DISTRIBUTION PATTERN OF UNDERWATER ILLUMINANCE FOR SQUID NET FISHERIES IN MALAYSIA

A study oIr the distribution pattern of underwater illuminance for squid net fisheries in Malaysiu rvas condueted fronr April to Septenrber, 1996 in sheltered waters of Kapas Island off the coast of Terenggatru, Peninsular Malaysia at Latitude E' 18.6'N and Longitude tog. lb.g.E. Three sets of paratuetets were collected fronr three cornmercial squid fishing boats and uuderwater illunrinaltce as estimated using a theoretical model. It was found that the underwater illutninance from the lighting systenrs of all the three boats managed to reach a depth of rnore than 40 ur (uraximuur depth of the fishing ground is 22 m). High Pressure Mercury iurrp" *""" fourrd to prodrrce higher lighting efficiencies as compared to incandescent lamis. Squid net fisheruretr in the study ared were found to be ernploying excess power for the fishing operation. to be the sea bottom (water depth in the fishing ground ranges from 8 mto22 m). At the depth of 25 m, schematic diagrarns frorn the light sources of the three boats managed to reach a depth ofrnore than 40 m below the sea surface.


INTRODUCTION
Artificial light has long been used in exploitation of cornrnercial frsh species (including cephalopodst in all parts of the world. This rnethod has been developed ernpiricallv and the intensity of light has been increased without any due consideration to the theoretical knowledge of fish attraction b5' light (Kawarnrrra et al.,lgg};Havase et al., 1983). The increase in the power of light intensity over the optirnurn lirnitation has becorne a serious concern for rnarine biologists (Nornura, 1985). Squid fisherrnen argrre that the increase of the power of frshing lights is necessary to attract rnore sqrdd in their effort to cornpete with other fisherrnen operating in the sarne fishing grorurd.
In Malavsia, sqrrid is rnainly landed by trawls, squid nets, sqrrid jigs, purse seines and traps (Sakri et al., 1995). With the exception of trawls, other gears are usrrally operated at nighttirne with the use of artificial light onboard the fishing boat as a rneans to aggregate squid for successftil harvesting operations (Ashirin & Ibrahirn,1gg2). Squid nets are one of the rnost popular squid frshing gears in Malay5in especially in the states of Kelantan and Terengganrr (on the east coast of peninsular Malal'sia). The gear is operated only at nighttirne especially druing rnoonless nights (after or before rtew rnoorr) b1' tahing advantage of the squid response to artificial light. This gear is ver), efficient at catching squids and has great potential in the near future. There are two t5,pes of lighting systerns installed onboard sqrrid netting boats that are used with the squid net; the attracting and the controllable light systerns. However, this study concentrated only on the attracting light system which is vital in aggregating squid before the harvesting operations. Knowledge of underwater light distribution patterns is important for the success and development of squid capture fisheries.
Apart frorn the reaction pattern of squid to light, the physical factors such as water transparency that affect underwater illuminance should also be considered in order to improve the catching efficiency and reduce the energy consumption of the squid fishing boats. Underwater illuminance is often very difficult to obtain by direct rneasurelnent due to the problems related to sea conditiohs that researchers encounter during their study. However, under-water illuminance can be estimated theoretically using a model as has been described by Hajisarnae ( 1996), Hamid (19g01 and Ogtrra et al. (L985). The purpose of this study is thus to deterrnine the distribution pattern of tmderwater ilhuninance of Malaysian squid netting boats using the theoretical rnodel based on Ogura's rnethod.

MATERIALS AND METHODS
Ogura et al. (1985) (Nornura, 1985). The obtained value was then converted to total candela using the following formula: Total candela = total lutnen / 4 2 b. Average height oflight source above the sea level The height of the light source was taken as the vertical distance from the light source to the sea level. This pararneter was measured from the three selected boats. c. Water transparency Water transparency was used to calculate the attenuation coeffrcient of light in water (new) of the selected fishing ground which was then approximated using the formula of p = I7l transparency (Ogura et a|.,1985). Based on the average transparency ofabout 13 m (the regional transparency in this fishing ground is 10-15 m)' the light attenuation in water for this fishing ground is cornputed to be approximately 0.13.
In addition to the above parameters, refraction of light in water also determines the intensity of underwater illurninance. The relationship between the angle of incidence to the angle of refraction for sea water is given in Table 1

RESULTS
The total nurnber of lamps and lighting characteristics used by the three selected boats are tabulated in Table 2. Boat A was equipped with 34 lamps; total power generated was 16,700 watts, Boat B with 31 lamps; 15,300 watts and Boat C with 26lamps; 12,800 watts. Boat A has the highest power light source among the experimental boats. The average heights of light sonrce for Boat A, Boat B and Boat C were rneasured to be 3.05, 2.80 and 2.65 m, respectir''ely Application of the estimated underwater light distribution for the three selected boats based on the theoretical rnodeling formula were calculated and shown in Table 3 for Boat A, Table 4 for Boat Itr''1. e-t" . c Tabel 2. Lighting characteristics of boats A' B and C Boats rvpes orrarnps )r",T#: -T;J:l" ""rif"tT; (

DISCUSSION
This study has presented a simple method for determining the underwater light distribution pattern using a theoretical rnodeling formula. The results obtained present an approxirnate value of underwater illurninance due to the influence of factors such as sea condition and fisherrnen's practice in handling lighting equiprnent. The main factor that could affect the results is the variation in the actual lurnen values of light used under actual field conditions. This is due to the fisherrnen's practice of occasionally changing the voltage of their electric generators to a higher or lower value than the standard (220-240 volts).
Referring to the illuminance diagrams of Boat A, Boat B and Boat C (Figures 1, 2 and 3), for an isoilluminance of 1 lux as a reference, the depths below the sea surface for Boat A, Boat B and Boat C are 30.5, 32.5 and 29.0 m respectively. The result shows that Boat B has the most effective vertical underwater illuminance followed by Boat A and Boat C, even though Boat A possesses the highest power light source among the selected boats (Table 2\. It can therefore be concluded that underwater light distribution does not only depend upon the power of the light source (total wattage) but also on the effrciency of the lamp (Table 2). This result differs from the study conducted by Ogura et al. (L985). They concluded from a study on the intensity of light lighted by incandescent lamps for squid lift net fisheries in Thailand that the distance of light in water terrds to increase proportionally with the power of light.
It was found from this study that even though Boat B had a lower power light source than Boat A, their total lumen is not. This means that the total lumen of light determines underwater illurninance more than the power of light source, On the other hand, Boat B which had a slightly higher power of light than Boat C (2500 watts) produced approximately twice the amount of total    appropriate lightine system. It would also enable squid frshermeD to have selective fishing based on the preferences of the squid species for underwater lieht illumiuance, This study also reveals that the squid netting boats in Terengganu waterg have been using excess power in their attracting light system. Hajisamae (1996) noted that the minimum preference level of underwater light illuminance for Sepioteuthie leeaoniono and Loligo chineneie is only 1.5 lux. However, it was found from this study that at a depth of 25 m, Boat C recorded an underwater light intensity of 2.2lux. This sbows that, even though Boat C employed tbe smallest power of lighting system, it was still excessively powered and illuminated beyond the 25 m depth. From tbe reeults of tbis etudy, it is recomrnended that high presBure rnercury lamps be used for the squid net fishery as they provide larger lightine efficiencies, longer life spau and lower energy consumption as compared to the incandescent lamps. This is supported by the fact that there is no significant difference in daily CPUE (Catch Per Unit Effort) between squid frshing boats using high pressure rnercury lamps and those using incandescent lamps as the rnain light attracting system (Hajisamae, f996).