|Scientific Name:||Merluccius bilinearis (Mitchill, 1814)|
Stomodon bilinearis Mitchill, 1814
|Taxonomic Source(s):||Eschmeyer, W.N. and Fricke, R. (eds). 2015. Catalog of Fishes: genera, species, references. Updated 1 October 2015. Available at: http://researcharchive.calacademy.org/research/ichthyology/catalog/fishcatmain.asp. (Accessed: 1 October 2015).|
|Red List Category & Criteria:||Near Threatened ver 3.1|
|Facilitator/Compiler(s):||Ralph, G. & Linardich, C.|
This species is widely distributed and often occurs in large aggregations over soft bottom habitat. It is sexually dimorphic with a maximum longevity of 15 years. Prior to 1977, this fish was heavily exploited due to unrestricted fishing conducted largely by foreign fleets, but also domestic. The passage of fishery laws in 1977 allowed for the exclusion of foreign fleets, the development of fishery management plans for domestic stocks (U.S. and Canada), and the implementation of restrictive regulations on this trawl fishery.
Based on estimated declines in fisheries independent surveys of 46-56% over three generation lengths in 75% of its global distribution, it is estimated that declines of 30-45% have occurred. Further, likely due to heavy exploitation in the past and targeting of large individuals, fish older than six years are now rarely observed. However, populations in both Canada and the United States appear to be stable or increasing. Therefore, we infer that the threat of overfishing has ceased and is reversible. As the estimated declines for this species approach the threshold for listing as Vulnerable under criterion A1, M. bilinearis is assessed as Near Threatened. Furthermore, since this species has been identified as an important trophic link in its ecosystem, additional emphasis towards maintaining healthy populations should be recognized. Solutions to issues such as the misidentification of this species within the fishery and quantifying natural mortality should be explored in order to reduce uncertainty in future stock assessments.
|Range Description:||Merluccius bilinearis is distributed in the northwest and central Atlantic Ocean from Canada south along the U.S. to southeast Florida (Cohen et al. 1990, Lloris et al. 2005, R. Robertson pers. comm. 2013). Its depth range is 0-914 m (Lloris et al. 2005), but is most abundant on sandy continental shelf between 50-300 m (Cohen et al. 1990). A record off Trinidad/Venezuela requires verification.|
Native:Bahamas; Canada; Saint Pierre and Miquelon; United States
|FAO Marine Fishing Areas:|
Atlantic – western central; Atlantic – northwest
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||This is a relatively common species in the northern parts of its range, becoming less common south of South Carolina (Cohen et al. 1990). It is often found in large aggregations.|
Total global catch peaked in 1965, subsequently declined by 84% over the next five years, increased by 148% over the following three years, and finally declined sharply after new fishery laws were enacted in 1977 that effectively reduced effort by at least 48-90%. Prior to 1977, the bulk of fishing effort was conducted by foreign fleets (Russia, Cuba, and Japan) and was unrestricted. From the early 2000s until present, this species has been targeted by only U.S. and Canadian fleets. Over the past three generation lengths (15 to 21 years), the population of M. bilinearis appears to be stable in Canadian waters (approximately 25% of its global distribution), but has been declining by 46-56% in US waters (approximately 75% of its global distribution). Therefore, the global population is estimated to have declined by approximately 30-45% over three generation lengths.
The U.S. commercial fishery for this species is separated into two stocks: the northern from the Gulf of Maine to Georges Bank and the southern from the southern Georges Bank through the Mid-Atlantic Bight. During the summer, fish from both stocks can co-occur on Georges Bank. During the winter, fish from the northern stock migrate to the Gulf of Maine while the southern stock moves further offshore to the outer shelf and slope. Between 1987-1999 (12 years), U.S. landings were relatively stable, gradually declined by 73% over the next 7 years, and then increased by 68% over the following 4 years (up to year 2010 with 9,600 metric tons). In 2012, U.S. landings were 6,940 metric tons. Recreational fishermen do not target Silver Hake and the species is taken in negligible amounts.
Fishery-independent trawl surveys conducted annually in the fall and spring by the NOAA Northeast Fisheries Science Center collect abundance data for marine species that occur over the U.S. Northeast continental shelf. Although the survey indices are variable, the fall survey suggests declines in biomass indices of 46-56% over 15 to 21 years (three generation lengths). The two most recent stock assessments, published in 2006 and 2011, concluded that both U.S. stocks of the Silver Hake are not overfished and are not undergoing overfishing (Northeast Fisheries Science Center 2006, 2011). However, Lloris et al. (2005) noted that M. bilinearis from United States waters rarely exceeded six years of age during the past few years, which is likely due to fisheries targeting larger individuals. The U.S. stock assessments for Silver Hake recognize a certain amount of uncertainty for the following reasons: trends in population size and fishery removals are not consistent between each other, there is some identification confusion with the Offshore Hake within the fishery (Garcia-Vazquez et al. 2012), and the level of natural mortality due to predators is not yet clearly quantified (Link et al. 2012).
The Canadian commercial fishery has been active on the Scotian Shelf, specifically the Emerald and LaHave basins, since 1995. A declining shift in the age composition from predominantly ages 2-4 to 1-2 occurred between the 1970s to the mid-1990s was observed during the transition from the foreign fishery to the domestic fishery. The current landings quota has been set at 15,000 metric tonnes since 2003 and has not been exceeded (averages 11,100 metric tonnes). Total landings are dictated by market demand, not reduced abundance. The Canadian government also maintains fishery-dependent and independent research surveys to advise biomass assessments. According to fishery-independent survey results, population biomass estimates indicate an increasing trend since 2008 and biomass in general has returned to similar levels recorded in the 1980s. Additionally, bycatch represents less than 4% of the total catch monitored by observers (DFO 2013). Biomass indices from the fisheries independent survey on the Scotian Shelf have been increasing since 2005; the trend over the past three generation lengths appears to be stable (DFO 2013).
|Current Population Trend:||Unknown|
|Habitat and Ecology:||Merluccius bilinearis is benthopelagic and occurs over continental shelves and slopes with sandy, muddy, or pebbly substrate. It most commonly found in temperatures between 7-10°C.|
It is considered to be an important component of the ecosystem where it plays significant roles as both prey and predator (Northeast Fisheries Science Center 2011). For protection from visual predators, juveniles persist in areas with high densities of amphipod tubes because the dorsal colouration of 0-year M. bilinearis mimic the pattern of amphipod tubes viewed against the bottom. Juvenile M. bilinearis preferred prey (amphipods and shrimp) are also found in these areas (Auster et al. 1997). Lloris et al. (2005) found that the recruitment of M. bilinearis in an area positively correlates with the abundance of Atlantic Mackerel, Scomber scombrus, a preferred prey species of M. bilinearis. It is a voracious predator with cannibalistic habits. Smaller M. bilinearis feed on crustaceans (euphausiids and pandalids), while larger M. bilinearis (over 40 cm total length (TL)) feed on fishes (clupeids, Scomber scombrus, Urophycis chuss, Gadus morhua) (Cohen et al. 1990, Lloris et al. 2005). It embarks on daily vertical migrations to hunt at night. During late spring and early summer, adults move to shallower waters. It returns to deeper waters in the autumn and winter with the older, larger fish in the deepest portion (Brodziak et al. 2001). Juveniles also display similar seasonal distribution patterns, only congregating in shallower waters (Lloris et al. 2005).
The maximum total length is 76 cm (Robins and Ray 1986, Cohen et al. 1990) and its longevity is ~15 years (Auster et al. 1997). However, there is evidence for age truncation due to fishery pressure whereas fish older than age six are now rarely encountered (Brodziak et al. 2001).
Cohen et al. (1990) and Lloris et al. (2005) found spawning to be related to water temperature. Spawning occurs in shallower waters from June to July in the mid-Atlantic region, July to August in the Gulf of Maine and to the north of Georges Bank, and August to September on the Scotian Shelf. Richards (2006) recorded spawning from May to November off New England and into the winter off mid-Atlantic states. Peak spawning occurs between May-June for the southern stock and July-August for the northern. After two months of remaining in the water column, embryos and larvae measuring ~17-20 mm standard length (SL) descend to the bottom (Auster et al. 1997). Fecundity is thought to be as high as other species of this genus (Lloris et al. 2005). Sexual maturity is similar in males and females, between two and three years (29 to 33 cm length) on Georges Bank and one to two years (females 26 to 27 cm length; males 23 to 24 cm length) on the Scotian Shelf (Lloris et al. 2005). Compared to males, females grow faster, live longer, and are larger (Cohen et al. 1990, Lloris et al. 2005). Females reach a maximum size of 76 cm and can live up to 15 years. Male M. bilinearis have a maximum size of 41 cm and can live up to nine years. Females release up to three batches of pelagic eggs per spawning season (Collette and Klein-MacPhee 2002).
|Generation Length (years):||5-7|
|Use and Trade:||This species supports a commercial fishery, largely due to the ease in capturing large numbers by bottom trawling. It is sold fresh, frozen, gutted, whole or in fillets, and in the past, as fishmeal (Lloris et al. 2005). Small-mesh trawl fisheries are currently operated on the Scotian Shelf, the Gulf of Maine, and Georges Bank by Canada and the United States. Between 1962-1977, foreign fleets comprised the bulk of the effort in this fishery. It is the most popular hake sold in the northeast United States.|
|Major Threat(s):||This species has been commercially exploited for many years and as a result, populations have shown evidence of overfishing.|
|Conservation Actions:||In U.S waters, this species came under management via the New England Fishery Management Council’s Northeast Multispecies Fishery Management Plan following passage of the Magnuson Fishery Conservation and Management Act in 1977. This action also caused the exclusion of foreign fleets which effectively reduced effort in the Silver Hake fishery. In 2000, bag limits on the small-mesh multispecies fishery were implemented based on net mesh size and gear restrictions to reduce bycatch were set. Recently, the council established annual catch limits and accountability measures for the fishery. In addition to these regulations, fishermen must undergo a permitting process, there is a cap on the amount of bycatch that each vessel may take, and the fishing itself is limited seasonally and spatially. In Canadian waters, the annual landings quota has been set at 15,000 metric tonnes since 2003 and the fishery is monitored by the Canadian Division of Fisheries and Oceans. The Canadian fleet is also required to use certain gear types aimed at reducing bycatch.|
|Citation:||Carpenter, K.E. 2015. Merluccius bilinearis. The IUCN Red List of Threatened Species 2015: e.T16466393A16509787.Downloaded on 16 October 2018.|
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