Rougheye rockfish species types I and II COSEWIC assessment and status report: chapter 2

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Species Information

Rougheye rockfish, Sebastes aleutianus (Jordan and Evermann, 1898) (sébaste à oeil épineux) belongs to the family Scorpaenidae. The name “rougheye” refers to a series of suborbital spines (along the lower rim of the eyes).

The described species includes two recently-discovered sympatric species, separable on the basis of allozymes and microsatellite and mitochondrial DNA. Morphologically, the two species may be distinguishable by gillraker number and length and relative body depth, but they are difficult to separate under field conditions. There is no detailed information on relative abundance, distribution, or impact of fisheries for the two species in Canadian waters. Accordingly it is assumed that available information on rougheye rockfish, Sebastes aleutianus (Jordan and Evermann, 1898) applies equally to each of the two new species.

To recognize the existence of two species without prejudging results of a future taxonomic revision that will formally name them, this report refers to Sebastes sp. type I (rougheye rockfish type I) and Sebastes sp. type II (rougheye rockfish type II), consistent with recent publications. Reference to information which does not distinguish the two species uses the term “species pair” or refers to the entity formally described: rougheye rockfish, Sebastes aleutianus (Jordan and Evermann, 1898).

Distribution

Rougheye rockfishes of this species pair occur in the Pacific Ocean north of Japan from the Kamchatka Peninsula to the Bering Sea, the Aleutian Islands, Gulf of Alaska, and the west coast of North America from British Columbia to southern California. In British Columbia (BC), they occur along the continental slope, and are typically captured at depths between 170 and 660 m. The estimated extent of occurrence in BC covers approximately 37 000 km². The relative distribution and abundance of the two newly-identified species in Canadian waters is unknown.

Habitat

Highest densities of rougheye rockfishes occur on bottoms with soft substrates, in areas with frequent boulders, and on slopes greater than 20° (observed via manned submersibles). The association with soft substrates coincides with the availability of preferred prey items (pandalid shrimps). Boulders may act as territorial markers, current deflectors, or structures to enhance prey capture. This species pair apparently avoids flat bottoms.

Biology

The biology of the two species in the rougheye rockfish species pair remains poorly known. Longevity exceeds that for most other Sebastes species, with a maximum age recorded anywhere of 205 years for a specimen from southern Alaska. Adults reach a maximum length of approximately 90 cm. Females are 20 years old at 50% maturity. Like all viviparous Sebastes species, fertilized eggs remain within the ovary until larval extrusion. Planktonic larvae and juveniles occur near the surface and at midwater depths. The calculation for generation time appropriate for this species pair yields 48 years, assuming an age at 50% maturity of 20 years and a natural mortality rate of 0.035.

Population Sizes and Trends

Commercial catch per unit effort (CPUE) indices computed over the years 1996-2005 for the rougheye rockfish species pair show little trend. Survey index trends are generally without trend or increasing; however, these series cover periods substantially less than the generation time of rougheye rockfishes. In addition, most of the longer time series were designed with other species in mind and do not cover suitable depth ranges. The large error bars associated with index points reflect the limitations of these surveys and indicate highly uncertain trends. Indices from the Queen Charlotte Sound synoptic groundfish survey (2003-2005) will describe abundance trends with reliable measures of error once the survey series covers longer time periods.

Limiting Factors and Threats

The primary threat to the BC population stems from overfishing a long-lived species that inhabits the continental shelf and upper slope. The observed decline of older age classes (50+) in the 2003 data compared to 1996 may reflect the effect of fishing pressure, and catch curve analysis indicates that the mean total mortality over these eight years has doubled from 0.045 to 0.091.  However, non-representative catch sampling from the commercial fishery may account for some of the perceived difference in proportion-at-age data.

The lack of information on relative abundance, distribution and threats for the two recently-identified species within the species pair constitutes a threat, since the existence of cryptic species of this sort increases the risk of loss of unrecognized biological diversity.

Special Significance of the Species

Rougheye rockfishes are possibly among the longest lived fish species on earth. In Alaska, scientists aged one specimen to 205 years. Early Aboriginal fisheries probably captured rougheye rockfishes with halibut and sablefish, but no records exist to verify this. The existence of two cryptic species within the complex recognized as rougheye rockfish, Sebastes aleutianus (Jordan and Evermann, 1898) is of considerable scientific interest with respect to speciation mechanisms.

Existing Protection

Fisheries management controls removals of this species pair through coastwide quotas that are administered through an individual-vessel-quota system. The preferred bottom types of rougheye rockfishes – steep-slope, boulder habitats – may act as potential deterrents to fishing, at least from bottom trawling. Longline gear can presumably access these sites. The depth preference of this species pair limits its exposure to recreational harvest. There is no official habitat protection for this species pair.