Roughhead grenadier (Macrourus berglax) COSEWIC assessment and status report: chapter 9

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Limiting Factors and Threats

M. berglax is susceptible to mortality caused by humans because of its life-history traits. These include the characters already mentioned: long life span, late maturity, slow growth rates, and long population turnover time, which make recovery subsequent to a reduction in the population probably difficult for this species.

Of the nine species of grenadiers found in the Canadian Atlantic region, only two are commercially exploited (Cohen et al. 1990). These are the roundnose grenadier (Coryphaenoides rupestris) and the roughhead grenadier. They are fished almost entirely by the Portuguese and Spanish in the Northwest Atlantic. The liver is prized for canning and for production of medicinal oil.

Roughhead grenadier is an unregulated species mainly taken as by-catch in the Greenland halibut fishery (Murua 2001). Duran et al. (1997) found that roughhead grenadier was one of the most important by-catch species in the Spanish Greenland halibut fishery from 1991 to 1994 in NAFO Divisions 3LMNO. Between these years the annual yield was between 29 and 48 kg/hr for large vessels. This same study found that the roughhead and roundnose grenadiers were the dominant species discarded. Little is known about the sex and age of commercial catches; however, in 2002 only about 4% of the catch in abundance and 20% in weight was above the female age at maturity (Murua 2003).

The revised catch history from 1987 to 2004 is presented in Table 2 (González-Costas & Murua 2005). Catches reported in this table are corrected for misreporting of roughhead grenadiers as roundnose grenadiers by Spain in 1992-1996. Catches increased sharply between 1989 and 1990. Estimated catches fluctuated between about 3000 and 4500 tonnes (t) from 1990 to 2004, except for catches near 7000 t in 1992, 1998 and 1999.

Catches for years prior to 1987 have not been reported in recent assessments of roughhead grenadier. The main fisheries catching this species in earlier years would have been the fisheries for roundnose grenadier and Greenland halibut (D. Power and D. Kulka, pers. comm.). Roundnose grenadier catches dropped sharply in 1979 (D. Power, pers. comm.), following the extension of jurisdiction by Canada in 1977. If this reflects a drop in effort, the by-catch of roughhead grenadier in this fishery would have been much lower in the 1980s than in the 1967 – 1978 period. Catches of Greenland halibut in NAFO Sub-area 2 and Divisions 3KLMNO rose sharply in the 1960s, fluctuated between about 30,000 – 40,000 t in the 1970s and early 1980s, declined to about 20,000 t in the mid- to late 1980s, increased to 50,000 – 60,000 t in 1990-1994, and then declined to lower levels (Healey and Mahé 2005). Estimated fishing mortality of Greenland halibut also declined throughout the 1980s before increasing sharply in the early 1990s (Healey and Mahé 2005).

In summary, the sharp decline in survey catch rates in the 1980s – early 1990s began at a time when catches and effort in the main fisheries with by-catch of roughhead grenadiers were lower than in earlier and later periods. This suggests that the declining catch rates of roughhead grenadier in the research surveys in the 1980s were not initiated by increased by-catch in fisheries. Based on estimated fishing mortality (Healey and Mahé 2005), effort in the Greenland halibut fishery increased sharply in the early 1990s and may have contributed to declines in roughhead grenadier at that time. Fishing mortality of Greenland halibut in NAFO Sub-area 2 and Divisions 3KLMNO declined to lower levels in the mid-1990s but has since returned to record high levels (Healey and Mahé 2005); that fishing may have contributed to latter part of the decline. Population modelling and a detailed analysis of fishery observer data are needed to assess the impact of fishery removals on roughhead grenadier more fully. Such analyses are beyond the scope of this report.