Longspine thornyhead (Sebastolobus altivelis) COSEWIC assessment and status report: chapter 2

Executive Summary

Longspine thornyhead
Sebastolobus altivelis

Species information

Longspine thornyhead (Sebastolobus altivelis Gilbert 1893) belongs to the scorpionfish family. This species exhibits red colouration with some black on the fins. The elongate body reaches 35 cm in length, with large eyes and strong, sharp head spines.

Distribution

The species ranges from Cape San Lucas, Baja California, to the Aleutian Islands at depths from 370 m to 1600 m. In British Columbia (BC), they occur along the continental slope at depths between 500 and 1,600 m. The estimated extent of occurrence is 17,775 km²; the observed area of occupancy is 11,700 km².

Habitat

The species prefers soft sand or mud bottoms in deep-water environments characterized by low productivity, high pressure, and reduced oxygen concentrations.

Biology

In spring, females release fertilized eggs in a gelatinous matrix that floats to the surface. Here, the eggs hatch and the larvae and early stage juveniles remain in the upper 200 m for 6 months. As the juveniles mature, they occur progressively deeper, generally remaining in the mesopelagic zone (~600 m) for one year. Eventually, young fish settle directly into adult habitat at 600-1,200 m. Juveniles eat euphausiids; adults target brittle stars and other benthic fauna. Longspine thornyheads have adaptations that allow them to live in deep water where oxygen is low and pressure is high. Assuming an age at 50% maturity of 20 years and a natural mortality of 0.10, the calculation of generation time yields 30 years.

Population sizes and trends

The bulk of the longspine thornyhead biomass lives in the fisheries management region WCVI (west coast Vancouver Island), with two smaller known populations in the Tidemarks and Rennell regions further north. These populations may be continuous. Commercial trawl CPUE (catch per unit effort) indices declined 8%, 9%, and 20% in WCVI (1996-2004), Tidemarks (2000-2004), and Rennell (2000-2004), respectively. A weighted coastwide index declined by 50% over eight years.  Although factors other than abundance changes probably influence the commercial CPUE index, this is considered a reasonably accurate index of population abundance.  Estimation of a “three generation” change for this population based on results from short time series remains uncertain as time series of observations are short and forward projection would depend on assumptions about future fisheries management.

Limiting factors and threats

The primary threat to the population stems from overfishing a deep-water species that occupies a low-productivity environment. Since the inception of the targeted commercial fishery in 1996 off the WCVI, most indices have exhibited a substantial decline. This may be consistent with the “fishing-down” of a previously unexploited species (removal of accumulated biomass, theoretically associated with increased productivity due to reduced density), since this species was not subject to exploitation prior to this time.  Recent reports from the industry suggest that the longspine thornyhead fishery has become less commercially attractive due to falling market prices for thornyheads, increasing fuel costs, and the high exchange rate for the Canadian dollar, but it is impossible to predict future conditions in the fishery.

Special significance of the species

In Canada’s Pacific waters, the predominant fish species in the deep benthic waters (>800 m) include the longspine thornyhead, which likely plays a significant ecological role within this environment. Longspine thornyheads caught in Canada are exported to Japan where they are considered a delicacy.

Existing protection

Currently, fisheries management has closed the Flamingo region (west coast of Moresby Island) to all directed trawling on longspine thornyhead. Despite steep bathymetry, this region contains some potentially large areas of suitable habitat. Additionally, the management region Triangle experiences no fishing pressure due to steep and rough terrain.  The fishery management plan does not include a strategy for adjusting exploitation in response to changing abundance.

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

Species
Any indigenous species, subspecies, variety, or geographically defined population of wild fauna and flora.

Extinct (X)
A species that no longer exists.

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

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

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

Special Concern (SC)*
A species of special concern because of characteristics that make it particularly sensitive to human activities or natural events.

Not at Risk (NAR)**
A species that has been evaluated and found to be not at risk.

Data Deficient (DD) ***
A species for which there is insufficient scientific information to support status designation.

* Formerly described as “Vulnerable” from 1990 to 1999, or “Rare” prior to 1990.
** Formerly described as “Not In Any Category”, or “No Designation Required.”
*** Formerly described as “Indeterminate” from 1994 to 1999 or “ISIBD” (insufficient scientific information on which to base a designation) prior to 1994.

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.

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

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