Commission staff working document

Дата канвертавання22.04.2016
Памер0.51 Mb.
  1   2   3   4   5   6   7   8



Brussels, 5.2.2009

SEC(2009) 106


European Community Plan of Action for the Conservation and Management of Sharks


Proposal for a


Shark Assessment Report

{COM(2009) 40 final}

{SEC(2009) 103}
{SEC(2009) 104}



Spurdog / Piked dogfish (Squalus acanthias)

North-east Atlantic Spurdog Squalus acanthias

Order: Squaliformes

Family: Squalidae

English: Spurdog, piked dogfish or spiny dogfish

French: Aiguillat commun

Spanish: Mielga

Overview: spurdogs are long-lived, slow growing, have a high age-at-maturity, and are particularly vulnerable to high levels of fishing mortality. Population productivity is low, with low fecundity and a protracted gestation period. In addition, they form size- and sex-specific shoals and therefore aggregations of large fish (i.e. mature females) are easily exploited by target long-line and gillnet fisheries. There is limited information on the distribution of spurdog pups, though they have been reported to occur in Scottish waters, in the Celtic Sea and off Ireland. The lack of accurate data on the location of pupping and nursery grounds, and their importance to the stock precludes spatial management for this species at the present time.

The spurdog is particularly vulnerable to over-fishing, it has a long life span of up to 100 years, a long generation time of between 25 and 40 years, slow growth rates of up to 3.3mm per year for adult spurdogs and a late age at first maturity of 12–23 years for females, and 6–14 years for males. These characteristics result in the intrinsic population growth rates for spurdog being between 2.3–7% growth per year. This is low for even the majority of shark species.

The spurdog is also highly migratory and strongly aggregated by age and sex, masking stock depletions and allowing targeting of the large pregnant females. This has led to a clear sex bias in heavily exploited populations (becoming male biased) with an associated reduction in pup production (Fordham, 2007). The rate of natural mortality is not known, though estimates ranging from 0.1–0.3 have been described in the scientific literature (Aasen, 1964; Holden, 1968).

The fishery

Spurdog is commercially exploited, principally for human consumption, but markets are limited and large parts of the catch may be discarded. Spurdog fisheries peaked in the late 1950’s and early 1960’s. Several species of small dogfishes and sharks occur in the North Sea, and these have often been reported as ‘mixed dogfishes and hounds’, with no information on the species composition.

Gear types, fishing fleets and their distribution: It is mainly caught as by-catch in trawl fisheries, especially otter-trawl fisheries, though directed fisheries using gillnets and long-lines operate at certain times of year, especially in inshore waters. Spurdog are captured less frequently in beam trawl fisheries, which may be due in part to gear selectivity (specifically the low height of the beam may affect the catch rate of a largely pelagic species), but also because most beam trawl activity occurs in the southern North Sea, where spurdog are less abundant.

EC directed catch trends and characteristics: Spurdog in the ICES area are considered to be a single stock, ranging from Sub-area I to Sub-area IX, although landings from the southern end of its range are likely also to include other Squalus species. Spurdog occurs throughout the water column along the continental shelf of north-west Europe and has been recorded to depths of 900 m (Compagno, 1984). However, it is most common from 10–200 m (McEachran, J.D. and Branstetter, S., 1986.). The majority of the landings are from the Norwegian Sea (IIa), Kattegat and Skagerrak (IIIa), North Sea (IV), North-West Scotland (VIa), Irish and Celtic Seas (sub-area VII) and northern Bay of Biscay (VIIIa).

For spurdog, the most accurate species-specific landings data occurred after the fisheries peaked. Annual landings from the North Sea and Skagerrak were in excess of 25 000 tonnes in the 1970’s, falling to 1 000 tonnes per year in the 1980’s and early 1990’s. Landings in recent years have generally been less than 5 000 tonnes per year, and between 1999 and 2003 were lower than the TAC allocated to EU vessels. Landings in 2004 on EU and non-EU fleets were 6 000 t but by 2006 the ICES-reported catch had fallen to less than 3 000, of which two-thirds were caught by EC Member States. The main EC countries exploiting spurdog are France, Ireland, Norway and the UK, and non-EC countries being Iceland and Norway.

In the UK (E&W), just over 50% of spurdog landings were taken in line and net fisheries in 2006, with most landings coming from Sub-area VII and in particular the Irish Sea (ICES, 2007a). Such fisheries are likely to be closer inshore and may target aggregating mature female spurdog. Recent reports from the fishing industry also indicate that fleet behaviour has been affected by rising fuel costs (ICES, 2007b) with many boats fishing closer to home to reduce costs. Such behaviour may mean that there could be increased fishing effort on inshore aggregations. Most Scottish landings are taken from the northern North Sea and west of Scotland. Effort in the Scottish demersal trawl fleet is likely to have reduced in recent years due to decommissioning of vessels and days at sea regulations, and therefore the effort on spurdog due to this fleet may well have been reduced, with about 45% of Scottish spurdog landings originating from demersal trawl fisheries.

The Irish fishery for spurdog mainly consists of bottom otter trawlers, with less than 30% of landings coming from line and gillnet fisheries. Most landings are reported from Division VIa and Division VIIg.

Incidental catch characteristics: While there is no EU minimum landing size for spurdog, there is some discarding of smaller fish, and it is likely that spurdog of <40 or 45 cm are discarded in most fisheries. A recent study on the estimated short-term discard mortality of otter trawl captured spurdog in the Northwest Atlantic showed that mortality 72 hours after capture was in some cases well below the currently estimated 50% for trawling (Mandelman and Farrington, 2006). The survivorship of discards of juvenile spurdog is not known.

Status of stocks

Northeast Atlantic Ocean stocks: a single stock of Squalus acanthias is present in the Northeast Atlantic Ocean from the Barents Sea to the Bay of Biscay, with a more southerly Iberian Peninsula stock that is probably distinct from the northern stock. The latest WGEF report (2007) states that in 2006 ICES advised that “The stock (of S.acanthias) is depleted and may be in danger of collapse. Target fisheries should not be permitted to continue, and bycatch in mixed fisheries should be reduced to the lowest possible level. A TAC should cover all areas where spurdog are caught in the northeast Atlantic. This TAC should be set at zero for 2007.”

Estimates of total amount of spurdog discarded are not routinely provided although some discard sampling does take place. A recent study on the estimated short-term discard mortality of otter trawl captured spurdog in the Northwest Atlantic showed that mortality 72 h after capture was in some cases well below the currently estimated 50% for trawling (Mandelman and Farrington, 2006). When catch weights exceeded 200 kg, there were increases in 72 h mortality that more closely approached prior estimates, indicating that as tows become more heavily packed, there was a greater potential for fatal damage to be inflicted. It should be noted that tow duration in this study was only 45–60 minutes, and additional studies on the discard survivorship in various commercial gears are required, under various deployment times.

In addition to the problems associated with obtaining estimates of the historical total landings of spurdog due to the use of some generic dogfish landing categories, there can be some misreporting (ICES, 2006). While there is no EU minimum landing size for spurdog, there is some discarding of smaller fish, and it is likely that spurdog of <40 or 45 cm are discarded in most fisheries. The survivorship of discards of juvenile spurdog is not known.

Length compositions were presented in ICES (2006), and no new analyses of length data from either market sampling or discard trips were undertaken. WGEF examined length frequency data collected from UK fisheries landings (ICES, 2006), and future studies should examine any data that may also available for other fisheries involved in the spurdog fishery (e.g. from Norway, France and Ireland).

Fishery-independent survey data are available for most regions within the stock area. The overall trends in the various surveys examined by the ICES WGEF indicated a trend of decreasing occurrence and decreasing frequency of large catches, with catch rates also decreasing, although catch rates are highly variable (ICES, 2006). It has been proposed that future studies of survey data for spurdog stock assessment could usefully examine surveys from other parts of the stock area not generally covered by the main fisheries, as well as sex-specific and juvenile abundance trends. (ICES WGEF Report 2007)

Although there have been several studies in the North Atlantic and elsewhere describing the age and growth of spurdog (Holden and Meadows; 1962; Sosinski; 1977, Hendersen et al., 2001), routine ageing of individual from commercial catches or surveys is not carried out.

The last stock assessments of spurdog in the Northeast Atlantic were undertaken by ICES in 2006, with earlier work by Heessen (2003) and Hammond and Ellis (2005). The latest ICES assessment included a delta-lognormal GLM-standardised index of abundance and a population dynamic model. Preliminary results from this model confirmed that spurdog abundance has declined, and that the decline is driven by high exploitation levels in the past, coupled with biological characteristics that make this species particularly vulnerable to such intense exploitation (ICES, 2006). The methods employed during the 2002 SGEF meeting (ICES, 2002) and DELASS project (Heessen, 2003) included catch curve analysis and separable VPA using length distributions sliced according to growth parameters from the scientific literature, and a Bayesian assessment using a stock production model, with a prior for the intrinsic rate of increase set by demographic methods.

The WGEF has provided estimates of total landings of Northeast Atlantic spurdog and has used these, together with UK length frequency distributions in the assessment described above. However, there are still concerns over the quality of these data due to:

  • uncertainty in the historical level of catches due to landings being reported by generic dogfish categories

  • uncertainty over the accuracy of the landings data due to species mis-reporting

  • lack of commercial length frequency information for countries other than the UK

  • low levels of sampling of UK landings and lack of length-frequency data in recent years

  • lack of discard information

Survey data are particularly important indicators of abundance trends in stocks such as this where an analytical assessment is not available. However, it should be highlighted that the survey data examined by WGEF cover only part of the stock distribution and surveys should be extended to other parts of the stock distribution and not just extrapolated from those areas covered and that survey data are difficult to interpret for the use of assessing the spurdog stocks due to the typically highly skewed distribution of catch per unit effort due to the aggregation effect of the adult females.

Currently no reference points have been proposed for the Northeast Atlantic stock of spurdog. The NE Atlantic stock of spurdog has been declining rapidly and is at its lowest ever level. Preliminary assessments making use of the long time-series of commercial landings data suggest that this decline has been going on over a long period of time and that the current stock size may only be a small fraction of its virgin biomass (< 10%). Although other models have not proved entirely satisfactory (due to the quality of the assessment input data), the exploratory assessments and survey data, also indicate a major decline in spurdog stocks and that most landings since 1946 have been above MSY. Biomass levels are at between 2% and 11% of initial biomass (B0). The latest stock assessment by ICES in 2006 concluded that the biomass levels were at 5.2 – 6.6% relative to 1905, and 5.2-7.1% relative to 1955 and warned that the stock was in a danger of collapse. The input data available are too limited to give an accurate estimate of current stock status in terms of absolute biomass and fishing mortality, but the trends that have been observed in the stock biomass are worrying.

Mediterranean and Black Sea stocks: spurdog are rare in the Mediterranean, with an estimated biomass of only 6 700t, no stock assessments have been carried out although there is some evidence for localised declines in abundance have been observed around the Balearics. Black Sea stocks have shown a 60% decline based on a previous stock assessment by Prodanov et al. (1997). They showed that the exploited stock in the Black Sea rose until 1981 where it peaked at 226 700t but had decreased by 60% to about 90 000t in 1992.

Northwest Atlantic stocks: the Northwest Atlantic stock can be considered one stock, shared by Canada, the United States. In Canada, spurdog quotas are based on historic levels. In the US, the National Marine Fisheries Service (NMFS) imposes science-based trip limits and quotas for spurdogs, but federal management measures are not compulsory in state waters and directed fishing has been occurring at unsustainable levels nearshore.

In 2006, US fishery scientists outlined several reasons for concern about the status of the Northwest Atlantic spurdog stock, including:

  • Very low recruitment in recent years

  • Imbalance in the sex ratio of the stock, strongly favouring males

  • Resulting contraction of overall length range in the population

  • Declining average size of females, resulting in fewer and smaller pups.

Research cruises have identified two periods of apparent change in spurdog abundance in the Northwest Atlantic. During the period from the early 1970s to 1992 to abundance and biomass indices from the research surveys increased, but from 1992 to 2002 the abundance had declined from 600 000t to 400 000t, with the majority of this being due to the removal of the larger individuals. When the same pattern is applied only to the biomass of spawning females the biomass has decreased by 75% from 1989 to 1998 and has remained constant since then. This level is at 29% of the target SSB Females.

Recent assessments of the recruitment of spurdogs in the Northwest Atlantic (1997 to 2003) were the seven lowest recruitment estimates (NFSC 2003). This has highlighted the susceptibility of this species to potential collapse due to the slow growth and recruitment rates not being able to replenish the spawning stock biomass quickly. Estimates made by the United States state that the current landings made by the United States and Canada are currently unsustainable.

Recent research on the pupping locations, growth rates, tagging and stock structure have allowed a preliminary population model to be developed for spurdog. The model developed by the DoF in Canada, is an age and sex structured, forward projecting population model, which estimates a starting population size and age structure (in 1960), and projects the population forward by adding recruits (age-1 fish) to the population and subtracting catches and natural mortality. The model is fit to the abundance indices obtained from Canadian and United States research surveys as well as the proportions at length found in the research surveys and commercial catch sampling.

Some of the data series used in the model are short and highly variable, and although the main Canadian data source (the annual summer survey) potentially indicates a stable or slightly increasing population, some of the other surveys indicate a declining trend. As a result, the model in its present form does not provide robust estimates of abundance. There has however been a decline in the total biomass that can be put down to the level of commercial exploitation.

The spring minimum trawlable biomass estimates for spurdog in Canadian and U.S. waters show similar trends, increasing from the early 1980s to the early 1990s, then declining. Mean values for both indices were around 500 000 mt in the early 1990s, declining to about 300 000 mt in 2007 for the Canadian index ( a reduction to 60% of the maximum level).

Spiny dogfish are relatively hardy fish, so it is only reasonable to assume that discard mortality is not 100%. There are a few available estimates for dogfish discarding mortality. Published studies report discard mortalities of 0-29% for dogfish caught with OTB (depending on catch size), and 55% mortality for gillnet-caught fish. Therefore, dogfish discard mortality in Canadian waters was calculated as per the following: 25% for OTB catches > 200 kg, 0% for OTB catches < 200 kg, 55% for gillnet catches, 10% for longline catches, and 25% for purse seine catches. The exact values are debatable, although all appear to be consistent with the experimental values reported above and observer observations of the manner in which fishers and their gear treat dogfish catch. Estimated dogfish discard mortality has averaged about 850 mt annually since 1986. Discard mortality often exceeded reported catch prior to 1999, but recent landings have greatly exceeded discard mortality.

Northeast Pacific stocks: the stock of spurdog in the Northeast Pacific has apparently already suffered from two stock collapses in 1910 and in the late 1940s, when it was the most valuable Canadian west coast fishery (Ketchen 1986) most probably for the vitamin A market. The stock has under low levels of commercial exploitation now recovered over most of its original range. The fishery within Canadian waters is now stable with catches of 5 000t – 7 000t from an available quota of around 15 000t. (Wallace et al. 2006)

In the US, federal management began in 2006 with trip limits pending stock assessment and development of quotas (possibly in 2007). In Washington State, spurdogs are loosely managed within bottom fish management plans, with mesh restrictions and closure of a pupping ground. Spurdogs are included in an “other species” TAC for bycatch in Alaskan fisheries. Canadian quotas for allocated catches and bycatch were capped at historic levels. Investigations are pending to determine current sustainable exploitation levels. Recent landings are only 30–50% of quotas. In Alaska, direct fishing for sharks is not allowed, although spurdogs are the most common shark species. Currently 90% of spurdog catches within the groundfish fishery is discarded, although the overall abundance appears to be stable or increasing.

Existing specific management measures

Spurdog in the North Sea are currently managed by quota, with a Total Allowable Catch (TAC). In 2007, the TAC was reduced by 20% to 841 t and spurdog bycatch in the North Sea was limited to 5% of the live weight of the retained catch. New for 2007 is a TAC covering areas outside the EC waters of IIa and IV, covering ICES sub-areas IIIa, I, V, VI, VII, VIII, XII and XIV (EU and international waters). The 2008 TAC was set to 2 004 t (total landings for all areas except IIa & IV was 2 087 t in 2006). New for 2008, the quota for this area is allocated eight Member States, with the UK, France and Ireland allocated the largest shares.

In 2007, Norway banned fishing and landing of spurdog in its waters and in international waters in ICES areas I-XIV, except for boats under 28 m using traditional gear inshore and in territorial waters (4 nm). Spurdog bycatch in other fisheries must be landed and Norwegian fisheries managers can stop fisheries when catches reach the prior year’s level. Norway has had a 70 cm minimum landing size limit on spurdog for many years (Shark Alliance, 2007).

Germany, on behalf of the European Community, proposed that Squalus acanthias should be included in Appendix II of CITES (CITES, 2007a). However the FAO Ad Hoc Expert Panel (FAO, 2007) concluded that: (i) the available evidence does not support the proposal to include Squalus acanthias under CITES Appendix II, (ii) the northeast Atlantic population meets the decline criterion for listing on Appendix II and (iii) that there are serious fisheries management failures for some individual populations. Catches from the northeast Atlantic stock, both internally traded in the EU and imported, need to be curtailed.

The quality of catch data for spurdog raises a number of issues including (i) landings being reported as generic dogfish categories, (ii) mis-reporting and (iii) a lack of discard information.

The WGEF has recommended that the next assessment for spurdog be made in 2009.

Effectiveness of management measures

Spurdog are long-lived, slow-growing, have a high age-at-maturity, and are particularly 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.

Recent management advice

According to ICES advice 2008, the only new information available for spurdog (Squalus acanthias) is landings data which does not offer any reason to change the advice from 2006. The advice for 2009 and 2010 is therefore the same as the advice given in 2006: The stock is depleted and may be in danger of collapse. Targeted fisheries should not be permitted to continue, and bycatch in mixed fisheries should be reduced to the lowest possible level. The TAC should cover all areas where spurdog are caught in the northeast Atlantic and should be set at zero (...).

In addition to the advice of 2006, ICES offers the following considerations:

Simulation modelling has shown there are strong potential benefits to the stock by protecting mature female spurdog in this long-lived species. If a non-zero TAC would be set, ICES recommends the introduction of a maximum landing length (MLL). This is expected to deter fisheries targeting areas where large females occur.

The maximum landing length should initially be set at 100 cm. The length at 50% maturity for female spurdog is just over 80 cm and the maximum size of females is about 120 cm. The maximum size of males is about 90 cm. Fecundity of spurdog increases with length and females of 100 120 cm length generally produce the highest amount of pups (10 21). Survivorship of spurdog released from longline fisheries is thought to be high, but will be lower in gillnet and trawl fisheries.

Tope (Galeorhinus galeus)

  1   2   3   4   5   6   7   8

База данных защищена авторским правом © 2016
звярнуцца да адміністрацыі

    Галоўная старонка