Canary rockfish (Sebastes pinniger) COSEWIC assessment and status report: chapter 8
Biology
Aging of canary rockfish is currently conducted with the break-and-burn method (MacLellan 1997). While the method is imprecise (Stanley 1999), recent analyses of B.C. canary rockfish specimens using lead-radium dating and a bomb radiocarbon chronometer indicated that the method is unbiased (Allen Andrews, pers. comm.). Maximum observed age for canary rockfish from B.C. waters is 77 and 84 for females and males, respectively (Fig. 5). Females grow faster, but older females are relatively rare in the samples (Figs. 5 to 8). The maximum length observed in B.C. samples is 68 cm for both sexes. U.S. data indicate a trend of increasing size-at-age with increasing latitude (Methot and Stewart 2005) (further analyses of length and age data are provided on pages 38-45).
The reason for the more truncated age composition of the females is unknown. It has also been observed in yellowtail rockfish (S. flavidus). Early assessments of both of these species entertained the possibilities that it was caused by an increasing rate of natural mortality with age in females or, decreasing selectivity/availability/vulnerability for older females in the fishery, or both. Most recent assessments attribute the effect to increasing M with age. Models appear to obtain their best fit if M is allowed to increase rapidly coincident with the age of maturation (see Methot and Stewart 2005). There is no evidence that the absence of older females is caused by higher F at earlier ages since the sexes appear to enter the fishery in equal proportions. There are also no reports of spatial refugia or a gear selectivity bias that could cause this effect.
Figure 5: Histogram of canary rockfish ages (cutoff at 80y): (a) Females from Area 3C+3D; (b) Males from Area 3C+3D; (c) Females from Area 5A+5B; (d) Males from Area 5A+5B
Data from 5E are omitted owing to the large gap in years between samples, see Fig.8.
The maximum observed weight for this species was a male of 5.70 kg. The average weight in commercial samples is 2.03 kg. Fish appear in small numbers at age five in the fishery but the age of full recruitment is probably about 13 or 14 y (Figs. 5 to 8).
Figure 6: Proportions-at-age by year for (A) female and (B) male canary rockfish from Area 3C+3D
The radius of each circle is scaled relative to the proportion-at-age within each sex, age 30 = 30+ group. Commercial and survey samples combined.
Figure 7: Proportions-at-age by year for (A) female and (B) male canary rockfish from Area 5A+5B
The radius of each circle is scaled relative to the proportion-at-age within each sex, age 30 = 30+ group. Commercial and survey samples combined (see Table 9).
Figure 8: Proportions-at-age by year for (A) female and (B) male canary rockfish from Area 5E
The radius of each circle is scaled relative to the proportion-at-age within each sex, age 30 = 30+ group. Commercial and survey samples combined (see Table 7).
Stanley (1999) reviewed the existing information on estimates of M and suggested plausible ranges of 0.02-0.04 for males and 0.06-0.08 for females. However, most catch-at-age analyses (Stanley and Haist 1997, Methot and Piner 2001, Methot and Stewart 2005) obtain the best model fits when female M is allowed to increase coincident with reproductive maturation. The current U.S. assessment fixes M for males and young females at 0.06, and then allows the model to fit a linear increase in M to age 14. To calculate the generation time for females, the U.S. assessment uses an age-averaged value of 0.09.
Some female canary rockfish in B.C. waters are mature at 8 y but 50% and 100% maturity occurs at about 13 y and 20 y, respectively (Fig. 9). Based on an estimate of an age-averaged M between 0.06 and 0.15, the generation time for canary rockfish lies between 20 and 30 y (A50% + 1/M). The current U.S. assessment assumes that M=0.09 and A50% = 8 y to derive a generation time of 22.8 y (Methot and Stewart 2005).
The live-bearing females undergo parturition from January-March in B.C. waters (Westrheim 1975). Fecundity in California specimens ranged from 260 000-1 900 000 (Love et al. 2002). Males in B.C. waters appear to be 50% mature at 7-8 y and 100% mature at about 15 y (Fig. 9).
Figure 9: Age-at-maturity for (A) female and (B) male canary rockfish
Love et al. (2002) report that pelagic juveniles are diurnal feeders on a diverse array of prey items. Adults and sub-adults primarily eat krill and small fishes. Herring and sandlance are probably important in B.C. waters, but no diet studies have been conducted. Predators are unknown; however, port sampling observations indicate that lingcod prey heavily on rockfish species.
There has been no directed work on the physiology of canary rockfish. Like other rockfish, they have physoclistic swim bladders (no direct opening) and typically die from barotrauma if released after typical fishing procedures.
No tagging studies have been conducted in B.C. waters. DeMott (1983) recovered 23 individuals from 348 tagged off Oregon in 1983. No information is available on the sizes which were tagged, but nine individuals moved more than 100 km south, with one moving 236 km to the south and offshore. Three moved more than 100 km to the north; one of the three moved 142 km. The tagging took place between June 1978 and September 1980; the recovery period was from June 1978 to January 1982. Trawl catches indicate a seasonal depth migration from 160-210 m in late winter to 100-170 m in late summer (data source: PacHarvTrawl).
The role and importance of canary rockfish in the ecosystem has not been directly examined. It is one of many rockfish species in B.C. waters. There is no basis for assuming canary rockfish are a “keystone” species, but large variations in canary rockfish abundance may have an unknown level of impact on specific elements of the ecosystem.
There is no information available on the adaptability of canary rockfish.
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