Bocaccio (Sebastes paucispinis) COSEWIC assessment and status report: chapter 8

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Biology

• General
• Reproduction/Life History
• Growth
• Survival
• Physiology
• Movements/Dispersal
• Nutrition and Interspecific Interactions
• Behaviour/Adaptability

General

There has been very little directed research on bocaccio in B.C. waters. GFBio, the groundfish specimen database of Fisheries and Oceans contains information on only 1503 specimens collected from 1967-2000 (Table 4). These data were collected from all regions, in different seasons, with different gears, and from both research and commercial catches. There is obviously not enough information to examine trends in mean size. The available data, however, are sufficient to indicate that most bocaccio caught during trawling are nearly fully grown and well above the acceptable market size limit for rockfish of approximately 32 cm (Fig. figure11 and figure12). There are virtually no age data from Canadian specimens. Most of the biological research on this species was conducted in California.

Figure 11: Cumulative Length-frequency Histogram of All Bocaccio Lengths from the Groundfish Biological Database (GFBio)

Figure 12: Von Bertalanffy Growth Curves for Male and Female Bocaccio

Parameters for males and females respectively are: L∝ = 76.6, 87.8; K = 0.130, 0.110; t₀ = -1.81, -1.73 (from Froese and Pauly 2000).

Reproduction/Life History

Bocaccio are ovoviviparous like all members of their genus. Copulation occurs in the early fall (Moser 1967) but there is delayed fertilization (Wyllie Echeverria 1987). The fertilized eggs are retained in the body of the female where the larvae undergo much of their development prior to release. Fecundity ranges from 20 000 to 2 300 000 eggs and increases with size of the female (Phillips 1964). Embryonic development takes approximately one month (Moser 1967).

Parturition occurs in the winter in B.C. waters (Westrheim 1975). More southern populations appear to have a longer period of parturition and may also release multiple broods in a single year (Moser 1967). Settlement to the littoral-demersal habitat begins in late spring in California and extends throughout the summer. Estimates of length at 50% maturity for females have varied from 36 to 50 cm in three different U.S. studies (Haldorson and Love 1991). Rogers (1995) suggests an age of between 4 and 5 years for the age of 50% maturity.

Growth

At the time of parturition, larvae are approximately 4-5 mm in length (Moser 1967). The larvae metamorphose into pelagic juveniles at between 19 and 40 mm over several months (Moser 1967, Moser and Boehlert 1991, Woodbury and Ralston 1991). Growth of juveniles is rapid at 0.56-0.97 mm/day (Love et al. 2002). They can reach 24 cm by the end of their first year (MacCall et al. 1999). Females grow to a larger size than males. The maximum recorded length is 91 cm for females and 75 cm for males. The maximum reported weight is 6.8 kg (Love et al. 2002). Growth curves are shown in Figure 12 (Froese and Pauly 2000).

Survival

Little is known about the mortality rates of younger stages. MacCall et al. (1999) used a range of 0.15-0.25 for the estimate of adult instantaneous natural mortality rate (M). Their model tended to indicate a better fit at M=0.20, but the fit was sensitive to which input data were used. Bocaccio are difficult to age and their maximum age is unknown. Radiometric dating of otoliths has supported an estimated maximum age of 40 but they may live as long as 50 years (Love et al. 2002). The estimates of M, age at maturity, and maximum age imply a generation time of about 9 years (4+1/0.2). Thus, a 3-generation window for assessing extinction risk would be about 27 years.

Physiology

Like all species in the genus, bocaccio have physoclistic swim bladders that cannot rapidly accommodate the sudden change in pressure as they are brought to the surface. The resulting barotrauma causes death for almost all fish when captured from waters deeper than 20-30 m (Starr et al. 2002). Little is known about their adaptability to other types of environmental change.

Movements/Dispersal

There have been two tagging studies of bocaccio off California. During a 1977-1981 study, 1149 juvenile and adult bocaccio were tagged (Hartman 1987). Of these, 66 bocaccio were recaptured. Nineteen traveled 0.9 to 148 km. Seven of these, all juveniles, traveled from 13 to 148 km. The adults tagged during that study moved very little; all were recaptured at their tagging site after periods at liberty of up to 827 days.

Starr et al. (2002) tagged 16 bocaccio, ranging in size from 35 to 58 cm, during a 1997-1998 study. Some of these showed site fidelity by remaining within the study area or by leaving and returning, while others moved large distances during the 3.5-month monitoring period. The authors suggested the sample size was too small to analyze movements by fish length or state of maturity. The results of these two studies indicate that bocaccio are mobile during the first few years of life but are perhaps more sedentary with age. Movement appears to decrease significantly after they reach a length of about 47 cm (Hartmann 1987).

Also in the 1997-1998 study, eight bocaccio were fitted with depth transmitters. Four of the fish made rapid vertical movements. Three of these rose vertically to near the surface and then returned to depth while the fourth fish dove to 220 m and rose back to 100 m in less than one day.

Nutrition and Interspecific Interactions

Based on feeding studies conducted in California, bocaccio are primarily piscivorous. Juveniles feed on the young of other rockfishes, surfperches, mackerel and various other small inshore fishes (Phillips 1964). They also consume larvae and euphausiids. The adult diet includes rockfishes, sablefish, anchovies, lanternfishes and squids (Phillips 1964, Eschmeyer et al. 1983). The main predators of juvenile bocaccio are sea birds such as least terns. The main predators of adults are marine mammals such as harbor seals and northern elephant seals (Love 1996).

Jensen (1976) comments that bocaccio may be the only host of one species of tapeworm, Parabothriocephalus sagitticeps. It is one of two tapeworm species in this genus. These conclusions were based on an examination of 19 species of rockfish captured in southern California. The presence of this parasite has not been confirmed in B.C. waters, however, no one has looked specifically for this tapeworm (D. Whitaker, pers. comm. Appendix 1). A second tapeworm, Bothriocephalus scorpii, has been reported in bocaccio from B.C. waters.

The reputation of “worminess” for this species in B.C. specimens results from a high prevalence and intensity of infection of a “cod/seal worm” or nematode (Phocanema decipiens). Once encysted it can live for long periods in the fish and is therefore accumulated by the fish over time such that an older fish can carry large numbers of the worm. Because the final host is a mammal (seal), it is a parasite that can be a human-health concern. However, freezing at –20° C for 72 hr, or cooking, removes that concern (D. Whitaker, pers. comm. Appendix 1).

Behaviour/Adaptability

The semi-pelagic distribution in the water-column, the likelihood of daily vertical migration, and the degree of movement by juvenile stages implies that bocaccio can respond to localized habitat disruption. This movement may also facilitate re-colonization, at least by juvenile stages, as would the larval planktonic phase.