CRD 01-16
APPENDIX
3
SUMMARY
OF AVAILABLE INFORMATION ON NORTH ATLANTIC RIGHT WHALE REPRODUCTION
|
| Reproductive parameter
|
Result/Conclusion |
Caveats |
Source |
Cf Southern Hemisphere |
|
Calving interval
|
Regression of observed calving intervals against
year shows significant increase from 1985 to 1998.
Mean 3.67 yrs (1980-1992), over 5 yrs (1996-98). |
Observed intervals only. Some of longer intervals
undoubtedly represent unobserved calvings (12/20 or 60% of 6-7 yr intervals).
But intervals between sightings of adult females similar in 1980s and 1990s.
|
Kraus et al (in press) |
|
|
|
Mean calving interval (likelihood model) 3.28
± 0.24 yrs in 1980s, 4.44 ± 0.43 yrs in 1990s.
Distribution of calving intervals shifted from 3-year
intervals in 1980s to 5+ intervals in 1990s, 4-year intervals unchanged. |
Annual sighting probabilities estimated to
have been close to 100% in recent years.
Shift in calving interval distribution consistent with increased
pre- or neonatal mortality in 1990s (2-yr intervals). |
Cooke & Glinka (SC/O99/RW1) |
3.26 ± 0.14 yrs in 1970s,
3.43 ± 0.14 yrs in 1980s (Cooke & Glinka)
|
|
|
|
Analysis does not include mature females that
have calved only once or not at all, so actual intervals are likely to be
even longer. |
SC/O99/Report |
|
|
%age of mature females that are reproductively
active
|
70% |
Potentially biassed low due to missed calvings
and some females reaching sexual maturity after 9 years of age. |
SC/O99/Report |
|
|
Average annual calf production rate per
mature female
|
12.94% |
Refers to 1990s B may well have been higher
in 1980s but not possible to estimate. Fluctuates substantially from year
to year. |
SC/O99/Report |
More than double that in N Atlantic (SC/O99/Report) |
|
|
Average annual calf production about 40% of
expected. |
Derivation unclear. |
White et al (SC/O99/RW6) |
|
|
Mean age at first calving
|
Mean age of first observed calvings = 9.53
± 2.32 (SD) yrs |
Assumes all first calvings observed. |
Kraus et al (in press) |
|
|
|
Likelihood model indicates 10.1 ± 0.5 years
in 1990s |
Too few known-age animals to test for temporal
trend |
Cooke & Glinka (SC/O99/RW1) |
9.8 ± 0.6 yrs in 1980s (Cooke & Glinka) |
|
Survival rate of calving females
|
0.94 in 1980, declining to 0.63 in 1995 |
Stage-structured model indicates that this
is the primary component of the decline in population growth rate and survival |
Fujiwara et al (SC/O99/RW7) |
|
|
|
0.982 ± 0.017 in 1980s, declining to 0.955
± 0.067 in 1990s |
|
Cooke & Glinka (SC/O99/RW1) |
0.984 ± 0.005 in 1970s and 1980s (Cooke &
Glinka) |
|
Survival rate of females from birth to
first calf
|
Overall rate 0.85 ± 0.29 in 1990s |
Implied rate required to account for estimated
rate of population increase B may be too high because increase rate over-estimated? |
Cooke & Glinka (SC/O99/RW1) |
1.01 ± 0.17 in 1980s (Cooke & Glinka) |
|
|
No significant trend in annual survival rate
of female calves or immature females from 1980 to 1995 |
|
Fujiwara et al (SC/O99/RW7) |
|
|
Annual population growth rate
|
+3% in 1980 shifting to B2% in 1995; overall
rate 1.3% (95% CI 0.1, 2.5%) |
Decline mainly due to vital rates of females
with calves |
Fujiwara et al (SC/O99/RW7) |
|
|
|
4.4% ± 2.8% for 1980-97 |
Likelihood model B estimate very imprecise
and may not be significantly different from zero |
Cooke & Glinka (SC/O99/RW1) |
7.1 ± 1.4 % for 1971-90 (Cooke & Glinka) |
SUMMARY
-
Annual calf production per female highly variable and, since 1990,
about half that expected from comparison with Southern Hemisphere (Eubalaena
australis) females: from 1998 to 2000, lower in absolute terms
than in all but one of the preceding 17 years
-
Calf production now largely from cows not taking their calves to
the Bay of Fundy nursery ground
-
Calving interval has increased significantly from 1980s to 1990s,
now averaging 5 years
-
This increased calving interval apparent in cows of all ages
-
Shift in distribution of calving intervals consistent with increased
pre- or neonatal mortality
-
Survival rate of calving females shows significant decline over time
-
Survival rate of immature females shows no significant decline
-
Age at first parturition similar to that in Southern Hemisphere animals
-
Population increase rate significantly lower than in Southern Hemisphere,
and since 1990 may be negative
|