This meeting examined the ecology, taxonomy, stock status and conservation threats to deep-sea chondrichthyans. It was noted that few studies on deepwater chondrichthyans exist and the majority deal with squaloids, reflecting their greater commercial importance. Deepwater chondrichthyans form a large bycatch in many fisheries though fisheries targeting deepwater chondrichthyans are also becoming more important. Chondrichthyans are particularly vulnerable to fishing owing to their slow growth, late sexual maturity and low reproductive output. Data on deepwater chondrichthyan catches are sparse and usually uninformative as landings data rarely provide accurate species composition information. To use landings data for assessments species must be known, which requires species to have been described taxonomically. The 2004 IUCN Red List of Threatened Species™ assessment of deepwater chondrichthyans followed the Workshop.
Presentations on chondrichthyan life history noted that sharks, especially, are apex predators, and that their depth distributions may be linked to surface water primary production as shark numbers are highest in the deeper waters areas where surface water primary production is highest. Age estimates were reported for the deepwater species Centroscymnus crepidater with maturity occurring at 9–15 years. It was noted that knowledge of the status of most deep-sea chondrichthyans is limited, if not ‘data deficient’ and that several deep-sea chondrichthyans are critically endangered.
Case studies on Namibia and Australia demonstrated that a small number of vessels can quickly deplete unexploited stocks whose recovery is likely to be extremely slow because of the sharks' life history characteristics. Indonesian chondrichthyan landings were noted as high and largely unreported. In areas where baseline data exists, mean relative catch rates have severely declined. Abundance measures were reported for three chondricthyans in the Mediterranean Sea.
Deepwater chondrichthyans do not require unique management measures but their management is more complex as the available stock and sustainable yield is lower, especially for the unproductive deepwater species. The depth and spatial segregation that often occurs within a chondrichthyan population may make different components of the population available to the fishery and thus it can be relatively easy to remove an entire component of a population. Reliable catch information is rarely available and landing of processed animals makes it extremely difficult to identify the species composition of the catch. Lamentably, catch statistics for many species are often reported as “shark various”, “black shark”, “skate”, “ray”,etc. Regulations should require the retention of heads, fins and tails and prohibit the landing of fins, skate wings and livers without the accompanying carcass.
The need for better identification keys and guides to identify species and stock distributions and genetic techniques to separate sympatric species was noted. While knowledge of longevity and age-at-maturity estimates is needed for stock assessments, ageing techniques tried for squaloids, chimaeras and rajids have not yet been validated. Age validation may require radiocarbon dating or radiometric isotope analysis.
Knowledge of trophic levels would allow definition of community structure and provide data for ecosystem modelling. Consumption rates, interspecies dynamics, energy partitioning between co-occurring species and ontogenetic regional and seasonal variations are largely overlooked and unrecorded. Information on basic metabolic physiology is also required.
Knowledge of reproductive biology, duration of development, inter-breeding intervals and natural mortality are required and reproductive cycles remain undefined. Research is needed on the survival of discards of juveniles of larger species as the smaller individuals are usually discarded. Different fishing methods result in different discard mortalities. Analysis of catches taken in shorter tows in cooler waters show that a high proportion of dogfishes landed are alive and assessments are required of the survivability of these animals if they are released quickly.
Marine Institute, GTP, Parkmore
In the northeast Atlantic, deepwater elasmobranchs are taken in several deepwater fisheries. Most deepwater fishing activity occurs west and north of Ireland. Two species of sharks are routinely landed for their flesh and livers, the leafscale gulper shark (Centrophorus squamosus) and the Portuguese dogfish (Centroscymnus coelolepis). These species are collectively called “siki” in French fishery records though they are also marketed elsewhere under this name. French vessels catch these species in the mixed-species trawl fishery. Spanish longliners target deepwater sharks (Pineiro, Casas and Banon 2001), but it is difficult to quantify landings as separate statistics for deepwater shark species are not collected from these vessels. In addition, fleets of UK and German registered longliners and gillnetters have been targeting deepwater sharks since the mid 1990s, though their catches are reported only as generic sharks or dogfish. More recently, longliners from Norway and Ireland and trawlers from Scotland and Ireland are catching these species. Other, smaller, species of deepwater sharks are now being landed, or in some cases livers or fins are retained and the carcasses discarded. In addition to trawl and longline, there are fisheries for deepwater sharks using gillnets and tangle nets, but there are no catch or effort data available for these gear types. Smaller species include Deania calceus, Centroscyllium fabricii and Centroscymnus crepidater, though these are mainly discarded. Some progress has been made by some countries in collecting deepwater shark data, though data are still incomplete. The process of collating landings data began in 2000, but ICES has not yet been able to produce a reliable set of data for deepwater sharks. This is due to the use, by many countries, of generic reporting categories. It is also due to the low priority assigned to this task by many states. It is hoped that ICES will have a reliable dataset available by 2005 when the next stock assessments are planned.
Relatively few studies on deepwater elasmobranchs have been reported in the scientific literature. The majority deal with members of the Squalidae, but little attention has focussed on the impacts of fisheries on these species, despite their commercial importance in several regions of the world. This paper presents an overview of studies conducted in Ireland on deepwater elasmobranchs biology and fisheries.
2. MATERIALS AND METHODS
The present study is based on three trawl and three longline surveys undertaken during 1993–2000 on the Rockall Trough and Porcupine Bank, between 50° N and 59° N in the depth range from 500 to 2 000 m. Fishing was carried out in eight fixed areas (Figure 1) of the continental slope from 500 m to 1 300 m. Some deeper settings were made during longline surveys. Commercial fishing gears were used in these surveys. Trawl surveys used a “bobbin” trawl (Gundry's©Ltd.) with a 105-mm mesh cod-end and 25-mm small-mesh liner. The foot-rope length was 23 m with rubber discs of 40cm. The bridles were comprised of 92 m of single warp and 46 m of double wires. Trawl hauls ranged in duration from 135 to 380 minutes. Longline surveys used the “Autoline” system with main lines of 9mm or 11.5 mm diameter, with Mustad© size 13/O EZ and smaller numbers of size 7/O EZ hooks. Snoods were 40–70 cm in length attached to the main line at 1.4 m intervals. Bait consisted of squid (60percent) and mackerel (40percent).
The eight areas where stations were completed and shark sampling carried out
Areas 1–5 were in the Rockall Trough, and areas 6 – 8 were in the Porcupine Bank area.
Dorsal spines were used for age estimation of Centrophorus squamosus and Deania calceus. The spines were cleaned in a 4 percent hypochlorite solution for up to 12 hours, washed in running tap water and air-dried. Spines were sectioned using a Buehler© low speed jewellers saw with a diamond blade. Sections were taken at a thickness of 500 μm at intervals of 2000 μm along the length of the external spine in order to make comparative counts. All bands (consisting of one translucent and opaque zone) present in the inner trunk layer (sensu Maisey 1979) were included in age estimates. Maximum band count was found in those sections immediately proximal to the constriction of the central cavity, therefore age estimation was based on this region of the spine. Sections were cleared in xylene, air-dried before mounting on glass slides using resin C. Spine sections were read using a Wild Heerbrugge© binocular microscope using x 50 magnification and transmitted light. The dentinal layers were differentiated using a Leitz Biomed© compound microscope at x 40 magnification with transmitted light.
The von Bertalanffy growth model was fitted to the combined data from the present study and that of Machado and Figueiredo (2000). The von Bertalanffy growth function can be represented as
|Lt= L∞ ( 1-exp - K (t -t0) )
|Lt= length at time t
|L∞= asymptotic length, or mean maximum length
|K = a rate constant with units of reciprocal time (years -1) and
|to= age of the fish at theoretical zero length.
The von Bertalanffy growth function was fitted to length at estimated age for males and females separately by means of the Levenberg-Marquardt algorithm using the non-linear regression routine in SPSS v. 9.1 (SPSS 1999).
Length-frequency distributions (5-cm groups), separated by sex, for Centrophorus squamosus, Centroscymnus coelolepis and Deania calceus were pooled by gear type (trawl, longline). The Kolmogorov-Smirnov Two Sample Test (Sokal and Rohlf 1995) was used to test for significant differences between length frequencies from trawl and longline catches in 1997 trawl and longline survey data.
Comparative selectivity ogives for trawls and longlines were constructed for Deania calceus, Centrophorus squamosus and Centroscymnus coelolepis. Selectivity ogives were estimated using the method of Sparre, Ursin and Venema (1989) where the descending limb of a catch curve is extrapolated backwards to achieve an estimate of the non-fully selected age groups. The difference between these expected catch numbers and the observed values provide an estimate of the combined effect of recruitment and selectivity of the gear for these age groups. The logistic model was assumed to describe the selectivity pattern for each species. Input data for D. calceus were age-based catch curves from the August 1997 trawl survey and the December 1999 longline survey. Initial runs displayed little difference between ogives for males and females, so data by sex were combined.
It was not possible to produce a catch curve for Centroscymnus coelolepis or Centrophorus squamosus, because von Bertalanffy growth parameters were not available. To simulate a selectivity ogive, length-frequency distributions from the 1997 trawl and longline surveys were used to produce length converted catch curves (Pauly 1984). In the absence of parameters for the von Bertalanffy growth function, the following hypothetical parameters were chosen:
C. coelolepis: K = 0.09, t0= 0, L∞= 115 cm
C. squamosus: K = 0.09, t0= 0, L∞= 136 cm.
The depth distribution of three species is illustrated by catch rates in kg per 1000hooks from longline surveys (Figure 2). The habitual depth range (300 m – 1 800 m) of each species was sampled. Centrophorus squamosus and Deania calceus were most abundant between 700 m and 900 m. Centroscymnus coleolepis was more abundant in deeper water (1 300 m). Table 1 shows the relative proportions of elasmobranchs and teleosts in trawl and longline catches in each area (Figure 1). In longline catches, the elasmobranchs outnumber teleosts in all areas, except Area 4, where shallower hauls took the dominant species (ling and tusk) shallower than 500 m. In trawl catches elasmobranchs were still well represented, but the ratio favoured teleosts. Clearly, the number of species is greater in trawls, and though elasmobranchs are present, they are a less important component of the catch. In longline catches, elasmobranchs dominate. There is also a trend for greater numbers of species in catches the more further southwards.
Catch rates (kg/1 000 hooks) from longline surveys 1995–2000
Each 100 m interval indicated by its lower value.
Relative numbers of elasmobranchs and teleosts from trawl and longline surveys of the same areas ofthe eastern and southern slopes of the Rockall Trough in 1997
Figure 3 shows the percentage catch composition by species from comparable trawl and longline surveys of the continental slopes of the Rockall Trough in 1997. Squalid sharks dominate longline catches deeper than 500 m in this area. Elasmobranch dominance increases with depth with catches deeper than 1 300 m almost totally composed of squalid sharks (98 percent). The non-commercial species Deania calceus is the largest component of the catch between 500 and 700 m and squalids are the dominant species at all depths in longline catches. In contrast, trawl catches display a greater diversity of species with less dominance. The roundnose grenadier (Coryphae noides rupestris), a teleost, dominated at depths greater than 700 m, but the remainder of catches at these depths comprised a variety of species both chondrichthyan and teleost. The large commercial squalids - Centrophorus squamosus and Centroscymnus coelolepis - were the most abundant in trawl catches. Whereas teleosts comprise a higher component of trawl catches than elasmobranchs, it is clear that the latter group is well represented in catches from towed gears. The percentage species composition of longline catches on the continental slopes of the Porcupine Bank is illustrated in Figure 4. The differing species composition in this more southern region is evident. D. calceus is dominant over a range of depths here, comprising more than 60 percent of the catch between 700 and 900 m.
The spines of Deania calceus (Plate 1) and Centrophorus squamosus (Plate2) displayed the same morphology as those described by Maisey (1979) and by Gullart(1998) for Centrophorus granulosus. While the cap tissues cover the anterior-lateral faces of the spines of Squalus acanthias, they are reduced to one or more ribs in the species in the present study and in other deepwater squalids Centrophorus granulosus (Gullart 1998) and Etmopterus spinax (Maisey 1979). Estimates of 21–70years (Centrophorus squamosus) and 11–35 years (Deania calceus) were obtained from cross-sections of first dorsal spines. Agreement for the first and second spines within one year was found for more than 93 percent of Deania calceus and 88 percent of Centrophorus squamosus. The present data for Deania calceus were combined with published data for small specimens of this species (Machado and Figueiredo 2000) and allowed the construction of von Bertalanffy growth models (Table 2 and Figure 5).
Length frequencies show the absence of smaller specimens of these species from the study area (Figure 5). These are based on trawl and longline surveys spanning all the areas. Trawls and longlines selected for significantly different (Kolmogorov-Smirnov two-sample test, p<0.05) for size ranges of Centroscymnus coelolepis and Deania calceus, though not Centrophorus squamosus. Large female D.calceus were well represented in longline catches, but less well represented in trawls, indicating that large, mature females can avoid these nets.
Percentage composition of total catch by species in trawl and longline catches from the continental slopes of the Rockall Trough
Percentages rounded to nearest integer and presented by 200 m depth interval
Percentage composition of total catch by species longline catches from the continental slopes of the Porcupine Bank
Percentages rounded to nearest integer and presented by 200 m depth interval
Estimates of the parameters of the von Bertalanffy growth model for Deania calceus based on age estimation data from the first dorsal spine in the present study and from empirical growth data presented by Machado and Figueiredo (2000)
|95 % confidence limits
An important finding is the absence of smaller specimens of these species from the study area (Figure 3). The length range for Centrophorus squamosus was 71–122 cm for males and 74–145 cm for females. The range for Deania calceus was 55–109 (males) and 52–117 for females, whilst for Centroscymnus coleolepis the range was 68–118 cm (males) and 70–121 for females. Small (7/0 EZ) hooks were deployed during the long-line surveys in 1997 and 1999 in an attempt to target small sharks but no smaller specimens were taken. Interestingly, the modal lengths for male and female Centroscymnus coleolepis were widely separated though those for Centrophorus squamosus were not, even though there was an obvious tendency for females to grow larger in both cases. Gravid female Centrophorus squamosus were entirely absent from the study area in contrast to Centroscymnus coleolepis where all maturity stages occurred. Evidently, larger mature Centrophorus squamosus are mainly absent from the study area.
Selectivity ogives for Deania calceus (Figure 7) display similar shapes for both gears and sexes. The model predicts that longlines select for older (larger) sharks than trawls. Age50 was estimated at 11 years for trawls and 15 years for longlines. Results of the simulated ogive analysis for Centroscymnus coelolepis (Figure 8) suggest different selectivity patterns between trawl and longline. For females, longlines appear to be less selective than trawls for younger (smaller) sharks. The ogive for longline-caught females displayed a lower Age50 and only slight increases in proportions selected with increasing age. In contrast the trawl ogive for females displayed a sudden increase in proportion selected around age 25. This suggests that longlines are less selective for female C. coelolepis than males and take a higher proportion of smaller sharks. This effect is also illustrated in the comparative length frequencies (Figure 5), smaller females being selected by hooks, but are absent in the catches of the towed gear. There is less difference in the ogives for male C. coelolepis for which longlines did not take greater numbers (Figure 5). When combined for both sexes, the differences were masked, however the longline ogive is slightly less steep than that of the trawl. For C. squamosus, trawls selected smaller individuals than longlines (Figure 9). The shapes of the selectivity ogives are however similar.
There are important differences between trawls and longlines with respect to catches of deepwater elasmobranchs. Clearly, the catch composition of deepwater sharks is depth dependent, as has been found by Gordon (1999). The present data show the composition of elasmobranch species in the total catch for commercial gears by depth. Of the two commercial species, Centrophorus squamosus has a shallower distribution between 800 and 1 000 m and Centroscymnus coelolepis is a deeper, and the dominant species in longline catches deeper than 1 100 m. Deania calceus is not commercially exploited, but dominates longline catches in intermediate depths on the slopes of the Porcupine Bank; it is a slightly less important component further north in the Rockall Trough. Because this species tends to occupy hooks that could otherwise attract commercially valuable species, longline fishermen tend to avoid these depths. Therefore two completely separate longline fisheries can be defined in this area, one on the upper slopes targeting ling (Molva molva) and tusk (Brosme brosme) with bycatches of greater forkbeard (Phycis blennoides), mora (Mora moro) and blue ling (Molva dypterygia). Deeper than 1 000 m there is a target fishery mainly for the two commercially important large sharks, C. squamosus and C. coelolepis.
Von Bertalanffy growth models for Deania calceus based on age estimate data from the current study -closed circles -and from published work by Machado and Figueiredo (2000) -open circles
Trawl catches are not dominated by elasmobranchs. On the slopes of the Rockall Trough, roundnose grenadier dominates trawl catches from 700 m and deeper. However, after this teleost deepwater sharks are the next most important species in terms of weight. Discards from trawling in this region are high and are composed of up to 30 different species, while the species diversity of discards from longlining is lower and is dominated by sharks. Trawl discards are composed of small individuals of commercial species such as Coryphaenoides rupestris, Molva dypterygia and Phycis blennoides. Some teleost species, notably M. moro and B. brosme, are taken mainly on longline and are mainly absent from trawl catches. Small specimens of the squalid sharks are not present in this region (see below). Trawl discards are also composed of a large range of non-commercial species, such as blue antimora (Lepidion eques), Murray's longsnout grenadier (Trachyrhynchus murrayi) and Baird's smoothhead (Alepocephalus bairdii). In contrast, longline fishery discards are mainly composed of non-commercial shark species such as blackmouth dogfish (Galeus melastomus), greater lanternshark (Etmopterus princeps), Deania calceus and Centroscymnus crepidater. Longlines take many small shark species, and smaller specimens of some of the larger species of shark than the trawls.
Comparison of length frequencies from trawl and longline surveys of the Rockall Trough in 1997
Clarke, Connolly and Bracken (2002b) estimate that 533 t of Deania calceus was discarded during trawling operations in the Rockall Trough and slopes of the Porcupine Bank in 1996 (corresponding to ICES Sub-areas VI and VII). It is more difficult to estimate discarding levels from longlining because landings data are less complete. However, from the species composition data it can be seen that non-commercial sharks will dominate the discards. In shallower longline settings the main species taken are D. calceus and Galeus melastomus, whereas in the deepest settings (commercial viability decreases below 1 500 m) Centroscymnus crepidater and Etmopterus princeps are most important. Markets for D. calceus and other non-commercial species are becoming available, which would lead to increased exploitation of these sharks.
Estimated selectivity ogives for Deania calceus, sexes combined, derived from catch curve analyses Estimated age 50 (trawl) = 11 and age 50 (longline) = 15
The biological data presented above, concerning age, growth and maturity are dealt with in more detail in Clarke, Connolly and Bracken (2001, 2002a, 2002b). These studies along with other biological work on deepwater sharks suggests that these species are particularly vulnerable to overexploitation. Of all the species caught in the deepwater fisheries in the northeast Atlantic, deepwater sharks will have the lowest resilience to fishing pressure and the slowest replacement rates (Clarke, Connolly and Molloy 2003). It can be seen from Figure 10 that sharks are taken in both the demersal trawl and longline fisheries of the region. Therefore, they are an especially vulnerable group to commercial fishing pressure. Some of these sharks are highly migratory as is evident by the absence of certain life history stages in certain areas. This might ameliorate the effects of heavy exploitation if this is confined to small portions of their overall range. However, for species such as Centroscymnus coelolepis, where all reproductive stages are present in the main fishing area (west of Ireland and UK) the effects on the population are likely to be severe.
Trawls and long-lines are fundamentally different fishing methods. Trawls herd fish into the opening of the net, but fish are attracted to long-lines by the smell of the bait. This results in both size and species selection (Hareide 1995). Long-lines tend to select for larger teleost fish (Hareide 1995, Jørgensen 1995). The present study shows that longlines selected for size ranges of Centroscymnus coleolepis and Deania calceus not taken on trawl. These results show that long-lines are not size-selective for squalid sharks and demonstrate that commercial longline gear selects for the entire free-swimming size-range of these exploited squalid sharks in the NE Atlantic.
Estimated selectivity ogives for Centroscymnus coelolepis, derived from length-converted catch curves developed with hypothetical von Bertalanffy growth parameters
Estimated selectivity ogives for Centrophorus squamosus, derived from length-converted catch curves developed with hypothetical von Bertalanffy growth parameters
More detailed analysis of selectivity in deepwater sharks is provided by Clarke, Borges and Officer (2005). The results show that longlines select for larger Deania calceus and Centrophorus squamosus than trawls. These results are in agreement with those found for many teleosts. However, results of the simulations for female Centroscymnus coelolepis suggest that longlines are not always more selective that trawl. Indeed, trawl catches displayed almost “knife-edge” selectivity for females of this species. These differences highlight an important property of longlining. This method can capture fish from a wider area than trawls, resulting in differing size distributions. This simulation predicts that exploitation of a stock of C. coelolepis by longlines will involve the removal of greater numbers of smaller females than exploitation by trawl. This suggests that longlines may be less size-selective for some deepwater sharks. This effect would suggest that a fishery for deepwater sharks, prosecuted solely by longline could result in greater removals of younger sharks, which is the opposite to what has been observed for teleosts.
Schematic representation of the interactions between the main deepwater fishing gear types in the area west of Ireland and Britain
Some species are caught by more than one gear. Data on bycatch in the pelagic trawl fishery for greater Argentine Argentina silus are lacking. No data are available for gillnet fisheries.
Longlines are more effective at catching sharks and shark species dominate in longline catches deeper than 500 m. Small elasmobranchs dominate the discarded fraction of the catch from longlines, but not trawls. Therefore, in general, elasmobranchs are more vulnerable to longlines than to trawls. For some species, longline selects larger specimens. In theory, this means that exploitation of these species by longline will result in more of the biomass being left in the sea. However, for Centroscymnus coelolepis, longlines actually select for smaller females. This implies that targeting of this species by longline will remove more of the spawning stock than trawling. Therefore, C. coelolepis is especially vulnerable to exploitation in the area west and north of Ireland because all stages of its reproductive cycle are found in this area. In contrast, mature and gravid Centrophorus squamosus are totally absent, and those stages of Deania calceus are largely absent. This implies that these two species are somewhat less vulnerable to fishing in this area.
Until recently, fisheries taking deepwater sharks in the NE Atlantic were unregulated. However, in 2003, the European Community introduced a management regime for deepwater fisheries in Community waters and by Community vessels (Clarke and Patterson 2003). No TACs for sharks were implemented because there were no data upon which to base fishing quotas rights. However, a restriction on the amount of effort that can be expended on fishing any of the main deepwater elasmobranchs was put in place. Management of deepwater fisheries in the Northeast Atlantic Fisheries Commission (NEAFC) regulatory area is now being negotiated. This area corresponds to the international part of ICES waters. Though NEAFC has set an interim freeze on effort that can be expended in catching deepwater species, including sharks, it is not clear how effective this measure is.
Another important consideration for deepwater sharks in the northeast Atlantic is the FAO International Plan of Action for Elasmobranchs (IPOA-Sharks). The European Community intends to produce such a plan in 2004. This plan should pay particular attention to deepwater elasmobranchs because of their widespread occurrence in deepwater fisheries of Europe. Other coastal states have yet to implement national plans.
The current paper presents some biological and technical information on fisheries for deepwater elasmobranchs in the Northeast Atlantic. Much more work is still required. In particular, it will be necessary to have better assessments of the status of the stocks. Some progress has been achieved, though much remains to be done (Clarkeet et al. 2002). The main impediment is the lack of species-specific landings data or even data at a level sufficient to identify deepwater sharks separately from pelagic or shelf-dwelling taxa. The ICES Working Group on Elasmobranch Fishes is attempting to collate and refine catch data for deepwater and other sharks. A particular problem is the absence of information from the gillnet fleets that target deepwater sharks.
In conclusion, deepwater elasmobranchs are vulnerable species with low resilience to fishing and slow replacement rates. Heavy fishing pressure may be offset by the fact that it is concentrated in small portions of the overall range of these highly-migratory species. Assessments have been hampered by lack of data. However, the biological information available, along with the selectivity and technical data allow for some informed management advice to be provided. As stated in FAO texts on the Precautionary Approach to fisheries management, lack of data should not be used as an excuse for postponing management actions. This statement is particularly relevant for deepwater elasmobranchs.
5. LITERATURE CITED
Clarke, M.W. & K. Patterson 2003. Deepsea fisheries management: The approach taken by the European Community. Paper presented to Deepsea 2003 Conference, Queenstown, New Zealand.
Clarke, M.W., L. Borges & R. Officer 2005. Comparisons of trawl and longline catches of deepwater elasmobranchs west and north of Ireland. J. of Northwest Atlantic Fish. Sci. Vol. 35, Art. 41.
Clarke, M.W., P.L. Connolly, & J.J. Bracken 2001. Aspects of reproduction of the deepwater sharks Centroscymnus coelolepis and Centrophorus squamosus from west of Ireland and Scotland. J.Mar. Biol. Ass. U.K. 81: 1019–1029.
Clarke, M.W., P.L. Connolly & J.J. Bracken 2002a. Age estimation of the exploited deepwater shark Centrophorus squamosus from the continental slopes of the Rockall Trough and Porcupine Bank. J. Fish Biol. 60: 501–514.
Clarke, M.W., P.L. Connolly & J.J. Bracken 2002b. Catch, discarding, age estimation, growth and maturity of the squalid shark Deania calceus west and north of Ireland. Fis. Res. 56: 139–153.
Clarke, M.W., M. Girard, N.-R. Hareide, P. Lorance & R. Officer 2002. Approaches to the assessment of deepwater sharks in the northeast Atlantic. NAFO SCR Doc. 02/136.
Clarke, M.W., C.J. Kelly, P.L. Connolly & J.P. Molloy 2003. A Life History Approach to the Assessment and Management of Deepwater Fisheries in in the Northeast Atlantic. Northwest Atlantic Fish. Science 31: 401–412.
Gordon, J.D.M. 1999. Management considerations of deepwater shark fisheries. In Case Studies of the Management of Elasmobranch Fisheries, Vol. 2 (ed. R. Shotton), pp.774−819. Rome, FAO.
Gullart, J. 1998. Contribucion al conocimiento de la biologia y la taxonomia del tiburon batial Centrophorus granulosus (Bloch y Schneider, 1801) (Elasmobranchii, Squalidae) en el mar Balear (Mediterraneo Occidental), Published Ph.D. Thesis. Valencia: Universitat de Valencia.
Hareide, N.-R. 1995. Comparisons between longlining and trawling for deepwater species -selectivity, fish behaviour, quality and catchability. In Proceedings of NATO Advanced Research Workshop on deepwater fisheries of the north Atlantic slope, (EdA.G.Hopper), pp.227–234. Amsterdam: Kluwer AcademiPublishers
Jørgensen, O. 1995. A comparison of deepwater trawl and longline research fishery in the Davis strait. In Proceedings of NATO Advanced Research Workshop on deepwater fisheries of the North Atlantic slope, (Ed. A.G. Hopper), pp. 420. Amsterdam, KluwerAcademic Publishers.
Machado, P. & I. Figueiredo 2000. A technique for ageing the birdbeak dogfish (Deaniacalcea, Lowe, 1839) from dorsal spines. Fish.Res., 45, 93–98.
Maisey, J.G. 1979. Finspine morphogenesis in squalid and heterodontid sharks. Zoological Journal of the Linnaean Society, 66, 161–183.
Pauly, D. 1984. Fish Population in Tropical Waters: a Manual for Use with Programmable Calculator. ICLARM Studies and Reviews 8, Manila, Philippines: 325 pp.
Pineiro, C.G., M. Casas & R. Banon 2001. The deep-water fisheries exploited by Spanish fleets in the Northeast Atlantic: a review of the current status. Fish.Res., 51, 311–320.
Sokal, R.R. & F.J. Rohlf 1995. Biometry: the principles and practice of statistics in biological research. WH Freeman, New York, 887pp.
Sparre, P., E. Ursin & S.C. Venema 1989. Introduction to tropical fish stock assessment. Rome: FAO. FAO Fish. Tech. Paper 306/1.
SPSS 1999. Applications Guide to the Statistical Package for the Social Sciences. Chicago:SPSS.
Sarah Irvine1,2, J.D. Stevens1 and L.J.B. Laurenson2
1CSIRO Marine Research
GPO Box 1538
Hobart, Tasmania, Australia 7001
2Deakin University, School of Ecology and Environment
PO Box 423
Warrnambool, Victoria, Australia 3280
In Australia, deepwater dogfishes are a major bycatch and, or, byproduct of commercial trawlers targeting orange roughy (Hoplostethus atlanticus) and drop and longliners targeting blue-eye trevalla (Hyperoglyphe antarctica) and pink ling (Genypterus blacodes).
Fishers are now targeting dogfishes to supplement their income outside the quota system with the flesh and liver oil of at least 11 species being marketed (Table 1).
Marketed products of deepwater dogfishes by species
Quantifying the market sales of dogfish is difficult as carcasses are sold at wholesale markets as:
The annual whole weight of dogfishes sold at the Melbourne and Sydney markets has increased from 221 t in 1992 to 844 t in 2002. The value has increased from $A292000 in 1992 to $A1 080 000 in 2002 (Figure 1).
Annual whole weight and value of deepwater dogfish sold in Australia
In Sydney, the mean price of black roughskin shark has increased from $A1.77 kg in 1992 to $A4.23 kg in 2002, while the price of endeavour shark has remained between $A3.10 and $A3.90 kg over the same period. Retail outlets sell long and thin dogfish fillets as flake and prices are generally over $10 kg.
2.2 Liver oil
Livers from most Centrophorus spp. are higher in squalene and are therefore more valuable than livers from other dogfishes. Fishers are paid about $A6/kg for Centrophorus spp. livers while Deania spp. and Centroscymnus spp. livers are worth $A3/kg. Etmopterus spp. livers are worth less than $A2.80/kg.
Fishers are permitted to take up to 150 kg of Centrophorus spp. a day of which only 30kg can be of C. harrissoni. There are currently no regulations governing the catching of mid-slope dogfishes although fishers collecting livers must also land the associated carcasses.
It is well documented that chondrichthyans are vulnerable to overfishing and serious declines in upper-slope dogfish (Centrophorus spp.) stocks off southeastern Australia have already been documented (Graham, Andrew and Hodgson 2001). As mid-slope dogfish products become more marketable there is increasing scrutiny with respect to their management and conservation.
5. LITERATURE CITED
Graham, K.J., N.J. Andrew & K.E. Hodgson 2001. Changes in relative abundance of sharks and rays on Australian South East Fishery trawl grounds after twenty years of fishing. Marine and Freshwater Research 52: 549–61.
Rachel Cavanagh1 and P.M. Kyne2
1IUCN Shark Specialist Group
219a Huntingdon Road, Cambridge, CB3 0DL, UK
2Department of Anatomy and Developmental Biology
University of Queensland
St Lucia, Queensland 4072, Australia
Deep-sea species are widely recognized as relatively unproductive, highly vulnerable to overfishing and potentially slow to recover from the effects of overexploitation. In the face of rapidly expanding deep-sea fisheries and lack of effective management, of particular concern is the impact, either through targeted fishing or bycatch, on deep-sea chondrichthyan1 fishes, an extremely vulnerable taxonomic group (Lack, Short and Willock 2003). Despite this concern, knowledge regarding such impacts and the conservation status of most of the deep-sea chondrichthyans is seriously limited. This paper summarizes the outcomes of a series of the IUCN Shark Specialist Group's Red List workshops for the assessment of the conservation status of chondrichthyans, focusing on case studies of deep-sea species and discussing some of the problems faced due to lack of data and taxonomic uncertainty.
1The cartilaginous fishes: sharks, skates, rays and chimaeras.
1. 2 Deep-sea chondrichthyans
Chondrichthyans are an evolutionarily conservative group that has functioned successfully in diverse ecosystems for 400 million years. Despite their evolutionary success, some populations may now be threatened with extinction as a result of human activities and the conservative life-history traits of this group of fishes: slow growth, late maturity, low fecundity and low natural mortality. These characteristics result in low rates of potential population increase with little capacity to recover from overfishing (either direct or indirect) and other threats such as pollution and habitat destruction (Holden 1974, Pratt and Casey 1990).
Nearly 35 percent of chondrichthyan species are confined to deepwater (defined here as >200m), although the number of chondrichthyans known to spend all or part of their lifecycle below 200 m depth includes at least half of the >1100 living species. The fauna of most deep-sea areas is poorly known and new deepwater chondrichthyan species are regularly recorded and described worldwide. For example, exploratory deep-sea fishery surveys resulted in the discovery of six-gilled stingrays (Hexatrygonidae) in the Pacific in the mid-1990s, as well as new skates and undescribed chimaeras in the South Atlantic (L.J.V. Compagno, South African Museum, pers. comm.) and in 2003 a research cruise on the seamounts and abyssal plains around Lord Howe and Norfolk Islands in the western Pacific also resulted in the discovery of new species and new records of deep-sea chondrichthyans <http://www.oceans.gov.au/norfanz/>.
Deep-sea chondrichthyans are considered to be less resilient to fishing pressures than coastal and epipelagic oceanic species (Gordon 1999). This is due to the characteristically limited reproductive capacity of cartilaginous fishes (usually even lower in deep-sea species) combined with a lower population biomass compared to shelf species and the limited productivity and geographic constraints that characterize cold, deep environments. Many deep-sea species are widely (albeit often disjunctly) distributed, while others are endemic, restricted to small areas such as isolated seamounts, submarine ridges, or the deep slopes off a single country (Compagno and Musick 2005).
There is increasing commercial development of new deep-sea fisheries (Gordon 1999, Lack, Short and Willock 2003) as traditional pelagic and inshore demersal stocks decline and fleets move further offshore and into deeper water in attempts to sustain or increase catch levels. The development and wide-scale deployment of non-selective deep fishing gear means that fisheries are becoming far less selective, wider ranging, and entering environments that have not yet been surveyed. Deep-sea chondrichthyans will increasingly be caught as bycatch, at least in the early phases of fisheries when they are still well represented in the zonal fauna. In the few deep-sea areas that have been surveyed, evidence shows that some chondrichthyan populations have suffered serious, perhaps even irreversible, damage while the fisheries are still removing a sufficient biomass of bony fishes and invertebrates (Graham, Andrew and Hodgson 2001). It is possible that deep-sea fisheries could drive some bathyal chondrichthyans (particularly endemics) to extinction before management can be implemented, and possibly even before a species has been seen and described by researchers.
The availability of trade data for deep-sea chondrichthyans is sparse. While many species have little or no commercial value and are discarded, others are valued for their liver oil (rich in squalene) and flesh (Irvine, Laurenson and Stevens 2005). The commercial value of these products, together with declining catches of other deep-sea resources, has seen an increase in targeted fishing effort towards these species in some regions (Lack, Short and Willock 2003).
1.3 IUCN Red List of Threatened Species™
The IUCN Red List of Threatened Species™ is widely recognized as the most comprehensive source of information on the global conservation status of plant and animal species used world-wide for focusing attention on species of conservation concern as a basis to enable management priorities to be targeted, and for monitoring the long-term success of conservation and management initiatives. Although the Red List is not a legal instrument, it is used by government agencies, non-governmental organizations, natural resource planners, educational institutions and others to promote improvements in management and the research necessary to deliver successful management.
Historically, marine species have been little considered for inclusion in the Red List. However, the IUCN Species Survival Commission (SSC), custodian of the IUCN Red List of Threatened Species™, plans a major effort over the next 5–10 years to address this. This initiative includes ongoing efforts by the IUCN SSC Shark Specialist Group (SSG)2 - the Red List Authority for chondrichthyans -to complete a global assessment of the >1100 species by 2006. Comprehensive assessment of all chondrichthyans will establish a baseline against which to monitor future changes in the global and regional status of chondrichthyans and improvements in our scientific knowledge of this group. This information will promote improvements in the fisheries management of these biologically vulnerable species. In the case of deep-sea chondrichthyans, the need is particularly urgent given the sparse information available on stock sizes and distribution, unresolved taxonomic issues and the low management priority afforded them.
2 The IUCN (World Conservation Union) comprises >7000 scientists, government officials and conservationists from 188 countries and provides advice to governments, international conventions and conservation groups throughout the world. It comprises several Commissions, one of which is the Species Survival Commission (SSC). The SSC established the Shark Specialist Group (SSG) in 1991, in response to growing awareness and concern of the severe impact of fisheries on chondrichthyan populations around the world. With >170 members around the world, this network provides leadership for the conservation of threatened species and populations of all chondrichthyan fishes and aims to at promote promoting their sustainable use, wise management and conservation.
This ‘Global Chondrichthyan Assessment’ is being undertaken through a series of regional expert workshops to facilitate discussions and sharing of knowledge. Although only partially complete, this process is already highlighting the serious plight of this extremely vulnerable group of fishes (close to 20 percent of the 377 species assessed thus far have been classified as ‘threatened’). In addition to identifying threatened species and elucidating the causative factors, this programme is documenting the distribution, life histories and other key parameters of the species assessed including trade and fisheries information, thus increasing our knowledge and creating an easy-accessed centralized dataset. This is already providing the international conservation community, treaties such as the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) and agencies such as the UN Food and Agriculture Organization (FAO)3, with a powerful tool for setting programme priorities.
3 The FAO International Plan of Action for the Conservation and Management of Sharks (IPOA-Sharks) recommends that States adopt a National Plan of Action for chondrichthyan stocks whether catches occur as a result of directed or non-directed fisheries.
For more than 40 years the IUCN SSC has been evaluating the conservation status of species and subspecies on a global scale for IUCN Red Books on individual taxonomic groups and, more recently, for the IUCN Red List of Threatened Species™. A major advancement was the adoption in 1994 of a new system of Red List Categories and Criteria, which includes explicit quantitative criteria as the basis for extinction risk assessment. The most recently revised Categories and Criteria (Version 3.1) came into use in 2001 (Hilton-Taylor 2000, IUCN 2001).
Red List assessments evaluate the conservation status of individual species, identify threatening processes affecting them and, if necessary, propose recovery objectives for their populations. There are nine categories in the Red List system: Extinct, Extinct in the Wild, Critically Endangered, Endangered, Vulnerable, Near Threatened, Least Concern, Data Deficient and Not Evaluated. Classification into the categories for threatened species (Vulnerable, Endangered and Critically Endangered) is through a set of five quantitative criteria based on biological factors related to extinction risk including: rate of decline, population size, area of geographic distribution, and degree of population and distribution fragmentation. Table 1 lists definitions of the categories and Appendix I a summary of the criteria. For more details see the Red List Categories and Criteria Version 3.1 (IUCN 2001) available at <http://www.redlist.org>.
The series of regional workshops, which bring together international experts and national scientists and fisheries staff, compile and analyze species data. All assessments produced at these workshops are circulated for comment to the entire SSG network before being adopted by consensus and submitted to the Red List Programme for inclusion in the Red List (Table 2).
3. RESULTS AND DISCUSSION
3.1 Assessment status
To date the SSG has assessed the global threatened status of 377chondrichthyan species (including those of deep-sea species), plus a further 67 assessments at the regional and subpopulation level. Sixty-five species are globally threatened (Critically Endangered, Endangered and Vulnerable), together with a further 27 subpopulations assessed as threatened at the regional level. Further Red List assessments for additional species have been undertaken recently, for which the review process is currently underway.
Of all chondrichthyan species assessed thus far (not only deep-sea species), 17.2 percent are threatened (Critically Endangered, Endangered or Vulnerable), 18.6 percent are Near Threatened, i.e. considered close to meeting the criteria for a threatened category, 25.7 percent are Least Concern and 38.2 percent are Data Deficient (note, one species was assessed as Conservation Dependent in 2000, this category is no longer in use by IUCN). Regarding deep-sea results, 109 species occurring only at depths of >200 m have been assessed to date, and of these 4.6 percent are threatened, 7.4 percent Near Threatened, 18.3 percent Least Concern and 69.7 percent Data Deficient. If species occurring at a wider depth range (i.e. species which occur >200m, but also occur shallower) are included, of 216assessed, 6.9 percent are threatened, 14.4 percent Near Threatened, 23.1 percent Least Concern and 55.6 percent Data Deficient, together with a further 5.6 percent threatened at the regional or subpopulation level. A detailed analysis will be published by the IUCN SSG on completion of the global programme.
Red List categories (IUCN 2001)
|A taxon is Extinct when there is no reasonable doubt that the last individual has died. A taxon is presumed Extinct when exhaustive surveys in known
|Extinct in the Wild (EW)
|A taxon is Extinct in the Wild when it is known only to survive in cultivation, in captivity or as a natural
|Critically Endangered (CR)
|A taxon is Critically Endangered when the best available evidence indicates that it meets any of the criteria A to E for Critically Endangered, and it is therefore considered to be facing an extremely high risk of extinction in the wild.
|A taxon is Endangered when the best available evidence indicates that it meets any of the criteria A to E for Endangered, and it is therefore considered to be facing a very high risk of extinction in the wild.
|A taxon is Vulnerable when the best available evidence indicates that it meets any of the criteria A to E for Vulnerable, and it is therefore considered to be facing a high risk of extinction in the wild.
|Near Threatened (NT)
|A taxon is Near Threatened when it has been evaluated against the criteria but does not qualify for Critically Endangered, Endangered or Vulnerable now, but is close to qualifying for or is likely to qualify for a threatened category in the near future.
|Least Concern (LC)
|A taxon is Least Concern when it has been evaluated against the criteria and does not qualify for Critically Endangered, Endangered, Vulnerable or Near Threatened. Widespread and abundant taxa are included in this category.
|Data Deficient (DD)
|A taxon is Data Deficient when there is inadequate information to make a direct, or indirect, assessment of its risk of extinction based on its distribution and, or, population status. A taxon in this category may be well studied, and its biology well known, but appropriate data on abundance and, or, distribution are lacking. Data Deficient is therefore not a category of threat. Listing of taxa in this category indicates that more information is required and acknowledges the possibility that future research will show that threatened classification is appropriate. It is important to make positive use of whatever data are available. In many cases great care should be exerczed in choosing between DD and a threatened status. If the range of a taxon is suspected to be relatively circumscribed, and a considerable period of time has elapsed since the last record of the taxon, threatened status may well be justified.
|Not Evaluated (NE)
|A taxon is Not Evaluated when it has not yet been evaluated against the criteria.
Regional Red List workshops
|Australia and Oceania
|Regional and, or, global assessments for 175 species submitted to 2003 Red List and a workshop report published in hardcopy and as pdf on the web (Cavanaghet et al.2003).
|Regional and, or, global assessments for 50 species submitted to 2004 Red List. Remainder undergoing consultation process and will be submitted to 2005 Red List.
|Regional and, or, global assessments for 33 species submitted to 2004 Red List. Remainder undergoing consultation process and will be submitted to 2005 Red List.
|Initial consultation underway. Will be submitted to 2005 Red List.
|Global assessments for 30 species submitted to 2004 Red List.
4 Note that Some of the wider ranging species have been assessed at more than one workshop for different regional subpopulations.
5 ThematicUndertaken by a thematic workshop held in conjunction with the Deep Sea 2003 Conference.
3.2 Case Studies: Deep-sea Chondrichthyans on the Red List
A review of the assessments undertaken to date indicate that the taxa at highest extinction risk include commercially exploited species of deep-sea sharks. However, many deep-sea species are categorized as Data Deficient due to insufficient data to make a valid assessment of their status, even though some of these are likely to be threatened. Case studies of deep-sea species assessments to illustrate some of the trends are presented here.
i. Harrisson's dogfish (Centrophorus harrissoni -McCulloch 1915)
Red List assessment
Global (endemic to Australia) Critically Endangered A2bd+3d+4bd6
6 See Appendix.
Notes: Endemic to Australia (New South Wales, Victoria and Tasmania). A demersal species occurring mainly at depths of 220–790m, but also known from as deep as 1050 m (Daley, Stevens and Graham 2002). Low fecundity (1–2 pups, every 1–2 years), high longevity (closely related species live for at least 46years) (Fenton 2001) and probable late age at maturity.
This species provides a good example of documented declines over time (in the majority of cases for deep-sea chondrichthyans such fishery-independent data are unavailable). The basis for this assessment was a study by Graham, Andrew and Hodgson (2001). Documented declines of over 99percent were recorded between 1976–77 and 1996–97 between Newcastle (central New South Wales (NSW)) and the Eden-Gabo Island area (southern NSW/northern Victoria) by a fishery-independent trawl research survey. The relatively narrow continental slope habitat of this species (which is fished throughout its entire depth range) suggests that it may now only be present in significant numbers in areas that are non-trawlable. However, as dropline fishers also harvest this species off NSW, further pressure may be placed on it in such areas. As with other deepwater sharks, particularly this genus, the low fecundity, high longevity and probable late age at first maturity of this species not only result in extremely rapid population depletion in fisheries, but prevent it from quick recovery after such depletion (Pogonoski and Pollard 2003).
The demersal multi-species trawl fishery operating on the continental slope off south-eastern Australia studied by Graham, Andrew and Hodgson (2001) illustrates the difficulties of sustainably harvesting deep-sea chondrichthyans, particularly when they form a relatively minor component of a multi-species catch and the fishery continues after the severe decline of the sharks and rays. In addition to C. harrissoni, other species seriously affected by this fishery include the southern dogfish C. uyato (Critically Endangered in Australia), Endeavour dogfish C. moluccensis (Endangered in Australia) and several Squalus species (Graham, Andrew and Hodgson 2001, Cavanagh et al.2003). Catches are now limited and C.harrissoni, C. uyato and C. moluccensis have been nominated for listing on the Australian Commonwealth Environment Protection and Biodiversity Conservation Act 1999. These deep-sea dogfishes also highlight taxonomic problems which further compound the difficulties in assessing and managing these species. For C. moluccensis, C. uyato and others, taxonomic uncertainties make it impossible to assess their threatened status on a wider geographical basis until species complexes are resolved and distribution better defined.
ii. Barndoor skate (Dipturus laevis -[Mitchell 1817])
Red List assessment
Global (endemic to Canada and USA): Endangered A1bcd
Notes: Restricted to the Northwest Atlantic continental shelf and slope of Canada and the USA (Kulka, Frank and Simon 2002). Found as shallow as the tideline (Bigelow and Schroeder 1953) down to 1400 m (Kulka,Frank & Simon 2002). Longevity has been estimated as 13–18 years, and age at maturity 8–11years (Frisk, Miller and Fogarty 2001). Egg production estimated as 47 a year (Casey and Myers 1998).
This Red List case study illustrates a situation where deep-sea areas can provide a refuge for species already vulnerable to exploitation in shallower shelf regions. The barndoor skate is highly vulnerable to exploitation because of its slow growth rate, late maturity, low fecundity and large body size. Although never directly targeted, it was a byproduct of multi-species trawl fisheries on the Georges Bank, Scotian Shelf, Grand Banks and Labrador Shelf and is also taken on longlines. Catch rates of barndoor skates in USA waters <400 m within the centre of its latitudinal range on the southern shelf (<43°N) declined by 96–99 percent from the mid-1960s to the 1990s. While the severity of this decline would theoretically be considered grounds for listing as Critically Endangered (directly applying the IUCN Categories and Criteria), there are several reasons for the lower Endangered listing: fishing effort on the shelf area has declined in the last decade, the latitudinal and depth range of this species is considerably wider than previously thought, and numbers of juveniles now appear to be increasing not only in no-take zones on Georges Bank and the Southern New England shelf but also in adjacent areas to the north and south and elsewhere. However, it is possible that in the event of opening the no-take areas, the subsequent increasing fishing effort would lead to the decline of the barndoor skate in these areas (Dulvy in press). A review of this Red List assessment is currently underway, particularly due to recovery of the population south of the Scotian Shelf (Gedamke and Kulka inprep).
The barndoor skate appears to be rare on the shallower continental shelf, and the main part of the population is now known to occur in shelf channels and along the continental shelf edge in waters >450 m deep (Kulka 1999, Anon. 2000). Further little fishing occurs at depths greater than 200m. Strict precaution must be exercized as any increases in trawl fishing effort at depth will likely lead to the decline of the barndoor skate in these areas. Any development of fisheries into such areas requires strong management control to ensure the decline of this, and similarly vulnerable species occurring in deep-sea refugia, is prevented from the outset.
iii. Leafscale Gulper Shark (Centrophorus squamosus -[Bonnaterre 1788])
Red List assessment7
Global: Vulnerable A2bd+3bd+4bd
7 This assessment is being updated due to more recent information from Europe. Red List assessments are continually updated as new information is obtained. For this reason, readers are urged always to consult the current Red List (<www.redlist.org>), updated annually, to obtain the most recent assessments.
Notes: Wide but patchy global distribution in the Atlantic, Indian and Pacific Oceans. A demersal species occurring mainly in depths of 230–2400 m, also pelagic in the upper 1250 m of oceanic water in depths to 4000 m (Compagno and Niem 1998). Fecundity 5–8 pups (Last and Stevens 1994), high longevity with varying age estimates of 21–70 years (Clarke, Connolly and Bracken 2002), and probable late age at maturity.
This example illustrates the case of a targeted Vulnerable deep-sea shark for which fisheries are increasing in some areas and where CPUE data are combined with similar species. Centrophorus squamosus has been exploited commercially for many years and is an important component of deepwater longline and trawl fisheries in certain areas within its range, such as the eastern Atlantic off Ireland, Spain, Portugal and France. It was targeted heavily by the Portuguese deepwater longline fishery for which exploitation peaked in 1986 but has been steadily declining since then (Correia and Smith in prep.). In Japan exploitation peaked during World War II, because of the high percentage of squalene in its liver, but quickly declined due to decreasing catches. Significant declines have been documented (ranging from 20–69 percent in one year to 80–90 percent in three years) in parts of the Northeast Atlantic, but these are based on CPUE for C. squamosus and Centroscymnus coelolepis combined for only part of the distribution area and cannot be related to fishing effort. It is extremely important that landings for this species are reported separately and no longer combined with C. coelolepis. However, these declines together with the acute vulnerability to exploitation of Centrophorus species as shown from NSW fishery-independent surveys (Graham, Andrew and Hodgson 2001), and the knowledge that C. squamosus has limiting life history characteristics, led to this species being assessed as Vulnerable as a precautionary measure. Due to the apparently long lifespan of this species, the recovery of a heavily fished population would require a long period of time (White2003, Hareide in prep.).
Further studies are required to determine this species' life history characteristics and other parameters necessary for management. There is an intention to analyse historic French landing data with the purpose of separating landings and CPUE for the two species and this assessment should then be revisited. The level of fishing pressure needs to be further examined in the various populations within its range to establish whether separate regional assessments are more appropriate. It should be noted that a Vulnerable assessment may be applicable to many other poorly-known deep-sea species that are currently being exploited by unmanaged expanding fisheries.
iv. Lizard catshark (Schroederichthys saurisqualus -Soto 2001)
Red List assessment
Global (endemic to Southern Brazil): Vulnerable B1ab (iii, v)
Notes: Known from Paraná State to Rio Grande do Sul State (25°S to 30°S), Southern Brazil in depths of 250–500 m on the upper continental slope and sporadically on the outer edge of the continental shelf. Oviparous. It uses patches of deep-sea corals for egg-laying.
Currently known from a restricted area off Southern Brazil, the status of this deep-sea species is of concern due to the destruction of vital habitat through fisheries activities. It appears that the distribution of coral patches used for egg-laying determines the distribution of Schroederichthys saurisqualus. These coral patches seem to be naturally scarce, are of small size and are vulnerable to destruction by demersal trawling operating in the area. Trawl surveys of areas that have previously captured egg-laying females on stony coral have revealed that once the coral patch is gone so are the catsharks. Given the low temperatures (~5–8 °C) at the depths of coral occurrence, recovery from destruction is expected to be extremely long. It is possible that important coral habitat is more widespread in areas with rough bottom, not surveyed by trawling, and so the preferred habitat of this species may be more widespread than currently known, however, further surveys are required to confirm this. At present , this species is considered to face a high risk of extinction due to its restricted range, low density and loss of habitat through fishing activities. While further survey work is required to accurately determine the range of this species, the exclusion of fishing from breeding habitat or the creation of marine protected areas may prove essential for the conservation of the species (Vooren and Soto 2004).
v. Deepwater catsharks (Apristurus sp. A-G [Last & Stevens 1994])
Red List assessment
Global (endemic to Australia and New Zealand): Data Deficient
Notes: Uncertain distributions in the Western Pacific and Eastern Indian around Australia and New Zealand, although some species may be more widespread. These species have been variably recorded from depths of 590–1500 m (Last and Stevens 1994). Virtually nothing is known of their biology.
There is great concern that some deep-sea fisheries are taking sharks for which there is little information and indeed some that are not yet taxonomically described, such as the poorly known deep-sea catsharks of the Apristurus genus. Their range is uncertain due to misidentification, although they are known to occur within some heavily fished areas, for example, some species from this genus are known to be taken as bycatch in orange roughy fisheries in both Australian and New Zealand waters (Lack, Short and Willock 2003). They are thought to be quite rare and there is concern regarding potential future expansion of deepwater demersal trawl fisheries. Although little is known about their biology, assuming they have life history characteristics similar to related species, they may not be sufficiently productive to withstand current and, or, future exploitation pressure (Cavanagh et al. 2003).
Despite the knowledge that they are likely to have limiting life history characteristics similar to better-studied deep-sea Squalus species, the lack of data on biology, extent of occurrence, population size or any indicator of population trends of some Australasian Squalus species results in their being given a Data Deficient listing (Cavanagh et al. 2003). Case studies show that knowledge of the status of many deep-sea chondrichthyans is extremely limited. Consequently the Data Deficient category was often assigned, despite concerns that chondrichthyans appear to be among the most vulnerable of deep-sea species. Although efforts were made to avoid this category by using all data available, around 50percent of deep-sea species are currently listed as Data Deficient, with inadequate information available on their distribution and, or, abundance to make a direct or indirect assessment of their extinction risk. It is clear that Data Deficient species are some of those most in need of urgent action. It is vital to direct funding for research efforts on these species as well as those in the threatened categories.
vi. Lined Lantern Shark (Etmopterus dislineatus -Last, Burgess & Séret 2002)
Red List assessment
Global (endemic to Australia): Least Concern
Notes: Endemic to a limited area in the central Coral Sea off Australia. Known from depths of 590–700 m on or near the bottom of the continental slope (Last and Stevens 1994). Little is known of their biology.
This example of a Least Concern species illustrates the situation when, despite little available information, there is enough evidence to assume there are no current or potential threats. There are presently no major fishing activities in the known area of occurrence and depth range of this small (to 45 cm total length) deep-sea lantern shark, which has no commercial value. The same applies to the similar species E. caudistigmus, E. dianthus, E. evansi and E. fusus. Overall, approximately a third of the deep-sea species assessed to date fall into the Least Concern category, usually for the same reasons as these lantern sharks. However, given the vulnerability of deep-sea species in general, it is essential that a precautionary approach be adopted to ensure they are protected. Many assessments incorporate a precautionary note that indicates the need to monitor the situation should deepwater trawling develop within their range (Kyne and Cavanagh 2003).
vii. Pale Ghostshark (Hydrolagus bemisi -Didier 2002)
Red List assessment
Global (endemic to New Zealand): Least Concern
Notes: Widespread on the upper and mid continental slope around New Zealand, it is recorded from depths of 86–1410m, but is most abundant at depths of 500–900m. Is is an oviparous species of unknown productivity, but this may be low.
This species illustrates an example of an exploited chondrichthyan species that is managed through a quota system and is assessed as Least Concern. This species is widespread around New Zealand with a wide depth range. It is a bycatch of trawling for hoki and other deepwater species with landings of around 1700t a year (Francis 2003a). Catches of this species together with the dark ghostshark (H. novaezealandiae) are regulated by the Quota Management System (QMS) through individual transferable quotas (ITQs) since 1998. Prior to 1998 there was no regulation and records of the catch were incomplete. Fishers are now required to report catches of the two species separately (Francis et al. 1998).
While biomass indices for this species are variable depending on location and depth, the overall population of H. bemisi is considered to be relatively stable and can support the current level of exploitation. For example, on the Chatham Rise, to the east of New Zealand's South Island, biomass indices show stability in the 200–800 m depth range, but are declining in the 750–1500 m depth range. The 200–800 m range encompasses the main depth range for the species (500–900m) (Francis 2003a). For H. novaezealandiae, also assessed as Least Concern, biomass indices are variable, but are possibly increasing in some areas (Francis 2003b). By setting appropriate output controls through the QMS these two species should continue to be sustainably harvested. The value of fisheries research and monitoring to produce biomass indices is highlighted by this case study.
4. 1 Taxonomic uncertainty and the lack of baseline data
The lack of species-specific reporting is a widespread problem in fisheries management. However, this is exacerbated in poorly studied deep-sea environments where taxonomic uncertainty may also be problematic. It is evident that knowledge of the taxonomy, stock structure, status and biology of most deep-sea chondrichthyan fishes is seriously limited. The lack of species-specificity of recorded data in many regions and the uncertainty surrounding the sustainability of current levels of fishing are issues in urgent need of attention. The Data Deficient category is often unavoidably assigned, despite concerns that deep-sea chondrichthyans are among the most vulnerable of species. This issue urgently needs to be addressed with research funding directed towards these species. There is a need for more fishery-independent data and research into the survivability of species caught by different fishing methods at various depths if they are released after capture. There are some important targeted deepwater chondrichthyan fisheries, some of which are driven by international demand for their products, particularly liver oil (Irvine 2005), and more data and regulation are required to better monitor and manage this trade.
4. 2 Multi-species fisheries and bycatch
Many assessments highlight concern for species caught as bycatch. Most deep-sea chondrichthyans are taken in multi-species fisheries or as bycatch in fisheries targeting more abundant, valuable teleosts and crustaceans. A number of threatened deep-sea species have been discussed that raise complex management considerations for species such as C. harrissoni, which could go extinct while more fecund and resilient species continue to support the fishery. Seriously threatened species include C. harrissoni and the southern dogfish (C. uyato), which have suffered dramatic declines as a result of commercial fishing. These declines emphasize the importance of obtaining baseline data prior to the development of new deepwater fisheries in previously unexploited areas, and continued research and monitoring of the bycatch of chondrichthyans in non-target fisheries is vital. Such drastic declines in species with low productivity are highly unlikely to be reversible in the short to medium term. It may be that closed areas as a fisheries management tool that provide refuges for stock recovery are the only management solution. Marine protected areas are another tool to restore, safeguard and halt negative impacts on the biodiversity of the oceans, including deep-sea regions (Gjerde and Breide 2003).
This paper has discussed some of the main issues and trends highlighted by the IUCN SSG's Red List assessments, which indicate that commercially exploited species of deep-sea sharks are among the marine taxa at highest risk of extinction, a trend inextricably linked to their restricting life history characteristics and sometimes restricted distributions. Comprehensive assessment and regular re-assessment of chondrichthyans using IUCN's Red List system is one of the SSG's most important tasks. The status of species assigned to a threatened category must be monitored closely, and research conducted without delay to better understand their biology, threats and conservation needs, and to implement management and recovery plans where necessary. More resources need to be directed towards species that are assessed as Data Deficient, yet are potentially threatened. Moreover, since data collection in the deep-sea environment is so difficult, it is important to take note of the evidence available and manage with the precautionary approach (Irvine 2005). Few marine animals have a lower international management priority than deep-sea chondrichthyans and commercial development of new deep-sea fisheries, which threaten them, is increasing. In many cases it is unclear whether current levels of catch are sustainable and any increases in fishing effort, particularly if unregulated, are an obvious cause for concern for chondrichthyans that, as a taxonomic group, are considered to have little capacity to sustain, or recover from, fishing pressure (Lack, Short and Willock 2003).
The work summarized in this paper was supported by the David and Lucile Packard Foundation, the FAO, the UK Department for Environment, Food and Rural Affairs (DEFRA), Department of Environment and Heritage, Australia (previously Environment Australia), the University of Queensland (Centre for Marine Studies, School of Biomedical Sciences, Faculty of Biological and Chemical Sciences) and Sea World (Gold Coast, Australia). We wish to thank all members of the IUCN Shark Specialist Group who have contributed to the Red List Programme and we extend our particular gratitude to Sarah Fowler, Mike Bennett, Ken Graham, David Pollard, John Pogonoski and William White.
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The 2001 IUCN Red List Criteria (Ver. 3.1) for Critically Endangered, Endangered and Vulnerable
|A. Reduction in population size based on any of the following:
|A1. An observed, estimated, inferred or suspected population size reduction of:
over the last 10 years or three generations, whichever is the longer, where the causes of the reduction are: clearly reversible AND understood AND ceased, based on (and specifying) any of the following a-e:
|A2. An observed, estimated, inferred or suspected population size reduction of:
over the last 10 years or three generations, whichever is the longer, where the reduction or its causes may not have ceased OR may not be understood OR may not be reversible, based on (and specifying) any of the following a-e:
|A3. A population size reduction of:
projected or suspected to be met within the next 10years or three generations whichever is the longer (up to maximum of 100 years), based on (and specifying) any of the following b-e:
|A4. An observed, estimated, inferred, projected or suspected population size reduction of:
over any period of 10 years or three generations whichever is longer (up to a maximum of 100 years), where the time period includes both the past and the future, and where the decline or its causes may not have ceased OR may not be understood OR may not be reversible, based on (and specifying) any of the following a-e:
a) direct observation
b) an index of abundance appropriate for the taxon
c) a decline in area of occupancy, extent of occurrence and, or, quality of habitat
d) actual or potential levels of exploitation
e) the effects of introduced taxa, hybridisation, pathogens, pollutants, competitors or parasites.
|B. Geographic range
in the form of either B1 (extent of occurrence) OR B2 (area of occupancy) OR both:
|B1. Extent of occurrence estimated to be (km2):
and estimates indicating any two of a-c:
|B2. Area of occupancy estimated to be (km2):
and estimates indicating any two of a-c:
|a. Severely fragmented or know to exist at”
|b. Continuing decline, observed, inferred or projected, in any of the following:
|i) extent of occurrence
|ii) area of occupancy
|iii) area, extent and, or, quality of habitat
|iv) number of locations or subpopulations
|v) number of mature individuals.
|c. Extreme fluctuations in any of the following:
|i) extent of occurrence
|ii) area of occupancy
|iii) number of locations or subpopulations
|iv) number of mature individuals.
|C. Population small and declining
Estimated to number fewer than(mature individuals) and either
|C1. An estimated continuing decline of at least
whichever is longer (up to a maximum of 100 years in the future)
|C2. A continuing decline, observed, projected, or inferred, in numbers of mature individuals AND at least one of the following:
a) Population structure in the form of one of:
i) no subpopulation estimated to contain more than (mature individuals), OR
ii) at least: of mature individuals are in one subpopulation
b) Extreme fluctuations in number of mature individuals.
|D. Population size
|D1. Population size estimated to number fewer than: (mature individuals) OR
|D2. Population with a very restricted area of occupancy (typically less than 20 km2) or number of locations (typically five or less) such that it is prone to the effects of human activities or stochastic events within a very short time period in an uncertain future, and is thus capable of becoming Critically Endangered or even Extinct in a very short time period.
|E. Quantitative analysis
showing the probability of extinction in the wild is at least
whichever is the longer
(up to a maximum of 100years)