Variation In Catch Research Articles

Measuring trap efficiency for bark beetles (Col., Scolytidae)

Abstract: The relative efficiency of cylindrical, linear and cross‐barrier traps for trapping bark beetles was investigated based on a theoretical model. Using this model, the effective trap interception area of each trap type was calculated and trap efficiency was defined as the ratio of the effective interception area to the trap surface area. The relative efficiencies of the three trap types were calculated as the ratios of their respective effective interception areas. Based on this approach, assuming random directional movement of dispersing beetles, the order of efficiency of the three trap types, from highest to lowest, was linear, cross‐barrier and cylindrical. The expected ratios of trap catches based on the relative efficiencies of the three trap types were fitted to data from trapping experiments with the mountain pine beetle (Dendroctonus ponderosae Hopkins). In general, there was large variation in trap catches among traps of the same type but the ratios of mean catches per trap conformed to the expected ratios. The results indicate that the model of trap efficiency could be used for designing efficient traps. The methods presented are amenable for assessing the efficiency of other trap designs.

Diel catch variations in a shallow-water fish assemblage at Duće Glava, eastern Adriatic (Croatian Coast)

An assemblage of shallow-water fish was sampled with a small beach seine over monthly 24-h periods between April 2000 and March 2001 at the sandy beach Duće Glava in the eastern Adriatic. Monthly sets of samples were divided into day and night catches to examine the stability of diel differences in assemblage structure over a 1-y period. A total of 61 species was caught, of which six were exclusively diurnal and 12 were nocturnal. According to abundance and biomass of individuals during day and night, the most abundant species were categorized into several groups. Ophidion rochei was exclusively nocturnal, while Nerophis ophidion and Echiichthys vipera were mostly nocturnal. Diplodus annularis and Mullus surmuletus were slightly nocturnal. Diplodus vulgaris, Pomatoschistus marmoratus and Atherina boyeri lacked a diel pattern. Sardina pilchardus, Lithognathus mormyrus, Atherina hepsetus, Sarpa salpa and Mullus surmuletus abundance peaked for a few months, probably related to timing of spawning and recruitment. At the assemblage level, the diel per cent similarity index indicates that there were major differences between the day and night assemblages in April, September, March, and August with respect to number of individuals and September, October, May and March with respect to biomass.

Use of generalized linear models in analyzing the catch and effort data on the western king prawn Penaeus latisulcatus Kishinouye in the Gulf St. Vincent, Australia

Abstract The western king prawn Penaeus latisulcatus occurs in coastal waters off Western Australia, the Northern Territory, Queensland, New South Wales, and South Australia. In South Australia, it supports a commercial trawl fishery with an annual landed value of about AU$ 35 million. In this paper, I derive generalized linear models from an observational model of a sex-, age- and time-dependent model for a single prawn population, provide them with a firm theoretical basis, and make explicit some of their assumptions. Following an exploratory analysis by use of a generalized additive model, I use generalized linear models to analyze the commercial catch and effort data for the changes in its stock size with time, in fishing efficiency among vessels, in catch with time of day, fishing effort and area, and the effects of searching on catch. The results obtained by assuming that the catch follows independent log-gamma, log-normal, log-negative binomial, or log-Poisson distribution were similar. The relative exploitable biomass in the population immediately before the fishery was closed in 1991 was 31% of that when it was resumed in December 1993, remained at about the same level of December 1993 until 30 June 1995, slightly declined from 1 July 1995 to 30 June 1997, and was 81% of the level of December 1993 from 1 January 1998 onward. The relative instantaneous rate of fishing mortality of prawns of a particular sex and age was largely unchanged, but became less variable with time. Fishing efficiency was similar among all vessels. Normal fishing shots (using three nets) produced about three times the catch of searching shots (using only one net). Fishers learned during a sequence of shots, for prawn catch initially increased with shot number and then leveled off. A significant variation in catch with the time of day was detected, with the maximum catch occurring at 22 h. Finally, catch did not change proportionally with fishing effort; a 1% of change in effort led only to a nearly 0.9% of change in catch, so that raw catch per unit of effort decreased with fishing effort and is a biased index of the size of a prawn population. This work suggests that the current level of fishing effort cannot sustain the exploitable biomass of the population at the level of December 1993.

Use of generalized linear models in analyzing the catch and effort data on the western king prawn Penaeus latisulcatus Kishinouye in the Gulf St. Vincent, Australia

The western king prawn Penaeus latisulcatus occurs in coastal waters off Western Australia, the Northern Territory, Queensland, New South Wales, and South Australia. In South Australia, it supports a commercial trawl fishery with an annual landed value of about AU$ 35 million. In this paper, I derive generalized linear models from an observational model of a sex-, age- and time-dependent model for a single prawn population, provide them with a firm theoretical basis, and make explicit some of their assumptions. Following an exploratory analysis by use of a generalized additive model, I use generalized linear models to analyze the commercial catch and effort data for the changes in its stock size with time, in fishing efficiency among vessels, in catch with time of day, fishing effort and area, and the effects of searching on catch. The results obtained by assuming that the catch follows independent log-gamma, log-normal, log-negative binomial, or log-Poisson distribution were similar. The relative exploitable biomass in the population immediately before the fishery was closed in 1991 was 31% of that when it was resumed in December 1993, remained at about the same level of December 1993 until 30 June 1995, slightly declined from 1 July 1995 to 30 June 1997, and was 81% of the level of December 1993 from 1 January 1998 onward. The relative instantaneous rate of fishing mortality of prawns of a particular sex and age was largely unchanged, but became less variable with time. Fishing efficiency was similar among all vessels. Normal fishing shots (using three nets) produced about three times the catch of searching shots (using only one net). Fishers learned during a sequence of shots, for prawn catch initially increased with shot number and then leveled off. A significant variation in catch with the time of day was detected, with the maximum catch occurring at 22 h. Finally, catch did not change proportionally with fishing effort; a 1% of change in effort led only to a nearly 0.9% of change in catch, so that raw catch per unit of effort decreased with fishing effort and is a biased index of the size of a prawn population. This work suggests that the current level of fishing effort cannot sustain the exploitable biomass of the population at the level of December 1993.

Modelling seasonal catchability of the southern rock lobster Jasus edwardsii by water temperature, moulting, and mating

Seasonal variation in catchability of legal-sized male and female southern rock lobster Jasus edwardsii in a scientific reserve in south-east Tasmania, Australia, over a 15-month period was described by modelling the effects of water temperature, moulting and mating. Seasonal changes in water temperature described 62% of the variation of catchability for males, but were a poor predictor of catchability for females outside winter. Both moulting and mating was highly synchronised, although males and females moulted at different times of the year. This had a significant sex-specific effect on catchability, because the models developed here indicate that feeding and therefore catchability is decreased during moulting and mating and followed by an increased food consumption to compensate for the lack of feeding during these periods. Gaussian probability density functions were used to represent the timing and intensity of moulting, mating and subsequent compensation periods, and were combined with the description of seasonal temperature changes. Four Gaussian functions in agreement with independent biological data considerably improved the model fits for the catchability of males (R2=0.84). Adding a single Gaussian function to the temperature model, representing a combined moulting and mating period, provided a good fit to the variation in catchability of females (R2=0.90). However, the biological relevance of this model remained unclear during a second period of moulting and mating where empirical observations were missing.

제주도 함덕 연안의 정치망 어획량 변동

Fish catch by a set net in Hamdeuk fishing ground off Jeju Island were studied to determine seasonal variation of species composition and catch from 1998 to 2000. A total 72,022.9 kg was caught during the survey period, including Scomber japonicus and Trachurus japonicus of <TEX>$76.4\%$</TEX> in the total. The other dominant species were Siganus fuscescens, Loligo chinesis, Seriola dumerili, Sepioteuthis lessoniana, Sardinops melanostictus, and Seriola lalandi accounting to <TEX>$20.0\%$</TEX> of the total. The fishing period conducted by a set net in Hamdeuk fishing ground were from May to November. The catch by a set net were higher in summer than in spring and autumn and closely related with the seasonal variation of sea water temperature. The catch was higher in 1998 than In 1999 and 2000, which was related to the sea water temperature in fishing ground.

Behavioural consequences of density-dependent habitat use in juvenile cod Gadus morhua and G. ogac: the role of movement and aggregation

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 272:257-270 (2004) - doi:10.3354/meps272257 Behavioural consequences of density-dependent habitat use in juvenile cod Gadus morhua and G. ogac: the role of movement and aggregation B. J. Laurel1,*, R. S. Gregory1,2, J. A. Brown1, J. K. Hancock1, D. C. Schneider1 1Memorial University of Newfoundland, Ocean Sciences Centre, St. John¹s, Newfoundland A1C 5S7, Canada 2Department of Fisheries and Oceans, St. John¹s, Newfoundland A1C 5X1, Canada *Email: blaurel@mun.ca ABSTRACT: Fish behaviour can change to accommodate a variable environment, but changes in behaviour have not been considered in the context of density-dependent habitat use. In Bonavista Bay, Newfoundland, we measured how fish density movement and schooling behaviour changed with habitat in 2 gadids, Atlantic cod Gadus morhua and Greenland cod Gadus ogac, using a combination of field-seines, mark-recapture and laboratory experiments. Density estimates from seines (n = 427) over 5 yr (1996, 1998 to 2001) indicated that these species associated with eelgrass but periodically were detected in high abundance over unvegetated habitat (i.e. sand). Within-site catch variation indicated both species aggregated more in sand than eelgrass habitat, and, in Atlantic cod, aggregations over sand increased as density in eelgrass increased. Although such patterns in catch data could be interpreted as due to the effects of differential mortality between habitats, a mark-recapture experiment indicated that both species of cod were not site-attached and moved between seine locations. Furthermore, video-analysis from laboratory experiments demonstrated that cod formed tighter aggregations over sand compared to eelgrass habitats. Our results suggest that juvenile cod modify their behaviour with changing density, possibly as a means of exploiting poor-quality habitats when high-quality habitats are saturated with conspecifics. Consequently, habitat suitability for Atlantic cod may be a dynamic rather than fixed variable in density-dependent habitat models. KEY WORDS: Density-dependence · Habitat selection · Atlantic cod · Greenland cod · Aggregation · Shoaling Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 272. Online publication date: May 19, 2004 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2004 Inter-Research.

Hydrometric and Meteorological Factors Affecting the Seaward Migration of Silver eels (Anguilla anguilla, L.) in the Lower River Shannon

European eels, Anguilla anguilla, L., are captured in coghill nets at three commercial weirs on the Irish River Shannon during their autumn/winter seaward migration. The variations in daily silver eel catches were analysed in relation to environmental conditions, especially hydrometric and meteorological factors. Three multivariate environmental axes were distinguished with which daily eel catches could be correlated. The relative importance of various hydrometric, meteorological and temporal (seasonality, lunar phase) factors was identified, showing how hydrological and meteorological factors generally obscure the underlying lunar periodicity of the silver eel migrations at Killaloe.

남서부 동해에서 1970년대의 기후체제전환이 생태계의 구조에 미친 영향

The changes in structure and abundance of taxon or species groups in the East Sea ecosystem were compared between pre- and post-Climatic Regime Shift (CRS) occurred in the mid 1970s using an ECOPATH model. Although the East Sea ecosystem consisted of primary producers, primary consumers, secondary consumers and terminal consumers most species groups were classified as secondary consumers. The mean trophic level between pre- and post-CRS increased from 3.09 during the pre-CRS period to 3.28 during the post-CRS period. Total biomass of the species groups in the East Sea ecosystem increased by due to the CRS, and total catch increased by The most significant differences between pre- and post-CRS models occurred at the mid/high trophic levels occupied by fishes and cephalopods. Relative contribution of the different species groups to the total energy flow was calculated for the trophic level III. As a result, the status by the dominant species in the East Sea ecosystem shifted from cephalopods to walleye pollock due to the CRS. Relative contribution of 5 species, which were commercially important, such as Pacific saury, Pacific sardine, filefish, walleye pollock and sandfish in trophic level III, were also changed due to the CRS. Finally, the CRS turned out to cause large variations in biomass and catch of fisheries resources as well as the status and role of the major species.

Seasonal variation and environmental influences on juvenile banana prawn ( Penaeus merguiensis) abundance in a subtropical estuary (Logan River) of eastern Australia

Although the life history–environment relationship for juvenile Penaeus merguiensis in tropical regions has been well documented, little is known about the species towards the subtropical limits of its range. Seasonal patterns of abundances of juvenile and postlarval P. merguiensis were studied in the Logan River, a subtropical estuary in eastern Australia from January 1998 to July 2000. Prawns were sampled using a small beam trawl at fortnightly intervals when they were abundant and monthly intervals at other times. The prawns ranged in size from 1.8 to 22 mm in carapace length (CL), with a mean size (±1 SE) of 6.7±0.1 mm CL and were caught at densities of up to 14.2±3.3 prawns m −2. Postlarvae were caught from January to July, with peaks in April and May; and juveniles were abundant from December to June, although this varied between years. The numbers of postlarvae, temperature and rainfall explained 23% of the overall variation in juvenile catches. Temperature and rainfall also explained some of the variation in postlarval catches (9.9%). Recruitment varied considerably between years, and was the highest in years when rainfall was low (1998 and 2000). In general, both the seasonal patterns of catches of postlarval and juvenile P. merguiensis, and environmental processes affecting their abundance were similar to tropical areas. However, one notable difference was that recruitment occurred over a more restricted time period in the Logan River than in tropical regions.

The Role of Estuaries in South African Fisheries: Economic Importance and Management Implications

Existing catch data for 129 of 255 functional estuaries on the South African coastline were reviewed and the relationships between fish catch and estuary size, type and biogeographical region analysed using simple and multivariate models. The best predictive models were obtained by analysing data separately for each biogeographical region. Estuary size alone explained >80% of the variation in catch in the warm temperate region and >90% of the variation in catch in the cool temperate and subtropical region. Further analysis of the two main estuary types, i.e.permanently open and temporarily open/closed estuaries revealed a steeper regression slope and therefore greater productivity for the permanently open systems. Estuary size (ha) and type (five) were used to explain catches within the warm temperate and subtropical regions using general linear models. The models were able to explain 82 and 98% of the variance in catches for the two regions respectively, and both were significant (p < 0.001). These models were applied to estuary type and size data for all 246 estuaries in the two regions and a total catch of 1 840 tons per year was estimated. Including the cool temperate region the total estuarine catch in South Africa was estimated at 2 480 tons per year. In all, 50% of the estuarine catch was attributed to commercial seine and gillnet fisheries, 46% to recreational angling and 4% to traditional trap and spear fisheries. Total catch value was R433 million per year, of which 99% could be attributed to recreational angling. Estuarine contribution to the inshore marine fisheries was estimated at approximately R490 million per year, estuarydependent species constituting 83% of the catch of the recreational shore and commercial seine and gillnet fisheries and only 7% of the catch of the recreational spearfishery and commercial and recreational boat fisheries. In 2002, the total value of estuarine and estuary-dependent fisheries was estimated to be R1.251 billion.

Fluctuation in stock properties of north‐east Arctic cod related to long‐term environmental changes

AbstractFrom a historic perspective, the north‐east Arctic cod stock, which is found in the Barents Sea–Svalbard region, has been the most productive gadoid stock in the Atlantic. Variation in catch has always been large, but during the last 10–15 years catch and stock abundance have reached the lowest level on record. Three major causes of variation have been discussed: (i) stock reduction through exploitation; (ii) environmental influences on recruitment; and (iii) species interaction effects on maturation, growth and mortality. In addition, interactions among these three sources might be important. The influence of each specific factor is difficult to evaluate from incidental observations and short‐term time series. In this respect, the time series on catches and on biological and environmental information of this stock, which partly extend back to the 19th century, occupy a unique position in comparison to data on most other stocks. In this paper, fluctuations in catch and stock abundance are compared with changes in recruitment, size/age and growth. This information is discussed in view of historic variation in ecology and environment. The stock has been under particularly high exploitation pressure since the mid‐1970s. Further, large changes in growth rates and poor recruitment to the commercially exploited stock are characteristic of late 1980s and throughout the 1990s. The analysis shows that substantial long‐term variation might underlie short‐term variability, and more importantly, that long‐term changes roughly coincide with similar fluctuations in the environment. Such factors might substantially affect the relationship between spawning stock and recruitment, which is also apparent from the difference in conclusions reached by various published studies. Consequently, it is suggested that using a steady‐state perspective for the population dynamics may lead to mismanagement and to a reduction of the long‐term yield from this stock.

Geographic Variation in Pheromone Chemistry, Antennal Electrophysiology, and Pheromone-Mediated Trap Catch of North American Populations of the Obliquebanded Leafroller

The total and relative amounts of (Z)-11-tetradecenyl acetate (Z11-14:Ac), (E)-11-tetradecenyl acetate (E11-14:Ac), (Z)-11-tetradecen-1-ol (Z11-14:OH) and (Z)-11-tetradecenal (Z11-14:Al), and the EAG response of male antennae to these pheromone gland compounds were compared in laboratory reared Choristoneura rosaceana Harris (Lepidoptera: Tortricidae) from British Columbia, Michigan, Ontario, New York, and Quebec. A field trapping experiment was conducted in each of these locations to determine the effect of Z11-14:Al on the numbers of moths captured. The amount of each of the four pheromone-gland compounds declined successively in moths from British Columbia, Quebec, Ontario, Michigan, and New York. The relative amount of Z11-14:Ac was greatest in moths from New York and smallest in moths from Ontario, whereas the relative amount of E11-14:Ac was greatest in moths from Ontario and smallest in moths from British Columbia. Moths from Ontario, Quebec, British Columbia, Michigan, and New York contained decreasing relative amounts of Z11-14:OH and Z11-14:Al. There was a trend of increasing antennal sensitivity to each of the four pheromone-gland compounds in moths from New York, Michigan, Ontario, Quebec, and British Columbia. The addition of 1% Z11:Al to a three compound blend of Z11-14:Ac, E11-14:Ac and Z11-14:OH (97:2:1) resulted in a >twofold increase in average trap catch in British Columbia, Ontario, and Quebec; this compound had no effect on trap catch in Michigan or New York.

INCIDENTAL CATCH OF DOLPHINS IN TRAWLING FISHERIES OFF PATAGONIA, ARGENTINA: CAN POPULATIONS PERSIST?

The incidental mortality of dusky dolphins (Lagenorhynchus obscurus) in the Patagonian trawling fishery is a well-known problem, especially in mid-water trawl fisheries for shrimp and anchovy. Therefore, it is necessary to determine if recent levels of dolphin bycatch are compatible with the persistence of the dusky dolphin population. This was assessed by comparing annual bycatch rates with a sequence of critical values. These values were based on the maximum rate of increase (rmax) = λ − 1, where λ is the finite rate of increase. The finite rate of increase was estimated from a Leslie matrix where Monte Carlo procedures were employed to incorporate parameter uncertainties (age at first reproduction, survival rates, and fertility). Model life tables were used for survival, and reproductive parameters were estimated from available data on calving interval and age at sexual maturity. Uncertainties associated with annual bycatch rates were also included in the analysis through another randomization procedure that incorporated the variability in dolphin catch per unit effort, nominal fishing effort, and population size. This modeling approach rendered frequency distributions for the parameters of interest. Considering the critical values for incidental mortality rate as (1/2)R = (1/2)rmax and (1/4)R = (1/4)rmax, and a 2-yr calving interval scenario, the probability that recent dolphin bycatch rates exceed the maximum annual removal rates were higher than 0.3. These results suggest that incidental mortality due to fishing could be, or may become, a threat for the dusky dolphin population off Patagonia. Therefore, a more accurate and intense monitoring program is needed to avoid the decline of this population. Also, this issue should be included in the fishery management strategies to be implemented in the near future.

Patterns in diel variation of cod catches in North Sea bottom trawl surveys

The international bottom trawl surveys (IBTSs) in the North Sea are mainly conducted during daytime to avoid bias in abundance indices based on survey data caused by variation in fish catch rates between day and night. In this analysis, we investigated variation of catch rates within daytime hours. We used fine scale information from the summer 1999 German small-scale bottom trawl surveys (GSBTSs) in 10 small areas evenly spaced in the North Sea. The analysis was performed for cod ages 0–4+ using generalised linear models, where catch rates are modelled as a function of time of day together with environmental covariates. Results show significant variation of catch rates within daytime. Catch rates in shallow areas, where the water column was not stratified, were relatively low in the early morning, increased to a peak at around 14.00 h and returned to low levels thereafter. Except for age 0 fish, rates in deep stratified areas decreased during day hours. To help interpretation of the patterns, analysis of data from hauls conducted around the clock during 1996 GSBTS in stratified areas were performed. Results indicated diurnal fluctuation with a peak at around 8.00 h and low night rates. Abundance indicators can be affected if surveys are not randomised with respect to time of day. This can be corrected with modelling if relevant information is collected.

Environmental influences on the trawl catches in a bay-estuarine system of Goa, west coast of India

The degree of relationship between trawl catch and environmental variables was assessed in a bay-estuarine system of Goa, west coast of India using multivariate techniques. The demersal fish assemblage was dominated by the families, Leiognathidae, Sciaenidae, Clupeidae, Cynoglossidae and Stromateidae and were considered to be typical for the Indo-Pacific. Patterns in community-structure were analyzed by principal component analysis (PCA) which identified five major species-groups that explained 66% of the variation in absolute fish biomass. PCA was also performed using 13 environmental variables to reduce data set variability to four components which accounted for 75% of environmental variation. The model that best explained variation in absolute biomass based on maximum R 2 (adjusted) and minimum Mallows' C p statistic was 71% and included six variables such as dissolved oxygen, macrobenthic density, sediment pH, photosynthetic pigment (Chl a), particulate organic carbon (POC) and seston. The regression coefficients were significant ( P<0.05) and small values of C p indicated the preciseness of the developed model. Path analysis was used to construct a hypothetical causal path diagram to depict the interaction between fish biomass and environmental variables. The study demonstrated the most important variables with regard to environmental–biotic interactions, although the measured variables did not account for all the variation in trawl catches. Further studies elucidating ecologically meaningful relationships should be helpful in bay-estuarine fisheries management.

Accounting for length- and depth-dependent diel variation in catchability of fish and invertebrates in an annual bottom-trawl survey

Abstract Diel variation in the catchability of 51 species of fish and 13 invertebrate taxa from an annual bottom-trawl survey of the southern Gulf of St. Lawrence was examined using generalized linear (Poisson) models. Two approaches were used: comparative fishing based on spatially paired day and night tows, and statistical control of spatio-temporal effects in regular survey data. The two approaches provided remarkably similar results. Furthermore, species-specific results were consistent between survey time periods where different vessels were used, and were quite comparable to results from other studies conducted in separate geographic areas. Where sufficient data existed, we considered both length and depth dependencies in diel variation in catchability. We commonly found significant length dependency for groundfish species and the pervasive pattern was for higher nighttime catches of small fish, the magnitude of the effect generally decreasing with increasing length. In contrast, water depth had a much less important impact, except for a few species. When considered jointly, however, patterns in length/depth dependency were not always clear. Given length-dependent geographic and bathymetric patterns in species distribution, the potential for confounding length and depth dependencies exists and correction factors for diel variation in catchability need to be applied cautiously.

The Biology of Wahoo (Acanthocybium solandri) in the Western Central Atlantic

This contribution summarizes aspects of the biology of the wahoo, Acanthocybium solandri (Scombridae), that are pertinent to assessment and management of this species in the western central Atlantic (WCA). In this region wahoo is a target species for both commercial and recreational fisheries, and annual landings appear to have increased steadily over the last 30 years to in excess of 2000 mt. Wahoo is believed to be migratory, but little is known of the migration patterns. Significant seasonal variation in catches within the region indicates that it is seasonally abundant in most locations. Periods of peak abundance occur from the fall through spring in the southeastern and northern Caribbean islands, and are restricted to the warmer months (late spring through early fall) in the more northerly locations (northern Gulf of Mexico, North Carolina, and Bermuda). Wahoo exhibits early sexual maturity (within the first year) and a spawning season that extends from at least May to October. Females are multiple batch spawners and are highly fecund. Limited age and growth studies indicate that it is a relatively fast-growing species, has high mortality, and probably lives for 5-6 years. Wahoo is primarily piscivorous, although some invertebrates including squids are eaten. A relatively small number of parasite species have been associated with it. There is no evidence of more than a single shared stock of wahoo in the WCA, and recent genetic studies, using RAPD markers, suggest that stock boundaries may extend beyond this region. The status of the wahoo resource in the WCA remains unclear. Reliable wahoo catch and fishing effort data from the entire WCA, improved knowledge of migration patterns, reproductive characteristics and critical habitat (e.g., preferred spawning areas), validation of age, growth and mortality estimates, and a more comprehensive analysis of stock structure for the entire Atlantic are needed for informed wahoo stock assessment and management.

Settlement and distribution of Age-0 juvenile cod, Gadus morhua and G. ogac, following a large-scale habitat manipulation

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 262:241-252 (2003) - doi:10.3354/meps262241 Settlement and distribution of Age-0 juvenile cod, Gadus morhua and G. ogac, following a large-scale habitat manipulation B. J. Laurel1,*, R. S. Gregory2, J. A. Brown1 1Ocean Sciences Centre, Memorial University of Newfoundland, St. John¹s, Newfoundland, A1C 5S7, Canada 2Department of Fisheries and Oceans, Science Branch, PO Box 5667, St. John¹s, Newfoundland, A1C 5X1, Canada *Email: blaurel@mun.ca ABSTRACT: In Bonavista Bay, Newfoundland, we monitored patterns of settlement and distribution of 2 species of gadids, Atlantic cod Gadus morhua and Greenland cod G. ogac, following a large-scale alteration of nearshore eelgrass Zostera marina habitat. Comparisons between control and experimental sites, based on bi-weekly sampling from 1995 to 2001, indicated a significant increase in cod abundance at sites enhanced with simulated eelgrass and a corresponding decrease in cod numbers at sites where eelgrass had been removed. These data supported predictions, demonstrating that: (1) there was a sufficient supply of juvenile cod within the areas that have historically been unoccupied (i.e. sand) and (2) both species preferred to settle in complex habitats. However, G. ogac responded significantly to the removal of eelgrass in more comparisons than G. morhua (70 and 37% respectively), suggesting that G. ogac has a higher affinity for complex vegetative habitats than G. morhua at the scale of manipulation (ca. 800 m2). Furthermore, despite an overall preference for eelgrass habitat, high within-site catch variation of post-settled juvenile cod indicated that both species were not restricted to a seine site. Such variation was occurring well after the settlement period, suggesting that juvenile cod were moving and occasionally aggregating (i.e. shoaling) throughout the study period. Our results support previously described associations between juvenile cod and eelgrass, but contradict other published accounts of high site-attachment and restricted movement in G. morhua following settlement. KEY WORDS: Eelgrass · Habitat selection · Atlantic cod · Greenland cod · Habitat enhancement · BACI design Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 262. Online publication date: November 07, 2003 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2003 Inter-Research.

Efficacy of a remote control closure of cod-end used in a bottom trawl experience

A total of 26 effective trawl hauls using a remotely operated trawl cod-end closure system were carried out to determine whether samples collected in a rear section of the cod-end and in a front section of the cod-end were homogeneous, and can be used as reliable replicates for community sampling and resource assessment. Comparative analyses of these sample hauls and 25 other hauls that did not use the cod-end closure system were also performed. The results indicate certain technical difficulties in the practical operation of the system and that samples were not homogeneous either between the cod-end sections in the same haul or between hauls. The causes of the sample variability in catches from trawl surveys are discussed.