Evaluation of the temporal development of the ovaries in Gadus morhua from the Sound and Kattegat, North Sea

Abstract

The gonadal development of cod Gadus morhua in the Sound and Kattegat, North Sea, was studied by investigating their histological structure on a temporal scale by intense sampling from September 2002 to May 2003. Different age classes were followed and the proportion mature in each age class within each area was analysed. Based on existing maturity criteria, a modified system, based on histological features, was developed in order to emphasize the crucial step in the developmental process, i.e. the passage from endogenous to exogenous vitellogenesis. Only fish that had attained exogenous vitellogenesis could be considered as being reproductively active in the forthcoming breeding season (Kjesbu et al., 2003). The histological based maturity scale will greatly improve the capability of separating mature from immature individuals in the studied areas, that is fundamental for an accurate and unambiguous estimate of the spawning stock biomass. Furthermore, the results showed a larger proportion of mature individuals per age class in the Kattegat stock compared to the Sound stock, which implied an earlier maturity for this stock. This difference in maturation pattern might have been related to a relaxation of competition, i.e. enhanced growth rate, as an effect of different levels of exploitation and technical fishing regulations between the two adjacent areas. # 2005 The Fisheries Society of the British Isles

Threshold-dependent climate effects and high mortality limit recruitment and recovery of the Kattegat cod

“…To reflect the oceanatmospheric conditions affecting regional climate in the area, the North Atlantic Oscillation Index (NAO) was used. Physical conditions were represented by spring averages (March to May) of sea surface temperature (SST) and salinity (at 40 to 80 m) during the extended period covering spawning as well as the pelagic egg and larval stages (Vitale et al 2005). To account for the effect of oxygen conditions impacting recruitment throughout the early-life history, particularly seasonally occurring hypoxia and anoxia (Conley et al 2007), we used the mean annual bottom oxygen concentrations.…”

The spatial distribution of cod (Gadus morhua L.) spawning grounds in the Kattegat, eastern North Sea

“…1) from 1996 to 2004 were provided by the Swedish Board of Fisheries. Only data from the first quarter of the year were used for mapping, as the spawning of cod in Kattegat mainly takes place from January to March (Vitale et al, 2005). Based on set position, landings of cod (in kg) from the three major bottom trawl fisheries (two cod bottom trawls and one Nephrops trawl) were aggregated in a grid of ∼10 by 10 km (5 × 5 nautical miles).…”

“…However, gutted body mass in November-December 2002 and November-December 2004 was not recorded, and was therefore calculated by the linear regression (GM = 0.8426 × M + 11.676; R 2 = 0.993), obtained from the data collected in December 2003 and 2005. Gonads and otoliths (sagittae) were stored and analysed as described in Vitale et al (2005). Based on a 7-stage scale for gonadal development (Table 3), females were classified as either immature (stage 1-3) or mature (stage 4-7).…”

Histological analysis invalidates macroscopically determined maturity ogives of the Kattegat cod (Gadus morhua) and suggests new proxies for estimating maturity status of individual fish

“…Cod in the Kattegat start maturing in November, peaking in FebruaryeMarch, then enter the spent stage (Vitale et al, 2005). In order to obtain a good temporal resolution, fish sampling took place on a monthly basis, from September Figure 1 and Table 2, respectively.…”

“…In this study, visual staging of sexual maturation of Kattegat cod was evaluated in concert with the newly introduced and validated histological analysis of reproductive organs (Vitale et al, 2005). By assuming that histological examinations accurately represent the reproductive status of individual fish, estimates of the deviation (or error) in using visual determination of maturity stage were obtained.…”