During the study period on the lantern fish stocks, 310 hauls were carried out. The trial fishing stations were randomly selected and if there were good traces of fish with high density on echosounder, a fishing tow was undertaken.. The specifications of the midwater trawl one given in Section 2.1.3 early mentioned. The catch from each haul was estimated and information, eg, time of towing, distance of towing, depth, date, length of wire, velocity, direction, ambient temperature, sea surface temperature, position, etc. were recorded on special sheets.

The distribution of surface temperature (isotherms) are illustrated in Figures 42 to 45.The amount of catch from each trial tow for cruises 1 to 4 are shown in the tables 3-6.

Since an appropriate small mesh size net for myctophids was not used during the first three days of the first trial fishing, the results show a trend following the installation of a NY210D/12-20mm net as a net lining of the cod-end as all target fishes passed through the net meshes so that the catch volume was approximately nothing. Thus, during the second stage, a nylon NY210D/6-9mm net was obtained from the Iranians and was installed within the cod-end (along with the small-sized one) and then it was installed on the trawl pieces numbered 5 to 6 on the body of the net. Following the installation of this internal net along with the NY210D/12- 20mm, the trial fishing was carried out from 23 to 30 September for 20 tows.

Table 2

Biomass estimates for different cruises

The mean catch for haul was 1.74t, with the maximum catch of 3t and the mean catch per unit of time (hour) was 0.47 t/h and the maximum was 0.82 t/h. These figures indicate negligible amounts of catch.

During the third cruise of the fishing using a NY210D/6-9mm small mesh size net, the internal net was extended up to the sixth piece on the body of the net (for 6m) and even further. Fishing operations continued from 1 to 12 October for 8 tows during which the mean catch per haul was 3.56t with a maximum of 8.5t. In terms of catch per hour, the mean was 0.94t with a maximum of 1.71t. Compared with the fishing gears applied during the second cruise, the catch amount was doubled.

During the fourthcruise, the internal net, along with a nylon small mesh size net, were extended up to the fifth piece on the body of the net. With such an arrangement, the length of the body of the trawl was extended by 12m, the side cod-end (supplementary) by 8m and the cod-end itself for 15m; which together totaled 35m. Its cross-sectional area was 24.54m².

These developments helped the users prepare, at the extreme upper end of the trawl, an internal net made of NY210D/12-20mm nylon for the fourth piece on the body of the net after which the trial fishing was launched. During this phase seven tows were undertaken, from 4 to 6 October. The average catch from each operation (per haul) was 9t and the maximum was 12t. The mean catch was 1.92t/h, with a maximum of 2.7t/h. These figures indicate a four times increase in the amount of catch compared to the gears used in the second cruise; the catch was doubled compared to the third cruise of operations.

Because about 80 of the trial tows were done using trawls whose catching capacity was low, the catch volume recorded during the trial fishing of the first expedition was also low. Furthermore, since most of the time was spent surveying, the frequency of hauling operations was limited and also the concentration of the myctophids in most of the South Western areas of Jask was almost negligible. The trial fishing pertinent to the second expedition was combined with an exploratory operation over the entire region, from Ras’l Kuh to Meidani.

In spite of the fishing being the main objective during the first six days of the second expedition (15-20 October), the operation was only carried out on the grounds facing Meidani. But due to the very small size of the target fishes in the area, the catch volume, recorded, 0.5-3t in each operation and 0.11 to 0.68t in terms of per haul, was very low. From 20 October, a dense stock of the fishes in the areas facing Ghirishkin was encountered and catches of 1.2t in each tow were obtained.

From 26 October till 19 November, trial fishing was done in the area between Jask and Jageen where the stocks were relatively dense. About 60trial tows were launched in the region and the mean of the catch in each operation (per haul) was 6.5t with a maximum of 12t. In terms of catch per hour, the mean was 1.71t; the maximum level was 5.3t. The mean of daily catch recorded 21.2t with an extreme of 29.0t.

Daily catch of lantern fish in Cruise 1

Daily catch of lantern fish in Cruise 2

Daily catch of lantern fish in Cruise 3

Daily catch of lantern fish in Cruise 4

Table 7

Catch volume in each operation out of 60 tows

Catch volume in terms of per time spent fishing

The major reason justifying the lack of improvement in the catch rate during the trial fishing of the second cruise was that, due to the availability of only the short trawl warps, it was difficult to change the depth of towing and the depth of the target fish was deeper than 270m. Even if making such an adjustment were feasible, it would have been impossible to reduce the towing speed to a rate of 2knots.

Out of the 74 tows undertaken during the third expedition, 69 were in the region facing Jageen and Jask. Because of the development of a very dense fish concentrations which used to migrate close to the coast from the beginning of December, the catch volume appeared to be satisfactory.

Regardless of two unusual fishing operations out of the 74 tows, of the other 72 tows, the average catch was 7.75t with a maximum of 15t.

Catch volume in all operations

Catch volume per hour from 72 tows

Mean of the catch per day = 23.3t

Maximum level per day = 52t

The status and amount of catch during the trial fishing of the third cruise was satisfactory, but because of some technical defects and problems in fish meal machinery, only 2-3 fishing operations (hauls) were carried out per day. Shortly after, the machinery was repaired and the daily production exceeded 3t. From 18 to 23 November the number of operations (hauls) increased until 4.4 times per day with a maximum of six hauls per day.

Compared with the results of the second and third expeditions in the same region, there was an increase of nearly two-fold, namely the amount of catch per hour was two times more in the third cruise compared with the second cruise.

In the fourth cruise, the status of the lantern fish resources was completely different with the previous cruises and there was no good catch in Jask and Jageen areas. Therefore, the detecting activities and trial fishings were restricted from the southern part of Ras’Ikuh to the western areas of Meidanie.

Compared to the beginning of December, myctophid fishes were not found far from the coastal areas, shallow waters. Even though the density of the resources was satisfactory, the schools of fish were not eye-catching enough and they were scattered in a way so that the outcome was a reduction in the level of catch.

Because there was a relatively dense school of the fish scattered 18miles off the southwestern part of Jask, trial fishing was undertaken during which the mean catch in each operation was 6t with the maximum of 12 mt. The mean of the catch per hour was 2.43t with a maximum level of 6t.

Catch volume per haul (December)

Catch volume per hour (December)

From 19-23 January, 20 tows were undertaken in the Jageen - Jask region in which the mean of the catch in terms of each operation was 5.5t with a maximum level 10t. The volume of catch per hour was 2t with a maximum of 4.5t. These rates did not appear to constitute a satisfactory volume.

Catch volume in each haul (January)

Catch volume per hour (January)

From 24 January until 7 February, the researchers encountered a relatively high number of fish schools in the grounds facing Ghirish Keen so that in 42 tows out of 45, the average catch was 8.5t and the maximum 17t. The mean of the catch per hour and its maximum were 4.45t and 20t, respectively which were not so large.

Catch volume in each haul (February)

Catch volume per hour (February)

The mean catch during the day in this region was 26.5t/day with a maximum of 47t/day.