ICES CM 2004 CC:37

Karsten Zumholz Uwe Piatkowski New data on the biology of the Lesser Flying , (Cephalopoda, ) in the North Sea

Karsten Zumholz & Uwe Piatkowski Leibniz-Institute of Marine Sciences, IFM–GEOMAR, Kiel, Germany

Abstract Materials and Methods A total of 319 specimens of the ommastrephid Specimens were collected on board of FRV squid Todaropsis eblanae, collected from “Walther Herwig III” during ten bottom trawl bottom trawl surveys in the North Sea were surveys carried out each winter (January/ examined. New information on seasonal length February) and summer (Juli/ August) from 1998 frequency distributions, reproductive biology to 2002. Trawls were carried out using the GOV- and relationships of beak size to mantle length trawl (mesh-size of 50mm in the codend, for and wet body mass from a hitherto not very detailed information see: IBTS Report, ICES well studied area is supplied. 2000) at depth from 20 to 180 meters during daytime from 7.00h to 19.00 UTC. T. eblanae has been described as rare in Scottish Waters, but occasionally it can appear in very large numbers and is found regularly in bottom trawls presented in the current study. Ecologically, squid play an important part in the North Sea both as predators and particularly prey. Former investigations showed very poor correlations between biological data from research cruises and from commercial landings in the North Sea. This emphasizes the importance of scientific Fig. 1: Map showing the survey area and sampling sites. ICES rectangles where trawls surveys and especially the value of long time were carried out are given in light grey, red dots stand for sampling sites of Todaropsis were frozen immediately after capture. data series like the one presented in this study. eblanae. Measurements and further analysis were done T. eblanae was present throughout the whole investigated area except from in the lab. The following data were analysed: the German Bight in the south-eastern survey region (Fig. 1). mantle length, body mass, sex, rostral length of The northernmost caught specimen was recorded from 61°15’,33 N. No the lower beak (LRL) and maturity stage differences in horizontal distribution between winter and summer were found. (I, immature; II-II, maturing; IV-V, mature) based Table 1. Numbers of Todaropsis eblanae on the appearance and relative size of the sampled in the North Sea on board of FRV reproductive organs. “Walther Herwig III” during 1998-2002.

Feb. Aug. Feb. Aug. Feb. Aug. Feb. Aug. Feb. Aug. 1998 1998 1999 1999 2000 2000 2001 2001 2002 2002

length frequency WH WH WH WH WH WH WH WH WH WH cruise no. summer Length frequencies 192 197 202 208 214 219 225 230 236 241 n 30 number of Length-frequency distribution of 32 77 81 50 24 2 8 21 0 29 25 T. eblanae female =78 T. eblanae varied significantly between 20 male = 99 15 summer and winter (Fig. 3a and 3b). number of hauls 66 107 70 168 101 74 70 74 78 152 10 During winter there were no

number of 5 differences in mantle length between T. eblanae per hour 1,0 1,4 2,3 0,6 0,5 0,1 0,2 0,6 0 0,4 0 males and females. In summer trawl time 5 25 45 65 85 105 125 145 165 185 ML (mm) females were notably bigger than

length frequency males. No interannual changes were winter obvious. Therefore data from all n 30 summer surveys and all winter surveys 200 600 25 are pooled. 20 female = 63 500 male = 79 15 An overall male:female ratio of 1: 0,78 150 10 was observed. Males were more 400 5 numerous than females in both winter 0 5 25 45 65 85 105 125 145 165 185 ML (mm) and summer samples. 100 300 Figs. 3a and b: Length frequency distributions for 200

Wet Body Mass (g) summer and winter. 50

Fig. 5: T. eblanae beak Mantle Length (mm) Dorsal LRL = 4,3mm 100 Reproductive biology

0 0 In summer most specimens of both 0123456 males and females were mature and Lower Rostral Length (mm) Maturity stages some were maturing. No juvenile Fig. 2: Lower beak rostral length of T. eblanae versus dorsal 100% was observed. In winter most mantle length (black dots) and body mass (green dots). 5 specimens were juvenile or maturing. Regression lines are given for both equations. N = 313 80% 4 Only few mature males were 60% 3 observed (Fig. 4). Beak analyses 2 40% Sexual maturity in males (stages IV We found no morphological differences between the 1 and V) occurred at 85-160mm mantle beaks of males and females, therefore equations were 20% calculated for both sexes. The observed equations for length, whereas in females it was 0% evident in bigger sizes (120-190mm). lower rostral length (LRL in mm) against both dorsal males females males females mantle length (DML in mm) and wet body mass (BM in winter winter summer summer Our findings suggest that in the g) in the investigated size window (ML=40mm- 190mm, Fig. 4: Seasonal relative proportions of maturity North Sea T. eblanae mates and LRL = 1,7- 6mm) were: stages observed for male /female T. eblanae spawns in late summer and autumn. A prolonged spawning season DML= 32,528 LRL –4,541 R = 0,943 seems probable. BM= 2,9042 LRL 2,724 R = 0,955 Acknowledgements Fig. 6: T. eblanae, mature male We are grateful to the crew and the scientific staff of FRV “Walther Herwig III“ for their help during on board DML = 134mm, BM = 135g sampling. Special thanks go to Siegfried Ehrich and Ingo Wilhelms (Institute for Sea Fisheries, Hamburg).