Roughhead grenadier (Macrourus berglax) COSEWIC assessment and status report: chapter 2

Executive Summary

Roughhead Grenadier
Macrourus Berglax

Species information

The roughhead grenadier belongs to the family Macrouridae, which as a group are often referred to as rattails. It is distinguished from similar species in the North Atlantic by its fairly broad head exhibiting ridges with scute-like scales bearing strong spinules that provide it with its common name. In this report,roughhead grenadier are treated as a single designatable unit in Atlantic Canada (including the Flemish Cap and other waters beyond the 200-mile limit).

Distribution

The roughhead grenadier is found in temperate to arctic waters of the North Atlantic generally on or near the continental slope. In the waters off Canada, roughhead grenadier have been observed from the Davis Strait to Georges Bank, but are most commonly found along the slope of the Labrador and Northeast Newfoundland Shelves, the northeastern slope of the Grand Bank and off the Flemish Cap. The range of the roughhead grenadier in the Northwest Atlantic extends beyond the 200-mile limit and outside Canada’s jurisdiction. As a straddling stock, it is assessed and managed by the Northwest Atlantic Fisheries Organization (NAFO).

Habitat

The roughhead grenadier is a benthopelagic species commonly occurring at depths between 400 and 1200 metres (m), although they may inhabit depths between 200 - 2000 m. In the waters off Newfoundland, densities tend to be highest at depths of about 500 – 1500 m. Their distribution extends beyond the offshore and northern limits of the annual monitoring surveys that are used to assess trends in marine fish abundance. 

Biology

M. berglax has a low fecundity, slow growth rate, late maturation, and low population turnover rate. Females mature at approximately 13 to 15 years and reach a maximum age of 25 years. Generation time is calculated to be 19 years. Recent estimates of their instantaneous rate of total mortality, 0.34 for females and 0.71 for males, are rather high in light of what is known of life history and fishing pressure, and instantaneous rate of natural mortality is assumed to be 0.2. They are generally found in water temperatures between 2.0 and 5.4 ºC. Roughhead grenadiers are non-specialist predators. The food type consumed by this species is usually dependent on the size of the individual fish, but includes a wide variety of invertebrates and some fish.

Population sizes and trends

Catch rates of roughhead grenadier in the Canadian bottom-trawl surveys of the Grand Bank and Newfoundland Shelf were roughly stable in the 1970s, declined precipitously in the 1980s, and have been stable or increasing slightly since the early to mid-1990s. The declines in the 1980s amounted to 90 – 95% declines over 10 – 15 yr. The extent to which these declines in survey catch rates reflect declines in population abundance is unclear. Densities of roughhead grenadier are greatest along and beyond the offshore margin of the areas covered by these surveys. The decline in survey catch rates coincided with a shift in distribution to the deep strata along the offshore margin of the survey area. In the 1970s and 1980s, grenadier density declined to relatively low levels in the deepest waters sampled; in the 1990s and 2000s, density remained near peak levels in these deep waters. This strongly suggests that there has been a decline in availability of roughhead grenadiers to the survey, and that the declines in survey catch rates overestimate population declines.

The NAFO assessment focuses on recent population trends (since 1995). In addition to the Canadian surveys, it considers European surveys of the Flemish Cap and the southern Grand Bank, conducted since 1988 and 1997, respectively. The most recent NAFO assessment concluded that biomass in 2004 was the highest in the time series from 1995.

Minimum population estimates based on catches in the Canadian fall survey in recent years average 102 million for all sizes and 1.4 million for adult females. These are likely underestimates, since catchability is probably less than 100% and only part of the distribution is covered by the surveys.

Limiting factors and threats

M. berglax have been subject to commercial exploitation mostly as by-catch in the Greenland halibut fishery. Catches of roughhead grenadiers in this fishery increased between 1989 and 1990. Low fecundity, slow maturity, and long life limit the species’ potential for recovery following a disturbance.

Special significance of the species

Macrourus berglax is the only species in the North Atlantic that belongs to this genus. There are only three other Macrourus species in the world; M. carinatus, M. holotrachys, and M. whitsoni, all from the southern hemisphere.

Existing protection or other status designations

The fishery for M. berglax is unregulated because it is mainly taken as incidental catch in fisheries targetting other species. The roughhead grenadier is not currently protected by any legislation or regulation and it has no status under any other species protection conventions.

COSEWIC History

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) was created in 1977 as a result of a recommendation at the Federal-Provincial Wildlife Conference held in 1976. It arose from the need for a single, official, scientifically sound, national listing of wildlife species at risk. In 1978, COSEWIC designated its first species and produced its first list of Canadian species at risk. Species designated at meetings of the full committee are added to the list. On June 5, 2003, the Species at Risk Act (SARA) was proclaimed. SARA establishes COSEWIC as an advisory body ensuring that species will continue to be assessed under a rigorous and independent scientific process.

COSEWIC Mandate

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) assesses the national status of wild species, subspecies, varieties, or other designatable units that are considered to be at risk in Canada. Designations are made on native species for the following taxonomic groups: mammals, birds, reptiles, amphibians, fishes, arthropods, molluscs, vascular plants, mosses, and lichens.

COSEWIC Membership

COSEWIC comprises members from each provincial and territorial government wildlife agency, four federal entities (Canadian Wildlife Service, Parks Canada Agency, Department of Fisheries and Oceans, and the Federal Biodiversity Information Partnership, chaired by the Canadian Museum of Nature), three non-government science members and the co-chairs of the species specialist subcommittees and the Aboriginal Traditional Knowledge subcommittee. The Committee meets to consider status reports on candidate species.

Definitions

Wildlife Species
A species, subspecies, variety, or geographically or genetically distinct population of animal, plant or other organism, other than a bacterium or virus, that is wild by nature and is either native to Canada or has extended its range into Canada without human intervention and has been present in Canada for at least 50 years.

Extinct (X)
A wildlife species that no longer exists.

Extirpated (XT)
A wildlife species no longer existing in the wild in Canada, but occurring elsewhere.

Endangered (E)
A wildlife species facing imminent extirpation or extinction.

Threatened (T)
A wildlife species likely to become endangered if limiting factors are not reversed.

Special Concern (SC)Footnotea
A wildlife species that may become a threatened or an endangered species because of a combination of biological characteristics and identified threats.

Not at Risk (NAR)Footnoteb
A wildlife species that has been evaluated and found to be not at risk of extinction given the current circumstances.

Data Deficient (DD)Footnotec
A category that applies when the available information is insufficient (a) to resolve a species' eligibility for assessment or (b) to permit an assessment of the species' risk of extinction.

 

Canadian Wildlife Service

The Canadian Wildlife Service, Environment Canada, provides full administrative and financial support to the COSEWIC Secretariat.

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