​Hake is one of the species showing the most dramatic changes in distribution. (Photo: ICES)

ICES identifies 'substantial' species distribution shifts

DENMARK
Wednesday, March 22, 2017, 01:40 (GMT + 9)

A total of 16 out of 21 species examined by experts of the Workshop on Fish Distribution Shifts (WKFISHDISH) in response to a request from the European Commission (EC) have shown changes in their distributions across the northeast Atlantic since 1985, with hake and mackerel shifting the most.

WKFISHDISH experts also revealed that of these, eight species exhibited distribution changes that crossed total allowable catch (TAC) management areas boundaries.

Furthermore, environmental conditions such as sea temperature, in addition to changes in the distribution and intensity of fishing effort, were found to be strong drivers for these patterns of change.

The evaluation coupled northeast Atlantic trawl data with information from literature to conclude that hake, mackerel, anchovy, cod, herring, horse mackerel, plaice, and common sole had either shifted their relative distribution between different TAC management​ areas or into areas not currently covered by TACs.

In addition, the study reveals that distributions of a further eight species – white- and black-bellied anglerfish, blue whiting, megrim, sprat, whiting, haddock, and saithe – were found to have shifted, though these did not affect the TAC areas.

The remaining five species exhibited no change, or the results were inconclusive regarding distribution shifts.

While distribution changes were detailed, it was not possible to evaluate the current relative abundance of each species within each TAC area the available surveys are not designed to consistent sampling across the regions​.

The surveys were useful for understanding the distribution of the species across the ICES survey areas as well as changes in their centres of distribution. Large, continuous, and directional changes in distribution determined from the survey data and the literature review were used by the experts to describe 'substantial changes in distribution'.

In addition to identifying the main drivers of distribution changes, environment and fishing, this study also identified the likely mechanisms through which these two drivers impact distribution, such as habitat selection, density-dependence, geographical attachment, or spatial dependency.

Environmental changes, mainly characterised in the literature as changes in temperature, influenced the distribution of all 16 species that exhibited substantial changes in distribution, while changes in fishing effort was found to have influenced the distribution of ten of these species.

Alan Baudron of the University of Aberdeen, co-chair of the WKFISHDISH workshop and invited expert to the advice drafting group, provided an example of how these interacting mechanisms helped drive the altered distribution of hake.

"Hake is one of the species showing the most dramatic changes in distribution. From its original distribution on the west of the British Isles, it has expanded eastwards into the North Sea. This change was evident from the trends in occurrence observed within the North Sea ICES areas as well as from the shifts in centre of biomass observed in the North Sea survey data,” pointed out Baudron.

All in all, it is the recommendation of the workshop that continual monitoring of the distribution is essential for future management. It is hoped that in the future, ICES will be able to use pelagic survey data as well as possible commercial catch data with high spatial resolution in order to better evaluate and monitor species distribution changes.
 
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