AGE AND RATE OF GROWTH OF THE INDIAN MACKEREL, RAS- TRELLIGER CANAGURTA (CUVIER) WITH NOTES ON ITS FISHERY AT KARWAR BY N. RADHAKRISHNAN {Central Marine Fisheries Research Institute) INTRODUCTION Information on the growth of a fish is an important pre-requisite in under­ standing the dynamics of fish populations. In fishery yield studies, such as those of Beverton and Holt (1957) the growth is a basic variable determining the exploitable stock and yield from the fishery. The present paper deals with the age and growth studies of the Indian mackerel incorporating the results of investigations carried out at Karwar from January 1954 to March 1959. At Karwar, the mackerel season generally commences in October and ends in the following March. After this period, only stray specimens are netted. LENGTH FREQUENCY STITDIBS For purposes of this study, the total length of the fish was taken into account. The specimens used in the present investigation were obtained from the inshore fishing grounds around Karwar by the shore seines {Rampan and Yendi) which are the most important gears used all along the Kanara coast. Text figures 1 to 4 show the length frequency distribution of samples obtained at monthly intervals from January 1954 to March 1959. In some months, where the samples were too small to form a comparison with other months, the data for these months were neglected from the length frequency analysis. Further, the monthly data of each year have been pooled into three periods, (t) January to March (2) April to September and (3) October to December. This was done for the sake of convenience, to make comparison from one period to the other more uniform. The yearly analysis as based on these three periods, can Be summarised as follows: — 1954: In 1954, the catches were heavy only during January, March, July and September to December. In April and June there were no landings and in May and August only a few specimens were present in the catch. Since in these months, the mmibers were too small to form a basis of comparison ffie data were omitted. The size ranges recorded during the various months of the year are given below:— January . 182—233 mm. July . 129—252 mm. February . 181—227 mm. August . 151—175 nun, 187 188 INDIAN JOURNAL OF FISHERIBS March . 183—222 mm. September . 153—229 mm. April . Nil landings October . 171—214 mm May . 113—161 mm. November . 184—245 mm June . Nil landings December . 171—237 mm January to March: These months represent the latter half of the 1953/ 1954 mackerel season. It can be seen from Text figure 1 that the mode "A" at 195 mm. group in January remained more or less unchanged during the corresponding two months — February and March. Besides this, another mode "B" at 215 mm. were noticed for all the three months. July to September: The mode "B" can be traced further at 225 mm. group in July 1954. During the same month, another mode "C" representing a new brood makes its first appearance at 135 mm. group. Three modes at 145 mm., 175 mm. and 195 mm. are visible in September. The mode at 175 mm. may have arisen from a group seen in July with mode at 135 mm. ("C"). while the modal group 145 mm. ("D") is a new brood entering the fishery for the first time. The group 195 mm. ("E") may have arisen from a still earlier brood whose existence cannot be traced owing to the lack of data during April-June period. October to December (First half of the 1954/1955 season): The mode "C" seen at 175 mm. in September 1954 enters the fishery at 195 mm. in October and at 205 mm. in November. The mode at 225 mm. seen for November and December may be the continuation of the mode "A". The mode "B" can be further traced at 235 mm. in November 1954. 1955: Large samples were available for January, February, May, Septem­ ber, October and November. Landings of mackerel were not recorded at Karwar during April and June. Even though the samples were not very large in March and July, yet they depicted a true picture of the size distribution of the species. The size ranges recorded for the year are shown below: — January 181—247 mm. July . 163—248 mm. February 195—247 mm. August . 115—145 mm. March . 212—246 mm. September . 120—169 mm. April Ni] landings October . 140—224 mm. May 121—251 mm. November . 171—247 mm. June Nil landings December , . 173—243 mm. Age and rate of growth of the Indian mackerel 189 JUME 85 NIL LANVINaS Kiiae la £ A MAY 1955 0 SO AVRIL'SS NIL LANOINQS -fX MAR 1999 N>aoa. FEB 1959 o N«aL&4 90 JM 1959 N»4ni KC 1994 N«(|4I NOV 1854 AU6 'S4 SAnpiE NCSLECTEB SO C JULY 1994 N«6I AfRILAKD JtAIG 1954< KIL lANDIHSS MAY 1954 SANP£ES MEOIBCTEO AZE atiOUP IN MIUmiTBRES Text Fig. 1. Length frequency distribution of the Indian mackerel in each month Ax>m January 1954 to June 1955, 190 INDIAN JOURNAL OF FISHERIES January to March: (Latter half of the 1954/1955 season): The mode "D" seen first in September 1954 at 145 mm. and later at 195 mm. in December continued to appear in the catches of January at 205 mm. (Text figure 1) The mode "E" seen in September at 195 mm. can be further plotted at 225 mm. for February and March, April to September: The mode "A" is traced further at 235 mm. in May and at 245 mm. in July, thus giving a clear indication of the growth which has occurred during this period. Thus, one could clearly see that the mode "A" which made its first appearance in January-March 1954 at 195 mm. continued to occur in the catches during November-December 1954 and when it entered into the month of July 1955 it attained a length of 245 mm. (Text Figure 2). Modes "F" at 155 mm. in May, "G" at 135 mm. in August and "H" at 145 mm. in September 1955 give indications of the entry of different broods of difi'erent size groups into the fishery of this period. October to December: (First half of the 1955/1956 season): In October, three dominant size groups were noticed, the mode "H" at 165 mm., "G" at 185 mm. and "F" at 215 mm. In November, the mode "F" is seen at the same position as it was for the previous month. 1956: During the period from May to June only stray specimens were recorded and hence this has been considered as insuflScient for analysis. Mackerel landings were not recorded for the month of April. The size ranges noted for the year are as given below: — January . 174—249 mm. July . 212—246 mm. February . 203—239 mm. August 98—246 mm. March . 201—249 mm. Septembe • . 132—168 mm. April . Nil! landings October . 161—235 mm. May . 219—262 mm. November . 105—246 mm. June . 259 mm. December . 131—248 mm. January to March: (Later half of the 1955/1956 season): The mode "F" seen first in May 1955 at 155 mm. can be traced further for February at 225 mm. (Text Figue 2). Viewing the frequency curve for March 1956, it is seen that the mode "H" has shifted to 215 mm. Age and rate of growth of the Indian mackerel 191 1* e SO o 20 0 20 o 20 0 JUNE ,'56] SAMPLES NEQLECTEB 20 MAY 5Gj ATRIL^Se NIL CATCH JULY 1956 S MAR.. 1956 il|9 190 130 140 ISO 160 190 tao 4«0 XOS 9|0 820 930 S4« a 50 SIZE CROUP IN MILLIMETET2S TEXT FIG. 2.—Length frequency distribution of the Indian mackerel in each month from July 1955 to December 1956. 16—lDCM/FRl/67 192 INDIAN JOURNAL OF FISHERIES April to September: In July 1956, the dominant size groups recorded were 235 mm. This can only be the continuation of the mode "F" seen during the 1955/1956 season. For August and September, individuals in the smaller size groups entered the fishery. The dominant group in August was 115 mm. (mode "I") which can be further traced in September at 155 mm. October to December: (The first half of the 1956/1957 season): In October, the presence of two modes one at 185 mm. ("I") and the other at 235 mm. ("F") were noticed. The "F" mode remained at the same position for November and December. In November, besides this mode, two other modes viz-, "J" at 115 mm. and "K" at 175 mm. are seen. The former mode can be further located at 155 mm. in December. 1957: Samples for April to September were not sufficient and therefore these have been omitted from the length frequency analysis. The size ranges recorded for the year are as follows: — January . 121--238 mm. July . 215—248 mm February . 191--236 mm. August . Nil landings March . 191--254 mm. September . 122—142 mm April . 154--240 mm. October . 122—245 mm May . 185--235 mm. November . 164—254 mm June . 196--237 mm. December . 191—249 mm January to March: (Latter half of the 1956/57 season): The mode "K" seen during November 1956 at 175 mm. contributed to the fishery again in February-March 1957 (Text Figure 3). This mode has progressed to 215 mm. thus showing an increase of about 40 mm. The mode "J" appeared at 185 mm. in January. The dominant groups seen at 225 mm.