|Ref.||ICES CM 2008/LRC:04. 119 pp.|
|Contributor(s)||Petitgas Pierre, Trenkel Verena|
In 2008 WGFE finalised its contribution to the OSPAR request to examine impacts of climate induced changes in the marine physical environment on the distribution and abundance of fish. The analyses the 2008 report are more succinct than in the 2007 report and many of the suggestions of WGECO were heeded. Analysis were broken down by species and OSPAR region and where direct data analysis could not be done by the group, literature was summarised and in particular the report of the EU funded project RECLAIM was integral for filling in gaps. Many demersal and pelagic species changed abundance and distribution in all areas and while some of these changes can be attributed to change in temperature between time periods, others cannot. It is also apparent that warming in some cases has meant that species once considered strays are become much more common. In other cases the warming has improved recruitment for some species thus creating a shift in the apparent range of the species though not necessarily a change in individual movement. Overall, many species have shown positive changes in abundance in most OSPAR areas. Southern species have tended to increase over all areas while northern species have tended to recede from the south and heavily exploited species such as cod have decreased in abundance everywhere. WGFE revisited work started in 2004 (see the 2004 WGFE report) examining the compatibility between ICES reference points for exploited stocks and IUCN decline criteria. On the whole it was concluded that it is unlikely that an IUCN list threshold would be breached for a declining stock before an ICES PA or limit reference point would be breached. The potential difficulties for managers is obvious if such a situation presented itself, i.e. they would be compelled to protect a stock under conservation legislation while at the same time the stock would be deemed sufficiently abundant to exploit commercially. This appears unlikely to occur especially if ICES manages stock to remain above Bpa as a stock’s biomass dropping below Bpa should trigger a sufficiently strong fishery management response to reverse the decline well before any IUCN decline criterion would take effect. Recovery of the North Sea demersal fish community to the EcoQO (fish community target state indicative of health) prescribed by WGECO was tested this year under a range of community fishing scenarios using a mass balance size‐based model. This model suggested that the fish community would react to changes in fishing pressure quickly and achieve a new steady state on the order of 5‐10 years. Further simulation work is required to determine the necessary change in fishing mortality required to achieve the particular EcoQO target. To this end, the potential modelling methods that may aid in this kind of projection were reviewed. Some models appear more suitable than others for exercises of this nature and in the coming years it is apparent that ICES will acquire the appropriate suite of tools and expertise to provide useful advice on fish community exploitation for achieving EcoQO targets. Essential fish habitat and abundance‐occupancy were addressed through three case studies. The first study examined the relationship between occupancy and abundance for several species in the Bay of Biscay and Celtic Sea accounting for habitat characteristics. Though large changes in total abundance were found, there were no changes in occupancy that transcended habitat variables. A second study examined how trawling affects fish abundance, habitat and subsequently species composition and habitat utilisation. Exploited fish species initially responded to the respite in fishery exclusion and over a longer period their productivity also increased in the non‐trawled area which seemed more related to the curtailment of destructive fishing practices. A final study of inter‐ and intra‐specific abundance‐occupancy relationships in the Georges Bank fish community showed that most species did contract their occupancy with a decline in abundance. When this relationship was examined over species but within years, it was apparent that the statistical quality of the relationship decreased over time from the 1960s to present and this has been interpreted a result of habitat loss and fragmentation over time which interferes with how fish use space on Georges Bank. WGFE has traditionally included studies proposing new indicators for characterising fish communities and testing how they respond to fishing, environment and their relation to other measure of fish community state. One study is presented here which examines redundancy between common community indicators for the a North Sea surveyed community such as diversity indices, total biomass, mean body size and mean largest body size. While some indicators were redundant others were not. Overall, if it is accepted that the indicators are meaningful for showing characteristic of fish communities, than it would take a suite of indicators to appropriate characterise the community. In 2007 WGFE constructed many maps of species distributions in relation to environmental variables in order to meet the demands of the OSPAR term of reference on species responses to climate change. Though the maps were helpful for presenting large amounts of information it was realised that there were few analyses that dealt with quantitative comparisons of maps or differencing them to find changes over time. WGFE in 2007 therefore proposed future work that would deal with comparisons between maps usually between time periods. The two studies are presented here: (1) a method to dimensionally reduce multivariate maps to a 3 variable representation and compare them over time; and (2) differencing maps (using three different methods) between periods in order to highlight changes in species distributions between periods. WGFE anticipates further work on these methods at future meetings.
ICES (2008). Report of the Working Group on Fish Ecology (WGFE), 3‐7 March 2008, ICES, Copenhagen, Denmark. ICES CM 2008/LRC:04. 119 pp. https://archimer.ifremer.fr/doc/00817/92911/