|Scientific Name:||Malacoraja senta|
|Species Authority:||(Garman, 1885)|
Raja senta Garman, 1885
|Red List Category & Criteria:||Endangered A2bcd ver 3.1|
|Assessor(s):||Sulikowski, J., Kulka, D., Gedamke, T. & Barker, A.|
|Reviewer(s):||Dulvy, N.K., Valenti, S.V., Pollard, D. & Fowler, S.L. (Shark Red List Authority)|
The Smooth Skate (Malacoraja senta) is a small western Atlantic skate, occurring from the banks off Newfoundland (Canada) to New Jersey (USA). It is known from depths of 25–1,436 m, although the huge majority of the population appears to occur at 70–480 m depth. Extensive separation between various areas suggests the possibility of four or five separate subpopulations. This species is not targeted, but is taken in mixed fisheries or as bycatch by trawls, longlines, crab pots and scallop dredges. Scientific survey data from Canada indicate large declines in adult abundance, ranging from 91% over 28 years (1977–2005) to 73% over 29 years (1976-2005) in two different areas. These areas comprise the majority of the Smooth Skate population (~67%). Elsewhere, a minority of the population is more stable; the species declined in the Gulf of Maine in the 1970s (91% from 1970–1993 in the Canadian portion), but then increased in recent years (370% during 1993–2005 in the Canadian portion; 729% during the past 10 years in the USA portion). Given the significant declines observed in the areas containing the majority of the population, the species is assessed as Endangered off Canada. In USA waters, the smooth skate is near the biomass threshold (0.19 vs. 0.16 kg/tow), and could become overfished in 2007. Biomass has not increased in almost 20 years despite a reduction in groundfish effort and a prohibited status and it is assessed as Near Threatened in USA waters. Globally, an assessment of Endangered is warranted, as the majority of the total population of M. senta (~75.6%) is found within Canadian waters.
|Range Description:||This species occurs in the western Atlantic from the banks off Newfoundland and southern Gulf of St. Lawrence in Canada to New Jersey, USA. The northern most record is at latitude 60° but records beyond latitude 56.5° are rare, and beyond that bound can be considered as vagrant. Similarly at the southern extent of its distribution, occurrences south of latitude 40° are also rare (Kulka et al. 2006).
Important sites are; the Gulf of St. Lawrence (Laurentian Channel), southwest Grand Bank, Flemish Cap, northeast Newfoundland Shelf and in a small area of the Labrador Shelf. M. senta is located primarily in the troughs separating shallower banks, from the Hopedale Channel on the Labrador Shelf south to the outer Georges Bank.
Native:Canada (Labrador, Newfoundland I, Nova Scotia); United States (Maine, New Hampshire, New Jersey, New York, Rhode Island)
|FAO Marine Fishing Areas:||
Atlantic – northwest
|Range Map:||Click here to open the map viewer and explore range.|
Little is known about the species’ population size or abundance except that it is not caught frequently enough to be of any importance to fisheries in both USA and Canada (McEachran and Dunn 1998). Population declines are described below.
This species is not distributed evenly within its global range. Rather, it forms four (possibly five) disjunct concentrations off Canada, separated by wide areas, where M. senta never occur (Kulka et al. 2006). These four distinct concentrations were identified by Kulka et al. (2006) as Designated Units (Dus) for the purposes of their analysis and include: Hopedale Channel; Funk Island deep, northeastern Newfoundland Shelf; the Flemish Cap/Pass and northeast Grand Bank; Laurentian Channel, southwestern Grand Bank, and eastern Scotian Shelf; Gulf of Maine, Fundy and western Scotian Shelf.
|Habitat and Ecology:||
This skate occurs in deep brackish and marine water over soft mud and clay bottoms of the deeper troughs and basins, sands and shells, gravel and pebbles of the offshore fishing banks (Bigelow and Schroeder 1953). The species is reported from a total depth range of 25–1,436 m, however depth range is narrower at specific latitudes, and 90% of survey sets containing Malacoraja senta occurs between 70 and 480 m (Kulka et al. 2006). M. senta is found over a relatively narrow range of temperatures, from -1.3–15.7°C, with most records from 2.7–10°C, avoiding the coldest of locations (Kulka et al. 2006).
M. senta is one of the smallest skates that inhabits the Northwest Atlantic reaching a maximum size of about 70 cm although fish >63 cm are rare in Canadian waters (Kulka et al. 2006). There is some variation in size data across this species’ range. Females mature at 41–54 cm total length (TL) and between 8–9.5 years of age, and males mature at 49–57 cm TL and between 8 and 10 years of age (Kulka et al. 2006, Sulikowski et al. in review). Average reproductive age, or generation period, is 10–13 years (Kulka et al. 2006, Sulikowski et al. In review). Like all skates, reproduction in this species is oviparous, and eggs (5.9 cm long and 3.8–4.5 cm wide, with stiff pointed horns) are deposited in the sand or mud (Funicelli 1972). In the United states this species was found to be reproductively active year round (Kulka et al. 2006; Sulikowski et al. 2007). Size at birth is ~10cm TL and average annual fecundity is et al. 2006).
In Canadian waters, average size of these skates decreased with depth. Average weight of fish was about 0.6 kg (equivalent to a TL of 50 cm) at 50–150 m, 250 m and 0.2 kg (35 cm) at 500–600 m indicating a distinct separation of fish with respect to size. This suggests that surveys using larger mesh gear and not reaching similar depths are underestimating the presence of smaller fish.
Feeding studies (McEachran 1973, McEachran et al. 1976, Bowman et al. 2000, McEachran 2002, González et al. 2006) indicate that M. Senta is quite selective in its diet, eating primarily small crustaceans throughout most of its life, and taking fish only at the largest sizes. This selective diet may further constrain where the species distributes and may relate to the size segregation observed (Kulka et al. 2006).
The main human-related threat over the species’ entire range is incidental capture in a variety of fisheries. Species-specific catch levels are not known, but in Canadian waters and it constitutes <1% of the skate incidental bycatch (Kulka et al. 2006). Skate landings in the USA are only now being separated by species, so specific catch data will begin to become available in a few years.
Adult (and juvenile in some cases) Malacoraja senta have declined in abundance over much of the species’ range, since the 1970s. However, in some areas, it has subsequently undergone recovery, in some cases reaching near historic high levels over a very short period (Kulka et al. 2006).
In the Hopedale Channel, there is not a sufficient time series to quantify changes in abundance, but preliminary data from the fall 2007 indicates that catch rates are among the highest observed for that area. In contrast, directly to the south, abundance of population on the Funk Island deep, northeastern Newfoundland Shelf underwent the largest decline observed, 91% for both adults and juveniles, based on a log model to fit 28 years (1977–2005). The period of decline corresponds with the coldest period in the area (Colbourne et al. 2006). There has been no sign of recovery during the recent warm period in spite of apparently very low fishing pressure observed since the late 1990s. A decline of 80% was calculated for adults during 1971–2005 for the Laurentian DU (Kulka et al. 2006).
The southern-most Gulf of Maine DU straddles the Canada-USA border. The trend in abundance is similar on both sides of the line: the adult Canadian and adjacent spring USA survey trends were similar, undergoing a decline in the 1980s then increasing since the 1990s to where the indices are presently near historic levels. However, over the entire range in the United States, the biomass of this species has not increased and has remained at stable but low levels for the past 20 years.
Although there are no directed commercial fisheries for M. senta, it is taken in mixed fisheries or as bycatch in fisheries targeting other species (NOAA 2000a, Kulka 1986). However, the vulnerability of skates to depletion is well-documented, even when low levels of bycatch are taken. Many elasmobranch species have a low reproductive potential and a low intrinsic rate of increase, characterized by slow growth, late maturation, low fecundity and long reproductive cycles (Smith et al. 1998), leading to low resilience to fishing mortality (Hoenig and Gruber 1990, Musick 2004; Kulka et al. 2006). Frisk et al.’s (2001) analyses of several northwest Atlantic skates also suggested that these long-lived, slower-growing species are vulnerable to exploitation.
Average annual catch across this species’ range off Newfoundland and Labrador has declined since 2002. Most bycatch in commercial fisheries appears to be taken from the southwest Grand Bank and Laurentian Channel, by the skate longline, crab pot, cod otter trawl and scallop dredge fisheries. The lowest observed catches occurred in the most recent years, with catches amounting to 2 t (Kulka et al. 2006). Fishing grounds overlap extensively with this species’ distribution and fishing mortality has clearly impacted this species.
Trawl effort has not covered the entire shelf but has been concentrated in relatively small areas, particularly in recent years. A comparison of rates of decline in areas of high intensity trawling compared to areas of no trawling indicated no difference in decline rate. However, this analysis only relates to trawls; longlines, gillnets, dredges, seines and pots also capture this species (Kulka et al. 2006). There may also be other factors contributing to the decline (Kulka et al. 2006).
In the United States, there are also no directed fisheries for this species. Despite this, the species is near its biomass threshold (0.19 vs. 0.16 kg/tow), and biomass has not increased, despite reductions in groundfish effort over the last 20 years and a prohibited status since 2003. While the population is considered stable, albeit at low levels, it has the potential to become overfished. Thus, similar to the Canadian population, there appears to be some other cause for the failure to rebound to more sustainable levels.
In the United States, there is currently a ban on landing this species.
There are currently no measures for this species in Canada, as its capture is only incidental in Canadian waters.
Recommendations for future conservation action are; begin developing estimates for target and limit reference points and reduce discard mortality by encouraging and/or mandating more careful handling and discard techniques.
|Citation:||Sulikowski, J., Kulka, D., Gedamke, T. & Barker, A. 2009. Malacoraja senta. The IUCN Red List of Threatened Species. Version 2015.2. <www.iucnredlist.org>. Downloaded on 29 August 2015.|
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