O.T. Albert1, A.-B. Salberg1, M. Zaferman2 and G.P. Tarasova2
1 Institute of Marine Research
POB 6404, N-9294 Tromsø, Norway
2 Knipovich Polar Research Institute of Marine Fisheries and Oceanography (PINRO)
6 Knipovich Street, Murmansk 183763, Russia
Development of methods for visual surveying in deepwater often rely on the use of constant artificial light. Conclusions relating to vulnerability and other aspects of fish behaviour in front of trawls during normal fishing operations may be biased due to the fish reacting in response to the light. The purpose of this study was to evaluate the effect of light on catch level and catch composition of Greenland halibut (Rheinhardtius hippoglossoides) in trawl surveys, and also to determine how the light influences behaviour of individual fish in front of the trawl. We used flash-photos to record behaviour in dark conditions and compared the results with hauls using video and constant artificial light.
In each of 16 locations, one bottom trawl haul was made with flash-photo equipment and another with video equipment. In addition, several hauls using both types of illumination were made on different locations. The actual angle of the cameras and the area and shape of the ground coverage varied between individual frames. For comparison of flash photos and video frames it was therefore necessary to establish a geographical coordinate image of the trawl from a reference image. Assuming that the shape of the trawl was fixed for all images, a set of corresponding points were established between the reference image and the individual photo and video images. Based on these points, the images were related to the geographical coordinates of the reference image using a non-linear least squares procedure. In addition some Russian data on fish angles of orientation were measured on actual pictures from vertically directed cameras.
Catch rates, in terms of number of Greenland halibut caught per nautical mile (nm) were 30 percent lower when constant light was used compared with the flash-photo stations (Figure 1). Paired comparison of catches from the trawl experiment showed that the effect was highly significant. The proportional reduction in catch rate due to use of light is similar to the proportion that was observed (on video) escaping under the footrope (Albert et al. 2003a).
Catch rates of Greenland halibut at individual localities when constant illumination was used (video-stations) as a function of the catch rates using flashlight (photo-stations)
The solid line represents 1:1 catch relation between the two forms of illumination and the hatched line is the fitted linear regression (i.e. correllation)
There was no difference in length or sex composition of the catches with constant artificial light and flashlight respectively (Figure 2). The trawl experiment showed no significant effect of light on mean length in catch.
For Greenland halibut that were observed close to, or on, the bottom, there were no effects of constant light on position of the fish relative to the ground-gear (Figure 3). The Russian flashphotos show some weakening of ordered orientation in comparison with video, but even with the extreme low light levels at 800 m depths during the dark high latitude winter, Greenland halibut showed a distinct ordered orientation away from the trawl. This is not in accordance with previous investigations on flatfish and other ground fish in shallower waters (Glass and Wardle 1989, Walsh and Hickey 1993, Weinberg and Munro 1999). They show in general, and especially at low light levels, only weak ordered reactions of flatfish in relation to an approaching trawl.
There were more fish swimming across the trawl direction when constant light was used (Figure 4). It may be that this increased zig-zag swimming activity increased the probability of their finding an opportunity to escape beneath the ground-rope of the trawl and that this was the main reason for the reduced catch rates of Greenland halibut when using constant illumination.
Video recording of fish behaviour in deepwater necessitates use of artificial light. Since video generates data that are not possible to achieve with flash-photos, e.g. holding times and links between different observations for individual fish, it is a crucial question to what degree patterns observed on video have relevance to the normal situation, i.e. vulnerability to capture without use of light. The present work indicates that although light reduced catchability, it did not have any major effects on orientation and distribution of Greenland halibut in front of the approaching trawl. Thus, video techniques seems likely to be useful for studying spatial distribution (Albert, Harbitz and Høines 2003b), but they should be accompanied with other methods in catchability, i.e. vulnerability, studies.
The Institute of Marine Research is currently developing methodology for automatic detection and analyses of large amounts of visual data on fish occurrence, position and angles in video and still photography and relating these observations on a common set of true world coordinates. This technique may be potentially useful for quantifying differences in fish abundance in front of trawls when observed with video/constant light and flash-photos respectively and may thus be used to estimate the proportion that escape under ground rope in the absence of light. This may be due to higher escape rates under the foot-rope or to higher degree of avoidance of entering into the trawl mouth area. Previous video recordings have indicated length-dependent escape under ground-gear. If the reduced catch rates in the video hauls were due to large increases in escape rates one would expect reduced mean length in the video hauls.
Length and sex composition of Greenland halibut using bottom trawls with flash-light (photo) and constant artificial light (video) illumination respectively
|Data from all sites combined.|
Position in real world coordinates of observed Greenland halibut individuals (dots) relative to the ground-gear (solid line)
|Data were taken from all photo frames with observations (upper panel) and every fourth video-frame from a 20-minute video recording (lower panel). The shading in each part of the picture is proportional to number of frames covered and so lightening the corresponding part of the sea floor.|
Distribution of orientation angle of individual Greenland halibut in front of ground-gear relative to the use of artificial light
Tow direction is towards the bottom of the page. Hatched areas represent individuals close to or resting on the sea bed and the solid lines represent fish swimming above the bottom (visible shadow).
5. LITERATURE CITED
Albert, O.T., A. Harbitz & Å.S. Høines 2003a. Greenland halibut observed by video in front of survey trawl: Behaviour, escapement, and spatial pattern. Journal of Sea Research, 50: 117–127.
Albert, O.T., A. Harbitz, R.B. Larsen & K.-E. Karlsen. Spatial structure and encounter rate of Greenland halibut in front of bottom-trawls. In R. Shotton (Ed) 2005. Deep Sea 2003: Conference on the Governance and Management of Deep-sea Fisheries. Conference Poster Papers (1–5 December 2003, Queenstown) and Workshop Papers (27–29 November 2003, Dunedin) New Zealand. FAO Fisheries Proceedings. No. 3/2. FAO, Rome 2005. Proceedings of the Deep Sea Conference: 147–151.
Glass, C.W. & C.S. Wardle 1989. Comparison of the reaction of fish to a trawl gear, at high and low light intensities. Fisheries Research, 7: 249–266.
Walsh, S.J. & W.M. Hickey 1993. Behavioural reactions of demersal fish to bottom trawls at various light conditions. ICES Marine Science Symposia, 196: 68–76.
Weinberg, K.L. & P.T. Munro 1999. The effect of artificial light on escapement beneath a survey trawl. ICES Journal of Marine Science, 56: 266–274.
O.T Albert1, A. Harbitz1, R.B. Larsen2 and K.-E. Karlsen1
1 Institute of Marine Research
POB 6404, N-9294 Tromsø, Norway
2 Norwegian College of Fishery Science
University of Tromsø
N-9037, Tromsø, Norway
Several studies have shown that the abundance of a fish species in the trawl mouth area may influence their vulnerability to capture. Generally the abundance of fish in a trawl mouth is a function of the overall abundance in the area and the distribution pattern of the species. For some large and fast-swimming fish species the behaviour is known to change with increasing abundance; when abundant even normally non-schooling species may form schools that influence their vulnerability to capture and thus the composition of the catch (Godø et al. 1999). Greenland halibut (Reinhardtius hippoglossoides) is a deepwater flatfish that is seldom observed live. It is generally conceived to be a vigorous swimmer and a roundfish-like flatfish. We made video recordings of this species in front of both a commercial groundfish trawl and a survey trawl at 500–800 m depths (Figure 1) and analysed the distribution pattern along the trawl path to see if they tended to clump together at any particular level of abundance. We also analysed how the encounter rate varied within the trawl hauls. Previous video recordings of Greenland halibut are limited and they indicate that the encounter rate is higher at the start of the hauls (Albert, Harbitz and Høines 2003, Albert et al. 2003). This may potentially affect survey indices and understanding these mechanisms may facilitate development of improved assessment techniques.
Video and trawl set-up. The dimensions given are for the Campelen survey trawl (first values) and the Alfredo-5 commercial groundfish trawl (last values) respectively.
2. ENCOUNTER RATE
Observations from the research survey in August 2003 corroborate the previous observed pattern from the previous survey in August 2002 of higher encounter and catch rates at the very beginning of the tows (Figure 2). The number of Greenland halibut observed during the first 200 m of the hauls were 3–4 times as large as for subsequent 200 m intervals. Encounters during the next 200 m interval (200–400 m after the trawl hit the bottom) were also significantly more numerous than in subsequent intervals. The individuals caught during the first few hundred meters were on average significantly larger than those caught later in the hauls.
This ‘start-effect’ may be related to some sort of surprise-effects on the Greenland halibut. Individuals distributed close ahead of where the trawl hits the bottom may be less able to establish their normal avoidance reaction towards the approaching trawl. If so, the question is if it is the encounter rate in the start, or after stabilizing, that best represents the true abundance in the survey area. With 20-minute hauls the start-effect of their encounter rate will affect 10–15 percent of the duration of each haul. Variation in this start-effect with, e.g. area, season, fish density and size-composition may potentially influence time series of abundance.
Encounter rate of Greenland halibut from the time the ground-gear hit the bottom onwards
No such start-effect was observed during hauls with the commercial groundfish trawl (Figure 2). These hauls were made in the same area as the rest, but at a different time of the year, with different gear and at much higher abundance levels of Greenland halibut. Further studies are needed to reveal how the start effect is influenced by gear type and fish density.
3. SPATIAL STRUCTURE
Neighbour fish distance, Dx, was defined as the estimated distance along the track between succeeding encounters of Greenland halibut determined by video recordings (Figure 3). For stations with low density (mean distance larger than 30 m), the neighbour fish distances were standardized by dividing the mean in the respective hauls. The neighbour fish distances for the large density stations (mean distance less than 6 m) were standardized by dividing by the inverse of the estimated fish density trends along their respective hauls. The fish density based on video is a better measure of abundance than the catch rate since it encompasses those individuals that escape under the footrope of the trawl.
Definition of neighbour fish distance along the trawl path (lower panel) and theoretical examples of distribution patterns
To analyse the distribution of neighbour fish distance, the standardized values were lumped together separately for large and small fish densities (Figure 4). The exponential distribution gave a good fit in both cases. The data indicate that individual Greenland halibut behave randomly in space and independent of each other. There was no tendency of clumped distribution even for the largest densities. However, commercial catches may be four times or more dense than the largest densities we analyzed.
Although significant trends were found for the four tracks with the greatest abundance (more than 600 fish observed), the maximum estimated coefficient of variation of these trends was 15 percent as compared to a much larger “between track”variance of fish density over the entire study area, based on catch rates from survey trawls. This means that short and frequent trawl hauls will minimize the coefficient of variation of abundance estimates, though bias aspects, such as the start-effect of encounters, should be taken into account when developing new survey designs (Figure 5).
Frequency distributions of neighbour fish distance compared with the exponential distribution
|Exponential distribution corresponds to random spatial distribution of individual Greenland halibut.|
Variation in fish density along the trawl tracks
|Data from hauls with high-fish density (N>600)|
The between-track variance of fish density dominates the within-track variance. The data should be further analysed to develop a sampling design that minimizes the variance of abundance estimates.
5. LITERATURE CITED
Albert, O.T., A. Harbitz & Å.S. Høines 2003. Greenland halibut observed by video in front of survey trawl: Behaviour, escapement and spatial pattern. J.Sea.Res. 50:117–127.
Albert, O.T., A.-B. Salberg, M. Zaferman & G.P. Tarasova 2003. Effects of artificial light on trawl catch and behaviour og Greenland halibut in front of trawl. Poster presented at Deep Sea 2003 on the theme “Population biology and resource assessment”.
Godø, O.R., S.J. Walsh & A. Engås 1999. Investigating density-dependent catchability in bottom-trawl surveys. ICES Journal of Marine Science, 56:292–298.
O.C. Wöhler1,2, P.A. Martínez1 and G.A. Verazay1
1 Instituto Nacional de Investigación y Desarrollo Pesquero (INIDEP)
Paseo Victoria Ocampo 1
7600 Mar del Plata, Argentina
2 Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)
Rivadavia 1917, 1033 Buenos Aires, Argentina
The Patagonian toothfish (Dissostichus eleginoides) exploited by the Argentine fleet is distributed in shelf and slope waters between 37°S and 56°S. Argentine catches are taken using two different fishing gears: bottom trawl and longline. Longliners mainly catch adult fish, while bottom trawlers often catch more juveniles, due to difficulties in operating in deeper waters or on bottoms less suitable for trawling. It has been observed that size selectivity is more dependent on the depth of fishing than on the fishing gear (Prenski and Almeyda 2000).
The Argentine fishery for Patagonian toothfish became important in the early 1990s (Figure 1). The largest catches of the species were obtained in 1995 (18 225 t), when large fishing boats were incorporated in the fleet, producing an expansion of the fishing grounds. Fishery statistics indicate that Argentine catches obtained by longliners have gradually declined from 1995. Trawler catches became more important in recent years, mainly since 1999, as a consequence of a management measure directed at other species. This resulted in a change in the fishing grounds by some of the larger trawlers and the subsequent change in the target species (Wöhler, Martinez and Giussi and 2001, Wöhler and Martinez 2002). During the last years the highest catches of this species come from a small area, where more than 80 percent of the total trawl catches were obtained (Figure 2). This area, which is situated to the South between Isla de los Estados and the Burwood Bank (54–55 °S and 62–64 °W), has shown to be an important recruitment area where juvenile fish aggregate, though adult fish are also abundant (Wöhler, Martinez and Giussi 2001, Wöhler and Martinez 2002).
Argentine catches of Patagonian toothfish obtained by bottom trawlers and longliners
Values of 2003 correspond to the period January–September.
Fishing grounds and catches of Patagonian toothfish exploited by the Argentine fleet during 2002
2. THE MANAGEMENT OF THE FISHERY
As a consequence of the declining trend in the CPUE obtained from adult fish (Wöhler, Martinez and Mari 2002) and the increase in the proportion of juveniles in the catches detected from 1999, and bearing in mind the biological characteristics that make the Patagonian toothfish susceptible to overfishing (high longevity, slow growth, considerable longevity and size of first maturity), the National Institute of Fishing Research and Development (INIDEP) suggested to the Argentine Fishing Authority that they establish precautionary measures to regulate toothfish exploitation with the aim of ensuring the long term sustainability of the fishery (Wöhler and Martínez 2002).
Since 2000, the Fishing Authority has enacted new management regulations that have been modified from time to time to enhance their efficiency. The main measures, implemented through different official resolutions, are listed below.
Establishing quarterly total allowable catches during 2003.
Juvenile protection area created by the Fishing Authority in October 2002 and enlargement in November 2003
3. THE NEW MANAGEMENT SCHEME
New management elements have been incorporated recently, one of them was the creation of an Advisory Commission for the Fishery, integrating different stakeholders, such as the administration, scientific research and the fishing industry (Figure 4). This Advisory Commission has the responsibility for advising the Federal Fishing Council and other fishing authorities about the best measures to efficiently implement the newly established management scheme. Another important element is the presence of the private sector in landings control and their participation in the Sub-Commission on landings control in addition to landing verification by government inspectors from the Fisheries Undersecretariat.
Structure of the Advisory Commission for the Argentine Fishery of Patagonian toothfish
Schematic diagram showing information sources used for the adaptive management established for the Argentine fishery of Patagonian toothfish by the Federal Fishing Council
(i.e. main fishing authority)
The Federal Fisheries Council has incorporated an adaptive fisheries management regime involving quarterly monitoring of the fishery, including the opening and closing of areas, penalizing those vessels that do not comply with the existing regulations and establishing a TAC for the next period. This adaptive management is based on real-time information from the fishery, obtained from three sources (Figure 5). This information is analyzed and controlled by the CASPMeN, with the objective of detecting management needs and correcting deficiencies. These activities include the following.
Reports of the Sub-Commission for landing controls, where the data on catch and juvenile proportion are verified and compared with skipper's declarations. These reports are also used as legal instruments for enforcement.
4. FINAL CONSIDERATIONS
The implementation of the new management scheme produced positive results during 2003. The Argentine Patagonian toothfish fishery has operated under new regulations since the end of 2002 and has developed with a different trend in respect to previous years. This change is reflected in a reduction of total catches (Figure 1) and a change in the fish size-selectivity pattern of the fleet, resulting in fewer juveniles being caught (Figure 6), a fact closely related to the depth restrictions imposed (Wöhler and Martínez 2003a, b, c).
Even in the short period of application of the new regulations, the functioning of the CASPMeN, control of landings at ports and the monitoring and assessment in real time by the Federal Fishery Council, have demonstrated to be effective tools for the management of the Argentine fishery for toothfish.
Size frequencies of toothfish caught by Argentine longliners and bottom trawlers during years 2000, 2001 and 2003 (January–September)
Note the reduction in the proportion of juveniles (specimens less than 82 cm TL) in the 2003 catches as a consequence of the new regulatory measures in force since the end of 2002.
5. LITERATURE CITED
Martínez, P.A., A.R.Giussi & O.C.Wöhler 2001. Area de operación de las flotas arrastrera y palangrera que capturaron merluza negra (Dissostichus eleginoides) en el período 1990–2000. INIDEP Informe Técnico Interno DNI № 73/01. 16 pp.
Prenski, L.B. & S.M. Almeyda 2000. Some biological aspects relevant to Patagonian toothfish (Dissostichus eleginoides) exploitation in the Argentine exclusive economic zone and adjacent ocean sector. Frente Marítimo, Vol 18 (A): 103–124.
Wöhler, O.C., P.A. Martínez & A.R. Giussi 2001. Características de la pesca por arrastre de merluza negra (Dissostichus eleginoides), en el Mar Argentino durante el año 2000 y recomendaciones tendientes a evitar la captura de juveniles. INIDEP Informe Técnico Interno DNI № 72/01. 22pp.
Wöhler, O.C., P.A. Martínez & N.R. Mari 2002. Estimación de índices de abundancia de merluza negra (Dissostichus eleginoides) en el Mar Argentino. INIDEP Informe Técnico interno DNI №13/02. 35 pp.
Wöhler, O.C. & P.A. Martínez 2002. La pesquería argentina de merluza negra en el período enero – septiembre de 2002: Aspectos preocupantes sobre su sustentabilidad en el largo plazo. INIDEP Informe Técnico interno DNI № 92/02. 14pp.
Wöhler, O.C. & P.A. Martínez 2003a. La pesquería de merluza negra en el mar argentino durante el primer trimestre de 2003: Resultados del programa de observadores a bordo de la flota dirigida al recurso y sugerencias acerca de las medidas de manejo para el segundo trimestre. INIDEP Informe Técnico interno DNI № 28/03. 11pp.
Wöhler, O.C. & P.A. Martínez 2003b. Descripción de la pesquería de merluza negra durante el primer semestre del ano 2003. INIDEP Informe Técnico interno DNI № 73/03. 13pp.
Wöhler, O.C. & P.A. Martínez 2003c. Análisis de la pesquería argentina de merluza negra durante el período enero–septiembre del año 2003. INIDEP Informe Técnico interno DNI № 99/03. 14pp.
1The research presented here is based on Anderson, O.F. & M.R. Clark 2003. Analysis of bycatch in the fishery for orange roughy, Hoplostethus atlanticus, on the South Tasman Rise. Marine and Freshwater Research54: 643–652.
O.F. Anderson and M.
National Institute of Water & Atmospheric Research Ltd.
PO Box 14–901, Kilbirnie
Wellington, New Zealand
The identification and measurement of the effect of a fishery upon associated species of deepwater fisheries is essential for their conservation. Benthic invertebrate communities are at particular risk in orange roughy fisheries because they tend to be fragile, erectile and slow growing, and because of the heavy nature of the fishing gear used. Estimates of the associated catch of the animals that make up these communities in the initial stages of a fishery are rarely made.
New Zealand Ministry of Fisheries observers have been present on New Zealand vessels in the South Tasman Rise orange roughy fishery, which is prosecuted in international waters south of Tasmania (Figure 1), from the early stages of the development of the fishery. These observers made detailed records of the catch weights of all species caught during 545 trawls between October 1997 and August 2000, covering between 10 percent and 22 percent of the total New Zealand and Australian annual catch.
Position of all recorded trawls (New Zealand and Australian) in the South Tasman Rise orange roughy fishery (grey dots) and all observed (New Zealand) trawls (black dots) for the period October 1997 and August 2000
AFZ, Australian Fishing Zone.
Bycatch ratios and the ratio of bycatch weight to tow duration were derived from these data and used to make estimates of total annual bycatch in the fishery for several species groups. Annual bycatch was estimated for three species of oreos (Oreosomatidae), for all coral species combined and for all other bycatch species combined, for the (1 October -30 September) fishing years from 1997–98 to 1999–2000.
Total oreo bycatch dropped from about 7 400 t to less than 300 t during this time. These estimates agreed well with recorded oreo landings data for three of the four years (Table 1). There was a considerable bycatch of coral, with both the bycatch ratio and the total bycatch declining during the period examined. The total bycatch declined from about 1760 t to less than 200 t a year. The coral bycatch comprised a large number of species and was dominated by Solenosmilia variabilis, a reef-forming stony coral that provides the structural habitat for a wide range of other invertebrate species. The long-term effect of such bycatch on the ecosystem is unknown. However, such bycatch needs to be considered in the management of a developing fishery. Annual bycatch of all other species combined, mainly rattails (Macrouridae) and dogfishes (Squalidae), was low (30–120 t). The bycatch of this group dropped sharply in each year, due a combination of a decreasing bycatch ratio and decreasing fishing effort.
Annual bycatch ratios and annual bycatch levels (with 95% confidence intervals) in the South Tasman Rise orange roughy fishery, divided into three species groups, and the reported landings of oreo species.
|Species||Fishing year||Bycatch ratio (kg/h)||Annual bycatch (t)||95% C.I.||Recorded landings (t)|
|Oreos||1997–1998||6 877||7 411||(4 336–12 841)||1 205|
|1998–1999||2 321||1 683||(1 072–2 471)||1 590|
|Corals||1997–1998||1 635||1 762||(480–3 298)||-|
O.F. Anderson, M. Clark and D. Gilbert
National Institute of Water & Atmospheric Research Ltd.
P.O. Box 14–901, Kilbirnie
Wellington, New Zealand
<firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org>
Some level of non-target catch and subsequent discarding is a feature of almost every commercial fishery and the bottom trawling method is considered to be among the most wasteful in this regard. To reduce the level of non-target (non-commercial) catch and discarding in fisheries we need to have an understanding of the scale of the problem and of the factors that contribute to the level of non-target catch and discards. Identification and measurement of the bycatch species associated with a fishery can also contribute to an improved understanding of fish communities and the possible impact of fishing on the long-term stability of the ecosystem.
NIWA has carried out several studies on behalf of the Ministry of Fisheries in recent years to determine the level of bycatch and discarding in New Zealand's major deepwater fisheries, and to identify factors specific to each fishery that contribute to it. These fisheries have included those for orange roughy (Hoplostethus atlanticus), oreos (Allocyttus niger, Pseudocyttus maculatus, and Neocyttus rhomboidalis), southern blue whiting (Micromesistius australis), hoki (Macruronus novaezelandiae), arrow squid (Nototodarus spp.), jack mackerel (Trachurus spp.), scampi (Metanephrops challengeri), and ling (Genypterus blacodes). Estimates were made by scaling up known catch and discard rates from the observed portion of the fishery to the total target fishery and were fine-tuned by stratifying the fishery according to factors identified from observer data as having a significant influence on bycatch and discards.
In most fisheries, and for most species categories, variation in bycatch and discard levels were most strongly associated with differences among the large numbers of vessels operating in each fishery. Other important factors were the target species (for jack mackerel, southern blue whiting, arrow squid, orange roughy and hoki), tow-type (mid-water or bottom trawl), time of year (for jack mackerel and arrow squid), and vessel nationality (for arrow squid and hoki). We found that while there was much variability in annual discard levels during the 1990s, they were tending upwards while catches slowly decreased (Figure 1). Annual bycatch also varied considerably from year to year, but again the overall trend was upwards with most of the higher values occurring in recent years (Figure 2).
These results provide a first step towards creating strategies for avoiding unwanted bycatch. Most of the fisheries examined proved to be relatively “clean”compared with published information on fisheries in other parts of the world. On average 0.05 kg of non-target fish were discarded per kilogram of hoki caught, the equivalent values for other species were: southern blue whiting, 0.02 kg; orange roughy, 0.06 kg; jack mackerel, 0.12 kg; arrow squid, 0.14 kg; and scampi, 3.5 kg.
Total annual discards in the seven fisheries examined (excluding ling) and the total reported catch for the 1990–91 to 2000–01 (1 October – 30 September) fishing years
Total annual bycatch in the seven fisheries examined (excluding ling) for the 1990–91 to 2000–01 (1 October–30 September) fishing years
P. Lorance1, V.M. Trenkel2 and F. Uiblein3
1 Laboratoire Ressources Halieutiques, IFREMER
B.P. 70, 29280, Plouzané, France
Rue de l'Ile d'Yeu, BP 21105
44311 Nantes Cedex 03, France
3 Institute of Marine Research
PO Box 1870 Nordnes, N-5817 Bergen, Norway
Behaviour studies of large commercially-exploited fish species provide information on both their life strategies and their potential vulnerability to capture by fishing gears. Data on the behaviour of slope species are currently sparse because their acquisition requires expensive, technologically-advanced means of observation.
During a study carried out in the bay of Biscay (West of France) at depths ranging from 1100 to 1500 m, natural and reaction behaviour of slope fish species were observed by the remotely operated vehicle ROV Victor 6000. Three areas were surveyed for a total duration of about 210 hours (see Trenkel et al. in press, for details). The behaviour of nine large benthopelagic species and families was analysed: roundnose grenadier (Coryphaenoides rupestris), orange roughy (Hoplostethus atlanticus), black scabbardfish (Aphanopus carbo), deepsea scorpionfish (Trachiscorpia cristulata echinata), Alepocephalus spp., chimaeroids, squalid and scyliorhinid sharks. Natural fish behaviour was classified in terms of (a) body position with respect to the bottom, (b) locomotion and (c) activity.
Individual reactions to the approaching ROV were categorized, providing not only the proportion of individuals reacting for each species but also their detailed reaction behaviour such as avoidance movements or an optomotor reflex leading to swimming in front of the ROV. Environmental conditions (depth, temperature, current speed and direction) and observation conditions (ROV speed and altitude) were recorded simultaneously with the fish observations in order to explain the variability in the observed reaction behaviours.
Multiple Correspondence Analysis (MCA) was used to characterise the behaviour repertoire of the different species and to identify similarities between species. The probability of reaction to the ROV was modelled as a function of environmental and observation conditions using generalised additive models (GAMs).
The species typology obtained from the MCA strongly separated T.c. echinata from all other species due it its motionless and generally non-reactive behaviour (Figure 1, Table 1). The other species formed two groups, (a) species actively swimming, distributed higher in the water column and more reactive and (b), species more or less passively drifting, closer to the bottom and less reactive responses. The second group comprised H. atlanticus and C. rupestris, two commercially important species previously shown as having strongly different life strategies and spatial distributions. H. atlanticus is an aggregative species, a good swimmer and a predator of large prey while C. rupestris is found dispersed, is a rather poor swimmer and feeds on small prey (Bulman and Koslow 1992, Koslow 1996, Mauchline and Gordon 1984). Despite these differences, their similar reaction patterns may make both highly vulnerable to bottom trawling. Chimaeroids and Alepocephus spp. belong to the same group with the exception of Alepocephalus spp. A noticeable proportion of individuals of these species were observed to swim slowly in front of the ROV, which may suggest that they are likely to show herding behaviour in front of a trawl.
First factorial plane of ACM of natural behaviour and reaction to the ROV
Taxon (■), Position in the water column (+), Locomotion (▞), Activity (◊), reaction to the ROV (●), Avoidance efficiency (○) were active variables and ROV speed () was illustrative (environment and other observation variables not represented).
Species groups and corresponding behaviour according to the MCA
|I||Trachyscorpia cristulata echinata||Sitting on bottom|
No reaction to the ROV
|Close to or touching bottom|
Station holding or drifting
No or light react to the ROV
|High up in water|
Strongly reactive to the ROV
Reaction behaviour modelling showed that the overall probability of reaction decreased with surveying speed. The results further suggested that the large benthopelagic predators displayed a range of species-specific behaviours that may change according to environmental conditions. As a consequence of the variability in both natural and reaction behaviour, the catchability by bottom trawls will vary between species and in time and space. Species specific behaviour, in particular the position in the water column, but also reaction behaviour will also affect population density estimates derived from visual transects counts (Trenkel, Lorance and Mahevas 2004).
Bulman, C.M. & J.A. Koslow 1992. Diet and food consumption of a deep-sea fish, orange roughy Hoplostethus atlanticus (Pisces: Trachichthyidae), off southeastern Australia. Marine Ecology Progress Series 82: 115–129.
Koslow, J.A. 1996. Energetic and life-history patterns of deep-sea benthic, benthopelagic and seamount-associated fish. Journal of Fish Biology 49: 54–74.
Mauchline, J. & J.D.M. Gordon 1984. Diets and bathymetric distributions of the macrourid fish of the Rockall Trough, northeastern Atlantic Ocean. Marine Biology 81: 107–121.
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M. Clark, I. Wright, R. Garlick, K. Mackay and M. Dunkin
National Institute of Water and Atmospheric Research
P.O. Box 14–901, Wellington, New Zealand
Multibeam echosounders are becoming increasingly and routinely used for detailed seafloor mapping up to several kilometres either side of the survey vessel. Such multibeam data have typically been used to map seafloor bathymetry and determine substrate composition for geological research. Such systems have powerful applications in benthic ecology and fisheries. They can accurately map submarine topography, such as seamounts or canyons where aggregations of commercial fish species may occur. In addition, the multi-beam seafloor acoustic backscatter data can differentiate between different substrate types, including sediment and exposed bedrock and hence be used to guide successful trawling operations. Multibeam mapping of fishing grounds is markedly more efficient than conventional single-beam echosounders and provides greater resolution and accuracy of both seafloor morphology and composition.
In 2003, during a fish and invertebrate biodiversity survey of the Lord Howe Rise and Norfolk Ridge seamounts (termed NORFANZ) the EM300 multibeam system on NIWA's research vessel Tangaroa was used extensively as a basis for sampling operations.
The existing charts of the region proved to be adequate for survey purposes on a large scale and indicated the approximate position of ridges or seamounts. However, on the scale of an individual feature, the depth, size, and shape of a seamount were often poorly charted. The width of seafloor mapped was four times the water depth, and so at 1 000 m depth the bathymetry was determined 2 km on either side of the vessel. This enabled rapid evaluation of the shape of the seabed, which was often very different from the chart.
The seafloor bathymetry was often rugged and complex (Figure 1) and the multibeam acoustic system proved essential to the success of fishing several sites. The backscatter intensity (Figure 2) gave an indication of substrate composition, which was used to plan trawling operations with less risk of damage to the trawl gear (Figure 3). It also gave data on the type of sediment and habitat, which may be used in later analyses of benthic community structure.
Hill shade model of a seamount surveyed during NORFANZ on the Lord Howe Rise
Hill shade model of the seamount showing the backscatter distribution
Dark colouration indicates higher reflectivity caused by hard rocky seafloor.
View from above of the seamount, showing the location of sampling sites
In this rugged terrain, these were undertaken where the topography and backscatter suggested there was less risk to the gear.
Funding for this work was provided by the Ministry of Fisheries (project ZBD2002/16) and the Foundation for Research, Science & Technology (contract C01X0224).
M. Haward and T. Potts
School of Government & Institute of Antarctic and Southern Oceans Studies and Antarctic
Climate and Ecosystems Cooperative Research Centre
University of Tasmania
Private Bag 22
Hobart 7001, Tasmania, Australia
Deep-sea fisheries by their nature provide a number of management challenges. Uncertainties in terms of stock assessment are matched by difficulties in compliance and enforcement, particularly when such fisheries are in areas outside national jurisdiction. Recent attention to the problems of unregulated fishing in areas outside national jurisdiction has centred on the efficacy of existing instruments, institutions and practices, and the opportunities provided by new management tools or measures. Providing effective management and combating illegal and, or, unregulated fishing is proving an extremely difficult task, even where deep-sea fisheries are regulated under regional fisheries arrangements or organisations. Several new or improved ‘tools’ including trade-related measures have been proposed to help increase effective management of deep-sea stocks outside national jurisdiction.
Trade-related measures such as certification and labelling provide means for reducing the financial incentives for catching fish illegally by restricting access to markets and, or, helping to inform consumer choice. Establishing trade-related measures requires regional fisheries organisations to establish a credible system of certification enabling port states and markets to identify with reasonable certainty the fish's provenance. The process of catch certification is distinct from processes to certify and then label fisheries products as derived from sustainably managed fisheries.
The concept of certification and eco-labelling as the basis of market based incentives for the development of sustainable fisheries is of recent origin. Over the last 10 years these approaches have grown in scope and have become increasingly visible to consumers. Certification refers to a focus upon the legal permissibility of the harvest and that the fish has been caught within an agreed regulatory framework. There are a wide variety of labels that could be considered to provide environmental information. These labels range from simple ‘appellation controlé’ (name/place of origin) approaches to labels issued by external parties after lengthy analysis of the product and production processes.
Certification primarily exists in regional fisheries agreements where cooperation on trade and management is necessary. Eco-labelling tends to move one step further than certification, where a label is granted on the basis of an investigation into the ecological integrity of the harvest, including ecosystem considerations within the fishery.
Labelling schemes and similar approaches centre on consumer interest in food quality and safety and the increasing interest in purchasing products that have been sustainably harvested. The analysis of certification and labelling arrangements and processes highlights opportunities and problems arising from developments in trade-related measures as tools for managing deep-sea fisheries.