Roughhead grenadier (Macrourus berglax) COSEWIC assessment and status report: chapter 8

Area Occupied

The area occupied by roughhead grenadier was estimated based on catches in the Canadian fall survey of NAFO Divisions 2GHJ3KLMNO. The method is outlined in Appendix B. Because this survey does not cover all grounds inhabited by this species in the waters off Atlantic and Arctic Canada, the values reported here will be underestimates.

Estimates are based on the surveys in 1996-1999, a period with wide survey coverage in the 2GHJ3KLMNO area. The area covered by these surveys varied by about 10% from year to year (Table 1) and no attempt was made to adjust for this variation. The area occupied by roughhead grenadier within the survey area varied between 119,500 and 129,100 km² (Table 1).

The analysis was repeated for adult females. All fish longer than 275 mm AFL were assumed to be adult females. The area covered by this analysis was reduced by about 15% due to the omission of tows with no length frequencies. The estimated area occupied by adult females was 13,300 – 21,550 km² (Table 1).

Table 1.  Area occupied (1000s km²) by roughhead grenadier (all sizes or adult female sizes) in the fall survey of NAFO Divisions 2GHJ3KLMNO in selected years with broad survey coverage.
Year All sizes
Surveyed
All sizes
Occupied
Adult females
Surveyed
Adult females
Occupied
1996
634.4
129.1
495.0
13.8
1997
562.8
119.5
496.2
13.3
1998
594.0
124.1
504.2
21.6
1999
572.1
121.1
474.5
15.7

In order to examine trends in area occupied, an analysis was conducted using a subset of “index” strata that were sampled in most years in the fall survey of areas 2J and 3K. Strata selection and summary data for these strata were kindly provided by M. Koen-Alonso and F. Mowbray (DFO St. John’s, pers. comm.). The area covered by this set of index strata varied little from year to year except for an increase in area in 1996 associated with the addition of deepwater (>1000 m) strata to the survey (Figure 14). Area occupied within this subset of strata declined steadily throughout the1980s and early 1990s but has been roughly stable since 1995 (Figure 14).

Figure 14. Area occupied by roughhead grenadier within a subset of index strata in the fall survey of NAFO Divisions 2J and 3K. The line shows the total area surveyed each year, circles show the area occupied by grenadiers (open circles – years fished by the Engels trawl, closed circles – years fished by the Campelen trawl).

Figure 14.  Area occupied by roughhead grenadier within a subset of index strata in the fall survey of NAFO Divisions 2J and 3K. The line shows the total area surveyed each year, circles show the area occupied by grenadiers (open circles – years fished by the Engels trawl, closed circles – years fished by the Campelen trawl).

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