9.4.21 Portuguese dogfish and leafscale gulper shark in the Northeast Atlantic (ICES Areas I XIV)
State of stocks
Total international landings of these species combined have risen from very low levels to around 11 000 t in 2003 and appear to have declined since. Substantial declines in CPUE series for both C. coelolepis and C. squamosus in Subareas VI, VII, and XII suggest that the stocks of both species are depleted. CPUE for both species in the northern area have displayed strong downward trends leading to the conclusion that the stocks are being exploited at unsustainable levels. In Division IXa, CPUE series, although short, appear to be stable.
Reference points
In common with other deepwater stocks, Ulim is set at 0.2 × virgin biomass and Upa is set at 0.5 × virgin biomass (ICES, 1998).
Single-stock exploitation boundaries
No target fisheries should be permitted unless there are reliable estimates of current exploitation rates and stock productivity. TAC should set at zero for the entire distribution area of the stocks and additional measures should be taken to prevent bycatch of Portuguese dogfish and leafscale gulper shark in fisheries targeting other species.
Exploitation boundaries in relation to high long-term yield, low risk of depletion of production potential and considering ecosystem effects
Portuguese dogfish and leafscale gulper shark are long-lived, slow-growing, have a high age-at-maturity, and are par- ticularly vulnerable to fishing mortality. Population productivity is low, with low fecundity and a protracted gestation period. In the light of this, the risk of depletion of reproduction potential is high. It is recommended that exploitation of this species should only be allowed when indicators and reference points for future harvest have been identified and a management strategy, including appropriate monitoring requirements has been decided upon and is implemented.
Management considerations
A long-term management strategy for fisheries on this species would consist of an initial low scientific fishery. This initial low fishery level should aim to identify harvest rates that are sustainable in the long term. A gradual expansion of the fishery from the initial low level should only be allowed if harvest rates that are sustainable in the long term are clearly identified and a management strategy has been identified and decided upon. Such gradual expansion should be accompanied by close monitoring, enabling adjustment of the management plan according to the outcome of the fisheries.
At present, there is insufficient information to determine stock identity. In the absence of such information, they are considered as single stocks for assessment purposes although smaller units may be appropriate for management.
CPUE of both species has shown a strong decline in northern areas (Subareas V, VI, VII, and XII). In the south (Sub- area IX), CPUE for both species appears to be stable.
Species-specific data have not been provided by all countries involved in these fisheries but are needed for the assessment of these two species and their management.
Factors affecting the fisheries and the stock
Regulations and their effects
A series of TACs is set for EC waters and EC vessels in international waters of Subareas V XII. The TAC applies to all deepwater sharks. The sum of these TACs is 7000 t for 2005 and 2006. It is clear that the quota is restrictive for some countries, if adequately enforced. For other countries, the quotas are not effective in regulating fishing effort.
These sharks are often taken in mixed fisheries. An effort restriction regime has been in place since 2003 (EC Reg. No. 2347/2002, 27/2005) for fisheries taking these sharks in EC waters and for EC vessels in international waters.
90 ICES Advice 2006, Volume 9 Norwegian vessels in EC waters are subject to a multi-species quota for these species and spurdog. This quota is about equal to recent Norwegian catches of deepwater sharks in EC waters and does not appear to be restrictive.
Changes in fishing technology and fishing patterns
The ban on gillnetting in EC and international waters may have diverted fishing effort to other gears, most likely to longline fisheries. Sharks are known to be vulnerable to longline fisheries.
The environment
Demersal fishing in deep water exploits species that are particularly sensitive to exploitation because of their life history characteristics (long-lived, slow growth, low fecundity, poor productivity). In addition, the impact of ghost fishing is considered to be more important in deep water because of the type of gear and their persistence in the environment. There are also many potentially vulnerable and sensitive habitats (e.g. biogenic reefs). Deepwater demersal communities tend to have high biodiversity which may be compromised by fishing.
Scientific basis
Data and methods
No analytical assessment was carried out in 2006. The assessment is based on commercial CPUE trends and survey trends.
Uncertainties in assessment and forecast
Landings data on these species remain very problematical and, in many cases, reliable data are only available for combined siki sharks. Many countries continue to report landings in amalgamated categories such as various sharks N.E.I. . Retrospective splitting of the data into species categories and reconstruction of historic data from mixed categories is based on limited information and is problematic.
The CPUE data available consisted of un-standardized point estimates, with an incomplete description of the sampling designs used to collect effort and landing/catch data either from surveys or commercial landings. There was no other auxiliary information to improve the standardization process. In particular; dates of collection, location and fleet composition.
Environment conditions
Comparison with previous assessment and advice
Evidence available in 2006 shows that the upward trend in 2001 was due to a movement of the fishery to new grounds within Subareas V and VI and that this masked the decline in catch per unit effort for traditional grounds.
Information available this year does not alter the perception of the state of the stocks from 2005 and the advice is consistent with last year.
Source of information
Report of the Working Group on Elasmobranch Fishes, 2006 (ICES CM 2006/ACFM:31).
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Year ICES Single-stock Predicted catch Predicted catch Agreed ACFM Disc. ACFM Advice exploitation corresponding to corresponding to TAC1 landings slip. Catch boundaries advice single-stock exploitation boundaries 1992 No advice 4.6 1993 No advice 5.2 1994 No advice 6.5 1995 No advice 6.5 1996 No advice 7.2 1997 No advice 8.2 1998 No advice 7.7 1999 No advice 6.5 2000 No advice 7.1 2001 No advice 10.1 2002 No advice 8.1 2003 No advice 10.9 2004 No advice 9.0 2005 No advice 7.1 5.1 2006 Zero catch F=0 7.1 2007 Zero catch F=0 Weights in 000 t.
92 ICES Advice 2006, Volume 9
12000
Unknown Area 10000 XIV XII )
s 8000 e X n n
o IX t (
s 6000 VIII g n i VII d n
a 4000 VI L Vb Va 2000 IV a
0 1 1 1 1 1 1 2 2 2 9 9 9 9 9 9 0 0 0 8 9 9 9 9 9 0 0 0 8 0 2 4 6 8 0 2 4
Year
Figure 9.4.21.1 Portuguese dogfish and leafscale gulper shark in the Northeast Atlantic: International landings by ICES Subarea or Division.
ICES Advice 2006, Volume 9 93
Figure 9.4.21.2 Portuguese dogfish and leafscale gulper shark in the Northeast Atlantic. French CPUE in ICES Subareas.
94 ICES Advice 2006, Volume 9