item with two common non-indigenous crabs, the green crab Carcinus maenas (L.) and the Japanese shore crab, Hemigrapsus sanguineus (De Haan). Agonistic interactions were evaluated when they occurred. In addition, each species’ potential to resist predators was examined by testing carapace strength. Results showed that C. maenas was a superior competitor to both C. sapidus and H. sanguineus for obtaining food, while the latter two species were evenly matched against each other. Regarding agonism, C. sapidus, was the “loser” a disproportionate number of times. C. sapidus carapaces also had a significantly lower breaking strength. These experiments suggest that both as a competitor, and as potential prey, juvenile blue crabs have some disadvantages compared with these common sympatric exotic crab species, and in areas where these exotics are common, juvenile native blue crabs may be forced to expend more energy in conflict that could be spent foraging, and may be forced away from prime food items toward less optimum prey.     

Age and growth in Peale's dolphin (Lagenorhynchus australis) in subantarctic waters off southern South America

The Peale's dolphin, Lagenorhynchus australis, is a mainly coastal and one of the most often seen species off southernmost South America from 33°S off Chile and 38°S off Argentina to south of Cape Horn. Although a common species, its IUCN status is “Data Defficient”, so any information on this species is relevant. Age, growth and physical maturity were examined in skeletons of 57 specimens of this species, mostly from the coasts of Tierra del Fuego, Argentina; this represents most of the known specimens of this species available in museum and private collections. Most specimens were by-catch in shore-set gillnets or had been harpooned for crab bait. Age was determined for 23 specimens, all from Tierra del Fuego. The maximum age was 13 years for a 199 cm female. The largest female in this survey was 210 cm, the largest male 205 cm in total length (12 years), but this probably does not represent the maximum length for this species. Only two animals, of 12 and 13 years, were physically mature. Animals reach asymptotic length (188 cm) with less than the 30% of the vertebral epiphyses fused. The animals in this study were mainly subadults, as has been found for other southern by-caught dolphins. Growth was studied for total length using 18 osteological characters with the Gompertz model. We propose that zygomatic width can be used to estimate total length for incomplete beach-cast specimens.     

Intraspecific Variation in Chemical Attraction of Rice to Insect Predators

The olfactory response of predators of the brown planthopper,Nilaparvata lugensStål, to different genotypes of rice (14 cultivars and breeding lines ofOryza sativaL. and 1 wild species,Oryza nivaraSharma et Shastry) was measured in an airflow olfactometer. Odor from rice plants attracted more females of the mirid predatorCyrtorhinus lividipennisReuter than plain air (control) on only 6 of the 15 rice genotypes. Orientation ofC. lividipennistoward volatiles of certain rice genotypes was apparent even when the plants were free of the brown planthopper. However, the predator distinguished between prey-infested and uninfested plants and preferred plants with eggs over plants with nymphs. The predator did not distinguish different stages of plant growth (vegetative, booting, or flowering). Plants artificially injured to simulate brown planthopper oviposition wounds were not as attractive to the predator as plants on which the planthopper had oviposited. The preassay preconditioning on the cultivar TN1 did not produce a predator bias for this genotype. This suggests that rearing effects or chemically mediated associative learning reported for some natural enemies did not influenceC. lividipennis'host response. Results with another predator, the coccinellidMicraspis hirashimaiSasaji, produced less consistent behavior. Planthopper-infested plants attracted more females ofM. hirashimaithan unifested plants in only 1 of the 12 rice genotypes evaluated. Implications for augmenting predators by rice cultivar selection and modification are discussed.     

Production, use and fate of Chilean brown seaweeds: re-sources for a sustainable fishery

Chile is an important producer of brown seaweeds representing 10% of world supply. Landings of Chilean kelp fluctuated between 40,000 t.year⁻¹ in the early ‘80s to 250,000 t.year⁻¹ more recently. Commercialized algae come from natural populations and no mass-cultures of involved species have been established. Four species of brown algae are commercially collected in the country: Lessonia trabeculata, L. nigrescens, Macrocystis pyrifera and M. integrifolia. Since 2000, the demand of alginate sources and food for cultivated abalones dramatically raised the harvesting of these species. Direct evaluations of Lessonia spp. and Macrocystis standing-stocks were made along 700 km of coast in northern Chile. Lessonia spp. estimated populations exceed 900,000 t, whereas M. integrifolia does not exceed 300 t. The insights provided indicate that sustainability of Chilean kelp subjected to intense harvesting would require management programs including the following bio-ecological recommendations: (1) to harvest the entire plant including the holdfast; (2) to harvest plants larger than 20 cm in diameter; (3) to harvest plants sparsely, selecting mayor specimens; (4) rotation of harvesting areas; and (5) for Macrocystis, to cut the canopy 1–2 m from the surface. They must be implemented in a National Program of Kelp Management, elaborated by government, scientists, fisherman, and industry.     

The infestation and dispersion patterns of Carcinonemertes spp. (Nemertea) on their crab hosts

Seasonal changes in the infestation and dispersion patterns of egg predatory nemerteans on their crab hosts were analyzed. Marked differences in the seasonal patterns of infestation were noted between worm species, yet, common patterns in the aggregation of the worms were found. Worm aggregation increased at the onset of the reproductive seasons of the hosts, and at the nadirs of the reproductive seasons for those hosts with year round breeding. The aggregation patterns of two worm species fluctuated with the physical environment of their estuarine hosts. Salinity changes as a result of seasonal rains may have caused changes in the underlying dispersion patterns of Carcinonemertes epialti on Hemiarapsus oregonensis, and C. mitsukurii on Portunus pelagicus. Lastly, the embryogenic cycle of the host species was significant in shaping the infestation and aggregation patterns of C. epialti on Cancer anthonyi and C. regicides on Paralithodes camtschaticus. Worm immigration and emigration were linked to crab embryogenesis and directly influenced the dispersion patterns of the worms.