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Wednesday, 1 March 2017

Lates news on 'big movers' like hake - ICES WKFISHDISH REPORT 2016

Here is the executive summary form the ICES WKFISHDISH REPORT 2016 

This report documents the work undertaken during the WKFISHDISH workshop
which took place at ICES headquarters (Copenhagen) on November 22nd 25th 2016. The purpose of this workshop was to inform an answer to a request from the EU Commission about the distribution shifts of commercial fish stocks in relation to TAC management areas which ICES tackled in two consecutive steps: 

(1) data analysis carried out by the ICES secretariat (2) identify, based on both the results from the analysis and existing literature, changes in distribution and the associated drivers. 

This second step was done by the WKFISHDISH workshop participants. The workshop was chaired by Thomas Brunel (Netherlands), Alan Baudron (UK) and Jose Fernandes (UK).

The WKFISHDISH workshop was articulated around three terms of reference: (ToR1) consider the findings of the analyses carried out by the ICES secretariat to identify distribution changes, (ToR2) where shifts in distribution were identified, literature was used to identify likely drivers, (ToR3) implications of the distribution shifts and the likelihood of further change were discussed. 19 species were considered: anchovy, anglerfish (2 species), blue whiting, cod, common sole, Greenland halibut, haddock, hake, herring, horse mackerel, mackerel, megrims (2 species), Norway pout, plaice, Pollack, saithe, sprat, spurdog and whiting. The ICES secretariat analysed available bottom trawl surveys data for these species (bar Greenland halibut for which no data was available, only existing literature was used for this stock) and produced the following outputs for each species: (i) presence/absence maps, (ii) trends in probability of occurrence within each ICES areas, (iii) centre of gravity with associated latitude and longitude trends within each ICES areas, (iv) significant differences in relative changes in abundance between adjacent ICES areas.

These outputs were analysed by WKFISHDISH workshop participants to answers
ToR1. To be consistent, during the literature review needed to address ToR2 efforts were made to assess the following potential drivers for each stock: 

(i) geographical attachment, (ii) environmental conditions, (iii) density-dependent habitat selection, (iv) spatial dependency, (v) demographic structure, (vi) species interaction, (vii) memory, (viii) other drivers such as fishing. 

‘Big movers’ species (i.e. species exhibiting distribution changes likely to be problematic regarding TAC management areas)
were identified as such if they conformed to at least one of the following two criteria: 

(1) a large, continuous and directional change in distribution was identified from the analyses and/or in the literature review, (2) a change in distribution resulting in subsequent changes in the relative distribution across TAC management areas was observed.

Based on the analyses and the literature available, all species were found to exhibit some changes in their distribution to some extent apart from Greenland halibut, Norway pout and spurdog for which no evidence was found. For these 18 ‘movers’ species, the main drivers distribution identified were environmental conditions (mainly temperature) for all species, followed by density-dependent habitat selection (7 species), geographical attachment (6 species), species interactions (4 species), demographic structure (3 species), and spatial dependency (2 species). Other possible drivers (fishing and colonisation) were also mentioned for 4 species. The following species were identified as ‘big movers’: anchovy (northward shift in the North Sea), anglerfish (regional changes in the North Sea), blue whiting (increase in the North Sea and west of Scotland), cod (northward shift), hake (expansion in the 2 | ICES WKFISHDISH REPORT 2016

North Sea), herring (changes across different TAC management areas), mackerel (major changes across northeast Atlantic), megrims (regional changes in the North Sea, Bay of Biscay and Celtic Sea), and plaice (increase in North Sea and Baltic Sea, changes across different TAC management areas). Despite showing clear changes in distribution, horse mackerel was not included in this list as current management measures already account for these distribution changes.

Both ecological and management implications of the changes in distribution were identified in ToR3. The main possible ecological implications include limited areas of suitable habitats (cod, sole and plaice), isolation between life stages habitats (herring), and new prey-predator interactions and subsequent competition between predators (hake and saithe). The main management implication identified is the mismatch between regional abundances and TACs allocation, with hake and mackerel being the two obvious examples. This mismatch, in combination with the landing obligation, could result in choke species issues and challenges the relative stability currently used to distribute quotas.

Regarding the likelihood of further changes in distribution, current climate scenarios project an increase in temperature and decrease on primary production and it is likely that future changes in distribution will occur. Based on the available information the following areas were identified most at risk: North Sea (warming and latitudinal shift), southern areas i.e. Celtic Sea and below (warming and lower primary production), west of Scotland (northward shift), Norwegian Sea and Skaggerak and Kattegat (increase in abundance). However, our ability to accurately predict the future distribution of fish species is hampered by both our understanding of the mechanism associated
with drivers, and our ability to predict these drivers.

In conclusion, the ‘big movers’ species identified here (i.e. anchovy, anglerfish, blue whiting, cod, hake, herring, mackerel, megrims, plaice) are most at risk of resulting in management issues. While there is no obvious solution to address this management problem, some form of adaptive management seems the best candidate to deal with changes in fish distribution. In addition, a better monitoring of fish stocks and ecosystems is needed to improve our knowledge of the processes at play in order to increase our ability to predict future changes and foresee potential ecological and management