Pacific Cod Gadus Macrocephalus Research Articles

Vertical position, specific gravity and swimming ability of Pacific cod Gadus macrocephalus yolk-sac larvae reared at four temperatures

Vertical position and movement rate were measured in the yolk-sac larvae of the Pacific cod Gadus macrocephalus at different rearing temperatures (3, 5, 7, and 9 °C) and an identical temperature of 5 °C in experimental columns during the initial 3 days post-hatch (dph). Larval specific gravity was also measured through sinking velocities. Yolk-sac larvae swam upward and initially (0 dph) remained in the upper section of the experimental column through intermittent upward swimming, and gradually moved to near-neutral buoyancy at 3 dph at corresponding rearing temperatures. Rearing temperature significantly affected the swimming ability: at 0 dph, vertical movement rates measured at 5 °C were low in the yolk-sac larvae reared at warm temperatures. However, no such difference was observed at 3 dph. The difference in vertical movement rate may have resulted from the temperature-mediated body sizes (standard length) and yolk-sac sizes (yolk-sac volume) at hatching. Specific gravity did not change for the varying temperatures during the initial 3 days, but decreased as ontogeny progressed. Therefore, we suggest that Pacific cod yolk-sac larvae achieve a demersal-pelagic habitat transition through upward swimming and increasing buoyancy.

Interactive effects of incubation temperature and salinity on the early life stages of pacific cod Gadus macrocephalus

The combined effects of incubation temperature and salinity on the early life stages of Pacific cod Gadus macrocephalus were examined under controlled laboratory conditions. Data were collected from two synchronized experiments. Experiment 1 was designed to evaluate the interactive effects of incubation temperature and salinity on the hatchability of fertilized G. macrocephalus eggs. Experiment 2 was set up to evaluate the interactive effects of incubation temperature and salinity on the time from hatching to 50% mortality of the non-fed yolk-sac larvae (M50). The results show that temperature could significantly influence the development and hatchability of the larvae, as well as the hatching characteristics of G. macrocephalus. Viable hatch was significantly influenced by salinity when the upper and lower thermal limits were approached and shows the synergism of low salinity on egg development at low-temperatures and conversely inhibitory effects of low-salinity at high-temperatures. Data on developmental rates as influenced by temperature were presented at each tested salinity level. No influence of salinity was found at the temperature levels tested. Dome-shaped quadratic curves were fitted to the relationship between temperature and the incidence of larval size and yolk storage at hatch for most of the tested salinity levels. The effect of salinity across all temperatures, however, had a much smaller influence on larval size and no effect on yolk storage at hatch. The influence of temperature on larval duration (time from hatching to M50) could be described in all cases by an exponential power function. Evidence on the synergism of low salinity at low-temperatures and conversely inhibitory effects of low-salinity at high-temperatures was also observed. The results were discussed in reference to salinity modified temperature effects on the early life stages of G. macrocephalus. Maximum hatchability and larval size at hatch, and moderate salinity tolerance and larval duration suggest an optimal temperature range of 4°C to 6°C for the survival and development of the early life stages of G. macrocephalus in the field.

Trophic status and trophic interactions of common predatory fish species of the West Kamchatka shelf

Feeding and trophic relationships have been studied for the common benthic predatory fish species of the West Kamchatka shelf in 2008—the Pacific cod Gadus macrocephalus, great sculpin Myoxocephalus polyacanthocephalus, plain sculpin M. jaok, sea raven Hemitripterus villosus, and whitespotted greenling Hexagrammos stelleri. Crustaceans and fish are the main food components of the great sculpin, plain sculpin, Pacific cod, and whitespotted greenling; sea raven feeds on the fish mostly. The ontogenetic changes of the food spectra have been tracked for all the studied species. The indexes of the food similarity evidence to the possible food competition between the Pacific cod and all the other species; however, the dissimilarity of the ecological niches may serve as the adaptation to decrease the food competition. The trophic levels of all the studied predators vary from 3.41–4.50; i.e., they are the tertiary consumers. It is justified that the Pacific cod, whitespotted greenling, plain sculpin, and great sculpin are the facultative polyphagous predators, and the sea raven is the obligate bentho- and ichthyophagous species on the West Kamchatka shelf.

On factors for separation of the stock of beluga whale <i>Delphinapterus leucas</i> in the Anadyr Gulf of the Bering Sea

New eco-ethological data on the Anadyr stock of beluga whales are presented based on 14-year (2000-2013) studies by methods of satellite tracking telemetry, multi-spectral aerial surveys and genetic analysis, as well as traditional and ecosystem-based approaches. Possible factors of the separate stock formation in the Anadyr Gulf are discussed, as geographic isolation, environmental conditions, foraging resources, elimination of the beluga whales, and biological isolation (on the results of genetic analysis). The beluga whales are well-adapted to oceanographic conditions and ice regime of the Arctic waters that is realized in their relationship with edge of the sea ice, ability to live in both salt and fresh waters (they enter rivers), and versatility in feeding. Their ice-associating, high sociality, and white protective coloration provide protection against killer whales and other predators and their eury-halinity allows to expand the feeding grounds both to the sea and rivers and hunt for both freshwater, anadromous and marine prey. The food spectrum of beluga whales in the Anadyr estuary is very wide and includes 12 fish species and 1 crustacean species. In the summer-autumn season, the salmons are the most significant part of the diet, as chum salmon Oncorhynchus keta , pink salmon O. gorbuscha and arctic char Salvelinus malma , whereas arctic smelt Osmerus mordax dentex , saffron cod Eleginus gracilis , sculpins Cottidae sp., anadyr whitefish Coregonus anaulorum , and siberian whitefish Coregonus sardinella are presented in the diet to a lesser extent. There is supposed on the base of episodic net surveys, that the beluga whales feeding in marine areas is more diverse, and the most important their prey in the sea are walleye pollock Theragra chalcogramma , pacific cod Gadus macrocephalus , flounders Pleuronectidae sp., sculpins Cottidae sp., capelin Mallotus villosus catervarius , polar cod Boreogadus saida , halibuts Pleuronectidae sp., stingrays Bathyraja , herring Clupeidae sp., and several species of decapod crustaceans Hyppolitidae sp. and Lithodidae sp. Natural enemies of beluga whales are killer whale Orcinus orca , polar bear Ursus maritimus , and predatory form of pacific walrus Odobenus rosmarus . Rather large number of beluga whales are eliminated by the sea ice, up to 80 animals annually, that exceeds in several times the aboriginal landings in Chukotka. Parasitic fauna of the beluga whale is still unclear and requires special investigations; the cases of epizooty are unknown in the Anadyr Gulf. Philopatry is proper to the Anadyr beluga whales, with preference of the Anadyr estuary and the Anadyr Gulf as their habitats, that is explained by optimal for them environments and high food capacity. Unique adaptation of beluga whales to the environments of the Anadyr estuary is their ultrasonic vocalization in the high-turbidity waters. Genetic analysis shows a differentiated distribution of the beluga whales haplotypes in different areas of the North Pacific, so the stock of the Anadyr Gulf is significantly isolated in the post-glacial times. Low anthropogenic pressure on beluga whales in the Anadyr Gulf allows them to maintain their stock there.

Specifics of the distribution of commercial fishes in the northwestern Bering Sea

Data of trawling censuses (1996–2005) are used to analyze the specifics of the distribution of commercial fishes present in the northwestern Bering Sea in summer and autumn and forming accumulations in the waters of the Olyutorsky-Navarin region. Areas with maximum fish density usually have a temperature range of 2.4–4.0°C in near-bottom water layers; they are observed in the same localities, with some interannual variation: in the middle shelf, with depths of 50–160 m southwest of Cape Navarin to Cape Khaiidin and between the Dezhneva Bay and Expeditsii Bay, and in waters of the continental slope adjacent to the first area, with depths over 270 m. The accumulations on the shelf mainly consist of such commercial species as the Alaska pollock Theragra chalcogramma, Pacific cod Gadus macrocephalus, saffron cod Eleginus gracilis, northern rock sole Lepidopsetta polyxystra, Alaska plaice Pleuronectes quadrituberculatus, and righteye flounders of the genus Hippoglossoides (H. robustus and H. elassodon); on the continental slope, they consist mainly of the Greenland halibut Reinhardtius hippoglossoides and Pacific halibut Hippoglossus stenolepis. The recorded density of fish in the Olyutorsky-Navarin region was the highest in 2004–2005 and the lowest in 1999, 2001, and 2002. This variation was determined mainly by the interannual variation in the fishing for cods (Gadidae), which reflected the emergence of abundant generations and migration activity in fishes of this family, as well as from differences in the efficiency of fishing gear. Fishing for many species can and should be performed simultaneously; special attention should be paid to the coastal areas of the Olyutorsky-Navarin region, where considerable fish resources (such as the saffron cod, Pacific halibut, and other righteye flounders) are present.

The effects of temperature and predator densities on the consumption of walleye pollock (Gadus chalcogrammus) by three groundfish in the Gulf of Alaska

Many multispecies models have assumed that prey density determines per-capita predator consumption rates, following a functional response relationship. However, empirical evidence suggests that a predator’s diet can also be influenced by a variety of environmental factors, including interactions with other predators. We used diet and abundance data from National Marine Fisheries Service (NMFS) bottom trawl surveys for three groundfish predators (Pacific cod (Gadus macrocephalus), Pacific halibut (Hippoglossus stenolepis), and sablefish (Anoplopoma fimbria)) in the Gulf of Alaska (GOA) to determine whether temperature or other species influence the consumption of walleye pollock (Gadus chalcogrammus). Using an information-theoretic approach, we tested for relationships between walleye pollock observed in predator stomachs and predator length, bottom temperature, prey availability (walleye pollock catch per unit effort (CPUE) scaled by observed prey lengths), and CPUE of the three predators and arrowtooth flounder (Atheresthes stomias). Predator length was positively related to walleye pollock presence and proportion of total diet mass in all predators. Increased temperatures negatively affected consumption of walleye pollock by Pacific halibut, but not the other predators. We found evidence for a number of interpredator effects of co-occurring predators, both positive (facultative) and negative (competitive). Surprisingly, observed prey density was not statistically significant with respect to consumption for these predators, suggesting that trawls sample the environment far differently than walleye pollock predators or species interactions are more complex than those used in previous multispecies models. These factors should be considered for future models contributing to ecosystem-based management.

Envelope surface ultrastructure and specific gravity of artificially fertilized Pacific cod Gadus macrocephalus eggs

The envelope surface ultrastructure and specific gravity of artificially fertilized eggs of the Pacific cod Gadus macrocephalus were examined. The unfertilized, demersal and slightly adhesive eggs of G. macrocephalus were almost spherical and had no oil globules. Wrinkled envelope surface with elaborated hexagonal reticulated patterns and type I micropyle were observed under a scanning electron microscope. The adhesiveness of the eggs was lost at the blastodermal-cap stage after fertilization. The micropylar canal was sealed by secretion of the perivitelline fluid, and the entire surface became rough. Numerous bacilli were deposited at the micropyle and the outer envelope surface at the late germ-ring stage and at the embryo five-eighths around the yolk stage. The micropyle was completely deformed at the embryo seven-eighths around the yolk stage. The specific gravity of the fertilized G. macrocephalus eggs ranged from c. 1·0316 to 1·0454. These values, however, sharply decreased towards the end stages of egg development to produce pelagic larvae. The ultrastructural changes in the micropyle and envelope surface of the G. macrocephalus eggs protected the embryo from microorganism infections and mechanical stress during the long incubation period. The adhesiveness and specific gravity of the eggs influenced their dispersion potential.

Observations of Seasonal Movement from a Single Tag Release Group of Pacific Cod in the Eastern Bering Sea

AbstractThe Pacific Cod Gadus macrocephalus in the eastern Bering Sea is the target of one of the most lucrative fisheries in Alaska; however, relatively little is known about the movement of Pacific Cod and how this interacts with intense fishing on local spawning aggregations of cod every spring (January–April). This study aimed to draw inferences on Pacific Cod movement using a single tag release group of fish and the fishery as a representative for movement by qualitatively examining both temporal and spatial patterns of tag recoveries. Based on the tag recoveries in this study and past genetic studies, there is evidence that Pacific Cod show both homing tendencies and site fidelity during the spring when large aggregations of cod form to spawn. This study also supports results from an earlier study on Pacific Cod movement in this region and presents new insights into cod movement patterns. The cod in this tag release group were widely distributed across the Bering Sea during the summer and fall months and returned to the vicinity of the release site in the spring, presumably to spawn. Understanding the movement of cod and their interactions with the fishery is essential to the successful management of the Pacific Cod stock.Received May 12, 2014; accepted October 7, 2014

The influence of maternal effects in larval survival on fishery harvest reference points for two life-history patterns

Increased larval viability with increased spawner age (i.e., maternal effects) have been observed in Atlantic cod (Gadus morhua) and Pacific rockfish (Sebastes spp.) stocks. Analytical results from a Beverton–Holt recruitment model indicate density-independent maternal effects affected the relative stock productivity and fishing rate reference points. We simulated populations based on Pacific cod (Gadus macrocephalus) and Pacific ocean perch (Sebastes alutus) to explore how estimates of reference points Fmsy and Fcrash are affected by maternal effects and potential interactions with life-history pattern, recruitment autocorrelation, and exploitation rate. Estimates of Fmsy and Fcrash were made from populations with maternal effects using either total larvae (proportional to eggs) or viable larvae (incorporating the maternal effect). Maternal effects have the largest impact upon estimated population productivity at high fishing rates. Estimates of Fmsy and Fcrash for cod were also affected by autocorrelated recruitment variability because of their reduced longevity compared with Pacific ocean perch. These results suggest the importance of evaluating the influence of maternal effects on estimated stock productivity on a case-by-case basis, particularly for depleted stocks composed of relatively young spawners.

Temperature‐mediated survival, development and hatching variation of Pacific cod Gadus macrocephalus eggs

Laboratory-validated data on the survival, development and hatching responses of fertilized Pacific cod Gadus macrocephalus eggs from the northern Japan stock were determined through an incubation experiment. The optimum temperature for survival until hatching ranged from 4 to 8°C. No significant difference in development rates was found between the populations from Mutsu Bay, Japan, and western Canadian coastal waters even though the samples may belong to different G. macrocephalus stocks. Gadus macrocephalus larvae hatched asynchronously from egg batches despite incubation under the same environment during their development. Both incubation temperature and temperature-mediated hatch rank affect size and yolk reserve. These data suggest that variations in water temperatures within an ecological range markedly influence the development rates, survival and hatching of the eggs, as well as the stage at hatch larvae of G. macrocephalus. Asynchronous hatching and the production of offspring with variable sizes and yolk reserves are considered evolutionary bet-hedging strategies that enable the species to maximize their likelihood of survival in an environment with variable temperatures.

Characterization of Acid-Soluble Collagen From Bone of Pacific Cod (Gadus macrocephalus)

Acid-soluble collagen (ASC) was isolated from Pacific cod (Gadus macrocephalus) bone. The ASC was rich in glycine. The amount of imino acid was lower than that of calf skin collagen, as was the transition temperature (48.6°C). Electrophoresis revealed two different α chains (α1 and α2), β-component, and γ-component. Fourier transform infrared spectroscopy measurement showed that ASC was in triple-helix structure. ASC had a solubility greater than 90% in a very acidic pH range (pH 1–4), and the solubility decreased with increasing NaCl concentrations up to 3%. Lyophilized ASC had a network ultrastructure with lace-like fibers, similar to calf skin collagen sponge.

Diel vertical migration of adult Pacific cod Gadus macrocephalus in Alaska

The diel vertical migration (DVM) of Pacific cod Gadus macrocephalus was examined using depth and temperature data from 250 recaptured archival tags deployed on G. macrocephalus in the eastern Bering Sea and in the Gulf of Alaska near Kodiak Island. DVM of two types, deeper during daytime (type I) and deeper during night-time (type II), occurred frequently (15-40% of all days) in G. macrocephalus released at all sites. Most individuals displayed both diel types, with each type of behaviour lasting up to 58 contiguous days, and day and night depth differences averaging c.8 m. Despite high among-individual variability, the occurrence of DVM varied significantly with the release site, season (i.e. day-of-year) and bottom depth, with the trend in seasonal occurrence nearly opposite for type I compared to type II DVM. No significance could be attributed to G.macrocephalus fork length, sex or ambient (tag) temperature. Trends in the magnitude of G. macrocephalus depth change were observed, with increased movement often occurring during night-time, dawn and dusk, and at release sites where the bathymetry was more complex. Both type I and type II DVMs were attributed to foraging on prey species that also undergo DVM, and increased vertical movements of G. macrocephalus during crepuscular and night-time periods were attributed to more active foraging during dim-light conditions when G. macrocephalus can potentially exploit a sensory advantage over some of their prey.

Phase transitions of phospholipids as a criterion for assessing the capacity for thermal adaptation in fish

This study examines the crystal-liquid crystal phase transitions of the major phospholipids, phosphatidylcholine (PC) and phosphatidylethanolamine (PE), from muscle tissue of marine fish living at temperatures of 0–4.1°C (the Pacific cod Gadus macrocephalus, banded Irish lord Hemilepidotus gilberti, Pacific halibut Hippoglossus hippoglossus, black edged sculpin Gymnocanthus herzensteini, dark colored flounder Pleuronectes obscurus, and plain sculpin Myoxocephalus jaok), as well as of fish living at 14 and 18°C (Pacific redfin Tribolodon brandti). The PC and PE phase-transition thermograms of all the investigated species displayed specific profiles. The largest share of the thermogram area at temperatures higher than those of the habitat was found for the PC (28–40%) and PE (47–82%) of the black-edged sculpin, dark-colored flounder, and the plain sculpin, which have reduced physiological activity at low temperatures. In the Pacific cod, banded Irish lord, and the Pacific redfin, this parameter was much lower, 0–18% (PC) and 0–39% (PE). The thermotropic behavior PC and PE was symbate in all fish, except for the cod and the plain sculpin. The transition enthalpy of PC in all the investigated species was 2.8 times higher than that of PE. To interpret the varied PC and PE thermogram profiles of fish with similar fatty-acid compositions, the data on the composition of the molecular species of these phospholipids appeared to be the most informative. This study suggests that each fish species has its own strategy for thermal adaptation, which is realized through a certain set of phospholipid molecular species.

Determining Environmental Impacts for Sensitive Species: Using Iconic Species as Bioindicators for Management and Policy

Environmental assessment of impacts, management, and policy are important aspects of protection of human health and the environment. Assessing the impacts of human activities requires selection of bioindicator species that can be used to assess, manage, and develop public policies that ensure ecosystem integrity, and therefore sustainability of social, cultural, and economic systems. With the use of Chinook Salmon (Oncorhynchus tshawytscha), Pacific Cod (Gadusmacrocephalus), Mallard (Anas platyrhynchos), and Red Knot (Calidris canutus rufa), we explore assessment and measurement endpoints, and their relationship to management and development of public policy. This combination of fish and birds provides a diversity of life histories, ecosystem roles, human values, and resource use to explore their use as bioindicators and endpoints. It also allows examination of 1) conservation and protection of species and biodiversity, 2) protection of ecosystems, 3) provision of goods and services, and 4) societal well-being.

Relationships between the Abundance of Pacific Lamprey in the Columbia River and Their Common Hosts in the Marine Environment

AbstractThe returns of Pacific Lamprey Entosphenus tridentatus to the Columbia River over the past decade have declined significantly compared with the peak returns of the 1950s and 1960s, with no quantifiable mechanisms identified. To determine if the abundance of documented host species in the marine environment is related to adult returns of Pacific Lamprey, we examined stock assessment data, commercial fishery statistics, and counts of adult fish at Bonneville Dam between 1997 and 2010. Significant positive correlations were observed between lamprey returns and abundance indices of Pacific Hake Merluccius productus, Walleye Pollock Theragra chalcogramma, Pacific Cod Gadus macrocephalus, Chinook Salmon Oncorhynchus tshawytscha, and Pacific Herring Clupea pallasii throughout the U.S. Pacific Northwest. Commercial landings of these species in Washington and Oregon were also significantly and strongly correlated to lamprey returns, with the exception of Walleye Pollock. Several of these fisheries have demonstrated significant reductions in mean landings since the 1950s and 1960s, and adult lamprey returns have declined proportionally. We further examined large‐scale and regional indices of oceanic productivity as a potential underlying mechanism. Multiple regression techniques indicated that host abundance was the principal factor in predicting lamprey returns, though inclusion of oceanic conditions increased the precision of the model. These results represent the first established relationship to recent trends of Pacific Lamprey returns to the Columbia River and indicate that spawning escapement is primarily a function of conditions experienced during the predatory phase of the life cycle. We hypothesize that Pacific Lamprey abundance in the Columbia River is cyclical in nature, but limited by availability of several host species over a potentially vast geographic range. Biologists and resource managers should reassess the relatively overlooked marine ecology of Pacific Lamprey.

Effects of temperature and gadid predation on snow crab recruitment: comparisons between the Bering Sea and Atlantic Canada

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 469:249-261 (2012) - DOI: https://doi.org/10.3354/meps09766 Effects of temperature and gadid predation on snow crab recruitment: comparisons between the Bering Sea and Atlantic Canada Laurinda A. Marcello1,*, Franz J. Mueter1, Earl G. Dawe2, Mikio Moriyasu3 1School of Fisheries and Ocean Sciences, University of Alaska Fairbanks, Juneau, Alaska 99801, USA 2Northwest Atlantic Fisheries Centre, Fisheries and Oceans Canada, St John’s, Newfoundland and Labrador A1C 5X1, Canada 3Gulf Fisheries Centre, Fisheries and Oceans Canada, Moncton, New Brunswick E1C 9B6, Canada *Email: laurinda.marcello@gmail.com ABSTRACT: Snow crabs Chionoecetes opilio are found in many subarctic ecosystems, where they are important components of marine food webs and support large commercial fisheries. Snow crab abundance is highly variable, but the causes of large changes in year-class strength are poorly known. We used a regression approach to examine the effects of snow crab spawning stock biomass, bottom water temperature, cold area or sea ice extent, and predation by Pacific cod Gadus macrocephalus or Atlantic cod G. morhua on snow crab recruitment in each of 3 ecosystems: the eastern Bering Sea, the Newfoundland-Labrador Shelf, and the southern Gulf of St. Lawrence. Comparing results across systems showed that cold ocean conditions during early life history were associated with increased snow crab recruitment or recruitment indices in all 3 ecosystems. However, we found no consistent evidence that spawning stock or gadid biomasses were significantly related to subsequent snow crab recruitment. Our results underscore the value of comparing multiple ecosystems and demonstrate the importance of ocean conditions in driving variability in snow crab populations. KEY WORDS: Snow crab · Recruitment · Environment · Predation · Spawning stock biomass · Eastern Bering Sea · Newfoundland-Labrador Shelf · Southern Gulf of St. Lawrence Full text in pdf format PreviousNextCite this article as: Marcello LA, Mueter FJ, Dawe EG, Moriyasu M (2012) Effects of temperature and gadid predation on snow crab recruitment: comparisons between the Bering Sea and Atlantic Canada. Mar Ecol Prog Ser 469:249-261. https://doi.org/10.3354/meps09766 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 469. Online publication date: November 26, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

Food habits of Pacific cod and walleye pollock in the northern Gulf of Alaska

Seasonal variations in the diets of Pacific cod Gadus macrocephalus and walleye pol- lock Theragra chalcogramma were examined from fish collected during 5 sampling periods from August 1998 to June 1999 in the Kodiak Island area in the Gulf of Alaska. Both species were shown to be generalist predators, eating a wide variety of fish and invertebrates. Pollock, which are limited to pelagic prey, can be considered more specialized than cod. Cod consumed 78 prey items, and pollock consumed 45 prey items, with 28 items shared by both species. Individual pol- lock, however, typically concentrated on a single prey item, while individual cod stomachs con- tained a wider variety of prey. The principal prey of Pacific cod was Tanner crab Chionoecetes bairdi, comprising >28% of the cod diet by weight. The most common prey item for walleye pol- lock was the euphausiid Thysanoessa. Over the 5 sampling periods, the prey evenness and niche width occupied by the 2 species were similar, but seasonal differences were evident.

On the spawning of Pacific cod Gadus macrocephalus in the southeastern waters off Onekotan Island

On the spawning of Pacific cod Gadus macrocephalus in the southeastern waters off Onekotan Island

표지방류 조사를 통한 거제 외포 주변해역 대구(Gadus macrocephalus) 자원량과 어획사망률 추정

We estimated the population size and fishing mortality of Pacific cod Gadus macrocephalus during the spawning season in waters off Woipo, Geoje Island, Korea, using a mark-recapture method. We marked and released 51 cod>50 cm in total length; six were recaptured by local fishermen during the period from December 15 to 31, 2009. The estimated population size was ca. 180,000 and the fishing mortality of the exploitable cod was 26%. Although we could assume a closed population due to the short survey period, we evaluated the uncertainty in the estimates by applying bootstrap resampling because the sample size was small. The estimated 95% confidence interval was 94,000-568,000 for the population size and 8-49% for fishing mortality. Our study demonstrated that the application of mark-recapture methods and bootstrap resampling can be useful in stock assessment for fisheries management in Korea, but requires a larger sample size, spatially extensive coverage, and sophisticated mark-recapture models based on a refined sampling design for reliable stock assessment and biological reference points in sustainable cod management.

모의실험을 통한 동남해안 대구(Gadus macrocephalus)의 가입당 생산 분석

We derived biological reference points for Pacific cod Gadus macrocephalus in southeastern Korean waters by applying a yield-per-recruit analysis based on a daily simulation that adopted size-dependent fecundity, growth, and natural mortality functions. This showed that the yield per recruit of Pacific cod can be maximized at an instantaneous rate of fishing mortality (F)