Aquatic Species at Risk - Longspine Thornyhead

Description

Longspine thornyhead, a rockfish species belonging to the scorpionfish family, is a slow growing fish that is adapted for survival in deep waters where oxygen concentrations are minimal and water pressure is high. In Canada’s Pacific waters, longspine thornyheads dominate the fish species that live in deep benthic waters (> 800 metres below the surface), and likely play a significant ecological role within this environment. This species has a reddish body and some black on its fins, grows to 35 cm in length, and features large eyes and strong, sharp head spines.

Credit: NOAA

Distribution & Population

Longspine thornyhead lives in the Pacific Ocean where it ranges from the southern tip of Baja California in Mexico up to the Aleutian Islands of Alaska, at depths from 370 m to 1600 m. In British Columbia this species occurs along the continental slope at depths between 500 and 1,600 m. The predominant population group can be found in DFO fisheries management region WCVI (West Coast Vancouver Island), with two smaller observed groupings in the Tidemarks and Rennell regions further north.

Although the absolute population level remains unknown, approximately 6,500 t of longspine thornyhead were captured from Canadian waters during the period 1996-2005.

Credit: NOAA

Habitat

The species prefers soft sand or mud bottoms in deep-water environments characterized by low productivity (slow growth), high pressure, and reduced oxygen concentrations. At these depths, where few species can survive, there is limited food available. Deep-water longspine thornyheads have adapted to this environment with extremely slow metabolisms and sedentary natures that allow them to wait an average of 130 to 180 days between feedings.

Biology

In spring, females release 20,000 to 450,000 fertilized eggs embedded in a gelatinous mass that floats to the surface. Here, the eggs hatch and the larvae and early stage juveniles remain in the upper 200 m of water for 6 months. As the juveniles mature they go progressively deeper, and generally remain at depths around 600 m for one year. Eventually, young fish settle directly into adult habitat at 600-1,200 m. Juveniles eat krill; adults target brittle stars and other species found on the ocean bottom. Larger longspine thornyheads regularly prey upon smaller ones.

Longspine thornyheads stop growing at a length of about 30 cm and an estimated age of 25 to 45 years. It is not yet known how long longspine thornyheads can live, although estimates range from 45 to 70 years.

Threats

The primary threat to the population stems from overfishing a deep-water species that occupies a low-productivity environment. Longspine thornyheads caught in Canada are typically exported to Japan where they are considered a delicacy.

Since the beginning of the targeted commercial fishery in 1996 there has been a substantial decline in the commercial catch per unit effort of over 50% in 8 years.

Protection

The Longspine Thornyhead Rockfish is listed as Special Concern under the Species at Risk Act (SARA). It also receives protection under the Fisheries Act and total allowable catches broken down by area and fleet are in place for longspine thornyhead. Fisheries management has closed the Flamingo region (west coast of Moresby Island) to all directed trawling on longspine thornyhead. There is also no trawling activity in the region known as Triangle due to the steepness and roughness of the bottom topography. As well, commercial trawlers do not usually fish at depths greater than 1,200 m, while longspine thornyheads were found to exist in waters as deep as 1,600 m (from 1996-2005).

What’s being done

A management plan for the longspine thornyhead rockfish will be developed by March 2012.

Profile is based on:
COSEWIC 2007. COSEWIC assessment and status report on the longspine thornyhead Sebastolobus altivelis in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. vi + 27 pp. (www.sararegistry.gc.ca/species/speciesDetails_e.cfm?sid=985#ot18).