Within the English Channel, the common cuttlefish Sepia officinalis is a semelparous species for which a 2-year life cycle was exclusively described in the 1980s. In the 1990s, new research indicated that whilst a 2-year life cycle was still evident for females and the large majority of males, a small proportion of males were actually maturing at only 1 year of age. Since 1980, the interest of French and UK fishers for this resource has increased and it is nowadays one of the most important demersal species of the area and is considered to be fully exploited. From the start of the 20th century, fishing effort and sea surface temperatures have increased in the English Channel and have probably impacted the life history traits of S. officinalis. A 2-year sampling programme was undertaken at French landing sites of the English Channel during the reproduction season in 2010 and 2011 to estimate if the proportion of 1-year-old mature animals has changed. Age determination was carried out by coupling polymodal decomposition and lipofuscin measurement. Size-at-maturity for each year and each sex was estimated by fitting a binomial error GLM. Results highlight that a variable percentage of males and females belonging to the first cohort are mature and that size-at-maturity was lower than that observed in the 1990s. Finally, different parameters, such as temperature and fishing pressure are explored to discuss changes in life history traits suggesting that cuttlefish could be an indicator of the temperature regime shift in the English Channel.

The cuttlefish (Sepia officinalis) is the most important traditional fishing activity in the Sado estuary. In order to analyse the spatial and temporal distribution patterns and to study the reproductive cycle of this species, twenty sampling areas were towed along the estuary on a monthly basis from May 2001 to April 2002. The higher densities were obtained in summer and autumn in the lower and southern area of the estuary while spring showed the higher biomass. Mature individuals prevailed in the inner zone of the estuary during spring while juveniles were dominant in autumn and concentrated in the lower part of the estuary. Almost all individuals leave the estuary during winter. The weight–length relationship was significantly different according to sex, being females heavier than males for individuals larger than 106 mm. Sex-ratio was similar to 1:1 in every season. Females had high values of gonadosomatic index during the spawning season with a major peak in June, while males showed similar values throughout the spawning season. The length at first maturity was estimated at 80 mm mantle length (ML) for females and 59 mm ML for males. In the Sado estuary only one generation of cuttlefish breeders were found with an average of 110 mm ML for males and 122 mm ML for females, which is consistent with breeders in their first year.

Significant differences were found between males and females in the fragmocone, external cone and widths of the cuttlebone in Sepia officinalis caught in the small-scale trap fishery off Gran Canaria Island (Spain). It is suggested that: (a) differences may depend on morphological adaptations of females for egg laying; (b) cuttlebones represent over 50% of the total cuttlefish caught (which is unrecorded in the fishery); and (c) the relationships between several morphometric measures of the cuttlebone and the mantle length and wet weight may allow more accurate biomass estimations of this species in the fishery.

Sepia officinalis produces a dark ink constituted of a suspension of melanin granules in a viscous colourless medium showing a large variability in composition. The examination of the spectra obtained by scanning electron microscopy of crude and the melanin-free ink showed slight variation in elemental composition related to the elimination of melanin substance after centrifugation. Ink elemental content varied also depending on the period of sampling. Temperature, light and oxygen can be considered as coagulation factors. Temperature around ambient temperature (e.g. 30°C) gave strong coagulation, while lower temperature (2–4°C), lack of oxygen and darkness greatly inhibited the ink coagulation process. Moreover, we showed that hydrogen peroxide activated the ink coagulation process and the coagulation rate depends on the amount of H2O2 added. Heat treatment (100°C for 5 minutes) of ink inhibited the coagulation. Interestingly, the addition of an adequate volume of fresh melanin-free ink to the heated sample activated significantly the coagulation process.

In the English Channel, the French cuttlefish landings of the smallest commercial category (body weight < 100 g) indicate that recruitment begins in autumn. Samples of recruits were collected in the Port-en-Bessin (Normandy) fish market once every fortnight from October to December 2000 to determine age-at-recruitment and juvenile growth variability. In addition, pre-recruit samples (mantle length: 53–90 mm) were collected in the Bay of Seine from August. Age was determined by statolith analysis: daily growth increments on the statolith lateral dome were observed under a light microscope. Increments were counted automatically, and manually when necessary, using the image analysis software TNPC. Readable statoliths were obtained in 236 cuttlefish, which revealed changes in age-at-recruitment during the study period. The cohort 2000 is recruited at an age ranging between 2 and 5.5 months (the bulk of recruits are 60–120 d old) and an increasing trend in average age is observed in autumn. The duration of the hatching period was derived from back-calculated hatching dates. A main hatching peak was observed between June and August. Juvenile growth variability was analysed at the individual level and between batches of hatchlings. Growth rates suggest that early hatched individuals grow faster than animals hatched later in the summer.