Trawling Operations Research Articles

Trawl operations in the South East Fishery, Australia: spatial distribution and intensity

Trawl areas and intensities were mapped at coarse (22 km 1986–99)and fine (1 km 1995–99)scales, and statistics reported by area and depth stratum. Total effort in hours was relatively stable to 1992, then increased substantially to 1999. The total distance trawled from fine-scale analysis showed a similar trend for the 1995–99 period. Coarse-scale analysis from 1986–99 indicated effort increases in north-east Bass Strait in particular, and also off western Tasmania and west of Bass Strait. There was little change in the total area of the fishery from 1995 to 1999, but grid cells on the periphery showed considerable interannual variation in the presence or absence of fishing. Increased or redistributed effort tended to further concentrate in the relatively small high-effort areas, rather than increasing equally across the grounds, or spreading to new grounds. In the total management area, a small proportion of the 1 km grids was fished. However, in 200–1000 m depth strata, ≥50%of the grids were fished with some intensity. The consequences and compromises of spatial scale are discussed in terms of data quality, the use of trawl effort as a surrogate for marine disturbance, and the interpretation of catch rates.

Species identification of pelagic fish schools using acoustic descriptors and ancillary information

It is shown that schools of similarly sized and behaving pelagic fish species can be accurately identified to species over a large spatial area, on the order of the broad spatial-scales typical of standard assessment surveys, and over a time-span of three years. Acoustic measurements of morphometric, energetic, and bathymetric features of anchovy, sardine, and round herring schools were extracted using commercially available software from acoustic data collected by a conventional single-frequency narrow-band echosounder during trawling operations of pelagic stock surveys of the South African continental shelf (November 1997, 1998 and 1999). Discriminant function analysis of 18 descriptors of the 214 schools for which the species composition was satisfactorily determined by trawl samples indicated that schools could be correctly identified to species in 88.3% of all cases (94.9% for anchovy, 82.6% sardine, 82.6% round herring). The three species were differentiated primarily on the basis of school bathymetric position and backscattered energy. Including ancillary information (latitude, longitude, sea surface temperature, bottom depth, and time of day) in analysis improved the accuracy of school identification to 94.9%, since such variables allowed discrimination on the basis of interspecific differences in habitat use, as well as in schooling behavior. a)Currently at MIT/Woods Hole Joint Program.

Discorhabdin R: A New Antibacterial Pyrroloiminoquinone from Two Latrunculiid Marine Sponges, Latrunculia sp. and Negombata sp.

Two sponges belonging to the family Latrunculiidae (Negombata and Latrunculia sp.) collected during scientific trawling operations in Prydz Bay, Antarctica, and by scuba off Port Campbell, Victoria, have yielded a new antibacterial pyrroloiminoquinone, discorhabdin R (2). The structure was assigned as 2 on the basis of detailed spectroscopic analysis and comparison with the known co-metabolite discorhabdin B (3).

Absorption spectroscopy:: A new approach to estimation of biomass

The results of an interdisciplinary experiment, Modal Lion, which was designed to isolate the effects of absorptivity due to fish with swim bladders from other effects on transmission loss, are described. The experiment was conducted at a 83 m deep site in the Gulf of Lion in September 1995. Absorption losses were measured between 0.6 and 5.0 kHz at a range of 12 km. Trawling operations indicated that the dominant fish in this region were 16.5 cm long sardines. Absorption lines were evident at 1.3 kHz (18 dB) when dispersed sardines were near the surface at night, and at 2.7 kHz (35 dB) when sardines were dispersed near the bottom at dawn just prior to school formation. In addition, an absorption line attributed to 6.5 cm long, dispersed juvenile sardines was evident at a frequency of 3.9 kHz (8 dB) at night. Measured resonance frequencies of 16.5 and 6.5 cm long dispersed sardines at night were in good agreement with theoretical computations based on swim bladder dimensions derived from trawling operations. Results suggest the possibility of spectral separation of juvenile from adult fish, and long term monitoring of the growth and mortality rates of juveniles with absorption spectroscopy measurements.

Echinosulfonic acids A-C and echinosulfone A: novel bromoindole sulfonic acids and a sulfone from a southern australian marine sponge, echinodictyum

The crude EtOH extract of an Echinodictyum sp. collected during trawling operations in the Great Australian Bight, Australia, displayed antibacterial and antiparasitic properties. Bioassay-directed fractionation yielded three novel sulfonic acids, the echinosulfonic acids A to C (1-3), and a new sulfone, echinosulfone A (4). Structures were assigned to these compounds on the basis of detailed spectroscopic analysis. It was determined that echinosulfonic acids A-C (1-3) and echinosulfone A (4) contributed to the antibacterial but not antiparasitic activity of the crude extract.

Amphilactams A−D: Novel Nematocides from Southern Australian Marine Sponges of the Genus Amphimedon

Bioassay-directed fractionation of the ethanol extracts of two Amphimedon spp. collected during trawling operations in the Great Australian Eight yielded four new macrocyclic lactone/lactams, amphilactams A-D (1-4). The amphilactams possess potent in vitro nematocidal properties, and their structures were assigned on the basis of detailed spectroscopic analysis and comparison with synthetic model compounds. The amphilactams feature both carbon skeletons and an enamino lactone/lactam moiety unprecedented in the natural products literature.

The AusTED II, an improved trawl efficiency device 2. Commercial performance

An Australian-designed bycatch reduction device (BRD), known as the AusTED, was modified to improve its efficiency and simplify its design. The modified version (the AusTED II) was tested under a range of conditions typical of prawn trawl fisheries of north eastern Australia. Trials occurred during commercial trawling operations to heighten industry awareness of research into BRDs and improve the credibility of research results to industry. Average bycatch reduction ranged between 15% and 49% depending upon fishery conditions, and the capture of large animals such as stingrays and sea turtles was significantly reduced. The AusTED II had a variable effect on prawn catches depending on trawling conditions, ranging from no significant difference to a 36% loss. The AusTED II offers commercial fishers the benefits of large animal exclusion plus reduced bycatch. Reductions in bycatch were explained in part by the exclusion of fish species with “fusiform” and “laterally compressed” body-forms. Unexpectedly, “weak swimming fish” were also excluded consistently by the AusTED II. The trialing of a single BRD across a range of trawling conditions in north eastern Australia demonstrated the variability in BRD performance that can be attributed mainly to the quantity and composition of bycatch species. It is highly likely that other exclusion systems like the AusTED II will not be immediately suitable to all north east Australian trawl fisheries. The acceptance of BRDs by the Australian trawling industry will depend upon efficient and pragmatic designs coupled with industry confidence in research results.

A GIS for the management of fisheries in West Africa: preliminary application to the octopus stock in Senegal

A preliminary application of a Geographical Information System (GIS), based on a georeferenced database including data from commercial fishing and oceanographic surveys, and on geographical objects describing the physical and juridical environment, trawl operations and artisanal fishing sites, is presented. An ArcView environment is used to show spatial and temporal phenomena. Seasonal distribution charts for Octopus vulgaris and for the main associated finfish species on the Senegalese continental shelf reveal that octopuses are particularly abundant on the deep part of the continental shelf off Casamance and the Grande Côte during the cool season. Warm-season distribution seems to be more coastal. The results allow the interactions between artisanal and industrial fisheries and areas of potential conflicts to be identified. The intensity of these interactions for resource access and space allocation is highly correlated to season. The results also provide alternative explanations for fisheries management, e.g. on the degree of respect for or the relevance of the limits of regulated fishing areas and spatial fishing unit strategies according to the main seasons.

Dragmacidins: new protein phosphatase inhibitors from a southern australian deep-water marine sponge, spongosorites sp

A Spongosorites sp. collected during trawling operations off the southern coast of Australia returned the new alkaloid dragmacidin E (3), the structure of which was secured by detailed spectroscopic analysis. Dragmacidin E (3), and its co-metabolite dragmacidin D (1) have been identified as potent inhibitors of serine-threonine protein phosphatases.

Cis-3-Hydroxy-N-methyl-L-proline: a New Amino Acid from a Southern Australian Marine Sponge, Dendrilla sp.

A specimen of the sponge Dendrilla sp. collected during commercial trawling operations in the Great Australian Bight, Australia, analyses for a very high natural abundance of the new amino acid cis-3-hydroxy-N-methyl-L-proline (1). The complete stereostructure for (1) was determined by spectroscopic analysis and chemical derivatization.

Rates of retained and discarded catches from demersal fish trawling off the north-eastern United States

The retained- and discarded-catch rates of fish, crustaceans and molluscs caught by demersal fish trawlers were quantified in a large-scale observer survey of fleets working off the north-eastern United States. The data presented come from catches sampled from 7757 tows on 1010 fishing trips during the four-year period from July 1990 to June 1994 and are summarized as the weights retained and discarded (per hour of trawling) for many of the important commercial and recreational species in the region. Problems with the spatial and temporal design of the programme restricted statistical analyses of the data and prevented summaries across all statistical areas and months. However, separate summaries for individual areas (over all months) and individual months (over all areas) identified several spatial and temporal patterns in retained- and discarded-catch rates for individual species and combinations of species. Noticeable increases and decreases in catch rates during the four-year period provided information on the relative health of certain stocks, and overall discard percentages indicated relative selectivities of the trawling operations sampled.

Catch and discards from experimental trawl and longline fishing in the deep water of the Rockall Trough

Comparative bottom trawl and longline surveys were carried out on two chartered commercial fishing vessels in the deep waters (350‐1300 m) of the Rockall Trough, an area subjected to heavy commercial exploitation. The species composition, catch rates and length distributions from each survey were very different and reflected the fundamental difference in the two types of fishing operations. Bottom‐trawled catches produced greater species diversity and higher discard rates. Longline catches produced larger specimens of teleost fish and were dominated by squalid shark. Trawl discards, expressed as kgs of discards per tonne of roundnose grenadier Coryphaenoides rupestris landed, were calculated for a broad range of the most abundant species taken in the catch. First estimates of total international discarding from deep‐water trawling operations in the Rockall Trough area (7530 tonnes; 26.5 million individuals) were made by raising the discard rates using international grenadier landings for 1995. The outlook for the continued exploitation of the deep‐water fish resource in the Rockall Trough and possible management options are discussed.

Incidental Catch of Chinook Salmon in Commercial Bottom Trawls off the U.S. West Coast

Abstract Data on chinook salmon Oncorhynchus tshawytscha caught during commercial bottom trawl operations off the U.S. west coast were collected during 1985–1987 and 1988–1990. Almost no salmon were encountered in depths exceeding 482 m. Chinook salmon were caught most frequently and in greatest quantity during winter months, when catches were dispersed throughout a depth range of 100–482 m. Catches were relatively low during summer and occurred primarily in shallow water (at depths less than 220 m). Chinook salmon catch rates were higher off the south-central Oregon coast (Pacific States Marine Fisheries Commission [PSMFC] area 2B) than in more northerly coastal areas sampled during the 1985–1987 study. The 1988–1990 study, however, indicated higher catch rates off northern California (PSMFC area IC), south-central Oregon (area 2B), and northern Washington (areas 3B–C) than in other coastal areas. Chinook salmon catch estimates by bottom groundfish trawls during 1987 totaled 7,761 fish for areas 2B, 2C, ...

Lamellarins O and P: New Aromatic Metabolites From the Australian Marine Sponge Dendrilla cactos

A specimen of Dendrilla cactos collected during trawling operations in Bass Strait, Australia, has yielded two new alkaloids, lamellarin-O (17) and lamellarin-P (18). Both these metabolites are examples of the lamellarin structure class, previously reported from tunicates and a mollusc; however, in these examples the pyrrole ring system is not fused to adjacent aromatic rings. The structures of (17) and (18) were secured by spectroscopic analysis and partial synthesis.

Carduusynes (A-E): Acetylenic Acids From a Great Australian Bight Marine Sponge Phakellia carduus

The marine sponge Phakellia carduus obtained during commercial trawling operations in the Great Australian Bight yielded a series of new C23 acetylenic acids, carduusynes (A-E) [(3)-(7)], which were isolated, characterized and identified as their respective ethyl esters [(8)-(12)].

The fishery for, and general biology of, the St JosephCallorhinchus capensis(Dumeril) off the South-Western Cape, South Africa

St Joseph Callorhinchus capensis are caught by a directed gillnet fishery off the coast of South Africa's Western Cape and also incidentally by trawl in shallow water on both South and West coasts. The fishery only became established in the early 1980s and landings have subsequently stabilized at approximately 800 tons per year, almost one-third of which is a by-catch of trawling operations. The gillnet fishery is centred in St Helena Bay and takes very little by-catch. Both trawl and gillnet operations take place in nursery areas of C. capensi and some species of true shark. C. capensi occurs widely off the southern African coast, from 1 to 366 m deep, but large numbers are only caught inshore (<50 m), the only area where immature fish are found. The fork length at 50% sexual maturity is 435 mm in males (3,3 years) and 496 mm in females (4,2 years). Mature fish have an annual onshore/offshore migration, most mature fish aggregating inshore in summer to breed and lay eggs. They then disperse to deep water...

Cometins (A-C), New Furanosesterterpenes From an Australian Marine Sponge, Spongia sp.

The known marine furanosesterterpene furospinosulin-1 (1), together with three new furanosesterterpenes, namely cometin-A (2), cometin-B (3) and cometin-C (4), were isolated from a marine sponge, Spongia sp., collected during commercial trawling operations in the Great Australian Bight. The structures of these metabolites were determined by detailed spectroscopic analysis and chemical derivatization . The antibiotic property of the crude ethanol extract of this sponge was attributed solely to the furanosesterterpene tetronic acid cometin -A (2).

Fishes of the Chatham Islands, New Zealand: A trawl survey and summary of the ichthyofauna

Abstract A total of 227 fish species, representing 113 families, are recorded from the Chatham Islands area (c. 860 km east of New Zealand): 148 are first records for the area and two, Scopelarchoides kreffti Johnson (Scopelarchidae) and Oneirodes whitleyi Bertelsen & Pietsch (Oneirodidae), are first records for New Zealand. Forty‐two species are identified from a single commercial trawling operation off the Chatham Islands; 13 of these species include juveniles. Notes are given on taxonomy, nomenclature, and distribution for selected fishes. Major conclusions reached are: some prominent New Zealand species are notably absent from the Chathams list, but many more fish species remain to be collected from the area; no endemic species are recognised; the observed abundance of juvenile fishes supports the hypothesis of larval transport from New Zealand to the Chathams by ocean currents; the main affinity of the fish fauna is with widespread and central New Zealand waters; small northern and southern elements ...

Description of Escape Responses of Krill (Crustacea: Euphausiacea), with Particular Reference to Swarming Behavior and the Size and Proximity of the Predator

Observations of the escape responses of Euphausia superba and Euphausia crystallorophias under pack ice (O'Brien, 1987) and of Nyctiphanes australis in southeast Tasmania (unpublished observations) are discussed together with previously published data on the escape reactions of these and other euphausiids. Similarities in the form of the escape response for surface-swarming species of euphausiids are apparent. It is proposed that there are three levels of escape response whose manifestation is primarily dependant upon the aggregative state of the prey and the size and proximity of the predator. The adaptive significance of the three levels of response is discussed in relation to predator evasion. Central to the study of the distribution and regional variations in the density of euphausiid species and to the success of commercial trawling operations is the efficiency of the locating and sampling equipment, especially since krill may actively avoid nets (Marr, 1962; Pavlov, 1969; Sameoto, 1980; Everson, 1983) and remote camera equipment (Kils, 1981). As stated by Hamner (1984) in reference to E. superba, a knowledge of the avoidance or escape responses and the general behavioral biology of krill is of fundamental importance to the design of sampling gear, harvesting strategies, and also to the evolution of its predators, e.g., whales. Published accounts of the escape responses of euphausiids are scarce and are restricted to direct observations of surface-swarming species such as Euphausia superba (Pavlov, 1969; Ragulin, 1969; Hamner, 1984), Euphausia vallentini (Ragulin, 1969), Euphausia pacifica (Hanamura et al., 1984), and Meganyctiphanes norvegica (Nicol and O'Dor, 1985) or indirect evidence from the use of remote cameras and echo sounders (Sameoto, 1980; Kils, 1981). In the present paper further direct observations of three species of surface-swarming euphausiids, E. superba, Euphausia crystallorophias, and Nyctiphanes australis are described in relation to the previously published data, and the general features of the escape response are discussed for the group as a whole. In the present context the term swarm describes any cohesive aggregation of krill, even schools when there is no purpose in distinguishing between the two terms. The term school refers to a cohesive group of krill in which all the individuals are polarized, i.e., show parallel orientation. With both terms there are no restraints on density or dimensions. All unacknowledged references to E. superba, E. crystallorophias, and N. australis are taken from O'Brien (1987), or are unpublished observations made by the author.

南アメリカ北東岸沖におけるピンクスポッテッドシュリンプＰｅｎａｅｕｓ ｂｒａｓｉｌｉｅｎｓｉｓの分布と回遊

Distribution and migration of the pink-spotted shrimp Penaeus brasiliensis off the northeastern coast of South America (Guyana-northern Brazil) were examined, based on the catch and size composition data from a trawl survey. The survey by a double-rigged shrimp trawler covered the central part of the area (off Surinam and French Guiana) and consisted of five cruises during 1981-1983. In each cruise, trawl operations were made at night at about 80 pre-determined stations.Pink-spotted shrimp was dominant in the shrimp catches, followed by southern brown shrimp P. subtilis. In all cruises, the catches of pink-spotted shrimp were confined to the outer part of the continental shelf. The mean sizes for both sexes were around 15cm (total length) at the westernmost stations and increased gradually from west to east with a tendency that larger animals occurred in the shallower part.So, it is estimated that the species may be recruited from Guyana and move eastwards on the outer part of the continental shelf off Surinam and French Guiana. It is further suggested that the spawning ground may widely spread over the most part of the distribution area off Surinam and French Guiana and that the eggs and larvae are possibly transported to Guyana by the South Equatorial Current running westwards.