Report of the Workshop on Sexual Maturity Staging of Redfish and Greenland Halibut (WKMSREGH)
The WKMSREGH met in Vigo 28th November–1st December 2011. The meeting was chaired by Fran Saborido-Rey, Spain, and Agnes Gundersen, Norway. The mandate of the group was to agree on a common maturity scale for Redfish (Sebastes mentella and S. marinus) and Greenland halibut across laboratories and propose optimal sampling strate-gies. These deep-water species are both particular; the redfish being viviparous and the Greenland halibut showing sexual dimorphism and a complex oocyte development. In addition, both show geographical variability in their life cycle.
In order to address these issues the WK compared existing maturity scales for both spe-cies for the countries present in the meeting (Canada, Germany, Iceland, Norway, Russia and Spain) and produced common and standardized scales that are compatible with previous national scales. The new macroscopic scales were calibrated microscopically and reflect the peculiarities of the reproductive cycle; in order to achieve this, fresh samples, fixed samples as well as histology samples were examined and blind tests were made.
For redfish, a first major issue raised in relation with the fact that in many areas the red-fish species are not distinguished, and it is known that redfish species show different ma-turity ogives. In these situations the estimation of maturity ogive is useless, at least estimating at regular basis. It is recommended to estimate the ogive in the species com-plex once every few years to be used in the assessment. Nevertheless, it is highly recommended that more effort should be allocated to a proper species identification at least during the research surveys. A scale of 6 stages was finally adopted in redfish females. This includes: 1. immature, 2. maturing, 3. Mature/fertilized, 4. embryogenesis-parturition, 5. regression-regenerating. However, skip spawning is well documented to happen in redfish during early-mid vitellogenesis and to account this feature stage 2 was divided in two stages to be used only in the period right before ovulation, when skip spawning fish resembling early maturing ones (2.1), and completely different to normal developing females in advance stage of vitelogénesis (2.2). It was agreed that for macro-scopic staging sampling should be conducted during the three months prior to ovulation-parturition, which varies by stock and species. Before and after this period only micro-scopic staging should be used.
With respect to Greenland halibut i was agreed on a seven stage scale. All reports on ma-turity to ICES should use the seven stage scale in future. However, in future one should consider the actual need of stage 7. A future combination of stage 6 and 7 was suggested in the report for future use after having tested the seven point scale for some time. Sam-pling should be conducted 2–5 months prior to spawning but the actual time of the year may vary due to geographical differences in life cycle. To reduce sampling costs it was suggested that histology samples only should be made when there was uncertainty be-tween immature and inactive mature. For both species more knowledge is needed with respect to the male maturity cycle. For Greenland halibut it is recommended that sepa-rate sex maturity oogives are used due to sexual dimorphism. The case of geographical area should be considered. For Greenland halibut the stock perception is not clear. There are areas resembling nursery areas but these are treated like areas for adults. For instance: Flemish area seems to differ from other areas, as do also the inshore Disko management unit. A reference collection for both species will be organised at IIM, Spain. To reduce costs it was suggested to establish reference laboratories that can receive, process and microscopically stage samples from other laboratories. This has, however, an economical aspect as at present no laboratories can do so without getting costs covered. For Greenland halibut reference laboratories suggested are DFO, Møreforsking, and IEO. For redfish IIM, was recommended as reference lab. This should be discussed further on the workshop of Chairs in June.
For the future it was decided to prepare a sampling protocol (a full illustrated manual) for both species including detailed descriptions and a wide selection of photos for all maturity stages of both species.
Published under the auspices of the following ICES Steering Group or Committee