2

AN OVERVIEW OF THE GRAND BANKS SKATE FISHERY

D.W. Kulka and F.K. Mowbray
Department of Fisheries and Oceans
P.O. Box 5667, St. John's Nfld. Canada. A1C 5X1

1. INTRODUCTION

Several species of skates (Raja. sp.) are commonly found on the Grand Banks of Newfoundland (Grand, Whale, Green and St. Pierre Banks inclusive, Figure 1), and are an important bycatch in many Newfoundland fisheries. Significant bycatches of skates have likely been taken since the start of offshore fishing in the late 1940s. Before the mid-1980s, foreign fleets, the largest component of offshore fisheries on the Grand Banks, retained and processed several thousand tonnes of skate each year. In contrast, the Canadian fishing industry did not consider skate to be a valuable product. As a result, most were discarded at sea. Kulka and Mowbray (1998) estimated that an average of about 5000t was discarded annually by the Canadian fleet during the 1980s and early 1990s while no more than a few hundred tonnes appeared in annual landing statistics.

Figure 1

The Grand Banks showing locations referenced in the text, bathymetry, the 200 mile limit and statistical (NAFO) divisions (picture of thorny skate after Scott and Scott 1988)

The limited interest by Canada in skate was due in part to the abundance of more lucrative species and also to the lack of domestic markets. With the collapse of major groundfish in the early 1990s stocks, attention was turned to other “non-traditional” species. Since skate was known to be a common bycatch, particularly on the Grand Banks, it was identified as a potential candidate for increased exploitation. Research into markets was conducted (Day 1991) and in 1993 the Newfoundland Provincial Department of Fisheries initiated an experimental fishery for this species. The Canadian Department of Fisheries and Oceans (DFO) continued the fishery in 1994 with the objective of finding commercial concentrations of skate while limiting catches of prohibited species (Anon 1994). This activity was successful in locating suitable fishing grounds on the Grand Bank and also in identifying suitable gear types and configurations. Further marketing studies (Anon 1994, Day 1994) and experiments with processing techniques and machinery resulted in the establishment of local buyers and processors willing to handle skate catches. Interest in fishing skate grew as markets in Europe, particularly France and Belgium, were developed.

In 1995 a regulated skate fishery was established by Canada inside the 200 mile limit. A Total Allowable Catch (TAC) was established, gear and bycatch policies implemented and the existing licensing system was applied. During the same period, a skate fishery was developed for the adjacent waters of the Scotian Shelf (Simon and Frank 1995). The two fisheries are managed as separate stocks although distributions of skate from both the Grand Banks and Scotian Shelf extend into the Laurentian Channel (Figure 1).

Most foreign fishing inside 200 miles was phased out during the 1980s resulting in reduced bycatches of skate. However, outside of Canada's jurisdiction on the tail of the Grand Bank (Figure 1), a non-regulated skate fishery was started by Spain in the late 1980s (Junquera Paz 1998). This fishery is ongoing. Bycatches of skate in other fisheries outside 200 miles also contribute significant amounts to the catches reported to NAFO (Northwest Atlantic Fisheries Organization), the regulatory body for fisheries outside 200 miles.

In this case study, we document the development and management of the fishery for skate on the Grand Banks. Given the limited information on the foreign fishery, the emphasis is placed on the Canadian fishery.

2. THE RESOURCE

2.1 The fishery

2.1.1 Species composition of the fishery

Thirteen species of skate are found in Atlantic Canadian waters (Scott and Scott 1988), five of which are fairly common on the Grand Banks of Newfoundland. Of these, thorny skate (R. radiata) is dominant, comprising about 80% of skate species taken in commercial offshore catches on the Grand Banks and Northeastern Shelf to the north (1981–1994) and 90% of skates caught in groundfish research surveys¹ 1951–1994 (Kulka et al. 1996). More species of skate were taken as bycatch in commercial fisheries than in research surveys because the commercial activity occurred over a wider range of depths. Deepwater species were seldom captured by research surveys as they did not extend beyond 500m in most years prior to 1994.

Kulka et al. 1996 examined bycatch of skates in individual catches from 1988–1995, as recorded by fisheries observers. They reported that otter trawls yielded the greatest proportion of skate in bycatch, while gillnets caught the least. Bycatch amounts were variable among areas. The species composition of skate taken as bycatch was also presented. Across all gears, the common species encountered, in addition to thorny skate were: spinytail (R. spinicauda) averaging 10% of the skate catch; barndoor (R. laevis) at 4%; smooth (R. senta) at 2%; and winter (R. ocellata) at 1%. Thorny and smooth skate were mostly concentrated on the Grand Banks at the location of the present day directed skate fishery. Spinytail and barndoor skates were more typically taken in deeper water fisheries primarily to the north along the edge of the Northeast Newfoundland Shelf. Closures of several groundfish fisheries since 1992 has meant greatly reduced incidental capture of all skates in Canadian waters, particularly the more northern and deepwater species.

¹ Groundfish surveys have been conducted annually since 1951. The area covered includes the Labrador coast, Grand Banks and Northeastern shore (NAFO Div. 2J3KLNO and Subdivision 3Ps). Tow duration and speed are standard. Since the early 1970's, tow sites have been identified using a stratified (by depth) random method with the number of tows roughly proportional to stratum area. An average of 590 sets are done annually on the Grand Banks (3LNOPs) in the spring and fall covering about 370 000km².

Little is known about the species composition from the directed skate fishery catch on the Grand Banks (1993–98). It was often not possible for fishery observers to determine species of skate due to small catches and rapid processing. However, when identified to the species level, thorny skate were dominant comprising more than 90% of the skate catch. In contrast, a mix of winter and thorny skate were taken in the directed skate fishery on the adjacent Scotian Shelf (Simon and Frank 1995 1996).

2.1.2 Distribution of the resource and the fishery

Thorny skate is a boreal to arctic species, distributed in both the eastern and western Atlantic (Scott and Scott 1988). In waters off Newfoundland, the distribution and abundance of this resource has undergone considerable change in recent years. Prior to 1991, thorny skate were more widely and continuously distributed than at present (Kulka et al. 1996). Until the mid to late 1980s, moderate to high densities covered much of the Grand Banks extending in significant concentrations onto the Northeast Newfoundland Shelf, as far north as Latitude 50°. However, after 1991, areas of high concentration were much smaller and found almost exclusively south of 47° (Figure 2, after Kulka and Mowbray 1998). These changes in distribution were associated with a reduction in thorny skate biomass (Kulka and Mowbray 1998) and were concurrent with southerly contractions in distribution and declines in abundance of many other groundfish species (Atkinson 1993). These changes also correspond with a period of increased fishing effort on the Grand Banks outside 200 miles.

An earlier tagging study (Templeman 1984a) indicated that thorny skate is a primarily a sedentary species. However, much of the tagging took place nearshore and the ability to recapture tags showing the fish's larger scale movements was limited. More recently, Kulka and Mowbray (1998) identified differences in distribution suggesting a seasonal migration (Figure 2). In the spring, moderate to high concentrations of skates formed a nearly continuous band around the periphery of the banks. The band was most dense and wide along the southwestern slope of the Grand bank and into the Laurentian Channel. This large (southern) spring concentration was located further west than fall concentrations. During the fall survey period, the main body of the skate was distributed more on the bank, inhabiting shallower waters.

Thorny skate is found in a wide range of depths from nearshore to at least 1400m (i.e. the deepest records from foreign fishing effort outside 200 miles on the slope). Sixty-five percent of the area covered during Grand Banks research surveys (Figure 3a) was between 51–200m but only 47% (spring) and 52% (fall) of the biomass was located within that depth range (Figure 3c). Skate were more densely concentrated and abundant in deeper waters in both seasons, although these densities varied between seasons (Figure 3b). In the spring, the average density in >500m was 25kg/tow (peaking at 80 kg/tow in 700–800m), five times the density and biomass of fall.

The distribution of thorny skate in relation to bottom temperature indicates that in relation to depth they were not evenly distributed across the available habitat. While skate are widely distributed over the Grand Banks (Figure 2), the densest aggregations are found on the warmer parts of the banks, more so in the fall (Figure 3d-f). Figure 3e shows that almost no skate were found in the waters less than 0°C at any time of the year. In the fall, density peaked where bottom temperature was 1.07– 2.94°C while in the spring, skate were most densely aggregated in the 4.4–5.27°C range, near the maximum available temperature. A similar pattern was observed in terms of biomass. Figures 3a and 3c show that in the fall (and spring) respectively, bottom temperatures between 0.24°C and 2.94°C occurred over 66% (42%) of the surveyed area but contain 40% (46%) of the biomass. In the warmest waters, above 4.4°C, fall (spring) area amounted to 22% (11%) of the total and contained 22% (41%) of the biomass.

Taking together observations of:

1. the change in spring and fall distributions (similarly noted for thorny skate on the Scotian Shelf by Simon and Frank 1996),

2. the higher density and greater proportion of biomass in deeper waters in the spring,

3. surveys estimates of biomass being on average 40% lower in the spring than in the fall,

4. differences in distribution in relation to temperature and depth between spring and fall,

5. high concentrations located in depths greater than 1100m in Spanish surveys in the spring, and

6. oubling of skate bycatch rates in deepwater slope fisheries in Dec.-June vs. in July-Nov. (outside the survey area).

Kulka and Mowbray (1998) suggest that a seasonal migration does occur.

Figure 2

Distribution of thorny skate on the Grand Banks in the spring (A) and fall (B). Darker areas denote higher densities of skate as kg per tow. Arrows indicate suggested direction of movement (Kulka and Mowbray 1998). Data in boxed area (left side, panel B) are from redfish surveys in August: these data are not used for calculation of abundance indices.

Figure 3

Distribution of thorny skate with respect to depth (A-C) and bottom temperature (D-F) on the Grand Banks. Panels A and D illustrate available habitat in the area surveyed, B and E show density of skate (kg per tow), and C and F percent of biomass (after Kulka and Mowbray 1998).

Little difference was noted in the spatial distribution between sexes in either season (Kulka and Mowbray 1998), or in the distribution of juveniles (immature) and adults in the spring (fish less than 60 cm length considered immature, based on Templeman 1987a). However, in the fall adult fish were more common in deeper waters with the opposite true for juvenile fish (Kulka and Mowbray 1998). It was also noted that in recent years, nearly all skate on the northern part of the Grand Bank in NAFO Div. 3L were juvenile. In earlier years (prior to the late 1980s) skate in this area were on average much larger (Kulka et al. 1996).

The distribution of fishing effort for skate was found to be much more restricted than the overall resource. As well, seasonal differences in distribution affected both fishing effort location and timing. Figure 4, of observed Canadian fishing effort by gear type for 1993–1998, shows that much of the Canadian effort by otter trawlers, gillnetters and longliners occurred along the southwestern slope of the Grand Bank. The activity occurred in a band about 50km long centered near the dividing line between NAFO Div. 30 and Subdiv. 3Ps. Most of this Canadian effort took place during March-June along the edge of the Grand Banks (at an average depth of 165m) when concentrations of large skate were available in that area. In contrast, the foreign directed fishery for skate (as indicated by enforcement inspections, area circled in Figure 4a) took place on the tail of the bank in the last half of the year when skate were concentrated up on the bank.

Kulka and Mowbray (1998) superimposed the distribution of fishing effort from the Canadian fishery onto the distribution of skate from research surveys in order to relate actual and potential fishing areas. They found that fishing occurred over an area totaling 16 000km², about one third of the area that contained skate in sufficient densities to warrant fishing (i.e. high-density areas identified by research surveys). Foreign effort occurring in the fall covered most of the area where skate were concentrated on the tail of the Grand Bank, outside 200 miles.

Figure 4

Distribution of fishing effort of thorny skate on the Grand Banks by gear type for 1993 to 1998 combined. Darker areas show areas of higher catch rates.

2.1.3 Associated species either as bycatch or discards

Exploratory work carries out by DFO indicated that the gear limitations set for skate (primarily minimum mesh size) generally limited bycatch of prohibited or regulated species below 10% of the skate catch (Anon 1994). This was true of both trawl and gillnets although bycatch in longlines was a problem.

Fishery observer data (1995–1998) indicate that bycatch amounts of regulated species, Atlantic cod (Gadus morhua), American plaice (Hippoglossoides platessoides) and Atlantic halibut (Hippoglossus hippoglossus) sometimes exceeded the regulated limit (5% of the skate catch), particularly for longline gear (Table 1). Exceeding the limit resulted in the vessel having to move to a different location or stop fishing. Otter trawls employing 300+ mm mesh were observed to be the most effective at minimizing bycatch. Vessels fishing with otter trawls were regularly successful in maintaining overall bycatches of regulated species within the limit. This was less frequently the case for the other gears.

¹ All species of skate combined.
² Bycatch species (cod, plaice, Atl. halibut) regulated to less than 5% of the skate catch.

The most common bycatch species taken by otter trawls, gillnets and longlines respectively were monkfish (Lophius americanus) (1.2, 25.8, 0%), cod (2.9, 6.9, 15.7%) and white hake (Urophycis tenuis) (0, 0.9, 8.1%). Most of the bycatches of monkfish, cod, white hake, Atlantic halibut, American plaice, haddock (Melanogrammus aeglefinus), pollock (Pollachius virens) and witch flounder (Glyptocephalus cynoglossus) were retained when they were of commercial size. Discarding (all species) was generally highest when fishing with gillnets. The main reason being damage caused by sea lice, hagfish or eels.

2.1.4 Discussion

The fishery for skates on the Grand Banks is, as for most other elasmobranch fisheries of the world, relatively small scale. It is not species specific although one species, thorny skate, dominates catches. Processors and buyers accept all skate wings landed with no price differentiation by species. According to Day (1994) once the skin is removed from the wings the meat is indistinguishable.

Minimum biomass estimates and analysis of biological characteristics have only been presented for thorny skate (Kulka and Mowbray 1998), although catch rates and distribution from research surveys and commercial catches have been presented for the other three species (Kulka et al. 1996). One of these species, barndoor skate, has been suggested by Casey and Myers (1998) to be at risk of extinction in Canadian waters, although records from ground fisheries of the 1980s and early 1990s suggest otherwise (Kulka et al. 1996).

2.2 Development and current status of means of prosecuting the fishery

2.2.1 The harvesting process

Although skate has always been an important bycatch in groundfish catches, Canadian vessels generally did not direct for skate until 1994 when about 30 vessels were licensed to participate in an exploratory fishery (Anon 1994). Since 1995 any groundfish licence holder could request a condition of licence to direct his fishing for skate. However, of the many vessels that have landed skate in the last few years only a few reported it to be the main species sought (Table 2)².

² Regulations pertaining to the licensing and management of the skate fishery are mostly in empirical measures. Conversion factors employed in fisheries management do not conform with those commonly used in scientific articles. To avoid confusion, all measures are presented using the units in which they are published in the regulations

The number of vessels directing fishing activity for skate have increased although they still amount to less than 1% of groundfish licence holders. Since regulation of the fishery in 1995, more than 90 % of vessels directing for skate (Table 3) were less than 19.79m. During 1994 and 1995 these small vessels took over 92% of the directed landings. However, in 1996 and 1997 large vessels (>19.79m) that constituted 4 and 7 % of directed fishing vessels landed 17% and 19% respectively of the directed catch. Incidental skate landings (taken as bycatch) were more evenly split between large and small vessels, but indications are that large vessels were more likely to land their bycatch. Large vessels accounted for less than 2% of the fleet but accounted for between 12 and 50% of the incidental skate landings.

In 1997, 55% of the reported Canadian catch was taken by otter trawls, 33% was taken by gillnets and the remainder by longlines (Kulka and Mowbray 1998). For the most part the gears were set in the same area. Areas fished sometimes corresponded to areas of high catch rates in research surveys, but were more closely aligned with areas where skate were the largest (Kulka and Mowbray 1998). Landings (1995–1997) have typically peaked in April or May with most of the annual catch landed by late summer.

A number of large offshore processing vessels (mostly Spanish) catch and retain skate outside 200 miles. Data obtained from boardings by Canadian surveillance officers indicate that most of these foreign vessels use otter trawls to target skate. Skate were also an important bycatch in other fisheries outside 200 miles (Kulka et al. 1996), particularly those directing for American plaice, turbot (Reinhardtius hippoglossoides) or redfish (Sebastes sp.). Duran and Paz (1997) reported that skate was one of the most common bycatch species in the Spanish trawl fishery (1991–1994) directing for turbot outside 200 miles.

2.2.2 Evolution of catch

From 1978 (the time of Canadian extension of jurisdiction to 200 miles) until 1984, skate landings reported to NAFO averaged 5000t (Atkinson 1995). Over the next several years, reported catches increased dramatically. This was due in part to the emergence in 1985 of a directed foreign fishery outside 200 miles and more recently, the establishment of the directed skate fishery in Canadian waters. Although poorly represented in landing statistics, this species was a common bycatch prior to 1994. Kulka et al. (1986) reported that skate consistently comprised the greatest portion of non-commercial bycatch in Newfoundland offshore trawl fisheries, but nearly all was discarded at sea. Foreign fleets on the other hand retained and processed most skate. Using observed groundfish catches and commercial catch records, Kulka and Mowbray (1998) estimated these incidental catches. Estimates of foreign catch both inside 200 miles (observer data) and outside 200 miles (surveillance estimates) have also been provided. It is likely that these estimates, taken along with reported landings, are a better proxy for fishing mortality than landing statistics alone.

Catches by area and fleet for 1985 to 1997 are presented in Figure 5. Skate catches can be grouped into four periods: pre-1980s when most were discarded at sea and not reported; 1980–1984 when most were discarded but discards were estimated from observer data (Kulka 1989); 1985–1991 when known catches were highest (discard estimates included), ranging from 16 000 to 23 000t; and 1992–1997 when catches declined to less than half the average for the previous period. The preliminary estimate of Canadian landings for 1998 is 2080t. Since 1992, catch outside 200 miles accounted for an average of 60% of the total annual catch. These catches were taken almost exclusively on the tail on the Grand Bank in NAFO Div. 3N. Canadian discarding, common in the pre-directed fishery, has been negligible since 1995. Foreign bycatch inside 200 miles averaged 11% of the pre-1994 total but has declined to less than 2% in recent years.

Figure 5

Estimated landings of skate from the Grand Banks, inside and outside 200 miles, 1985–1997 (from Kulka and Mowbray 1998)

2.2.3 Fleet characteristics, evolution of the fleet and fishing effort

Starting in 1995, the option to direct for skate was added to the Integrated Fisheries Management Plan for Atlantic Groundfish (IFMPAG). Prior to 1997, any groundfish licence holder could request a condition of licence that would permit them to direct for skate on the Grand Banks. In 1997, it became a standard condition for all groundfish licences (6744 groundfish licences issued in 1998 for Newfoundland) except for vessels >65ft wanting to fish skate in Div. 3N or 30. These vessels still had to request a separate licence condition for skate.

The Canadian Atlantic groundfish fleet is classified by vessel length and gear type (fixed gear or mobile). This fleet represents the potential rather than actual skate fishing effort. To date, only a small portion of eligible fishers have taken advantage of the option to direct for skate (Table 4). Not included in this table are two other groups of potential skate fishing vessels. A few Nova Scotian vessels which are given access to 3N and 3O skate because they have traditionally fished in the area, and several large mobile gear vessels based outside Newfoundland, but owned by companies holding enterprise licences which allow them to fish throughout Atlantic Canada.

Prior to 1995 a variety of gear types and sizes were used to catch skate. However, since 1995 only three types of gear have been allowed: trawls, gillnets and (with special approval only) longlines. Mesh sizes used in trawls ranged between 300mm and 310mm in the codend and 250mm to 300mm in the body. Gillnets employed 10.5 inch and 12 inch mesh (depending on the distance from shore). Longliners surveyed used # 16 hooks.

Otter trawls are the most common gear used in the foreign directed skate fishery outside 200 miles. Mesh sizes in foreign trawls are considerably smaller than the 300mm employed by the Canadian fleet, usually less than 200mm and often as small as 150mm.

2.3 Markets and economics

2.3.1 Market information

Information concerning skate fishery markets and revenues is limited, particularly for before 1993. Marketing studies carried out in the early 1990s (Day 1991, Anon. 1994) do not necessarily reflect current practices or values. Most of the information given in this section refers to the current situation and has been collected through interviews with Newfoundland buyers and processors, and from purchase slip records by DFO Policy and Economics Branch personnel (Cahill 1999).

2.3.2 The product

Skate are landed as skin-on wings by fish harvesters. Processors skin both sides of the wing using mechanical skinners and manually trim them. The product is individually poly-wrapped (IPW) and blast frozen in boxes prior to shipment. Larger skate (wings 400–1000grams each) are caught chiefly in gillnets, while smaller skate (wings less than 400 grams each) are caught in bottom stern trawls. Skate caught using gillnets are preferred not only for their size, but also because of their better appearance. A good quality skate wing is characterized by a pinkish hue and minimum bruising. While gillnets tend to bruise the wing more so than stern trawls, processor's yields are greater from larger sized wings. The average yield for all sizes of skate wings is 67%. Some experiments are being done with hook and line fishing gear and early indications are that the size, color and quality of the catch are exceptionally good.

2.3.3 Revenues

Until the early 1990s there were few markets developed for Canadian caught skate, although records indicate that a small amount of skate was exported to Europe in the 1970s and mid-1980s. A small amount of skate is sold locally, some of which is shipped out of the province in a fresh state for further processing elsewhere. Most of the product is exported to European markets, mainly in France. Processors sell almost exclusively through brokers. The majority of the exported fish is thought to be portioned and sold in grocery stores and restaurants as a kind of “poor man's scallop” although it may also be sold in the fish and chip industry (Day 1991). Markets are characterized as being small and relatively supply-sensitive. There is a significant amount of skate entering the European market from the U.S.A. and South America and changes in the amount of product entering the marketplace at any given time can negatively affect prices in the entire market.

Revenues for the fishery have been calculated using purchase slip information for Newfoundland landings. These do not represent the entire value of the Grand Banks skate fishery since some fish caught are landed in Nova Scotia. Nova Scotian landings have typically accounted for less than 15% Grand Banks skate sales.

Landed values give a good indication of ex-vessel price. Prices paid for skate taken as bycatch were considerably lower (<40%) than prices paid for directed catch. As indicated in Figure 6, ex-vessel prices for directed catch have increased since the beginning of the directed fishery, averaging $Can0.59/kg since 1994. Landed values (all sales) have ranged from under $Can200 in 1989 to a high of $Can1.3 million in 1995 (Figure 6).

Figure 6

Ex-vessel price (bars), and landed value (line) of skate sold in Newfoundland, 1987–1997. Ex-vessel prices are for the directed fishery only. Landed values include skate sold from both directed and incidental catch. Values for 1996 and 1997 are preliminary.

2.3.3 Economics of the fishery

Prices for skinned frozen skate wings in the European marketplace range from US$0.90/lb to US$1.05/lb. Manual trimming which occurs after the mechanical skinning of wings is very labour intensive. Labour costs account for roughly $Can0.26/lb. One eight-hour shift of 40–45 workers can produce 15 000 to 20 000lbs of finished product. Profit margins are small and fish harvesters and processors alike benefit from access to bycatches of more profitable species (including cod). However, the fishery provides 4–6 weeks employment in the rural communities where processors operate. This is an intangible benefit to processors as it helps to maintain workers cutting skills and productivity and keeps them attached to the local harbor market in areas where out-migration due to a lack of employment alternatives is a constant concern to employers.

There is no subsidization of the skate fishery at present. DFO Development Branch government did subsidize some of the initial investigations into a skate fishery, but it is now self-sustaining. Interest in fishing skate is growing slowly and annual requests for licence conditions to direct fishing for skate increase each year.

2.3.4 Finished product

Finished skate product amounts and values were only available for 1981–1996 (Table 5). Although most product is sold frozen, small portions have been marketed fresh. Product values have increased tenfold since the regulation of the directed fishery. The highest annual product value was over $Can3 million sold in 1995, almost twice the amount sold in 1994.

¹ Preliminary.

3. MANAGEMENT OBJECTIVES

3.1 The fishery within the context of national fisheries policies

Management aspects discussed in the following sections apply to the Canadian fishery. For Canada, the 1997 Groundfish Management Plan (Anon 1997), which regulates skate, states that the “objective is to manage the fisheries on a sustainable level to ensure the long-term economic viability of the industry”. This description differs little from the more general objective applied to all Canadian fisheries (commercial, exploratory and recreational), in which conservation is emphasized and a precautionary approach advocated.

The objectives for managing the fishery for skates are no different than the national objectives for other fisheries, although in the case of skate they are not applied at the species level. All skate species are managed as a unit. This could have implications for the conservation of less abundant species. In the exploratory phase of the fishery (1993–1994), different objectives were applied. These included managing on a small scale in order to gain scientific information and to assess future viability for the species/stocks. This too was applied to all skates combined, regardless of species.

3.2 Objectives for the management of skate fisheries

Fisheries for non-traditional species such as skate have been seen as an opportunity to create diversification and relieve some of the pressure on traditional species. These fisheries also increase the ability to meet growing market demands for fish products. A particular concern in the development, and on-going management, of the skate fishery is creating an opportunity for a sustainable skate fishery without jeopardizing existing groundfish fisheries or stocks, particularly those under moratorium.

Skate are often mixed with cod and other species on the Grand Banks (Section 2.1.3). Hence, a fundamental objective is to develop policies that will allow for the exploitation of skate while minimizing bycatch of the depleted stocks. Some compromises have been made in order to deal with these, sometimes conflicting, objectives. These include the closure of potential skate fishing areas because of excessive cod bycatch, and the allowance of small amounts of bycatch (5%) as stipulated in the groundfish management plan.

3.3 The objective setting process

The Department of Fisheries and Oceans (DFO) sets objectives for the management of skate in consultation with the Fisheries Resource Conservation Council (FRCC). The FRCC is an independent extra-governmental forum that separately reviews stock status information supplied by DFO, and compiles information from stakeholders (including industry and provincial representatives) through public meetings and consultations.

3.4 Discussion

Directions for the regulation of the skate fishery are adequately set out by the management objectives. Specific objectives such as a TAC or the need for precautionary measures are provided to managers by the FRCC.

4. MANAGEMENT POLICIES AND POLICY SETTING PROCESS

4.1 Identification and evaluation of policies

Polices regulating the Canadian skate fisheries (elaborated in other sections) were first introduced in 1995. Previously there were no regulations pertaining to retention, discarding or directed fishing of skate. Measures introduced in 1995 include total allowable catch, limited access (groundfish licence holders only), season and area closures, and gear restrictions. Canadian regulations apply to all Canadian vessels whether fishing inside or outside 200 miles. The foreign fishery outside 200 miles is not regulated.

4.2 Policies adopted

Since 1995, only vessels with a groundfish licence could direct their fisheries for skate. Restrictions regarding gear, seasons and areas are specified on each licence. Minimum allowable mesh size for otter trawls was 300mm for the codend and 254mm in the remainder of the trawl. Minimum mesh size for gillnets was 300mm when fishing over 12nm from land and 263mm when inside 12nm. Minimum hook size on hook and line fisheries was #14 circle or equivalent. Hook and line fisheries were only approved after consideration of a written submission presented to DFO.

The seasons set out at the beginning of the year for vessels <65ft using fixed gear were 1 August to 31 December outside 12nm, and 1 April to 31 December inside 12nm. The season for vessels <100ft using mobile gear was set for 1 April to 31 December while vessels >100ft with mobile gear, or >65ft with fixed gear, were able to fish year round. In-season closures may occur when quotas are filled or bycatch of restricted species (cod, plaice and Atlantic halibut) exceeds 5%. There is no small fish protocol³ (minimum size regulation) for skate.

Industry initially suggested that an unrestricted skate fishery around Newfoundland, similar to the current regime outside the Canadian 200 mile limit be allowed (Atkinson 1995). However, because of concerns over the sustainability of the resource, particularly in light of the seemingly low reproductive capacity of skate and low biomass levels, a more conservative approach was adopted.

Although limited scientific information was available at the time it was used as the basis for setting a TAC for 1995. Catch limits were set at 20 % of the minimum trawlable biomass in research surveys (1991–1993). Catch quotas were separated between two areas, the Grand Bank (Divisions 3LNO) and St. Pierre Bank (Subdiv. 3Ps) in an attempt to spread out fishing effort. In 1996 concerns over large foreign catches of skate outside the 200 miles, contraction in skate distribution, and questions over the propriety of an exploitation rate of 20%, led to a reduction in the TAC to 2000t. In 1997 and 1998 the quota was set at 3000t annually, split 15% for 3LN, 50% for 30 and 35% for 3Ps. The quota was also split between fleet sectors and gear types (54% fixed gear, 46% mobile gear). For 1999, the 3090t TAC will cover a 15 month period from 1 January 1999 through 31 March 2000. It is divided between NAFO Divisions and fleet sectors in the same proportions as previous years (Table 6). Catch quotas for the inshore sector (<65ft) are fished competitively while enterprise allocations, i.e. company quotas, are given to the offshore fleet.

³ That is the fishery is closed if catch of undersized fish exceeds 15% of the catch.

4.3 Discussion

The policy setting process for skate, as for other groundfish species, is complex. Following the development of management objectives as described in Section 3.3, policy is established in Conservation Harvesting Plans (CHP) proposed by industry and submitted to DFO for approval. A separate CHP is developed for each sector of the groundfish fleet. Each CHP contains details on conservation measures including species that can be directed for, open areas and seasons, gear restrictions, small fish protocol, catch monitoring and test fishing. In-season adjustments (i.e. early closures) are communicated to fishers by public notices.

The policy setting process as it stands is generally adequate in terms of meeting management objectives although there are still some outstanding problems. Bycatch of regulated species, particularly in the longline fishery, needs to be addressed. Lack of accessibility for small boats that would usually fish in bays that are closed due to concerns over bycatch potential is frustrating for some inshore fishers. Monitoring catch weights based on landed weights may lead to inaccuracies in records of the actual catch. Skate are commonly landed as wing. However, depending on whether the wings are removed with a straight or curved cut, manually, or by machine, the ratio of wing weight to round weight may vary. More wing product is retained from manual removals. Prior to 1995 DFO statistics branch used a conversion factor of 4:1 for round weight to wings. This was revised in 1994 to 2.7, based on information from the industry. Recently, an industry independent evaluation of conversion factors for Scotian Shelf fisheries (Smith 1998) found round weight to wing weight yields of 2.22:1 for hand cut wings.

5. THE MANAGEMENT PLANNING PROCESS AND PROVISION OF MANAGEMENT ADVICE

Management objectives and polices are reviewed annually by the FRCC upon receipt of a Stock Status Report from DFO Science Branch, an example of which is shown in Appendix 1. This report is a summary of the scientific stock assessment and indicates the state of the stock, assesses reliability of the information and outlines areas of concern with regard to the sustainability of the resource. Recommendations on specific management targets (i.e. TAC, management areas etc.) are made by the FRCC and submitted to DFO. DFO communicates any changes in Management objectives to industry and solicits new CHP's if required.

5.1 Fishery statistics

5.1.1 Methods used for collection of catch and effort data

Catch and effort data are collected through four independent systems: purchase slips, dockside monitors, logbooks and fishery observers. Fish product purchase slips (i.e. sales receipts) are the primary, but probably the least reliable, source of information. Nonetheless, it is the only source that provides coverage of the entire fleet. Buyers must provide purchase slips for all catch sold commercially. Purchase slip records should include landed weight, effort (number of days and hours used to catch it) and the number of gear deployed. However, since only landed weights are recorded there is no account of discarded fish. Also, effort data is frequently missing from the slips, particularly for smaller vessels and is difficult to interpret as it may (incorrectly) include search and travel time.

Purchase slips can be verified against information obtained by dockside monitors. Dockside monitors record landed fish weights and fishing effort. Although they work under contract to industry they are accredited by DFO. They are thought to provide a more accurate value for landed weights but can only record effort data as it is communicated to them by industry. Vessels >35ft are obliged by law to keep a fishing logbook that includes catch weight, effort and location. However verification of these data with dockside monitoring records and information from fishery observers have shown that logbook data are not always accurately recorded. As with purchase slip data, the interpretation of effort is problematic. The most reliable source of catch and effort information is that recorded by fishery observers. For each set, observers record the weights of all portions of the directed catch (kept and discarded) as well as kept and discarded weights of bycatch. However, observers are deployed on only about 8% of the total fishing trips to the Grand Banks.

5.1.2 Data processing and storage and accessibility

Commercial catches

Biological sampling of commercial skate catches has been nearly non-existent. In most years few, if any, samples have been obtained from port sampling. Because skate are usually landed as wings, opportunities to measure lengths are rarely available. Also, since buyers are only interested in skate with wing widths greater than 46 cm, smaller skate are discarded at sea and thus not represented in the landed sample. As a result of these practices, no corresponding data on sex, or age composition, are available.

A small number of length frequencies of skate catches (discards included) separated by sex are available from observers. However, conditions on board small vessels can make it difficult to obtain samples. For these reasons, samples are few and may not be representative of the entire fishery. No data on maturity or age are available for the observed commercial fishery.

Research surveys

Length frequencies by species and sex are available from groundfish research surveys made during the spring and the fall of each year. No information on age or maturity status has been collected since 1965.

5.1.3 Data processing and storage and accessibility

All data pertaining to biological sampling and abundance of skate are stored in ASCII files in a standard format used for all groundfish species in Newfoundland and Labrador waters. Data are readily available to scientists and researchers within DFO. Data may also be made available externally upon request; excepting data deemed confidential such as information on individual boats or fishers.

5.2 Stock assessment

5.2.1 The Assessment Process and its Development

Discards of skate by the Newfoundland offshore fleet have been estimated since 1981 (Kulka 1982, 1984, 1985, 1986a, 1986b, 1989) but no comprehensive review of landings for the period pre-1985 are available. Prior to 1993 there was no formal assessment of skate stock(s) in NAFO Divisions 3LNO and Subdivision 3Ps. As part of an analysis of commercial and non-commercial groundfish abundance trends, Atkinson (1993) presented for the first time abundance indices for skate from the fall research survey (1981-1991). Following this, formal skate assessments have been presented by Atkinson (1995), Kulka et al. (1996) and Kulka and Mowbray (1998).

Due to the limited amount of data available from commercial fisheries, scientific assessments have focused on information on thorny skate available from groundfish surveys. This includes an estimate of minimum trawlable biomass (spring and fall) and sexed length frequencies for most sets. Mean fish weight, calculated as the estimated biomass divided by the estimated abundance by number, has also been presented. Atkinson (1995) summarized information on maturity status (1959–65) of thorny skate and found that length at maturity may differ among NAFO Divisions.

Kulka et al. (1996) presented for the first time an analysis of species composition in skate catches from research surveys and commercial operations. Distributions of thorny, barndoor, spinytail and smooth skate from research surveys were mapped and changes in distribution (1971–1994) noted. Catch rate distributions of the commercial fishery (observer data) was also presented. Kulka and Mowbray (1998) assessed thorny skate resources only. New information or analyses in this report included seasonal estimates of abundance and distribution, estimates of foreign catches outside 200 mile limit (1985–1997), foreign catches inside 200 miles (pre-1994), and domestic discards inside 200 miles. Distribution and catch rates of the foreign fishery outside 200 miles were also presented.

Included in this evolution of skate assessment methodology are many useful additions. However, the mainstay of the assessment continues to be research survey information since this is the only time series available. Unfortunately even this indicator of abundance is discontinuous due to a change in the trawl type used, starting in the fall of 1995. Prior to 1995 an Engel trawl was employed, but a Campelen trawl has been used in years since. No information is available on the relative vulnerability of skate to capture by the two trawls.

Analyses of skate distribution have gained favor as an indicator of stock strength and have also proven useful in identifying areas where skate aggregations are dense enough to fish. Because of the relatively short time series available for commercial data, it is not yet possible to determine whether it might serve as an alternative index of abundance. Also, the impact of bycatch restrictions on choice of fishing location or timing has not been assessed. This could be of particular concern if bycatch regulations change as previously closed fisheries re-emerge. No cohort analysis can be carried out for thorny skate due to the lack of ageing data. Likewise no estimation of fishing mortality (F) has been attempted.

5.2.2 Biological advice review process

Results of analyses are presented to open meetings attended by DFO scientists, interested academics, fishers, representatives of the Newfoundland provincial government and the FRCC. Analyses are generally done by DFO scientists, but other information and comments are welcome. Methodology, results and conclusions are reviewed and suggestions implemented. Precise wording of the end product (to be forwarded to the FRCC), the Stock Status Report, is arrived at through consensus.

5.2.3 Biological management reference points

Because biological data are limited and the fishery new, no conservation level or single biological management reference level has been established. Instead the following indices are used.

• Minimum spring biomass estimate (research surveys)

• Size (length and weight) composition (research surveys)

• Spatial distribution (research surveys)

• Catch statistics (commercial)

5.2.4 Sustainability of the resource

The present state of the thorny skate resource is uncertain. The changeover (fall 1995) in the trawl type used in research surveys means that no direct comparison is possible between current biomass levels and those of previous years. Current abundance and biomass estimates for both spring and fall are well above the pre-1995 levels (Kulka and Mowbray 1998). However, comparative tows with the two trawls have shown that for other commercial species the (new) Campelen trawl catches more than twice the amount taken by the Engels trawl. As a result it is not known whether increased catches since 1996 reflect an actual is increase in biomass or a gear effect (Figure 7).

Minimum abundance estimates differ between seasons, probably due to seasonal migration out of the surveyed area (Kulka and Mowbray 1998). Skate aggregations have been consistently more dense and numerous (by an average of 40%) in fall surveys than in the spring (refer to Figure 2). However, one statistical area, 3Ps is not surveyed in the fall so estimates for this season are incomplete. Consequently, biomass estimates derived from the spring survey (that include all areas) have been used to determine the minimum biomass value.

Figure 7

Biomass of thorny skate estimated from spring research surveys on the Grand Banks of Newfoundland, 1985–1998 (after Kulka and Mowbray 1998).

Mean weight of skate from research surveys has been calculated from spring surveys in each division as the estimated biomass divided by the estimated abundance in numbers. Mean weights were similar in all divisions in the late 1980s averaging between 1.5 and 2 kg. During 1990–1995, mean weight in 3L and 3N declined dramatically accompanied by slight declines in the other divisions (Figure 8). Since the changeover in trawling gear used in the research surveys, there has been less disparity among divisions, and the mean weight on average has increased. However, it is not clear whether this increase is due to a change in skate size composition or to differences in selectivity between the two survey trawls.

Figure 8

Mean weight of thorny skate from spring research surveys on the Grand Banks of Newfoundland, 1985–1998 (after Kulka and Mowbray 1998)

5.2.5 Discussion

Due to the scarcity of data on catches and catch samples and the lack of any age dis-aggregated indices estimates of recruitment, or renewal rates, common stock evaluation methodology can not be applied. A rough estimate of fishing mortality rate is attempted by using total estimated catch and minimum spring survey biomass However, this method has inherent inaccuracies. It is known that not all skate are available to the spring survey due to a seasonal migration out of the survey area. Also, the effect of gear selectivity is unknown. Observed behaviour of skate when encountering survey gear (Walsh 1992) suggests that their vulnerability to capture is quite different from other groundfish species.

Even if fishing mortality could be calculated, it is uncertain what an appropriate rate of exploitation should be. Skate, like other elasmobranchs, often have a low reproductive potential since they only produce between 6 and 40 egg cases per year. But, because the young hatch in a well-developed form, compared with most teleost fishes, early life mortality may be relatively low. Although Holden (1974) has argued that life history characteristics of elasmobranchs make them vulnerable to overfishing, it has been suggested that there should be a reasonably good recruitment relationship (Hoenig and Gruber 1990). We do not know if this is the case for skates. Survival rates are unknown and empirical data on recruitment are lacking. In short, though it is possible to estimate a minimum exploitable biomass, and roughly estimate fishing mortality (through catch statistics), there is no information on the stock's rate of renewal.

What is known is that during the 20 odd years preceding 1995, Grand Banks skate decreased in size, became less abundant, and underwent a contraction in distribution, all signs of a stressed population. It would be useful to know if other life history parameters such as growth rate and size at maturity have also changed since they were last examined with samples taken in 1959–1965 (Templeman 1987a,b). Such information would certainly help with the interpretation of current trends, particularly in light of the disruption of the research survey time series. Additional research on basic biological characteristics has been identified as a priority for future work by DFO scientists (Kulka and Mowbray 1998).

The DFO is attempting to manage this resource in a conservative and sustainable fashion but it is clear that they do not have the baseline information necessary to determine whether this is being accomplished. Also, considering that this is a multi-species fishery managed as a single species, what may be sustainable level of exploitation for thorny skate may not be the case for the other species. At present, there is little recognition by government and industry of the need to identify and treat species separately. However, concerns have been expressed by outside interests, particularly in the case of barndoor skate (Casey and Myers 1998).

5.2.6 The managers' perspective

Skate is, and has been, managed based on the biological advice forwarded by the FRCC. Party politics have little or no role in the management strategy or policy. There are no problems with conflicts among stakeholders, and management policies based on biological advice have been generally well received. Uncertainties in the biological resource advice are usually dealt with by the FRCC before the advice goes to managers. This is done by incorporating the views of stakeholders into the FRCC recommendations. Since the conservative TACs have not been caught in any year, pressures for quota increases are not anticipated.

6. THE LAW AND ENFORCEMENT

6.1 Legal Status

The Grand Banks skate fishery is a commercial fishery open to groundfish licence holders. Thus, the fishery is common property managed by the federal government through the DFO. The DFO also holds legal responsibility for the fishery. The legal basis for enforcement of skate fishing regulations is the same as for all marine fisheries in Canada, the Canadian Fisheries Act (currently under revision). Current regulations pertaining to the fishery can be found at http://www.ncr.dfo.ca/home_e.htm under Departmental Publications, Acts, Orders and Regulations, Fisheries Act.

6.2 Enforcement problems

Enforcement is achieved through the deployment of fisheries officers who board vessels at sea and in port. They are granted the authority through the Canadian Fisheries Act to issue warnings or to arrest individuals and seize vessels where necessary. Since the start of this fishery as a commercial activity in 1995, only two irregularities have been recorded on vessels directing for skate suggesting reasonable adherence to the regulations. Clear guidelines provided in the CHP and fishing licence ensure that the industry is fully aware of the regulatory framework pertaining to this fishery. Gear size limitations keep the catch of non-marketable fish to a minimum, although it is not always adequate for limiting bycatch. The greatest problem with respect to enforcement is fishing activity that may go unmonitored. Only 8% of the fishing activity is covered by fishery observers and an even smaller proportion is subjected to inspection boardings by fisheries officers. Such things as excessive bycatch of restricted species may go undetected.

6.3 Surveillance

Adherence to regulations for skate and other Atlantic Canadian fisheries is monitored in several ways: direct observation by fishery observers contracted to the government of Canada during the fishing operation, overflights (air surveillance) also contracted, and inspections by government fishery officers at sea and at dockside. Landings for vessels less than 65ft are also recorded at dockside by monitors contracted by the fishing industry. For skate, observers deployed to about 8% of the total fishing operations are the primary method for assuring adherence to the regulations for this fishery. Between 1995 and 1998, 16 deployments covering about 35 fishing trips were made. Observers gathered information on catch, and fishing activity in general. Surveillance overflights occur daily but must cover a large territory hence the skate grounds are only covered irregularly. While overflights can determine vessel position and so identify vessels fishing in closed or illegal zones, they cannot be used to identify other infractions since target species and other details pertaining to fishing procedures cannot be determined.

6.4 The legal process

Fishery officers (employees of Fisheries and Oceans) have the authority to charge vessels and their crew under the Fisheries Act. Once charged, the courts are responsible for determining culpability and levying penalties, except in cases where administrative sanction is introduced. From 1994–1996, licences could also be revoked or withheld by administrative sanction. The maximum fine for fisheries offences is $Can100 000 and/or up to one year imprisonment, however fines for groundfish and skate infractions usually range between $Can500 and $Can3000 (K. Anderson, DFO St. John's, Nfld, Pers. Comm.). Officers also have the right to seize catch, and vessels or vehicles used in the commission of an offence. Seized belongings may be forfeited at the discretion of the court. Prohibition orders that deny the offender access to certain waters or fisheries may be placed.

7. ACKNOWLEDGEMENTS

We wish to express our appreciation for the contributions of Ben Rogers, Kevin Anderson, Paul Cahill, Len Knight, Max Grandy and Joanne Morgan who provided information and reviews of an earlier draft. We would also like to thank the many fishery observers and other DFO personnel who collected the various biological and catch statistics.

8. REFERENCES

Anon 1994. Development of the skate fishery. Newfoundland Region Gear Conversion - Project Report 194–259: 18pp.

Anon 1997. Integrated Fisheries Management Plan Atlantic Groundfish 1997. DFO St.John's, Nfld.

Atkinson, D.B. 1993. Some observations on the biomass and abundance of fish captured during stratified random bottom trawl surveys in NAFO Divisions 2J3KL, fall 1981–1991. NAFO SCR Doc. 93/29, Serial No. N2209, 18pp.

Atkinson, D.B. 1995. Skates in NAFO divisions 3LNO and subdivisions 3Ps: A preliminary examination. DFO Res. Doc. 95/26.

Cahill, P. 1999. Economic facts concerning the Grand Banks (NAFO Divisions 3LNOPs) skate fishery. Unpublished report. Policy and Economics Branch, DFO, St. John's, Newfoundland.

Casey, J.M. and R.A. Myers 1998. Near extinction of a large, widely distributed fish. Science 281:690–692.

Duran, P. and X. Paz 1997. Witch flounder (Glyptocephalus cynoglossus) in the Spanish fishery in NAFO regulatory area (Divisions 3LM and 3NO) 1991–94.

Day, W.J. 1991. A marketing plan for the underutilized species Skate. Work report submitted to Carter, L., Faculty of Business Administration, Memorial University of Newfoundland, St. John's, Newfoundland, 33pp.

Hoenig, J. M. and S.H. Gruber 1990. Life-history patterns in the elasmobranchs: implications for fisheries management. NOAA Tech. Rept. 90: 1–16.

Holden, M. J. 1974. Problems in the rational exploitation of elasmobranch populations and some suggested solutions. In: Harden Jones, F. R. (Ed.), Sea Fisheries Research. Logos Press, London, pp. 117–137.

Junquera, S. and X. Paz 1998 Non-traditional resources: Skate fishery and survey results in Division 3NO. NAFO SCR Doc. 98/26, Ser. No. N3011. 6pp.

Kulka, D. W. 1982 Estimates of discarding by the Newfoundland offshore fleet in 1981. CAFSAC Res. Doc. 82/34. 22pp.

Kulka, D. W. 1984 Estimates of discarding by the Newfoundland offshore fleet in 1982. NAFO SCR Doc. 84/28, Ser. No. N809. 16pp.

Kulka, D. W. 1985 Estimates of discarding by the Newfoundland offshore fleet in 1983. NAFO SCR Doc. 85/75, Ser. No. N1033. 19pp.

Kulka, D. W. 1986a Estimates of discarding by the Newfoundland offshore fleet in 1984 with reference to trends over the past four years. NAFO SCR Doc. 86/12, Ser. No. N1120. 20p.

Kulka, D. W. 1986b Estimates of discarding by the Newfoundland offshore fleet in 1985 with reference to trends over the past 5 years. NAFO SCR Doc. 86/95, Ser. No N1221. 20p.

Kulka, D. W. 1989 Bycatch of commercial groundfish species in the northern shrimp fisheries, 1980– 1994 DFO Atlant. Fish. Res. Doc. 95/48. 16pp.

Kulka, D. W., E.M. DeBlois and D. B. Atkinson 1996 Non-traditional groundfish species on Labrador Shelf and Grand Banks - Skate. DFO Atlant. Fish. Res. Doc. 96/98. 29pp.

Kulka, D. W. and F.K. Mowbray. 1998. The status of thorny skate (Raja radiata), a non-traditional species in NAFO Divisions 3L, 3N, 3O and Subdivision 3Ps. DFO Atlant. Fish. Res. Doc. 98/131. 70pp.

Scott, W. B. and M. G. Scott 1988 Atlantic Fishes of Canada. Can. Bull. Fish. Aquat. Sci No. 219 730p.

Simon, J.E., Frank, K.T. 1995. An assessment of the skate fishery in Division 4VsW. DFO Res. Doc. 95/71 32pp.

Simon, J.E., Frank, K.T. 1996. Assessment of the Division 4VsW skate fishery. DFO Res. Doc. 96/105. 51pp.

Templeman, W. 1982a. Development, occurrence, and characteristics of egg capsules of thorny skate, Raja radiata, in the Northwest Atlantic. J. Northw. Atl. Fish. Sci. 3(1): 47–56.

Templeman, W. 1982b. Stomach contents of the thorny skate, Raja radiata, from the Northwest Atlantic. J. Northw. Atl. Fish. Sci. 3(2): 123–126.

Templeman, W. 1984a. Migrations of thorny skate, Raja radiata, tagged in the Newfoundland area. J. Northw. Atl. Fish. Sci. 5(1): 55–64.

Templeman, W. 1984b. Variations in numbers of median dorsal thorns and rows of teeth in thorny skate (Raja radiata) of the Northwest Atlantic. J. Northw. Atl. Fish. Sci. 5(2): 171–180.

Templeman, W. 1987a. Differences in sexual maturity and related characteristics between populations of thorny skate (Raja radiata) in the Northwest Atlantic. J. Northw. Atl. Fish. Sci. 7(2): 155– 168.

Templeman, W. 1987b. Length-weight relationships, morphometric characteristics and thorniness of thorny skate (Raja radiata) from the Northwest Atlantic. J. Northw. Atl. Fish. Sci. 7:89–98.

Walsh, S. J. 1992. Size-dependant selection at the footgear of a groundfish survey trawl. N. Am. J. of Fish. Mgmt. 12:652–633.

APPENDIX 1
DFO Stock Status Report for Division 3 Skate

SKATE IN DIVISIONS 3L, 3N, 3O AND SUBDIVISION 3Ps

Background

There are 8 to 10 species of skate in the waters around Newfoundland. Of these, thorny skate (Raja radiata) is by far the most common, comprising greater than 90% of those caught during research surveys. The second and third most common are the smooth (Raja senta) and spinytail skate (Raja spinicauda). Although data on skate are routinely collected during research surveys, until recently, there has been only limited examination of these data. Most of the work to date has been done on thorny skate.

Thorny skate is widely distributed in the waters around Newfoundland being found in depths ranging from about 18 meters (10 fathoms) to over 1500 meters (820 fathoms), in temperatures from -1.4° to about 6°C on the Grand Banks and on both hard and soft bottoms. Tagging information suggests that they are sedentary species and generally do not undergo long migrations, moving less than 100 kilometers during their lives. However, recent distributional studies indicate that thorny skate on the Grand Banks perform an annual migration toward the shelf edge in the winter returning onto the bank in midsummer.

It is not known how long thorny skate live in the waters around Newfoundland. The time between tagging and recapture of some individuals suggests that they can live at least 20 years. They deposit between 6 and 40 egg cases per year (also known as mermaids' or sailors' purses) that contain single embryos. Males mature at smaller sizes than females, and size at maturity increases from north to south. Limited data suggest that reproduction occurs year round on the Grand Banks. Thorny skate feed on a wide variety of items including both invertebrates and fish. As well, significant amounts of offal have been found in the stomachs of skate captured in the vicinity of commercial fisheries.

Until recent years, there has been only limited interest in fishing for skate in the waters around Newfoundland. Previously, skate was usually discarded even though it constituted the most common non-commercial by-catch in offshore trawler catches. These by-catches were not reported in the catch statistics. Most of the reported catches before 1994 are attributable to non-Canadian fleets. With the decline of other groundfish resources, Canadian interest in skates increased, and quotas were first put in place for 1995 inside Canada's 200 mile limit. The quota was based on a 20% exploitation rate of the survey biomass estimate for 1993. This rate was subsequently considered too high and was reduced to 10%. The current TAC is set at 3,000 metric tons.

Fishers are interested in the width of the skate wing, as the wing is the product. Based on market conditions, the minimum acceptable size is about 46 cm. (18 inches).

The Fishery

Interest in skate was limited when other groundfish stocks were healthy. Catches reported to NAFO from the time of extension of jurisdiction averaged less than 3,000 metric tons (t) until 1985 when the reported catches from Division 3N increased significantly.

Reported Landings (thousand metric tons)

¹ Estimated by Canadian Surveillance
² for Canadian waters only

The elevated catches that continued into the last half of the 1980's were due to directed effort and bycatch from outside 200 miles. Canadian surveillance has determined that some of these catches during the 1980's, reported as skates, may have actually been other species such as flatfish or cod. During the 1990's however, Canadian surveillance estimated catches outside 200 miles that were higher than those reported. Surveillance estimates rather than statistics reported to NAFO were used for landing statistics for countries other than Canada (1985– 1997).

As well, reported Canadian catches prior to 1995 are higher than actual because of the conversion factor between wing weight and round weight used by Statistics Branch. Prior to 1995 a conversion of 4 was used. More recent work indicated that a conversion of 2.7 is more appropriate and this value has been applied by Statistics Branch since 1995. In the figure below, landings prior to 1995 have been adjusted using the 2.7 factor.

Based on observer data, unreported discarded bycatch in other fisheries averaged about 3,000 t annually during the early- to mid-1980's in Divisions 3LNO and Subdiv. 3Ps. Estimates from the more recent period are unavailable but are thought to have been about the same until the collapse in the 1990's of many of the offshore fisheries that had generated the skate bycatch in the 1980's.

After 1993, the Canadian catch component, previously less than 2%, made up about 35% of the total reported catches.

As the new Canadian fishery developed, reported catches increased from about 90 t in 1993 to about 3,300 t in 1994 and 4,500 t in 1995. The quota for 1995 was 6,000 t, lowered to 2,000 t in 1996 then increased to 3,000 t in 1997 based on the recommendation of the FRCC. The lowered quota resulted in catches of about 1,900 t and 2,800 t in 1996 and 1997 respectively. Allocations were set at 45.8% for mobile and 54.2% for fixed gears.

Steps were also taken in 1996 and 1997 to spread fishing effort throughout the management area to minimize possible negative effects of concentrating it in any one area. This too was based on the recommendation of the FRCC. The 1997 and 1998 quota of 3,000 t was split among areas as follows: 3LN-15%, 3O– 50%, and 3Ps–35%. These divisional allocations were based on biomass distribution observed during the 1992 to 1996 research surveys.

Observer data (refer to the map below, darker shades denoting more intensely fished areas) indicate that although the quota was spread among 3 areas, the Canadian effort remained concentrated in southwestern 3O and southern 3Ps.

Preliminary data to October 1998 indicate a Canadian catch of about 2,100 t, with 1,200 t being taken in 3Ps and most of the remainder in 3O. Foreign catches for 1998 are not yet available.

Resource Status

A comparison of thorny skate distribution from 1995–1997 spring and fall research vessel surveys suggests that skate move off the Grand Banks towards the shelf edge in the winter/spring, with a portion of the population moving into deeper, un-surveyed waters.

Further support for this movement into unsurveyed areas can be derived from fishery data. Bycatch rates of skate in deepwater (slope) fisheries during Dec.-Jun. 1995–1997 were about double those of Jul.-Nov. Such movement out of the surveyed area would affect skate availability to research surveys and hence, account for the observation that spring biomass indices were on average 40% lower than those for fall.

Although fall research surveys yielded higher measures of biomass (for the reasons discussed above), both indices show the same trends over time. Spring surveys were used to examine trends over time because they provided a larger spatial coverage (3Ps is not surveyed in the fall) and a longer time series.

Historic research vessel catches suggests that thorny skate on the Grand Banks and north-east Newfoundland Shelf started a slow decline over its entire distribution as early as the late 1970's or early 1980's. Biomass indices (1986–1997) indicate that the biomass of thorny skate was most affected in Div. 3L, fluctuating until 1989 then declining rapidly thereafter. The biomass in Div. 3NO and Subdiv. 3Ps (3NOPs) remained relatively stable between 1986 and 1991 then also declined until 1994. Biomass in 3NOPs reduced slightly from 1996 to 1997, but increased in 1998.

Overall, thorny skate had declined to the lowest historical levels by 1993 or 1994. A similar decline was seen in the fall surveys for areas surveyed. A change in gear from Engel to Campelen in fall 1995 likely affected catchability of skate. Thus the two periods are not comparable and trends since 1995 cannot be interpreted.

The average size of the skate in spring research survey data has been declining over the time period examined, particularly in Divisions 3L and 3N. A slight increase in size has been observed since the introduction of Campelen gear. However, whether this is due solely to the change in gears is uncertain.

Based on sampling carried out from 1947 to 1972, females were larger at maturity in 3OPs than in 3LN. While about 50% of female skates with a wing width of 46 cm. (18 inches) are mature in divisions 3LN, only about 20% of the females in 3O and 3Ps are mature at that size. In 3O and 3Ps, about 50% are mature when the wing width is 56 cm. (22 inches).

Sources of Uncertainty

There are a number of important limitations to our knowledge of skates in the waters around Newfoundland. We lack information on such things as growth rates and age of maturity and details of the age structure of the population(s).

As well, as with numerous other species, what proportion of the decline is attributable to changes in fishing mortality vs. environmental influences remains uncertain. Whatever the cause, the stock remains at its lowest historical level.

Assuming skates are a renewable resource, one would expect some evidence of renewal, some sign that skates that are caught are somehow replaced by fresh stock. Such evidence is lacking: the apparent decrease in survey biomass comes so close to matching the cumulative reported catches that it is not possible to establish a positive lower bound on the production of the stock.

Given the available data, it is not possible to determine the most appropriate exploitation rate for a sustainable fishery. The average total catch for 1996–97 was 8,930 t, which represents approximately 13% of the average spring survey estimate for the same period. This constitutes a substantial reduction from the 20% exploitation rate set in 1995. However, there is insufficient information to judge its suitability at this time.

Catches of skates outside 200 miles remain unregulated. There are indications that catch information from outside 200 miles continues to be unreliable. As well, discarding inside 200 miles for the period since 1985 still remains to be quantified.

Outlook

Analysis of research data suggests that thorny skate declined earlier and at a greater rate to the north. The decline starting in the early 1980's accelerated in the early 1990's. For the last few years, after reaching its lowest level in all areas, the biomass shows no sign of recovery through 1997.

Distributional studies suggest that a portion of the skates go through an annual migration. As they move onto the shelf in the summer and fall, they tend to aggregate into an area overlapping Divisions 3N, 3O and Subdiv. 3Ps partially separated from a smaller concentration in Div. 3L. Historically, the two concentrations were more closely associated. Skates also tend to be sedentary, forming local aggregations, except for this apparent seasonal migration. For this reason local concentrations can be easily depleted. This suggests that management on a scale finer than the Division might be prudent. Still, in the absence of detailed data on stock structure, a first cautious approach would be continued allocation among divisions. Therefore it is important that management continue to ensure that effort is not concentrated in any one area. The biomass proportions in the 1996–97 spring survey were: 22% in Divisions 3LN, 47% in Div. 3O and 31% in Subdiv. 3Ps. The total biomass average over the two years was 73,650 t.

Considering the historical decline in biomass indices, the lack of comparable data on current stock status, and the uncertainty about the stock(s) ability to rebuild, an increase in harvest levels would not be considered prudent.

For More Information

Research Documents:

Kulka, D. W., D.B. Atkinson and E. DeBlois 1996. Non-traditional groundfish species on the Labrador Shelf and Grand Banks - skate. DFO Atl. Fish. Res. Doc. 96/98.

Kulka, D.W. and F.K. Mowbray. 1998. The status of Thorny skate (Raja radiata), a non-traditional species in NAFO Divisions 3L, 3N, 3O and Subdivision 3Ps. DFO Atl. Fish. Res. Doc. 98/131.

Contact: David W. Kulka
Tel. (709) 772-2064
Fax. (709) 772-4188
e-mail: [email protected]

This report is available:

Science Branch Dept. of Fisheries and Oceans Newfoundland Region P.O.Box 5667 St. John's NF A1C 5X1 (709) 772–4355 e-mail address: [email protected] Internet address: http://www.nwafc.nf.ca