Abstract:
A system for reducing trawl bycatch, the system including at least one light arranged externally of the net to stimulate a phototactic response in the major bycatch species present to reduce entry of such species into the net.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a filing under 35 U.S.C. 371 of International Application No. PCT/AU2013/000148 filed Feb. 20, 2013, entitled “System, Apparatus and Method for Reducing Trawl Bycatch,” which claims priority to Australian Patent Application No. 2012900652 filed Feb. 21, 2012, which applications are incorporated by reference herein in their entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a system, apparatus and method for reducing trawl bycatch. 
       BACKGROUND OF THE INVENTION 
       [0003]    Previously proposed arrangements to reduce trawl bycatch have focussed on allowing undesired catch (juveniles and non-target species) to escape from trawl nets. For example, bycatch reduction devices (BRDs) have been proposed to allow undesired catch to escape from codends of trawl nets. A significant problem with this is that of loss from the required catch. Another problem is that an unknown, but potentially significant, proportion of escaping catch die (termed “post-escape mortality”). 
         [0004]    What is needed is a solution for reducing trawl bycatch that addresses the above difficulties. 
       SUMMARY OF THE INVENTION 
       [0005]    According to the present invention, there is provided a system for reducing trawl bycatch, the system including at least one light adapted to be arranged externally of the net to stimulate a phototactic response in the major bycatch species present to reduce entry of such species into the net. 
         [0006]    The light may illuminate downwardly to exploit negative phototaxis, upwardly to exploit positive phototaxis, or at a range of intermediate orientations. In practice, the orientation of the light can be selected by the user depending on the major bycatch species likely to be present at any particular location, season or time. 
         [0007]    According to the present invention, there is also provided a system for increasing trawl catch, the system including at least one light arranged externally of the net to stimulate a phototactic response in the major species present to attract such species toward the net. 
         [0008]    The light may illuminates downwardly to exploit positive phototaxis. The light may also illuminate at an angle inclined to the vertical. 
         [0009]    Alternatively or in addition to varying the orientation of the illumination, the wavelength and/or intensity of the illumination can be varied and/or a strobe effect can be provided. 
         [0010]    For prawn (or shrimp) trawling the light is arranged in advance of or at a mouth of the trawl net whereas for fish trawling the light may be arranged towards the rear of the net. 
         [0011]    There is also disclosed an underwater light apparatus for use in the systems defined above, the apparatus including a waterproof housing, a towing attachment arranged on the housing, a generator inside the housing, a turbine for driving the generator, when the apparatus is forced through the water with the net, and a light source connected to the generator and arranged in the housing to illuminate through a light transmissive portion of the housing. 
         [0012]    In one embodiment, the turbine which is arranged externally of the waterproof housing, is at the forward end thereof, the orientation of the light transmissive portion determining the orientation of the illumination. 
         [0013]    The present invention also provides an underwater light apparatus for use in the system defined above, including a waterproof housing, coupling means for coupling the apparatus proximal to the net, and at least one light source, the apparatus being configured to selectively illuminate in different orientations comprising a downwards direction, a forwards direction and an upwards direction. 
         [0014]    The coupling means can be arranged on the housing and adapted for coupling to the headline. 
         [0015]    The at least one light source can include an upward facing light source, a forward facing light source and a downward facing light source, each being selectively operable. 
         [0016]    The present invention also provides a method for reducing trawl bycatch, the method including the step of providing illumination externally of a trawl net during towing thereof so as to stimulate a phototaxis response in at least some undesired species which causes at least some of them to avoid entering the trawl net. 
         [0017]    The present invention further provides a method of increasing trawl catch, the method including the step of providing illumination externally of a trawl net during towing thereof so as to stimulate a phototaxis response in at least some species which causes at least some of them to be attracted toward the trawl net. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    An embodiment of the invention will be described by way of example only with reference to the accompanying drawings, in which: 
           [0019]      FIG. 1  is a perspective view of an embodiment of a trawl bycatch reduction system of the invention; 
           [0020]      FIG. 2  is a top plan view of the system; 
           [0021]      FIG. 3  is an embodiment of an underwater light apparatus used in the system; 
           [0022]      FIG. 4  is a perspective view of a further embodiment of an underwater light apparatus used in the system; 
           [0023]      FIG. 5  is a top plan view of the underwater light apparatus of  FIG. 4 ; 
           [0024]      FIG. 6  is a side view of the underwater light apparatus of  FIG. 4 ; 
           [0025]      FIG. 7  is rear view of the underwater light apparatus of  FIG. 4 ; 
           [0026]      FIG. 8  is a front view of the underwater light apparatus of  FIG. 4 ; 
           [0027]      FIG. 9  is an exploded perspective view of the underwater light apparatus of  FIG. 4 ; 
           [0028]      FIG. 10  is a schematic wiring diagram of the underwater light apparatus of  FIG. 4 ; and 
           [0029]      FIG. 11  is a perspective view of a further embodiment of a trawl bycatch reduction system. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0030]      FIGS. 1 and 2  illustrate an embodiment of a system  10  for reducing trawl bycatch. The system  10  is attached to a conventional trawl net  12  having a mouth defined by a headline  14  and a footrope  16  vertically spaced apart by trawl doors (or otter boards)  18 . The system  10  includes a plurality of lights  20  arranged generally equidistant from one another along the headline  14  to illuminate downwardly across and over the mouth of the trawl net  12 . 
         [0031]    During towing of the trawl net  12  by a trawler (not shown), the lights  20  are activated so as to produce a plurality of downwardly diverging illumination cones having at least partially overlapping illumination footprints on the seabed or in the water column underlying the mouth of the trawl net  12 . 
         [0032]      FIG. 3  illustrates one embodiment of an underwater light apparatus  20  used in the system  10 . The apparatus  20  includes an elongate waterproof housing  22  having forward and rearward ends. An upper towing attachment  24  is arranged on the housing  22  between the forward and rearward ends to removably connect the apparatus  20  to the headline  14  of the trawl net  12 . A turbine  26  is arranged forwardly of the housing  22 . A generator  28  inside the housing  22  is connected to the turbine  26  by a coupling  30 . The generator  28  powers a light source  32  arranged in the rearward end of the housing  22  to illuminate downwardly and forwardly through a lower light transmissive portion  34  of the housing  22 . 
         [0033]    The housing  22  is, for example, formed as an injection moulding in high density polycarbonate. The upper towing attachment  24  is, for example, a twin bolt double saddle which allows the apparatus  20  to be easily and quickly installed on the headline  14  of the trawl net  12 . The turbine  26  is, for example, an open blade axial-flow horizontal turbine made of high density rubber with a low aspect ratio and a high thickness and rake so as to shed debris encountered during towing. The coupling  30  is, for example, a magnetic coupling that is pressure rated to a water depth of 300 metres. The light source  32  is, for example, a 3 Watt, 98° beam angle LED light emitting diode (LED) which uses heat sink into the surrounding water to achieve a burn time in excess of 30000 hours. The light transmissive portion  34  is, for example, an optical quality light lens that is integrally formed in the polycarbonate housing  22 . Other equivalent components and materials may also be used in the underwater light apparatus  20 . 
         [0034]      FIG. 4  illustrates another embodiment of an underwater light apparatus  120  for use in the system  10 . The apparatus  120  includes a housing in the form of a front casing  122   a  and a rear casing  122   b,  between which a pair of o-ring seals  123  are disposed to seal the apparatus  120 . The apparatus  120  includes at least one light source and is configured to selectively illuminate in different orientations comprising a downwards directions, a forwards direction and an upwards directions. In the illustrated embodiment the apparatus  120  includes three light sources in the form of LED assemblies, a downward facing LED  132   a,  a forward facing LED  132   b,  and an upward facing LED  132   c.  It will be appreciated that a single light source may be provided within the housing and configured to be pivotable so as to vary the orientation of illumination as required. Furthermore, although the LED&#39;s are shown to be either vertical or horizontal, they may be otherwise inclined, such as at intermediate angles in between those shown. 
         [0035]    The LED&#39;s  132   a,    132   b,    132   c  can be selectively operated, individually or in combination, as required. The apparatus  120  is electrically coupled to the system  10  via connector  150  and physically coupled proximal to a mouth of the trawl net via a coupling means, which in the described embodiment is a pair of rigid mounting points  124   a,    124   b  which are arranged on the housing and fixed to the front casing  122   a.    
         [0036]    As illustrated in  FIG. 9 , the front casing  122   a  can be separated from the rear casing  122   b  so as to provide access to internal components of the apparatus  120 . Within the apparatus  120  is an electronic module  140  that includes a battery  142 , battery charger  144  and a LED driver  146 . The LED&#39;s are powered by the battery  142 , which may be charged in situ or removable for charging. In other embodiments, the LED&#39;s may be powered via a power cable extending from the system  10  and connected to the connector  150 . 
         [0037]    In  FIG. 9 , the upward facing LED  132   c  is shown in an exploded configuration. The LED  132   c  includes a housing  150 , a lens  152  and a lens retaining ring  154 . Disposed on either side of the lens  152  are sealing o-rings  156   a,    156   b.  The LED  132   c  also includes an optical element  158  and a PCB  160 , each of which are fixed to the LED  132   c  by a retaining clip  162 . Each LED of the apparatus  120  is, for example, a 7 Watt 35° beam angle LED, though it will be appreciate that LED&#39;s of other configurations could similarly be used. 
         [0038]      FIG. 10  illustrates a schematic diagram of the apparatus  120 , illustrating how a plurality of apparatuses  120  can be electrically coupled to each other within the system  110 . A data link is provided so as to allow communication between a controller (not shown) and the apparatuses  120  so that the LED&#39;s can be selectively operated. 
         [0039]      FIG. 11  illustrates a further embodiment of a trawl bycatch reduction system  110 , incorporating a plurality of underwater light apparatuses  120 . It will be appreciated that system  110  could include a plurality of underwater light apparatuses  10  as previously described, and that system  10  could similarly incorporate a plurality of underwater light apparatuses  120 . 
         [0040]    The trawl bycatch reduction system  110  includes a conventional trawl net  112  having a mouth defined by a headline  114  and a footrope  116  vertically spaced apart by trawl doors (or otter boards)  118 . The system  110  includes a plurality of lights  120  arranged generally equidistant from one another along the headline  114  to illuminate downwardly across and over the mouth of the trawl net  112 . The lights  120  are electrically coupled, via a cable  164 , to each other and a charging node  166 . The charging node is connected via a cable  168  to a controller  170 , which in the illustrated embodiment is a computer, and a power source  172 . 
         [0041]    In use, the system  10 ,  110  provides illumination generally directly downwards in advance or at the mouth of the trawl net  12 ,  112  which stimulates negative phototaxis (a flight response with movement away from light) in at least some undesired species which causes at least some of them to avoid entering the trawl net  12 ,  112  thereby at least partially reducing trawl bycatch. The system  10 ,  110  obviates the problem of catch loss and post-escape mortality by deterring undesired species from entering the trawl net. 
         [0042]    Although the system described above provides illumination generally downwards, as previously explained the illumination could alternatively be generally upwards for positively phototactic species or at an intermediate orientation. Illumination generally upwards and away from the mouth of the net can act to draw fish which exhibit a positive phototactic response away from the mouth of the net. In this regard, if an unwanted species which is known to exhibit a positive phototactic response, such as pony fish, is present in the area, providing illumination which is generally upwards and away from the mouth of the net can reduce the catch of that species because it is drawn away from the mouth of the net. The orientation of the illumination from apparatus  20  can be varied by varying the position of the light transmissive portion  34  in the housing  22 . The orientation of illumination from apparatus  120  can be varied by selectively operating the desired LED  132   a,    132   b  or  132   c.    
         [0043]    Embodiments of the invention can be used in all types of trawling, but are particularly advantageous in prawn (or shrimp) trawling which is known to have the highest rate of bycatch. For example, it is estimated 7.3 million tonnes of fish are discarded as bycatch each year. Tropical shrimp trawling is estimated to be responsible for a quarter of this annual bycatch. For every kilogram of marketable prawns, there are between 3 and 20 kilograms of undesired fish discarded at sea as bycatch. 
         [0044]    It has been surprisingly found that when embodiments of the invention are attached to prawn trawl nets, fish bycatch is reduced by up to 30 percent, and prawn catch is increased by up to 30 percent. Based on these results, embodiments of the invention have the potential to reduce significantly global bycatch, thereby significantly improving the sustainability of non-target species, as well as the sustainability of juvenile commercial species that cohabit with prawns. 
         [0045]    It will be appreciated that different species of marine life will exhibit a different phototactic response, and that this response may vary according to the prevailing conditions at the trawl site and throughout the lunar cycle. Accordingly, the configuration of the system  10 ,  110  may be varied as required, having regard to the target catch and the species of unwanted catch present in the trawl area at that time. In this regard, parameters of the illumination, such as wavelength, brightness and beam orientation may be varied to suit the prevailing conditions. Also, the illumination may be in the form of a strobe or flashing light. 
         [0046]    The decrease in bycatch means trawlers will have reduced fuel costs as they are trawling with less drag from their trawl nets. The surprising and unexpected increase in prawn catch that accompanies the decreased bycatch means that prawn fishermen can reduce their number of fishing days to catch a given quota of prawns. Moreover the reduction in bycatch means that net shape is not compromised and subsequent processing time, and hence labour costs, is reduced. 
         [0047]    This proposed system for reducing bycatch may also be used in conjunction with other systems for reducing bycatch. 
         [0048]    It will be appreciated that the described system  10 ,  110  may also be used to increase trawl catch of species which exhibit a positive phototactic response. In this regard, the illumination can act to attract that species toward the net to increase the catch. 
         [0049]    The embodiments have been described by way of example only and modifications are possible within the scope of the invention disclosed.