The fecundity of Clyde witches was estimated from 1958 to 1962, and has been found to vary from over 49,000 eggs for a 26·8 cm fish to more than 599,000 in a 42 cm witch. Annual variations in the fecundity were found but there are not sufficient data to relate the changes to the population density as can be done with plaice. It appears that Clyde witches may grow faster, and they certainly attain a larger size than those in the Irish sea.

The fecundity of 180 long rough dabs caught in the Clyde Sea Area from 1957 to 1961 ranged from 9700 eggs in a 12.2 cm fish to 251,300 eggs in one of 30.0 cm. The mean lengths of the fish in the samples each year were different so the comparisons between one year and another were based on the fecundity expected of a 22 cm fish. The differences between years were statistically significant, though successive years did not differ significantly when tested in pairs. The trends of increase and decrease in fecundity were very similar to those of the witch (and different from the plaice). It is suggested that, since witches and long rough dabs (in contrast to plaice) both prefer a muddy bottom, the fecundity variations from year to year might be caused by fluctuations in the abundance of some common food organisms.

This paper is the fifth in a series dealing with the fecundity of flatfish (Bagenal, 1957a, b; 1958, i960), and is concerned with the numbers of eggs in, the roes of ripening female plaice Pleuronectes platessa L. caught off the south and west coasts of Ireland during November and December 1958. The fish were obtained from Wexford, Ballycotton, Schull, Dingle, Galway and Killybegs (Fig. 1).

During the last 30 years the fecundity of the plaice, Pleuronectes platessa L., has been widely studied over its complete geographical range. In this paper all this previous work is brought together and a distinct pattern (with two exceptions) emerges. The fecundity is lowest in the Southern Bight of the North Sea, and radiating from there in all directions the fecundity increases, while in Faxa Bay (Iceland) and in the Barents Sea it is lower again. The possible factors producing this pattern are examined in detail and it is concluded that the amount of food available, which in turn is related to population density, is the most important. Only in Trondheim Fjord and in the Baltic is the fecundity so different that it is necessary to postulate racially distinct populations. Finally the importance of fecundity variations in natural population regulation is stressed.

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 Dublin Prawn or Norway Lobster, Nephrops norvegicus (L.), is widely distributed on soft muddy bottoms, usually between 10 and 50 fathoms. It is found as far north as Iceland and the North Cape, is common in the North Sea and off the Atlantic shores of the British Isles, and extends as far south as the coast of Morocco; a variety, v. meridionalis (Zariquiey-Cenarro, 1935) is found in the Mediterranean and Adriatic (see Havinga, 1929, and Heldt & Heldt, 1931, for details of its distribution). Some aspects of the general biology of Nephrops have been dealt with by Höglund (1942) and Poulsen (1946) for Scandinavian waters, and by McIntosh (1904, 1908) and Storrow (1912)for the waters off north-east England. To a large extent all these workers relied on market catches.

An analysis has been made of plaice fecundity at four localities in Norway. The fish tended to be larger than those used in other fecundity investigations, and the comparison between localities has been made by considering the average egg number expected in a 50 cm fish. In general the plaice off Norway had more eggs than in the North Sea or round the British Isles. At Arendal in the Skagerrak the fecundity was 355 thousand for 50 cm, which is lower than has been found in the Kattegat, but a little higher than I found at Bergen (317 thousand eggs). At Arendal and Bergen the fecundity was higher than has been found in the North Sea but lower than in localities farther north in Norway. In Trondheim Fjord the plaice fecundity was very high indeed. Among the eleven fish examined it varied from 673 thousand to nearly ½ million eggs, and for an average 50 cm plaice would be 819 thousand. The female fish on the coast outside the fjord were quite different and contained about half the number of eggs (407 thousand for 50 cm). These coast plaice were very similar to those caught in the vicinity of Tromso where a 50 cm fish would have about 400 thousand eggs.

The variation in the fecundity of a fish species from year to year has not received much attention, although the changes in the numbers of young fish in the plankton are well documented for the Plymouth area (Russell 1930–47; Corbin, 1948–51). The most important work considering fecundity fluctuations is that of Simpson (1951) who, working onPlaice, Pleuronectes platessa L., concluded that during 1947,1948 and 1949 there was a steady decrease in the number of eggs laid, this being due to a decrease in the mean size of the spawning fish which he showed to be correlated with the egg numbers. Simpson's interest in the fecundity was to provide a more accurate estimate for determining the number of plaice in the total population from planktonic egg surveys similar to the work of Buchanan-Wollaston (1923). He did not consider in detail whether the fecundity for a given length might change from year to year. It is this problem which will be considered here. Estimates of fecundity of Long Rough Dabs, Hippoglossoides platessoides (Fabr.), will be analysed, and Simpson's Plaice data will also be considered.

The biometry of the Clyde population of long rough dabs has been studied and compared with the descriptions of the European race given by Norman in his monograph of the flat-fishes. The data consist of various body measurements together with the results of scale counts, fin ray counts and vertebral counts. The fin ray numbers fit into a pattern of increasing number with high latitudes when compared with other published data. There is a correlation between the number of anal and dorsal fin rays, and between these and the number of vertebrae. The variations that were found in the vertebrae of fifty-one fish are described. Only one sinistral long rough dab has been found out of 2357 specimens examined. From the British fishing statistics it is shown that the long rough dab is of little, and declining, commercial importance. In Canada, however, the American subspecies is becoming more important commercially.

This paper is the fourth in a series dealing with the fecundity of flatfish (Bagenal 1957 a,b, 1958), and is concerned with the egg numbers in ripening female plaicePleuronectes platessa L. caught in the English Channel.

On 27 November 1957, eighty-five plaice with maturing ovaries were caught in Rye Bay, Sussex; on I December, eight similar fish were caught in Lyme Bay, and duringDecember sixty-four locally caught female plaice were brought in to the Plymouth Laboratory. The dates of the collections were chosen because in January 1957 I had found that a small proportion of the Plymouth plaice were spent. All the fish caught in November and December were at a suitable stage for fecundity estimation: that is, the eggs were well developed though none had begun to turn translucent.

The ages of 1426 female, and 135 male Long Rough Dabs have been determined from otolith readings. The females were found to live into their seventh year and reach 30.5 cm, compared with males that live to their fifth year and reach 19.0 cm in length. However, the mean increase in length per year for a given length, has been found to be the same. The growth of the females has been shown to fit the equation lt=26.437 (I—0.574t) and of the males lt=17.754 (I —0.585t). In the case of the females the observed and calculated values agree quite closely, but with the males there is a greater difference, and it is believed that the discrepancy is due to net selection. The suggestion is made that the calculated mean lengths for each age group are better estimates of those of the population than are the observed sample means. The two standard deviations limits can be estimated about the population means and the sample values are found to be within these limits.

Comparison with previous studies shows that the Clyde fish are smaller and shorter-lived than more northern specimens, though broadly speaking the rate of growth for comparable ages is not so dissimilar.

Details are given of the breeding biology, including the fecundity, of the Long Rough Dab deduced from samples taken in the Clyde Sea area from October 1953 to April 1955. Where possible breeding is related to the condition of the fish; the index of condition is based on the length-weight relation.

The weight of Long Rough Dabs of each sex and stage in maturity increases as a power, slightly greater than the cube, of the length. An annual cycle of fluctuations of this power is seen in the immature females, and indicates how changes in condition at different seasons affect the different size-groups. The measure of condition is taken as the expected weight of a 20 cm Long Rough Dab, and the changes in this weight are followed through the sampling period for males and for immature, maturing and spent females. All groups tend to be in best condition during November and December followed by a decline to the spawning time, in March and April, after which there is a slow recovery.

This paper is concerned with the number of eggs in the roes of ripening female plaice, Pleuronectes platessa L., caught off La Rochelle during the winter of 1960–61. The fecundity of plaice has been studied over a number of years in fish collected over a wide area (Bagenal, 1958,19600,6,1962) and the results given in this paper apply to plaice caught as near the southern limit of their distribution as possible. Although plaice have been recorded from farther south (Wimpenny, 1953), La Rochelle is the most southerly port where they can be obtained in sufficient numbers.

The fecundity of Clyde plaice, which has been studied from 1956 to 1961, has not been found to change as the breeding season approaches. However, there was a marked fecundity change from about 137 thousand eggs to around 161 thousand after 1957. The fecundity of all age groups increased and this appears to be associated with the fishing intensity and so the population density. Heavy fishing leads to fewer fish with the same food supply which in turn allows higher fecundity. The changes in fecundity therefore seem to be part of a density dependent population regulating mechanism.

This paper is one of a series on the fecundity of the plaice Pleuronectes platessa L. over a wide area of its geographical distribution and is concerned with the number of ripening eggs in the roes of female Icelandic plaice prior to spawning (see Bagenal, 1962, for references to other areas).

Thirty-eight plaice were caught by the Icelandic research vessel ‘Maria Julia’ on 23 and 24 March 1961 in the Midnessjor area. They were measured and weighed and the otoliths were extracted. The ovaries were preserved in modified Gilson's fluid (Simpson, 1951). I am very grateful to Mr Jon Jonsson who kindly made all the arrangements and Mr Gunnar Joakimsson who prepared the material in Iceland. The fish were very ripe and a few had developed translucent eggs, but spawning had not begun. The subsampling and statistical treatment of the results were the same as before (Bagenal, 1962). The otoliths, after being kept dry, were very difficult to read.

The Icelandic plaice are an isolated population, separated by deep water from the rest of Europe, and there are several spawning areas. currents move clockwise round Iceland and will carry the fertilized eggs and young larvae from Midnessjor and the S.W. coast spawning areas (Thomsen, 1948) to the good nursery grounds of Faxa Bay. Tåning (1929, 1948) has given accounts of the Faxa Bay plaice biology and suggests that ‘the eggs and tiny fry, which are found in the Bay in the spring months, seem mainly to come from the outside, for the greater part most probably from S.W. Iceland’. The eggs from the population offish considered in this paper, from Midnessjór, would drift into Faxa Bay which forms a good nursery ground.

In a recent paper (Bagenal, 1955) on the growth rate of the Long Rough Dab Hippoglossoides platessoides (Fabr.) in the Clyde Sea area, a serious mistake was made.

The ages of 1561 Long Rough Dabs, which were collected from October 1953 to September 1954, were determined from an examination of the otoliths, and from the age analysis each fish was allocated to a population f to a, de-pending on when it was supposed to have spawned. This procedure was designed to obviate the difficulty during the winter and spring when fish of the same year-class would be grouped differently according to the condition of the otolith edge.

Hake belonging to the genus Merlucdus are large fish often growing to overa metre in length; they are predators, being well streamlined and armed with formidableteeth; they feed pelagically on smaller fish of their own and other species. Of the various species distributed round the ocean basins, the European Hake, M. merlucdus (L.), ranges from Lofoten on the coast of Norway, to Dakar on the African westcoast; it is found most plentifully along the edge of the continental shelf of Western Europe but also extends into the Mediterranean and North Sea, whilestragglers occasionally range as far as Iceland.

The variability in catch of a series of hauls with a V.D. trawl taken under, as far as possible, controlled working conditions has been determined.

For analysis the species were divided into ‘round’ fish and ‘flat’ fish together with Nephrops; for both groups the coefficient of variation varied from 40 to 85 %. Taking 75 % as a representative value, the 2σ fiducial limits are 30–300 % for a single species from a single haul of half an hour duration.

It has been found that the standard deviation is roughly proportional to the mean, and that the variance is greater than the mean and increases with the mean. This suggests aggregation of the population.

The species are considered over the whole sampling period (4 weeks). Except for haddocks and dogfish the ‘round’ fish constituted a constant population. Changes were found in the other groups and their origin is discussed.