Cod End Research Articles

Survival of vendace (Coregonus albula) escaping from a trawl cod end

Many young (0 group) vendace (Coregonus albula) are thought to die after passing through trawl cod ends during commercial vendace fishery in Finnish lakes. Survival of 2- to 4-month-old vendace (5–10 cm) after escaping from a 24-mm square mesh trawl cod end was therefore studied in Lake Puulavesi, Finland, during July–August 1993. Escapees were collected in a hooped netting cage that was released from the cod end after the tow, closed, and left at the depth of capture for 3–7 days. The data consist of 59 cagings. On average, 50% of the escaped vendace died, although mortality varied considerably. Most mortality occurred during the first day after escaping. Hauls conducted in the late evening and at night were accompanied by the highest mortality (60–80%). Mortality was 30–40% in the afternoon and early evening hauls. Generally, higher mortality was observed in August than in July. Comparisons with caged fish caught by a purse seine suggested that the experimental procedure did not substantially contribute to the observed total mortality of escapees. Scale loss and exhaustion experienced by vendace during trawl capture may have caused the rapid death of escapees through loss of osmoregulatory control.

Trawling stress and mortality in undersized (

Trawling stress and mortality in undersized brown trout ( Salmo trutta L.) were examined at openwater seasons in 1989 and 1990 on the big lakes in eastern Finland. Large scale trawling on inland waters in this area is a new phenomenon and it has caused conflicts between different fishing groups. It has generally been assumed that undersized trout freed after being caught in trawls do not survive. Blood lactate and glucose concentrations and plasma chloride concentrations were measured from blood samples taken immediately after trawling. The recovery of the fish from trawling stress was also monitored by blood sampling and following the mortality of fish caged for 7 days after capture. The trout were observed to become considerably stressed by trawling. Abundant catch and high water temperature increased stress of the trout. These variables and the duration of trawling haul as well as the cod end empting technique explained 72% of the increase of blood lactate. The indicators of stress had not returned to control values by 4 h post-capture, but blood lactate showed an abrupt decrease over 2 h. Plasma chloride concentration was, however, still decreasing 4 h after the end of trawling. The percentage of caged fish which survived a week was 85.5. Lifting of the cod end to the vessel clearly increased the mortality of trout. Without the extra stress connected with caging, the proportion of surviving fish would probably have been considerably greater. On the basis of the results it can be said that if undersized trout were freed immediately by emptying the cod end in small portions directly in the water, trawling would not cause them considerable mortality.

屋外長水路での曳網模型による角目と菱目袋網の網目選択性の比較

For the regulation of fishery resources, an appropriate mesh size of traditional diamond mesh cod end is always chosen in the belief that undersized fish can escape from the cod end to grow to a suitable size for fishery later. However, because a diamond mesh cod end becomes too narrow at the middle, and the meshes are almost closed (with the exception of the end of the cod end) during trawling, the benefit of mesh regulation is insufficiently attained. To alleviate the problem, an improvement in selectivity was achieved by using square-mesh cod ends that have more open meshes. The experiments were conducted using cod ends with 4 mesh sizes (26, 31, 36 and 41mm) in a long waterway. The results for rainbow trout (Oncorhynchus mykiss) demonstrated that the square-mesh cod end, as compared with the diamond mesh cod end, could significantly reduce the catch of juveniles and obtain good selectivity.

Labyrinth of doom: A device to minimize the “swimmer” component in sediment trap collections

A simple device used to discriminate between “swimmers” and “nonswimmers” in sediment trap collections has been developed. It consists of a series of funnels which concentrate passively sinking material into a central collection tube, whereas swimmers are distributed randomly between the inner and outer collection tubes. The degree to which swimmer/nonswimmer fractionation is achieved depends on the number and spacing of funnels and the ratio of inner to outer collection tube areas. Although inner collection tube samples contain a few swimmers, there are considerably fewer than are collected in cod ends without this device. Furthermore, outer tube contents are devoid of passively sinking material providing a “pure swimmer” fraction which can be compared to inner collection tube contents. This device has been successfully deployed on many occasions in traps of the Soutar (conical) and Knauer (cylindrical) type as part of the VERTEX program in the NE Pacific.

The statistical design of comparative fishing experiments

Experimental designs for alternate tow gear experiments are described and evaluated, considering situations with and without randomized complete blocks. Variance components relevant to the performance of these designs are identified, and a method for estimating them is presented and applied using data for the Pacific multispecies groundfishery. The aim of the Pacific experiment was to estimate the magnitude of changes in fish length for various species and total tow catch value due to changes in cod end mesh size. Alternative experimental designs are compared with regard to the sample sizes needed to reject the null hypothesis that there is no treatment effect. For the specific application examined, there is a 4–10-fold reduction in sample size when randomized complete blocks are used within a vessel trip, compared with an unblocked experimental design using only one treatment type per vessel trip.

Reducing Mortality of Striped Bass Captured in Seines and Trawls

Abstract Between 1984 and 1987, more than 30,000 striped bass Morone saxatilis were captured for tagging in the Hudson River, New York, with trawls and seines. Handling before tagging was the major source of mortality. Immediate mortality decreased from 16.1 to 1.2% for striped bass captured in seines and from 17.7 to 1.0% for striped bass captured in trawls when the handling procedure was modified. The modified procedure involved guiding the cod end into a partially submerged holding tank beside the capture vessel instead of lifting the cod end out of the water to transfer the catch to a holding tank aboard the capture vessel. A significant interaction between immediate mortality, water temperature, and fish length was observed before the handling procedure was modified but not afterward. When the unmodified handling procedure was used, immediate mortality increased with increasing fish length and water temperature. However, recapture rates within a year after release also increased with increasing water...

A continuous pump sampler for profiling copepods and chlorophyll in the upper oceanic layers

A continuous profiling pumping system has been developed for obtaining biological profiles of copepods, chlorophyll, temperature, and light irradiance in the upper mixed layers to depths of ≈ 100 m. The sampler minimizes the problem of zooplankton avoidance of pump intakes by entrapping animals in a descending plankton net and subsequently removing them by pumping on the cod end. Measured profiles of copepods and chlorophyll indicate a vertical resolution of ≈ 3 to 4 m resulting from mixing in the hose and pump for a sampler descent rate of 0.5 to 1.0 m s −1. The pumping system delivers ≈ 50 to 60 1 min −1 of seawater on deck. Residence time and mixing in the hose are estimated. Pump and Niskin bottle samples used in primary production measurements are compared and indicate minimal damage to organisms during the production measurements. Applications of the pumping system to production measurements are presented.

Cod end feeding by the euphausiid Meganyctiphanes norvegica

Daytime surface swarms of Meganyctiphanes norvegica in the Bay of Fundy were sampled by hand-held dip nets and by plankton nets. A comparison between the “food baskets” of the animals from samples obtained by the two collection methods showed that those from plankton nets contained many items whereas those from dip nets rarely contained anything. Samples from towed-nets also had significantly more animals with fuller stomachs than those obtained by dip nets at approximately the same time. It is concluded that the observed differences are due to feeding by the euphausiids in the cod end of plankton nets.

Notes on the occurrence of some poorly known Decapoda (Crustacea) in the southern North Sea

INTRODUCTION Since April 1972 an ecological trawl-survey programme has been undertaken by the Netherlands Institute for Sea Research (NIOZ), Texel, in the southern North Sea with the R. V. Aurelia. The main object is to obtain information on distribution, density, biomass and fluctuations of crawling or swimming demersal (epibenthic) fauna such as small fishes, shrimps, prawns, crabs, asteroids, ophiuroids and some gastropods, for the evaluation of the role of these carnivores in the benthic ecosystem of the southern North Sea. Sedimentological aspects of the area are described by Creutzberg & Postma (1979). Within the context of the present paper the most important feature is the mesh of 5 x 5 mm2 of the cod end of the 51/2 m beam-trawl used and the extensive area of 5000-10,000 m2 covered during each haul. These exceptional circumstances resulted into faunistically interesting catches which gave rise to a cooperation with taxonomic specialists of the Rijksmuseum van Natuurlijke Historie (RMNH), Leiden. The present paper deals with decapod crustaceans, collected during Aurelia-cruises, which are considered to be scarce or rare in the southern North Sea, completed with data from bottom-samples and other sources. The species in question are: Pandalina brevirostris, Spirontocaris lilljeborgii, Alpheus macrocheles, Pontophilus spinosus, Pontophilus bispinosus, Galathea dispersa, Ebalia tuberosa, Ebalia tumefacta, Ebalia cranchii, Atelecyclus rotundatus, Monodaeus couchii, Callianassa subterranea, Callianassa tyrrhena, Upogeb ia stellata and Upogebia deltaura. Of the genus Macropodia a number of specimens have been collected, which partly were identified as M. linaresi. Other specimens, however, represent one or two new species. On Macropodia in the southern North Sea a seperate paper will

Power Begins at the Cod End

Power Begins at the Cod End

'Power Begins at the Cod End': The Newfoundland Trawlermen's Strike, 1974-75.

'Power Begins at the Cod End': The Newfoundland Trawlermen's Strike, 1974-75.

Thermally protecting cod ends for the recovery of living deep-sea animals

Abstract The use of thermally protecting cod ends for the recovery of living midwater animals is described. The designs and construction details of two such devices are described. These devices have proved effective for the recovery of living animals from depths as great as 2500 m.

Longhurst-hardy Plankton recorders: their design and use to minimize bias

Field studies and tow basin experiments of Longhurst-Hardy Plankton Recorder (LHPR) biases were conducted by injecting various types of particles into an LHPR having a variety of net and recorder box configurations. Tow speed and clogging were also considered. The following factors contributed to biases: (1) low recorder gauze aperture area to throat area ratios, causing backing up of flow into the net cod end, (2) tunnel gauze slot design, allowing significant losses of particles; (3) steep side angles of the net at the recorder entrance due to bagging or radial stretching; (4) clogging of the neta head of the LHPR; (5) short nets; and (6) tow speeds greater than about 125 cm s−1. Experiments with an LHPR modified to minimize biases showed that resolution to 15 m in oligotrophic waters is possible. In eutrophic waters, we doubt it is feasible to use a net with the LHPR.

Recovery of deep seawater at constant pressure.

WE wish to report here a significant stage in the development of equipment which will recover deep sea animals at constant pressure and temperature. Organisms in the deep sea live at hydrostatic pressures which are lethal to ordinary surface living forms. Pressure increases by 1 atmosphere (14.7 pounds/inch2) for each 10 m depth and rises to 1,000 atmospheres in the deep trenches. Pressures in the range 0–1,000 atmospheres affect the dissociation and hydration of ions1,2, and alter the colloidal structure of cytoplasm, inhibiting cell division and similar phenomena3–5. Pressure may accelerate or retard the rates of many biological reactions6–8, and affect the normal functioning of muscle and nerve9,10 and various complex cellular structures11,12. The variety of organisms found at depth13 shows that pressure adaptation is common, but there have been all too few experiments carried out on deep sea organisms14. We are proposing to filter planktonic animals at various depths and recover them without loss of pressure in a pressure vessel fitted to the cod end of a plankton net. On recovery the plankton suspension will be transferred to an experimental pressure vessel without serious pressure fluctuation. Optical and polarographic techniques are already available for the measurement of respiration, activity and survival of plankton suspensions at pressure.

THE GROWTH AND SIZE DISTRIBUTION OF CURRENT YEAR CLASS LOLIGO PEALEI.

1. This paper reports estimates of the growth rate and size distribution of current year class L. pealei based upon the population statistics of daytime, otter trawl collections in Menemsha Bight during the second half of 1967. 2. The selectivity of a #35 otter trawl with a 1.25-inch mesh (3.2-cm.) stretched measure cod end liner was estimated by a 50% retention of L. pealei with a dorsal mantle length of approximately 3.7 cm. 3. The current year class, summed older year classes and individual older year classes of L. pealei were found to have lognormal size-frequency distributions. 4. The current year class could readily be separated from the older year classes by the use of Cassie's method on lognormal probability paper. 5. The growth rate of a median individual in the current year class of 1967 was found to be 1.8 cm. dorsal mantle length per month for the first four months past hatching. 6. Approximately one-half of the one-year-old L. pealei did not mature sexually before the second fall migration. None of the current year class L. pealei matured before the first fall migration. 7. The results indicate that L. pealei egg deposition is isolated in time and location, and repeated throughout the Vineyard Sound area from at least June through September.

水中における各種嚢網の抵抗について-V

水中における各種嚢網の抵抗について-V

On the results of field trials with various big sized otter trawls : Koyama Takeo, 1965. (In Japanese; English abstract). Bull. Tokai req. Fish. Res. Lab., No. 43: 13–71.

In the Spencer Gulf prawn fishery prawns are caught at night by trawling. Groups of dolphins, the short-beaked common dolphin (Delphinus delphis) and the bottlenose dolphin (Tursiops truncatus), and seabirds, the silver gull and the pacific gull (Larus novaehollandiae, Larus pacificus), feed on discarded by-catch. The dolphins follow the cod ends as they appear close to or on the surface. Here they pick or bite fish protruding through the cod end mesh or forage on discards. Seabirds pick floating objects. In order to quantify the importance of dolphins and seabirds as consumers of discarded by-catch, four series of surveys were undertaken using prawn trawlers engaged in commercial fishing thereby obtaining a large number of observations simultaneously over a large area and at different seasons. On three successive nights, each night on three occasions, after the first trawl shot, at midnight and after the last shot of the night, the trawler skippers recorded the numbers of seabirds and dolphins feeding on discarded by-catch. The mean number of dolphins per boat and observation varied between seasons with 0.5–1.3 dolphins/boat/observation. At the northerly Site 1, 3.4 dolphins were recorded per boat and observation while at the more southerly sites (Sites 2–5), 0.5–0.8 dolphins were observed per boat and observation. No significant difference between observations at night was observed. The occurrence of seabirds varied between sites but not between season and time of night. The largest numbers of seabirds was observed at Sites 1 and 4 with a mean of 2.2 and 2.8 seabirds per observation. It was concluded that an estimated 18–183 t of discards are consumed per year by dolphins constituting 0.3–2.6% of the discarded by-catch. Seabirds potentially consume 1647–165 kg discards per year from the Spencer Gulf prawn fishery, which constitute less than 0.03% of the discarded by-catch.

Selectivity of Four Trawl Cod Ends toward Smelt

Three short-term experiments on selectivity of cod ends with various mesh sizes for smelt, Osmerus mordax (Mitchill), were conducted in Lakes Ontario and Erie during 1961. In each experiment the paired tow method was used. Four cod ends were attached alternately to a “Western bottom trawl” fished by the MV Erie I. Estimates of percent retention within 0.3-inch length strata were obtained from a comparison of length-frequency distributions in catches made by the different cod ends fishing approximately the same population of smelt on the same date. Additional information was gained from the weight of catches by different cod ends. Under the conditions of the experiment, cod end mesh sizes of 1 3/16 to 1 3/8 inches appeared most suitable for smelt trawling given market preferences as they existed in October 1961.

The Northern Rockling in the Clyde Sea Area

ON August 15, 1960, a northern rockling, Ciliata septentrionalis (Collett 1875), was caught in the Clyde Sea area. The fish was caught at a depth of 30–40 fathoms in a small mesh cover that had been fitted over the cod end of a trawl used by R.V. Calanus. It is 10.6 cm. in length and agrees closely with the descriptions of Smitt1 and Schnackenback2.

International Commission for the Northwest Atlantic Fisheries

The sixth annual meeting of the International Commission for the Northwest Atlantic Fisheries was held in Halifax, Canada, June 11–15, 1956, under the chairmanship of Captain T. de Almeida (Portugal). After the opening addresses the panels reviewed the research programs being carried out in each regional sub-area and proposed various improvements in sampling, reporting the tag recaptures and statistics of catch and effort, and related matters. An ad hoc committee, which had been appointed to consider difficulties reported by the French Commissioner in connection with the mesh regulation proposed at the fifth annual meeting, recommended that research should be undertaken to determine the consequences of using multiple cod ends and to find methods of strengthening the cod end without diminishing the selective effect of the gear. Another ad hoc committee was appointed to deal with a suggestion that the exemption from mesh regulations be amended. With respect to the establishment of the two ad hoc committees, the Commission decided to discuss at its next meeting whether it should refer regulatory and enforcement questions to ad hoc committees, or whether a standing committee should be formed to deal with such problems.