NE ATLANTIC PORBEAGLE SHARK SURVEY PROPOSAL

Questions about the status of the stock

The porbeagle population is considered to form a single stock in the NE Atlantic which extends from the Barents Sea to northwest Africa. For management purposes the southern boundary of the stock is 36°N and the western boundary at 42°W.

The stock is considered to be depleted (ICES, 2008), mainly because the available information from Norwegian and Faeroese fisheries shows a strong decline in landings,that have almost ceased in the Northern part of the stock area since the beginning of the nineties (Figures 1a and 1b).In 2009, new data were analysed by the Working Group on the Elasmobranch Fishes (ICES, 2009). A new series of French logbook data was presented (Biais and Vollette, 2009) which is longer than that presented to the 2008 EFWG (Figure 2). This CPUE series shows five above average values at the beginning (1000 to 1500t/day at sea from 1972 to 1977) but from 1978 onwards, the CPUE ranges between 500 and 1000 t/day at sea. A GLM annual index was estimated from this data by the WG (Figure 3[sk1]). Spanish CPUE data were also presented (ICES-ICCAT, 2009). These data are catch rates of porbeagle caught as by-catches of a swordfish directed fishery which extends over a larger area than that of the French fishery. A GLM approach was also performed using these data to get a standardized CPUE series which does not exhibit any trend (Figure3).

Based on these data, exploratory assessments were undertaken in the 2009 joint ICES/ICCAT meeting using a Bayesian Surplus Production (BSP) model and an age structured production model (ASPM). The results are considered to be highly uncertain, given that the majority of the fishery removals occurred before CPUE data were available to estimate abundance trends (ICES-ICCAT, 2009).

The EFWG porbeagle stock status assessment remains consecutively mainly supported by the large decrease of Nordic catches after the beginning of the sixties. The effect of changing fishing effort in this decrease in porbeagle landings is not well documented. However, the decrease is at least partially related to a change in the fishing area used by the Norwegian fleet. This fleet moved to the North-western Atlantic when Norwegian boats discovered that good catches could be obtained off Newfoundland. Before leaving the North-East Atlantic, the Norwegian fleet explored grounds to the west of the British Isles because of declining catches in the North Sea. It appears that good fishing grounds were discovered around Ireland, but the fishery in Irish waters ceased after only few years. Given the lack of information on this fishery, it remains unknown if the Norwegian fishermen gave up on this area because of a decrease in catch rate or because the catches in the NW Atlantic were more attractive.

Consequently, the current porbeagle stock assessment gives rise to the following questions:

  • What substantive evidence is there for a significant decrease in porbeagle abundance in the European Western shelf area?
  • Can Norwegian and Danish catch and CPUE data be provided at a spatial scale that allows a better understanding of population dynamics in the NE Atlantic?
  • What are the exchange rate of sharks between the western European shelf population and the North Sea? [sk2]
  • Do the horizontal and vertical movements of porbeagle sharks in their main areas of distribution affect their availability to capture, and hence influence fishery abundance indices?

These questions underline the need for a better understanding of the temporal and spatial distribution of porbeagle in relation to environmental/ecosystem features (including population structure[sk3]) to assess the stock.

Because of the recent ban on porbeagle catches[sk4] set by the last EU Fishery Ministers Council in December 2009, surveys and tagging experiments are now required in order to increase this knowledge. However, even if the fishery were to be re-opened in the future, the data-requirements outlined above will remain essential, because, as underlined by the 2009 ICES-ICCAT WG in its research recommendations: "The reliance of fishery-dependent data for assessments is problematic, as such data are not necessarily informative. Fisheries-independent surveys for porbeagle are required in the main stock areas." [sk5]

A porbeagle tagging survey on the south-western European shelf

A porbeagle survey is already carried out in the NW Atlantic by Canadian fishermen working in conjunction with scientists (commenced June 2007 then subsequently in 2009) (Campana et al., 2009). A survey in the NE Atlantic should follow the same overall design, namely adopting an equivalent systematic sampling scheme and being executed as a fishing industry and science partnership, so as to draw on fishermen’s expertise.[sk6]

However, a survey of this type will be difficult to realise in the near future, as French fishing vessels do not habitually operate north of 50°N along the western European shelf edge, mainly because of their relatively small size (18 to 20 m long). A full survey from the south of the Bay of Biscay to the North of the British Isles, would by necessity, need to address the following requirements:

-to find an adapted survey vessel,

-to obtain information on former fishing areas and periods of the Danish, Faroese and Norwegian porbeagle fishery.

The fulfilment of these requirements needs more than one year and aEuropean program is likely necessary to carry out a survey of the NE Atlanticporbeagle stock, given the largeness of this stock area. Ifremer is investigating possible partnerships to make this program possible in 2011. In a shorter term, it is however possible to improve the knowledge on the structure of the NE Atlanticporbeagle stock by a tagging program which can be carried out in 2010 only by France[sk7].

This tagging surveywill be limited to the Bay of Biscay and the South-west of the British Isles (Figure 4),and will be carried out by one or two French commercial vessels of Yeu Island (where are based the boats of the French porbeagle directed fishery) and by fishermen working in conjunction with scientists (at least one scientific observer per vessel).

This project will aim at:

-assessing the connectivity between the Bay of Biscay and South-west of British Isles population and the rest of the NE Atlanticstock,[sk8]

-increasing knowledge of critical habitats for porbeagle [sk9]in this region.

In the absence of commercial fishing in 2010, and to ensure data retrieval, the use of pop-up archival satellite tags (PSAT) is planned to provide detailed information on the spatial and temporal distribution of porbeagles. The aim is to tag at least 20 fish in 3 to 5 areas from the south-west of Ireland to the south of the Bay of Biscay. It will complete information collected from 4 tagsettings in the entrance of the Bristol Channel in 2007 ( Pade et al., 2009) and from 3 other tagsettings off the northwest coast of Ireland in 2008 (R. Saunders, personal communication). Additional tagging with conventional tags is also planned. It is thought to be interesting, given its low cost, even if directed catch are banned in 2010 because by-catch may happened and in case of fishery reopening in the future. [sk10]

The success of the survey would to an extent be dependent on finding adequate numbers of adult porbeagle (several consecutive days without fishing are possible) and likely working constraints due to bad weather (given the relatively small size of the French boats).Consequently, the survey is planned to extend over a month and an half,if using a single boat, to ensure the tagging of mature porbeagles in several different areas. Depending on catch success and on the weather, the survey could potentially be extendedbeyond 50°N to investigate abundance variation in an area where no directed fishing has been carried out for some decades.

All live fish captured by the survey will be tagged and released using plastic conventional tags or PSAT. Dead individuals will used for biological analysis (age and maturity determination, stomach contents, isotopic and genetic analysis). Recent catch ratesin the French fishery (700kg/day i.e. about 16 fish/day) and estimates of live catch (about 70%), (EPPARTIY, 2009) suggest a plausible estimate of total live fish to be tagged for mark-recapture would be in the region of 400-500individuals.The corresponding number of dead fish during a survey extending over a month and an half is estimated to be less than 250 fish (i.e. less than 10t).

References :

Biais and Vollette, 2009. CPUE of the French porbeagle fishery. WGEF Working Document,3 pp.

Campana S.E., A. J.F. Gibson, M. Fowler, A. Dorey and W. Joyce, 2009. Population dynamics of porbeagle in the Northwest Atlantic, with an assessment of status to 2009 and projection for recovery. Joint ICES/ICCAT Porbeagle Stock Assessment Meeting, Copenhagen, 22-27 June 2009, SCRS/2009/095, 61p.

EPPARTIY, 2009. Etude de la pêche palangrière de requin taupe de l'île d'Yeu. Rapport intermédiaire. Décembre 2009. 65p.

ICES. 2008. Report of the ICES Advisory Committee, 2008. ICES Advice, 2008. Book 9: 92-96.

ICES, 2009, Report of the Joint Meeting between ICES Working Group on Elasmobranch Fishes (WGEF) and ICCAT Shark Subgroup, 22–29 June 2009, Copenhagen, Denmark, ICES CM 2009/ACOM:16, 405p.

ICES-ICCAT, 2009. Report of the 2009 porbeagle stock assessment meeting. Copenhagen, Denmark, June 22 to 27, 2009. SCRS/2009/014 – Sharks Stock Assessment SCI-032/2009, 42p.

Pade, N., Queiroz, N., Humphries, N., Witt, M., Jones, C., Noble, L. & Sims, D. 2009. First results from satellite-linked archival tagging of porbeagle shark, Lamna nasus: Area fidelity, wider-scale movements and plasticity in diel depth changes. Journal of experimental marine biology and ecology, vol. 370, no. 1-2, pp. 64-74.

Figure 1a : ICES Working Group on Elasmobranch Fishes (WGEF) estimates of landings of porbeagle in the NE Atlantic for 1971–2008 and longer-term trend in landings (1926–1970) for those fleets reporting catches (ICES, 2009).
Figure 1b : ICES Working Group on Elasmobranch Fishes (WGEF) estimates of landings of porbeagle in the NE Atlantic for for 1973–2007 by country (ICES, 2009).
Figure 2. Porbeagle in the NE Atlantic. Nominal cpue (kg/day at sea) for porbeagle taken in the French fishery (1972–2008) with confidence interval (± 2 SE of ratio estimate). (Trip mean estimate in red an ratio estimate in black).
Figure 3 . Porbeagle in the NE Atlantic. Temporal trends in standardized cpue for the French target longline fishery for porbeagle (1972–2007) and Spanish longline fisheries in the NE Atlantic (1986–2007) (ICES, 2009).
Figure 4. Porbeagle in the NE Atlantic. Planned tagging area.

1

[sk1]which shows that the fishing luck is more variable in spain than in france ? : there is negative correlation in these data observations

[sk2]not in the report

[sk3]what is this, especially ?

[sk4]

[sk5]why to use standard tags, then ?

[sk6]basically good

[sk7]viva la france

[sk8]very likely high: what do the old tag data sets say ?

[sk9]critical in which respect ?

[sk10]we need good estimates in the future, not now