The fecundity of Clyde plaice

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(1)J. mar.. biol. Ass. U.K. (1958) 37, 3°9-313 Printed in Great Britain. THE. FECUNDITY. OF CL YDE PLAICE. By T. B. BAGENAL The Marine Station, Millport. (Text-fig. 1) In early 1956 and again in 1957 small samples of mature female Plaice Pleuronectes platessa L. were collected for fecundity estimates to be compared. with Simpson's (1951) results for the North Sea populations, and the data from elsewhere that Simpson summarizes. The fish were collected on 22 and 27 February 1956 and 7 January 1957 by trawling off Mountstuart House, Isle of Bute, at ca. 40 m. The treatment, of the fish was similar to that of the Long Rough Dabs collected for fecundity estimation and which has been described in detail (Bagenal, 1957a). This paper on Long Rough Dabs should be consulted for details of the collection and treatment of the fish, and of the laboratory methods for the estimation of the egg numbers and also of the statistical analysis of the data. I should like to thank the master and crew of M.F.V. Calanus, and Miss Sheila Morris who counted the eggs. RESULTS The data are shown in full in the Appendix, and summarized in Table 1. The relation of fecundity and length of the plaice is shown in the scatterdiagram (Fig. 1), in which the curves for Simpson's North Sea Southern Bight and Flamborough grounds, and the curve for Kandler & Pirwitz's (1957) Baltic plaice from the Bornholm area, are also shown. Kandler & Pirwitz unfortunately, do not give the raw data for each fish and the curve in Fig. 1 has been calculated from the mean values they give. From Table 1 it can be seen that the fecundity adjusted to a common length was greater in 1957, but the' condition' of the fish (as expressed as the expected weight of a 37 em. plaice) was greater in 1956 (cf. Bagenal 1957b). However, neither the general level of fecundity nor the condition was significantly different. This is shown in Table 2 which summarizes the covariance analyses of the regressions of the logarithms of length and weight on log fecundity and also that oflog length on log weight, for both sets of data. None of the regressions are significantly different and the data may be pooled. Comparisons with the results of other workers are shown in Table 3. It is clear that the Clyde plaice fecundity adjusted for length is considerably. /.

(2) T, B. BAGENAL. 310. 500. Bornholm Southern. Bight. 400. •. >-.. X. .~. -0 C. x. (3 200. x~. <lJ. LL. •. x. x.·x. *• XX eJ!1. X. X. •. ,. .x •••. 100. X X. 40. 45. Length. (em). Fig, 1, Scatter diagram showing the relation of fecundity and length of plaice from the Clyde, and the calculated curves for Flamborough, Southern Bight and Bornholm fish (from Simpson, and Kandler & Pirwitz), ., 1956; X, 1957, TABLE. 1.. SUMMARY OF CLYDE PLAICE FECUNDITY DATA GIVEN IN THE APPENDIX. Year Number of fish Mean length (cm) Mean weight (g) Mean age (years) Mean fecundity Wfor 37 cm F for 37 cm. 1956. 1957. 31. 31. 39'76 653'1 5'4 171,080 530'7 136,693. 36'91 518'6. 5'1 I36,6u 522'2 137,840.

(3) THE FECUNDITY. OF CLYDE PLAICE. 3II. higher than that of the North Sea, and much lower than the Baltic plaice fecundity. These differences are statistically significant. Simpson (1957) has recently given a preliminary account of the fecundity of plaice from the Irish Sea; this appears to be similar to that of the Clyde fish given here. TABLE 2. SUMMARY OF THE ANALYSIS OF COVARIANCE TESTING THE FECUNDITY-LENGTH, FECUNDITY-WEIGHT AND LENGTH-WEIGHT RELATIONS FOR CLYDE PLAICE IN 1956 AND 1957 Fecundity on length. Source Due to total regression Difference between means regression and average within subgroups regression Between adjusted subgroup means Between regression coefficients. **. Regression of fecundity on weight. **. Length on weight. **. N.S. N.S. N.S.. N.S.. **, indicates significance at I % probability level. N.S., indicates not significant at 5% probability level. - , indicates mean square less than that against which it is tested. TABLE 3. MEAN FECUNDITY GRESSION COEFFICIENTS ON LOG LENGTH. ADJUSTED FOR FISH OF 37 eM, AND THE REOF THE REGRESSIONS OF LOG FECUNDITY. (From data given in this paper, by Simpson, and by Kandler & Pirwitz (1957).) Author This paper Simpson Kandler & Pirwitz. Region. Date. Clyde Clyde North Sea Southern Bight North Sea Southern Bight Flamborough Kieler Bucht BornhoIm area. 1956 1957 1947/48 1948/49 1948/49 1952/53 1952/53. F for. 37 cm 136,693 137,840 82,996 87,152 96,492 37°,954 322,771. Regression coefficient. 3'II 3'81 3'13 3'28 2'85 3'12 3'58. Simpson (1951) showed that, among the 1947/48 and 1948/49 Southern Bight fish of the same length, there was only a negligible increase in fecundity with age, whereas for fish of the same age there was a considerable fecundity increase with length. He concludes: 'Thus age alone, apart from its relation to size, appears to have played an insignificant part in determining the fecundity of these fish.' This applied to fish of the same population. On the other hand, when comparing different populations (from the Southern Bight and Flamborough) he showed that the faster-growing Flamborough fish were more fecund. 'These observations lend weight to the view already expressed that fast growing, well fed fish have a higher mean fecundity than slow growing fish.' Age of course comes into this, since fast-growing fish are younger for a given length than slow-growing ones. In Table 4 the mean lengths and fecundities are given for each age group of the Southern Bight, Flamborough.

(4) T. B. BAGENAL. 312. and Clyde plaice. Here Simpson's remarks are confirmed and shown to apply to the Clyde fish also, which are faster growing and more fecund than even the Flamborough fish.. XVI. TABLE 4, THE MEAN LENGTH AND MEAN FECUNDITY (TO THE NEAREST THOUSAND) FOR DIFFERENT AGE GROUPS OF SOUTHERN BIGHT, FLAMBOROUGH AND CLYDE PLAICE Southern Bight "No, II8 61 616 66 106 4°'0 47'0 31'1 47'7 43'7 42'9 4I6S 123 174 127 47 42'2 182 3S 49'S 4S'o SO'3 37'0 32'2 2fecunditylength 144 142 129 Mean Mean 32'1 34'4 72No, 2IS2 172 41'6 96 II2 37'2 4S'3 so'6 3S'S 36'S 30'S ,,' II 67162 189 434 43 87 24'4 42'6 28'4 4°'2 3I21 23 84 42'9 43'6 108 S1'8 16 37'6 176 fecundity length Flamborough 42'6 46'4 24 34'1 3MeanMean 32 length Clyde 23 31 19 13 423284 194 136 163 78 39'9 (thousands) (cm) (thousands) (cm) 2°9 34'6 43 IS Region. -- -. ,. REFERENCES. BAGENAL,T. B., 1957a. The breeding and fecundity of the long rough dab Hippoglossoidesplatessoides (Fabr.) and the associated cycle in condition. J. mar. bioI. Ass. U.K., Vol. 36, pp. 339-75. -1957b. Annual variations in fish fecundity. J. mar. bioI. Ass. U.K., Vol. 36, PP·377-82. KANDLER,R. & PIRWITZ,W., 1957. Uber die Fruchtbarkeit der Plattfische im NordseeOstsee-Raum. Kieler Meeresforsch., Bd. 13, I, pp II-34. SIMPSON,A. C. 1951. The fecundity of the plaice. Fish Invest., Land., Ser. 2, Vol. 17, NO.5, 27 pp. -1957. The spawning of the plaice (Pleuronectesplatessa) in the Irish Sea. Paper No. 54 read at the annual meeting of LC.E.S., Bergen, 1957..

(5) 1 Total uary 1956 5, 1957 TABLE THE. LENGTH,. 2 A VII 618 VI IV 1011 812 V 682 X 1060 estimate 4°2 III 32'7 260 206 33'0 622 2826 200,200 IX 801 37'7 33'3 367 37'0 34'2 277 4°1 386 395 733 744 378 837 499 34'7 216,300 1°39 1041 1°41 246 418 243 337 37'1 35'0 33'8 37'1 101,600 508 491 594 IV 39'9 634 320 743 34'8 32'1 38'6 35'6 42'2 4°'0 32'8 39'3 189,95° 139,550 244,200 375 37° 1366 1147 1423 1137 1144 763 968 971 1184 847 786 344 575 VIII 42'5 104,100 607 46'5 866 1028 204,300 421 76,800 327 389 44'2 38'1 44'9 38'7 160,600 225,200 628 2230 447 443 5°3 841 772 Illegible 1060 35'8 (em) 481 1021 1°53 877 VII 1010 38'9 48'3 49'5 37'9 31'7 36'4 1328 3°2,45° 149° 918 917 792 321 1601 828 I Fecundity 33'8 38'2 4 3 464 644 465 34'4 382 79,000 412 583 774 40'5 606 639 573 596 33'6 1386 13°1 557 38'4 34'5 39'8 809 939 429 43° 47° 43'8 934 40'7 1°90 652 9°° VI 381 36'5 354 83,9°0 587 482 75>400 78,850 66,650 395 49° 115,7°° 595 249 172,150 1189 658 447 110,700 571 70,850 333 124,750 7°,75° 615 339 46'3 552 845 V 123,350 594 33'4 948 374 796 56'6 434,350 22°4 96,850 204,650 1019 1479 609 529 Illegible APPENDIX 561 516 458 391 427 152,700 755 512 681 194,200 202,850 1°97 197,9°0 1058 943 36'2 4°4 365 1056 247,650 544 2017 5°3 567 179,200 921 443 54° 43'0 5°4 89,25° 684 347 364 355 369 72,050 47° 336 15°,95° 106,800 517 518 55° 32'9 3°'5 58,650 368 486 531 511 689 132,850 328 34° 360 338 283 46'7 37'8 174,200 136,600 292 1179 739 678 789 850 843 819 644 943 732 737 1232 431 314 445 478 585 870 598 664 670 378 633 872 7°4 917 1249 39'2 692 684 814 172,950 199,250 1083 858 894 841 564 930 858 565 988 187,9°0 849 414 118,750 514 664 2581 2388 543 11°5 115° 7°7 512,75° 544 2460 1067 498 853 1063 532 45'1 1056 316 696 363 545 480 535 Illegible 486 42'0 603 933 35'4 1°7,000 2236 492 4°° 4°2 length 139,200 123,600 689 652 7°2 791 164,650 117,05°• 809 839 844 523 1214 394 1246 115,25° 118,600 974 670 562 625 984 414 1146 4°4 933 871 793 825 36'5 379 416 3°° 512 7°5 12°5 138,150 234,950 932 53,850 527 143,100 672 731 117,5°0 587 1°94 1192 975 1004 959 547 526 634 Age (g) group 1°39 1743 77,15° 396 Weight 1479 695 527 671 579 257,350 85,150 427 185,3°0 1025 959 Egg count FEMALE CLYDE PLAICE WEIGHT, AGE AND EGG COUNTS OF.

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